UV-Mediated Photochemical Treatment for Low-Temperature Oxide-Based Thin-Film Transistors

Abstract

Solution processing of amorphous metal oxides has lately been used as an option to implement in flexible electronics, allowing a reduction of the associated costs and high performance. However, the research has focused more on the semiconductor layer rather than on the insulator layer, which is related to the stability and performance of the devices. This work aims to evaluate amorphous aluminum oxide thin films produced by combustion synthesis and the influence of far-ultraviolet (FUV) irradiation on the properties of the insulator on thin-film transistors (TFTs) using different semiconductors, in order to have compatibility with flexible substrates. An optimized dielectric layer was obtained for an annealing of 30 min assisted by FUV exposure. These thin films were applied in gallium-indium-zinc oxide TFTs as dielectrics showing the best results for TFTs annealed at 180 °C with FUV irradiation: good reproducibility with a subthreshold slope of 0.11 ± 0.01 V dec and a turn-on voltage of -0.12 ± 0.05 V, low operating voltage, and good stability over time. Finally, the dielectric layer was applied in solution-processed indium oxide (InO) TFTs at low temperature, 180 °C, with a short processing time being compatible with flexible electronic applications.

Printed, Highly Stable Metal Oxide Thin‐Film Transistors with Ultra‐Thin High‐κ Oxide Dielectric

“…Also, only a slight saturation mobility degradation of 7.3% occurs during stress for the highest PBS (1 MV cm −1 ), as depicted in Figure S10e, Supporting Information. Hereafter, the device shows a fast recovery which is coherent with charge trapping 35. For NBS, the ∆SS (0.01 V dec −1 ) and ∆ V T (0.04 V) under −0.5 MV cm −1 did not show significant changes, but for −1 MV cm −1 a maximum shift of −0.11 V was observed in the V T .…”

“…Since the second peak in the combustion xerogel occurs at a higher temperature, (233 °C) than the annealing temperature used to form the dielectric thin films, UV treatment was applied. When low‐wavelength far‐UV (FUV) irradiation (160 nm) is combined with thermal annealing the required process temperature is decreased as the high‐energy UV photons enhance the degradation of organic residuals and improve the M‐O‐M densification through radical mediated reactions 28,35,36…”

“…When the films are exposed to high‐energy photons, the cleavage of alkoxy groups into active metals and oxygen atoms occurs to simplify the metal–oxygen–metal (M‐O‐M) network formation through radical‐mediated chemical reactions. Consequently, the thin films' densification is improved 28,35,36. Even higher efficiency can be achieved by combining solution combustion synthesis (SCS) with UV curing at low temperature as previously reported by our group.…”

“…Aluminum‐oxide dielectric precursor ink (Al(NO 3 ) 3 ·9H 2 O, Merck, 99.997%) was dissolved in 2‐methoxyethanol (2‐ME, C 3 H 8 O 2 , ACROS Organics, 99%). Afterwards urea (CO(NH 2 ) 2 , Sigma, 98%) was added to guarantee the redox stoichiometry of the reaction in a molar proportion of 2.5:1 to aluminum nitrate 35. The prepared solution was maintained under constant stirring for 12 h at room temperature.…”

“…Finally, a combined FUV and thermal annealing (180 and 200 °C) was performed in dry N 2 glovebox (MBraun MB 200, H 2 O ≤ 1 ppm, O 2 ≤ 0.1 ppm) for 30 min. A deuterium UV source (Hamamatsu L11798, 160 nm) with MgF 2 window was used as reported in previous work 28,35,36…”