Direct tunneling diode structure with a multilayer charge injection barrier

We report the fabrication and testing of a silicon-based tunnel diode structure that incorporates a multilayer tunneling dielectric. The barrier consists of two thermally grown silicon oxide layers of direct tunneling thickness, similar to 3.5 nm each, separated by an ultrathin nanocrystalline silicon layer approximately 5 nm thick. The diode displays current-voltage characteristics that are similar to those of a Fowler-Nordheim device, with a strong current turn-on beyond threshold positive and negative biases, and a "window" region between these two levels where charge transport across the barrier is negligible. In contrast to Fowler-Nordheim devices, the barrier doss not appear to degrade significantly when biased in either of its conduction regimes. This property is attributed to the intrinsic degradation resistance of direct tunnel oxides. Additionally, capacitance-voltage characteristics show that the structure is of high quality. Because of its current-voltage and endurance capabilities, this structure shows promise for nonvolatile memory and other applications which require improved endurance and charge retention. (C) 1998 American Institute of Physics. [S0003-6951(98)01451-X].