Quantum Mechanical Simulation of Defect Migration and Phase Transition Dynamics Unterlying Resistive Switching in TiO2

忆阻器是无源电子元件，其欧姆电阻可以通过外部施加的电流在不同的稳定状态之间切换。由于这些状态保持稳定，即使外部电流被切断，忆阻器特别适合取代闪存单元，用作非易失性存储器。电阻式随机存取存储器（RRAM）存储单元将比复杂的基于晶体管的闪存更便宜、更小。然而，技术上相关的氧化物材料记忆行为的微观机制到目前为止还没有被很好地理解，无法进行基于知识的工程。由于缺乏对电阻开关机制的基本理解，阻碍了RRAM器件的改进。实验数据表明，在由缺氧氧化物材料制成的忆阻器中，导电细丝的形成和溶解与缺氧相关缺陷的迁移有关。在TiO2中，氧原子的迁移和空位被认为是至关重要的，这是一个特别的技术兴趣。本课题将对外部电场和温度梯度驱动下TiO2中点缺陷迁移动力学进行原子分辨量子模拟，同时对TiO2−x中氧空位有序进行动态模拟。为了实现基于知识的RRAM工程，需要建立缺氧TiO2电阻开关机制的经验模型。

Memristors are passive electronic elements, the ohmic resistance of which can be switched between different stable states by an externally applied current. Because these states remain stable, even if the external current is switched off, memristors are especially suitable to replace flash memory cells for use as nonvolatile memory. Resistive random access memory (RRAM) memory cells would be significantly cheaper and smaller than complex, transistor based flash memory. However, the microscopic mechanisms underlying the memristive behavior of technically relevant oxide materials are so far not understood well enough to allow knowledge-based engineering. The improvement of RRAM devices is hindered by a lack of basic understanding of the resistive switching mechanism. Experimental data indicate that in memristors manufactured from oxygen deficient oxide materials, conducing filaments are formed and dissolved, connected to the migration of oxygen deficiency related defects. In TiO2, which is of particular technological interest, the migration of oxygen atoms and vacancies is assumed to be of crucial importance. In the proposed project, atomically resolved quantum simulations of the dynamics of point defect migration in TiO2 under the driving forces of external electric field and temperature gradients shall be pursued together with dynamic simulations of oxygen vacancy ordering in TiO2−x. An empirical model of the resistive switching mechanism in oxygen deficient TiO2 shall be developed to enable knowledge based RRAM engineering.