Oh Seung Jin, Kwon Jeong Hyun, Lee Sangmin, Choi Kyung Cheol, Kim Taek-Soo
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.
Department of Display and Semiconductor Engineering, Sun Moon University, Asan 31460, Republic of Korea.
ACS Appl Mater Interfaces. 2021 Apr 14;13(14):16650-16659. doi: 10.1021/acsami.0c23112. Epub 2021 Mar 31.
A fundamental understanding of the mechanical behavior of the indium tin oxide (ITO) layer is very important because cracking and delamination of the ITO layers have been a critical obstacle for mechanically robust flexible electronics. In this study, the intrinsic mechanical properties of ITO thin films without a substrate were measured by utilizing a freestanding tensile testing method. Young's modulus (89 ± 1 GPa), elongation (0.34 ± 0.02%), and tensile strength (293 ± 13 MPa) of amorphous as-deposited ITO thin films were successfully measured. The sheet resistance, transparency, and thickness of the as-deposited films were 32.9 ± 0.5 Ω/sq, 92.7% (400-700 nm), and 152 ± 6 nm, respectively. First, we investigated the effects of annealing temperature on the mechanical properties of ITO thin films. For 100- and 150 °C-annealed ITO thin films, which were amorphous, Young's modulus, elongation, and tensile strength were enhanced by increasing the packing density and reducing the structural defects. For 200 °C-annealed ITO thin films, which were polycrystalline, Young's modulus was further increased because of their highly packed crystalline nature. However, there was a significant decrease in elongation and tensile strength because grain boundaries act as critical defects. Next, the annealing time was varied from 0.5 to 6 h for a better understanding of the effects of the annealing time. As a result, the maximum elongation (0.54 ± 0.03%) and tensile strength (589 ± 11 MPa) were obtained at 150 °C for 1 h. Annealing for 1 h was appropriate for sufficient defect reduction; however, excessive annealing for more than 1 h increased the degree of partial crystallization of the ITO thin films. The proposed annealing conditions and the corresponding mechanical properties provide guidelines for the optimum annealing process of ITO thin films and quantitative data for mechanical analysis to design mechanically robust flexible electronics.
对铟锡氧化物（ITO）层的力学行为有基本的了解非常重要，因为ITO层的开裂和分层一直是机械坚固的柔性电子产品的关键障碍。在本研究中，通过使用独立拉伸测试方法测量了无衬底ITO薄膜的本征力学性能。成功测量了非晶态沉积态ITO薄膜的杨氏模量（89±1 GPa）、伸长率（0.34±0.02%）和拉伸强度（293±13 MPa）。沉积态薄膜的方块电阻、透明度和厚度分别为32.9±0.5 Ω/sq、92.7%（400 - 700 nm）和152±6 nm。首先，我们研究了退火温度对ITO薄膜力学性能的影响。对于100℃和150℃退火的非晶态ITO薄膜，通过提高堆积密度和减少结构缺陷，杨氏模量、伸长率和拉伸强度得到了提高。对于200℃退火的多晶ITO薄膜，由于其高度堆积的晶体性质，杨氏模量进一步增加。然而，伸长率和拉伸强度显著下降，因为晶界充当了关键缺陷。接下来，将退火时间从0.5小时变化到6小时，以更好地了解退火时间的影响。结果，在150℃下退火1小时获得了最大伸长率（0.54±0.03%）和拉伸强度（589±11 MPa）。退火1小时适合充分减少缺陷；然而，超过1小时的过度退火增加了ITO薄膜的部分结晶程度。所提出的退火条件和相应的力学性能为ITO薄膜的最佳退火工艺提供了指导方针，并为设计机械坚固的柔性电子产品的力学分析提供了定量数据。
