Cho Man-Ho, Cho Won-Ju
Department of Electronic Materials Engineering, Kwangwoon University, 447-1, Wolgye-dong, Nowon-gu, Seoul 139-701, Korea.
J Nanosci Nanotechnol. 2020 Nov 1;20(11):6920-6924. doi: 10.1166/jnn.2020.18811.
In this study, a low-thermal-budget microwave irradiation (MWI) technique was applied as a post-deposition annealing (PDA) process to lower the trap densities that exist in transparent amorphous oxide semiconductor thin film transistors (TAOS TFTs). As channel layers of TAOS TFTs, two types of indium gallium zinc oxide (IGZO) with different compositions as well as aluminum zinc tin oxide (AZTO) and zinc oxide (ZnO) thin films were deposited with various thicknesses through radio frequency (RF) magnetron sputtering at 25°C. Cost-effective and energy-efficient MWI was conducted to enhance the electrical performance of transistors by removing traps and defects. The electrical characteristics of IGZO (1:1:1 and 4:2:3)-, ZnO-, and AZTO-based TFTs treated by MWI were evaluated by measuring the transfer curves. In particular, the relation between the interface trap density (Dit) and bulk trap density of microwave-irradiated TFTs was quantitatively evaluated by the subthreshold swing (SS) variation based on channel thickness. The results indicated that of the four types of channel layers, the performance of IGZO (4:2:3) TFTs was the best and that of AZTO TFTs was the worst, in terms of electrical properties such as on/off current ratio, mobility SS, and trap density. In particular, it was demonstrated that the trap density of MWI-treated TAOS TFTs was much lower than that of conventional furnace annealing (CFA)-treated devices. Despite the short annealing duration of a few minutes, the MWI more effectively reduced the trap sites than did the furnace treatment, and significantly enhanced the electrical properties of the TAOS TFTs. It is expected that high-performance TAOS TFTs can be fabricated by applying MWI, which is a highly efficient and low-thermal-budget annealing method, to the PDA process and can thus reduce trap density.
在本研究中，采用低热预算微波辐照（MWI）技术作为沉积后退火（PDA）工艺，以降低透明非晶氧化物半导体薄膜晶体管（TAOS TFT）中存在的陷阱密度。作为TAOS TFT的沟道层，通过射频（RF）磁控溅射在25°C下沉积了两种不同成分的铟镓锌氧化物（IGZO）以及铝锌锡氧化物（AZTO）和氧化锌（ZnO）薄膜，厚度各不相同。通过去除陷阱和缺陷，采用经济高效的MWI来提高晶体管的电学性能。通过测量转移曲线评估了经MWI处理的基于IGZO（1:1:1和4:2:3）、ZnO和AZTO的TFT的电学特性。特别是，基于沟道厚度的亚阈值摆幅（SS）变化定量评估了微波辐照TFT的界面陷阱密度（Dit）和体陷阱密度之间的关系。结果表明，在开/关电流比、迁移率SS和陷阱密度等电学性能方面，四种沟道层类型中，IGZO（4:2:3）TFT的性能最佳，AZTO TFT的性能最差。特别是，结果表明经MWI处理的TAOS TFT的陷阱密度远低于传统炉退火（CFA）处理的器件。尽管退火持续时间仅几分钟，但MWI比炉处理更有效地减少了陷阱位点，并显著提高了TAOS TFT的电学性能。预计通过将MWI（一种高效且低热预算的退火方法）应用于PDA工艺，可以制造出高性能的TAOS TFT，从而降低陷阱密度。
