A Wide-Dynamic Range (-40 °C to 180 °C) Active Wireless MEMS Temperature Sensor With 7m °C Sensitivity

We demonstrate a highly accurate active wireless microelectromechanical systems (MEMS) temperature sensor with the largest reported dynamic range (–40 °C to 180 °C) among active MEMS temperature sensors. The sensor uses a 27.2-MHz high quality factor (
${Q} >$
3200) aluminum nitride-on-silicon (AlN-on-Si) thin-film piezoelectric-on-silicon (TPoS) MEMS resonator to enable highly accurate temperature sensing, with minimum sensitivity (
${S}$
), better than 0.011 °C across this wide temperature range. The wireless sensor uses an innovative frequency shift keying (FSK) 900-MHz direct upconversion transmitter. The transmitter uses frequency multipliers for upconversion, obviating the need for a temperature-stable frequency reference clock, thereby preserving the temperature coefficient of frequency (TCF) of the resonator and, consequently, the sensitivity of the sensor. The experimental results show a very high correlation (< 0.03% error) between the TCF of the MEMS oscillator and that of the transmitter output signal, demonstrating the viability of the proposed direct upconversion technique. A detailed analysis of the Allan variance for MEMS temperature sensors, which can be used to design for a given minimum sensitivity, is also presented in this article.