Sub-micron field-effect transistor using granular NbN thin films

The conductance modulation induced by an electrostatic field is observed in highly resistive NbN granular thin films at low temperatures. The measurement is performed using a three-terminal device with FET structure, whose channel is made of NbN thin films. The field effect is interpreted based on the single electron charging effect of small intergrain junctions. The submicron-size channel (0.5 mu m) is fabricated by using the electron-beam lithography technique. The conductance modulation is found to be enhanced by the reduction of the channel size. In order to assess the feasibility of the FET using FET phenomena, the gate voltage dependence of the I-V curve and of the conductance of the channel part is examined. The charging effect is discussed on the basis of a one-dimensional array model of the small tunnel junctions.<
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