We report on a novel probe technology applied to the measurement of high-speed guided electrical signals. The probe, based on the optoelectronic technique of photoconductive sampling, consists of a high-impedance gate fabricated using an interdigitated electrode structure on semi-insulating low-temperature-MBE-grown GaAs or on Silicon-on-Sapphire. Its resistance is 100 MΩ and its capacitance is less than 0.1 f, making this probe very attractive for the non-invasive, external circuit testing of ultrahigh-speed devices and circuits with a 120-GHz measurement bandwidth. A 30 ps switching time was measured for an E/D-Mode InAlAs/InGaAs HIGFET inverter using the probe.
