CMOS-MEMS multi-sensor single chip with high heat dissipation and low-temperature hermetic sealing

This paper presents a single chip of a three-axis CMOS-MEMS accelerometer, a chopper-stabilized automatic offset calibration readout circuit driven by a MEMS resonator oscillator, and a built-in Pirani vacuum sensor for verification of low-temperature hermetic sealing and thermal effects. The minimum output noise floor of the accelerometer measured in the range of 0–3 G is
$145\ \mu \mathrm{G}/\text{Hz}^{1/2}$
and the minimum output DC offset voltage can be controlled within 40 mV. A MEMS resonator oscillator with a natural frequency of 185 kHz serves as the reference clock of the chopper amplifier, and the phase noise is −74 dBc at 10 kHz offset. Because the integrated sensing chip is fabricated using standardized CMOS-MEMS technology, this research uses a gold-bump flip-chip bonding technology with high-thermal-conductivity silicone rubber (2 W/mK) to achieve low-temperature (≤300 °C) CMOS back-end hermetic sealing. According to the experimental results of the control group (hermetically sealed and unsealed vacuum sensors), the sealed vacuum sensor can maintain normal operation within the pressure range of 0.05–10
³
mbar and the thermal effect of the vacuum sensor is only
$204\ \mu \mathrm{V}/^{\circ}\mathrm{C}$
.