Abstract
We examined the effects of aluminum (Al) capping layer thickness on the electrical performance and stability of high-mobility indium–gallium–tin oxide (IGTO) thin-film transistors (TFTs). The Al capping layers with thicknesses (tAls) of 3, 5, and 8 nm were deposited, respectively, on top of the IGTO thin film by electron beam evaporation, and the IGTO TFTs without and with Al capping layers were subjected to thermal annealing at 200 °C for 1 h in ambient air. Among the IGTO TFTs without and with Al capping layers, the TFT with a 3 nm thick Al capping layer exhibited excellent electrical performance (field-effect mobility: 26.4 cm2/V s, subthreshold swing: 0.20 V/dec, and threshold voltage: −1.7 V) and higher electrical stability under positive and negative bias illumination stresses than other TFTs. To elucidate the physical mechanism responsible for the observed phenomenon, we compared the O1s spectra of the IGTO thin films without and with Al capping layers using X-ray photoelectron spectroscopy analyses. From the characterization results, it was observed that the weakly bonded oxygen-related components decreased from 25.0 to 10.0%, whereas the oxygen-deficient portion was maintained at 24.4% after the formation of the 3 nm thick Al capping layer. In contrast, a significant increase in the oxygen-deficient portion was observed after the formation of the Al capping layers having tAl values greater than 3 nm. These results imply that the thicker Al capping layer has a stronger gathering power for the oxygen species, and that 3 nm is the optimum thickness of the Al capping layer, which can selectively remove the weakly bonded oxygen species acting as subgap tail states within the IGTO. The results of this study thus demonstrate that the formation of an Al capping layer with the optimal thickness is a practical and useful method to enhance the electrical performance and stability of high-mobility IGTO TFTs.
Highlights
Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) are of significant interest for applications in active matrix displays, sensors, memories, and other electronic systems because of their excellent electrical properties, good uniformities, and low fabrication costs [1,2,3,4]
We studied the effect of Al capping layer thickness on the electrical performance and stability of high-mobility indium–gallium–tin oxide (IGTO) TFTs
An Al capping layer with tAl values of 3, 5, and 8 nm were were deposited on top of the IGTO thin film and the fabricated IGTO TFTs without and with Al deposited on top of the IGTO thin film and the fabricated IGTO TFTs without and with Al capping capping layers were thermally annealed at 200 ◦ C for 1 h in air
Summary
Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) are of significant interest for applications in active matrix displays, sensors, memories, and other electronic systems because of their excellent electrical properties, good uniformities, and low fabrication costs [1,2,3,4]. Ji et al examined the effects of titanium (Ti) capping layer formation and subsequent thermal annealing on the electrical properties of indium–zinc oxide (IZO) TFTs [23]. They showed that the Ti capping layer could enhance the μFE and positive bias stress (PBS) stability of IZO TFTs. Kim et al compared the transfer characteristics of zinc oxynitride (ZnON) TFTs with and without the tantalum (Ta) capping layer and observed that the Ta capping layer could increase μFE of the ZnON TFTs [24]. We investigated the effects of Al capping layer thickness (tAl ) on the electrical characteristics, PBS stability, and negative bias illumination stress (NBIS) stability of high-mobility. A systematic study was performed to analyze the effects of the Al capping layer with each thickness on the electrical characteristics and stabilities of IGTO TFTs
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