Fabrication of the Differential Microwave Power Sensor by Seesaw-Type MEMS Membrane

In this letter, a differential capacitive power sensor is proposed based on the seesaw-type microelectromechanical systems (MEMS) membrane. When the microwave power is applied, the center part of the membrane is pulled down toward to the substrate. Meanwhile, the end parts are turned away from the substrate, because two anchors act like pivots. Hence, the capacitance between the center part and the electrodes increases, while the capacitance induced by the end parts decreases. This device is based on the MEMS technology and fabricated by GaAs monolithic microwave integrated circuit (MMIC) process. The tested return loss is about -29 dB at 1 GHz, -18 dB at 5 GHz, and -13 dB at 10 GHz. The insertion loss is better than 1.5 dB over 1-10 GHz. For the incident power from 1 to 100 mW, the measured capacitance change magnitude AC
_in
increases from 0.1 to 7fF, while the capacitance change AC
_out
magnitude varies from 0.1 to about 3 fF. Therefore, the sensitivity of the proposed power sensor is improved and on the order of 0.1 fF/mW.