Development of capacitive temperature sensors with high sensitivity using a multiuser polycrystalline silicon process

Abstract

A MEMS capacitive temperature sensor is presented that displays high sensitivity over a specific temperature range using out-of-plane thermal actuators and capacitive electrodes. The sensor is suitable for applications that require high precision in relatively small temperature range, such as biomedicine, food processing and food safety. The device uses a combination of bilayer, rigid and flexible beams to create a nonlinear capacitance-temperature response over a short temperature range. The bilayer beams act as the out-of-plane thermal actuator and move the top electrode of the sensor up and down to change the capacitance. The capacitance is inversely proportional to the electrodes' gap and a decrease in the gap increases the sensitivity of the capacitance-temperature (C-T) response. Sensors with different geometries have been simulated using ANSYS to show the possibility of geometric modification to shift the temperature range with high sensitivity. Fabricated sensors are used in an experimental set up to demonstrate the applicability of the proposed design concept. The measured data verify the simulation results and demonstrate that the proposed sensor design can provide high sensitivity of 20 fF/°C in a desired range of ambient temperature where low sensitive region display noticeably smaller sensitivity of 5 fF/°C.