Method for investigating threshold field of charge injection at electrode/dielectric interfaces by space charge observation

Abstract

We propose a dielectric sample model to investigate the threshold field for charge injection at electrode/dielectric interfaces by space charge observation. The model sample consists of a dielectric layer and two thin charge blocking layers, respectively, placed at the inside and one side of the dielectric layer. The method has been applied to investigate the threshold field for charge injection from Al, Au, or semiconductive electrode into polyethylene. Experimental results show that charge injection occurs so long as the interface electric field is nonzero, i.e., there is no indication of a threshold field for the charge injection.

Low field thermally assisted charge injection at electrode/polyethylene interfaces observed by space charge measurements

“…In addition, if the metal-induced gap states also truly exist in metal/dielectric interfaces, electrons would be transferred at a very low field by a thermal assistance from occupied metal-induced gap states to localized states of the dielectric and the Schottky emission would no longer be a required process for the electron transfer. This has been confirmed by other authors'results [7], also by our recent results on the basis of direct observation of space charge, where charge injection at the semicon, Au, or Al electrode/polyethylene (PE) interface occurred at the temperature of 40 °C so long as the interface electric field was nonzero [9].…”

“…In this work, to determine whether the charge injection is a thermal assistance process, we further investigate the charge injection at the electrode/PE interfaces at 20 °C and 60 °C, and compare the results with the previous results in the recent publication [9].…”

“…Same with those samples used for the previous study [9], samples used for this study consists of a PE film and a PE plate with thicknesses of about 0.17 and 0.80 mm, which were prepared by hot-pressing the additive-free PE resin pellets (LL1004) supplied by Exxon Mobil Chemical Company at 130 °C under 15 MPa for 12 min. Before the film and the plate were thermally bonded together at 110 °C under 0.3 MPa for 10 min to achieve an intimate contact, both surfaces of the plate were fluorinated in a stainless vessel at about 95 °C under 0.1 MPa for 60 min by the F 2 /N 2 mixture containing 12.5% F 2 in volume.…”

“…Space charge was measured for these samples subjected to a dc field of positive or negative 5 kV/mm same with the recent publication [9], but at the different temperatures of 20 °C and 60 °C from the previous poling temperature of 40 °C. The electric field is much smaller than commonly applied fields (several tens of kV/mm).…”

Determination of threshold electric field for charge injection in polymeric materials

“…4 Their sample consists of two dielectric layers and two thin charge blocking layers (fluorinated polyethylene), placed in alternative between the two electrodes. The blocking layers are able to block charge movement, leading to charge accumulation at the interface.…”