Thickness dependence of conduction currents in ultra thin evaporated polypropylene films

A ultra thin polypropylene film (thin PP film) was deposited on a glass substrate by the vacuum evaporation method. A thin PP film deposited on a glass substrate at room temperature was annealed for one hour in N₂. Thin PP films are about 60~1.50 A in thickness. Aluminum electrodes (2 mm square) were evaporated on both sides of a thin PP film [evap.Al/Thin PP/evap.Al (Al/thin PP/Al)]. The conduction current for a 150A-thick PP film was explained with Schottky conduction and a tunneling conduction for a 60 A-thick film. When the area of the upper electrode was reduced to 85% of the initial area by self-healing breakdowns, the electrical field strength was about 7.5 MV/cm for the 150 A-thick film, and 16 MV/cm for 60 A thick film. These show that the breakdown strength of a thin film has the thickness dependence. In other words, it suggests the avalanche breakdown