A Possible Source of Error in On-Wafer Calibration

A common practice when calibrating an Automated Network Analyzer (ANA) for use with a wafer prober involves measurement of standards (e.g., short, open, load) placed directly under the coplanar waveguide probe tips. In this paper, we show that this placement changes the nature of the probe. Thus,, the " error" two-port, which separates the device under test from the ANA, depends on the particular standard being measured. This inserts an unremovable error into the calibration. An electromagnetic analyses of several coplanar waveguide standards is provided to support this hypothesis. A means of testing when the error is significant, compared to other measurement errors, and a solution to the problem are presented.