Optimization of a microelectromechanical systems (MEMS) approach for miniaturized microcantilever-based RF microwave probes

Abstract

In this study, microelectromechanical systems (MEMS) technology-based miniaturized microwave ground-signal-ground (GSG) probes are designed, fabricated, tested and optimized in the context of on-chip microwave characterization of the miniaturization of microelectronics. The probe structure is designed using coplanar technology on a micrometre scale. In contrast to conventional macroscopic on-wafer probing structures, a 2μm width signal line and 2.5μm width spacing between signal and ground conductors are demonstrated. The microcantilever-based probe structure is optimized to ensure good radio frequency (RF) performances. The fabrication steps of the probe structures have been developed by means of MEMS technologies using silicon-on-insulator (SOI) wafers. Hundreds of probe structures have been fabricated on a single 3inch diameter SOI wafer–the fabrication yield is close to 100%. Measurement performances demonstrated using a back-to-back probe structure exhibit return loss better than 15dB and insertion loss lower than 2.5dB (∼1.8dBmm−1) up to 50GHz. Measurements indicate that a microcantilever composed of a 20μm thick, high resistivity silicon device layer of SOI performs well up to 50GHz—agreeing well with previous microelectromechanical modelling. DC measurements exhibit a very low contact resistance (0.02Ω). Finally, on-wafer RF measurements using the miniaturized probes have been achieved using direct probing onto a CPW load (68Ω) up to 4GHz by coupling a vector network analyser (VNA) to a scanning electron microscope (SEM).