1. RF MEMS variable capacitors Tae Yong Song Micro wave devices term project SNU 2004. 6. 22

2. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 2 What are RF MEMS? RF MEMS Radio-Frequency: Transporting 9kHz ~ 300GHz signals Micro: Feature size (1~500 um) Electro-Mechanical: transferring electrical energy into mechanical motion Systems

3. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 3 Applications – RF MEMS Integrated RF transceiver

4. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 4 Applications- Capacitor (1) In wireless communication systems –tunable capacitors and inductors often need a high quality factor and high self-resonant frequency. Reduce power consumption Better phase noise and power in voltage-controlled oscillators (VCOs) Wide tuning range (VCOs)

5. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 5 Applications- Capacitor (1) Advantages over conventional varactor based filter –Increase dynamic range and dramatic part reduction –Two pole UHF filter : much smaller system (a) Varactor and (b) MEMS capacitor-based tunable two-pole UHF filter. Ref [3] :Robert R, et al. “Variable MEMS Capacitors Implmented into RF Filter Systems”

6. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 6 MEMS Capacitors-Type I (1) University of Waterloo IEEE, Transaction on Electron Devices, Vol. 50, No.3, March 2003

7. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 7 Analysis (1) A schematic model of a conventional eletrostatically actuated two-parallel-plate tunable capacitor

8. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 8 Analysis (2) A schemetic model of the novel wide-tuning-range tunable capacitor

9. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 9 Fabrication process A schematic illustration of the fabrication process for the widetuning- range tunable capacitor. Microscopic pictures of the novel wide- tuning-range tunable capacitor.

10. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 10 Measurement (1) When Vdc is greater than 19V, h1 changes directly from 1 um to zero –Pull in voltage is about 19V from simulation The measured data is not zero over pull in voltage –Surface roughness –Curvature of the plates –The damping between the plates have an effect on the space

11. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 11 Measurement (2) Quality factor as a function of frequency Quality factor of about 30 at 5 GHz Self-resonant frequency far beyond 10 GHz

12. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 12 MEMS Capacitor-type II 40 um thick single-crystal silicon actuator suspended over a glass substrate : Long operational lifetimes Through the use of a large throw electrostatic comb drive and a separate area tuning capacitor –Wide tuning range and high Q can be achieved Only added to aluminum conductive layer –reduce series resistance SEM of a 40-m-thick tunable capacitor

13. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 13 Fabrication a)Aling marker is etched and 2 um Al is deposited and patterned. b)Epoxy bonding c)The handle wafer side and buried oxide are removed d)Silicon etching using the Bosch process e)Released by isotropically etching the epoxy in an oxygen plasma  After released, additional metal can be sputtered onto the structure to increase device Quality factor

14. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 14 Measurement (1) Exceptionally large tuning range, larger than 8:1 Resistance of the MEMS tunable capacitor is less than 1Ω –Lead to a high Q Tuning range of the device measured at 500 MHz. Q factor of the device from 100MHz to 3 GHz

15. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 15 Measurement (2) Some filter applications require lifetimes of over 10- billion cycles. MEMS tunable capacitor is fabricated from single-crystal silicon –A material that has a large elastic deformation region and shows very little fatigue Change in series resistance after 11.1- billion cycle Change in capacitance versus tuning voltage

16. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 16 Conclusion Capacitor 의 양 평판에 bias 전압을 가하여 발생하는 정전력 을 이용하는 일반적으로 방식은 이론적으로는 1.5:1 로 작은 단접이 있지만 구조적 변화를 통해 향상시킬 수 있다. MEMS device 는 high Q-factor, wide tuning range, low phase noise 가 가능하다. MEMS 기술로 제작된 capacitor 는 저 전압, 빠른 tuning 및 작은 크기로 구현이 가능하다.

17. June 21, 2004 Tae Yong Song, Micro/Nano Systems & Controls Lab. 17 Reference [1] Jinghong Chen, Member, IEEE, Jun Zou, Chang Liu, Senior Member, IEEE, José E. Schutt-Ainé, Senior Member, IEEE, and Sung-Mo (Steve) Kang, Fellow, IEEE “Design and Modeling of a Micromachined High-Q Tunable Capacitor With Large Tuning Range and a Vertical Planar Spiral Inductor”, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 50, NO. 3, MARCH 2003. [2] Robert L. Borwick, III, Philip A. Stupar, Jeffrey F. DeNatale, Member, IEEE, Robert Anderson, and Robert Erlandson, Member, IEEE “Variable MEMS Capacitors Implemented Into RF Filter Systems”, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 51, NO. 1, JANUARY 2003 [3] Borwick, R.L. III, Stupar, P.A., DeNatale, J., Anderson, R., Chialun Tsai, Garrett, K., ” A high Q, large tuning range, tunable capacitor for RF applications”, Micro Electro Mechanical Systems, 2002. The Fifteenth IEEE International Conference on, 20-24 Jan. 2002 Pages:669 – 672 [4] Mansour, R.R., Bakri-Kassem, M., Daneshmand, M., Messiha, N.,” RF MEMS devices”, MEMS, NANO and Smart Systems, 2003. Proceedings. International Conference on, 20-23 July 2003 Pages:103 - 107 [5] Zhiping Feng; Wenge Zhang, Bingzhi Su, Harsh, K.F., Gupta, K.C., Bright, V., Lee, Y.C.,” Design and modeling of RF MEMS tunable capacitors using electro-thermal actuators”, Microwave Symposium Digest, 1999 IEEE MTT-S International, Volume: 4, 13-19 June 1999 Pages:1507 - 1510 vol.4 [6] De Coster, J., Puers, R., Tilmans, H.A.C., van Beek, J.T.M., Rijks, T.G.S.M.,” Variable RF MEMS capacitors with extended tuning range “, TRANSDUCERS, Solid-State Sensors, Actuators and Microsystems, 12th Innational Conference on, 2003, Volume: 2, 8-12 June 2003 Pages:1784 - 1787 vol.2