Thickness dependent studies of dielectric breakdown in Langmuir thin molecular films

Abstract The usefulness of Langmuir thin molecular films for making devices has made it necessary to study their dielectric breakdown behaviour. Study of thickness dependence of the breakdown field in these films is important from the point of view of device applications as well as the understanding of breakdown phenomenon. In the present paper, thickness dependence of two breakdown events corresponding to ‘onset breakdown’ and ‘maximum breakdown’ voltages have been reported for the ‘build-up’ Langmuir films of barium palmitate, margarate and behenate in the thickness ranges (23–300 A) and (370–2400 A), respectively. These two events are of particular interest because the former determines the permissible operating voltage and the latter leads to the ‘practically’ important ultimate dielectric strength of the film. The Langmuir films have been chosen because of their accurately known and controllable uniform thickness, high dielectric strength and high structural perfection. The onset breakdown strength of all the substances is found to vary as d -1 ( d being film thickness) in the ultra-thin range which have been explained qualitatively in terms of boundary effects. The maximum breakdown strength is also found to be almost inversely proportional to the film thickness but the results remain inexplicable because the actual mechanism of destructive breakdown is not yet fully understood. The typical J-V characteristics in the ‘non-destructive’ phase have also been given.

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