PLASMA POLYMERIZED THIN INSULATING FILMS

Volatile organic materials, in argon as a carrier gas, can be deposited as thin insulating films after polymerisation in an r.f. plasma discharge. When deposited on n-type silicon with evaporated gold electrodes, diodes of the Metal - Insulator - Semiconductor type can be produced. Using toluene as the monomer, these can be made with high reverse bias breakdown fields in the thin-film insulator (50-2500 V/mum). The conduction appears to be determined by charge injection processes. The thin film capacitance is voltage dependent and the reverse bias characteristic is photosensitive. Thin films of polymerised toluene between metal electrodes have shown well defined hysteresis loops (1) at frequencies below 10 Hz. The polarisation changes giving rise to the hysteresis loops following the application of a step voltage have been investigated. The results did not show a true ferroelectric coercivity for thin films of polymerised toluene. This technique does give thin insulating films in which very high electrical fields can be maintained and could be used to prepare thin polymeric films of more highly polar volatile materials.