Design and fabrication of low-insertion loss and high-isolation CMOS-MEMS switch for microwave applications

This paper presents a design of RF MEMS contact switch with high isolation, low insertion loss, small chip area and low power consumption. The switch is fabricated by standard 1P6M 0.18μm CMOS process from TSMC which is compatible with CMOS process. A dc-bias voltage is applied between the cantilever beam and bottom electrode. The switch is actuated by electrostatic force that drove the tail of the cantilever beam contact with the transmission line. In order to avoid RF signal loss, DC and RF signal are separated by SiO₂. The simulation results show that SiO₂ can effectively avoid RF signal loss. The spring structure of cantilever can effectively reduce the driving voltage and improve residual stress (used by the warpage problem.) The cantilever structure of switch is based on aluminum and the scarified layer is used by the aluminum and silicon oxide. RIE etching was applied to remove the scarified layer of silicon oxide to form wet etching channels. So, the structure was easy to be released by wet-etching. At last, the supercritical CO₂ drying was used to release the structure (annoying stiction problem.) Finally, we successfully demonstrate the fabrication of RF MEMS contact switch by standard 1P6M 0.18μm CMOS process from TSMC. Also, the post-processing is implemented to manufacture the RF MEMS contact switch. The proposed RF MEMS contact switch can be used in microwave CMOS RF front-ends where multiband functionality and reconfigurability is required. The measurement results as below, the pull-in voltage of RF MEMS contact switch is 2.8V, isolation is -60dB, respectively. Since the CMOS silicon has a very low resistivity (8Ω · cm), it will increase the isolation of RF MEMS contact switch. So, the Metal_1 layer is designed as ground which could greatly improve isolation.