Improvement of isolation for MEMS capacitive switch via membrane planarization

A new membrane planarization method on uneven surfaces of sacrificial layer is developed in this work to enhance the isolation of the capacitive shunt switch using microelectromechanical systems (MEMS) technology. In this method, the coplanar waveguide (CPW) slots are filled with the photoresist to planarize the uneven surfaces of the sacrificial layer. The surface contact area between the metal bridge and the dielectric layer is greatly increased after the planarization. Measurement results show that the isolation can be improved by 2.2 dB at 15 GHz and 10 dB at 40 GHz. In the up-state of switch, the insertion loss is less than 0.4 dB and the return loss is more than -15 dB up to 40 GHz. The proposed planarization method is relatively simple and cheap compared to the chemical mechanical polish (CMP) in terms of fabrication and engineering implementation.