Active Probes for Millimeter-Wave On-Wafer Measurements

Significant advances in millimeter-wave devices and integrated circuits have been achieved over the past several years, yet the majority of measurements reported have been extrapolated from DC-65 GHz data, relying only on linear projections to predict the EHF performance of these devices and circuits. The only solution to this problem is to develop measuring instruments with greater bandwidths. Recently, we developed a 1.6 psec pulser, and a 300 GHz MMIC sampler and directional bridge. These components were assembled in a microwave package and S-parameter measurements were made to the 60 GHz limit of the V-connector used. In order to increase the frequency range of our measurement system to 300 GHz, the parasitics due to the connection between the MMIC samplers and the device under test must be eliminated by integrating the probe contact tip with the GaAs MMIC multipliers, samplers, bridges, and IF amplifiers. This requires a probe tip that is itself fabricated in GaAs. As a first goal, we have developed a through-line GaAs probe, with no integrated circuit components, which will allow repeatable measurement at microwave frequencies up to 50 GHz. Since GaAs cannot be flexed, it was necessary to develop a parallelogram flexure probe so that a controlled normal force could be applied to a micromachined GaAs tip. This tip had a CPW pitch of 40 microns to minimize radiation at millimeter frequencies and was anisotropically etched to allow the user to see the exact contact location of the tip to the device under test.