HfOx基薄膜微观结构缺陷及其电致电阻转变机制研究

In recent years, HfOx-based resistive random access memory (RRAM) has been attracted increasing attention as the next-generation nonvolatile memory due to its compatibility with the CMOS process. The oxygen vacancies and elements doping have been reported to be the key factors which influence the resistive switching characteristics of HfOx films. However, the switching mechanism for a HfOx-based RRAM device is still uncertain, which limits the practicality of the RRAM devices. In this project, the effects of the oxygen vacancies and the elements doping on the resistive switching characteristics of HfOx films will be investigated. The main contents include three parts as follows: (1) The nonstoichimetric HfOx thin films will be deposited on ITO substrates. The concentration and the structure of oxygen vacancies, and the defect energy levels of HfOx films will be analyzed. The main study point is the influence of oxygen vacancies on the carrier transportation in HfOx films. (2) The addition of different elements doping into HfOx thin films will be investigated. The chemical structure of doped ions in the film, the defect energy levels introduced by the doped ions, the coupling effects between the doped ions and oxygen vacancies and the influence of doped ions on the carrier transportation in HfOx films are the main research contents. (3) The effects of temperature, light and electrical field on the performance of HfOx-based resistive switching devices will be studied systematically. The internal connection between the carrier transportation and resistive switching characteristics will be revealed. Based on the experiment results, the physical models show the effects of oxygen vacancies and elements doping on the resistive switching mechnism of HfOx thin films will be established. This research provides theoretical guidance in improving the storage characteristics of HfOx-based RRAM devices.

HfOx基阻变存储器因其工艺兼容性，被认为是下一代存储技术的关键器件。研究表明，氧空位和元素掺杂是影响HfOx薄膜电阻转变特性的关键因素，但其机理尚不清楚,制约了RRAM存储器的实用化。本项目将系统研究氧空位和元素掺杂与HfOx薄膜电阻转变特性的内在定量关系，主要包括：（1）研究不同化学计量比HfOx薄膜中氧空位的浓度、结构和引入的缺陷能级，重点分析氧空位对薄膜载流子输运特性的影响规律；（2）对HfOx薄膜进行不同元素掺杂，分析杂质元素在薄膜中的分布特性和引入的缺陷能级，研究掺杂元素与氧空位的耦合作用关系，和对薄膜载流子输运特性的影响规律等；（3）系统研究温度、光照等外界条件对不同氧空位浓度和不同元素掺杂HfOx薄膜阻变特性的影响规律，揭示薄膜载流子输运特性和阻变特性的内在关联，最终建立氧空位和元素掺杂影响HfOx薄膜电阻转变特性的微观物理模型，为提高HfOx薄膜的存储特性提供理论指导。

随着传统Flash存储器技术限制的临近，阻变存储器（RRAM）以制备简单、操作电压低、读写速度快、存储密度高等优势获得了工业界和学术界的广泛关注。HfO2薄膜具有稳定的化学结构和电学性能，在CMOS器件中可以用作高k栅介质材料，制备工艺较为成熟，这些优点使其成为RRAM器件阻变层材料的最有力竞争者。目前，基于HfO2薄膜阻变存储器件的研究已经取得了较大的进展，然而其电阻转变机理仍不清楚，电阻转变参数还不稳定，这些都成为制约其应用的关键因素。本项目系统研究了不同元素掺杂对HfO2薄膜微观结构和电阻转变特性的影响，重点研究了基于掺杂HfO2薄膜阻变存储结构单元的载流子输运特性，揭示了不同元素掺杂对薄膜电阻转变特性的影响机理，获得的主要研究成果如下：.（1）在HfO2薄膜中掺入适量的Au，可以增加薄膜中氧空位的浓度；Cu/HfO2: Au/Pt MIM结构表现为双极电阻转变特性，其电阻转变机制为电子通过氧空位跃迁而产生的导电细丝，在适量Au掺杂浓度时，MIM结构具有较低的set电压，较好的保持特性和耐受性。.（2）在HfO2薄膜中掺入Cu会导致氧化铜的生成，增加薄膜中氧空位的浓度；Cu/HfO2: Cu/n+Si结构表现为双极电阻转变特性，其载流子输运特性符合SCLC效应，其中Cu金属细丝和氧空位细丝共同作用于电阻转变行为；此外，Cu掺杂可以减小MIM结构的set电压，明显提高MIM结构的保持特性和电阻转变参数的均一性。.（3）HfO2薄膜中氧空位浓度随着Ti掺杂量的增加而增加；Cu/HfO2: Ti/Pt结构表现为双极电阻转变特性，其载流子输运机制符合受缺陷控制的SCLC效应，阻变行为主要是由于薄膜中电子在氧空位之间的跃迁导致。随着Ti掺杂浓度的增加，MIM结构的set电压减小，且Ti掺杂明显提高了样品电阻转变参数的稳定性。.结果表明，掺杂的HfO2薄膜非常有潜力应用于非挥发性阻变存储器件中。本项目的研究结果可为RRAM的实际应用提供理论指导。