Low-motional-impedance highly-tunable I/sup 2/ resonators for temperature-compensated reference oscillators

A new capacitive micromechanical resonator design optimized for high Q, low motional impedance, and large tuning range is presented. The I/sup 2/ resonator was fabricated using a conservative, by present standards, HARPSS-on-SOI process, and demonstrated quality factors up to 57000 in vacuum. From the designed resonators between 3MHz and 6MHz, the lowest measured impedance is 24k/spl Omega/ and the largest electrostatic tuning coefficient is -10ppm/V/sup 2/. An oscillator interface circuit comprising of a trans-impedance amplifier and an automatic tunable charge pump providing an automatic temperature-compensating bias voltage was also designed and fabricated in a standard 0.5/spl mu/m CMOS process. Preliminary tests show temperature drift reduction of a 4MHz resonator from 2400ppm to 240ppm over a 90/spl deg/C range.