A wafer-scale encapsulated RF MEMS switch with a stress-reduced corrugated diaphragm

A wafer-scale encapsulated DC-contact RF MEMS switch with a stress-reduced corrugated diaphragm is proposed and developed. The design, fabrication and characterization aspects of the MEMS switch are presented in this paper. The introduction of corrugation is proven to be an effective and easier way to reduce the residual stress in the diaphragm as compared to the approach by the stress control in the thin film deposition process. The measured pull-in voltage of the MEMS switch is significantly reduced from 105 V for a flat diaphragm to 51 V and 42 V for two-corrugation and four-corrugation diaphragms, respectively, which agree well with the calculation results by derived analytical equations. The estimated equivalent stresses in the two corresponding corrugated diaphragms are 11.9 MPa and 5.9 MPa, respectively, which are much lower than 56 MPa in the flat diaphragm. The fabricated MEMS switch can operate well, achieving more than 1 billion switching cycles for signal currents below 1 mA. The RF performance of fabricated switches was also characterized. The isolation is below −30 dB up to 5 GHz, and about −22 dB at 15 GHz. The insertion loss is about −0.8 dB up to 4 GHz, and −2.9 dB at 15 GHz.