Total Ionizing Dose Effects in Back and Top Gated IGZO Thin-Film Transistors

Abstract

Indium–gallium–zinc–oxide (IGZO) thin-film transistors (TFTs) have emerged as promising candidates for advanced displays and radiation-hardened electronics due to their high electron mobility, large-area uniformity, and low-temperature processability, yet their reliability under ionizing radiation remains a concern. This dissertation examines the total-ionizing-dose (TID) response of IGZO TFTs with different architectures to clarify mechanisms of charge trapping, threshold-voltage shifts, and transconductance degradation. In back-gated devices with HfO₂ dielectrics, negative-bias irradiation produces the worst-case degradation, primarily from enhanced charge trapping in the SiO₂ overlayer, while the relatively small transconductance decrease indicates greater resilience compared with amorphous Si TFTs. Device scaling studies further reveal no significant geometry dependence, supporting technology downscaling. In contrast, top-gated IGZO TFTs with SiO₂ oxygen-penetration layers show larger threshold-voltage shifts and more severe interface-trap formation, with hydrogen-related defects—likely from SiN oxygen-blocking layers—playing a key role in their degradation. Partial recovery during annealing suggests dynamic defect neutralization and tunneling processes. Comparisons with alternative semiconductors including ZnO, ZITO, MoS₂, black phosphorus, InGaAs, and carbon nanotube FETs demonstrate that IGZO achieves a favorable balance of electrical stability, radiation tolerance, and scalability. These results provide new insight into bias-dependent TID degradation in oxide semiconductors and establish IGZO TFTs as strong candidates for future display and space applications requiring both high performance and long-term reliability.