TiN/HfO2基铁电/β-Ga2O3存储结构的制备与界面调控研究

As the space science and space technology advances, greater demands are being placed on the service life of the ferroelectric field-effect transistor memory (FeFET) under a complex space radiation environment. Using β-Ga2O3 as a semiconducting channel and HfO2-based ferroelectric thin film as a gate dielectric provides a new pathway to improve the service life of FeFETs under a complex space radiation environment. An understanding of the interface-controlled mechanism is critical for realizing such FeFETs. Since physical properties and applications of ferroelectric materials are fundamentally determined by the ferroelectric domains and their dynamics, the studies on ferroelectric domain structures and their evolution in the MFS or MFIS structures would be crucial for clarifying the interface-controlled mechanism. In this project, we will study effects of buffer layer insertion and growth parameters of HfO2-based thin film on the microstructures of TiN/HfO2-based ferroelectric thin film/β-Ga2O3 structures, and uncover the mechanism for ferroelectric phase transition in the HfO2-based thin films. Meanwhile, ferroelectric domain structures and their evolution in the TiN/HfO2-based ferroelectric thin film/β-Ga2O3 structures will be studied, and thus the relationship among microstructures, ferroelectric domain structures and their evolution, and electrical properties could be derived. Therefore, the interface-controlled mechanism in the TiN/HfO2-based ferroelectric thin film/β-Ga2O3 structure could be elucidated.

航天技术的发展对铁电场效应晶体管存储器(FeFET)在复杂空间环境下的服役寿命提出了更高的要求。用HfO2基铁电薄膜作为存储介质，β-Ga2O3作为沟道材料，为长寿命FeFET的实现提供一种新的途径。理解界面调控作用机理是实现长寿命FeFET的必要前提。由于电畴结构及其演变是铁电材料及其应用的物理基础，所以研究铁电存储结构(MFS或MFIS)的电畴结构及其演变是理解界面调控作用机理的根本。基于此，本申请项目将通过研究缓冲层的插入和HfO2基薄膜生长工艺参数的变化对存储结构的微观结构的影响，揭示β-Ga2O3衬底上HfO2基薄膜中铁电相的形成机制。同时，通过对铁电存储结构中电畴结构及其演变进行研究，建立TiN/HfO2基铁电/β-Ga2O3存储结构的微观结构、电畴结构及其演变和电学性能之间的关联，从而阐明TiN/HfO2基铁电/β-Ga2O3存储结构的界面调控作用机理。

HfO2基铁电薄膜具有与先进CMOS(互补金属-氧化物-半导体)工艺兼容、可微型化潜力大等优点，为我国实现大容量铁电存储器的自主可控提供了机会。目前人们基本上认为HfO2的铁电性来源于正交相。然而，由于正交相比单斜相能量要高，所以在常温常压下正交相不能稳定存在。因此，弄清HfO2铁电相的形成机制和阐明HfO2基铁电存储结构的界面调控作用机理是实现HfO2基铁电存储器可控制备的关键。基于此，本项目主要针对HfO2基薄膜中铁电相的形成机制、HfO2基铁电存储结构的制备、HfO2基铁电存储结构界面调控作用机理开展了理论和实验研究，主要工作概括如下：(1)基于第一性原理计算与分子动力学模拟，发现氧空位、受主掺杂与氧空位构成的复合缺陷、压应变能够促进铁电相的形成，电场激活能使HfO2从极化沿面内方向的铁电相转变成极化方向垂直于应变平面的铁电相，并从电畴演化的角度揭示了HfO2铁电体极化翻转的微观机制。通过控制HfO2基薄膜中杂质浓度、氧空位浓度和晶粒尺寸，在顶电极的夹持作用下，制备出了性能较好的HfO2基铁电薄膜。(2)系统研究了不同氮化物电极材料、不同绝缘膜材料及其制备工艺参数对HfO2基铁电场效应晶体管(FeFET)存储窗口、保持性能和抗疲劳性能的影响，采用两种和与非门型闪存(NAND)阵列兼容(改变栅极脉冲幅值和宽度)的编程/擦除方法实现了HfO2基FeFET的多值存储，在85oC下4值(2-bit/cell)的保持性能外推可达10年；并基于HfO2基铁电薄膜的畴翻转动力学阐述了其FeFET多值存储的物理机制。(3)采用中带电压法对HfO2基FeFET的疲劳失效机理进行了系统的研究，发现HfO2基FeFET抗疲劳性能差的主要原因来源于氧化层陷阱电荷引起的中带电压漂移和由界面陷阱电荷引起的电压漂移，从而采用ZrO2种子层对FeFET栅结构中HfO2基铁电薄膜与Si衬底之间的界面进行了调控，改善了HfO2基FeFET的存储窗口和抗疲劳性能。最后，通过优化制备工艺，制备出了性能较好的Hf0.5Zr0.5O2/β-Ga2O3铁电存储结构和FeFET。