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Thru-Wafer Interconnects for Double-Sided (TWIDS) fabrication of MEMS

This paper reports a new approach for fabrication of high-aspect ratio low resistance vertical interconnects, providing an electrical interface between the front-side and the backside of the Silicon-on-Insulator (SOI) wafer. The method of Thru-Wafer Interconnects for Double-Sided (TWIDS) fabrication of MEMS is based on seedless copper electroplating, and allows for voids free features and high aspect ratio (copper diameter to wafer thickness ratio is 10:1). We introduced the fabrication sequence, implemented and characterized prototypes of a MEMS toroidal ring gyroscope with thru-wafer interconnects, thus illustrating the process feasibility. Furthermore, the critical issue of mechanical stability in air-gap interconnect structures under 15,000 g shock was investigated using 3D Finite Element Analysis (FEA) models. Our simulations revealed that a partial filling the gaps with Parylene C allows for 1.55x improvement in mechanical stability without a significant increase in via parasitic capacitance values.