Electro-Optic Sampling of a Packaged GaAs Integrated Circuit

We describe the use of electro-optic sampling to characterize the performance of a packaged high-speed GaAs planar integrated circuit. Because the circuit is wire-bonded on a substrate, the only access for a probe beam is from the active (front) side. The conventional back-side probing geometry used by previous workers is impossible to implement. We therefore use a front-side probing geometry, which we demonstrate to be effective for electo-optic sampling of integrated circuits. We compare the voltage sensitivity and spatial resolution of front-side probing to back-side probing. We have characterized the crosstalk when the probe beam is positioned between adjacent lines. Front-side probing enables internal signals to be monitored with little or no modification to the circuit or its package.