Controlled barrier modification in Nb/NbOx/Ag metal insulator metal tunnel diodes

Abstract

The nonlinear electrical transport properties of metal-insulator-metal tunnel diodes based on a barrier of naturally grown niobium oxide have been measured at room temperature and analyzed. In most cases excellent agreement is found between the measured current-voltage characteristics and fits to the trapezoidal barrier model, over large ranges in conductance (up to several times the zero-bias value), and including the asymmetry induced by the differing electrode materials, niobium and silver. Moreover, we find that an in situ, Ar plasma etch may be used to modify the tunnel barrier in a controlled fashion. Specifically, as the etch time is increased from 0 to 120 s, the barrier thickness is continuously reduced from ∼2.8 to 1.1 nm, while the barrier height at the base (Nb) electrode remains roughly constant at $\text{300±40\hspace{0.17em}}\mathrm{mV}.$ Simultaneously, the barrier height at the Ag counterelectrode is lowered from an initial value of 800 mV to the asymptotic value implied by the difference in work functions of the electrode materials, namely, $\text{230±40\hspace{0.17em}}\mathrm{mV}.$