Impact of Al2O3 deposition temperature on the performance and initial stability of nanocrystalline ZnO thin-film transistors

• Published in: Microelectronic engineering 2019-09, Vol.217, p.111114, Article 111114
• Main Authors: Rodriguez-Davila, R.A., Chapman, R.A., Bolshakov, P., Young, C.D., Quevedo-Lopez, M.
• Format: Article
• Language: English
• Subjects: Al2O3; Aluminum oxide; Chemical vapor deposition; Deposition; High-k; Photolithography; Roughness; Saturation; Semiconductor devices; Stability analysis; Temperature; Thin film transistors; Thin films; Thin-film transistors (TFTs); Threshold voltage; Ultrasonic testing; Vt instability; Zinc oxide; Zinc oxides
• ISSN: 0167-9317; 1873-5568
• DOI: 10.1016/j.mee.2019.111114

The initial performance and “time-zero” instability of ZnO TFTs are evaluated using different Al2O3 deposition temperature. Fully-patterned bottom-gate and top-contact devices were fabricated and used as the test structures. The initial TFT performance shows a decrease of saturation mobility from 9.2 to 5.6 cm2/Vˑs; increase in threshold voltage from 2.2 to 2.5 V; and subthreshold swing increase from 115 to 225 mV/DEC, with increasing deposition temperature. The time-zero instability (t = 0 s) shows an increase in threshold voltage shifting of 4.0, 12.8, and 13.6%; a decrease in the subthreshold swing of 5.3%, 17.7%, and 16.3%; and an increase in saturation mobility of 0.8%, 2.8%, and 4.3% with increasing deposition temperature. Results indicate that the primary mechanism of the threshold voltage shifting is the increase in roughness induced interface states due to possible dangling bonds increasing along with the roughness. [Display omitted] •The increasing Al2O3 DT degrades the TFT performance.•The degradation is associated with the increase in interface states.•Gate dielectric stack roughness increases with increasing deposition temperature.•Roughness induces interface states causes electrical degradation of TFTs.