MEMS Technologies for Communications

Transcription

1 MEMS Technologies for Communications Clark T.-C. Nguyen Program Manager, MPG/CSAC/MX Microsystems Technology Office () Defense Advanced Research Projects Agency Nanotech 03 Feb. 25, 2003

2 Outline Introduction: Miniaturization of Transceivers need for high-q MEMS Components for RF Front Ends micromechanical RF switches tunable micromechancial C s & L s vibrating micromechanical resonators Micromechanical Circuits Chip-Scale Atomic Clocks Conclusions

3 Frequency Division Multiplexing Information is transmitted in specific frequency channels within specific bands Transmitted Power Band GSM Band Adj. Band DCS1800 Band Frequency

4 Frequency Division Multiplexing Information is transmitted in specific frequency channels within specific bands Transmitted Power Band Filter GSM Band Adj. Band DCS1800 Band Frequency

5 Frequency Division Multiplexing Information is transmitted in specific frequency channels within specific bands Transmitted Power Band Filter GSM Band Adj. Band DCS1800 Band Need: high frequency selectivity Need: high frequency stability Frequency

6 Frequency Division Multiplexing Information is transmitted in specific frequency channels within specific bands Transmitted Power Band Filter GSM Band Adj. Band DCS1800 Band Need: high frequency selectivity Need: high frequency stability need high Q Frequency v i i o i v o i Higher Higher Q Resonant Circuit ω ο ω

7 Attaining High-Q Problem: IC s cannot achieve Q s in the thousands transistors consume too much power to get Q on-chip spiral inductors Q s no higher than ~10 off-chip inductors Q s in the range of 100 s Observation: vibrating mechanical resonances Q > 1,000 Example: quartz crystal resonators (e.g., in wristwatches) extremely high Q s ~ 10,000 or higher (Q ~ 10 6 possible) mechanically vibrates at a distinct frequency in a thickness-shear mode DARPA

8 So Many Passive Components! The total area on a printed circuit board for a wireless phone is often dominated by passive components passives pose a bottleneck on the ultimate miniaturization of transceivers Transistor Transistor Chips Chips Quartz Quartz Crystal Crystal Inductors Inductors Capacitors Capacitors Resistors Resistors IF IF Filter Filter (SAW) (SAW) RF RF Filter Filter (ceramic) (ceramic) IF IF Filter Filter (SAW) (SAW)

9 Surface Micromachining Fabrication steps compatible with planar IC processing

10 Single-Chip Ckt/MEMS Integration Completely monolithic, low phase noise, high-q oscillator (effectively, an integrated crystal oscillator) To allow the use of >600 o C processing temperatures, tungsten (instead of aluminum) is used for metallization Oscilloscope Output Waveform [Nguyen, Howe 1993]

11 Benefits of MEMS: Size Reduction Quartz Quartz Crystal Crystal Inductors RF Inductors RF Filter Filter Transistor Capacitors Transistor Capacitors IF IF Filter (ceramic) Filter (ceramic) Chips Resistors Chips Resistors (SAW) (SAW) IF IF Filter Filter (SAW) (SAW) MEMS Technology Single-Chip Transceiver

12 MEMS Replaceable Components Next generation cell phones need multi-band reconfigurability even larger number of high-q components needed Micromachined versions of off-chip components, including vibrating resonators, switches, capacitors, and inductors, could maintain or shrink the size of future wireless phones

13 Micromechanical Switches

14 Switchable SwitchableLC LC Bandpass BandpassFilter μmechanical RF Switch Uses Switch Switch in in capacitors capacitors to to program program the the filter filter center center frequency frequency Again, Again, switch switch in in elements elements to to program program center center frequency frequency

15 Micromechanical Switch Operate the micromechanical beam in an up/down binary fashion Input Output Electrode Dielectric [C. Goldsmith, 1995] Performance: I.L.~0.1dB, IIP3 ~ 66dBm (extremely linear) Issues: switching voltage ~ 50V, switching time: 1-5μs

16 Zipper-Actuated RF MEMS Switch Tri-layer cantilever AC switch comp-sio 2 / Al / tensile-sio 2 zipper actuator allows low V actuate ~35-40V, V hold ~8-10V tri-layer stress pull-up force can tailor actuation waveform for best performance Reliability Performance: >100 B mechanical cycles ~ 10 hr hold-down times 7W max cold switched power [Keast 2002] Need: more indep. testing

17 Phased Array Antenna

18 Medium-Q Resonators

19 Medium-Q Resonator Needs Problem: Switch loss compromises filter loss Switchable SwitchableLC LC Bandpass BandpassFilter Medium-Q best achieved via tunable micromachined capacitors and inductors

20 Medium-Q Resonator Needs Eliminates Eliminates switch switch loss loss better better insertion insertion loss loss Tunable Tunable LC LC Bandpass BandpassFilter Medium-Q best achieved via tunable micromachined capacitors and inductors Mechanically Mechanically tunable tunable LC LC tank tank with with higher higher Q than than conventional conventional on-chip on-chip tanks tanks

21 Voltage-Tunable High-Q Capacitor Micromachined, movable, aluminum plate-to-plate capacitors Tuning range exceeding that of on-chip diode capacitors and on par with off-chip varactor diode capacitors DARPA Challenges: microphonics, tuning range truncated by pull-in

22 Larger Capacitive Tuning Range Use comb-transducers to actuate multiple plate capacitors V tune [Yao 1999] [Rockwell] Left: lateral combcapacitor in deep RIE ed silicon Nearly 250% tuning range with ~100V of actuation input

23 Suspended, Stacked Spiral Inductor Strategies for maximizing Q: 15μm-thick, electroplated Cu windings reduces series R suspended above the substrate reduces substrate loss

24 Out-of-Plane Micromachined Inductor Molybdenum-chromium metal solenoids perpendicular to the plane of the substrate reduced substrate loss high Q Assembled out-of-plane via curling stresses, then locked into place Record Q s: ~70 on glass, ~40 on 20Ω-cm silicon Stress Curled Metal Design/Performance: D=600μm, t=1μm t=1μm On On Glass Glass Substrate: L = 8nH, 8nH, Q = 70 1GHz 1GHz On On 20Ω-cm Silicon: L = 6 nh, nh, Q = 40 1GHz 1GHz [Chua, Locking Hilton Head 02] Mechanism [PARC] Solenoid Inductor D

25 High-Q Resonators

26 High-Q Resonator Needs Best Best if if Q >300 >300 Would Would like like Q s Q s >2,000 >2,000 Would Would like like Q s Q s >5,000 >5,000 Would Would like like Q s Q s >10,000 >10,000 High-Q best achieved via vibrating micromechanical resonators Best Best when when highest highest Q used used

27 Thin-Film Bulk Acoustic Resonator (FBAR) Piezoelectric membrane sandwiched by metal electrodes extensional mode vibration: 1.8 to 7 GHz, Q ~500 dimensions on the order of 200μm for 1.6 GHz link together in ladders to make filters Agilent FBAR Limitations: Q only 500 (would like >2,000) difficult to achieve several different freqs. on a single-chip

28 CC-Beam μmechanical Resonator To date, most used design to achieve HF frequencies Smaller mass higher frequency range and lower series R x

29 Fabricated 8.5-MHz CC-μBeam Surface-micromachined, POCl 3 -doped polycrystalline silicon Extracted Q = 8,000 (vacuum) Freq. and Q influenced by dc-bias and anchor effects

30 92 MHz Free-Free Beam μresonator Free-free beam μmechanical resonator with non-intrusive supports reduce anchor dissipation higher Q

31 92 MHz Free-Free Beam μresonator Free-free beam μmechanical resonator with non-intrusive supports reduce anchor dissipation higher Q

32 DARPA Nanomechanical Vibrating Resonator Constructed in SiC material w/ 50 nm Al metallization for magnetomotive pickup [Roukes, Zorman 2000] h Wr Magnetomotive Resp. [nv] Lr Design/Performance: Lr =3 μm, Wr =150 nm, h= 259 nm fo=732.9mhz, Q=7, Frequency [MHz] 194.0

33 Scaling-Induced Performance Limitations Mass Loading Noise Contaminant Molecules [J. R. Vig, 1999] Temperature Fluctuation Noise Photons f = o 1 2π k m mass ~10-13 kg volume ~10-15 m 3 Differences in rates of Absorption/emission of adsorption and desorption photons of contaminant molecules temperature fluctuations mass fluctuations frequency fluctuations frequency fluctuations Problem: If dimensions too small phase noise significant! Solution: operate under optimum pressure and temperature

34 156 MHz Radial Contour-Mode Disk Micromechanical Resonator Below: Balanced radial-mode disk polysilicon μmechanical resonator (34 μm diameter) μmechanical Disk Resonator Metal Electrode Design/Performance: R=17μm, t=2μm d=1,000å, V P =35V f o =156.23MHz, Q=9,400 Metal Electrode R Anchor f o =156MHz Q=9,400 [Clark, Hsu, Nguyen IEDM 00]

35 733 MHz Self-Aligned Radial Contour- Mode Disk μmechanical Resonator Self-aligned stem for reduced anchor dissipation Polysilicon electrodes for better gap stability Q > 6,000 seen even in air (i.e., atmospheric pressure)! DARPA Below: 20 μm diameter disk Polysilicon Electrode Self-Aligned Stem R Polysilicon Electrode Design/Performance: R=10μm, t=2.1μm, d=800å, V P =6.2V f o =732.9MHz (2 nd mode), Q=7,330 Transmission (db) f o = 732.9MHz Q = 7,330 (vac) Q = 6,100 (air) f o =433MHz Q=4,066 μmechanical Disk Resonator Ground Plane Frequency (MHz) [Wang, Nguyen 2002]

36 1.14-GHz Self-Aligned Radial Contour- Mode Disk μmechanical Resonator Self-aligned stem for reduced anchor dissipation Operated in the 3 rd radial-contour mode Q > 1,500 seen even in air (i.e., atmospheric pressure)! DARPA Below: 20 μm diameter disk Polysilicon Electrode μmechanical Disk Resonator Self-Aligned Stem Polysilicon Electrode R Ground Plane Transmission [db] Design/Performance: R=10μm, t=2.1μm, d=800å, V P =6.2V f o =1.14 GHz (3 rd mode), Q=1, Frequency [MHz] [Wang, Nguyen 2003] f o = 1.14 GHz Q = 1,595 (vac) Q = 1,583 (air)

37 Polysilicon Resonator f o -Q Product Frequency-Q Product Intrinsic Intrinsic material material Q limit limit nowhere nowhere in in sight? sight? Year Freq.-Q product rising exponentially over the past years In the process: sizes of resonators have not changed much

38 733 MHz Self-Aligned Radial Contour- Mode Disk μmechanical Resonator Self-aligned stem for reduced anchor dissipation Polysilicon electrodes for better gap stability Q > 6,000 seen even in air (i.e., atmospheric pressure)! DARPA Below: 20 μm diameter disk Polysilicon Electrode Self-Aligned Stem R Polysilicon Electrode Design/Performance: R=10μm, t=2.1μm, d=800å, V P =6.2V f o =732.9MHz (2 nd mode), Q=7,330 Transmission (db) f o = 732.9MHz Q = 7,330 (vac) Q = 6,100 (air) f o =433MHz Q=4,066 μmechanical Disk Resonator Ground Plane Frequency (MHz) [Wang, Nguyen 2002]

39 Research Issue: Impedance Matching Antenna Gap = d Resonance Resonance V P μmechanical Disk Resonator V DD r h Minimum Size Inverter R x = 1 k d ( 2πr ) ω Q V h k r = 7,350,000 N/m o r P Impedance matching needed not a new problem 4 5kΩ 50Ω Mismatch! V SS 2fF Progressively Larger Inverters Off-Chip Capacitor (2 pf)

40 Micromechanical Circuits A single mechanical beam can t really do much on its own But use many mechanical beams attached together in a circuit, and attain a more complex, more useful function Input Force F i Output Displacement x o F i x o t Key Design Property: High Q t

41 Desired Filter Characteristics Small shape factor generally preferred

42 Micromechanical Filter Circuit

43 DARPA Spring-Coupled μmechanical Filter Below: 7.81 MHz, 2-resonator, CC-beam μmechanical filter in POCl3-doped polysilicon Design: Design: Wr=8μm, h=2μm, LLr=40.8μm, r=40.8μm, W r=8μm, h=2μm, LLs12=20.35μm, =20.35μm,VVP=35V =35V s12 P Mechanical, Mechanical,not notelectrical, electrical, interconnect Ö reduced interconnect Ö reduced susceptibility susceptibilityto toemi EMI Performance: Performance:(70 (70mTorr mtorrvacuum) vacuum) fof =7.81 MHz, BW=18 khz, Qres=6,000 o=7.81 MHz, BW=18 khz, Q res=6,000 PPBW=0.23%, =0.23%,Ins. Ins.Loss Loss<<11dB db BW

44 MEMS-Based Receiver Front-End Provides Provides robustness robustness against against jammers jammers and and extends extends battery battery lifetime lifetime Low Loss Reduces Reduces loss loss and and removes removes power power consumption consumption by by active active devices devices Eliminates Eliminates active active phase-locking phase-locking ckt. ckt. power power consumption consumption Miniaturization Miniaturization

45 Chip-Scale Atomic Clocks

46 Chip-Scale Atomic Clocks NIST- F1 Vol: : ~3.7 m 3 Power: ~500 W Acc: State-of- Practice HP 5071A Vol: 29,700 cm 3 Power: 50 W Acc: $50K Datum R2000 Vol: 9,050 cm 3 Power: 60 W Acc: $7K Temex RMO Vol: 230 cm 3 Power: 10 W Acc: $2K NG MC250 Vol: 27 cm 3 + Power: 220 mw+ Acc: State-of- Research Kernco Vol: 20 cm 3 + NIST CPT cell Power: 300 mw+ Acc: Vol: 30 cm 3 + Power: 300 mw+ Acc: CSAC Vol: : 1 cm 3 Power: 30 mw Stab:

47 Modulated Laser 133 Cs vapor at 10 7 torr Chip-Scale Atomic Clock Photo Detector Mod f Atomic Clock Concept MEMS and Photonic Technologies GHz Resonator in Vacuum VCSEL Cs or Rb Glass Detector Substrate Key Challenges: cell design for maximum Q GHz high-q reference resonator thermal isolation for low power Chip-Scale Atomic Clock

48 Conclusions Integrated mechanical technologies, whether micro or nano, possess high-q and low loss characteristics capable of revolutionizing the performance of wireless communications MEMS or NEMS offer the same scaling advantages that IC technology offers (e.g., speed, low power, complexity, cost), but they do so for domains beyond electronics: Size resonant frequency (faster speed) actuation force (lower power) # mechanical elements (higher complexity) integration level (lower cost) Debate over micro vs. nano: a waste of time opportunities abound in both domains More important: MEMS or NEMS have brought together people from diverse disciplines this is the key to growth!