New integrated polysilicon photoconductors for ultrafast measurements on silicon

A fully-integrated silicon-optical-switch technology is reported that demonstrates one picosecond sampling aperture 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. Application of the optical switch in a high speed sampling system for the measurement of striplines on a silicon wafer demonstrated dispersive effects that have been observed for the first time.