Characterization of Real Permittivity Change in Thin-film Virgin Polyether Ether Ketone with Relation to Temperature

Experimentation on native Polyether Ether Ketone (PEEK) investigated the effects of ambient to cryogenic temperatures on its complex permittivity. Permittivity data were collected at frequencies between 200 Hz and 15 MHz using an impedance analyzer with a custom-designed parallel-plate geometry test fixture in high vacuum using a closed-cycle He cryostat. Multiple tests were performed on vacuum-baked thin-film PEEK samples around 540 $\mu $m thick between 296 K and 90 K at 1 K increments. The material showed an overall 0.5{\%} drop in real permittivity at frequencies \textless 1 MHz at the temperature range tested. Further analysis showed tighter temperature ranges in which permittivity change was most apparent. Similar results were found for the dissipation. Absolute calibration used a PTFE standard, with corrections made for the thermal expansion of the sample and test fixture. These studies were prompted by applications for cryogenic spacecraft antenna, as PEEK is a versatile thermoplastic polymer with wide-spread application including for spacecraft, ultrahigh vacuum compatible insulators, and high frequency antenna due to its resistance to thermal degradation, low outgassing, and low thermal and electrical conductivity.