Increasing Capacitance and Self-Resonant Frequency of the MEMS Switched Capacitor Using High-kappa TiO2 and SU-8 Bridged Beam Structure

Abstract

In order to increase two important factors of capacitance and self-resonant frequency (SRF) of the microelectromechanical systems (MEMS)-switched capacitor, we developed a room-temperature-grown high-kappa TiO2 dielectric layer in the metal-insulator-metal (MIM) capacitor and an SU-8 bridged beam structure in the MEMS switch. The high-kappa TiO2 dielectric layer, which has a relative dielectric constant of up to 32, was utilized to minimize the MIM capacitors' sizes while maintaining their high capacitance values. In addition, the SU-8 bridged beam structure of the MEMS switch, whose radio frequency (RF) signal interconnecting part is electrically isolated from the switching mechanism, was introduced to shorten the RF signal path. Because of the high-kappa dielectric and the bridged beam structure, we have achieved a very high capacitance of up to 14.3 pF with an SRF of 1.8 GHz (the MIM capacitor size was 50 mu m x 1200 mu m). The same-sized MIM capacitor with a conventional Si3N4 dielectric layer and a conventional cantilever beam-switched capacitor showed only 4.9 pF with an SRF of 2.8 GHz. In a similar capacitance value, the proposed switched capacitor showed 22% increase in SRF (7.1 GHz at 0.92 pF) compared with the conventional cantilever beam switched capacitor with a Si3N4 dielectric layer (5.8 GHz at 1.01 pF). The high SRF was attributed to the short RF signal path and the minimized capacitor size, thereby reducing parasitic inductance.