A Research On Resistance Variation Characteristic And Simulation Of Synapses Based On Vanadium Oxide Material

Memristor,as the fourth kind of passive circuit basic device,has attracted wide attention from various research fields.Because of its low power consumption,simple structure,easy to be integrated,and resistance memory characteristics,memristor has become an ideal component of the future intelligent computer.Several research groups have used different materials to make memristors to simulate the biological activities of synapses.Vanadium oxide as a transition metal oxide got a lot of attention.Electrically-driven semiconductor-metal transition of polycrystalline VO₂ thin films has great application potential in smart window,light modulators,and neuromorphic computing.But the driving mechanism is still under debate.Moreover,the electrical properties of amorphous vanadium oxide?VO_x?are significantly dependent on the external field.This indicates that VO_x may be an excellent memristor material.The important role of joule heat in the phase transition was investigated in detail by regulating the heat exchange between VO₂ and the environment.Furthermore,a two-layer VO_x memristor device was prepared by controlling the oxygen flux in the sputtering process to simulate the synaptic functions.The main results are as follows:?1?We prepared polycrystalline VO₂ thin film on quartz substrate and silicon substrate,and we found the threshold voltage of cooled VO₂ is higher than the one of uncooled VO₂,when the phase transition occurs.The threshold voltage of the VO₂ film on the quartz substrate increased from 45V to 81.7V,while the phase transition voltage of the VO₂ film on the Si/SiO₂ substrate was 56.1V in the uncooled condition,but no phase transition occurred at 106V after we opened the refrigerator.This is attributed to the higher thermal conductivity of Si/SiO₂ and the cooling conditions can transfer the joule heat fast,which provably proves the important role of the joule heat in electrically-driven semiconductor-metal transition of polycrystalline VO₂ thin films.?2?We conducted synaptic simulation using a two-layer amorphous vanadium oxide structure.The resistance of the double-layer amorphous vanadium oxide was stable in the dc scanning test,and we simulated many activities,such as Long-term potentiation/depression?LTP/LTD?,paired pulse facilitation?PPF?and spike timing-dependent plasticity?STDP?.The results were consistent with biological neural activity with stable performance and high repeatability.?3?We have tested the forgetting phenomenon of the two-layer vanadium oxide memristor and proved that our sample has the characteristics similar to the human forgetting phenomenon.We proposed a method of auxiliary electrical signal pulse to modulate the forgetting curve,and effectively changed the relaxation time and memory retention percentage of the forgetting curve.