Micromechanical IBARs: Tunable High-Q Resonators for Temperature-Compensated Reference Oscillators

This paper presents a unique capacitive micromechanical resonator and oscillator architecture for temperature-compensated frequency references. The I-shaped bulk acoustic resonator (IBAR) is designed to have excellent electrical tunability for temperature compensation (TC) and dynamic frequency control. High quality factor and low motional resistance are also achieved. The applicable range of frequencies is 1-30 MHz, in which quality factors exceeding 100 000 have been measured. Resonator metrics, including the electrostatic tuning coefficient, normalized dynamic stiffness, and relative dynamic compliance, are introduced. A small-signal resistance in the resonator is reported and explained. This unexpected resistance is beneficial for oscillator functionality over a large temperature range. The interface IC, inclusive of all blocks for sustaining oscillations and TC, is also presented. A two-chip 6-MHz oscillator with a temperature stability of 39 ppm over 100°C is demonstrated. The interface IC consumes 1.9 mW.