Micromechanical Circuits for Communication Transceivers

Micromechanical (or "pmechanical) communica- tion circuits fabricated via IC-compatible MEMS technologies and capable of low-loss filtering, mixing, switching, and fre- quency generation, are described with the intent to miniaturize wireless transceivers. Receiver architectures are then proposed that best harness the tiny size, zero dc power dissipation, and ultra-high-Q of vibrating pmechanical resonator circuits. Among the more aggressive architectures proposed are one based on a pmechanical RF channel-selector and one featuring an all-MEMS RF front-end. These architectures maximize performance gains by using highly selective, low-loss pmechanical circuits on a massive scale, taking full advantage of Q versus power trade-offs. Micromechanical filters, mixer-filters, and switchable synthesiz- ers are identified as key blocks capable of substantial power sav- ings when used in the aforementioned architectures. As a result of this architectural exercise, more focused directions for further research and development in RF MEMS are identified. I. Introduction Due to their need for high frequency selectivity and low noise frequency manipulation, portable wireless communication trans- ceivers continue to rely on off-chip resonator technologies that interface with transistor electronics at the board-level. In particu- lar, highly selective, low loss radio frequency (RF) and intermedi- ate frequency (IF) bandpass filters generally require ceramic, SAW, or quartz acoustic resonator technologies, with Q's in excess of 1,000. In addition, LC resonator tanks with Q's greater than 30 are required by voltage-controlled oscillators (VCO's) to achieve sufficiently low phase noise. These off-chip resonator components then contribute to the substantial percentage (often up to 80%) of portable transceiver area taken up by board-level, passive components. Recent advances in IC-compatible microelectromechanical system (MEMS) technologies that make possible micro-scale, mechanical circuits capable of low-loss filtering, mixing, switch- ing, and frequency generation, now suggest methods for board- less integration of wireless transceiver components ( 11. In fact, given the existence already of technologies that merge microme- chanics with transistor circuits onto single silicon chips (2-51, sin- gle-chip transceivers may eventually be possible, perhaps using alternative architectures that maximize the use of passive, high-Q, pmechanical circuits to reduce power consumption for portable applications. This paper presents an overview of the pmechanical circuits and associated technologies expected to play key roles in reducing the size and power consumption of future communica- tion transceivers.

[1]  Paul J. McWhorter,et al.  Embedded micromechanical devices for the monolithic integration of MEMS with CMOS , 1995, Proceedings of International Electron Devices Meeting.

[2]  R. Howe,et al.  Vacuum encapsulation of resonant devices using permeable polysilicon , 1999, Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291).

[3]  Cam Nguyen,et al.  Frequency trimming and Q-factor enhancement of micromechanical resonators via localized filament annealing , 1997, Proceedings of International Solid State Sensors and Actuators Conference (Transducers '97).

[4]  S. Eshelman,et al.  Micromachined low-loss microwave switches , 1999 .

[5]  R. Howe,et al.  Batch transfer of microstructures using flip-chip solder bonding , 1999 .

[6]  C. Nguyen,et al.  High-Q HF microelectromechanical filters , 2000, IEEE Journal of Solid-State Circuits.

[7]  R. Howe,et al.  An integrated CMOS micromechanical resonator high-Q oscillator , 1999, IEEE J. Solid State Circuits.

[8]  Ark-Chew Wong,et al.  Micromechanical Mixer+Filters , 1998 .

[9]  G. R. Kline,et al.  Development of miniature filters for wireless applications , 1995, Proceedings of 1995 IEEE MTT-S International Microwave Symposium.

[10]  Michiel Steyaert,et al.  A 1.8-GHz low-phase-noise CMOS VCO using optimized hollow spiral inductors , 1997, IEEE J. Solid State Circuits.

[11]  H. Tilmans,et al.  Electrostatically driven vacuum-encapsulated polysilicon resonators part II. theory and performance , 1994 .

[12]  T.H. Lee,et al.  A 1.5 V, 1.5 GHz CMOS low noise amplifier , 1996, 1996 Symposium on VLSI Circuits. Digest of Technical Papers.

[13]  D. Leeson.  A simple model of feedback oscillator noise spectrum , 1966 .

[14]  J. Bustillo,et al.  Surface micromachining for microelectromechanical systems , 1998, Proc. IEEE.

[15]  J. F. Parker,et al.  A 1.6-GHz CMOS PLL with on-chip loop filter , 1998, IEEE J. Solid State Circuits.

[16]  Kun Wang,et al.  High-order medium frequency micromechanical electronic filters , 1999 .

[17]  S. Sherman,et al.  Fabrication technology for an integrated surface-micromachined sensor , 1993 .

[18]  Anatol I. Zverev,et al.  Handbook of Filter Synthesis , 1967 .

[19]  R. Howe,et al.  Post-CMOS integration of germanium microstructures , 1999, Technical Digest. IEEE International MEMS 99 Conference. Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.99CH36291).

[20]  Gabriel M. Rebeiz,et al.  Micromachined devices for wireless communications , 1998, Proc. IEEE.

[21]  Ark-Chew Wong,et al.  VHF free-free beam high-Q micromechanical resonators , 2000, Journal of Microelectromechanical Systems.