EXPERIMENTAL AND THEORETICAL-STUDY OF ULTRA-THIN OXIDES

We report on an experimental and theoretical study of transport throug h thin oxides. The experimental study was carried out on the tunnel sw itch diode (TSD) which consists of an MOS junction on top of a pn junc tion. The properties of the TSD depends critically on the properties o f the tunnel oxide layer. Our results indicate that these devices can exhibit two different modes of behaviour depending on the stress histo ry of the oxide. An unstressed device exhibits a thyristor-like I-V ch aracteristic with fairly low current density. As the oxide is stressed , however, the I-V characteristic discontinuously shifts into a higher -current thyristor-like mode in which current transport appears to be highly non-uniform and depends strongly on stress history. This sugges ts a possible structural change in the oxide layer which is not comple tely destructive in that the device continues to function. We present a possible theoretical model of such a structural change in which micr oscopic filaments are generated in the oxide. Calculations of J-V curv es for such structures with varying filament heights qualitatively mat ch stressed MOS I-V curves found in the literature and qualitatively e xplain the dual-mode behaviour of the TSD.