EE C245 ME C218 Introduction to MEMS Design Fall 2010

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1 Basic Concept: Scaling Guitar Strings EE C245 ME C218 ntroduction to MEMS Design Fall 21 Prof. Clark T.-C. Nguyen Dept. of Electrical Engineering & Computer Sciences University of California at Berkeley Berkeley, CA 9472 Lecture Module 2: Benefits of Scaling EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 1 Guitar Guitar String Vib. Amplitude Freq. Vibrating Vibrating A A String String (11 (11 Hz) Hz) Low High 11 Hz Freq. Stiffness Freq. Equation: 1 kr fo = 2π m r Mass μmechanical Resonator [Bannon 1996] f o =8.5MHz vac =8, air ~5 Performance: L r =4.8μm m r ~ 1-13 kg W r =8μm, h r =2μm d=1å, =5V Press.=7mTorr EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 2 Transmission [db] Performance: ff o =9MHz, o BW=2kHz, PBW=.2%.L.=2.79dB, Stop. Stop. Rej.=51dB 2dB 2dB S.F.=1.95, 4dB 4dB S.F.= CC 3λ/4 Bridged μmechanical Filter -2 P in =-2dBm Sharper -3 roll-off Design: L r =4μm -4 Loss Pole W r =6.5μm h r =2μm -5 L c =3.5μm -6 [S.-S. Li, Nguyen, FCS 5] L b =1.6μm =1.47V P=-5dBm R Frequency [MHz] i =R o =12kΩ [Li, et al., UFFCS 4] EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 3 n Out 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); ~1,1 (air) Below: 2 μm diameter disk Polysilicon Electrode Polysilicon Stem (mpedance Mismatched to Diamond Disk) R -1 CVD Diamond μmechanical Disk Ground Resonator Plane Frequency [MHz] EE C245: ntroduction to MEMS Design LecM 2 [Wang, C. Nguyen Butler, Nguyen 8/2/9 MEMS 4] 4 Mixed Amplitude [db] Design/Performance: R=1μm, t=2.2μm, d=8å, =7V f o =1.51 GHz (2 nd mode), =11, f o = 1.51 GHz = 11,555 (vac) = 1,1 (air) = 1,1 (air)

2 163-MHz Differential Disk-Array Filter Linear MEMS in Wireless Comms Com. Array Couplers Filter Coupler High High and and good good linearity of of micromechanical resonators Filters Filters for for front-end frequency selection v i+ v i- λ Port1 Port1 Port2 Port2 Diff. Array Couplers λ/4 λ/4 EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 5 Port3 Port3 Port4 Port4 v o+ λ v o- [Li, Nguyen Trans 7] Micromechanical Bandpass Filter Filter Frequency [MHz] Antenna Mixer Diplexer Wireless o RF PLL Xstal Osc Phone RF RXRF LO BPF Mixer EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 6 Transmission [db] Miniaturization of RF Front Ends 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 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 Antenna Mixer Diplexer Wireless o Xstal RF PLL Osc Phone RF RXRF LO BPF Mixer EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 7 Antenna CDMA CDMA-2 Multi-Band Wireless Handsets Duplexer Duplexer Duplexer GSM 9 PCS 19 DCS 18 o o WCDMA EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 8 RXRF LO Tank (N+1)/N Xstal Osc RXRF Channel Select PLL The number of off-chip high- passives increases dramatically Need: on-chip high- passives

3 All High- Passives on a Single Chip.25 mm Vibrating Vibrating Resonator Resonator 1.5-GHz, 1.5-GHz, ~12, ~12, CDMA RF Filters ( MHz) GSM 9 RF Filter ( MHz) PCS 19 RF Filter ( MHz) DCS 18 RF Filter ( MHz) CDMA-2 RF Filters ( MHz) Vibrating Vibrating Resonator Resonator 62-MHz, 62-MHz, ~161, ~161, WCDMA RF Filters ( MHz) EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 9.5 mm Optional RF Oscillator Ultra-High Tanks Low Freq. Reference Oscillator Ultra-High Tank Chip-Scale Atomic Clocks (CSAC) EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 1 NST F1 Fountain Atomic Clock Benefits of Accurate Portable Timing Better Timing Networked Sensors Vol: : ~3.7 m 3 Power: ~5 W Acc: Stab: 3.3x1-15 /hr After 1 sec Error: sec Loses 1 sec every 3 3 million years! Physics Package EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 11 Secure Communications More efficient spectrum utilization Longer autonomy periods Faster frequency hop hop rates Faster acquire of of pseudorandom signals Superior resilience against jamming or or interception Larger networks with with longer autonomy GPS Fewer satellites needed Higher jamming margin Faster GPS acquire EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 12

4 NST F1 Fountain Atomic Clock 1 st Chip-Scale Atomic Physics Package Vol: : ~3.7 m 3 Power: ~5 W Acc: Stab: 3.3x1-15 /hr NST s NST schip- Scale Scale Atomic Atomic Physics Physics Package Package 1.5 mm Photodiode Cell After 1 sec Error: sec 4.2 mm Optics Loses 1 sec every 3 3 million years! Physics Package EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 13 ND uartz Si ND Lens 1.5 mm 1 mm Glass VCSEL Total Total Volume: mm mm 3 Stability: x 1 1s 1s Alumina Cell Cell nterior Vol: Vol:.6.6 mm mm 3 Power Power Cons: Cons: mw mw EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 14 Tiny Physics Package Performance NST s NST s Chip-Scale Chip-Scale Atomic Atomic Physics Physics Package Package 1-9 Cs Drift Drift Cs (D (D 2 ) Drift Drift to to Be 2 ) ssue ssue Be Removed Removed 5.67 =1.3x16 6 in in Phase Phase Sufficient 7.1 khz Sufficient to to meet meet 5.66 CSAC CSAC 1-11 program Contrast:.91% program goals Rb 2.4e-1 2.4e-1 Allan Allan goals deviation Rb (D (D 1 ) deviation 1 1 s 1 hour 1 day Frequency Detuning, Δ [khz] from 9,192,631,77 Hz ntegration Time, τ [s] EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 15 PD Signal [V] Dime Dime Open Loop Resonance: Experimental Conditions: Cs D2 Excitation External (large) Magnetic Shielding External Electronics & LO Cell Temperature: ~8 ºC Cell Heater Power: 69 mw Current/Voltage: 2mA / 2V RF Mod Power: 7μW Allan Deviation, σ y Stability Measurement: CSAC Goal Frequency determined by an atomic transition energy Excite e- e-to to the the next orbital m = f = 4 Atomic Clock Fundamentals m = Cs Opposite e- e-spins Energy Band Diagram m = f = 3 ΔE = 1.46 ev ν = ΔE/h = 352 THz nm ΔE =.38 ev ν = ΔE/ħ = Hz EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 16

5 Miniature Atomic Clock Design Chip-Scale Atomic Clock Sidebands Carrier (852 nm) Modulated 9.2GHz 4.6GHz λ 133 Cs vapor at 1 7 torr Atoms become transparent to to light at at nm nm Photo ν = ΔE/ħ = Hz Hyperfine Hyperfine Splitting Splitting Freq. Freq. 133 Cs vapor at 1 7 torr v VCXO o 4.6 GHz μwave osc Atomic Clock Concept MEMS and Photonic Technologies Photo GHz Resonator in Vacuum VCSEL Cs or Rb Glass Substrate v VCXO o 4.6 GHz μwave osc Close feedback loop to to lock lock EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 17 Key Challenges: thermal isolation for low power cell design for maximum low power μwave oscillator Chip-Scale Atomic Clock Vol: : 1 cm 3 Power: 3 mw Stab: EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/ Challenge: Miniature Atomic Cell Challenge: Miniature Atomic Cell Large Vapor Cell 1,X Volume Scaling Tiny Vapor Cell Large Vapor Cell 1,X Volume Scaling Tiny Vapor Cell Buffer Gas Wall collision dephases atoms lose lose coherent state Surface Volume EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 19 ntensity lower Atomic Resonance More wall wall collisions stability gets worse 9.2 GHz lowest Soln: Add Add a buffer gas gas EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 2 ntensity Lower the the mean free free path of of the the atomic vapor Atomic Resonance 9.2 GHz Return to to higher

6 v o 4.6 GHz Chip-Scale Atomic Clock 133 Cs vapor at 1 7 torr Atomic Clock Concept MEMS and Photonic Technologies VCXO μwave osc Key Challenges: thermal isolation for low power cell design for maximum low power μwave oscillator Photo GHz Resonator in Vacuum Chip-Scale Atomic Clock VCSEL Cs or Rb Glass Substrate Vol: : 1 cm 3 Power: 3 mw Stab: EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/ Macro-Scale Atomic 8 o C Thermally solating Feet R th = th 7 7 K/W K/W C th = th J/K J/K Micro-Scale Oven-Control Advantages 3 cm P (@ (@ 8 8 o o C) C) =.8.8 W Warm Up, Up, τ = 3 3 min. Macro-Oven (containing heater and T sensor) nsulation 25 o C T = P x R th P R th C th support length R th ~ X-section area C th ~ volume 38x lower power 3x3x3 μm 3 Atomic 8 o C 18,x faster warm up T Sensor (underneath) Micro-Scale Heater Long, Thin Polysilicon Tethers R = th 83, K/W th K/W C th = th 6.3x J/K J/K P (@ (@ 8 8 o o C) C) = mw mw Warm Up, Up, τ =.1.1 s EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 22 Physics Package Power Diss. < 1 mw Achieved via MEMS-based thermal isolation Cesium cell VCSEL / Photodiode Heater/Sensor Suspension Frame Spacer VCSEL Suspension Symmetricom Symmetricom // Draper Draper Physics Physics Package Package Assembly Assembly 7 mm 2 pin LCC Temperature [ o C] EE C245: ntroduction to MEMS Design LecM 2 C. Nguyen 8/2/9 23 Power [mw] Only Only ~5 ~5 mw mw heating power power needed to to achieve 8 8 o o C cell cell temperature Measured Model