Performance of the focused-ion-striped transistor (FIST)—A new MESFET structure produced by focused-ion-beam implantation

We report the fabrication and performance of the focused-ion-striped transistor (FIST), which is a GaAs MESFET structure having a channel with stripes of high conductance, going from the source to the drain, separated by regions of semi-insulating material. Calculations show that this structure produces a depletion layer that wraps around the conducting channel stripes and this should result in improved transconductance and output resistance. Experimental results are reported for devices having 1-µm gates and the FIST channels produced by focused-ion-beam implants of silicon with a width of 0.2 µm and a spacing that is varied from 0.2 to 0.5 µm. These verify the basic performance characteristics of the FIST including an increase in stripe transconductance, a two-fold increase in output resistance, and larger values of fTfor small values of Idsnear pinchoff.