Dynamic electrostatic force-gradient microscopy employing mechanoelectric cross modulation

Abstract

This article describes a dynamic mode electrostatic force-gradient microscopy technique capable of high-frequency voltage measurement. The technique employs a wide-bandwidth implementation of a mechanoelectric cross-modulation scheme, where a microfabricated probe is driven by an amplitude-modulated sampling pulse and the sample is mechanically vibrated at a frequency different to that of electrical modulation. The resulting probe oscillation at the cross-modulation frequency provides local high-frequency voltage information. Unlike the force detection method, which is susceptible to poor resolution due to large coupling to the probe tip sidewall and cantilever, the force-gradient method provides an enhancement of spatial resolution. A significant reduction of interference from adjacent signal traces is demonstrated when performing integrated circuit testing. Quantitative high-frequency voltage measurement with high accuracy is achieved by using a null-force-gradient approach, but at the expense of reduced sensitivity.