Contact properties of a low-resistance aluminum-based electrode with metal capping layers in vertical oxide thin-film transistors

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 11; no. 41; pp. 14177 - 14186
• Main Authors: Jeon, Sori, Lee, Kwang-Heum, Lee, Seung-Hee, Cho, Seong-In, Hwang, Chi-Sun, Ko, Jong Beom, Park, Sang-Hee Ko
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 26.10.2023
• Subjects: Aluminum; Augmented reality; Capping; Contact resistance; Electric contacts; Electrical properties; Electrode materials; Electrodes; Electrons; Molybdenum; Oxidation; Photoelectrons; Semiconductor devices; Spectrum analysis; Thin film transistors; Titanium; Transistors; Virtual reality; X ray photoelectron spectroscopy
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d3tc02880a

Thin-film transistors (TFTs) with a small pitch size are necessary to realize high-resolution displays for virtual reality and augmented reality applications. Particularly, electrodes require low-resistance metals to reduce the resistance-capacitance delay caused by the increased pixel density. However, low-resistance Al can easily oxidize in bottom-contact structures of vertical TFTs owing to the oxidative deposition environment. This study quantitatively analyzed the contact properties of an Al-based metal with Mo and Ti capping layers. The Mo/Al/Mo and Ti/Al/Ti were adopted as the source/drain (S/D) electrodes, and their contact properties were compared. The top-gate bottom-contact device with Mo/Al/Mo S/D exhibited better contact properties, with a 0.02 V turn-on voltage ( V on ), 3.5 × 10 7 ON/OFF ratio, and 5.7 kΩ contact resistance ( R SD ). By contrast, the device with Ti/Al/Ti S/D exhibited degraded characteristics, with a −0.3 V V on , 0.9 × 10 7 ON/OFF ratio, and 17 kΩ R SD owing to metal oxidation. The contact properties were further examined through ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Vertical TFTs were fabricated using Mo/Al/Mo and Ti/Al/Ti electrodes, and their electrical properties were investigated. The vertical TFT with Mo/Al/Mo electrodes exhibited reasonable performance, with a field-effect mobility of 3.3 cm 2 V −1 s −1 and R SD of 15 kΩ. Conversely, the device with Ti/Al/Ti electrodes yielded degraded transfer characteristics, with a mobility of 0.05 cm 2 V −1 s 1 and R SD of 984 kΩ. The analysis indicates that electrode materials significantly influence the electrical performance of vertical TFTs. Therefore, electrode materials must be carefully selected and structured to realize high-end vertical TFT arrays. Vertical thin-film transistors (TFTs) with low contact resistance are necessary to realize high-resolution displays for virtual reality and augmented reality applications.