Voltage-controlled negative differential resistance in metal-sputtered alumina-Si structures

We report on the observation of voltage-controlled stable and repeatable negative differential resistance (NDR) in Al/Al2O3/n-type Si structures. The NDR is shown to be stable and repeatable both during multiple scans on the same device and between different devices. NDR peak-to-valley ratios up to 100 were measured, with a valley at 2 x 10(-13) A. The maximum peak-to-valley ratio was observed for a voltage step of 0.05 V with dV/dt = 0.1 Vs(-1) and a step delay time of 0.1 s. The effect is transient, meaning that it tends to disappear for dc conditions. The observed NDR is markedly different from other previously reported NDRs in insulators since it only depends on interface trapping and is not influenced by the leakage current through the device which is below the noise floor of our measurement system (2 x 10(-14) A). The origin of the observed NDR is attributed to charging and discharging of traps at the metal-insulator interface.