Investigation of Amorphous InGaZnO Based TFT Interface Properties with Synchrotron Radiation Analysis
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1108-A09-08
Investigation of Amorphous InGaZnO Based TFT Interface Properties with Synchrotron Radiation Analysis Minho Joo1, Jongkwon Choi1, Seokhwan Noh1, Kyuho Park1, Kyuwook Ihm2, Kijeong Kim2, and Taihee Kang2 1 Devices & Materials Laboratory, LG Electronics Advanced Research Institute, 16 Woomyeon-Dong, Seocho-Gu, Seoul 137-724, Korea. 2 Beamline Research Division, Pohang Accelerator Laboratory, POSTECH, Pohang, Kyungbuk 790-784, Korea. ABSTRACT We investigated the amorphous indium gallium zinc oxide (IGZO) based TFT interface properties using synchrotron radiation analysis. Near edge x-ray absorption fine structure shows the presence of N2 molecules between gate dielectric layer and active channel layer. The physical damage enhanced by the sputtering process was the origin of the device degradation evolving molecular state N2. INTRODUCTION Flexible displays are of great interest for future applications, such as wearable displays, cell phone displays, and electronic papers. Recently ZnO based TFTs (thin film transistor) have attracted much attention from researchers and engineers because of their novel potential for the realization of flexible displays. Hosono et. al. reported the high performance TFTs with amorphous In-Ga-Zn oxide (a-IGZO) channel layers deposited by physical vapor deposition [12]. These TFTs showed high mobility (>10 cm2/V s) for a-IGZO TFTs, which is comparable to those of the polycrystalline ZnO TFTs, even in the amorphous phase. An important issue to be considered for realizing improved performance is the influence of source/drain electrodes, gate electrodes, gate insulators, active layers, and their interface properties. Nevertheless, most previous works have focused on the improvement of the TFT characteristics [1-4]. Low temperature TFT processes were easily degraded by process damages or current-driven damages. It is important to understand how process damages affect the overall device characteristics of aIGZO TFTs in order to fabricate TFT arrays showing high performance and high reliability. In this work, we report on the a-IGZO based TFT interface properties using synchrotron radiation analysis for top gate and bottom gate structures. SiNx film was used as gate dielectric layer for the transistors. Top gate type of TFT exhibited that high saturation mobility (> 61 cm2/V s) and large drain current on-off ratio (> 106). The damages originated from sputter process were increasing the hybridized unoccupied π* molecular orbitals of the interface between gate insulator and active channel layer showing low performance characteristics in the bottom gate TFTs. EXPERIMENT DETAILS
The a-IGZO based TFTs were fabricated on glass substrates. The TFT structures have a configuration of top gate type and bottom gate type as shown in figure 1. These structures were defined using standard photolithography and lift-off processes. The TFTs have a dimension of channel length (L) = 20 um and width (W) = 50 um. SiNx film was used as gate dielectrics (400 nm-thick) for the transistors by plasma enhanced
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