Packaging of RF MEMS switches and performance improvement

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2019
Comart, İlker
This dissertation presents a novel zero-level packaging method for shunt, capacitive contact RF MEMS switches where BCB acts as the adhesive interlayer between the cap and device wafers. Initially, the packaging concept is realized for 50 Ω CPW transmission lines. A microwave characterization procedure (circuit modeling) is performed by curve fitting five packaged CPW transmission line performances to the proposed circuit model. The circuit model consists of cascaded transmission line segments, in which lumped capacitances are utilized for modeling the discontinuities in the planar feedthrough regions. The microwave characterization procedure demonstrated 0.1 dB/transition with the implemented packaging approach. Afterward, shunt, capacitive contact RF MEMS switches are packaged by exactly the same package structure. Endurance analysis (shear strength tests), mechanical analysis (optical profiler measurements), actuation analysis (C-V measurements), RF performance analysis (S-parameter measurements), transient analysis (switching-time measurements), and lifetime analysis (lifetime measurements) assessed the overall performance of the BCB packaged RF MEMS switches. The packaging method demonvstrated 18.3 MPa average shear strength. One of the five tested switches reached 26.9 MPa, which exceeded the counterpart packaging methods in this regard. Optical profiler measurements of the MEMS bridge before and after the packaging process presented 71 nm average center deflection. Actuation analysis presented consistent results with the optical profiler measurements where the actuation voltages increased 4.2 V in the average during the packaging process. The S-parameter measurements indicated negligible effect on the RF performance of the switch. The return loss and insertion loss at 35 GHz (operating frequency) in the upstate are 28 dB and 0.4 dB, respectively. Moreover, the isolation characteristics indicate 35 dB at 35 GHz for most of the packaged switches. The transient analysis showed 10 µs rise time and 8.5 µs fall time for the packaged RF MEMS switches. Lifetime measurement demonstrates 10.2 billion cycles without failure in the RF performance. A sensitivity analysis based on EM simulations presented the robustness and insensitivity of the package in terms of possible process variations. The dissertation also presents a novel piecewise wideband characterization method based on CPW transmission line measurements to demonstrate the dispersive nature of the utilized glass and high-resistivity silicon wafers.
Citation Formats
İ. Comart, “Packaging of RF MEMS switches and performance improvement,” Thesis (Ph.D.) -- Graduate School of Natural and Applied Sciences. Electrical and Electronics Engineering., Middle East Technical University, 2019.