NATIONAL TSING HUA UNIVERSITY

FULLY DIFFERENTIAL INTERNAL ELECTROSTATICFULLY DIFFERENTIAL INTERNAL ELECTROSTATIC TRANSDUCTION OF A LAME-MODE RESONATOR

Ref[1] : MEMS 2009

S k W Chi Ch (陳文健)Speaker : Wen-Chien Chen (陳文健)

Professor : Cheng-Hsien LiuProfessor : Cheng Hsien Liu

Date : 2009/11/3

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Outline• Introduction

+ Micromechanical resonators in Wireless Transceiver+ High Q LAME mode microresonator+ Electrostatic air-gap transduction v s Internal dielectric transduction+ Electrostatic air-gap transduction v.s Internal dielectric transduction+ Fully Differential LAME mode resonator

• Design and conceptDesign and concept• Fabrication and measurement

S• Summary

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Micromechanical resonators in Wireless T iTransceiver

Ref [2]: UFFC• Surface micromachining microresonator•Vibrating at resonance•Mech. transduce Elec.•Frequency generation•Frequency generation•Frequency selection•Need high Q & high freq.

Cl d Cl d B F F BClamped-Clamped BeamQ 8, 000 @ 10 MHz (vac)

Q 50 @ 10 MHz (air)

Free-Free BeamQ 28,000 @ 10-200 MHz (vac)

Q 2, 000 @ 90 MHz (air)

Wine Glass Disk Contour Mode Disk Spoke Supported Ring

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Wine-Glass DiskQ 161,000 @ 62 MHz (vac)

Q 8, 000 @ 98 MHz (air)

Contour-Mode DiskQ 11,555 @ 1.5 GHz (vac)Q 10,100 @ 1.5 GHz (air)

Spoke-Supported RingQ 15,248 @ 1.46 GHz (vac)Q 10.165 @ 1.46 GHz (air)

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High Q LAME mode microresonatorHigh Q LAME mode microresonator

•Mechanical quality factor of a resonator:

⎞⎛

WWQΔ

= π2 ⎟⎟⎠

⎞⎜⎜⎝

⎛

Δ=

dB

resonance

ffor

3@

+ C ti l i f diff t

W : maximum vibration energy stored per cycle∆W : energy dissipated per cycle of vibration

WΔ ⎠⎝ Δ dBf 3@

4

+ Cross-sectional view of different layers from the SOIMUMPs. Ref [3]: Transducer 2007

Ref [4]:JMM 2009

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Electromechaical transduced mechanism Example: Air-Gap 2-port Cantilever beam

Vpio

Output Electrode (port2)Input Electrode (port1)vi

C⎟⎞

⎜⎛ ∂

Driving

xC ∂⎟⎞

⎜⎛ ∂

SensingioRx Lx Cx vo

igap

Pd vx

CVF ⎟⎟

⎠

⎞⎜⎜⎝

⎛∂

∂−=

tx

xC

Vi gapPx ∂

∂⎟⎟⎠

⎞⎜⎜⎝

⎛∂

∂=

RLvi

2o

Pe dAV εη = io

X iv

AVQdmkR == 222

4

ε

gap) (air, Key: Gap Spacing!!

5

2od xPo iAVQε

Motional resistance

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Air gap v.s Solid gap (Internal dielectric)g p g p ( )• Why use the dielectric as solid gap?

+ To lower the motional resistance Rx

- Rx ~ 4 orders-of-magnitude of gap (d0 )- Rx ~ 2 orders-of-magnitude of dielectric constant( ε0 )o de s o ag tude o d e ect c co sta t( ε0 )- Dielectric constant of silicon nitride (Si3N4) is about 9 (air~1)

+ Avoid the stiction , increasing the yield + Application to rigorous environment

222

4

, ~AVQ

dmkivR

Po

o

x

iX ε

gap) (solid =Motional resistance: Q Pox

6Ref [6]: FCTTIS 2005

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Fully Differential LAME mode resonator y+ Poly-SiC LAME mode resonator

+ Fully-differential, mean there are two electrodes for differential actuation d t l t d f diff ti l i f th t tiand two electrodes for differential sensing of the resonator motion:

- (1) reduced capacitive feedthrough between drive and sense electrodes- (2) reduced ohmic losses in the resonator suspension and anchor thereby ( ) p y

increased Q

7Ref [7]: MEMS 2005

NATIONAL TSING HUA UNIVERSITY

Outline• Introduction

+ Micromechanical resonators in Wireless Transceiver+ High Q LAME mode microresonator+ Electrostatic air-gap transduction v s Internal dielectric transduction+ Electrostatic air-gap transduction v.s Internal dielectric transduction+ Fully Differential LAME mode resonator

• Design and conceptDesign and concept• Fabrication and measurement

S• Summmary

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Fully Differential Internal Electrostatic Transduction

of A Lame-mode Resonator

+ Transduction electrodes are integrated+ Transduction electrodes are integrated within the vibrating plate

+ 4 arrays of internal electrodes are optimally placed in the quadrantsplaced in the quadrants

+ Adjacent edges vibrate 180° out of phase+ multiple dielectric gaps increase

t d ti ffi i (A R )4dmkvi

9

transduction efficiency (A ↑ Rx ↓)+ Very small dielectric gap (ε ↑, d ↓ Rx ↓ )222, ~

AVQdmk

ivR

Po

o

x

iX εgap) (solid =

NATIONAL TSING HUA UNIVERSITY

Outline• Introduction

+ Micromechanical resonators in Wireless Transceiver+ High Q LAME mode microresonator+ Electrostatic air-gap transduction v s Internal dielectric transduction+ Electrostatic air-gap transduction v.s Internal dielectric transduction+ Fully Differential LAME mode resonator

• Design and conceptDesign and concept• Fabrication and measurement

S• Summary

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Manufacturable double nanogap processg p p

+ 1μm, thermal silicon oxide, isolation μ , ,+ 200nm, LPVD silicon nitride, etch stop+ (1) 500nm, polysilicon is deposited, then

RIE f tiRIE, for routing.+ (2) 1μm, sacrificial silicon oxide deposited+ (3) patterned and etched , define the(3) patterned and etched , define the

anchors.+ (4) 2.5um, LPCVD structural polysilicon

- followed,0.25μm, oxide hard mask+ (5) defined trenches , width 600nm , 2-

step RIEp+ (6) 50nm (solid gap, d), silicon nitride

defines the transducing dielectric

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Manufacturable double nanogap processg p p+ (7) trench is filled, conformal doped

LPCVD polysilicon, defines electrodes + (8) CMP, planarize surface, remove the

polysilicon on top, isolate the electrode+ (9) RIE resonating plate and contact+ (9) RIE, resonating plate and contact

pads are defined+ (10) released in a buffered HF

- critical point drying, to prevent stiction.

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(a) polysilicon electrodes and silicon nitride gaps(b) trenches filled with silicon nitride/polysilicon

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Fabrication results• Nanoscale high-aspect ratio

b f b i t d igaps can be fabricated using optical lithography.

• The four corner electrodes are connected to the resonator body, used for biasing the resonator.

• Four electrodes are used for drive and sense. Isolationbetween pads is done by properly arranging the p p y g gdielectric routing.

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Fully differential measurement setupy p

+ The input signal was divided into two signals that are 180° out of+ The input signal was divided into two signals that are 180 out of phase using a power splitter

+ These two signals were applied to the two adjacent electrodes (1) and (2)

+ The signals from the two other electrodes (3) and (4) were again combined together using a second power combinercombined together using a second power combiner

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Fully differential measurement setupy p+ Towards higher frequencies, the current due to feedthrough

capacitance increases and eventually completely masks the motionalcapacitance increases and eventually completely masks the motional current of the resonator.

+ Fully differential drive and sense be able to matched internal electrodes to suppress feedthroughto suppress feedthrough.

+ Electrostatic charges are internal between the electrodes and there is no current that passes through the anchors

Pin = 0dBm, VDC =20V

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Summaryy• A polysilicon Lame-mode resonator driven and

d b i t l iti l t d tsensed by internal capacitive electrodes at 128.15MHz.

• By optimally placing and orienting the electrodes. • Nanoscale high-aspect ratio gaps can be fabricated g p g p

using optical lithography.• Fully differential drive and senseFully differential drive and sense

+ Ohmic losses through the anchors are minimized + Quality factor exceeding 12000 in air.+ Rx~31k Ohm+ f X Q ~ 1.53 X1012

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Reference• [1] M. Z-Moayyed, D. Elata, J. Hsieh, J.-W. P. Chen, E. P. Quevy, and R. T.

Howe, “FULLY DIFFERENTIAL INTERNAL ELECTROSTATIC TRANSDUCTION OF A LAME-MODE RESONATOR,” IEEE Intl. Conference of Micro Electro Mechanical Systems, Sorrento, Italy, January 25 -29, 2009, pp. 931-934

• [2] Clark T.-C. Nguyen, “MEMS Technology for Timing and Frequency Control,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, , , q y ,Vol.54, No.2, 2007, pp. 251-270

• [3] L Kline M Pilaniapan and W K Wong “6 MHz bulk mode resonator with Q• [3] L. Kline, M. Pilaniapan, and W.-K. Wong, 6 MHz bulk-mode resonator with Q values exceeding one million,” Transducers 2007, Lyon, France, June 2007, pp. 2445-48

• [4] L. Khine and M. Palaniapan, “High-Q bulk-mode SOI square resonators with straight-beam anchors,” J. Micromech. Microeng,” Vol.19, 2009, pp. 1-10

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Reference• [5] Z. Hao, and F. Ayazi, “SUPPORT LOSS INMICROMECHANICAL DISK

RESONATORS,” MEMS 2005, Miami, Florida, January 30 - February 3, 2005, y ypp.137-141

• [6] Y -W Lin S -S Li Z Ren and C T -C Nguyen “Vibrating micromechanical[6] Y. W. Lin, S. S. Li, Z. Ren, and C. T. C. Nguyen, Vibrating micromechanical resonators with solid dielectric capacitive-transducer ‘gaps’,” Proceedings, Joint IEEE Int. Frequency Control/Precision Time & Time Interval Symposium, Vancouver, Canada, Aug. 29-31, 2005, pp. 128-134., , g , , pp

• [7] S. A. Bhave, D. Gao, R. Maboudian, and R. T. Howe, “Fully-Differential Poly-SiC Lame mode Resonator and Checkerboard filter ” IEEE Intl Conference ofSiC Lame-mode Resonator and Checkerboard filter, IEEE Intl. Conference of Micro Electro Mechanical Systems, Miami, Florida, January 30 - February 3, 2005, pp. 223-226

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Thanks for your attention!!

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Energy dissipation mechanismsgy p• Q is mainly the combination of these dissipation

h imechanisms:

lossenergy11111+++ lossenergy ~

surfaceSupportTEDairtotal QQQQQ+++=

+ Air, be eliminated in vacuum+ Support, not yet been studiedy+ Thermal elastic damping, TED, very small in LAME mode! + Surface, reduce by large surface-to-volume ratios+ Others

High Q means lo loss !20

• High Q means low loss !Ref [5]: MEMS 2005

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