Space charge behavior of polyimide at cryogenic temperatures

Abstract

In this paper, the space charge behavior of polyimide at cryogenic temperatures is studied. The pulsed electro-acoustic (PEA) and thermally stimulated current (TSC) methods are exploited to evaluate the space charge distribution, quantification of space charge accumulation and trap characteristics of polyimide. The results show that the change of space charge accumulation at 273 to 123 K is divided into three temperature regimes. At 273-223 K, the space charge accumulation decreases significantly with decreasing temperature, which is mainly due to the suppression of charge generation and migration. At 223-173 K, the negative space charge gradually increases with decreasing temperature and dominates the space charge distribution. Analysis shows that this is due to the significant decrease of trap level in the sample, which improves the carrier mobility and promotes the electron injection and migration. According to quantum chemical calculation and dielectric spectroscopy measurement, the rotational displacement motion of water molecules related to γ relaxation in polyimide produces more shallow electron traps, which may be the main reason for the decrease of trap level. When the temperature is below 173 K, the space charge accumulation decreases with decreasing temperature. This study provides guidance for low temperature insulation design.