Suspended Thermopile for Microwave Power Sensors Based on Bulk MEMS and GaAs MMIC Technology

In this letter, the effects of the suspended thermopile on the microwave and sensing performances of 0.01-30 GHz thermoelectric microwave power sensors are researched by experiments, in order to obtain the reasonable back-cavity dimension. The back-cavity underneath the thermopile is used to depress thermal losses of the power sensors and is fabricated using the bulk microelectromechanical systems process. Three thermoelectric power sensors with different suspension lengths of the thermopile are accomplished with the GaAs monolithic microwave integrated circuit technology. The three power sensors show good microwave matching impedance, with measured reflection losses of less than -21 dB up to 30 GHz. The good linearity between the input power and the output thermovoltages is obtained. When the suspension length of the thermopile is 20, 50, and 80 μm, the average sensitivity of these power sensors is 186.9, 238.9, and 286.0 μV/mW at 30 GHz, respectively. In addition, the relationships of the sensitivity with the microwave power and frequency are quantified under different suspension lengths of the thermopile.