Inline capacitive RF power sensor based on floating MEMS beam for GaAs MMIC applications

A 0.01–20 GHz inline capacitive radio frequency (RF) power sensor with a floating microelectromechanical system (MEMS) beam is proposed. It is based on sensing the capacitance change of the MEMS beam above the coplanar waveguide line due to the electrostatic force. In the design, anchors of the MEMS beam are floating for accurate capacitive detection and flexible for increasing the sensitivity, and an impedance matching technique is utilised to improve the microwave performance. The fabrication of this sensor is compatible with the GaAs monolithic microwave integrated circuits (MMICs) process. The measured reflection loss of the capacitive sensor is <−18 dB, whereas the insertion loss is better than −0.38 dB up to 20 GHz. Experiments show that approximate linear relationships between the measured capacitance change and the input RF power are obtained, and the resulting average sensitivities are 120.8, 76.7, 87.6 and 61.0 aF/mW at 5, 10, 15 and 20 GHz, respectively.