Analysis and Design of MEMS RF Probe

Recently, there are many researches on the design of RF probes. Usually the materials of RF probe are tungsten and copper beryllium. They employed fabrication process of soldering and drawing of metal wire, which are not compatible with MEMS or IC fabrication process. Precise and high skill assembly is needed to finish the final probe module therefore results in high cost. This paper presents a novel RF probe module design which can be fabricated by Micro Electro Mechanical (MEM) fabrication process to reduce the cost. We use microwave simulation software, such as IE3D, Microwave Office, and Fidelity for design and analysis, and to know what kind of probe can reach the optimal impedance match and S-parameter. The design flow chart is coaxial cable to transform square coaxial cable, finally, in order to match up CPW standard pitches, therefore, design rectangular coaxial transition and success suitable ratio. Probe can match 50 Omega. The RF probe fabrication includes multi-layers thick photoresist spin coating and electroplating to finish the CPW and rectangular coaxial transition. The fabricated probes by MEMS fabrication process and electroplating are assembled by housing and SMA connectors. The material of the probes can use plating nickel or copper or nickel alloy or other kinds of alloy, and then use an insulator such as polyimide to enclose transmission line as interlayer dielectrics. Because of using the batch-type MEMS fabrication method, the proposed RF probes are low cost and can be expected to have good performance for measuring S-parameters of small RF ICs. The final step is to measure RF probes in order to complete the specification analysis. Probe micro assembly is connects to substrate and to facilitate increasing strength as upward view. Using fixed screw to fix probe, forward and behind shielding. Inner probe is rectangular coaxial transition. Upper cover can connect SMA connector and signal probe. This design uses rectangular coaxial transition to air coplanar-waveguide (CPW) transmission line. Then, use one geometric dimension of CPW transition to the other geometric dimension of CPW. This design can adjust different probe contact center-to-center pitch or get different probe standard pitches according to different needs.