The possible ways of using some approximation in the theory of thermally stimulated currents in dielectrics

Abstract

The analysis of the thcrmallly stimulatcd short-circuit currents in a imonoelectrct with nonblocking electrodes shows that for practically relevant cases it is possible to use the drift approximation as well as the approximation of uniform space charge carriers distribution and the approximation of time distribution and the approximation of time of flight. In electroneutral dielectric (with space-charge polarization) the external short-circuilt currcnt equals to the average diffusion current in a dielectric. However, as it is shown here, the drift current in local regions of a dielectric can influence the kinetics of the thermally stimulated c!urrent and the process of charge carriers recomhination as well.Thermally stimulated shon-circuit currents (TSSCC) are one of the most efficient techniques for the investigation of electrically active defects (for example charge caniers capture centers) which are responsible for the electret state in a dielectric [1,21. The theory of thermally stimulated currents allows to obtain analytical dependencies of current versus temperature (at a given heating rate) using a number of relevant assumptions and approximations. The prcsent paper deals with the issue of possibility to use the common approximations in the TSSCC theory taking as an example a dielectric with space-charge polarization. s in aLet's consider a one-dimension model of homogeneous dielectric with one type of mobile charge carriers. The discharge current density is defined by the equation for total current which for the discussed model is a aE 8P j ( t ) = ~j )~( x , f ) + q~~( x , f )~(~,~) -q D -+ & &~--+ -where h -equilibrium conductivity of a dielectric: q, w, D and n -charge, mobil~iry, diffusion coefficient and concentration of free charge carriers correspondingly; E -high frequency dielectric permitivity defined by elastic polarization of a dielectric (that is, it doesn't take into account the input of relaxation polarization): E,, -electrical constant; E(x,t) -electric field strength inside of the diefectric; P(x,t) -module of polarization vector, generated by all types of relaxation except CH35808/96/0-7803-2695-4$04.00

Numerical analysis of space charge electric field and its effect on TSDC measurement in thin polymer films

“…TSDC is one of the most efficient techniques and is widely used to investigate space charge relaxation process in solids [6] . However, some approximations adopted in the TSDC theory [6][7][8] are susceptible because the present analysis incorporates a number of idealizations. Some of the approximations are that the charges are distributed uniformly and all charges injected are swept out of film and neutralized with the image charges and the internal electric field doesn't contribute to the trapping and detrapping process [6] .…”