Impact of GSG Probe to Pads Contact Repeatability for On-Wafer RF Measurements

Improving the contact repeatability for on-wafer measurements is required to address accurate characterization of microwave and millimeter-wave extreme impedance devices foreseen in future RF semi-conductor industry. In this effort, residual error terms introduced by conventional on-wafer probe measurements are quantified in the frequency range 50 MHz – 67 GHz. In particular, two sets of measurements considering movements of the probes in the Z-direction only and in X-Y-Z directions are considered. Controlling the probe in the XY axis showed better results in terms of repeatability, more than 10 times à 10 GHz and more than 5 times à 60 GHz. The residual error terms are propagated to determine the measurement uncertainty on the complex impedance of capacitances theoretically tested. Capacitance value of 1 fF measured at 10 GHz was measured with an error around 80 %. Moving the probe on the Z-direction only demonstrated that, if the X and Y movements of the probe are theoretically controlled, the error could be reduced to $\sim 7$%. In addition, preliminary design and fabrication of a new compact on-wafer probe station built up with nanorobotics is proposed. Both chuck and RF probes are equipped with nano-positioning stages operating in close loop operation.