A high power-handling RF MEMS tunable capacitor using quadruple series capacitor structure

This paper presents an RF MEMS tunable capacitor that achieves an excellent power-handling property with relatively low actuation voltage. The tunable capacitor consists of two fixed MIM (Metal-Insulator-Metal) capacitors and two MEMS capacitor elements, all connected in series. This quadruple series capacitor (QSC) structure enables reduction of the actuation voltage without sacrificing the power-handling capability, since the MIM capacitor reduces the RF voltage amplitude applied to the MEMS capacitors. The measured result demonstrates +36dBm hot-switching at 85°C with 21V pull-in voltage.

I. Introduction

RF MEMS tunable capacitors are suitable for tunable components of multiband/multimode cellular handsets, thanks to their low loss and excellent linearity [1], [2]. In order to employ the MEMS tunable capacitor in a cellular system including GSM, a high power-handling up to 35dBm is needed [3]. A primary issue in realizing such power-handling is to achieve a hot-switching, which means to actuate the MEMS movable element even when the high RF power is applied. To date, several groups have reported structures and techniques that improved the power-handling capabilities [3]–[7]. Unfortunately, their actuation voltages were usually high, larger than 30V. As is well known, generation of the large actuation voltage requires long ramp-up time and large power consumption. The large charge pump size, the noise coming from the circuit, and the enhanced dielectric charging are also issues brought about by the high voltage. In view of this, we started to develop a high power-handling RF MEMS tunable capacitor with relatively low actuation voltage.