Electrical field effect in highly resistive NbN microbridge

We investigate conduction properties and electrical field effect of highly resistive NbN microbridges. The bridge region consists of NbN thin films which have granular structure with /spl sim/10 nm. The dimension of the microbridge is approximately /spl sim/200 nm in length and /spl sim/50 nm in width. The highly resistive (100 k/spl Omega/) microbridges exhibit nonlinear current-voltage (I-V) characteristics at low temperatures which are similar to those of an array of single electron tunneling (SET) junctions. The offset voltage ranges from 2 mV to 300 mV at 4.2 K depending on the bridge resistance and the bridge width. Periodic modulation of bridge conductance is observed when external gate electric field is applied to the bridges. These results coincide fairly well with the simulation based on the SET array model.<>