A temperature-stable mems oscillator on an ovenized micro-platform using a PLL-based heater control system

Abstract

In this work, an oxide-refill process is used to null the first-order temperature coefficient of frequency (TCF) of silicon MEMS resonators and to achieve high thermal resistance isolation structures. The technology enables fabrication of a low-power ovenized micro-platform on which multiple MEMS devices can be integrated. The intrinsic frequency-temperature characteristic of two resonators is utilized for temperature sensing, and closed-loop oven control is realized by phase-locking two MEMS oscillators at a specific temperature. PLL-based control circuitry is implemented in 0.18 μm CMOS to interface with the MEMS resonators. The ovenized MEMS oscillator exhibits an overall frequency drift of ± 5.5 ppm over -40 °C to 70 °C. The MEMS oscillator exhibits near zero phase noise degradation in closed-loop operation.