A Temperature-Stable Piezoelectric MEMS Oscillator Using a CMOS PLL Circuit for Temperature Sensing and Oven Control

In this paper, design, analysis, and implementation of a piezoelectric microelectromechanical systems (MEMS) oscillator on an ovenized microplatform is presented. An oxide-refill process is used to compensate the first-order temperature coefficient of frequency of MEMS resonators, as well as to realize thermal isolation structures. The technology enables fabrication of low-power ovenized device fusion platforms using standard silicon on insulator wafers. Utilizing the intrinsic frequency-temperature characteristic of two MEMS resonators, temperature sensing and closed-loop oven-control is realized by phase-locking two MEMS oscillators at an oven-set temperature. The design of the phase-lock control loop is studied using multidomain linear models. Control loop dynamics, noise properties, and nonideal effects are analyzed. Low-power and low-noise phase-locked loop-based control circuitry is designed in 0.18-μm CMOS to interface with the MEMS resonators. Using the developed technology, an oven controlled MEMS oscillator exhibits an overall frequency drift of <;8 ppm over -40 °C to 70 °C without the need for system calibration. In addition, the MEMS oscillators exhibit near zero phase noise degradation in closed-loop operation.