A micro-machined high-Q film bulk acoustic resonator for chip-scale atomic clock

Taking advantage of its low power consumption and small volume, Chip-Scale Atomic Clock (CSAC) will play a critical role in portable applications, underwater communication systems, unmanned aerial vehicles, underwater sensor systems and geophysical equipments. It has aroused great research interest in these years. Traditionally, the 3.4GHz Voltage Controlled Oscillator (VCO) applied to 87Rb atomic clock is based on the frequency multiplier method of a high stable crystal oscillator. It's power hungry and can not satisfy the requirement of CSAC. Based on the fact that SiO2 film can both compensate the Temperature Coefficient of Frequency (TCF) of Film Bulk Acoustic Resonator (FBAR) and improve the Q-factor of FBAR's high-order resonance, a film bulk acoustic resonator with resonant frequency 3.4GHz, Q-factor better than 500 and TCF better than 20ppm per K was designed and fabricated with a micro-machined method, which satisfied the requirement of CSAC. The authors would thank National Natural Science Foundation of China for the support under contract number 11104313.