Dielectric Materials for Electrical Engineering

Chapter 3

Conduction Mechanisms and Numerical Modeling of Transport in Organic Insulators: Trends and Perspectives 1

3.1. Introduction

Most of the physical concepts currently used to describe charge transport and breakdown in solid dielectrics have been known for over 20 years. With regard to polymers which are disordered materials, these concepts essentially stem from amorphous semiconductor physics [DIS 92] with the fundamental notions of hopping conduction, space-charge controlled current, interface states, etc. The dielectric nature of the media under consideration explains the references to the concept of the polaron [see Chapters 1 and 2; BLA 01] which describe the coupling between an electrical charge and its environment, or that of molecular charge states in polymers [DUK 78]. Some excellent review articles, among which some very recent, describe the basis of our current knowledge in this domain [LEW 02], [LEW 90], [WIN 90], [BLA 98], [WIN 99], [LEW 98], [MIZ 04], [BOG 05].

Despite this background in physical mechanisms, work on charge transport modeling has been rare over the course of the past 20 years. Most of the time, they have concerned analytical models in simple case studies or under very restrictive conditions when compared with real conditions of materials in electrical systems. The difficulty for the development of such models has been the lack of basic data, such as the nature of carriers and traps, charge mobility and their local density, etc.

Furthermore, ...