Resistive switching in oxides for nonvolatile memories and neuromorphic computing

Summary form only given. Resistive switching (RS) phenomena in oxides have received a large interest for ultra-scaled and high-density non-volatile memories, and many prototypes have been proposed at industrial level. Recently, RS have been also exploited for new type of applications, such as reconfigurable logic and synaptic electronics. In the latter field, the interest is towards RS devices which can be used to fabricate artificial synapses, able to emulate the synaptic functions of biological synapses, and to be integrated with standard CMOS circuits to build neuromorphic systems. These RS devices, also named memristive systems, are of particular interest due to their simple two terminal structure, low power operation, high-scalability, low thermal budget fabrication and, depending on material system, easy integration into CMOS based platform. This talk will first introduce the current state of the art and materials systems investigated for non-volatile memories as well as synaptic devices for neuromorphic circuits, highlighting the materials/device differences versus target application. Then, the talk will present our recent advancements on HfO2 and Al-doped-HfO2 based RS devices. The oxide layers (binary and doped oxides) are deposited by atomic layer deposition and the resistive switching properties are analysed from micro- to nanoscale. The fabrication of high-density and nanoscale HfOx-based memristive devices is achieved by block-copolymer lithography. Furthermore, in view of application of these devices as synaptic elements, the long term plasticity, as potentiation and depression typical of biological synapses, are characterized by various pulsed operation schemes. Special emphasis is given to programming algorithms based on a train of identical pulses. It will be shown that a careful choice of the pulse amplitude/pulse width combination is fundamental to achieve an analogue modulation of the device.