Design and development of RF CMOS MEMS switches for configurable RF circuits.

摘要

Radio Frequency Micro-Electro-Mechanical System (RF MEMS) switches have been used extensively in configurable circuits, antennas, and other RF applications. The work reported in this dissertation illustrates a novel RF MEMS capacitive switch design that is Complementary Metal-Oxide Semiconductor (CMOS) process-compatible, allowing possible integration of the CMOS circuit with the RF MEMS switch. This series capacitive MEMS switch solves the substrate loss and down-state capacitance degradation problems commonly plaguing MEMS switches. The switch structure is cantilever with fingers for capacitive coupling. The vertical bending characteristic of bimorph cantilever beams under different temperatures is utilized to turn the switch on and off. A set of electrical, mechanical, and thermal models is established, and cross-domain electro-thermo-mechanical simulations are performed to optimize the design parameters of the switch. This switch is designed and fabricated using a commercial CMOS AMI 0.6 Dm process through Metal Oxide Semiconductor Implementation Service (MOSIS). Two maskless postprocessing Reactive Ion Etching (RIE) steps are used to release the cantilever structure. The measured results show the insertion loss and isolation are 1.67 dB and 33 dB respectively, at 5.4 GHz, and 0.36 dB, and 23 dB at 10 GHz. The actuation voltage is 25 V. This switch has a vast number of applications in the RF/microwave field, such as configurable voltage control oscillators, filters, and configurable matching networks.;To illustrate the applications of the switch, two broadband communication applications for the designed MEMS switch, broadband voltage controlled oscillator (VCO) and broadband filter, were demonstrated. The RF MEMS switch model developed in this dissertation is used in VCO simulation to reduce the noise introduced by the traditional PMOS switch. The low-loss, low-noise nature of the MEMS switch improved VCO phase noise performance. The MEMS technology also can be used to improve the inductor quality factor by using finite element simulation; it is found that the quality factor (Q factor) of a micromachined inductor is improved to 11.5 compared to the previous Q factor of 7. In addition, we demonstrate the use of MEMS switches to enable large corner-frequency adjustments in high-frequency, lowpass filter designs. The frequency corner of the filter was demonstrated to be configurable over a very wide range, from 944 MHz to 3.06 GHz.;Overall, this work demonstrates how high-performance configurable microwave circuit design can benefit from the introduction of the novel MEMS switch.