| Direct electrooptic sampling is widely used for ultrafast measurements GaAs integrated circuits. The backside approach in particular provides excellent spatial resolution and access to all internal nodes. The reliability of a test technique depends on its ability to accurately return the desired measurement in any environment. To characterize the accuracy of direct electrooptic probing, measurements and calculations have been made of electrooptic crosstalk and absolute calibration errors as a function of conductor geometry and beam parameters. A general theory permits the incorporation of arbitrary optical and microwave fields. Extensive measurements reveal that electrooptic errors depend most strongly on the spacing of ground conductors on the front surface.;We have examined the invasiveness of direct electrooptic sampling by studying the induced perturbations to interconnects, diodes, and MESFETs. Probe light scattered from surface roughness waveguides within the GaAs, generating free carriers that backgate the PET. Because the light reaching a device is weak, deep-level absorption based on average power determines the magnitude of the perturbation. |
