Self-Healing Breakdown at Spherulite Boundaries of Polyethylene Thin Films

Abstract

A polyethylene (PE) thin film consisting of two-dimensional spherulites of thickness 0.7–1.4 µm are prepared with heat treatment of a solution-grown film. Most breakdown measurements are made on the Al(top)-PE-Al(base) systems with ramp voltages at rising speeds of 10 2 , 10 4 and 10 6 V s -1 at room temperature. Breakdown occurs mostly at the boundaries between the spherulites. At 10 6 V s -1 the electric strength when the top electrode is a cathode and is smaller than that in the base cathode case, while at 10 2 V s -1 they are nearly identical irrespective of the polarity. In the base cathode case, the rising speed of 10 6 V s -1 yields a larger electric strength than that of 10 2 V s -1 . These results are interpreted in terms of roughness of the top surface and space charge formation. The results on the Au-PE-Al and Al-PE-Au systems are also consistent with the above interpretation. Decay of the space charges are also discussed.