Micromachined probes for on-wafer measurement of millimeter- and submillimeter-wave devices and components

Terahertz components and devices are typically interfaced with measurement instrumentation and characterized using fixtures equipped with waveguide flanges. Because such fixtures are known to introduce significant uncertainty and error in measurement, it is preferable to characterize such devices in-situ, where the device under test can be measured on-wafer, prior to dicing and separately from the circuit housing to which it is ultimately affixed. This is common practice in the RF and millimeter-wave region using probe stations equipped with coplanar launchers. Commercial coplanar waveguide probes have generally been available to the WR-2.2 band (325-500 GHz) but few options currently exist for on-wafer measurements above these frequencies. This paper describes recent work at the University of Virginia and Dominion Microprobes, Inc. to extend on-wafer measurement capabilities to terahertz frequencies through the design and implementation of coplanar probes based on silicon micromachining. At present micromachined on-wafer probes operating to WR1.2 (600 to 900 GHz) have been demonstrated and exhibit typical insertion losses lower than 7 dB with return loss of 15 dB or greater over a full waveguide band.