Self-Healing Breakdown at Spherulite Boundaries of Polyethylene Thin Films

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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 102, 104 and 106 V s-1 at room temperature. Breakdown occurs mostly at the boundaries between the spherulites. At 106 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 102 V s-1 they are nearly identical irrespective of the polarity. In the base cathode case, the rising speed of 106 V s-1 yields a larger electric strength than that of 102 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.