High-q integrated CMOS-MEMS resonators with deep-submicron gaps

Integrated CMOS-MEMS free-free beam resonators using pull-in mechanism to surmount the limitation of CMOS minimum feature size and hence achieve deep-submicron electro-to-resonator gap spacing have been demonstrated to overcome Q-degradation and frequency variation caused by modulated boundary conditions, greatly improving resonator Q and at the same time reducing motional impedance to allow direct measurement without the use of readout circuitry. The key to attaining high Q and to stabilizing resonance frequency of resonators is to effectively decouple the pull-in scheme and mechanical boundary conditions of resonators. In this work, CMOS-MEMS resonators with deep-submicron gaps have been measured with motional impedance down to 172kΩ and Q´s greater than 2,000. In addition, such a resonator monolithically integrated with CMOS amplifier, totally occupying die area of only 300μm × 130μm, was also tested with enhanced transmission. With such improved performance, this technique may pave a way to realize fully-integrated CMOS-MEMS oscillators, therefore benefitting future single-chip applications.