Impact of proton-beam irradiation on the electrical reliability and performance of LTPS and a-IGZO thin-film transistors

Abstract

We investigate the impact of 5 MeV proton beam irradiation on the electrical reliability of low-temperature polycrystalline silicon (LTPS) and amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs). After irradiation, the threshold voltage (V_th) of a-IGZO TFTs shifted from 0.31 to - 7.87 V, while field-effect mobility (μ_FE) increased from 8.4 to 11.7 cm²/V∙s due to oxygen vacancy (V_o) formation, enhancing channel conductivity. In contrast, LTPS TFTs exhibited severe degradation, with V_th shifting from - 3.18 to - 33.51 V and μ_FE dropping from 78.9 to 0.01 cm²/V s. Bias temperature instability tests showed significant deterioration in irradiated LTPS TFTs, whereas a-IGZO TFTs remained stable. This is attributed to the metastable a-IGZO lattice, which suppresses radiation-induced defect formation, whereas the LTPS lattice undergoes amorphization. X-ray Photoelectron Spectroscopy (XPS), and density of states (DOS) confirmed these mechanisms. Finally, we confirmed electrical performance recovery of irradiated TFTs through rapid thermal annealing (RTA) process. These findings provide insights into TFT degradation under radiation exposure and highlight the potential of a-IGZO and LTPS TFTs for radiation-hardened applications in radiography, military, aviation, and aerospace industries.

Keywords: Amorphous In–Ga–Zn–O (a-IGZO); Density of state (DOS); Electrical reliability; Low-temperature polycrystalline silicon (LTPS); Radiation; Thin-film transistors (TFTs).

Fig. 1

(a) Schematic diagram of TFT device structure (channel layers: LTPS, a-IGZO) and image of (b) a flexible test device used in this study. Images of (c) MC-50 cyclotron and (d) vacuum chamber with test device at the Korea Institute of Radiological and Medical Science (Republic of Korea) for proton beam irradiation test. Transfer curves of (e) a-IGZO and (f) LTPS TFTs under different proton beam irradiation dose levels (pristine, 10¹², and 10¹³ p/cm²).

Fig. 2

Electrical characteristic parameters comparison of LTPS and a-IGZO TFTs at different proton beam irradiation doses.

Fig. 3

Output curves of (a), (b), (c) a-IGZO TFT and (d), (e), (f) LTPS TFT under different proton beam irradiation doses.

Fig. 4

The electrical characteristics (ΔV_th, ΔV_on, and |ΔSS|) of pristine and irradiated a-IGZO and LTPS TFTs (10¹³ p/cm²) stressed under PBTS and NBTS, respectively. The bias instability tests were performed at 70 °C with V_GS =  ± 3 MV/cm for 3600 s.

Fig. 5

XPS results of (a) before (b) after O 1s spectra of a-IGZO thin films and (c) before (d) after Si 2p spectra of Poly-Si thin films at proton beam irradiation (dose : 10¹³ p/cm²).

Fig. 6

Schematic diagrams of proton beam irradiation induced damage mechanisms for (a) flexible bond network of a-IGZO channel (b) rigid bond network of LTPS channel.

Fig. 7

DOS distributions for defect quantification extracted of (a) a-IGZO and (b) LTPS MOS devices.

Fig. 8

Transfer curves before and after proton beam irradiation at a dose of 10¹⁴ p/cm², along with the recovery of TFT performance through RT annealing and RTA processes for (a) a-IGZO and (b) LTPS TFTs.