Ultra-small Ni/NiOx/Ni tunnel junctions for terrahertz and ir applications

We have studied current-voltage, conductance, second derivative and temperature dependence of Ni/NiOx/Ni tunnel junctions having areas less than 0.1 um2. These overlap junctions have very small capacitance and are being studied for use as room temperature, high frequency detectors. The junctions are fabricated using a photolithography derived shadow mask and angular depositions of the Ni. The oxide barrier is formed using a plasma oxidation process. Electron micrographs of the overlap junctions are used to estimate junction area. For RT operation a nonlinear i-v is required and is generally observed. The temperature dependence of the iv characteristics from 100 C to 4 K appears to be that of tunneling although at RT other parallel conduction paths may exist. The nonlinearity of the iv curves at 4 K is much greater than at RT the ratio being about 5 to 1 at 0.1 V applied. Tunneling spectroscopy studies at 4 K reveal scattering mechanisms that can be related to Ni-O excitations. Detailed simulation of both the temperature dependence and the i-v curves shows that the barrier height is about 0.2 eV.