RF MEMS switches with novel materials and micromachining techniques for SOC/SOP RF front ends

This dissertation deals with the development of RF MEMS switches with novel materials and micromachining techniques for the RF and microwave applications. Research on several projects is presented. In the first project, Finite Ground Coplanar (FGC) waveguide transmission line on CMOS grade silicon wafer are studied; the second project and the third project investigated novel dielectric materials for RF MEMS switches. The second project is a low cost Radio Frequency (RF) Mirco-electromechanical Systems (MEMS) switch using photo-definable mixed oxide dielectrics, and the third project developed RF MEMS switches on flexible Liquid Crystal Polymer (LCP) substrate to enable the implementation of multi-band and reconfigurable modules. The fourth project is focused on tunable RF MEMS switches using a Barium Strontium Titanate (BST) dielectric layer. In the fifth project, preliminary research on reliability considerations of MEMS switches are discussed and implemented, and the sixth project showed the implementation of several reconfigurable RF circuits with the developed RF MEMS capacitive switches in this dissertation.; In the first project, Finite Ground Coplanar (FGC) waveguide transmission lines on CMOS grade silicon wafer (<0.01 ohm-cm) with a thick embedded silicon oxide layer have been developed using micromachining techniques. Lines with different lengths were designed, fabricated and measured. Measured attenuation and s-parameters are presented in Chapter II. Results show that the attenuation loss of the fabricated FGC lines is as low as 3.2 dB/cm at 40 GHz.; In the second project, a novel approach for fabricating low cost capacitive RF MEMS switches using directly photo-definable high dielectric constant metal oxides has been developed. In this approach, a radiation sensitive metal-organic precursor is deposited via spin coating and converted to a high dielectric constant metal oxide via ultraviolet exposure. The feasibility of this approach is demonstrated by fabricating bridge-type and cantilever-type switches with a photo-definable mixed oxide dielectric film. These switches exhibited significantly higher isolation and load capacitances as compared to comparable switches fabricated using a simple silicon nitride dielectric. Electrical characterization of the mixed metal oxide and the measurement results of the fabricated switches will be shown in Chapter III.; The third project presents an RF MEMS switch developed on a low cost, flexible liquid crystal polymer (LCP) substrate. Its very low water absorption (0.04%), low dielectric loss and multi-layer circuit capability make it very appealing for RF Systems-On-a-Package (SOP). In chapter IV, a capacitive RF MEMS capacitive switch on an LCP substrate and its characterization and properties up to 40 GHz is presented for the first time.; The fourth project is to develop a tunable RF MEMS switch on a sapphire substrate with BST as dielectric material, which is deposited by a Combustion Chemical Vapor Deposition (CCVD) technology. BST has a very high dielectric constant (>300) making it very appealing for RF MEMS capacitive switches. The tunable dielectric constant of BST provides a possibility of making linearly tunable MEMS capacitor switches. Here we present for the first time a capacitive tunable RF MEMS switch with a BST dielectric and its characterization and properties up to 40 GHz, and the details will be shown in Chapter V.; Chapter VI shows the basic research for reliability issues of RF MEMS switches like dielectric charging effect on capacitive MEMS switches. In chapter VII, integration of two reconfigurable RF circuits with RF MEMS switches are discussed, the first one is a reconfigurable dual frequency (14 GHz and 35 GHz) antenna with double polarization using RF MEMS switches on a multi-layer LCP substrate; and the second one is a tunable Ka band bandpass filter with tunable BST capacitors and RF MEMS switches on sapphire substrate.