A Non-contact Electro-optic Prober for High Speed Integrated Circuits

Abstract

Electro-optic sampling has been used extensively for the characterization of picosecond electronic devices such as photodetectors, transistors, and diodes [1,2]. For the large part, these studies have been with discrete devices coupled to specialized electro-optic modulators in a hybrid electrode geometry. However, there is great interest in being able to probe internal points of integrated circuits in order to characterize device and circuit operation in situ. Recently, a specialized embodiment of electro-optic sampling [3] was developed to perform sampling directly in the substrate of, specifically, GaAs integrated circuits. With this technique, almost any internal point of the circuit could be accessed. However, GaAs is the only commonly used semiconducting material that is also electro-optic. The substrate probing technique, or internal electro-optic sampling, also requires the surfaces of the integrated circuit to be of optical quality and the sampling laser beam to have a photon energy below the band gap energy of the substrate material.