In RF MEMS, our research is highly focused on developing next generation of wireless communication technology such as subminiature RF MEMS components & modules, microsystem packaging and intelligent switches/capacitors. We do also emphasize on intelligent filters, smart antenna for miniaturization, low cost realization, weight lightening, integration and high performance development of portable information electronics and wireless communication electronics.
MEMS Air-Suspended High-Q Inductor
Integrated air-suspended inductors were newly developed on silicon substrate for on-chip radio frequency (RF) circuit and system applications. For the improvement of Q-factors and self-resonant frequencies of the integrated inductors, they were designed and fabricated by using air-suspended spiral conductor lines, photoresist sacrificial layer, and electroplating technique. For forming the air-suspended conductor lines without selectively etching the substrate and using any metal or insulating posts, the conductor lines were designed to have a shape of ‘U’ at the center of each conductor line.
Electrostatic RF MEMS Capacitive Switch
A multi-resonant electrostatic RF MEMS capacitive switch with wide bandwidth and high isolation was successfully designed and fabricated for ultra-wideband (UWB) applications. To achieve the high isolation and wide operation frequency bandwidth, three capacitive shunt-connected membranes and meander-shaped inductors with several inductances were utilized in serial connection. Moreover, for achieving a large ‘ON’/‘OFF’ capacitance ratio, a high dielectric aluminum nitride (AlN) film was applied.
Electrostatic RF MEMS Tunable Capacitor
MEMS tunable capacitor was successfully designed and fabricated using an aluminum nitride film and a gold suspended membrane with two air gap structure for commercial RF applications. Unlike conventional two-parallel plates tunable capacitors, the proposed tunable capacitor consists of one air suspended top electrodeand two fixed bottom electrodes. One fixed and the top movable electrodes form a variable capacitor, while the other one provides necessary electrostatic actuation.
MEMS Corner Cube Retroreflector
A bulk-micromachined corner cube retroflector (CCR) was designed and fabricated for free space optical communications with ultra-low voltage operation and negligible power consumption. The proposed CCR was comprised of a bulk-micromachined vertical mirror which has two mutually orthogonal reflective surfaces and a horizontal mirror with piezoelectric actuator. The vertical mirror was fabricated using a double silicon-on-insulator (SOI) wafer and the anisotropic wet etching of a (110) silicon wafer. The horizontal mirror was comprised of two supporting and one actuating lead zirconate titanate (PZT) cantilevers. The supporting cantilevers were utilized for the accurate angular alignment of the mirror by balancing and isolating the residual stresses occurring in the PZT cantilevers.