金属氧化物半导体阻变存储器中的磁性开关效应研究

Weak room temperature ferromagnetism in 3d elememt doped and undoped metal-oxide semiconductor has become a bottleneck for its application in spintronic devices. As the next generation of non-volatile memory, resistive switching (RS) effect induced by electric-field in metla-oxide semiconductor films has recently attracted intensive attention. Magnetic switching during RS is of significance for the low power and high density non-volatile memory devices and spintronic devices. Considering that the resistance and the magnetism of this material are related to each other, in this project, we study magetic switching induced by electric field during RS. We’ll prepare ZnOx、TiOx、HfOx films with and without 3d elements doping using PLD technique under different oxygen pressure and investigate the change of the magnetism (magnetic switching) during RS using semiconductor measurement system and physical property measurement system (PPMS). We’ll study the migration and distribution of the oxygen vacancy during RS using X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometer (EDS) and scanning probe microscopy (SPM). Combined with the first principles calculations, we’ll investigate the influence of the distribution of oxygen vacancy and 3d element on the formation of conductive filaments and the magnetic switching during RS. This work will reveal the relationship between RS and magnetic switching and clarify its mechanism. This project is expected not only to break through the bottleneck of the weak room temperature ferromagnetism in this materials, but also to play a positive role on the origin of the RS and magnetism and their correlation.

3d元素掺杂及零掺杂的金属氧化物半导体材料由于室温铁磁性弱成为制约其在自旋电子学应用的瓶颈；作为下一代非挥发性存储器，外电场调控的氧化物半导体薄膜的阻变(RS)效应备受关注。如能在RS的同时伴随磁性的开关效应，则对实现高集成度、低能耗的新型存储器和自旋电子器件意义重大。本课题从磁性与电性关联的视角，研究该类材料RS存储器中外电场调控的磁性开关效应。在不同氧压下采用PLD制备3d元素掺杂及零掺杂的ZnOx、TiOx、HfOx薄膜，利用半导体测量设备和PPMS研究RS特性与磁性开关效应的关联规律；利用分层XPS,截面EDS,SPM等技术研究RS过程中氧空位的迁移和分布规律；结合第一性原理计算，研究氧空位分布和3d元素掺杂对导电细丝的形成和RS过程中磁性开关效应的影响，揭示二者关联的物理机制。该研究不仅有望突破该类材料铁磁性弱的瓶颈，同时有助于揭示阻变和磁性的起源及其关联的物理机制。

一、项目背景：.3d元素掺杂及零掺杂的金属氧化物半导体材料由于室温铁磁性弱成为制约其在自旋电子学应用的瓶颈；作为下一代非挥发性存储器，外电场调控的氧化物半导体薄膜的阻变(RS)效应备受关注。该项目研究3d元素掺杂及零掺杂的氧化物薄膜阻变过程中的磁变现象。.二、主要研究内容：.以3d元素掺杂及零掺杂的ZnOx、TiOx、HfOx等为介质层，研究其RS特性与磁性开关效应；研究RS过程中氧空位（Vo）的迁移和分布规律；结合第一性原理计算，研究Vo分布和3d元素掺杂对导电细丝的形成和RS过程中磁性开关效应的影响，揭示物理机制。.三、重要结果、关键数据及其科学意义：.1. Vo在电场作用下易于集中在掺杂元素附近并与掺杂离子之间产生交换作用从而极大地提高了薄膜的室温铁磁性和磁变比率。施加正电场时零掺杂的TiO2薄膜的磁矩只有31.5µemu，为制备态的2.9倍。而Co:TiO2在施加正电场时的磁矩达到67.3µemu，为该薄膜制备态的3.6倍。.2.采用第一性原理研究了3d元素X(X=Mn, Fe, Co, Ni)掺杂对ZnO基阻变存储器中Vo迁移势垒和形成能的影响。计算表明Ni掺杂使ZnO中Vo的形成从0.854减小到了0.307eV。实验发现Ni掺杂ZnO器件的Set和Reset电压约为0.24V和0.34V，比未掺杂器件减少了80%和38%..3. Hf/HfO2/Pt器件的磁变比率达到四倍多，操作电压只有0.4/0.3V。我们认为Hf与氧结合的吉布斯自由能较高以及Hf离子与O离子的双离子迁移对器件阻变和磁性开关效应的改善起到了关键的作用。.4. 3d元素的掺杂有利于电场下Vo在迁移的过程中向3d元素聚集，进而影响Vo的迁移和重新分布，从而对室温铁磁性起到了关键的作用。正向电场下Ni:ZnO，Mn:TiO2和Co:TiO2的磁矩分别达到了19.7，63.6和39.3µemu，分别是制备态的5.0倍，3.2倍和2.5倍。