Impact of AlSnO Back-Channel Layer on the Performance of AlSnO/InSnZnO Heterojunction Thin-Film Transistors

• Published in: IEEE transactions on electron devices Vol. 71; no. 4; pp. 1 - 8
• Main Authors: Liu, Han-Yin, Lin, Min-Kuan, Liao, Yu-Jie, Chen, Han-Wei, Song, Cheng-Yi
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aluminum tin oxide; amorphous; Conduction bands; Crystallinity; Design parameters; Electron mobility; Energy gap; heterojunction; Heterojunctions; Indium tin oxide; indium–tin–zinc oxide; Lattice vacancies; Logic gates; Oxygen; Photoelectrons; Photonic band gap; Semiconductor devices; Substrates; Thin film transistors; thin-film transistors (TFTs); Threshold voltage; Transistors; X ray photoelectron spectroscopy
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2024.3362759

In this study, Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.1}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.9}}</tex-math> </inline-formula>O and Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.3}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.7}}</tex-math> </inline-formula>O are used as the back-channel materials of Al<inline-formula> <tex-math notation="LaTeX">_{\textit{x}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{1}-\textit{x}}</tex-math> </inline-formula>O/InSnZnO heterojunction thin-film transistors (HTFTs) to investigate the effect of Al/Sn mole ratio on the electrical performance of Al<inline-formula> <tex-math notation="LaTeX">_{\textit{x}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{1}-\textit{x}}</tex-math> </inline-formula>O/InSnZnO HTFTs. The Tauc plot, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are used to characterize the bandgap energy, crystallinity, and oxygen vacancy content of the films. The results show that Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.3}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.7}}</tex-math> </inline-formula>O has a wider bandgap energy and fewer oxygen vacancies than Al<inline-formula> <tex-math notation="LaTeX">_\text{0.1}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.9}}</tex-math> </inline-formula>O. In addition, Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.1}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.9}}</tex-math> </inline-formula>O is polycrystalline, while Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.3}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.7}}</tex-math> </inline-formula>O is amorphous. This difference in crystallinity results in Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.1}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.9}}</tex-math> </inline-formula>O having higher electron mobility than Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.3}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.7}}</tex-math> </inline-formula>O. Therefore, Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.1}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.9}}</tex-math> </inline-formula>O/InSnZnO HTFT exhibits better electrical performance, including a higher field-effect mobility of 71.33 <inline-formula> <tex-math notation="LaTeX">\pm</tex-math> </inline-formula> 6.13 cm<inline-formula> <tex-math notation="LaTeX">^{\text{2}}</tex-math> </inline-formula>V<inline-formula> <tex-math notation="LaTeX">^{-\text{1}}</tex-math> </inline-formula>s<inline-formula> <tex-math notation="LaTeX">^{-\text{1}}</tex-math> </inline-formula> and a steeper subthreshold swing (SS) of 151.23 <inline-formula> <tex-math notation="LaTeX">\pm</tex-math> </inline-formula> 14.06 mV/dec. In contrast, Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.3}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.7}}</tex-math> </inline-formula>O/InSnZnO HTFT exhibits worse field-effect mobility and SS than InSnZnO TFT, which is used as a reference device in this study. These results suggest that the mobility of Al<inline-formula> <tex-math notation="LaTeX">_{\textit{x}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{1}-\textit{x}}</tex-math> </inline-formula>O and the conduction band offset between Al<inline-formula> <tex-math notation="LaTeX">_{\textit{x}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{1}-\textit{x}}</tex-math> </inline-formula>O and InSnZnO are important parameters to design high-performance HTFTs. Moreover, both Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.1}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.9}}</tex-math> </inline-formula>O/InSnZnO and Al<inline-formula> <tex-math notation="LaTeX">_{\text{0.3}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{0.7}}</tex-math> </inline-formula>O/InSnZnO HTFTs exhibit relatively insignificant threshold voltage shift compared to InSnZnO TFT during negative bias illumination stress (NBIS). This indicates that the present Al<inline-formula> <tex-math notation="LaTeX">_{\textit{x}}</tex-math> </inline-formula>Sn<inline-formula> <tex-math notation="LaTeX">_{\text{1}-\textit{x}}</tex-math> </inline-formula>O back-channel design is helpful to enhance the stability of the HTFTs.