Silicon carbide micro-electromechanical resonators for highly integrated frequency synthesizers

A low temperature (<300ºC), low-stress micro-electromechanical systems (MEMS) fabrication process based on a mechanically superior silicon carbide structural layer is outlined. The process is designed for low-cost film deposition and CMOS post-integration, stemming from chemical and thermal compatibility. MEMS beam resonators and arrays are fabricated, and have higher power handling capabilities and operating frequencies, compared to those of similar polysilicon-based resonators. A tuning method based on integrated heaters is introduced, yielding constant insertion loss tuning and wide tuning ranges. Quality factors of up to 1493 and resonant frequencies of up to 26.2 MHz are measured. A MEMS beam resonator model that accounts for electrostatic and mechanical non-linearities, and that may be used in circuit simulators is proposed. The model captures non-linear effects such as resonant frequency shifting and Duffing behaviour. It offers valuable insights into the trade-offs involved in the design optimization of MEMS resonator-based oscillators. Such oscillators are designed using an integrated high gain-bandwidth trans-impedance amplifier (TIA) combined with a resonator. The TIA employs automatic gain control to mitigate the inherent low power handling capabilities and the non-linearities of the MEMS device, thus minimizing their effect on phase noise. A highly integrated 1.7-2.0 GHz digitally programmable fractional-N frequency synthesizer using a MEMS resonator-based oscillator as its frequency reference is presented. Due to the dimensions of the MEMS device (e.g. 25 um by 114 um), the entire system with a total area of 6.25 mm2 can be housed in a small standard chip package. This considerably reduces the form factor and cost of the system, compared to using an external crystal as a reference. The synthesizer has a fine frequency resolution (~11 Hz) in order to allow for high output frequency stability when used with an appropriate control loop. A fully integUne technologie de fabrication de microsystèmes électromécaniques (MEMS) à basse température (