DIRECT-CURRENT AND RADIOFREQUENCY CHARACTERIZATION OF SUBMICRON STRIPED-CHANNEL FIELD-EFFECT TRANSISTOR STRUCTURES USING FOCUSED ION-BEAM AND ELECTRON-BEAM LITHOGRAPHY

Submicrometere-gate GaAs metal-semiconductor field effect transistors (MESFETs) have been fabricated using focused ion beam (FIB) and electron-beam lithography. The channels of these devices are composed of several high conductance implanted stripes of 1 mum width, connecting source to drain. These conductive stripes are formed by Si implantation using FIB and annealed for 30 s at 850-degrees-C. The region between the conductive stripes are semi-insulating GaAs having width of ''S.'' MESFETs with stripe width of 1 mum and stripe separation of 0.1, 1, and 2 mum were fabricated and characterized. The device with 0.1 mum separation represents the control sample with a uniformly doped channel due to overlap of conductive stripes upon the postimplant annealing. Devices with higher stripe separations showed higher effective transconductance (g(m)), lower output conductance (g(o)), higher breakdown (V(br)), and higher current gain cut-off frequency (f(T)). All transistor showed well behaved direct-current output performance with excellent pinch-off characteristics and low leakage currents as small as 50 muA for source-drain voltage of 4 V and gate bias of -9 V without any soft breakdown. Transconductance of 200 mS/mm, gate-drain breakdown voltage as high as 20 V, output conductance of 4 mS/mm, and f(T) of 9 GHz from a device with 0.35 mum gate length with stripe separation of 2 mum.