Study of a 10Â MHz MEMS oscillator with a TPoS resonator

- An interdigital electrode for TPoS resonator is discussed. It improved the Q by 43%.
- Revised the equivalent circuit model of the first order lateral extensional mode.
- Manufacturing an oscillator based on this resonator with a phase shift of 90°.

This paper reports a low phase noise 10 MHz oscillator based on a lateral-extensional mode thin-film piezoelectric-on-silicon (TPoS) resonator. A novel design of interdigital electrodes is introduced to improve both the insertion loss and quality factor of the resonator. The average quality factor gets improved by 43% by this method. The equivalent circuit model of the fundamental lateral-extensional mode is analysed. An oscillator is also designed and manufactured. The whole circuit includes a single common emitter BJT amplifier, LC network filter, a phase shifting unit and a MEMS resonator. Tuning the phase shifter in the feedback circuit, the MEMS resonator works at the best operating point while the phase shifting of the peripheral circuit is 90°. With an operating input power around 0 dBm, the resonator is not driven at its bifurcation point. Little nonlinearity is observed in the output waveform. The phase-noise is measured below −105 dBc/Hz@100 Hz, −135 dBc/Hz@1 kHz offset and the far-from-carrier noise reaches below −150 dBc/Hz.