Probes Promise Precise On-Wafer Measurements At THz Frequencies

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Terahertz-frequency integrated circuits (ICs) offer tremendous promise in terms of available bandwidth for short-range communications. Although such devices have been fabricated for use at frequencies through 3000 GHz (3 THz), the on-wafer commercial probes for characterizing these high-frequency ICs are limited to about 340 GHz. As a solution, Theodore J. Reck, Lihan Chen, Chunhu Zhang, Alex Arsenovic, Christopher Groppi, Arthur W. Lichtenberger, Robert M. Weikle II, and N. Scott Barker—who combined their talents from the University of Virginia and Arizona State University—have presented a scalable approach to the fabrication of high-frequency wafer probes that integrates a rectangular-waveguide probe and coplanar-waveguide (CPW) wafer probe onto a single silicon chip. The wafer probes feature a ground-signal-ground (GSG) configuration on a 15-micron-thick silicon substrate.
The experimental probe consists of an E-plane split waveguide block that houses the silicon chip. Tabs of silicon electroplated with gold are clamped between the two halves of the block, both for mechanical support and alignment of the housing. The probe chip couples from rectangular waveguide through a radial E-plane waveguide probe into a transmission-line channel. This channel emerges from the block where the signal mode is converted to the GSG wafer probe.
To verify that the design was capable of providing sufficient force to achieve a low-resistance contact with an IC under test, a probe with a single tip was fabricated and evaluated with different contact forces. A contact resistance of 0.07 Ω was achieved for a contact force of 1 mN. See “Micromachined Probes for Submillimeter-Wave On-Wafer Measurements—Part 1: Mechanical Design and Characterization” and “Part 2: RF Design and Characterization,” IEEE Transactions on Terahertz Science and Technology, November 2011, pp. 349 and 357.