Surface-Charge Decay in Insulators with Nonconstant Mobility and with Deep Trapping

Abstract

The motion of space charge initially located at the free surface of an insulator is studied as a function of time. Analytic results are given for the following cases: (a) mobility proportional to a power of the field; (b) mobility proportional to a power of the free-carrier concentration; and (c) fast deep trapping which goes to completion. After one transit time, the surface voltage becomes a unique function of time, independent of its initial value. The available experimental data for polyethylene do not fit these simple models, and the discrepancies are discussed. It is also shown that the observation of thermally stimulated currents in thin-film electrets implies that they are electrically inhomogeneous.

A new model for surface potential decay of corona-charged polymers

“…The fielddependent mobility can also be easily implemented in the proposed model. A power law proposed by Wintle [16] has been given as…”

“…Batra et al [11][12][13] assumed field-dependent mobilities and negligible penetration depth of the surface charge but neglected the effect of partial instantaneous injection and trapping. Wintle, in his papers [14][15][16], developed theories that include fielddependent mobilities of various forms as well as trapping but none of them explained the cross-over effect. Wintle also made an assumption that the depth of penetration of the initial charge is field independent.…”

Decay of electric charge on corona charged polyethylene

“…However, the surface conduction may only become important when high humidity is encountered [12]. Consequently, a majority of theories and models [2][3][4][5] for the surface potential decay are based on bulk transport process. The observed potential from the bottom layer of the corona charged two-layer films provides a direct experimental evidence to support the bulk charge transport process as there is no alternative process that can form the electric potential on the bottom layer.…”

“…the initial sample charged with a high potential decays more rapidly as compared with the sample that is charged with a lower potential [1]. Over the years, various theories and models have been proposed to explain this crossover phenomenon [2][3][4][5]. One proposed mechanism is the existence of deep traps on the surface and shallow traps in the bulk.…”

Measurement of the surface potential decay of corona-charged polymer films using the pulsed electroacoustic method

“…The surface conduction may only become important when high humility is encountered. Consequently, the majority of theories and models [4][5][6][7] for surface potential decay have been developed in terms of bulk transport. In addition, a polarization process has also been proposed to explain the potential decay in the case of polar polymeric materials.…”