New integrated polysilicon photoconductor for ultrafast measurements on silicon

A fully integrated, silicon optical-switch technology is reported that demonstrates one picosecond sampling apertures when excited by a femtosecond laser. Fabrication of the polycrystalline silicon switch structure is accomplished with standard integrated circuit processing techniques to insure full compatibility with standard VLSI processes. Photoresist-masked, ion-beam irradiation is used to generate trapping sites in the photoconductive layer and tailor the switch on-time. Limited optimization of process parameters resulted in photoconductors demonstrating 3-dB measurement bandwidths over 100 GHz when used as sampling gates. A model for the device performance has been developed and is compared with experimental results. The optical switches were used in a high-speed sampling system to measure dispersive effects in striplines on a silicon wafer for the first time.