Oxide Heterojunction Applied In Resistive Random Access Memory

Recently, the research work on RRAM devices with oxide heterostructures demonstrates their superior performance over single-layer based devices, including improved cycling, nonlinear switching, and complementary resistive switching (CRS) behavior to prevent internal parasitic circuit in devices. Furthermore, the oxide heterostructures as switch cells allow the role of each layer and interface on the switching characteristics. So there are more degrees of freedom for device optimization compared to conventional approaches of trying to obtain several functionalities in a single layer device. In this thesis, three kinds of oxide heterostructures have been investigated, including inOur main research works are as follows:(1) The effect of oxide/oxide interface for controlling the migration process of oxygen vacancies (or oxygen ions) on resistive switching behaviors has been investigated by fabricating the ZrO2ZnO oxide heterostructures. Completely different resistive switching behaviors are observed in the heterostructures with a set process under a different bias polarity. It is demonstrated that the change of the oxide/oxide interface barrier height determining the migration of oxygen vacancies (or oxygen ions) leads to the current direction-dependent resistive switching. Furthermore, the ZnO/ZrO2heterostructure with the homogeneous resistive switching behavior could be potentially applied as a controllable and stable multistate memory by controlling reset-stop voltages. Our method opens up an opportunity to explore the resistive switching mechanism and develop resistance switching devices with specific functions through engineering oxide/oxide interfaces in oxide heterostructures.(2) We successfully prepared the electromagnetic PPy composite films with different contents of Co NPs by electrochemical depositing. The magnetism and resistive switching behavior of Co nanoparticles dispersed polypyrrole (PPy) composite films is studied. A novel design method for Resistive Random Access Memory (ReRAM) is proposed. The conducting polymer films with metal nanocrystals (NCs) dispersed carbon chains induce the spontaneous oxidization of conducting polymer at surface. The resistive switching behavior is achieved by an electric field controlling the oxygen ion mobility between metal electrode and conducting polymer film to realize the mutual transition between intrinsic conduction (low resistive state) and oxidized layer conduction (high resistive state). Furthermore, the formation process of intrinsic conductive paths can be effectively controlled in the conducting polymer ReRAM by using metal NCs in films, because the inner metal NCs induce electric-field lines converging around them and the intensity of the electric field at the tip of NCs can greatly exceed that of the other region. Metal NCs can also bring new characteristics for ReRAM, such as magnetism by dispersing magnetic metal NCs in polymer, to obtain multifunctional electronic devices or meet some special purpose in future applications. Our works will enrich the application fields of the electromagnetic PPy composite films and present a novel material for ReRAM devices.(3) A novel resistive random access memory device is designed with SrTiO3/La2/3Sri/3MnO3/MgAl2O4/Cu structure, in which metallic epitaxial La2/3Sr1/3MnO3(LSMO) is employed as the bottom electrode rather than traditional metal materials. In this device, the critical external compliant current is no longer necessary due to the high self-resistance of LSMO. The LMSO bottom electrode can act as a series resistor to offer a compliant current during the set process. Besides, the device also has excellent switching features which are originated in the formation of Cu filaments under external voltage. Therefore it provides the possibility of reducing power consumption and accelerating the commercialization of resistive switching devices.