EE C247B ME C218. EE C245: Introduction to MEMS Design. Spring EE C247B/ME C218: Introduction to MEMS Lecture 3m: Benefits of Scaling II

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1 EE C247B/ME C218: ntroduction to MEMS Basic Concept: Scaling Guitar Strings Guitar String Vib. Amplitude EE C247B ME C218 ntroduction to MEMS Design Spring 2015 Prof. Clark T.- Freq. [Bannon 1996] Freq. Equation: 1 kr fo = 2π mr Guitar 1 Freq. Mass R nput 3 Output Out vi v vo vo i Transmission [db] -10 Pin=-20dBm Sharper Sharper roll-off roll-off -30 Loss LossPole Pole [S.-S. Li, Nguyen, FCS 05] [Li, et al., UFFCS 04] Frequency [MHz] 2 Bridging Beam Coupling Beam 0-20 Micromechanical Circuit n Performance: Lr=40.8µm mr ~ kg Wr=8µm, hr=2µm d=1000å, =5V Press.=70mTorr fo=8.5mhz vac =8,000 air ~50 Stiffness 3CC 3 Bridged µmechanical Performance: Performance: ffo=9mhz, BW=20kHz, =9MHz, BW=20kHz,PBW=0.2% PBW=0.2% o.l.=2.79db,.l.=2.79db,stop. Stop.Rej.=51dB Rej.=51dB 20dB 20dBS.F.=1.95, S.F.=1.95,40dB 40dBS.F.=6.45 S.F.=6.45 High Vibrating Vibrating A A String String(110 (110Hz) Hz) Lecture Module 2: Benefits of Scaling Low 110 Hz Dept. of Electrical Engineering & Computer Sciences University of California at Berkeley Berkeley, CA µmechanical R ω Design: Lr=40µm Wr=6.5µm hr=2µm Lc=3.5µm Lb=1.6µm =10.47V P=-5dBm 9.3 Ri=Ro=12kΩ 1:ηe mr 1/kr cr 1:ηc ηc:1-1/ks -1/ks mr 1/kr cr 1:ηc 1/ks Co ηc:1-1/ks -1/ks mr 1/kr cr 1/ks 1:ηb ηe:1 Co ηb:1 1/kb 1/kb -1/kb Regents of the University of California 4 1

2 EE C247B/ME C218: ntroduction to MEMS 1.51-GHz, =11,555 Nanocrystalline Diamond Disk µmechanical 163-MHz Differential Disk-Array mpedance-mismatched stem for Com. Array Couplers reduced anchor dissipation Operated in the 2nd radial-contour mode ~11,555 (vacuum); ~10,100 (air) Design/Performance: Below: 20 µm diameter disk R=10µm, t=2.2µm, d=800å, =7V Polysilicon Electrode R CVD Diamond µmechanical Disk Ground Plane Port1 Port1 vi λ λ = 10,100 (air) vi1508 Port2 Port Diff. Array Couplers Port4 Port4 Frequency [MHz] [Wang, Butler, Nguyen MEMS 04] 5 High Highand andgood goodlinearity linearityof of micromechanical micromechanicalresonators resonators Power Power Amplifier Amplifier Transmission [db] MHz MHz SAW SAW MHz MHz SAW SAW Antenna 26-MHz 26-MHz Problem: Problem:high- high-passives passivespose poseaa bottleneck bottleneckagainst againstminiaturization miniaturization MHz MHz VCO VCO Mixer BPF Osc PLL RX LO Wireless Phone Mixer 6 Dual-Band Dual-BandZero-F Zero-F Transistor TransistorChip Chip Wireless Phone 897.5±17.5MHz 897.5±17.5MHz SAW SAW Frequency [MHz] Mixer Miniaturization of Front Ends s sfor forfront-end front-end frequency frequencyselection selection Micromechanical MicromechanicalBandpass Bandpass vo- [Li, Nguyen Trans 07] Linear MEMS in Wireless Comms Antenna fo = 1.51 GHz = 11,555 (vac) = 10,100 (air) vo+ Port3 Port3 fo=1.51 GHz (2nd mode), =11,555 Mixed Amplitude [db] Polysilicon Stem (mpedance Mismatched to Diamond Disk) Coupler Regents of the University of California BPF PLL RX LO Osc Mixer 8 2

3 EE C247B/ME C218: ntroduction to MEMS Multi-Band Wireless Handsets All High- Passives on a Single Chip Duplexer 0.25 mm CDMA BPF BPF Antenna PCS 1900 DCS 1800 Duplexer CDMACDMA-2000 WCDMA BPF Osc Tank CDMA-2000 s ( MHz) The number of off-chip high- WCDMA s ( MHz) Need: on-chip high- passives Low Freq. Reference Ultra-High Tank DCS 1800 ( MHz) passives increases dramatically Optional Ultra-High Tanks PCS 1900 ( MHz) RX Channel Select PLL BPF Duplexer (N+1)/N CDMA s ( MHz) GSM 900 ( MHz) RX LO Vibrating Vibrating 62-MHz, 62-MHz,~161,000 ~161,000 m BPF Vibrating Vibrating 1.5-GHz, 1.5-GHz,~12,000 ~12, m BPF GSM NST F1 Fountain Atomic Clock Vol: Vol: ~3.7 m3 Power: ~500 W Acc: Stab: 3.3x10-15/hr Chip-Scale Atomic Clocks (CSAC) After After11sec sec -15 Error: Error: sec sec Loses Loses11sec secevery every 30 30million millionyears! years! Physics PhysicsPackage Package Regents of the University of California 12 3

4 EE C247B/ME C218: ntroduction to MEMS Benefits of Accurate Portable Timing NST F1 Fountain Atomic Clock Better Timing Networked Sensors 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 GPS acquire 13 Vol: : ~3.7 m 3 Power: ~500 W Acc: Stab: 3.3x10-15 /hr After 1 sec Error: sec Loses 1 sec every million years! Physics Package 14 NST s NST schip- Scale Scale Atomic Atomic Physics Physics Package Package ND uartz Si ND Glass Alumina 1 st Chip-Scale Atomic Physics Package 4.2 mm Lens 1.5 mm 1.5 mm Photodiode Optics 15 Cell Total Total Volume: mm mm 3 3 Cell Cell nterior nterior Vol: Vol: mm mm mm Stability: x s 1s Power Power Cons: Cons: mw mw Tiny Physics Package Performance NST s NST s Chip-Scale Chip-Scale Atomic Atomic Physics Physics Package Package 10-9 Cs Drift Drift Cs (D (D 2 ) Drift Drift to to Be 2 ) ssue ssue Be Removed Removed 5.67 =1.3x106 6 in in Phase Phase Sufficient 7.1 khz Sufficient to to meet meet 5.66 CSAC CSAC program Contrast: 0.91% program goals Rb 2.4e e-10 Allan Allan goals deviation Rb (D (D 1 ) deviation 1 11 ss 1 hour 1 day Frequency Detuning, [khz] from 9,192,631,770 Hz ntegration Time, τ [s] 16 PD Signal [V] Dime Dime Open Loop Resonance: Experimental Conditions: Cs D2 Excitation External (large) Magnetic Shielding External Electronics & LO Cell Temperature: ~80 ºC Cell Heater Power: 69 mw Current/Voltage: 2mA / 2V Mod Power: 70µW Allan Deviation, σ y Stability Measurement: CSAC Goal 2015 Regents of the University of California 4

5 EE C247B/ME C218: ntroduction to MEMS Atomic Clock Fundamentals Miniature Atomic Clock Design Frequency determined by an atomic transition energy Excite e- e-to to the the next next orbital m = 1 Cs Energy Band Diagram E = 1.46 ev ν = E/h = 352 THz nm E = ev ν = E/ħ = Hz Sidebands Carrier (852 nm) Modulated 9.2GHz 4.6GHz λ Cs vapor at 10 7 torr Atoms become transparent to to light light at at nm nm Photo ν = E/ħ = Hz Hyperfine Hyperfine Splitting Splitting Freq. Freq. m = 0 f = 4 Opposite e- e-spins m = 0 f = 3 17 v VCXO o 4.6 GHz µwave osc Close feedback loop loop to to lock lock 18 v o 4.6 GHz Chip-Scale Atomic Clock Cs vapor at 10 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 in Vacuum Chip-Scale Atomic Clock Cs or Rb Glass Substrate Vol: : 1 cm 3 Power: 30 mw Stab: Challenge: Miniature Atomic Cell Large Vapor Cell Wall Wall collision dephases atoms lose lose coherent state 1,000X Volume Scaling Surface Volume Tiny Vapor Cell 20 ntensity lower Atomic Resonance More wall wall collisions stability gets gets worse 9.2 GHz lowest 2015 Regents of the University of California 5

6 EE C247B/ME C218: ntroduction to MEMS Challenge: Miniature Atomic Cell Large Vapor Cell 1,000X Volume Scaling Soln: Add Add a buffer gas gas Tiny Vapor Cell 21 ntensity Lower the the mean free free path path of of the the atomic vapor Atomic Resonance 9.2 GHz Buffer Gas Return to to higher v o 4.6 GHz Chip-Scale Atomic Clock Cs vapor at 10 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 in Vacuum Chip-Scale Atomic Clock Cs or Rb Glass Substrate Vol: : 1 cm 3 Power: 30 mw Stab: Macro-Scale Atomic 80 o C Thermally solating Feet R th = th K/W K/W C th = th J/K J/K Micro-Scale Oven-Control Advantages 3 cm P (@ (@ o o C) C) = W Warm Up, Up, τ = min. 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 550x lower power 300x300x300 µm 3 Atomic 80 o C 7,300x faster warm up T Sensor (underneath) Micro-Scale Heater Long, Thin Polysilicon Tethers R = th 83,000 K/W th K/W C th = th 6.3x J/K J/K P (@ (@ o o C) C) = mw mw Warm Up, Up, τ = s 23 Cesium cell / Photodiode Physics Package Power Diss. < 10 mw Achieved via MEMS-based thermal isolation Heater/Sensor Suspension Frame Spacer Suspension Symmetricom Symmetricom // Draper Draper Physics Physics Package Package Assembly Assembly 7 mm 20 pin LCC Temperature [ o C] 24 Power [mw] Measured Model Only Only ~5 ~5 mw mw heating heating power power needed needed to to achieve achieve o o C cell cell temperature 2015 Regents of the University of California 6