A field‐sensitive photoconductive probe for sampling through passivation layers

Abstract

A field‐sensitive photoconductive sampling technique has been demonstrated in measurements performed through an insulating layer without the need for conductive contact. Sampled signals are sensed by a virtual‐ground, floating‐gate amplifier without draining charge from the device under test or the photoconductive switch. The minimum detectable signal is 2.5 μV/Hz1/2 with a spatial resolution of 7 μm, while the sampling bandwidth is essentially that observed using photoconductive sampling with a conductive contact to the device under test. The photovoltaic and shot current noise are negligible in comparison with the lock‐in amplifier noise since the current flowing in this high‐impedance, floating‐gate probe is negligible. © 1996 American Institute of Physics.