A Wet Etching Post-process for CMOS-MEMS RF Switches

The fabrication of a micromachined radio frequency (RF) switch using the commercial 0.35 mum complementary metal oxide semiconductor (CMOS) process and a post-process has been implemented. The RF switch, which is capacitive shunt type, is composed of coplanar waveguide (CPW) transmission lines, supported springs and a suspended membrane. The post-process requires only a wet etching sacrificial layer, and to release the suspended membrane. The switching effect of the RF switch depends on the dielectric thickness under the suspended membrane, which the dielectric thickness can be controlled by the etching time. A test-key on the chip is used to monitor the dielectric etching, and to obtain an optimal dielectric thickness of the RF switch. Experimental result shows that the switch had an insertion loss of -1.5 dB at 40 GHz and an isolation of -16 dB at 40 GHz.