Analysis of Cross-Talk Induced Measurement Errors in Model-Based RF Voltage Sensing

Abstract

Contactless sensing methods using capacitively cou-pled probes can enable local radio frequency (RF) voltage measurements without the need for large contact pads. This enables a measurement of internal voltage distributions and can significantly facilitate the development of integrated microwave devices. The achievable spatial resolution of these methods is typically limited by parasitic capacitive cross-talk between the probe and adjacent circuit parts. When RF voltage measurements are performed at multiple tip-surface distances, cross-talk can be reduced by employing a suitable model of the distance dependent tip-circuit capacitance. In this paper, the achievable spatial reso-lution and its limitation by cross-talk induced errors is analysed. Electrostatic simulations of the capacitance between a probe tip and different test structures on a passivated circuit are performed and the results are verified by RF voltage measurements on m}-sized test structures at a frequency of 13 GHz. The analysis shows, that the achievable spatial resolution is mainly limited by the passivation layer and that cross-talk induced measurement errors limit the minimum structure size to two times the layer thickness.