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In recent years, considerable attention has been paid to amorphous indium gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) for high performance flat panel display, such as liquid-crystal displays (LCDs), active-matrix organic light-emitting diode (AMOLED) display and flexible display. This is because IGZO TFTs are more suitable for pixels and circuit integrations on display panel than the conventional silicon-based devices. The merits of IGZO TFT technology include high mobility, decent reliability, low manufacturing cost, and excellent uniformity over large fabrication area. However, it was reported that the electrical characteristics of IGZO TFT are susceptible to shift after electrical aging measurement under illumination, which is caused by the activation of trapped electrons from sub-gap states to conducting states. Therefore, it is necessary to introduce light shielding layer to suppress the electrical characteristic shift under illumination aging measurements. Lim et al. demonstrated the characteristics of IGZO TFT with additional light shielding metal layer, and proved that the threshold voltage of TFT can be tuned linearly by adjusting the biasing voltage of the light shielding metal. Taking advantage of this tunable threshold voltage, AMOLED pixel circuit with a threshold voltage shift compensation function can be implemented. However, drawback of this method lies in the adding of additional biasing line, which increases the circuit area and restricts the integration of high-resolution pixel circuits. Thus, Zan et al. proposed adopting floating (unbiased) light shielding metal layer to improve the characteristics of device. However, Zeng et al. demonstrated the abnormal output characteristics of the IGZO TFT, as it cannot be saturated due to the introduction of floating light shielding metal layer. It seems that the IGZO TFT with floating metal is different from the conventional double-gate or single gate structure. To date, the current conducting mechanism of IGZO TFT with floating metal has not been discussed yet. In this paper, the distribution of electrical potential in the IGZO TFT with a cross sectional view is thoroughly analyzed. It is confirmed that the abnormal output characteristic of IGZO TFT is caused by the capacitive coupling between the floating gate and the drain electrode of the transistor. On the basis of the voltage distribution relationship between the equivalent capacitances, a threshold-voltage-dependent current-voltage model is proposed. The simulated results by technology computer-aided design tool and those by the proposed model are in good agreement with each other. Therefore, the mechanism of floating gate effect for IGZO TFT is comprehensively demonstrated. The illustrated conducting mechanism and the proposed current-voltage model are helpful in developing the device and process of IGZO TFT with novel structure.
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Keywords:
- InGaZnO /
- floating gate /
- thin film transistors /
- device model
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[24] Zhao J Q, Yu P F, Qiu S, Zhao Q H, Feng L R, Ogier S, Tang W, Fan J L, Liu W J, Liu Y P, Guo X J 2017 IEEE Electron Dev. Lett. 64 2030
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[1] Arai T 2012 J. Soc. Inf. Display 20 156
[2] Li X F, Xin E L, Shi J F, Chen L L, Li C Y, Zhang J H 2013 Acta Phys. Sin. 62 108503 (in Chinese)[李喜峰, 信恩龙, 石继锋, 陈龙龙, 李亚春, 张建华 2013 物理学报 62 108503]
[3] Xu P R, Qiang L, Yao R H 2015 Acta Phys. Sin. 64 137101 (in Chinese)[徐飘荣, 强蕾, 姚若河 2015 物理学报 64 137101]
[4] Kim Y, Kim Y, Lee H 2014 J. Display Technol. 10 80
[5] Qian C, Sun J, Zhang L, Huang H, Yang J, Gao Y 2015 J. Phys. Chem. C 119 14965
[6] Zhang C, Luo Q, Wu H, Li H, Lai J, Ji G, Yan L, Wang X, Zhang D, Lin J, Chen L, Yang J, Ma C 2017 Organic Electron. 45 190
[7] Zheng Z, Jiang J, Guo J, Sun J, Yang J 2016 Organic Electron. 33 311
[8] Liu F, Qian C, Sun J, Liu P, Huang Y, Gao Y, Yang J 2016 Appl. Phys. A:Mater. Sci. Process. 122 311
[9] Chen T C, Chang T C, Hsieh T Y, Tsai C T, Chen S C, Lin C S, Hung M C, Tu C H, Chang J J, Chen P L 2010 Appl. Phys. Lett. 97 192103
[10] Oh H, Yoon S M, Ryu M K, Hwang C S, Yang S, Park S H K 2010 Appl. Phys. Lett. 97 183502
[11] Oh H, Yoon S M, Ryu M K, Hwang C S, Yang S, Park S H K 2011 Appl. Phys. Lett. 98 033504
[12] Chen W T, Hsueh H W, Zan H W, Tsai C C 2011 Electrochem. Solid-State Lett. 14 H297
[13] Zeng M, Chen S, Liu X D, Zeng L M, Li W Y, Shi L Q, Li S, Chou Y F, Liu X, Lee C 2017 Sid Symposium Digest of Technical Papers 48 1234
[14] Lim H, Yin H, Park J S, Song I, Kim C, Park J, Kim S, Kim S W, Lee C B, Kim Y C, Park Y S, Kang D 2008 Appl. Phys. Lett. 93 063505
[15] Takechi K, Nakata M, Azuma K, Yamaguchi H, Kaneko S 2009 IEEE Trans. Electron Dev. 56 2027
[16] Park J S, Jeong J K, Mo Y G, Kim H D, Kim C J 2008 Appl. Phys. Lett. 93 033513
[17] Seok M J, Choi M H, Mativenga M, Geng D, Kim D Y, Jang J 2011 IEEE Electron Dev. Lett. 32 1089
[18] Abe K, Takahashi K, Sato A 2012 IEEE Trans. Electron Devi. 59 1928
[19] Baek G, Kanicki J 2012 J. Soc. Inf. Disp. 20 237
[20] Seok M J, Mativenga M, Geng D, Jang J 2013 IEEE Electron Dev. Lett. 60 3787
[21] Zan H W, Chen W T, Yeh C C, Hsueh H W, Tsai C C, Meng H F 2011 Appl. Phys. Lett. 98 153506
[22] Qin T, Huang S X, Liao C W, Yu T B, Deng L W 2017 Acta Phys. Sin. 66 097101
[23] Ning H L, Hu S B, Zhu F, Yao R H, Xu M, Zou J H, Tao H, Xu R X, Xu H, Wang L, Lan L F, Peng J B 2015 Acta Phys. Sin. 64 126103 (in Chinese)[宁洪龙, 胡诗犇, 朱峰, 姚日晖, 徐苗, 邹建华, 陶洪, 徐瑞霞, 徐华, 王磊, 兰林锋, 彭俊虎 2015 物理学报 64 126103]
[24] Zhao J Q, Yu P F, Qiu S, Zhao Q H, Feng L R, Ogier S, Tang W, Fan J L, Liu W J, Liu Y P, Guo X J 2017 IEEE Electron Dev. Lett. 64 2030
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