Design And Process Of A Novel RF MEMS Latching Switch

A novel electrostatic, capacitively shunt RF MEMS switch is presented. The switch utilizes the buckling effect of the clamped-clamped membrane under critical compressive stress to realize latching function. The structure's characteristic is that when the control voltage is removed the state of the switch is not changed, i.e., latching.First, the detailed design procedure of the switch is presented. The buckling characteristic of composite membrane is analyzed. Finite element analysis (FEA) shows that driving voltage increases exponentially with the increase of gap between the membrane and driving electrodes and that driving voltage increases with the increase of membrane stress. The 50Ω coplanar waveguide is designed and the loss characteristics are discussed. The equivalent electrical model of the switch is given and the simulation by ADS shows that the insertion loss of the switch is very low (<0.13dB@50MHz-30GHz) and the isolation is relatively high (25dB@30GHz). On this basis, the operational principle of a tri-state latching RF MEMS switch is illustrated.Then, the switch sample based on P (100) high-resistivity silicon substrate is fabricated by surface micromachining process and the preliminary test result is achieved. We mainly investigate such key processes as planarizaiton and etching of the sacrificial layer, membrane deposition, stress control and membrane etching. We apply the Contact Planarization(CP) technique to the planarization of organic sacrificial layer for the first time and achieve very good results. CMP is also studied to compare with CP process. The stresses of several membranes such as silicon nitride, gold, Aluminum are investigated. The problem of Ion Beam etching during fabrication is discussed and the solution is presented. Test result shows that the insertion loss and isolation of the switch is 0.3dB@30GHz and 15dB@30GHz respectively. Finally, the methods to improve the switch performance are discussed.