MEMS probes for on-wafer RF microwave characterization of future microelectronics: design, fabrication and characterization

Abstract

This article presents microelectromechanical system (MEMS) ground-signal-ground (GSG) probes based on silicon-on-insulator (SOI) technology for on-wafer microwave characterization of radio-frequency (RF) microelectronics. The probe is designed using optimized coplanar waveguide structures with the aim of ensuring a low-contact resistance between the probe and the pads of the device under test (DUT). The probes are batch fabricated using SOI substrates and employ a simple silicon micromachining process. The probes have a pitch of 4.5 µm with miniaturized dimensions for a DUT pad area with a similar size. Electrical (dc) measurements show that the fabricated probe has a low-contact resistance (~0.02 Ω) on gold pads. Excellent extracted RF performances of the probe are observed up to 30 GHz, showing an insertion loss better than 2.2 dB and return loss better than 20 dB over the frequency range. An ageing study shows the probes are capable of forming this dc contact for over 6000 contact cycles. The preliminary result of the repeatability of on-wafer one-port measurements with the miniaturized probe shows a consistent RF performance maintained through several contacts. The data indicates that the proposed MEMS probe is suitable for the high-frequency characterization of integrated nanoscale devices having reduced pad dimensions.