Temperature compensated single-device electromechanical oscillators

This work presents temperature compensated single-device fully micromechanical (circuit-less) oscillators. Thermal-piezoresistive interactions in certain micromechanical resonant structures can lead to self-sustained mechanical vibrations. Self-sustained single crystalline silicon oscillators with frequencies in the few MHz range have been fabricated and their temperature drift behavior is characterized. Temperature drifts as high as - 38ppm/°C measured for the fabricated devices were sharply reduced to less than ±1.5ppm/°C by high concentration phosphorous doping of the structures. TCF as small as 0.4ppm/°C has been demonstrated for a 2.4MHz MEMS oscillator. Furthermore, the TCF of the oscillators has been found to be dependent on the resonator bias current making very close to zero TCF achievable for such devices.