Forming-free flexible memristor with multilevel storage for neuromorphic computing by full PVD technique

Flexible resistive random access memory(RRAM) has shown great potential in wearable electronics.With tunable multilevel resistance states,flexible memristors could be used to mimic the bio-synapses for constructing high-efficient wearable neuromorphic computing system.However,the flexible substrate has intrinsic disadvantages including low-tempe rature tolerance and poor complementary metal-oxidesemiconductor(CMOS) compatibility,which limit the development of flexible electronics.The physical vapor deposition(PVD) fabrication process could prepare RRAM without requirement of further treatment,which greatly simplified preparation steps and reduced the production costs.On the other hand,forming process,as a common pre-programing operation in RRAM,increases the energy consumption and limits the application scenarios of RRAM.Here,a NiO-based forming-free RRAM with low set voltage was fabricated via full PVD technique.The flexible device exhibited reliable re sistive switching characteristics under flat state even compre s sive and tensile states(R=10 mm).The tunable multilevel resistance states(5 levels) could be obtained by controlling the compliance current.Besides,synaptic plasticities also were verified in this device.The flexible NiO-based RRAM shows great potential in wearable forming-free multibit memo ry and neuromorphic computing electronics.

Polarization readout analysis for multilevel phase change recording by crystallization degree modulation

Four different states of Si15Sb85 and Ge2Sb2Te5 phase change memory thin films are obtained by crystallization degree modulation through laser initialization at different powers or annealing at different temperatures. The polarization characteristics of these two four-level phase change recording media are analyzed systematically. A simple and effective readout scheme is then proposed, and the readout signal is numerically simulated. The results show that a high-contrast polarization readout can be obtained in an extensive wavelength range for the four-level phase change recording media using common phase change materials. This study will help in-depth understanding of the physical mechanisms and provide technical approaches to multilevel phase change recording.

Flexible 3D memristor array for binary storage and multi-states neuromorphic computing applications

The demand of flexible neuromorphic computing electronics is increasing with the rapid development of wearable artificial intelligent devices.The flexible resistive random-access memory(RRAM)is one excellent candidate of highdensity storage devices.However,due to the limitations of fabrication process,materials system and device structure,it is difficult to prepare flexible 3D highdensity network for neuromorphic computing.In this paper,a 3D flexible memristors network is developed via low-temperature atomic layer deposition(ALD)at 130C,with potential of extending to various flexible electronics.The typical bipolar switching characteristics are verified in RRAM units of 3D network,including first,second and third layers.Besides binary storage,the multibit storage in single unit is demonstrated and the storage density is further increased.As a connection link between binary storage and brain-inspired neuromorphic computing,the multibit storage capability paves the way for the tunable synaptic plasticity,for example,long-term potentiation/depression(LTP/LTD).The 3D memristors network successfully mimicked the typical neuromorphic functionality and realized ultra-multi conductance states modulation under 600 spikes.The robust mechanical flexibility is further demonstrated via LTP/LTD emulation under bending states(radius=10 mm).The 3D flexible memristors network shows significant potential of applications in high-performance,high-density and reliable wearable neuromorphic computing system.