Investigation of degradation mechanisms and post-annealing effects in polymer field-effect transistors under x-ray irradiation

Abstract

This study examines the effects of x-ray irradiation-induced degradation on polymer DPPT-TT field-effect transistors (PFETs) with different gate dielectrics, including poly(methyl methacrylate) (PMMA) and polystyrene (PS). For the PFETs with PMMA dielectric, the threshold voltage (Vth) shifts negatively during radiation exposure and with a variation (ΔVth) of 6 V at the total dose of 1 Mrad(Si), and the subthreshold swing (SS) and off-current markedly elevate with the radiation dose. In contrast, the PFETs with PS dielectric experience a negligible variation of Vth and SS, and a minor increase in off-current—less than an order of magnitude—at a total dose of 2 Mrad(Si). The excellent radiation resistance is attributed to the conjugated benzene ring structure in the side chains of the PS dielectric, which exhibits higher radiation tolerance compared to PMMA, as confirmed by Raman analysis. It is also observed that the PS-based device has fewer radiation-induced traps at the dielectric/channel interface, as confirmed by low-frequency noise analysis. In addition, the irradiation-damaged PFETs were effectively repaired by low-temperature post-annealing (LTPA) at 80 °C, which helped restore polymer morphology and remove shallow traps. These findings offer a promising route for enhancing the radiation resistance of PFETs in harsh environments.