Resistive switching in HfO2-based metal-insulator-metal structures for non-volatile memory

非易失性存储器（NVM）对于基于Si的CMOS技术内的若干应用（诸如高价值和移动的计算机、消费电子产品、传感器和医疗保健）具有高度兴趣。在现有的NVM技术中，通过施加电压来切换金属-绝缘体-金属（MIM）结构的电阻的电阻随机存取存储器（RRAM）是有希望的候选者。从众多的可切换材料中，我们选择了基于HfO 2的器件，因为这种材料已经集成到CMOS技术中。一个重要的问题是通过施加成形电压来控制导电细丝的感应。在目前的项目中，我们已经表明，对于强缺氧HfO 2-x几乎电铸自由设备可以实现。这些氧空位引起的费米边附近的导电缺陷态大大降低了形成电压。申请人新开发了一种在操作中测量技术，通过该技术，可以在现代同步加速器源PETRA III上通过硬X射线光电子能谱（HAXPES）来研究切换期间的微观结构和化学变化以及杂质（例如碳）的影响。在这个后续项目中，我们希望了解等价和异价替代元素如Zr 4+和La 3 +/Y 3+的影响。第一个实验表明，三价掺杂也降低了形成电压，并且可以获得具有更高开/关比的更稳定的器件。通过研究形成电压对器件面积的依赖性，并通过在操作中使用微（纳）束X射线吸收精细结构（µ-XAS），我们打算通过表征完整的MIM单元来实现对导电细丝的清晰理解。使用HAXPES和µ-XAS，将在操作中研究替代器械的疲劳机制，例如，为了通过材料科学方法稳定脉冲诱导开关。在材料建模领域的外部合作的支持下，我们希望了解可开关（Hf，X）O2-x（X = Zr，La，Y，Nb）的缺陷物理和化学以及与电极材料相关的界面，并将它们与合成参数和开关行为相关联。总之，我们的建议预计将作出根本性的贡献，以优化器件结构的HfO 2为基础的RRAM的材料科学和理解其疲劳行为。

Non-volatile memory (NVM) is of high interest for several applications within Si-based CMOS technology such as high-value and mobile computers, consumer electronics, sensors and medical health care. Among existing NVM technologies resistive random access memory (RRAM) where the resistance of a metal-insulator-metal (MIM) structure is switched by applying a voltage, is a promising candidate. From the large variety of switchable materials we have chosen HfO2-based devices since this material is already integrated into CMOS technology. One important issue is the controlled induction of conducting filaments by applying a forming voltage. Within the current project we have shown that for strongly oxygen deficient HfO2-x almost electroforming free devices can be realized. Conducting defect states in the vicinity of the Fermi edge induced by these oxygen vacancies reduce the forming voltage considerably. The applicants have newly developed an in operando measurement technique by which microstructural and chemical changes as well as the influence of impurities (such as carbon) during switching can be investigated by hard X-ray photoelectron spectroscopy (HAXPES) at the modern synchrotron source PETRA III. Within this follow-up project we want to understand the influence of isovalent and aliovalent substitutional elements as Zr4+ and La3+/Y3+. First experiments indicate that trivalent doping also reduces the forming voltage, and that more stable devices with higher on/off ratios can be obtained. By investigating the device area dependence of the forming voltage and by using in operando micro(nano)beam X-ray absorption finestructure (µ-XAS), we intend to achieve a clear understanding of the conducting filaments by characterizing the complete MIM-cell. Using HAXPES and µ-XAS the fatigue mechanisms of substituted devices will be studied in operando, e.g. in order to stabilize pulse-induced switching by material scientific approaches. Supported by an external collaboration in the field of materials modeling we want to understand the defect physics and chemistry of switchable (Hf,X)O2-x (X = Zr, La, Y, Nb) and the involved interfaces to the electrode materials and correlate them with synthesis parameters and switching behavior. In summary, our proposal is expected to make a fundamental contribution to the materials science of an optimized device structure for HfO2-based RRAM and to the understanding of its fatigue behavior.