铁电栅极调控ZnMgO/ZnO界面二维电子气及其非易失存储应用研究

Ferroelectric gate control of the metal-insulator transition for the two-dimensional electron gas (2DEG) at oxide heterointerfaces opens the door to new-generation ferroelectric non-volatile memory with high scalability and reliability. However, this conceptual device is still elusive due to the non-ideal on/off ratio of channel current and the low electron mobility. To overcome these obstacles, we design the scheme to combine tetragonal BiFeO3 with ZnMgO/ZnO interfacial 2DEG in this project. Tetragonal BiFeO3 has the largest spontaneous polarization among known materials, enabling an electrostatic doping level of the channel far larger than those of the other ferroelectrics. On the other hand, ZnMgO/ZnO holds the mobility record among all the oxide interfacial 2DEG systems, and its electron sheet concentration can be easily tuned within a rather large range. In this project, we aim to find out avenues to improve the electrical performance of ZnMgO/ZnO 2DEG, and plan to disclose the polarization symmetry and the tetragonal-to-rhombohedral structural relaxation route of tetragonal BiFeO3. Based on these studies, we will fabricate model devices of ferroelectric field-effect transistor and explore possible ways to reduce the leakage current of the gate stack. Moreover, it is our ultimate goal to achieve a reversible and efficient control on the on- and off-states of 2DEG channel current by the polarization switching of tetragonal BiFeO3. To conclude, our study not only enables an in-depth understanding on the underlying mechanism of ferroelectric gate modulation of the 2DEG systems, but also paves a possible avenue for the future applications of ferroelectric nonvolatile memories.

通过铁电栅极调控氧化物异质界面二维电子气(2DEG)金属-绝缘转变，打开了通向高集成度、高可靠性的新一代铁电非易失存储器的大门。但是，小的沟道电流开关比和低电子迁移率限制了这一新概念器件的应用。为解决该问题，本项目提出将四方相铁酸铋与ZnMgO/ZnO界面2DEG系统外延集成的研究方案。四方相铁酸铋具有迄今已知最大的极化强度，可实现远大于其它铁电体的沟道静电掺杂浓度。而ZnMgO/ZnO保持着氧化物界面体系的迁移率记录，且其载流子面密度大范围灵活可调。本项目中，我们将探索提高ZnMgO/ZnO界面2DEG电学性能的可行方法，澄清四方相铁酸铋极化对称性，阐明四方-三方结构弛豫规律。在此基础上，构建铁电场效应晶体管原型器件，探寻抑制栅极漏电的途径，通过四方相铁酸铋极化翻转实现沟道电流的高效可逆调控。期望通过项目研究，深入理解铁电栅极调制2DEG的内在机理，为铁电非易失存储器的未来应用奠定基础。

通过铁电栅极调控氧化物异质界面二维电子气(2DEG)，为面向非易失存储的新一代铁电场效应晶体管发展提供了可能。但是，由于常用氧化物2DEG室温迁移率不理想及传统铁电体自发极化强度较低，其应用受到很大限制。为解决上述问题，本项目提出将四方相铁酸铋与ZnMgO/ZnO界面2DEG集成的研究方案。四方相铁酸铋具有迄今已知最大的自发极化强度，可对二维沟道实现高达1×10^15/cm^2的静电掺杂浓度。另一方面，ZnMgO/ZnO界面2DEG迁移率远远大于其它的氧化物2DEG系统。通过项目实施，我们提高了ZnMgO/ZnO界面2DEG迁移率，研究了四方相铁酸铋极化对称性，阐明了四方相到三方相的结构弛豫规律。在此基础上，构建了铁电场效应晶体管原型器件，利用四方相铁酸铋极化翻转实现沟道电流的可逆调控。此外，我们实现了大厚度三方相Hf0.5Zr0.5O2外延薄膜与ZnO的外延集成，并利用对称性失配及带电氧空位的引入解释了其稳定存在的原因。此外，我们还证实了将Hf0.5Zr0.5O2/ZnO(ZnMgO/ZnO)体系用于非易失存储器构建的可能性。我们提出了基于氧空位迁移的HfO2基材料非内禀铁电机理，并基于其设计了新型的Si基场效应存储器件。利用该机理，我们成功解释了唤醒（wake-up）、劈裂（split-up）、耐久性差、瞬态负电容等一系列与器件应用密切相关的实验现象。通过项目研究，为高速、高集成度、高可靠性非易失存储器的发展奠定基础。