Design and Simulation of MEMS Based Varactor with High Tunability for Digital Communication Systems

Abstract

Over the past few years, RF MEMS varactor and switches have attained significant interest in the field of telecommunication and Microwave engineering. These RF MEMS varactors have many advantages over the conventional based varactors. Conventional solid state varactor use PIN diodes and are composed of GaAs metals and semiconductors. But these varactors have poor performance as compared to RF MEMS varactors in terms of various parameters. RF MEMS varactors requires low voltage, consumes less power, have high reliability,with high tunability, high isolation and less insertion loss than the conventional solid state varactors. This thesis presents a novel design and modelling of RF MEMS Varactor to achieve low actuation voltage and wide tunability. The proposed design consist of 3-bit tunable capacitor connected with beam. There are slits are used in central plates to increase the area tuning capability of varactors. A new beam design is proposed to reduce the stiffness of the beam which results in reduction of pull in voltage to 3.8V. Optimized result is obtain using finite element method (FEM) and CST microwave studio. Electrostatic actuation is used in this model because of its low power consumption and simplicity of fabrication. The proposed design is optimized using length, width of beam, electrode and central plate. A 50 Ω coplanar waveguide line is used, and optimized scattering parameter results are achieved for both actuated and unactuated state. A standardized process having low losses gold CPW, which is used to make complex circuits on high resistive silicon wafer and can be used for frequency range upto 100GHz. There are eight states of capacitance and at pull in voltage of 3.8V maximum tunability is achieved that is 159 %. Total Varactor design dimensions are 750 µm x 750 µm. The beam having 2 µm thickness and low losses CPW is of gold material. Mechanical simulation is done on Intellisuite software while electrical analysis done on CST microwave studio.