This article speaks about the different energy domains, sensors, actuation techniques, transduction techniques, fabrication materials, physical strength requirements, substrate materials and De Vries formula used in MEMS technology.

1. MEMS
Sensors, Transducers & Actuator

2. Contents
1. MEMS Sensors Domains
2. MEMS Transducers
3. MEMS Actuators
4. MEMS Fabrication Materials
5. MEMS Fabrication Material Properties
6. MEMS Substrate
7. Die Per Wafer (DPW)
Micro-Electro Mechanical Systems 2

3. MEMS – Sensor Domains:
 Sensor – Senses one form of energy.
 The MEMS technology ventures in the following domains by using different sensors,
1. Physical/ Mechanical Sensors deal with – Force, Pressure, Velocity, Acceleration,
Position.
2. Chemical Sensors deal with – Concentration, Material composition, Reaction Rate.
3. Electrical Sensors deal with – Voltage, Current, Charge, Phase, Resistance, Capacitance,
Inductance.
4. Thermal Sensors deal with – Temperature, Entropy, Heat, Heat Flow.
5. Magnetic Sensors deal with – Magnetic Field Intensity, Flux Density, Magnetization.
6. Radio Frequency Sensors deal with – EM Wave Intensity, Wavelength, Polarization.
7. Optical Sensors deal with – Reflectance, Refractive Index, Transmittance, Dispersion.
Micro-Electro Mechanical Systems 3

4. MEMS Transducers -
 Core of the MEMS device
1. Micro-sensing,
2. Micro-transduction,
3. Micro-actuation.
 A transducer is a device that converts one form of energy into another form of energy.
 An actuator is a part of or a machine that is responsible to control the output using movable parts
by some control mechanism, and therefore it is generally referred to as “Mover”, e.g., Valve.
Micro-Electro Mechanical Systems 4

5. MEMS Transducers -
 The current MEMS-based technology is operational with the following transduction.
1. Tribo-electric – Glass (𝑆𝑖𝑂4), Silk, Hard rubber ( 𝐶5𝐻8 𝑛), fur.
2. Electrostatic – Amber Rod (𝐶10𝐻16𝑂).
3. Piezoelectric – Quartz (𝑆𝑖𝑂2), Lead Zirconate Titanate (𝑃𝑍𝑇), Polyvinylidene Fluoride
(𝑃𝑉𝐷𝐹), Zinc Oxide (𝑍𝑛𝑂), Bone, DNA.
4. Ferroelectric – Barium Titanate (𝐵𝑎𝑇𝑖𝑂3), Lead Titanate (𝑃𝑏𝑇𝑖𝑂3) Lead Zirconate Titanate
(PZT) and Rochelle salt (i.e. Potassium Sodium Tartrate Tetra-hydrate
(𝐾𝑁𝑎𝐶4𝐻4𝑂6. 4𝐻2𝑂))
5. Magnetostrictive – Cobalt Ferrite ( C𝑜𝐹𝑒2𝑂4 𝐶𝑜𝑂. 𝐹𝑒2𝑂3 ), Alloys like Terfenol-D
[Terbium-Iron-Dysprosium (𝑇𝑏𝑥𝐷𝑦1−𝑥𝐹𝑒2 )], Galfenol (Gallium-Iron), Metglas 2605SC
[Metallic Glass]
6. Magnetic – Iron, Steel, Nickel, Cobalt.
Micro-Electro Mechanical Systems 5

6. MEMS Transducers -
7. Electromagnetic Acoustic Transducer (EMAT) – Magnet, and Electric Coil.
8. Radio-frequency – Short range device frequency 315 MHz to 868 MHz.
9. Thermal – Metallic Oxides, Semiconductors, Platinum.
10. Optical – Smart polymers, metal, metal oxide and semiconductor materials LED, Light
Modulators.
11. Chemical (micro-fluidics) – Calorimetric transducers, Chemi-capacitors, Chemi-resistors,
Chemo-mechanical sensors.
12. Biological and biomedical – Bio-receptors viz. Enzymes, Ligands, Nucleic Acids, DNA.
Micro-Electro Mechanical Systems 6

7. MEMS Actuators -
 Major MEMS Actuation Techniques:
Micro-Electro Mechanical Systems 7
Fig. 3. MEMS based actuations

8. MEMS Actuators -
 Widely used MEMS actuators:
1. Electrostatic Actuator – Parallel-plate actuator, Comb-drive actuator (inter-digitated finger
structure).
2. Piezoelectric Actuator – Stack Actuators (multiple-layered piezo element) and Stripe
Actuators (bi-laminar flexing element).
3. Electro-Magnetic Actuator – Solenoid actuator (electromagnetic), Moving-coil actuator.
4. Electro-Thermal Actuator – V-type, hot arm/U-type, and bimorph (double-layered
cantilever).
5. Optical Actuator – Charge-coupled Devices (CCD) (integrated circuit linked capacitors).
6. Physical Actuators - Shape Memory Alloy (SMA) Actuator (elastically deformable).
7. Chemical Actuator – Microelectrodes (bio-compatible).
Micro-Electro Mechanical Systems 8

9. MEMS – Fabrication Materials:
 The materials that are widely used in MEMS device manufacturing are,
1. Non-metals/Metalloid – Silicon, Germanium, Gallium Arsenide (𝐺𝑎𝐴𝑠).
2. Polymer (long, repeating chains of molecules) – SU8 (Bisphenol A Novolac 8-epoxy),
Polyamide (𝑛 − (𝐶𝑂 − 𝑁𝐻)))
3. Ceramic – Diamond, Silicon Carbide (𝑆𝑖𝐶), Silicon Dioxide (𝑆𝑖𝑂2), Silicon Nitride (𝑆𝑖3𝑁4).
4. Metal – Nickel, Aluminium, Copper, Titanium, Tungsten.
Micro-Electro Mechanical Systems 9

10. MEMS Fabrication Materials –
 The Polymer materials used in MEMS fabrication process are
1. SU-8, epoxy based negative photoresist,
2. Polyimide (imide group (= 𝑁𝐻)) which are high performance plastics,
3. Parylene (𝑃𝑎𝑟𝑎 − 𝑥𝑦𝑙𝑒𝑛𝑒 𝐶8𝐻10 , 𝑝𝑎𝑟𝑎 − 𝑏𝑒𝑛𝑧𝑒𝑛𝑒𝑑𝑖𝑦𝑙 𝑟𝑖𝑛𝑔𝑠 (𝐶6𝐻4)),
4. Poly-dimethyl-siloxane (𝑃𝐷𝑀𝑆) (polymeric organosilicon (𝐶 − 𝑆𝑖) compounds),
5. Liquid Crystal Polymers (𝐿𝐶𝑃𝑠),
6. Cyclic Olefin Polymers (𝐶𝑂𝑃𝑠),
7. Poly-methyl Methacrylate (𝑃𝑀𝑀𝐴 𝑜𝑟 𝑝𝑙𝑒𝑥𝑖 − 𝑔𝑙𝑎𝑠𝑠),
8. Polycarbonate (𝑃𝐶) (𝑂𝐶 𝑂𝐶 2 𝑐𝑜𝑟𝑒),
9. Polystyrene (𝑃𝑆) (𝑝𝑜𝑙𝑦 − 𝐶6𝐻5𝐶𝐻 = 𝐶𝐻2)
10. Poly-Vinylidene Fluoride (𝑃𝑉𝐷𝐹) (𝑝𝑜𝑙𝑦 − 𝐶2𝐻2𝐹2).
Micro-Electro Mechanical Systems 10

11. MEMS – Fabrication Materials Properties:
 The properties which are looked up carefully before choosing the material for fabrication are,
1. Elastic Properties – Young’s Modulus (elasticity) and Poisson’s Ratio (deformation).
2. Inelastic Properties – Plastic deformation, Fatigue (break-point stress).
3. Strength Properties – Tensile Strength (breaking resistance), Fracture Strength, Flexural
Strength (rupture modulus) and Yield Strength (elastic-behavior limit).
Micro-Electro Mechanical Systems 11

12. MEMS Substrate -
 Substrate (wafer or slice) - Base upon which a design and processing is carried out.
 It is a thin semiconductor slice.
 It produces new films, or material layers like deposited coatings.
 Commonly used substrate materials - Crystalline Silicon (𝑐 − 𝑆𝑖), Electronic-grade Silicon
(𝐸𝐺𝑆).
 EGS is exceptionally pure polycrystalline Silicon (impurity in few ppb).
 The (𝑐 − 𝑆𝑖) can be polycrystalline Silicon (𝑝𝑜𝑙𝑦 − 𝑆𝑖 𝑜𝑓 𝑠𝑚𝑎𝑙𝑙 𝑐𝑟𝑦𝑠𝑡𝑎𝑙), or mono-crystalline
Silicon (𝑚𝑜𝑛𝑜 − 𝑆𝑖 𝑜𝑓 𝑐𝑜𝑛𝑡𝑖𝑛𝑢𝑜𝑢𝑠 𝑐𝑟𝑦𝑠𝑡𝑎𝑙).
Micro-Electro Mechanical Systems 12

13. MEMS Substrate -
 “Die” – Colloquial term for the block of semiconducting material on which the circuit is to be
fabricated.
ICs are produced on single wafer EGS or semiconductors like Gallium Arsenide (𝐺𝑎𝐴𝑠),
Gallium Nitride (𝐺𝑎𝑁), Silicon Carbide (𝑆𝑖𝐶 ) in large batches using photolithography
techniques.
The single large wafer is cut into multiple identical pieces with one piece having the circuit lay-
out. Each of these pieces of wafer is individually called a “Die” (plural die, dies, dice).
The typical thickness of the Wafer is in the range of micrometers (𝜇𝑚).
Micro-Electro Mechanical Systems 13
Silicon-on-Insulator Substrate

14. MEMS – Die per Wafer (DPW)
 The number of ‘Die per Wafer’ (DPW)
𝑫𝑷𝑾 =
𝝅𝒓𝟐
𝑺
=
𝝅𝒅𝟐
𝟒𝑺
𝑑 = 𝑤𝑎𝑓𝑒𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑚𝑚 , 𝑆 = 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑒𝑎𝑐ℎ 𝑑𝑖𝑒 𝑚𝑚2 , 𝑟 = 𝑟𝑎𝑑𝑖𝑢𝑠
The total area of the number of dies that can fit on the wafer is less than the wafer area.
The wafer is divided into individual dies, out of which few dies are partially patterned.
 The De-Vries Correction Factor to maximize the completely patterned dies
𝑫𝑷𝑾 =
𝝅𝒅𝟐
𝟒𝑺
−
𝝅𝒅
𝟐𝑺
𝒐𝒓 𝑫𝑷𝑾 =
𝝅𝒅𝟐
𝟒𝑺
𝟏 −
𝟐 𝑺
𝒅
𝟐
Micro-Electro Mechanical Systems 14

15. MEMS – Die per Wafer (DPW):
 The figure below shows how the Dies or Dice are patterned on a Wafer substrate.
Micro-Electro Mechanical Systems 15
Fig. 4. 2-inch (51 mm), 4-inch (100 mm), 6-inch (150 mm), and 8-inch (200 mm) wafers

16. References:
1. P.C https://www.mems-exchange.org/MEMS/what-is.html
2. P.C https://www.bosch-sensortec.com/about-us/our-company/mems-expertise/
3. P.C https://wpo-altertechnology.com/mems-packaging/
4. Gabriel K, Jarvis J, Trimmer W (1988). Small Machines, Large Opportunities: A Report on the Emerging
Field of Microdynamics: Report of the Workshop on Microelectromechanical Systems Research. National
Science Foundation (sponsor). AT&T Bell Laboratories.
5. Waldner JB (2008). Nanocomputers and Swarm Intelligence. London: ISTE John Wiley & Sons.
p. 205. ISBN 9781848210097.
6. Angell JB, Terry SC, Barth PW (1983). "Silicon Micromechanical Devices".
7. Sci. Am. 248 (4): 44–55
8. Bibcode:1983SciAm.248d..44A. doi:10.1038/scientificamerican0483-44.
9. Dirk K. de Vries (2005). "Investigation of gross die per wafer formulas". IEEE Transactions on
Semiconductor Manufacturing. 18 (February 2005): 136–139.
10. https://en.wikipedia.org/wiki/Flexural_strength
Micro-Electro Mechanical Systems 16