Frequency Stability of RF-MEMS Disk Resonators

This paper systematically investigates the frequency stability of a radial-contour-mode micromechanical disk resonators with high quality factor (Q-factor) and high resonance frequency. Microelectromechanical system (MEMS)-based oscillator prototype consisting of the resonator and off-chip circuit is realized for frequency reference. The sustaining circuit is designed using impedance matching networks and two op-amp stages with automatic gain control circuit. The oscillator reaches a short-term frequency stability of +/- 1 ppm and a medium-term frequency stability of +/- 5 ppm over industrial temperature range (-40 degrees C-85 degrees C), which outperforms some of the best MEMS oscillators. Meanwhile, the phase noise is -95 dBc/Hz at 10 kHz offset and 149-MHz carrier. This paper also presents a simple and effective compensation scheme by combining built-in microoven and bias voltage tuning, which can achieve a frequency stability range of 2 ppm at temperature ranges from 20 degrees C to 100 degrees C.