The Electrical Conductivity Characteristics of Polyimide During the Thermal Cycle

Abstract

2 K/min and even faster rates of thermal cycle environments in low earth orbit alter the electrical conductivity characteristics of polyimide, which may exacerbate charge accumulation and electrostatic discharge (ESD) and seriously threaten the safety of spacecraft. This work focuses on the conductivity characteristics during the thermal cycle by leakage current measurement and demonstrates that the multiple energy levels traps play an important role in conductivity by the thermally stimulated depolarization current (TSDC) measurements. The results show that the current has a nonmonotonic temperature dependence with polar peaks and decreases periodically during the 5 K/min thermal cycle. After 24 thermal cycles, there is a 77.3% reduction in conductivity at 343 K and a 54.0% reduction compared with the 343 K steady-state temperature. The conductivity increases when the thermal cycle rate increases to 10 K/min. The results attribute to the combined effect of nonunidirectional dipole steering, thermally stimulated detrapping effects dominated by the shallower energy levels $\beta _{{1}}$ and $\beta _{{2}}$ traps, and trap-filling effects dominated by the deeper energy levels $\beta _{{3}}$ and $\alpha $ traps. The findings in this study can provide experimental support to reveal the conductivity variation mechanisms in time-varying temperatures.