useful for 4th year students of mechanical engineering in memes subject

2. Wireless technology utilizes RF Signal which is EM
Signal
RF operates in the range 9khz to 300Ghz
RF MEMS is afield that is concerned with the
development of micro machined devices such as
1.filters
2.oscillators
3.switches
4.resonators
5.capacitors
6.inductors

3.  RF MEMS are the product of
 material science
Circuit technology
Mechanical engineering& communication methods
RF MEMS to deliver integrated RF components on same Wafer
RF MEMS can be used for achieving
transmission and reception
VCO Tuning
RF band select filters
intermediate frequency filtering
time delay for phased arrays
Variable delay lines

4.  Any communication systems consists of 3 main
building blocks namely
1.transmitter
2.receiver
3.communication media
1.transmitter:-
 the transmitter transmits the baseband
original signal by adopting appropriate modulation
techniques.
The modulated signal is transmitted to the channel
through an impedance machining unit

5. 2.receiver:-
 the receiver receives modulated signal from
the channel and demodulates it to get back the
original signal
There exist various types of channels ,including optical
fiber, conducting wire, cable and air.
When air is used as the channel antennas are required
at both ends namely
1. one at transmitting end :- to transmit the
modulated RF signal
2. at receiving end :- to receive RF signal

6. 3.communication system:
the basis of communication system is to
deal with the transmission of spectral power of
the desired frequency component or band one
point to another in an effective way

7. Original
Signal
To be
transmitt
ed
modulator
RF
oscillator
tuner Mixer fitter
RF
oscillator
Amplifier and
other units
De
modular
channels
Transmitter receiver
Fig :-RF based communication systems

8. List-1 List-2
Amplifier tuner
Modulator resonator
Mixer coupler
Isolator phase shifter
Phase locked loop

9. Dedicated MEMS device used for RF
applications are called RF MEMS
RF MEMS technology is a
high quality
Three dimensional
Microscale structure

10.  Aerospace
 Defense
 commercial
 Instrumentation
 RF communication
 Microwave communication
 Global positioning systems
 Broadband wireless access and wireless data link
 Mobile communication
 Mobile robots
 Navigation

11.  Low power consumption
 High switching speed
 Low signal level operations
 Low allowable losses
 Low cost
 very high quality factor

12.  conductor coils are called inductors
 Inductors are basic building blocks of all all types of
Oscillator delay and actuating circuits
 RF inductors are used at RF Frequency Range
 Types of inductors :-
straight
spiral
solenoid
toroidal

13.  RF micro :inductors are two types:- namely
planer coil inductor
solenoid type inductor
planer coil inductor:-
 planer inductors are either rectangular or circular
 in planer inductors Q ( high quality factor ) value can
be determined with the help of this formulae
Q= wLs/Rs
Where Ls = inductance
Rs = resistance inductor

14.  RF antennas are of various types ,one type is
solenoid structure .
 Solenoid inductor can be used for tuning
applications
 In a receiving antenna the time variant radiated
electromagnetic current appears at the surface of
the solenoid structure

15.  A varactor is also called varicap
 The short form of variable capacitor is called
varactor
 Varactor is an active device whose capacitance
value is varied by some means
Types of varactors
1.semiconductor varactors
2.MEMS varactors

16.  It have long been in use not only in the RF
communication systems but also in many other
applications like instrumentation and control
MEMS varactors :
 MEMS varactor is recent development
 The MEMS varactor coupled with an inductor ina
feedback loop sustained by negative resistance
amplifier .

17.  Low power consumption
 High quality factor
 Low harmonic distortion
 large tuning range
 Tolerance for high voltage swing

18.  A simple capacitor inductor circuit be act as the tuner
for RF receiver
 it is usually connected to the antenna
 When the induced RF signal in antenna matches with
this frequency resonance occurs .
 The method of producing resonance is known as
tuning and achieved by tuner circuit
 Q (high quality factor ) mathematically for tuners
Q=fr /(f +1/2 – f _1/2)

19.  Resonators are papular where the need of high
stability and selectivity arises
 Resonators are used for high frequency applications at
which the Lcoscillator does not have a reach
 Resonator is simply occlitor ,gometrically it is a hallow
chamber
 The dimension of chamber plays an important role
 The hallow space normally bounded by an electrically
conducting surface in which oscillating
electromagnetic energy is stored

20. MEMS RESONATORS
• mechanical system of a spring with spring constant k and a
mass m has a resonant frequency
• In electronics, this is analogous to a series or parallel
combination of capacitor and inductor, with a small series
resistance (damper).
1
2
r
k
f
m
 
  
 

21. MEMS RESONATORS
• Illustration of Q (review from before)

22. MEMS RESONATORS
• quartz crystals
• IC oscillators have not been able to achieve large Q
• typical quartz crystal has a Q that reaches 10,000 or
more
• quality factors above 1,000 are considered high for many
electronic and RF applications
• frequencies of interest cover the range between 800 MHz
and 2.5 GHz for front-end wireless reception and
intermediate frequencies at 455 kHz and above

23.  Patch resonator and via resonator
 Micro disk resonator
 Bulk mode resonator

24.  Resonator three dimensional high resistibility silicon
substrate filled cavity resonators
 fr=C

26. COMB DRIVE RESONATOR
• folded springs supporting a shuttle
plate
• plate oscillates back and forth in
the plane of the wafer surface
• applied voltage, either positive or
negative, generates an electrostatic
force between the left anchor comb
and shuttle comb that pulls the
shuttle plate to the left

27. COMB DRIVE RESONATOR

28. Comb Drive Resonator
• A comb-drive resonator made of polycrystalline silicon
• standard surface-micromachining
• beams with a thickness 2 µm, widths of 2 µm, and
lengths of 185 µm
• system spring constant of 0.65 N/m
• moveable mass equal to 5.7 × 10-11 kg
• resonates at 17 kHz
• same beam thickness and width but reducing the
length to 33 µm
• resonates at 300 kHz
• Q can be over 50,000 in vacuum but rapidly decreases
to below 50 at atmospheric pressure
• damping in air

29. Beam Resonator
• MEMS with higher resonant frequency
• beam resonators
• University of Michigan, Ann Arbor
• reference frequency oscillators to
replace quartz crystals in cell phones
• much smaller size
• ability to build several different
frequency references on a single chip
• higher resonant frequencies
• ability to integrate circuitry, either
on the same chip or on a circuit chip
bonded to the MEMS
• all at a lower cost than the
traditional technology

30. Coupled Resonators as Band pass Filters
• in phase
• no relative
displacement
between two masses
• oscillation
frequency equal to
natural frequency of
a single resonator
• out of phase
• displacements in
opposite directions
• higher oscillation
frequency

31. Coupled Resonators as Band pass Filters
• physical coupling of the two masses
effectively split the two overlapping
resonant frequencies into two distinct
frequencies
• how far apart these frequencies are
depends on the stiffness of the coupling
flexure
• for compliant coupling spring, the two
split frequencies are sufficiently close to
each other that they effectively form a
narrow passband.

32. COUPLED RESONATORS AS BANDPASS FILTERS
• physical coupling of the two
masses effectively split the two
overlapping resonant frequencies
into two distinct frequencies
• how far apart these frequencies are
depends on the stiffness of the
coupling flexure
• for compliant coupling spring, the
two split frequencies are sufficiently
close to each other that they
effectively form a narrow pass band.

33. MEMS SWITCHES
• key desirable parameters in RF switches are
• low insertion loss and return loss (reflection) in closed state
• high isolation in the open state
• high linearity
• high power-handling capability during switching
• low operating voltage (for portables)
• high reliability (particularly a large number of cycles before failure)
• small size
• and low cost
• MEMS switches to be designed into new products, must surpass the
performance of, or offer some other advantage over existing

34. MEMS SWITCHES
• MEMBRANE SHUNT SWITCH
• University of Michigan
• 2-µm-thick layer of gold suspended 2 µm above a 0.8-
µm-thick gold signal line
• coated with ~0.15 µm of insulating SiN
• membranes span 300 µm and lengths of 20 to 140 µm
• 15-V dc voltage to signal line (in addition to the ac
signal) pulls gold membrane down to the nitride

35. MEMS SWITCHES

36. capacitive coupled switch
capacitive coupling
switching is better than the contact
based switching
capacitive couplings are of two
types
1.shunt coupling
2.series coupling