10 May 2012 Analytical design of polymer-encapsulated radio frequency microelectromechanical devices
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Abstract
An analytical design of radio frequency microelectromechanical (RF MEMS) devices and fabrication and encapsulation results is discussed. The encapsulated MEMS device is an in-plane variable capacitor (varactor), continuously tuned up to 115% at 3.25 V, showing a Q factor of 49 at 1 GHz at zero bias and self-resonance frequency above 5 GHz. The 60-μm-thick device measures 0.6  mm×0.6  mm and is fabricated using high-aspect ratio single-crystal and polysilicon technology, having an air gap of 0.8 μm for tuning and 2 μm for actuation. The effect of gap size, substrate doping, and gold coating on Q is studied. The wafer-level encapsulation is done by the thermal decomposition of a sacrificial polymer through a polymer overcoat at 130°C-150°C, followed by gold evaporation to provide a degree of hermeticity. The overcoat polymer is patterned instead of screen printed, which defines the package boundary, providing a small amount of interconnection. The encapsulated device measures 0.7  mm×0.7  mm, which is only 35% larger than the MEMS device. The insertion loss of the 1 μm/20 μm gold/Avatrel package is measured to be 1.4 dB at 1 GHz and 1.51 dB at 5 GHz, and the calculated nitrogen permeability is less than 1 Barrer. The temperature stability of the rest and the maximum capacitance is better than 7%, in the range of −30-50°C.
© 2012 Society of Photo-Optical Instrumentation Engineers (SPIE)
Pejman Monajemi, "Analytical design of polymer-encapsulated radio frequency microelectromechanical devices," Journal of Micro/Nanolithography, MEMS, and MOEMS 11(2), 021207 (10 May 2012). https://doi.org/10.1117/1.JMM.11.2.021207 . Submission:
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