Integrated RF-MEMS switch based on a combination of thermal and electrostatic actuation

Abstract

We have demonstrated the feasibility of a fully integrated RF microswitch. It is based on a combination of thermal actuation and electrostatic latching hold. This method enables to combine the advantages of both actuation modes : the low voltage power supply and high reliability of the thermal actuation, and the low power consumption of the electrostatic latching. An analytical model was developed in order to predict the shape of the beam versus the temperature. An algorithm was also developed in order to evaluate the damping behavior of the switch taking the beam shape deflection into account. A design composed of a 400/spl times/50 /spl mu/m silicon nitride clamped beam was selected. The beam includes titanium nitride heating resistors, and aluminum blocks for bimorph actuation. The RF lines and the contacts are made of a 1 /spl mu/m thick gold layer. The 3 /spl mu/m air gap is fabricated using a polymer sacrificial layer. The driver of the switch, for the thermal actuation and the electrostatic latching, was manufactured in a 0.25 /spl mu/m BiCMOS technology. For each activation, the switch requires a 20 mA current under 2 V during /spl sim/200 /spl mu/s. For the electrostatic hold, the MEMS was designed for less than 10 volts. Due to residual stress in the beam material, a 5 V shift of the hold voltage has been experimentally observed on first prototypes. Reliability of thermal actuation has been tested with more than 10/sup 9/ cycles without any failure or contact degradation. Very interesting RF performances were measured, even with standard wafer (15/spl Omega/.cm) : -57 dB isolation and 0.18 dB insertion loss at 2 GHz.