The effects of process variations on microstrip wafer calibration

The coplanar-to-microstrip transition part of on-wafer microstrip line-reflect-line (LRL) calibration structures has been modeled and measured to determine calibration repeatability due to variations in this structure. On-wafer small-signal device characterization is dependent on the quality and repeatability of the calibration, which depends on the calibration structures. When these are fabricated on the same wafer as the devices to be characterized they are also affected by process variations, the most important of which, when using LRL calibration structures in microstrip, is the variation in the thickness of the wafers. The LRL calibration solution is modified to include the process variation in the microstrip calibration structures in terms of propagation constant and effective line length. Both probe contact and probe position repeatability are identified in the experimental results as they are inevitably measured with process variations