Optimal design and performance analysis of a RF MEMS series switch for high isolation and low-loss RF systems

Abstract

In this thesis, a RF MEMS switch for a high isolation and insertion loss having a coplanar waveguide (CPW) signal line and a corrugated membrane are presented using a normal GaAs process. And design optimizations and device fabrications are executed. The device structure of metal-to-metal (resistive) contact and series topology with a fixed-fixed membrane is focused. Mechanical design of RF MEMS switches is to define the spring constant of the membrane. With small deflections, an external force, F (N) is obtained using the deflection Δg(m) and the spring constant, k (N/m). And the spring constant, k is calculated with variations of the electrode area and related parameters, electrostatic force, switching time, up state capacitance, and contact area are calculated. Also, corrugated membrane is designed and the effects of the up and down capacitances are calculated. A signal transmission Coplanar waveguide (CPW) line as a lower metal electrode plate is designed using 2.5 D electromagnetic simulator (MOMENTUM, Agilent). Finite element analysis using ANSYS is carried out. Material parameters as a membrane plate are considered and various thickness of the gap is simulated and compared with analytically calculated results. Process sequences of the switch are designed and optimized using modular and unit fabrication processes. As results, proposed a RF MEMS series switch for high isolation and low insertion loss having a CPW signal line and a corrugated membrane is measured. A pull down voltage of about 38 V is measured by using DC parameter analyzer. The isolation and insertion loss of the MEMS switch are -52 dB and -0.2 dB, respectively. Using the simple model parameters, isolation and insertion loss are simulated and compared with the measured data. Also improved CPW configuration and the thickness of the CPW layer are presented. So, the insertion loss can be reduced to -0.05 dB at 5 GHz. The switching time of the switch is measured with optical interferometer...