Effect of defect creation and migration on hump characteristics of a-InGaZnO thin film transistors under long-term drain bias stress with light illumination

• Published in: Solid-state electronics Vol. 144; pp. 95 - 100
• Main Authors: Cho, Yong-Jung, Kim, Woo-Sic, Lee, Yeol-Hyeong, Park, Jeong Ki, Kim, Geon Tae, Kim, Ohyun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2018
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/j.sse.2018.03.009

•The hump phenomenon in I-V characteristics was occurred in a-IGZO TFTs under drain bias illumination stress.•A two-dimensional device simulation shows that the hump phenomenon was related with shallow donor-like states.•Stretched-out C-V for the drain and simulated electric field distribution indicated that VO2+ were generated near the drain side.•Generation of VO2+ near the drain and migration of it to the source side causes the hump phenomenon. We investigated the mechanism of formation of the hump that occurs in the current-voltage I-V characteristics of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) that are exposed to long-term drain bias stress under illumination. Transfer characteristics showed two-stage degradation under the stress. At the beginning of the stress, the I-V characteristics shifted in the negative direction with a degradation of subthreshold slope, but the hump phenomenon developed over time in the I-V characteristics. The development of the hump was related to creation of defects, especially ionized oxygen vacancies which act as shallow donor-like states near the conduction-band minimum in a-IGZO. To further investigate the hump phenomenon we measured a capacitance-voltage C-V curve and performed two-dimensional device simulation. Stretched-out C-V for the gate-to-drain capacitance and simulated electric field distribution which exhibited large electric field near the drain side of TFT indicated that VO2+ were generated near the drain side of TFT, but the hump was not induced when VO2+ only existed near the drain side. Therefore, the degradation behavior under DBITS occurred because VO2+ were created near the drain side, then were migrated to the source side of the TFT.