A readout circuit implementation to reduce the flicker noise in MEMS electrothermal sensors

The electrothermal displacement sensors are doped silicon resistors. The electrical current through the doped silicon generates flicker and thermal noise which degrades the sensitivity of these sensors. We propose an alternative readout method in which driving the silicon heaters with a high frequency voltage instead of a dc voltage leads to a lower flicker noise. The output of the sensor, in a simple wheatstone bridge configuration, is amplified by a low noise differential amplifier which attenuates the heating high frequency voltage as a common mode input. The proposed technique has been applied to a MEMS electrothermal sensor fabricated in the standard silicon on insulator (SOI) process. Experimental results demonstrate an 8dB improvement in SNR compared to the conventional measurement technique. The achieved noise floor is less than -100 dBVrms around the 20 Hz measured signal which translates to equation to 0.1nm/√(Hz) displacement noise in a MEMS nanopositioner.