Radio frequency mems
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This document discusses RF MEMS and their applications in wireless communication systems. RF MEMS can be used to develop micro-machined devices such as filters, oscillators, switches, resonators, capacitors and inductors. These devices integrate RF components onto a single wafer using material science, circuit technology, mechanical engineering and communication methods. Some key applications of RF MEMS include transmission/reception, VCO tuning, RF filtering and variable delay lines.
Radio frequency mems
- 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
- 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