Extremely low resonance frequency MOEMS vibration sensors with sub-pm resolution

The majority of MEMS vibration sensors requires relatively high resonance frequencies of several kHz to avoid mechanical contact of moving parts such as plates or electrodes. In contrast to that, the presented hybrid micro-opto-electro-mechanical system (MOEMS) principle enables displacement sensors applicable at low frequencies. This work describes a distinct MOEMS featuring extremely low resonance frequencies of below 200 Hz. The discussed sensor operates in ambient air without closed loop feedback, extensive electronics, or cooling. Due to the soft suspension of the micro-mechanical sub-system, the fundamental limit, i.e., the Brownian noise floor, is reached for frequencies below the resonance frequency. The related noise equivalent displacement is 1.9 pm/√Hz. Above resonance, the measured noise of 0.86 pm/√Hz, which is equivalent to 0.29 μg/√Hz is dominated by the noise of the electrical components. Also a discussion about feasible improvements regarding the sensitivity and pushing the mechanical resonance frequency below 100 Hz is given.