用于AMOLED 的非晶氧化物薄膜晶体管稳定性的研究

AM-OLED is the mainstream of flat panel display. The thin film transistor (TFT) backplane is the core of AM-OLED. Oxide TFT is a promise backplane for OLED Due to its better performances, lower cost, green process. In this project, we put the emphases on the stability of Oxide TFT. The device stability is sensitive to bias/current stress, temperature, light illuminating, and water vapor exposure. We will study Bias voltage stress induced instability (the shift of threshold voltage) without light illumination or under light illumination, especially, Negative Bias- light illumination instability: Investigate the dependences of the shift of threshold voltage on the stress time, stress temperature, intensity and wavelength of light illumination , further analyze the mechanism for the instability and adopt the corresponding measures to improve the stability. 1) For channel layer, to incorporate tetravalent elements (Hf4+, Cr4+, Si4+) ,which have high metal-oxygen bonding-strength, into the IZO system can strongly bond with oxygen, resulting in the reduction of oxygen vacancy, which acts as the subgap hole traps, leading to improvement of stability. 2) Fabricate the high K insulator layer with high insulation strength by using Atomic Layer Deposition (ALD) method, such as Al2O3, instead of PECVD. ALD method is particularly suitable for preparing high k material, since it can grow dense thin film and have no H+ suspend bond, which is favor to stability. 3) Improve the interface between channel layer and insulator. Study the interface by using capacitance-voltage method. In order to reducing the defect and traps in the interface and modified the interface, we will adopt the steps, including annealing in wet oxygen , which has stronger oxidation power provided by H2O; plasma treatment in the various atmosphere : and inset a thin buffer layer (HfO2) to modify interface. 4) Passivation: For the bottom gate TFT, the instability can produce from the exposed back channel due to the water vapor, it may be avoided by adopting dense, gas-tight passivation layers and etching stopper to seal the all device. The alternative is to make Top gate TFT, where the channel layer is covered by the insulator layer, acts like a passivation layer. At last, we will complete a 2-3 inch mono-color with resolution 160x120 display prototype.

AM-OLED是平板显示未来的主流,TFT基板是核心。氧化物TFT由于它低成本绿色等优势是即将取代现有的TFT背板技术。而其稳定性是目前阻碍其应用的关键。本项目以氧化物TFT的稳定性为重点。研究正负偏压不稳定性，偏压光照不稳定性，特别是负偏压光照不稳定性等现象，通过各种物理测试、分析其机理及提高稳定性的对策。1) 对于有源层：添加IV族元素减少氧空位减少带间能级及探索新结构和组分的有源层 2）采用ALD等方法研制Al2O3等高介电常数，高绝缘强度绝缘层3）有源层与-绝缘层的界面：用C-V 方法研究其界面，通过加入薄的缓冲层以及各种界面处理来，减少界面缺陷，改善界面。4）封装：对底栅结构，使用etching stopper 及抗水抗氧的钝化层对有源层进行全封闭。研制顶栅结构，有利稳定性。最终研制出性能稳定的有实用价值的2-3英寸单色氧化物TFT-OLED显示屏及其关键工艺。

TFT稳定性既是学术问题也具有重要应用价值，本课题在以下方面获得重要进展： .一、高质量绝缘层的获得 ：在TFT中，高介电常数，低漏电的介质层是最重要的。本项目中使用原子层沉积法（ALD）: (1）成功制备出高介电常数介质，Al2O3（=8）和ZrO2（=25） (2）使用ALD制成 ZrO2（220nm）/ Al2O3(10nm)复合介质层，不仅保持了高介电常数，还大大降低了漏电。， .二、有源层的掺杂，复合有源层， 及溶液法生长；有源层是TFT器件的又一个重要部分，其重要进展有：（1) 利用双源共溅射法进行有源层的掺杂，有效控制材料组分：用HfO 和 InZnO双源共溅得到HfInZnO高稳定性器件（2）制成双有源层结构：依次生长高载流子浓度层和高稳定性层，得到（HfInZnO-InZnO）有源层， 其TFT 既有高迁移率，又有高稳定性（3) 利用溶液法制备多种四元化合物，BaZnSnO，LaZnSnO-TFT为器件材料的选取开拓了道路。（4）利用阴离子氮掺杂大大改善NBIS 稳定性。 .三、稳定性的研究：(1)正偏压稳定性： 当TFT器件经受正偏压作用时，阈值电压有移动。这种正栅偏压不稳定性是界面及绝缘层中的缺陷引起的，阈值电压偏移的大小符合stretched-exponential time dependence是charge trapping机理， 它可以通过退火来改善。(2) 负偏压光照stress(NBIS)稳定性：在光和负偏压作用下，阈值电压的负飘移。是和有源层半导体带内能级态密度Subgap density of states (DOS) 有关的，它是氧空位形成的不稳定性。.四．态密度(DOS)的导出和稳定性的关联研究：(1) 态密度的导出: 研究有源层半导体的带内能级态密度Subgap density of states (DOS) 是TFT稳定性研究的重要课题。我们应用Temperature Stress 方法，提高温度，源漏电流是热激活型的。研究激活能随栅极电压变化的速度，可得出DOS. (2) 研究稳定性和态密度的关联：利用改变有源层厚度；应用共溅射制成掺杂有源层HfZnSnO；应用复合有源层 HfZnSnO- ZnSnO；阴离子N掺杂； 这些手段有效改善NBIS 稳定性，研究其改善器件的态密度发现，所有改善都伴随态密度降低。