A Novel Thermistor-Based RF Power Sensor With Wheatstone Bridge Fabricating on MEMS Membrane

A novel thermistor-based RF power sensor with Wheatstone full-bridge structure is proposed using MEMS technology combined with monolithic microwave integrated circuit (MMIC) process in this paper. A MEMS substrate membrane is carefully designed beneath the hot area by back etching technology. Such a design can effectively suppress the longitudinal heat loss, which facilitates the improvement of sensitivity. In addition, in this design, low TCR (temperature coefficient of resistance) TaN (tantalum nitride) resistors are adopted to achieve the stability of impedance matching. Measurement results show that the output response of this device has excellent linearity with the power from 1 to 200mV. Considering the effect of the distance between the hot and cold areas, three sensor configurations with different arrangements of thermistors were investigated experimentally. And their corresponding sensitivities are 0.16 mV/mW, 0.19 mV/mW and 0.22 mV/mW at 10GHz, respectively. Meanwhile, the measured response times of these three configuration sensors are 20.7 ms, 22.3 ms and 27.2 ms, respectively. Therefore, there is a trade-off consideration between high sensitivity and fast response time. Moreover, the measured return losses are less than −20 dB in the frequency range from 10 MHz to 20GHz. This indicates that these devices have good matching characteristics. The proposed thermistor-based RF MEMS power sensor demonstrates a good performance, especially high sensitivity and stable impedance match, providing great application potential. [2020-0260]