基于GaN纳米线铁电场效应晶体管及相关电性能

With the development of device micromation, high integration, high storage and high speed, the nanodevices with the conducting channel based on semiconducting nanowire (NW), are attracting a great interest in scientific research of information technology. Due to its excellent properties of direct and wide bandgap, high mobility and thermal stability, and radiation resistance, the GaN NW will be assembled as the conducting channel of ferroelectric field effect transistor (FeFET) with ferroelectric/substrate back-gate, and the electrical characteristics and reliability of the GaN NW-based FeFET will be investigated in this project. In particular, three key issues will be mainly focused on, which are nanofabrication and characterization technology, temperature-dependent electrical properties, and radiation-dependent electrical properties as well as corresponding mechanism. The project will be devoted to experimentally developing nanotechnology for the characterization of the electrical characteristics and reliability of the GaN NW-based FeFET, and on the other hand, it will be also devoted to building the thought system info on the basis of the interaction of materials science, semiconductor physics and reliability engineering, in order to discover the failure mechanism of nanodevice. The project refers to the basic research and major science research programs of the national medium- and long-term program for science and technology development (2006-2020), and the research results will provide the theoretical and experimental basis for the nanodevice and its reliability.

随着器件向小型化、高集成、高密度存储和超快传输方向发展,以半导体纳米线为导电沟道的纳电子器件成为信息高新技术研究前沿和热点之一。本项目以具有宽带隙、高电子迁移率、高热导率和抗辐射等优点的GaN半导体纳米线为导电沟道，设计铁电/基片复合层式背栅，自组装GaN纳米线铁电场效应晶体管，并探索其电学性能及相关可靠性。重点研究三个关键科学问题：纳电子器件微纳加工及表征测试技术；基于纳米线铁电场效应晶体管温度相关的电学特性与内在机制；基于纳米线铁电场效应晶体管辐照相关的电学特性与物理机制。一方面发展表征基于纳米线铁电场效应晶体管相关电学特性的测试技术；另一方面建立材料学、半导体物理学和器件可靠性工程相互交叉的理论分析方法，揭示纳电子器件失效的物理机制。本项目符合《国家中长期科学和技术发展规划(2006-2020)》的基础研究和重大科学研究计划，研究结果将为纳电子器件及可靠性研究提供理论和实验基础。

铁电存储器因具有非易失、高读写速度和抗辐射等优点，被认为是下一代最具潜力存储器之一。本项目以具有高电子迁移率和抗辐射等优点的GaN纳米线为导电沟道，设计了铁电/基片复合层式背栅，成功自组装了GaN纳米线铁电场效应晶体管与MFIS铁电电容，探索了器件转移、输出特性，温度、辐照相关电特性，揭示了相关物理机制，为铁电器件设计及可靠性研究提供理论和实验基础。具体结论如下：(1) 成功获得了适于自组装用、高质量的GaN纳米线，纳米线为六方纤锌矿结构的GaN晶体，其生长方向为[100]晶向，表面平直光滑，长度为几十到几百微米，直径分布在100-200 nm之间；(2) 成功获得了适于自组装用PZT/Pt/Ti/SiO2/Si层状背栅结构，铁电层为钙钛矿结构，具有良好铁电性能，表面平整，无大颗粒堆积和裂纹，晶粒直径在2-5 μm范围内，厚度约为500 nm；(3) 成功组装了以GaN纳米线为导电沟道、PZT/Pt/Ti/SiO2/Si为背栅的铁电场效应晶体管，该晶体管为n型耗尽模式场效应晶体管，具有良好存储性能，数据存储窗口高达5 V，零栅压时的开关电流比高达103，亚阈值摆幅S为0.93 V/decade，峰值跨导gm为1.7 μS；(4) 获得了基于GaN纳米线铁电晶体管、MFIS铁电电容与温度相关电特性，并揭示了温度相关物理机制。不同温度 (300K、360K)下，晶体管输出特性变化不明显，而转移特性受到一定影响，表现为存储窗口变小；基于SBT的MFIS电容在300K至220K之间，最大存储窗口高达1.26 V。随温度从300K升至400K，存储窗口变小。漏电电流密度增大最高达一个数量级；(5) 获得了基于GaN纳米线铁电晶体管、MFIS铁电电容与辐照相关电性能。在Co60源总剂量为800Krad的辐照下，晶体管输出特性变化不明显，但转移特性发生一定变化，其存储特性稍变差；基于SBT的MFIS电容经过辐照(总剂量为1Mrad)后，存储窗口减小，这归因于铁电层矫顽场在辐照后减小。辐照后电容漏电流亦增大，这归因于电容经辐照后电极及铁电层中界面态陷阱电荷增多。(6) 发现了氢导致基于SBT的MFIS铁电电容存储窗口显著减小，存储特性严重退化甚至消失，这因为H扩散至铁电层内并导致矫顽场减小。漏电流密度增大达一个数量级，这因为反应产生的氧空位Vox和H原子的离子化释放电子。