Time-Resolved Radiation-Induced Conductivity of Polyimide and Its Description Using the Multiple Trapping Formalism.

Andrey Tyutnev,Vladimir Saenko,Evgenii Pozhidaev,Aleksei Zhadov

doi:10.3390/polym11122061

Andrey Tyutnev, Vladimir Saenko + Show 2 more

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https://doi.org/10.3390/polym11122061

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Abstract

Polymer dielectrics subjected to intense radiation fluxes exhibit a radiation-induced conductivity (RIC). Polyimide is a good dielectric with excellent mechanical and thermal properties featuring high radiation resistance currently widely used in the spacecraft industry. Its RIC has been extensively studied in several laboratories. The purpose of the present study is to make a direct measurement of the RIC for both pulsed and continuous irradiation using a current sensing technique, which is contrary to the indirect method employing a surface-potential decay technique that is now preferred by spacecraft charging engineers. Our experiments are done in a small-signal regime excluding any recombination and dose effects. In combination with existing computer codes, we managed to develop further the conventional multiple trapping formalism and the RIC theory based on it. The main idea is to supplement an exponential trap distribution responsible for a dominant dispersive carrier transport in polymers with a small concentration of inherent deep traps which may or may not have an energy distribution. In line with this reasoning, we propose a tentative set of RIC model parameters for polyimide that accounts for the observed experimental data. The findings and their implications are discussed in a broad context of previous studies.

Highlights

The radiation-induced conductivity (RIC) in insulators refers to an additional conductivity in excess of their dark one when subjected to intense radiation fluxes
RIC studies in polymers have a long and fortuitous history dating back to 1956 [1] and, from the very beginning, used an approach first suggested by Rose in 1953 [2], which later became known as a quasi-band multiple trapping (MT) formalism [3,4]
The most unambiguous information is provided by the RIC current curves relating to 20 μs square pulses (Figure 3a)

Summary

Introduction

The radiation-induced conductivity (RIC) in insulators (polymers included) refers to an additional conductivity in excess of their dark one when subjected to intense radiation fluxes. RIC studies in polymers have a long and fortuitous history dating back to 1956 [1] and, from the very beginning, used an approach first suggested by Rose in 1953 [2], which later became known as a quasi-band multiple trapping (MT) formalism [3,4]. Charge carriers (electrons and holes) generated by an ionizing radiation emerge in a conducting state. Their lifetime in this state is only too short, due to the presence of numerous traps distributed exponentially in the binding energy. Trapped carriers can be thermally de-trapped into the conduction zone to be re-captured immediately again. We developed a powerful computer code to numerically

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