A Model for Filament Growth and Switching in Amorphous Oxide Films

The forming process, by which changes are brought about in the electronic conduction of thin films of various binary amorphous oxides and halides, is first described, and experimental evidence is put forward which contradicts an earlier theory of the forming process in gold-silicon monoxide-metal structures. A theory is developed, in terms of the growth and thermal rupture of many conducting filaments through the insulating layer, to explain the observed voltage controlled negative resistance, electron emission, electroluminescence and memory phenomena. The model is presented firstly in its simplest phenomenological form, after which some atomic mechanisms which may be involved are tentatively discussed. It is further shown that there is evidence to suggest that the forming process is important in a wide range of systems. These include metal-oxide-silicon capacitors and transistors, surface-barrier junctions on silicon, oxide-coated thermionic cathodes and anodic oxide layers. Electronic conduction in each of these cases is held to take place through localized filamentary paths. The relationship between this and other filamentary conduction models is briefly discussed, and a general classification of negative-resistance devices into regenerative and non-regenerative systems is made.