PROJECT TITLE :
A Fully Integrated Oven Controlled Microelectromechanical Oscillator—Part I: Design and Fabrication
This paper, the primary of two elements, reports the design and fabrication of a totally integrated oven controlled microelectromechanical oscillator (OCMO). This paper begins by describing the limits on oscillator frequency stability imposed by the thermal drift and electronic properties ( $Q$ , resistance) of both the resonant tank circuit and feedback electronics required to create an electronic oscillator. An OCMO is presented that takes advantage of high thermal isolation and monolithic integration of both micromechanical resonators and electronic circuitry to thermally stabilize or ovenize all the elements that comprise an oscillator. This was achieved by developing a processing technique where both silicon-on-insulator complementary metal–oxide–semiconductor (CMOS) circuitry and piezoelectric aluminum nitride, AlN, micromechanical resonators are placed on a suspended platform among a commonplace CMOS integrated circuit. Operation at microscale sizes achieves high thermal resistances ( $sim 10~^circ textC$ /mW), and hence thermal stabilization of the oscillators at terribly low-power levels when compared with the state-of-the-art ovenized crystal oscillators, OCXO. A constant resistance feedback circuit is presented that includes on platform resistive heaters and temperature sensors to both measure and stabilize the platform temperature. The boundaries on temperature stability of the OCMO platform and oscillator frequency imposed by the gain of the constant resistance feedback loop, placement of the heater and temperature sensing resistors, also platform radiative and convective heat losses are investigated.[2015-0035]
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