Electrical phenomena in amorphous oxide films

Thin layers of insulators, from 100 A to 20 000 A thick, have a number of interesting electrical properties. These properties include forming, which is a profound and essentially permanent change produced by an electrical field, and, after forming, differential negative resistance together with switching and memory phenomena. Electroluminescence and electron emission also occur. These features are shown by most amorphous or microcrystalline insulators of the appropriate thickness, and are particularly clearly shown by the oxides, such as Al2O3, Ta2O5 and SiO. In our review we survey the observed properties of metal-insulator-metal devices involving such insulating layers, and discuss the mechanisms which have been proposed for their operation. Further, since the unusual properties may be technologically important, we outline some of the possible uses of these devices and the relevance of the phenomena to the mechanism of corrosion of certain metals.