RF-power: driver for electrostatic RF-MEMS devices

Abstract

The RF-power handling capability is an important characteristic for RF-MEMS switching devices. Apart from excessive heat dissipation, the power handling capability is mainly limited by the so-called self-biasing and/or RF-latching. These two phenomena result from the fact that the available RF-power from the source induces a non-zero electrostatic pulling force on the suspended structure. So far, self-biasing of RF-MEMS switches has always been studied assuming a perfect match of the device to the network in the ON-state (i.e. no reflection) and thus a fixed dc-equivalent rms voltage on the capacitor. If the RF-power exceeds a critical value, pull-in or self-biasing occurs. In practice, however, the assumption of the perfect match is not correct as the switch capacitance increases with increasing RF-power. This will cause a change in the reflected signal and thus a decrease in the dc-equivalent voltage source. This paper gives a new insight into the RF-power handling of RF-MEMS shunt switches and, per extension, of RF-MEMS shunt tunable capacitors. We analytically show how the negative feedback on the electrostatic force introduced by the capacitive mismatch changes the pull-in characteristics of the structure and can even stabilize it, totally avoiding the pull-in phenomenon.