Enhancement of electrical stability of a-IGZO TFTs by improving the surface morphology and packing density of active channel Jayapal Raja a , Kyungsoo Jang a , Hong Hanh Nguyen a , Thanh Thuy Trinh a , Woojin Choi a , Junsin Yi a, b, * a School of Electronic Electrical Engineering, College of Information and Communication Engineering, Sungkyunkwan University, 300, Cheoncheon-dong, Jangan-gu, Suwon 440-746, Republic of Korea b Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea article info Article history: Received 9 April 2012 Received in revised form 6 July 2012 Accepted 17 July 2012 Available online xxx Keywords: a-IGZO TFTs Film densification Interface trap density IGZO refractive index Surface roughness abstract a-IGZO films were deposited on Si substrates by d.c sputtering technique with various working power densities (p d ) in the range of 0.74e2.22 W/cm 2 . The correlation between material properties and their effects on electrical stability of a-IGZO thin-film transistor (TFTs) was studied as a function of p d . At a p d of 1.72 W/cm 2 a-IGZO film had smoothest surface roughness (0.309 nm) with In-rich and Ga-poor cation compositions as a channel. This structurally ordered TFTs exhibited a high field effect mobility of 9.14 cm 2 /Vs, a sub-threshold swing (S.S.) of 0.566 V/dec, and an oneoff ratio of 10 7 . Additionally, the V th shift in hysteresis loop is almost eliminated. It was shown that the densification of the a-IGZO film resulted in the reduction of its interface trap density (1.83  10 12 cm 2 ), which contributes for the improvement in the electrical and thermal stability. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Amorphous InGaZnO 4 (a-IGZO) based thin film transistors (TFTs) have attracted much attention for possible replacement of the conventional amorphous and poly-Si TFTs in active-matrix liquid crystal displays (AM-LCDs), owing to their high field-effect mobility (>10 cm 2 /Vs), and expected good uniformity over large area [1]. The next-generation AM-LCDs will require high resolution (reduce pixel size), compatibility with glass/polymer film (substrate), large dynamic range and high operational speed, which can be possible using the a-IGZO instead of conventional Si for active layer material in TFTs. In general, the channel quality of fabricated TFT devices can be controlled by various sputtering parameters, such as substrate temperature, argon (Ar) flow rate, working pressure [2], and in particular, the sputtering power [3,4]. Among them, the sputtering power has significant effect on device performance. The change of sputtering power had effect on the change of interfacial (N t ) and bulk traps (N b ) of a-IGZO TFT devices. Kim et al. [4], reported that the interface trap densities are more dominant effect rather than bulk trap densities on the device performance of a-IGZO TFTs by varying r.f power on sputtering process. The proper control of the deposition parameters for the densification of the channel film during their growth plays an important role in achieving excellent gate sub-threshold swing (S.S.) and field-effect mobility (m FE ) for fabricated a-IGZO TFTs [2]. Generally, energetic sputtered atoms, and/or molecules with high energy species are responsible for the film densification during sputtering. Clin et al. observed film densifications are correlated with higher refractive index (n) of the amorphous carbon thin films with increasing r.f power [5]. Jeong et al. reported the strong dependence of the surface morphology and trap density of a-IGZO TFTs on the sputtering pressure, which is the kinetic energy of plasma particles [2]. Zhang et al. showed the improvement of mobility in In 2 O 3 TFTs through densification of channel layer using low pressure deposition [6]. However, a study about the effects of target d.c power density (p d ) on the physical properties (e.g. the roughness, n and p) of IGZO films has not been investigated clearly. The surface roughness plays an important role in TFTs devices with a smooth surface films lead to enhanced higher m FE [7] and the reliability. * Corresponding author. School of Electronic Electrical Engineering, College of Information and Communication Engineering, Sungkyunkwan University, 300, Cheoncheon-dong, Jangan-gu, Suwon 440-746, Republic of Korea. Tel.: þ82 31 290 7139; fax: þ82 31 290 7159. E-mail address: yi@yurim.skku.ac.kr (J. Yi). Contents lists available at SciVerse ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap 1567-1739/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cap.2012.07.016 Current Applied Physics xxx (2012) 1e6 Please cite this article in press as: J. Raja, et al., Enhancement of electrical stability of a-IGZO TFTs by improving the surface morphology and packing density of active channel, Current Applied Physics (2012), http://dx.doi.org/10.1016/j.cap.2012.07.016