complete m.tech project report_2017 (Based on MEMS Technology)

Design and Simulation of Capacitive Pressure Sensor for Structural Health Monitoring Applications 2017
M.Tech, VLSI Design & Embedded Systems, Dept. of ECE., A.I.E.T. Moodbidri Page 1
CHAPTER 1
INTRODUCTION
1.1 OVERVIEW
Nowadays, the use of pressure sensors in the field of medical, automobile, aerospace,
commercial and industrial applications are gradually increasing. Due to the technological
improvement in the microscale fabrication, the Micro Electro-Mechanical Systems
(MEMS) pressure sensors are designed in which the pressure varies between ultra-low to
extremely high pressures. In modern fabrication technique, the metal square diaphragm
weight sensor is replaced by the silicon and polymer materials. The sensor is a device
which senses the mechanical and electrical parameters. Hence this can reduces the cost
and materials used during the fabrication thereby it also reduces the device cost/unit.
MEMS pressure sensor is widely gaining more importance due to its miniature size, low-
weight, high reliability, best interfacing features. It can also be easily integrated during
the process of Integrated Circuits (IC‟s) fabrication.
There are different types of pressure sensing mechanisms which are being used
in MEMS pressure sensors namely capacitive, piezoelectric, piezoresistive etc. In the
recent improvement of MEMS pressure sensor design, modeling and fabrication the
capacitive, piezoresistive, resonance, optical and acoustic transduction principle is used.
Among all these the capacitive pressure sensor and piezoresistive sensors are widely
gaining attention in many works. For transduction mechanism, the MEMS pressure
sensor mostly uses piezoresistive which converts pressure into a change in resistance.
The piezoresistive sensors are considered as first Micromachined products to be
mass - produced and these sensors are highly temperature sensitive and have high power
consumption. Hence these sensors are not preferred for high temperature applications
[1].

1.2 FUNDAMENTALS OF MEMS TECHNOLOGY
MEMS an abbreviation of “micro electro mechanical structures”, are the improvements
of very small gadgets. MEMS is a technology which shows evident exponential growth
from the last decades in terms of device miniaturization as its feature size varies in the
micron range. It mainly combines electrical and mechanical components which might be
made using the strategies of microfabrications. MEMS enlarge the fabrication techniques
installed for the IC industry to feature mechanical factors which includes gears, springs,
diaphragms, and beams to the devices [1].
In the beginning of the 1990s, MEMS emerged to the improvement of integrated
circuits (IC) manufacturing procedures, in which the actuators, sensors and the control
functions are fabricated in silicon. From that view ahead, the great significance
examination improvement has been done in MEMS. MEMS era exhibited flexible uses
in telecommunication, aerospace, life science and biology for their new and advanced
characteristics. Micromachining has grown to become out to be the important
innovations for the advent of MEMS devices. Silicon micromachining is considered as
the most mounted of the micromachining improvements and it considers for the
introduction of MEMS devices and these are ranging in sub-millimeter range. The
MEMS inventions are used for improving the performances of numerous devices namely
accelerometer, Radio Frequency (RF), micro-optics and pressure sensor devices. There
are a significant number welfares from claiming MEMS which depends upon their
applications, the critical function being integration of their respective electronics and
hence the miniaturize size, high functionality and its overall integrations are obtained
resulting in the power budgets reduction.
MEMS technology is not only about single device or application, nor it is
featured by only one manufacture procedure or they are restricted to some materials.
They may be considered as a fabrication method that grants the benefits of shrinking,
numerous components and microelectronics to the creation and designing of integrated
MEMS technology. There are mainly three specific features in the fabrication
technology such as microelectronics, miniaturization and multiplicity. The

microelectronics gives intelligence activity to the MEMS devices. The miniaturization
develops fast response and compact devices. Multiplicity describes as the clump of batch
fabrication inalienable in the semiconductor procedure, which permits thousands
alternately more than millions of components that are effortless and simultaneously
fabricated.
There are as many examples that are actually referring to MEMS gadgets such
are actuators and sensors in which they can perform plenty of functions like controlling,
sensing and switching on the mechanisms. Mechanisms may be in the array or in
individually that can produce the change in the macro level size. MEMS guarantees to
transfigure almost all product division by using micromachining technology by
combining together silicon based microelectronics, making the things can be done as the
comprehension of full systems placed on single chip. MEMS is a very powerful
technology permitting the growth for advanced product items, augmenting the
computational ability of Micro-electronics with the conviction and manage abilities of
micro actuators and micro sensors and furthermore the increasing the distance of feasible
applications and designs. In the last few years there is a gradual improvement in the
micro devices technology that depicts the huge strength of MEMS. Such micro devices
have the quality that permits various functions such as actuation, physical and chemical
detection.
1.2.1 Advantages of MEMS
 MEMS are used to make gadgets by no means before practicable at a scale of
macroscopic.
 To increase the performance and uniformity of commonly used microscopic
devices.
 It is very easy to customize and to integrate.
 It is used to lower the amount (through minimization of assembly, reducing the
cost of materials is used to minimize the mass, scale, size and power
consumption).
 It uses a batch fabrication technique.

 Micro elements make the devices to run faster, more portable, low cost, easily
integrated and can be easily replaced and maintained, more reliable and consume
low power.
 It uses IC technology i.e. integrating many complex functions on a single chip
that forms a complete system (combination of sensors, processing, and
actuators), reduction with no harm on functionality and with high performance.
 One of the most important advantages of MEMS is their ability that can
communicate semiconductor chips very easily with the electrical elements.
1.3 RESEARCH MOTIVATION
The main motivation for this research work is to design a capacitive pressure sensor with
high sensitivity using MEMS technology. Nowadays the pressure sensors are gaining
much more attention due to its low cost, high performance, miniaturize size, easy to
integrate components and high temperature sensitive. In some of the gas turbines as an
example, pressures and temperature will reach up to about 2230ºC and 3 to 4 MPa (435-
580psi), normally. And in oil or gas exploration, pressures and temperature will reach up
to 180ºC and pressure of 140MPa (20,305psi). In conjunction with the presence of
corrosive state, it will become a very challenging atmosphere for the pressure sensors.
In automotive filed, the pressure sensor have a very wide marketing for the harsh
atmosphere with major applications in the hydraulic fluid systems, engines and in power
train. In the olden days, greenhouse gas emissions are restricted and hence it has pushed
forward automotive industries to extend fuel potency and it decreases the pollutants and
emissions. In order to improve the efficiency of fuel in diesel engines, as an example, the
common rail equipment is used in the combustion chamber to inject the fuel into it at a
ultra-high pressure ranges up to 200 MPa i.e. 29,007 psi to boost combustion and to
enhance fuel potency. Hence the pressure detector is used measure the pressures in fuel
injection system.
Moreover, the Piezoresistive pressure sensor is considered as the first
micromachined element for mass production in which these sensors consumes high

power and high temperature sensing. Hence these types of sensors are not used for
higher temperature applications as it needs extra temperature compensatory circuit. To
overcome this problem, the capacitive pressure sensors are coming to an existence and it
is observed that, the effects of the temperature of the devices are very negligible. Apart
from this, it also gained more attention due to its low power consumption, higher
resolution, less temperature coefficient, low cost, high volume manufacturing and high
performance. Therefore, the capacitive pressure sensor mechanism is adapted to design.
1.3.1 ADVANTAGES OF CAPACITIVE PRESSURE SENSOR
 MEMS based capacitive pressure sensors are less temperature sensitive.
 It is more robust in nature.
 Its accuracy, sensitivity and reliability is more.
 Easy to design and integrate.
 Very low cost and consumes low power.
 These sensors are high volume manufacturing.
 Performance of the sensor is very high.
1.3.2 APPLICATIONS OF CAPACITIVE PRESSURE SENSOR
 In automotive applications:
 Side airbags and seat occupancy
 Tyre pressure monitoring systems.
 In industrial applications:
 Gas and meters analyzers.
 Hydraulic systems
 In consumers applications:
 Smartphones.
 Household applications.
 Tablets.
 In medical appliances:
 Blood Pressure monitoring systems.

 Drug Delivery.
 CPAP machines.
1.4 PROBLEM DEFINITION
1.4.1 Problem Statement
Nowadays, the conventional altimeter is replaced by the MEMS based altimeter which is
realized in a single chip. MEMS capacitive pressure sensors have an advantage of high
temperature sensitivity over the piezoresistive sensors. Therefore, the problem statement
is to design and simulate capacitive pressure sensor by using different springs that are
integrated at each corner of the square diaphragm to obtain higher and better sensitivity.
1.4.2 Requirements
 Software Requirements
 Comsol Multiphysics.
 Coventorware Turbo 2010.
 Hardware Requirements
 Recommended to have internet connection during the software installation.
 To run the comsol tool, Minimum 1 GB of memory, but recommended to have 4
GB or higher per processor core.
 1-5 GB disk space is recommended.
 Windows-7 operating system is recommended for better and faster results.

1.4.3 Design Methodology
Fig. 1.1 Methodology of proposed work
1.5 OBJECTIVES OF THE PROJECT
The objectives of the projects are
 Design a required capacitive pressure sensor structure and modelling of suitable
diaphragm materials.
 Now compute the design study and characterize for a better model.
 To find the micro gadgets parameters like surface length of the deformed
diaphragm, center deflection, surface area, capacitive characteristics and length,
develop the required mathematical equations.
 Compute the design by using the MEMS CAD tools such as COMSOL
MULTIPHYSICS and COVENTORWARE TURBO.
 Compare the different structure simulation results in order to determine the
overall better sensitivity with respect to its structure.
 This design methodology set free as many design potentials in which these are
not available in the previous methodology. Because this project main goal is to
Literature
review on
MEMS based
Capacitive
Pressure Sensor
Design of different
MEMS capacitive
pressure sensor
structures
Study and compute to
get the simulation
results on Comsol and
Coventorware tools
(Displacement,
capacitance)
Comparison
of the
capacitance
sensitivities
Analytical representation
of the simulation results
(Displacement,
capacitance and
sensitivity)
Conclusion and
future scope
Final Report
generation

design the capacitive pressure sensor in miniaturize size which uses
microfabrication technique.
1.6 DISSERTATION OUTLINE
This project mainly gives the analysis of displacement and capacitance sensitivities on
different types of structures and comparison of them.
 Chapter 1 gives a brief introduction of the MEMS, why MEMS for sensors,
motivation, objectives and problem statement for the capacitive pressure sensor.
 Chapter 2 gives the literature review of different papers which describes their
motivation for work, further improvement and future works to be carried out.
 Chapter 3 gives a detailed representation of capacitive pressure sensing technique
along with its mathematical formulation that are required to propose the parallel
plate square diaphragm of MEMS capacitive pressure sensor.
 Chapter 4 gives a brief perceptivity about MEMS CAD tools such as COMSOL
MULTIPHYSICS and COVENTORWARE TURBO tools.
 Chapter 5 gives the design and implementation of different structures of the
capacitive pressure sensor using COMSOL and COVENTORWARE tools.
 Chapter 6 gives Comsol and Coventorware simulation results of capacitive
pressure sensor that includes a displacement (µm) and capacitance (pF) and final
comparison of different structures sensitivities.
 Chapter 7 finally, the conclusion and future enhancement of the project work is to
be carried out.

CHAPTER 2
LITERATURE REVIEW
The most important chapter in the project work is the literature review. It collects all the
necessary information that is needed for project work. It contains the motivation for the
work, problems faced during the project work, possible solutions required and finally the
simulation results. In this chapter a detailed literature survey of previous works which
are related to capacitive pressure sensor is carried out that gives the basic knowledge
towards the present work.
Jaehyuk Choi et al. [2] have designed the capacitive pressure sensor by taking
additional Air chamber. Here, the authors have presented how the additional air chamber
affects the sensitivity of the flexible diaphragm by using FEM simulation and analytical
method. They have observed that, by using natural rubber latex (NRL) type of Air -
sealed pressure sensor diaphragm with additional Air chamber, the sensitivity is
enhanced by 15 times of that compared to the NRL capacitive pressure sensor without
having an additional air chamber. The results obtained from capacitive pressure sensor
having an additional air chamber for applying pressure ranges from 1-10kpa is pressure
sensor sensitivity of 8986 ppm/kpa and responsivity of pressure sensor is 1.391
MHz/kpa.
Akhil K. Ramesh et al. [3] have designed the MEMS based Capacitive Pressure
Sensor for touch - mode applications. When the sensitivity of the sensor is improved, the
MEMS based capacitive pressure sensor dynamic range has been slightly varied. In this
work the authors have designed and compared the sensitivities of sensors between
normal diaphragm and centre bossed square diaphragm structure with range limit. Here
the analysis is done by using COMSOL MULTIPHYSICS Tool.
The pressure ranges between 0.05 MPa to 2MPa has been applied to the square
diaphragm resulting in the displacement sensitivity for the normal diaphragm is

2.02µm/kPa whereas for the Centre bossed diaphragm, displacement sensitivity is
2.94µm/kPa. The Fig. 2.1 has two plots in it and it is plotted displacement with respect
to different pressures. First, it is plotted the deflection sensitivity for the normal
diaphragm and other plot is deflection sensitivity for bossed diaphragm.
Fig. 2.1 Displacement sensitivity (Adapted from [3])
Similarly, Fig. 2.2 shows the capacitance sensitivities between normal diaphragm
and bossed diaphragm structure.
Fig. 2.2 Capacitance sensitivity (Adapted from [3])
The capacitive sensitivity for normal diaphragm is observed as 0.011pF/kPa
whereas for the bossed diaphragm, capacitance sensitivity is 0.012pF/kPa. By observing
the above results it is noted that, the capacitance sensitivity of 0.92 µm/kPa is increased

between normal diaphragm and bossed structure diaphragm. But the range is limited by
20kPa for the center bossed diaphragm.
Hui-Yang Yu et al. [4] has proposed MEMS capacitive - pressure sensor that is
compatible with a process of CMOS. The design consists of mainly three parts which are
as follows: Top electrode, Bottom electrode and Dielectric layer. Here, polysilicon is
used as material for bottom electrode during the CMOS methodology. The release of
sacrificial layer forms a gap between the electrodes and the gap is sealed by an Al vapor
technique and photolithography that forms a top electrode plate. The silicon oxide
material is used as dielectric material with air gap. The fabrication method for this
structure relates Post-CMOS MEMS method with CMOS system.
The author has designed sensors with three different diaphragm sizes i.e. for
100µm, 130µm and 150µm and compared them with their capacitance sensitivities. The
Pressure is applied at the top Electrode plate which ranges between 100hPa to 1100hPa.
As a result, the sensitivity to diaphragm size 100µm is 0.085Ff/hPa. As the Pressure
increases, the diaphragm with size 130µm and 150µm contacts with the substrate and the
sensitivity decreases linearly. Hence the capacitance sensitivity is about 0.104Ff/hPa and
0.099fF/hPa.
Anil Sharma et al. [5] have proposed the paper on MEMS capacitive pressure
sensor design and simulation for tyre pressure monitoring system [TPMS] application.
The static and dynamic simulations are done by using thermo-electro mechanical [TEM]
tool which is a part of Intellisuite software. The capacitance varies with respect to
pressure applied on the diaphragm. The pressure is applied on the rectangular diaphragm
of thickness 5µm and ranges between 0 KPa to 300 KPa. As a result, the sensitivity
observed is 0.12fF/KPa. The simulation of the sensor design gives rise to static results
which is compatible with the theoretical result. In the same way, the response time and
the natural frequency of the diaphragm is obtained by dynamic results.
L. Chitra et al. [6] has presented a paper on designing a MEMS based capacitive
pressure sensor in the application of Lubricating systems. Here, the comb-drive based

capacitive sensor is designed to measure the pressure of the sensor which is situated
inside the lubricating oil system. This type of comb-drive sensors isolates the sensor
diaphragm from its comb plates which are capacitance sensing and the pressure
sensitivity is linearly increased by mechanical coupling.
The thickness of the square diaphragm with its combs is 200µm × 200µm ×3µm
respectively. The material that is used for the pressure sensing diaphragm is aluminium
and for comb plates, gold is used. The pressure is applied on the sensing diaphragm
which ranges between 0 -10 bar and these sensors works very effectively in the
temperature ranges between 30ºC - 270ºC. The designing and its simulation is carried
out using COMSOL MULTIPHYSICS V4.4. As a result, the capacitance sensitivity
achieved for this proposed structure is 36aF/1bar.
Edgar A. Unigarro et al. [7] have designed the planar capacitive pressure sensor
and its implementation using interdigitated electrodes (IDE) and special sealed polymer
cavity. The analysis is done using COMSOL tool. There are about 21 fingers used in the
IDE electrodes with the diaphragm thickness 11mm × 11mm. The pressure varied
between 0 to 40 psi and the capacitance sensitivity of 3.35 fF/psi is obtained.
Muslihah Ali et al. [8] have proposed the paper on Optimization of MEMS based
Intraocular capacitive pressure sensor which is used for observing the glaucoma disease.
The four slotted square diaphragm with the thickness of 550 × 550µm is used and a
pressure is applied on the diaphragm which ranges between 0 - 60mmHg. The analysis
of the capacitance pressure sensor is done by using COMSOL MULTIPHYSICS tool.
For this proposed study, it is observed that the thickness, slot lengths and slot widths are
optimized as 4.2µm, 100µm and 25µm respectively. The optimized parameters are
analyzed using “Taguchi and Two-Level Factorial” design approach. The maximum
capacitance sensitivity of >5.916e-7 is observed and by comparing the initial and
optimal conditions, the sensitivity of optimal condition is 1.06 times higher than the
initial conditions.

M. Srinagesh et al. [9] have proposed the paper on design and its simulation of
MEMS based parallel plate capacitors for measuring the pressure. The main objective of
this paper is to design the circular shaped diaphragm and analyze its analytical solution
and finally comparing the values obtained using the SOLVER software. The goal of the
author is the sensor must work in any harsh environment so the material opted is SIC
(Silicon Carbide). Because SIC has a better stability for electrical properties, chemical
inert property and mechanical robustness. Hence these sensors have applications in the
field of automotive industries, oil equipment‟s, nuclear stations, aerospace and in power
stations.
The diaphragm is designed with a diameter of 300µm of circular plates and a gap
between the plates is 10µm. The uniform pressure applied on the diaphragm ranges from
0Mpa to 1Mpa. As a result, the maximum displacement of 0.226 µm and capacitance is
linearly increased with respect to applied pressure variation and noted 80 pF. But due to
the gap variation between two plates, the nonlinearity about 9.46 % is obtained.
Nagendra Reddy et al. [10] have designed and modeled a capacitive pressure
sensor with four different structures like square pressure sensor, square with slotted,
circular pressure sensor and circular with slotted pressure sensors with different
dimensions. The simulation is done using COMSOL MULTIPHYSICS tool. The silicon
is used as a diaphragm material because of its highly unusual properties. The
displacement and capacitance values are linearly increased at different applied pressure.
They have noticed that there is a more change in the displacement of slotted pressure
sensors as compared with the normal pressure sensors and sensitivity is more in circular
pressure sensor as compared to square sensors.
Nisheka Anadkat & Rangachar [11] have designed and analyzed the capacitive
pressure sensor with square shaped diaphragm using COMSOL MULTIPHYSICS tool
by Electromechanics interface. This paper mainly contains the performance analysis of
capacitance pressure sensor such as diaphragm displacement, capacitance, sensitivity,
linearity analysis and some thermal considerations. At zero applied external pressure the
sensitivity of the diaphragm is about 7.3e-6 pF/Pa (one quadrant of total sensor). Hence

the sensitivity of the total diaphragm is 29e-6 pF/Pa. When the external pressure of
25Kpa is applied on the diaphragm, the sensitivity is 13.2e-6 pF/Pa (one quadrant of
total sensor). The total sensitivity of the diaphragm is 52.8e-6 pF/Pa is observed.
Due to thermal stress, the sensitivity is linearly changes. At zero applied uniform
pressure the sensitivity has been increased. For 25Kpa pressure, the sensitivity is 19.6e-
6pF/Pa (one quadrant of total sensor). For total diaphragm sensor the sensitivity is 78.4e-
6pF/Pa is observed. By this performance analysis, it is noted that the sensitivity of the
sensor is 1.5 times increased due to the stress during packaging. The total temperature
sensitivity of the sensor is 13.2e-4 pF/K. The total diaphragm sensitivity is increases
about 1.5 times compared to the diaphragm sensitivity without any stress. Hence these
capacitive pressure sensors are used in high sensitivity applications.
Siavash Zargari et al. [12] have proposed a paper on the design and analysis of
MEMS capacitive pressure sensor using Nano composite electrode as CNT/PDMS using
finite element analysis. In this analysis the new type of electrode attribute was examined
for MEMS based capacitive pressure sensor where the diaphragm deflection affects the
electrode plate‟s imbrication area rather than the separation in any commercial based
sensors. The simulation analysis of the design is done using the COMSOL
MULTIPHYSIS tool. The square diaphragm having a dimension of 2.5mm × 2.5mm
was designed and an external pressure of 0-100 KPa was applied on it. As a result, the
total displacement is 29.66 µm and the capacitance of the sensor is about 0.365pF is
obtained. Hence the overall sensitivity of the square diaphragm is 1.374e-6 1/Pa. During
simulation, the spectral analysis is carried out which ranges between 0 to 1MHz. The
resonant frequency of the diaphragm obtained is 163.5 kHz.
Khalilullah Ibrahim & Gargi Khanna [13] have proposed the optimum design of
a MEMS based capacitive pressure sensor which have its application in intraocular
pressure (IOP) for a glaucoma patient. The main motto of this design is to compare the
maximum displacement of parallel plate capacitor diaphragm having different design
structures. The simulation results are carried out using COMSOL MULTIPHYSICS
software. The clamped, corner side slotted and edge side slotted diaphragms are

designed. The uniform pressure is applied on the diaphragms, as a result, the clamped
0.9088 µm displacement is obtained for corner side slotted and clamped 4.6811 µm of
displacement for edge side slotted diaphragm is observed.
Amin Nikoozadeh & Pierre T. Khuri- Yakub [14] have designed and simulated
conventional type of capacitive micro-machined ultrasonic transducer usually called as
CMUT using finite element method (FEM) with substrate embedded springs for the non-
flexural movement of plate. Because of the spring elements used in the design, there is
no need for plated to operate in any flexural modes. The CMUT mainly designed using
many sub cells, which are connected in parallel. By the simulation analysis, it is noticed
that the average deflection of the upper plate is above 90% as compared to its peak
displacement for applying pressure of 1.5 MPa peak to peak to the transducer face.
Zita Holland et al. [15] have designed the MEMS capacitive pressure sensor for
structural health monitoring which have an application in the layered polymer design
structure. The sensor is designed from the segregated layers of polymer design structures
which are separated by a polymer layer having a high dielectric constant. When the
sensor is introduced into hydraulic hose, the capacitance of the capacitive sensor is
slightly increased. An applied pressure of 0 pasi, the capacitance measured is 1.1230nF
and at 2000psi the capacitance observed is 1.1496nF. Hence 2.46% of total capacitance
change is obtained. The same results are observed for the highway tires and total
displacement of lumbar applications.
Cruz et al. [16] have proposed the paper on pressure sensing design for health
monitoring applications which is used in Inkjet printing technology. These sensing
platforms are consists in elastic PCB which are manufactured using a suitable
technology with two flexible polymer membranes that are printed with inkjet for
designing the electrodes. The simulation results are carried out using MATLAB. When
the uniform external pressure is applied on the sensor diaphragm, the capacitance
sensitivity of 100fF/kPa is observed. Here capacitance values are measured by
capacitance to digital converter (CDC). As the load increases the capacitance sensitivity

is also increases. Hence, for uniform applied load, the sensitivity of 25.3fF/N is
obtained.
Scardelletti et al. [17] have designed wireless capacitive pressure sensor with
additional RF antenna for higher temperature surroundings which are mainly used in
aircraft engines. The sensor is characterized from the room temperature ranges from
25ºC to 300ºC, at applied pressure ranges between 0 to 100 psi. The frequency obtained
for this wireless capacitive pressure sensor design is 127 MHZ and at 1 kHz offset the
observed phase noise margin is less than -30dBc/Hz and at 10 kHz offset the phase noise
further decreases to -80 dBc/Hz.
Kubba et al. [18] have presented a paper on design and modeling an MEMS
capacitive pressure sensor used in the application of tyre pressure monitoring. In this
paper the authors have designed the elliptical shaped diaphragm which is having high
sensitivity and the results are compared with a circular shaped diaphragm which is in
terms of pressure, temperature sensitivity and thermal stress. By decreasing the gap
between the plates and capacitance area, the temperature sensitivity of the diaphragm
and thermal stress is increased. The design analysis is done by using finite element
method (FEM).
Balavalad et al. [19] have proposed the article on comparison of design and
simulation analysis of perforated type MEMS based capacitive pressure sensor. The
authors have designed different structures like slotted, conventional and perforated type
of capacitive pressure sensor and compared these models with their sensitivities. The
polysilicon is used as a diaphragm material. In this work, the square diaphragm whose
length is 50µm and the gap between two parallel plates is 3µm is designed and
simulated. The simulation is done using COMSOL MULTIPHYSICS and
COVENTORWARE MEMS software‟s.
The pressure applied on the conventional type diaphragm is ranging between 0 to
8Mpa and achieved displacements of 1.0189µm and 1.2800µm. In the same way, the
pressure ranges from 0 to 12 MPa is applied on the slotted diaphragm and the

displacement of 1.0449µm and 1.0784µm are observed. Finally the pressure which is
ranges from 0 to 16 MPa has been applied on the perforated type of diaphragm and the
displacement of 1.0407µm and 1.300µm are obtained. The capacitance sensitivity for all
three models is linearly increased as applied pressure varies which is measured in terms
of Farads (F/Pa).

CHAPTER 3
RESEARCH METHODOLOGY
In this chapter the main aim is to focus on the background and mathematical modeling of
MEMS capacitive pressure sensor.
3.1 BACKGROUND
The Pressure sensor is a type of sensing device which measures the pressure in any states
i.e. in liquid or gaseous states. In most of the processes, the pressure measurement is
considered as one of the most necessary parameters. So before starting with the actual
capacitive pressure sensor, it is important to study about basics of the pressure sensor.
The basic block diagram of the pressure sensor is shown in the Fig. 3.1. Similarly the
conventional structure of the pressure sensor is shown in Fig. 3.2
Fig. 3.1 Basic block diagram of Pressure sensor
Fig 3.2 Structure of pressure sensor with applied pressure (Adapted from [5])
Pressure
Sensing
Element
Physical
movement
Transduction
mechanism Electrical
signals

The uniform external pressure is applied to the diaphragm and the sensing
element senses the pressure and there will be a physical deflection occurred on the
diaphragm. Hence the pressure sensor converts the actual mechanical signal whose
magnitude mainly depends upon the applied pressure and converts the mechanical signal
into an analog electrical signal. There are many types for measuring the pressure. Some
of them are listed below.
 Absolute measurement
 Differential measurement
 Gauge measurement
The pressure sensors are mainly classified into three types. They are:
 Piezoelectric pressure sensor
 Piezoresistive pressure sensor
 Capacitive pressure sensor piezoelectric
A piezoelectric is a type of pressure sensor which uses a piezoelectric effect and
converts the pressure into an electrical charge. It mainly measures the variation in
temperature, pressure, strain, acceleration or force. When the applied pressure increases
the diaphragm will start to deflect. It provides a very high range of elasticity to the
devices and can work in any harsh environment. They have a tendency to generate the
voltage which is proportional to the obtained velocity. Thus the power source is not
required for deformation of the diaphragm. But the main drawback of piezoelectric
sensor is they cannot be used for a static measurement and have a high impendence. To
overcome this problem, the piezoresistive sensors are coming to an existence.
Piezoresistive sensors are the type of pressure sensor devices which uses the
piezoresistive effects which detects the strain due to the applied pressure. As the applied
pressure increases the diaphragm starts to deflects, thus the resistances increases by a
decrease in the voltage. Most of the commercialized MEMS based pressure sensors uses
the piezoresistive effects as the change in the transconduction technique of applying
pressure to the chance in some resistance. These pressure sensors have a very high factor

of gauge, but the temperature coefficient of the piezoresistivity is only 0.27% per ºC.
Thus the operating temperature is limited, and it requires an additional circuitry for
temperature compensation. Hence, these pressure sensors are very high temperature
sensitive and it consumes more power. So they are not suitable for the applications
where it requires high temperature [20]. In order to operate in high temperature
applications, the capacitive pressure sensors are preferred.
The capacitive pressure sensor is a type of pressure sensor which uses the
diaphragm membrane and a pressure cavity to form a variable type of capacitor that
detects the strain by applying the uniform pressure. There is a change in a capacitance
with respect to the change in applied pressure. The capacitive pressure sensor uses some
common technologies which use metal, silicon and ceramic diaphragms. These sensors
are widely used because of its low temperature sensitivity, consumes low power,
fundamental noise floor is less, higher frequency permeability, low cost, smaller volume,
easier to fabricate and high resolution.
In the next section, the fundamental basics of capacitance, capacitive pressure
sensor, Mathematical equations related to the capacitive pressure sensor, mechanism of
capacitive sensor in the MEMS devices can be conferred.
3.2 TRANSDUCTION MECHANISM OF CAPACITIVE
PRESSURE SENSOR
3.2.1 CAPACITANCE
In general the capacitor is an electrical device which stores an electric charge that
reposes on two semiconducting plates that is notched by a tiny lower distance, with the
total surface area and the distance between the plates displaying a part within the overall
capacitance of the capacitor device. A capacitor charges a transient current in it, where
the one plate is charged with positive charge and the other plate of the capacitor is
charge with negative charge. Once the charge formed on the both plate, the voltage
potential difference is formed between the two plates. Hence this obtained voltage

potential difference change the conductor can sustain to border till it meets the voltage
supply.
The following equation 3.1 shows the amount of charge stored in the capacitor. It
is given by the factor Q.
Q = CV …… (3.1)
Where Q = Total charge that is stored in capacitor.
C = Capacitance
V = applied voltage.
3.2.2 BASIC STRUCTURE
A capacitive/electrical phenomenon pressure plate sensing element determines the
change in pressure with respect to the change in deformation of conducting diaphragm
owing to applied external pressure. The Capacitive pressure sensor can be made up two
parallel plate capacitors which are separated by a dielectric material. Between two
electrode plates there is a presence of electric field and also the deformation within the
diaphragm membrane yields a change in the capacitance. Capacitive pressure sensors
impoverished with a membrane which interact a dielectric material coated, and at a very
high range of pressure a graph of nonlinear response is achieved by a ground plane. The
general view of the capacitive pressure sensor is shown in the Fig. 3.3
Fig. 3.3 General view of capacitive pressure sensor (Adapted from [12])

A preliminary pressure is critical to carry the conducting plane that is associated
with the ground plane, and also the presence of pressure within the membrane provides a
widespread resistance to deflection linked to the actuation builds by the pressure applied.
The residual stress contracts the capacitance sensitivity at very low pressures and thus
the nonlinear signal is produced. The mechanism of capacitive sensing are often
effortlessly be involved to understand pressure sensor, despite that, this capacitive
sensing mechanism is in and of itself nonlinear, on account that capacitance is
reciprocally proportional to the width of plate gap. Hence in the modern days the MEMS
based capacitive pressure sensors gains a lot of attention over a piezoresistive type of
pressure sensors due to low power consumption, very high sensitivity, IC compatibility
and free from all the temperature effects, etc.
The measure of the drop-off within the gaps between two parallel plates is known
as the change in applied pressure. The applied pressure continuously deforms the
diaphragm membrane till the response elastic force of the membrane balances it. The
tiny change of depth has additional deformation; if the pressure applied is more then the
deformation within the moving plate is more. If the depth of the diaphragm membrane is
small, then it causes more deflection in the membrane. If the dimension of diaphragm
membrane increases thereby decreasing the depth of diaphragm and reduction in gap the
high capacitance sensitivity of the sensor can be achieved.
Electrostatic capacitance detecting is an intermittently utilized as a part of
transduction technique for MEMS gadgets. MEMS creation procedures can
enthusiastically deliver parallel plate or interdigitated comb-drive capacitors which can
move subsequently of physical variable excitation (weight or increase in speed) in a
MEMS gadget.
3.2.3 MATHEMATICAL MODELING
In general the capacitors consists of two plates/electrodes which are placed in parallel
having equal area „A‟ and gap between the two plates i.e. distance dₒ, and separated by
an dielectric materials as air or vacuum as shown in Fig. 3.4

Fig. 3.4: Schematic representation of capacitive pressure sensor (Adapted from [18])
The mathematical expression of capacitance for a fixed-parallel plate capacitor is
given by C which is shown in equation 3.2. Here the bounds for a fixed parallel plate
capacitor are constant.
C = εₒεᵣ …… (3.2)
Where εₒ = free space permittivity (8.854 × F/m)
εᵣ = permittivity of a dielectric material in parallel plate capacitor
A = area of the electrode plate in meter square (m²)
dₒ = separation gap between the electrode plates in meters (m)
In order to obtain, the more capacitive transduction then any one of the
individual variables must be changed in Eq. (3.2)
In the same way, for variable capacitors which are in parallel, the
movable/versatile capacitor plate moves for the most of the fixed plate as particular by
the coordinate z. hence the mathematical expression of capacitance for a movable
parallel plate capacitor is shown in the equation 3.3.
C = …… (3.3)
The energy of the capacitor „W‟, with an applied voltage „V‟, across the parallel
plates is shown in the equation 3.4.

W = ( …… (3.4)
By differentiating the above obtained energy function (W); the electrostatic force
(F) between the two plates with respect to the coordinate which is in the direction of
force can be determined and it is shown in the equation 3.5.
F = = ( …… (3.5)
The maximum deformation occurs at the center of the diaphragm membrane. The
general relation between the applied pressure and the deflection of the parallel plates
which acts normal to the plane by fourth order derivative is shown in the equation 3.6.
( ) ( ) ( ) = …… (3.6)
The change in the capacitance „ΔC‟ of the diaphragm w.r.t the change in
deflection is shown in the equation 3.7.
ΔC = [0.01512(1- ) ] [ ] …… (3.7)
The capacitance and force in the parallel plate capacitor is reciprocally
proportional to the distance between the two parallel plates within the capacitor. Hence
these two parameters are highly nonlinear. If the gap between the two plates is zero; and
coordinate Z (Eq.3.5) increases then the electrostatic force within the diaphragm
becomes large. This change in the effect is referred as PULL-IN effect. The zero gap
problem occurred between the two parallel plates can be avoided by attaching a spring
„k‟ on it which is shown in the Fig. 3.5.
At pull-in stage, the moveable capacitor plate is unstable and it closes the gap
between plates to zero by moving forward. By observing the pull-in effect very closely,
the balanced force between the electrostatic force and the spring is shown in the equation
3.8.
= ( …… (3.8)

Fig. 3.5 Circuitry of parallel plate capacitor with springs (Adapted from [22])
By solving the Eq. 3.8 for the applied voltage squared i.e.
= ...… (3.9)
When the differentiation of applied voltage w.r.t position is made zero, then the
pull-in effect is exist. The deflection/displacement „z‟ at which differentiation of applied
voltage with respect to position is made zero can be treated as the deflection occurred at
pull-in „ ‟ which is shown in equation 3.10.
= …… (3.10)
Similarly, the voltage „ ‟ during which pull-in occurs is shown in the equation
3.11.
= √ …… (3.11)
Apart from pull-in effect, one more important effect occurred in the design which
involves a variable parallel plate is an electro-static spring softening effect. With the use
of two terms Taylor series approximation method of Eq. 3.8, this phenomenon can be
explained. It is given by,
= ( + z …… (3.12)

The constant term, negative electrostatics stiffness „ ‟ will eliminates the
elastic stiffness during pull-in effect which is given by equation 3.12.
= …… (3.13)
In order to electrostatically tune or soften the spring stiffness electrostatic spring
softening technique can be used or the natural frequency of the design which is a critical
as shown in the equation 3.14.
( ) z = …… (3.14)
Another important capacitor type is an interdigitated Comb-capacitor. It mainly
consists of a movable plate which is placed in between the two-fixed plates. The two
main electrostatic forces which are applied on the moveable plate are parallel plate force
and a fringe field type of force. The movement of the movable capacitor can be strained
and they maintain a distance between the two fixed plates. The Mathematical expression
of capacitance of interdigitated comb-capacitor is given by equation 3.15.
C = …… (3.15)
Where w = width of the comp-fingers
L = length of the comb-fingers
= displacement
= Distance between the two fixed plates
2 in the above Eq. 3.15 refers that the capacitance of the fixed-plates at two sides
of moveable plates.

CHAPTER 4
MEMS SOFTWARE TOOLS
4.1 COMSOL MULTIPHYSICS DESIGN ENVIRONMENT
4.1.1 INTRODUCTION
The Comsol Multiphysics tool is a Finite element method based analysis, simulation
software package and also acts as a solver for many physics and engineering based
applications. It is basically general purpose software based on the advanced numerical
methods which are used for modeling the various designs and simulating the problems of
physics based designs. Using COMSOL MULTIPHYSICS, it is able to account for all
the Multiphysics and coupled phenomena. The main advantage of using Comsol tool is
that, it provides a significant amount of modeling the physics functionality and
Multiphysics ability. The modeling power can be increased by adding application
specific modules with ideal tools for mechanical, electrical, chemical and some fluid
flow applications. Additional to theses, CAD and ECAD softwares interfacing products
also connects to COMSOL MULTIPHYSICS tool.
System requirements mandatory to install COMSOL tools:
 32 or 64-bit operating system
 Graphical system requirements such as openGL version 1.4 or DirectX
version 9 on the local console are required.

 It supports Visual Studio 2010
 JAVA Requirement: Java files with JDK 1.6 or less can be compiled by
COMSOL JAVA API.
4.1.1.1 PROCESS FLOW
When designing any models, its miles essential to understand whether the model to be
designed is a 2-D or a 3-D models. Then the favored physics that are suitable for the
model is used and the applicable examine is chosen that is craved for the model. The
preferred three-dimensional structure is built on the work-plane and required material is
selected and based on the physics used the conditions are applied on the design model,
and the design model is meshed, which divides the whole design structure into small
finite elements, and finally the model is computed to acquire results which are based on
the physics applied and then based upon the initial design performance, the obtained
results are analyzed.
4.1.1.2 PHYSICS
COMSOL MULTIPHYSICS is a very powerful interactive tool for modeling the design
and fixing all sorts of scientific and engineering problems. The tool gives effective
integrated computing device environment with a model-Builder wherein the complete
review of the structure is obtained and additionally gives access to many capabilities.
With COMSOL MULTIPHYSICS there can be very ease extension from traditional
models for one sort of physics into Multiphysics structures that resolve coupled physics
process.
4.1.1.3 MESHING
The mesh functions permit the discretization of the geometry structure into tiny units of
some simple shapes which are referred as Mesh components. Automatic and semi-
computerized meshing equipment‟s are present in the COMSOL MULTIPHYSICS, such
as free tetrahedral and swept meshing. The default set of rules is automated tetrahedral

meshing for physics referred in solids and a sequence of tetrahedral and boundary layer
type of meshing for a fluid. The sequence of different operations which are used for
creating a mesh is fully controlled by defining, referred as mesh sequence. A Mesh
series permits for a combination of tetrahedral, hexahedral, or a prismatic component
that are made parametrically driven.
4.1.1.4 SOLVER AND STUDY TYPES
The Solver is the process of solving a numerous of problems in COMSOL models. There
are different types of studies used in COMSOL; some of them are listed below.
 Eigen frequency: Computes the Eigen frequency.
 Eigen value : Computes Eigen values/ Eigen modes using an Eigenvalue Solver
 Frequency domain: Gives solution to a frequency response or wave equation.
 Mode analysis: Computes the modes for an electromagnetic or acoustic wave.
 Stationary: It is used when all the time derivatives are remove.
 Time-dependent: Used to compute solutions over time.
 Time-dependent model: used for analyzing time-dependent wave problems.
4.1.2 COMSOL SIMULATION PROCUDURE
STEP 1: CREATING MODEL IN 3D
Fig. 4.1 creating a model in 3D plane

The following steps are used to create a model in 3D which is shown in Fig. 4.1
 Open COMSOL MULTIPHYSICS software.
 Go to model wizard window > click Next
 In a physics tree, select Structural Mechanics > Electro Mechanics.
 Click Next.
 In a Studies tree, select stationary > click done.
STEP 2: GEOMETRY
The following steps are used to create a capacitive pressure sensor design.
 Select geometry > Right click > select work plane.
 Select plane geometry.
 Select a square structure of required dimensions.
The Fig. 4.2 shows how to design the model using mentioned above in order to create a
3D model structure.
Fig. 4.2 creating geometry of required model in 3D plane
STEP 3: Materials
 Select materials > Right click > Add material.
 At a right corner, new window pop ups > select MEMS.
 Select required material > Right click > select Add to component 1.
 Continue the above step till all the required materials are added to the model.

Fig. 4.3 3D model with required materials used
Select the required materials and add to a component. Make sure that, the
young‟s modulus, Poisson‟s ratio and the density have the exact value.
STEP 4: ELECTROMECHANICS
 Select Electromechanics > right click > select Linear Elastic material.
 Select Electrical > select Electrical material model.
 Select Structural > Add Fixed constraint and boundary load.
 Select electrical > Add terminal and ground.
This is the main step in designing the 3D model. For Linear Elastic materials,
select the upper and bottom plate along with the springs. For fixed constraint, select the
bottom plate and apply the boundary load on the upper plate with applied pressure of
1pa. The terminal is applied at the upper electrode plates whereas the ground is at the
bottom electrode plate
STEP 5: MESHING
 Select Mesh > Right click > Build all.

Fig. 4.4 Meshed model
In this step, the model is divided in to number of finite elements and the model is
meshed with a swept mesh technique with the minimum element size of 1.5µm.
STEP 6: STUDY
To compute the model, the below mentioned steps are followed.
 Select Study > Right click > select Compute
STEP 7: RESULTS
To find the Displacement of the model:
 Select Result > choose displacement and drag down the small icon.
 Select surface > choose Expression and drag down small icon > select
Electromechanics (Solid Mechanics).
 Select Displacement > choose emi.disp-Total displacement > select plot.

Fig. 4.5 Required settings to view displacement of the model
From the above settings and plotting the results, the displacement of the model is
obtained in the range of micrometers (µm).
To find the capacitance of the model:
 Select 3D plot group 3 , by dragging down the small icon > select surface
 New dialog box pop ups.
 Select Expression and drag down the small icon > select Electromechanics
 Select Terminals > choose emi.C11 (Capacitance) > plot the result.

Fig. 4.6 Required settings to view the Capacitance value of the model
From the above settings and plotting the results, the Capacitance of the model is
obtained in the range of Farads (F).
 Finally, save the model for further inspection.

4.2 COVENTORWARE DESIGN ENVIRONMENT
4.2.1 INTRODUCTION
Coventorware Turbo is a MEMS software tool used for designing 3-D design structures
and simulating the microfluidics and MEMS devices. This software tool can support two
different design flows in which they can be used in combination or in separate. The
DESIGNER and ANALYZER modules will work in combination to give a conventional
physical design flow process, whereas the ARCHITECT module can work separately to
provide system level condition to MEMS structures. The users can create a design in 2-D
or 3-D layout in a layout editor window which automatically builds a solid model in 3-D
and processor editor window prepares the 3-D structure for automatic mesh generation.
Once the mesh has been generated, then the user can choose the field solver which
actually simulates the microfluidics and MEMS device physical character using “Finite
Element Method” (FEM).
The physical characteristic of a MEMS Capacitive pressure sensor may be
examined using simulations. The simulation results can provide a verification regarding
the physical assumptions that are made in model defining. Apart from this, these
simulations are used to find the layout parameters which optimize the overall device
performance by minimizing the cost, effort and time required to design and simulate the
actual software tool. The simulation is done by using a COVENTORWARE TURBO
2010 tool. In micro electro-mechanical system technology, CAD tool is a tightly created
set of computer programs which enables the computation of device working operation,
manufacturing process and packaged micro-systems character in a continuous order by a
micro-system engineer.
4.2.2 COVENTORWARE SIMULATION PROCUDURE
For designing the Capacitive pressure sensor, the simulation is done using Coventorware
turbo 2010 FEM (Finite Element Method) program. The following steps are considered
to design the process.

STEP 1: Start opening the window
 Open the terminal window.
 Create a new project file or existing project file by selecting icon new
project/Existing project, and give the project name/open existing file as shown
in the below Fig. 4.7
Fig. 4.7 open project window
 This window loads and takes user to the main screen where the user can access
design and simulation tools.
 Select the Build solid model at the top of the main screen.
 A New Solid Model Builder window pop ups which is shown in the Fig. 4.8.
 Select the required material database file.
 Now the user is ready to fabricate the MEMS Capacitive pressure sensor.

Fig. 4.8 Designer window
STEP 2: Creating process file.
The process Editor Window provides a route for creating and editing parameters which
are required for fabrication processes that are stored in this process file. This process
files gives the process information that are required for creating a 3-D structures. The
fabrication process flow for creating wafer can be shown by a sequence or series of
material deposition and etching steps. These parameters along with a layout of 2-D, are
used to build a 3-D solid model structure. The PolyMUMPs process flow is shown in the
Fig. 4.9.
STEP 3: Once the process file is defined, now create a mask and generate a mesh for the
model using designer tab. Select an icon of Layout Editor to open the layout window to
define the required masks which are needed for capacitive pressures sensor. The
designer window is shown in Fig. 4.10

Fig. 4.9 process flow
Fig. 4.10 designer window for layout design
STEP 4: Creating mask
 The layout Editor works similar to the CAD tools like AutoCAD tool.

 The 3-D design is created by selecting the required icons in the main toolbar or
by entering the required coordinates and commands using Command prompt.
 Here the mask names mentioned in the process file display as layers and they are
selected from the drop-down menu at left corner of the window.
 The layout of Capacitive pressure sensor is shown in Fig. 4.11
Fig. 4.11 Layout of capacitive pressure sensor
STEP 5: Design pre-processors
 Here the pre-processor can be used to mesh the 3-D model which defines
different layers and surfaces for further simulation which is shown in Fig. 4.12.
 The users can hide the layers, set the names faces, define conductors and
generate a mesh.
 In order to enter into the pre-processor, select the Pre-processor icon which is
present in the designer tab.
 The meshed model of capacitive pressure sensor is shown in the Fig. 4.13

Fig. 4.12 3-D structure of capacitive pressure sensor
Fig. 4.13 Meshed model
STEP 6: Analysis of design
 Once the model is meshed, the next step is to do Finite Element Analysis (FEA).

 In order to enter the analyzer window, select the Analyzer tab which is present
in the main window.
MemElectro Analysis:
 Select MemElectro solver in order to perform Electrostatic analysis.
 Select Start a new analysis > click solver setup to open MemElectro settings>
click next.
 To obtain the output, select Conductor BCs > click next > set 5volts to the
upper electrode and 0volt to the bottom electrode plates > click OK.
 Click Run.
 View the 3-D results to view the Capacitance of the model.
MemMech Analysis:
 Select MemMech solver to perform the mechanical analysis.
 Select start a new analysis > click solver setup to open MemMech settings >
click next.
 To obtain mechanical parameters of capacitive pressure sensor, select Surface
BCs > click next > select Fixed and Load patches respectively > set the pressure
of 1Pa at the top plate > click Ok.
 Click Run.
 View the 3-D results to view the displacement of the model.

CHAPTER 5
DESIGN OF MEMS CAPACITIVE
PRESSURE SENSOR
5.1 DESIGN SPECIFICATIONS
Table.5.1: Design specifications of capacitive pressure sensor
Sl.No Layers Materials Size [µm] Thickness
[µm]
1. Top and Bottom
plates
Silicon 10000×10000 525
2 Top and Bottom
Electrodes
Platinum 9500×9500 2
3 Air block (Gap
between two
plates)
Air 9500×9500 180
4 Springs Platinum 80 20
5.2 MODELLING OF DIFFERENT STRUCTURS OF
CAPACITIVE PRESSURE SENSOR USING COMSOL
MULTIPHYSICS
5.2.1 CAPACITIVE PRESSURE SENSOR WITH 1-SPRING
The capacitive pressure sensor is made up of a two plates which are placed in parallel to
each other, as one end of the plate is freely moveable which is called a diaphragm
whereas the other end is fixed. The insulator is placed in between two plates such as
vacuum or air. The capacitive pressure sensor is designed based on the Micro Electro-

Mechanical system (MEMS) technology with Finite Element Method (FEM). The model
geometry of the capacitive pressure sensor with 1-spring attached at each corner of the
diaphragm is shown in the Fig. 5.1
Fig. 5.1 Modelled geometry of capacitive pressure sensor with 1-spring
The structure shown in the Fig. 5.1 is the capacitive pressure sensor with one –
spring is attached at all the four corners of the square diaphragm. The senor has a top
and bottom plates which are designed with dimension of 10000×10000 µm in length and
thickness of 525µm and the gap between the two plates is 400µm.
The structure also has a top and bottom electrode plates with the length of
9500×9500 µm and thickness of 2µm. the bottom electrode of placed above the bottom
plate whereas the top electrode is placed below the top plate of the diaphragm. In
between two electrode plates, the air block is placed with the dimension of
9500×95000µm in length and thickness of 180 µm which acts as a dielectric medium.
When a large amount of pressure is applied on the diaphragm, the top plate touches to
the bottom plate and gap between the two plates become zero. Hence the pull in effect
occurs between the plates which causes reduce in sensitivity of the device. To overcome
this problem, the spring elements are attached at each corner of the square diaphragm in

between top and bottom plates with the length of 80 µm and width of 20 µm. The main
advantage of using the spring elements is to achieve a better sensitivity.
The silicon is used as a diaphragm material for top and bottom plates because of
its rich properties. The top and bottom electrode plate along with the springs uses
platinum as its material. The dielectric material such as vacuum or air is used for the air
block. The material parameters are listed in the Table.5.2.
Table.5.2: Material parameters
Name Value Unit
Density 21450[kg/m^3] Kg/m^3
Relative
permittivity
1 1
Young‟s
modulus
168e9[pa] Pa
Poisson‟s ratio 0.38 1
Once the structure is designed, the next step is to mesh the model which is shown
in Fig. 5.2.
Fig. 5.2 Meshed model of capacitive pressure sensor with 1-spring

The structure shown in the Fig. 5.2 is meshed model of capacitive sensor with
one-spring attached. Here the complete model is divided into a finite number of elements
and each element is analyzed with a minimum element size of 1.5 µm.
The top plate of the diaphragm is free moveable and the bottom plate is fixed.
The boundary load is applied on the top plate of the diaphragm. The Electromechanics
interface is used to find the electrical and mechanical parameters of the design. The
structure is analyzed for the applied pressure ranges from 1pa to 10000pa.
5.2.2 CAPACITIVE PRESSURE SENSOR WITH 4-SPRINGS
Fig. 5.3 Modelled geometry of capacitive pressure sensor with 4-springs
The structure as shown in the Fig. 5.3 is the capacitance pressure sensor with 4-springs
attached. In order to increase the sensitivity of the model, the capacitance pressure
sensor with 1-spring can be modified into 4-springs. Here the model is designed with the
same specification as mentioned in the table 1. The four-springs are attached at each
corner of the sensor in order to improve the device sensitivity and to overcome the pull
in effect between the two plates.

Fig. 5.4 Meshed model of capacitive pressure sensor with 4-springs
The structure shown in the Fig. 5.4 is the meshed model of capacitive pressure
sensor with four springs attached at each corner of the diaphragm. The swept mesh is
used to mesh the model with the minimum element size of 1.5 µm.
Fig. 5.5 (a) Modelled geometry of capacitive pressure sensor with 9-springs

Fig. 5.5 (b) Close view of 9-springs at one edge of sensor
The structure shown in Fig. 5.5 (a) is the modeled geometry of the capacitive pressure
sensor with 9-springs attached at all the four corners of the square diaphragm and
Fig.5.5(b) is the close view of the 9-springs attached at each edge of the sensor. Hence
there are 36-springs are attached from all the four corners of the proposed structure. The
sensitivity of the device can be increased much better in 9-spring structure as compared
to the 1-spring and 4-springs capacitive pressure sensor structures. Once the model
design is completed, the next step is to mesh the design. The meshed model of capacitive
sensor with 9-springs is shown in the Fig. 5.6.

The structure shown in Fig. 5.6 is meshed model of a capacitive sensor with 9-
springs. By attaching more number of springs at each corner of the square diaphragm,
the pull in effect can be reduced by increase in the sensitivity of the sensor so that the
sensor displacement can be constrained.
Hence this proposed work mainly highlights the modeling of different structures
of MEMS based capacitive pressure sensor that gives a better sensitivity using
COMSOL MULTIPHYSICS tool for the structural health monitoring applications.
5.3 MODELLING OF DIFFERENT STRUCTURES OF
CAPACITIVE PRESSURE SENSOR USING
COVENTOR-WARE
The capacitance pressure sensor can be designed with two plates that are placed in
parallel to each other. The capacitive pressure sensor can be designed using
POLYMUMPs process flow that acts as a prevailing process which is shown in Fig. 5.7
POLYMUMPs stand for “POLYSILICON MULTI-USER MEMS
PROCESSES”. Using POLYMUMPs, the cost of the devices can be reduced because
many diverse IC‟s can be designed using single batch process flow. The process flow
consists of stack materials such as silicon, platinum and oxide that are required for the
designing the structure with an appropriate depth and thickness. Each layer of the
materials is followed by a “Deep Reactive-Ion etching” in order to form an anchor. The
“+ve – photoresist” or “–ve – photoresist” can be used depending upon the model
required. The oxide layer is used to avoid the contact between metal layer and a
polysilicon layer.
Apart from these, the metal and silicon layers present within the process flow
that can allow the movable mechanical parts of the sensor for gentle electrical approach.

Fig. 5.7 POLYMUMPs process flow
The capacitive pressure sensor with 1-spring is attached at each corner is designed and
simulated using COVENTORWARE TURBO tool with POLYMUMPs process flow.
The sensor is designed with a design specifications listed in the table-1. To design any
structure in Coventorware, first step is to draw the layout of the model. The layout of
capacitive pressure Sensor with 1-spring is shown in Fig. 5.8
Fig. 5.8 (a) Layout of capacitive pressure sensor with 1-spring

Fig. 5.7 (b) Close view of 1-spring attached at one corner
The structure shown in Fig. 5.8 (a) is the capacitive pressure sensor with 1-spring
attached at all the four corners of the diaphragm and Fig. 5.8 (b) is the close view of 1-
spring that is attached at one corner. Hence there are total four springs attached from all
the four corners of the diaphragm.
Once the layout is drawn, next it is to build solid model to get the 3-Dimenstional
structure. The 3D structure of capacitive sensor with 1-spring is shown in the Fig. 5.8.
Fig. 5.8 3-D structure of capacitive pressure sensor with 1-spring
The structure consists of a top and bottom plates with the length of 10000 ×
10000µm and thickness of 525µm. The top and bottom electrodes is designed along with

Air block which is placed in between two electrode plates with a length of 9500 ×
9500µm and thickness of 2µm and 180µm respectively. The distance between top and
bottom plate is 400µm. The springs are attached at all four corners of the diaphragm in
between top and bottom plates with a length of 80µm and width of 20µm is designed.
The use of springs can reduce the PULL-IN effect by increasing sensitivity of the sensor.
During this step, the one can hide the unwanted layers, generate mesh, set names
for different faces and can define the conductors which are required for MemMech and
MemElectro domain analysis. The model is analyzed for the applied pressure of 1Pa.
The meshed model of capacitive pressure sensor with 1-spring using FEM analysis is
shown in Fig. 5.9
Fig. 5.9 Meshed model of capacitive pressure sensor with 1-spring
In achieve a better sensitivity of the structure; the capacitive pressure sensor with 1-
spring model is modified into a capacitive sensor with 4-springs. Here four springs are
attached at each corner of the square diaphragm and hence there are total 16-springs are
attached from all the edges of the structure. As the number of spring elements increases,
the sensitivity of the device varies. The layout of capacitive pressure sensor with 4-

spring is shown in Fig. 5.10 (a). Fig. 5.10 (b) shows the close view of 4-springs attached
at one corner.
Fig. 5.10 (a) Layout of capacitive pressure sensor with 4-springs
Fig. 5.10 (b) Close view of 4-springs attached at a one corner
To get 3-D structure of the design, it is to build the solid model of the layout. The
3-D model of capacitive pressure sensor with 4-springs is shown in the Fig. 11

Fig. 5.11 3-D structure of capacitive pressure sensor with 4-springs
The structure shown in Fig. 5.11 is the 3-D model of capacitive pressure sensor
with 4-springs attached. Once the 3-D model is ready, the next step is to generate mesh.
The meshed model of capacitive sensor with 4-springs is shown in Fig. 5.12
To overcome the PULL-IN effect causes between two plates when large external
pressure is applied, the capacitive pressure sensor with 9-springs is designed which is a

modified design of capacitive pressure sensor with 1-spring and 4-springs. This design
structure increases the sensitivity of capacitive sensor.
Fig. 5.13 (a) Layout of capacitive pressure sensor with 9-springs
Fig. 5.13 (b) Close view of 9-springs attached at one corner
The layout consists of top and bottom plates with design specification as
mentioned in table-1, the electrode plates along the air block is integrated on two plates.
At each edge of the design, 9-springs are attached and hence from all the four edges of
diaphragm there are 36-spring elements are integrated. This increases the sensitivity of

the sensor. The 3-D structure of capacitive pressure sensor with 9-springs attached is
shown in Fig. 5.14 (a) and Fig. 5.14 (b) is close view of 9-springs integrated at a corner.
Fig. 5.14 (a) 3-D structure of capacitive pressure sensor with 9-springs
Fig. 5.14 (b) Close view of 9-springs attached at one corner
The 3-D structure is made to generate a mesh. The “Manhattan bricks” type of
mesh setting is used to generate a mesh. The meshed model of capacitive sensor with 9-
springs is shown in Fig. 5.15

Hence in this proposed design work, the different structures of capacitive
pressure sensor are designed and simulated using COVENTORWARE TURBO tool
with POLYMUMPs process flow. By this work, one can find the actual structure of
capacitive pressure sensor that outputs a better sensitivity by comparing the simulation
results (Displacement, capacitance and sensitivity). Hence these structures can be used in
the high sensitivity applications.

CHAPTER 6
SIMULATION RESULTS AND DISCUSSIONS
In this proposed project work, the different structures of capacitive pressure sensor have
been designed and simulated using COMSOL MULTIPHYSICS and
COVENTORWARE MEMS CAD tools. The obtained simulated results for these
structures are then compared (sensitivity) to get a better sensitivity structure that can be
used in higher sensitivity applications. Also different analysis can be done for the
proposed designs such as displacement, capacitance and sensitivity.
6.1 COMSOL MULTIPHYSICS RESULTS
Fig. 6.1 Simulation result (Displacement) of capacitive pressure sensor with 1-spring
The structure shown in Fig. 6.1 is the simulation result of capacitive pressure sensor with
1-spring. The model is analyzed for the applied pressure ranges from 1Pa to 10000Pa.
Fig. 6.1(a) shows the maximum displacement of 4.66e-4µm when the uniform external
pressure of 1Pa is applied on top of the diaphragm. The total distance between the two
parallel plates is 400µm; hence the maximum displacement should be less than the
Fig. 6.1(a): Maximum displacement
: 4.66e-4 µm
Fig. 6.1(a): Displacement of 1-
Spring at a corner

actual distance between plates. Fig. 6.1(b) shows the close view of 1-spring displaced at
a corner. The electric potential of the sensor is measured in terms of a volt (V) which is
applied for determining capacitance. The electric potential of 1.21V is obtained and is
shown in Fig. 6.2.
Fig. 6.2 Simulation result (Electric potential) of capacitive pressure senor with 1-spring
The capacitance of the capacitive pressure sensor with 1-spring attached is shown
in the Fig. 6.3.
Fig. 6.3 Simulation result (Capacitance) of capacitive pressure sensor with 1-spring
The structure shown in Fig. 6.3 is the simulation result (capacitance) of
capacitive pressure sensor with 1-spring. When a uniform external pressure of 1Pa is
Fig. 6.2: Electric potential = 1.21V
Fig. 6.3 Maximum capacitance : 5.13e-12
F

applied, the maximum capacitance of 5.12e-12 F for applied bias voltage of 5V 1pa is
obtained. The sensitivity of the sensor is 5.12e-12 F/Pa.
The different applied pressure ranges from 1Pa to 10000Pa is exerted on the
diaphragm and the obtained result of Displacement and capacitance is tabulated in
Table.6.1
Table.6.1: Variation of different parameters of capacitive pressure sensor with 1-spring
Sl.No Pressure
[Pa]
Displacement
[µm]
Capacitance
[F]
Sensitivity
[F/Pa]
1 1 4.66e-4 5.13e-12 5.13e-12
2 100 2.33e-3 5.14e-12 5.17e-14
3 500 0.12 5.14e-12 1.028e-14
4 1000 0.23 5.15e-12 5.15e-15
5 5000 1.17 5.17e-12 1.034e-15
6 10000 2.33 5.19e-12 5.19e-16
By observing the above results, it clearly shows that as the applied pressure
increases the displacement of the sensor increases.
Fig. 6.4(a) Maximum displacement =
2.44e-4 µm
Fig. 6.4(b) Displacement of 4-springs
at a corner

The structure shown in Fig. 6.4 is the simulation result of capacitive pressure sensor with
4-springs. The structure is examined for applied external pressure ranges from 1Pa to
10000Pa. The Fig. 6.4(a) depicts the maximum displacement of 2.44e-4 µm for applied
pressure of 1Pa. Fig. 6.4(b) is the close view of 4-springs deformed which are attached at
a one corner of the sensor diaphragm. Hence the displacement of 4-springs capacitive
sensor is increased by 2.22e-4µm as compared to capacitive pressure sensor with 1-
spring at applied pressure of 1Pa. The electric potential of 1.11V is observed and is
shown in Fig. 6.5
Fig. 6.5 Simulation result (Electric potential) of capacitive pressure sensor with 4-springs
The capacitance of capacitive pressure sensor with 4-springs at bias voltage of
5V is shown in Fig. 6.6
Fig. 6.6 Simulation result (Capacitance) of capacitive pressure sensor with 4-springs
Fig. 6.5: Electric potential = 1.11V
Fig. 6.6: Maximum Capacitance =
6.4e-13 F

The structure shown in Fig. 6.6 is the simulation result of capacitance for
capacitive pressure sensor with 4-springs. Here the maximum capacitance of 6.4e-13 F is
obtained at bias voltage of 5v.
The variation of different parameters such as displacement, capacitance and
sensitivity of the capacitance pressure sensor with 4-springs at uniform applied pressure
ranges from 1Pa to 10000Pa are tabulated in the table.6.2
Table.6.2: Variation of different parameters of capacitive pressure sensor with 4-springs
Sl.No Pressure
[Pa]
Displacement
[µm]
Capacitance
[F]
Sensitivity
[F/Pa]
1 1 2.44e-4 6.4e-13 6.4e-13
2 100 0.02e-2 6.14e-13 6.14e-15
3 500 0.12 6.37e-13 1.274e-15
4 1000 0.24 6.38e-13 6.38e-16
5 5000 1.22 7.87e-13 1.574e-16
6 10000 2.44 1.75e-12 1.75e-16
Fig. 6.7 Simulation result (Displacement) of capacitive pressure sensor with 9-springs
Fig. 6.7(a): Maximum displacement =
1.57e-4 µm
Fig. 6.7(b) Displacement of 9-springs
at a corner

The structure shown in Fig. 6.7 is the simulation result (displacement) of capacitive
pressure sensor with 9-springs. It is the modified structure of capacitive sensor with 1-
spring and 9-springs. Fig. 6.7(a) shows the maximum displacement of 1.57e-4 µm at
applied pressure of 1Pa. By observing the above obtained result, at applied pressure of
1Pa the displacement of capacitive sensor with 9-springs is increased as compared with
1-spring and 4-springs structure.
The applied voltage of 1V is applied to the diaphragm, in which the electric
potential of 1.05V is observed which is shown in Fig. 6.8
Fig. 6.8 Simulation result (Electric potential) of capacitive pressure sensor with 9-springs
The capacitance of the capacitive pressure sensor with 9-springs at bias voltage
of 5V is shown in Fig 6.9
Fig. 6.8: Electric Potential = 1.05 V

The structure shown in Fig. 6.9 is the simulation result i.e. capacitance of
capacitive pressure sensor with 9-springs. Here the capacitance of 5.12e-14 F at applied
bias voltage of 5V is observed. The capacitance can be increased by reducing the gap
between two parallel plates.
Table.6.3: Variation of different parameters of capacitive pressure sensor with 9-springs
Sl.No Pressure
[Pa]
Displacement
[µm]
Capacitance
[F]
Sensitivity
[F/Pa]
1 1 1.57e-4 5.12e-14 5.12e-14
2 100 0.02e-2 5.13e-14 5.13e-16
3 500 0.08 5.15e-14 1.03e-16
4 1000 0.16 5.23e-14 5.23e-17
5 5000 0.79 5.27e-14 1.054e-17
6 10000 1.57 5.28e-14 5.28e-18
The table.6.3 shows the different parameters such as displacement, capacitance
and sensitivity of capacitive pressure sensor with 9-springs. It is observed that as the
Fig. 6.9 Maximum capacitance = 5.12e-14 F

applied pressure increases the displacement of the sensor increased by decrease in
capacitance.
Table.6.4: Comparison of the sensitivities for different capacitive pressure sensor structures
Sl.No Structures Displacement
[µm]
Capacitance
[F]
Sensitivity
[F/Pa]
1 Capacitive pressure
sensor with 1-
spring
4.66e-4 5.13e-12 5.13e-12
sensor with 4-
springs
2.44e-4 6.4e-13 6.4e-13
sensor with 9-
springs
1.57e-4 5.12e-14 5.12e-14
Table.6.4 shows the comparison of displacement, capacitance and sensitivity for
different structures of capacitive pressure sensor which has been simulated at applied
pressure of 1Pa using COMSOL tool. Sensitivity can be defined as the change in
capacitance with respect to applied pressure. The sensitivity of the sensor structure can
be given by equation 6.1
S= ΔC/ΔP ….. (1)
By comparing the above results, the capacitive pressure sensor with 9-springs has
got better sensitivity as compared to other structures. In further, the obtained simulation
results of Displacement and Capacitance of capacitance pressure sensor with 9-springs,
the graph is to be plotted with Pressure versus Displacement and Pressure versus
Capacitance. The graph which is plotted with pressure versus Displacement is shown in
Fig. 6.10

Fig. 6.10 Graph of applied Pressure Versus Displacement
The Fig. 6.10 shows that, by plotting the obtained values of displacement by
varying the applied pressure, the displacement is linearly increases as the applied
pressure increases.
The graph for applied pressure versus Capacitance is shown in Fig. 6.11
Fig. 6.11 Graph of applied Pressure Versus Capacitance
The Fig. 6.11 shows that the graph is plotted for obtained capacitance values by
varying the applied pressure. It shows that the capacitance increases as the applied
pressure increases.

6.2 COVENTORWARE TURBO RESULTS
The structure shown in Fig. 6.12 is the simulation result (Displacement) of capacitive
pressure sensor with 1-spring. The structure is designed and simulated using
COVENTORWARE with POLYMUMPs process flow. The maximum displacement of
1.456e-4 µm is obtained at applied pressure of 1Pa. As compared to the COMSOL result
with COVENTOWARE result, at applied pressure of 1Pa, the displacement of the sensor
with 1-spring attached has been increased by 3.204e-4µm. The analysis of MEMMECH
domain obtained during the simulation is shown in Fig. 6.13
Fig. 6.13 Analysis of MEMMECH domain of capacitive pressure sensor with 1-spring
1.456e-4 µm
Fig. 6.12(b): Displacement of 1-
spring at a corner

The charge density also referred as capacitance of the capacitive pressure sensor
with 1-spring at applied voltage of 5Vis shown in Fig. 6.14
Fig. 6.14 Simulation result (Capacitance) of capacitance pressure sensor with 1-spring
The Fig. 6.14 shows at applied pressure of 1Pa the maximum capacitance of
3.23e01 pF is obtained at applied bias voltage of 5V. By comparing the capacitance
value obtained in COVENTORWARE result with a COMSOL result, it shows that the
capacitance value is increased in the Coventorware which is measured in terms of Pico
farad (pF). The MEMELECTRO analysis of capacitive pressure sensor with 1-spring is
shown in Fig. 6.15
Fig. 6.14: Maximum capacitance = 3.23e01 pF

Fig. 6.15 Analysis of MEMELECTRO domain of capacitive pressure sensor with 1-spring
The Fig. 6.16 shows the simulation result (Displacement) of capacitive pressure sensor
with 4-springs attached at all the corners of the square diaphragm. At external pressure
of 1Pa, the displacement of 4.909e-5 µm is obtained. As the more number of springs
attached to the structure the displacement may be constrained. The MEMMECH analysis
of capacitive pressure sensor with 4-springs at applied pressure of 1Pa is shown in
Fig.6.17
Fig. 6.16(b) Displacement of 4-
springs at a corner
4.909e-5 µm

Fig. 6.17 Analysis of MEMMECH domain of capacitive pressure sensor with 4-springs
The capacitance of capacitive pressure sensor with 4-springs is analyzed for
applied bias voltage of 5V and is shown in Fig. 6.18
The Fig. 6.18 shows the capacitance of 7.879e0 pF is observed for capacitive
pressure sensor with 4-springs. Here the capacitance sensitivity of the model is increased
by 4.649 pF as that of capacitance sensor with 1-spring. The MEMELECTRO analysis
of capacitive pressure sensor with 4-spring is shown in Fig. 6.19
Fig. 6.18: Maximum capacitance = 7.879e0 pF

Fig. 6.19 Analysis of MEMELECTRO domain of capacitive pressure sensor with 4-springs
The structure shown in Fig. 6.20 is the simulation (displacement) of capacitive pressure
sensor with 9-springs. Here the maximum displacement of 3.288e-5 µm is obtained at
applied pressure of 1Pa. The analysis of MEMMECH domain is carried out for
capacitive sensor with 9-springs and the result obtained is shown in Fig. 6.21
Fig. 6.20: Maximum displacement = 3.288e-5 µm

Fig. 6.21 Analysis of MEMMECH domain of capacitive pressure sensor with 9-springs
The capacitance of two plates that are placed in parallel can be given by
Equation.6.1
C = ….. (6.1)
Where = permittivity of Air Medium
A = Area of the plates
D = Distance between two parallel plates
From the Equation 6.1, it shows that capacitance is inversely proportional to the
distance between the two parallel plates. It means the capacitance can be increases by
decreasing the gap between parallel plates. In this proposed work, at applied pressure of
1Pa the capacitance can be obtained. The MEMELECTRO analysis of capacitive
pressure sensor with 9-springs is shown in Fig. 6.22. MEMELECTRO can be analyzed
by contact of voltage-ground. The capacitance of 1.013e0 Pf is obtained for applied
pressure of 1Pa. Here negative sign can be neglected.

Fig. 6.22 Analysis of MEMELECTRO domain of capacitive pressure sensor with 9-springs

Table. 6.5: Comparison of sensitivities for capacitive pressure sensor structures
Sl.No Structures Displacement
[µm]
Capacitance
[pF]
Sensitivities
[pF]
1 Capacitive
pressure sensor
with 1-spring
1.456e-4 3.23e01 3.23e01
2 Capacitive
pressure sensor
with 4-springs
4.909e-5 7.879e0 7.879e0
3 Capacitive
pressure sensor
with 9-springs
3.288e-5 1.013e0 1.013e0
The table.6.5 shows the comparison of displacement, capacitance and sensitivity
for different structures of capacitive pressure sensor at applied pressure of 1Pa. By
observing the above results, the capacitive pressure sensor with 9-springs gives the high
sensitivity of 1.013e0 pF at applied pressure of 1Pa. hence these sensors can be preferred
for high sensitivity applications in the field of automotive, Industries sectors, medical
appliances etc.

CHAPTER 7
CONCLUSION AND FUTURE SCOPE
CONCLUSION
In this proposed work, different structures of capacitive pressure sensor have been
designed and simulated using COMSOL MULTIPHYSICS and COVENTORWARE
TURBO MEMS CAD tools. The capacitive pressure sensor can be designed using two
plates that can be placed in parallel to each other. The spring elements are attached in
between two plates at each corner of the structure in order to improve the device
sensitivity. Silicon is the material used for the diaphragm due to its better properties.
There are three different structures of capacitive pressure sensor have been designed.
The first structure is a capacitive pressure sensor with 1-spring using COMSOL
MULTIPHYSICS with Finite Element Method (FEM) analysis. The obtained sensor
result exhibits
 Displacement of 4.66e-4 µm.
 Capacitance of 5.13e-12 F.
 Sensitivity of 5.13e-12 F/Pa.
The same structure is also designed and simulated using COVENTORWARE
TURBO which is fabricated using POLYMUMPs Process Flow. The obtained sensor
result exhibits
 Capacitance of 3.23e01 pF.
 Sensitivity of 3.23e01 pF.
The second structure is a capacitive pressure sensor with 4-springs using
COMSOL MULTIPHYSICS by FEM analysis. The obtained result exhibits

The same structure of capacitive pressure sensor with 4-springs can also be
designed and implemented using COVENTORWARE TURBO which is fabricated using
POLYMUMPs Process flow. The result obtained exhibits
The third structure is the capacitive pressure sensor with 9-springs using
COMSOL MULTIPHYSICS by FEM analysis. The obtained result exhibits
The same structure of capacitive pressure sensor with 9-sprigs can be cesigned
and implemented using COVENTORWARE TURBO which can be fabricated using
POLYMUMPs Process Flow. The obtained result exhibits
Hence, depending upon the applications and high sensitivity requirements these
structures of capacitive pressure sensor can be used.
FUTURE SCOPE
 The proposed work of capacitive pressure sensor can be further Fabricated and
Characterized using POLYMUMPs Process Flow which can be used in many
structural health monitoring applications.

complete m.tech project report_2017 (Based on MEMS Technology)

complete m.tech project report_2017 (Based on MEMS Technology)

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