柔性基底碳纳米管薄膜器件阈值电压非稳机理研究

In recent years, there has been tremendous interest in flexible electronics. The electronics fabricated on flat flexible substrate enable promising applications such as low-cost RFID tags, smart cards, flexible displays et al. Single-walled carbon nanotube (SWCNT) has been regarded as one of the most promising materials candidates for flexible electronics owing to its exceptional electrical, mechanical, optical, and thermal properties.. Unfortunately, an effective method for synthesizing electronically homogeneous SWCNTs is yet to become inavailable and consequenly reproducibility of device performance based on individual SWCNTs has been a serious challenge in the research community. Utilizing SWCNT thin films involving large quantities of nanotubes in the form of random networks, instead of individual SWCNTs, to fabricate electronics can avoid these statistics-related challenges. Thin film transistors (TFTs) based on SWCNT networks have therefore become a research focus in both academia and industry. In addition, the solution phase processing of SWCNTs is compatible with the inkjet printing technology. Since both processing techniques are ambient-condition based, their combination can enable fabrication of electrical elements and printed circuits on flexible substrates. However, the technological developments of SWCNT-network TFTs into a reliable device and circuit solution is severely challenged by issues such as threshold voltage instability and control. .Therefore, the proposed project has a primary focus on systematically exploring the physical origin(s) and associated mechansim(s) of the threshold voltage instability in SWCNT network TFTs. We aim at establishing electrical charaterization methodologies that will assist us in identifying practically effective schemes, both physical and chemical, for treatment of the substrate, gate dielectric and SWCNTs in order to eliminate the threshold voltage instability. stable and low voltage SWCNT-based TFTs will be the final demonstration of the project. Extensive knowledge in SWCNT devices will be generated during the course of this project, which not only is the essense of research but also will be a valuable exploration for the development of flexible electronics.

碳纳米管网络结构薄膜器件避免了单根碳纳米管所带来的个体差异和制备工艺上的复杂性，并且具有在任意柔性衬底上通过喷墨印刷工艺实现的优点，而成为目前工业界和学术界研究热点。然而碳纳米管薄膜器件中的阈值电压非稳现象是其成为真正可靠逻辑器件的一大障碍。因此，本项目针对柔性基底上单壁碳纳米管网络结构薄膜器件中出现的阈值电压非稳现象，系统的研究各种可能导致阈值电压飘移的物理来源，阐明其中物理机制，建立一套电学测量和表征测试系统，进而对衬底、栅介质和碳纳米管进行相应的物理化学处理以达到消除阈值电压漂移的目的，最终在柔性基底上通过喷墨印刷方式实现性能稳定的低电压驱动碳纳米管薄膜晶体管，为柔性电子器件的应用发展进行有益探索并提供参考借鉴价值。

单壁碳纳米管是一种性能优良的准一维材料，基于单壁碳纳米管网络结构的场效应晶体管，能够同时获得较高的开态电流和大的开关电流比，逐渐成为性能突出的薄膜开关器件。与此同时，碳纳米管溶液制备工艺与喷墨打印技术相兼容，有利于在柔性衬底上制备各种元器件和打印电路。然而作为一个可靠的逻辑器件，其最基本的要求就是器件的阈值电压不随外界环境而变化，因此消除阈值电压不稳定因素成为碳纳米管薄膜器件能够在集成电路中大规模应用的前提条件。本项目通过对碳纳米管薄膜器件阈值电压非稳定性的系统性研究，揭示了导致薄膜器件性能发生变化的内在机理，提出水氧电化学反应模型，并且该模型适用于其他各种有机薄膜晶体管。该研究成果发表在国际著名期刊《Nature Communications》上。在大气环境下，空气中大量存在的水分子（H2O）和氧气分子（O2），这些水氧分子在薄膜表面发生可逆电化学反应，并且该电化学反应受栅压影响。在正向电压作用下，水氧分子发生正向电化学反应，在器件表面产生大量带负电荷的氢氧根离子（OH-）。当施加反向电压后， OH-发生逆向电化学反应产生新的水氧分子，整个过程是个可逆过程，从而引起器件电流出现非稳定现象。通过工艺改进和开发，我们已经获得高性能碳纳米管薄膜器件，并实现低电压驱动的碳纳米管薄膜晶体管。器件工作电压Vd =1.5V，阈值电压︱Vt︱=0.2V，器件迁移率=10cm^2/Vs，电流开关比为10^6。碳纳米管薄膜晶体管展示了其在有机电子学领域广阔且诱人的发展前景。基于其特殊的制备方法以及市场上对大面积、可折叠性、低温制备工艺，尤其是低成本器件的需求，以碳纳米管器件为代表的有机薄膜晶体管器件在一些特定的领域展现了强大的优势。总而言之，正是由于当年解决了Si MOSFET器件中由于Na＋，K+等可动离子导致器件阈值电压漂移现象以后，从20世纪60年代开始，基于Si MOSFET的大规模集成电路才得以蓬勃发展，开创了如今的信息化社会。同样，只有全面了解并解决碳纳米管薄膜晶体管的阈值电压漂移现象以后，才能进一步拓展碳纳米管薄膜器件的应用范围和领域，同时也为其他柔性薄膜器件的研究提供良好的参考价值和借鉴意义。