A single-chip oscillator based on a deep-submicron gap CMOS-MEMS resonator array with a high-stiffness driving scheme

This work reports the design of a monolithic oscillator based on a low motional impedance (R
_m
) CMOS-MEMS resonator array with a high-stiffness driving scheme in a standard 0.35 μm CMOS. Combined with the previously developed polysilicon release process and the proposed “contact-array-assisted” transducer design, a tiny equivalent transducer's gap (d
_eff
) of only 190 nm is successfully attained. Based on this feature, a low R
_m
of 10 kΩ is achieved under a medium bias voltage (V
_P
) of 36 V for a 4.22-MHz resonator, which demonstrates the lowest R
_m
among its CMOS-MEMS counterparts to date. The combination of the mechanically coupled array and high-stiffness driving scheme significantly enhances oscillator performance in terms of far-from-carrier phase noise. The 4.22-MHz single-chip CMOS-MEMS oscillator exhibits the phase noise of -90 dBc/Hz at 1-kHz offset and -121 dBc/Hz at 1-MHz offset, respectively.