高性能柔性透明金属氧化物/碳纳米管复合薄膜晶体管研究

In recent years, the development of the display technology call out higher challenge for thin film transistor performance. The advanced thin film transistor devices require fast response, that is， the high mobility and high transmission speed; excellent on/off current ratio and low power consumption in order to meet the mobile or wearable device needs. Thin film transistors and the substrate need to be flexible, bendable, and its preparation process needs to be compatible with flexible substrate technology. The active channel material is expected to be thin and transparent as to meet the requirements of light transmission rate and to increase the aperture ratio of the display panel. The fabrication process also needs to be compatible to the panel material. Current thin film transistors have the advantages as well as their own shortcomings on performance and process. To meet the requirements above, in this project we propose to achieve independent-gate Indium-Gallium-Zinc-Oxide /carbon nanotubes (IGZO/CNT) composite thin film transistor based on mainly the sputtering process for the large-area high- uniformity applications. The transistors own high mobility, superior mechanical flexibility and stability, as well as better contact resistance by combining the advantages of carbon nanotubes and IGZO. Carrier mobility of the composite TFT is expected to be more than 30cm2/Vs, and the on/off current ratio keeps above 1E6. The channel length can cover 2µm-20µm simultaneously. Threshold voltages of the devices are adjustable and device uniformity and stability are improved by the CNT features and density. The flexible transparent electrodes and high-k dielectric will also be explored to be integrated into the novel composite devices to improve the light transmission rate and higher current, to meet the expectation of various large-area active matrix backplane applications including the flexible display, sensor networks, wearable devices etc. The composites are mainly fabricated based on sputtering process which is more easily compatible with IGZO thin film transistor process equipment and will further promote the IGZO/CNT composite material and carbon based flexible electrode toward industry applications.

显示技术发展对新型薄膜晶体管提出了更高要求。要求薄膜晶体管反应速度快，具备较高的迁移率；优良的开关比和低功耗；柔性可弯折，其工艺需要与柔性衬底及显示面板材料工艺相兼容；材料轻薄透明，满足透光率要求。现有的薄膜在具备各自优势同时都有各自不足。在该项目中，我们创新提出和实现柔性透明的独立栅氧化铟镓锌/碳纳米管复合薄膜晶体管。通过结合碳纳米管的高迁移率、优越机械柔韧性和稳定性，以及IGZO的较成熟工艺和IGZO-金属较好的金半接触，并引入ITO电极、碳基柔性透明电极和高-K介质，优化器件结构工艺，实现同时具备高性能、柔性透明、独立开关的先进薄膜晶体管,以满足各种有源矩阵背板的要求，可应用于大面积高均匀性的柔性显示和可穿戴设备等领域。目标实现载流子迁移率为30cm2/Vs以上，为同等条件下IGZO薄膜晶体管的两倍以上，同时器件开关比为1E6以上，器件阈值电压可调，并具备较好的器件均匀性。

非晶铟镓氧化锌（a-IGZO）因具有高透光性、较高迁移率以及低温制备工艺等优点，成为学界和业界近年来普遍看好的薄膜晶体管材料。然而， a-IGZO薄膜晶体管的迁移率相对较低，不能满足未来高分辨率显示的需求。此外，目前a-IGZO薄膜晶体管的电极材料均为金属或金属氧化物，不能满足未来柔性透明显示的需求。碳纳米管有高迁移率、柔性可弯折、稳定性较好等优势，已经在各柔性领域展示了其应用潜力。.针对以上问题，本项目结合碳纳米管与a-IGZO的各自优势，研究碳纳米管在a-IGZO薄膜晶体管中的应用。本项目主要进行了以下三方面工作：.一、碳纳米管/a-IGZO复合沟道薄膜晶体管.本项目提出采用磁控溅射 a-IGZO 和LB金属型碳纳米管作为有源区制备碳纳米管/a-IGZO复合沟道薄膜晶体管，该器件的开关电流比达1E7，迁移率最高可达15.3 cm2/Vs，是a-IGZO薄膜晶体管迁移率的两倍。我们分析了碳纳米管浓度，密度，种类，形貌以及a-IGZO的厚度和层数对混合沟道器件性能的影响，并得出明确结论。.二、碳纳米管/a-IGZO TFT在柔性透明衬底上的实现.本项目实现了碳纳米管/a-IGZO复合沟道器件在柔性透明衬底上的制备，该器件的迁移率为1.13 cm2/Vs，其最大弯折曲率半径为3 mm，最大弯折次数为400次。整个器件包括衬底透光率高达84%，不包括衬底的透光率高达98%。.三、碳纳米管电极a-IGZO薄膜晶体管.本项目提出采用碳纳米管薄膜电极制备a-IGZO薄膜晶体管，使其能满足未来柔性透明显示的需要。本文研究了硅基衬底上单壁碳纳米管电极a-IGZO薄膜晶体管的制备并实现该器件在PEN衬底上的制备。研究了退火温度对器件性能的提升，器件迁移率从1.70 cm2/Vs提升至8.0 cm2/Vs。对PEN衬底上的器件进行了透光率的分析，整个器件包括衬底的透光率为73%，不包括衬底的透光率高达81%。碳纳米管作为电极推进了a-IGZO薄膜晶体管在柔性透明显示上的应用。.本文将混合型单壁碳纳米管引入到a-IGZO沟道中在提高器件有效迁移率的同时还避免了金属碳纳米管和半导体碳纳米管的共存问题。.碳纳米管/a-IGZO复合沟道薄膜晶体管以及碳纳米管电极的a-IGZO薄膜晶体管的设计为未来高速，柔性，透明电子提供了高速薄膜晶体管的解决方案。