An 8-12GHz capacitive power sensor based on MEMS cantilever beam

In this paper, an 8-12GHz capacitive power sensor based on MEMS cantilever beam is proposed. When the displacement of the cantilever beam is far less than the initial height of the air gap, the capacitance between the measuring electrode and the cantilever beam has a linear dependence on the input power of the RF signal. The novelty of the presented design provides not only negligible disturbance of the input signal but also an improved sensitivity because of small elastic coefficient of the cantilever beam. Impedance compensating technology by modifying the slot width of the CPW transmission line is adopted and the validity is verified by the simulation of HFSS software. The presented power sensor has been designed, optimized and fabricated using GaAs MMIC process. The measured return loss is less than -25dB and the insertion loss is around 0.1dB at 8-12GHz. DC voltage measurement and RF power measurement have been performed to test against the validity of the design. A sensitivity of 6aF·mW^-1 is obtained which is limited by the thickness of the cantilever beam, the initial height of the air gap and the area of the measuring electrode.