A micromachined silicon capacitive temperature sensor for wide temperature range applications

A micromachined capacitive temperature sensor is designed and fabricated based on a multilayer cantilever. The top and bottom layers of the cantilever are Al and Si, respectively, which also serve as electrodes of the sensing capacitor. A composite Si3N4/SiO2 layer, a dielectric layer, is sandwiched between the top and bottom electrodes. The cantilever thermal response is due to differences in thermal expansion coefficients for the Al, Si3N4/SiO2 and silicon materials. With the effect of strain on the dielectric property as well as the geometry impact on the capacitance, the temperature variation is sensed and translated to an electrical capacitance change. The mechanical characteristics of the sensor are theoretically analyzed with the extension of Timoshenko's bilayer strip model. The sensor was fabricated with the silicon-on-insulator substrate. Experimental results show that the sensor provides a sensitivity of 7 fF degrees C-1 in the -70 to 100 degrees C range. This makes it suitable to serve as a temperature sensor for low power and wide temperature range applications.