MEMS Technologies and Devices for Single-Chip RF Front-Ends

Transcription

1 MEMS Technologies and Devices for Single-Chip RF Front-Ends Clark T.-C. Nguyen Dept. of Electrical Engineering & Computer Science University of Michigan Ann Arbor, Michigan CCMT 06 April 25, 2006

2 Outline Motivation: Miniaturization of Transceivers need for high- merged transistor/mems process High- Vibrating Micromechanical Resonators clamped-clamped beams micromechanical disks micromechanical circuits Low-loss Micromechanical Switches Tunable C s and L s Conclusions

3 Motivation: Miniaturization of RF Front-Ends Wireless Phone RF RF Power Power Amplifier 897.5±17.5MHz RF RF SAW SAW Filter Filter Dual-Band Zero-F Transistor Chip Chip MHz VCO VCO Antenna Diplexer RF BPF Mixer 0 o 90 o Mixer LPF RXRF LO LPF AGC RF PLL AGC Diplexer MHz RF RF SAW SAW Filter Filter MHz RF RF SAW SAW Filter Filter 26-MHz Xstal Xstal Oscillator Problem: high- passives pose a bottleneck against miniaturization A/D A/D Xstal Osc

4 Multi-Band Wireless Handsets Antenna CDMA GSM o 90 o LPF AGC A/D PCS 1900 DCS o 90 o LPF RXRF LO AGC RXRF Channel Select PLL A/D (N+1)/N Xstal Osc CDMA-2000 WCDMA Tank The number of off-chip high- passives increases dramatically Need: on-chip high- passives

5 Surface Micromachining Fabrication steps compatible with planar C processing

6 Single-Chip MEMS/Transistor ntegration Completely monolithic, low phase noise, high- oscillator (effectively, an integrated crystal oscillator) Oscilloscope Output Waveform [Nguyen, Howe [Nguyen, Howe 1993] JSSC 99] To allow the use of >600oC processing temperatures, tungsten (instead of aluminum) is used for metallization

7 Single-Chip ntegration RF RF Power Power Amplifier 897.5±17.5MHz RF RF SAW SAW Filter Filter Dual-Band Zero-F Transistor Chip Chip MHz VCO VCO MEMS Technology Diplexer MHz RF RF SAW SAW Filter Filter MHz RF RF SAW SAW Filter Filter 26-MHz Xstal Xstal Oscillator Wrist-watch-sized multi-band wireless device might be be possible! Single-Chip Transceiver

8 All High- Passives on a Single Chip 0.25 mm Vibrating Vibrating Resonator Resonator 1.5-GHz, 1.5-GHz, ~12,000 ~12,000 CDMA RF Filters ( MHz) GSM 900 RF Filter ( MHz) PCS 1900 RF Filter ( MHz) DCS 1800 RF Filter ( MHz) CDMA-2000 RF Filters ( MHz) Vibrating Vibrating Resonator Resonator 62-MHz, 62-MHz, ~161,000 ~161, mm Optional RF Oscillator Ultra-High Tanks Low Freq. Reference Oscillator Ultra-High Tank WCDMA RF Filters ( MHz)

9 Thin-Film Bulk Acoustic Resonator (FBAR) Piezoelectric membrane sandwiched by metal electrodes extensional mode vibration: 1.8 to 7 GHz, ~500-1,500 dimensions on the order of 200μm for 1.6 GHz link individual FBAR s together in ladders to make filters h Agilent FBAR Limitations: ~ 500-1,500, TC f ~ ppm/ o C difficult to achieve several different freqs. on a single-chip freq freq ~ thickness

10 Vibrating RF MEMS

11 Basic Concept: Scaling Guitar Strings Guitar String μmechanical Resonator Vib. Amplitude Low High 110 Hz Freq. Guitar Freq. Vibrating Vibrating A A String String (110 (110 Hz) Hz) Stiffness Freq. Equation: 1 kr fo = 2π m r Mass [Bannon et al JSSC 00] f o =8.5MHz vac =8,000 air ~50 Performance: L r =40.8μm m r ~ kg W r =8μm, h r =2μm d=1000å, V P =5V Press.=70mTorr

12 1.51-GHz, =11,555 Nanocrystalline Diamond Disk μmechanical Resonator mpedance-mismatched stem for reduced anchor dissipation Operated in the 2 nd radial-contour mode ~11,555 (vacuum); ~10,100 (air) Below: 20 μm diameter disk Polysilicon Electrode Polysilicon Stem (mpedance Mismatched to Diamond Disk) CVD Diamond μmechanical Disk Resonator R Ground Plane Mixed Amplitude [db] Design/Performance: R=10μm, t=2.2μm, d=800å, V P =7V f o =1.51 GHz (2 nd mode), =11, Frequency [MHz] f o = 1.51 GHz = 11,555 (vac) = 10,100 (air) = 10,100 (air) [Wang, Butler, Nguyen MEMS 04]

13 Radial-Contour Mode Disk Resonator Disk nput Electrode Supporting Stem R Output Electrode ~10,000 i v o i v i i o ωο ω Frequency: f o Stiffness = 1 2π Mass k m r r V P Young s Modulus E ρ Density (e.g., m r = r kg) kg) 1 R V P C(t) Note: f f V P = P 0V 0V device off off V dc dt Smaller mass higher freq. range and and lower series R x x i o = P

14 Multi-Band Wireless Handsets Antenna CDMA GSM o 90 o LPF AGC A/D PCS 1900 DCS o 90 o LPF RXRF LO AGC RXRF Channel Select PLL A/D (N+1)/N Xstal Osc CDMA-2000 WCDMA No No need for for switches! Tank Capacitively transduced micromechanical resonators switch themselves

15 1.51-GHz, =11,555 Nanocrystalline Diamond Disk μmechanical Resonator mpedance-mismatched stem for reduced anchor dissipation Operated in the 2 nd radial-contour mode ~11,555 (vacuum); ~10,100 (air) Below: 20 μm diameter disk Polysilicon Electrode Polysilicon Stem (mpedance Mismatched to Diamond Disk) CVD Diamond μmechanical Disk Resonator R Ground Plane Mixed Amplitude [db] Design/Performance: R=10μm, t=2.2μm, d=800å, V P =7V f o =1.51 GHz (2 nd mode), =11, Frequency [MHz] f o = 1.51 GHz = 11,555 (vac) = 10,100 (air) [Wang, Butler, Nguyen MEMS 04]

16 ntegrated Micromechanical Circuits

17 Micromechanical Filter Design Basics R Disk Resonator Coupling Beam Bridging Beam Termination Resistor v i V P R v o x o v i x o v i v o v i v o v i Loss Pole ω o ω ω o ω ω o ω ω o ω

18 3CC 3λ/4 Bridged μmechanical Filter Performance: f o f=9mhz, o BW=20kHz, PBW=0.2%.L.=2.79dB, Stop. Stop. Rej.=51dB 20dB 20dB S.F.=1.95, 40dB 40dB S.F.= V P n Out Transmission [db] P in =-20dBm [Li, et al., UFFCS 04] [S.-S. Li, Nguyen, FCS 05] Frequency [MHz] Sharper roll-off Loss Pole Design: L r =40μm W r =6.5μm h r =2μm L c =3.5μm L b =1.6μm V P =10.47V P=-5dBm R i =R o =12kΩ

19 Disk Array Composite μmechanical Filter Disk array composite end end resonator reduces impedance & suppresses spurious modes λ/2 λ/2 Array Coupler Transmission [db] Performance: f o f=155.9mhz o BW=201kHz PBW=0.13%.L.=2dB [S.-S. Li, Nguyen, 2006] Frequency [MHz] Filter Extensional-Mode 3λ/4 3λ/4 Coupling Beam Design: Disk Radius, R =17μm Thickness, h =2μm Nitride Gap, d =3.5μm Array Coupling Beam Length, L a =26.9μm Filter Coupling Beam Length, L c =40.4μm V P =4V R i =R o =13kΩ

20 Low Loss Switch Needs Antenna CDMA GSM o 90 o LPF AGC A/D PCS 1900 DCS o 90 o LPF RXRF LO AGC RXRF Channel Select PLL A/D (N+1)/N Xstal Osc CDMA-2000 WCDMA Low loss switch Tank For lowest on-chip loss, replace with RF RF MEMS switch

21 Micromechanical Switch Operate the micromechanical beam in an up/down binary fashion nput Output Electrode Dielectric [C. Goldsmith, 1995] Performance:.L.~0.1dB, P3 ~ 66dBm (extremely linear) ssues: switching voltage ~ 50V, switching time: 1-5μs

22 Metal cantilever DC switch 3-terminal device Pt contact interface high R silicon substrate electrostatic actuation V actuate ~ 90V Package: wafer-to-wafer glass frit bonded cap low cost env. protection RF MEMS Switch (Radant) Drain Reliability (gov t tested): >1 T mechanical cycles >700 B cycles 100mW RF cold switch Reliability (Radant tested): >2.5 B cycles 2W RF cold switched >100 B cycles 0.5W RF cold switched Contact Detail 100 μm Gate Beam [Radant] Source Packaged Device

23 Medium nductor & Capacitor Needs Antenna CDMA GSM o 90 o LPF AGC A/D PCS 1900 DCS o 90 o LPF RXRF LO AGC RXRF Channel Select PLL A/D (N+1)/N Xstal Osc CDMA-2000 WCDMA Tank GSM VCO attainable by by on-chip L and switched C s C s Tunable MEMS C s C s and μmachined L s L s have higher

24 Voltage-Tunable High- 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 Challenges: microphonics, tuning range truncated by pull-in

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

26 Out-of-Plane Micromachined nductor Molybdenum-chromium metal solenoids perpendicular to the plane of the substrate reduced substrate loss high Assembled out-of-plane via curling stresses, then locked into place Record s: ~70 on glass, ~40 on 20Ω-cm silicon (85 w/ Cu underside) Stress Curled Metal Design/Performance: D=600μm, t=1μm t=1μm On On Glass Glass Substrate: L = 8nH, 8nH, = 70 1GHz 1GHz On On 20Ω-cm Silicon: L = 6 nh, nh, = 40 1GHz 1GHz ( ( ~ w/ w/ Cu Cu underside) [Chua, Locking Hilton Head 02] Mechanism [PARC] Solenoid nductor D

27 Reference Oscillator Needs Antenna CDMA GSM o 90 o LPF AGC A/D PCS 1900 DCS o 90 o LPF RXRF LO AGC RXRF Channel Select PLL A/D (N+1)/N Xstal Osc CDMA-2000 WCDMA Tank Today, use quartz crystal to to attain >10,000 Replace with vibrating μmechanical resonator

28 GSM-Compliant Oscillator Output nput Custom C C fabricated via via TSMC TSMC 0.35μm process [Y.-W. Lin, Nguyen, EDM 05] Satisfies Global System for for Mobile Communications (GSM) phase noise specifications! All All made possible by by mechanical circuit design! Phase Noise [dbc/hz] Wine-Glass Disk Disk Array Array = 118,900,, R x = x kω kω Single Single WG WG Disk MHz MHz 9-WG 9-WG Disk Disk Array MHz MHz Down Down to to MHz MHz GSM GSM spec spec 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 Offset Frequency [Hz]

29 Multi-Band Wireless Handsets Antenna CDMA GSM o 90 o LPF AGC A/D PCS 1900 DCS o 90 o LPF RXRF LO AGC RXRF Channel Select PLL A/D (N+1)/N Xstal Osc CDMA-2000 WCDMA Tank The number of off-chip high- passives increases dramatically Need: on-chip high- passives

30 RF Channel-Select Filter Bank Bank Bank of of UHF UHF μmechanical filters filters Switch Switch filters filters on/off on/off via via application and and removal of of dc-bias V P, P, controlled by by a decoder Transmission RF Channels Freq. Transmission n Freq. Transmission Removes all all interferers! Freq.

31 Conclusions ntegrated micromechanical technologies possess high- and low loss characteristics capable of greatly enhancing the performance of wireless communications Probable evolution of products based on vibrating RF MEMS: timing devices using micromechanical resonators communication-grade frequency synthesizers single-chip of all needed high- passives single-chip radio (cognitive radio) mechanical radio front-ends n Research: : Time to turn our focus towards mechanical circuit design and mechanical integration maximize, rather than minimize, use of high- components e.g., RF channelizer paradigm-shift in wireless design even deeper frequency computation using VLS micromechanics Beginnings of a revolution reminiscent of the C revolution?

32 Acknowledgment Much of the work presented (of mine and others) was supported by funding from DARPA.