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A Monolithic CMOS-MEMS Oscillator Based on an Ultra-Low-Power Ovenized Micromechanical Resonator

A fully monolithic complimentary metal-oxide- semiconductor-microelectormechanical systems (CMOS-MEMS) oscillator comprised of an ovenized double-ended tuning fork resonator to enable ultra-low heater power operation of only 0.47 mW over entire temperature span (-40 °C to 85 °C) and a low noise sustaining circuit to achieve low phase noise has been demonstrated in a Taiwan Semiconductor Manufacturing Company (TSMC) 0.35-μm CMOS process. The combination of low thermal conductivity material and high thermal isolation design is the key to attaining ultra-low-power heater operation in a sub-mW level. Passive temperature compensation scheme is also conducted in the proposed CMOS-MEMS resonator by an oxide-metal composite structure, showing a low temperature coefficient of frequency (TC f ) of only +5.1 ppm/°C, which is suited for the use in ovenized oscillator systems. By implementing a constant-resistance temperature control scheme, the frequency drift of the resonator smaller than 120 ppm from -40 °C to 85 °C is demonstrated in this paper, indicating an equivalent TC f smaller than 1 ppm/°C, a record-low value against its CMOSMEMS counterparts. The CMOS-MEMS oscillator operating at 1.2 MHz demonstrates a phase noise of -112 dBc/Hz at 1-kHz offset and -120 dBc/Hz at 1-MHz offset while drawing less than 1.3 mW. The entire power consumption of the ovenized oscillator system is confirmed to be less than 1.8 mW (oscillator + micro-oven), verifying the great potential of low power oven-controlled MEMS oscillators realized in CMOS-MEMS technology.