Memristive Devices Based On Two-dimensional Materials With Phase Transition Mechanism And Bio-inspired Optoelectronic Multifunctions

In the big data era of with explosive data growth,tranditional digital computers based on von Neumann architecture is becoming increasingly inefficient due to the ever-increasing demand for data processing,especially in the artificial intelligence tasks,and there is an urgent need to develop new high-efficiency computing architecture.The human brain is a highly intelligent and efficient computing system that can achieve the integration of storage and computing.Therefore,constructing a bio-inspired neuromorphic computing system is one of the feasible paths to realize a high-efficiency computing.Fortunately,the emergence of memristor with inherent dynamics resembling biological synapses and neurons provides a feasible way to construct large-scale neuromorphic computing systems.However,the mainstream memristors reported rely on filamentary switching mechanisms,and they suffer from unavoidable cycle-to-cycle and device-to-device variability,which seriously hampers their practical applications.Moreover,some new functions are required in the face of optoelectronic interconnection in building optical neuromorphic computing systems.As an emerging semiconductor material,two-dimensional（2D）transition metal chalcogenides（TMDs）have many intriguing features,such as phase transition characteristics and multifunctional optoelectronic characteristics.Therefore,it is expected to solve the limitations in mechanism and meet new functional requirements in the devices based on 2D materials.This thesis focuses on memristive devices based on 2D TMDs,to realize fast and uniform resistive switching based on 2D phase transition mechanism,and multi-terminal optoelectronic synaptic functions.The main research results of this paper are as follows:In terms of mechanism,stable and ultrafast MoTe₂-based memristors are successfully fabricated.The phase transition of MoTe₂ between 2H and 1T’phases is observed in real time through in-situ Raman characterization.It is found that Te vacancies introduced by Ar plasma treatment can facilitate the implementation of phase transition of MoTe₂ through first-principles calculations.Based on this phase transition mechanism,the MoTe₂ device exhibits ultrafast switching（～5 ns for SET and～10 ns for RESET）and excellent environmental stability（negligible degradation in switching behaviors one year after preparation）.This MoTe₂ device surpasses most reported 2D-materials based memristive devices in switching performance and stability.Furthermore,memristor array is successfully fabricated based on large-area chemical vapour deposition MoTe₂ film.These devices show a yield of 80%,and initial resistance state,forming voltage,SET voltage and RESET voltage exhibit a narrow distribution,indicating that the devices have excellent uniformity.And it is estimated that the array size can be increased to 870×870 when the MoTe₂device is connected in series with the Pt/Ta O_x/Ti O₂/Ta O_x/Pt selector（with nonlinearity of over 10⁴）.Finally,the modulation of the device conductance is used to recognize MNIST handwritten digits through simulation,and the recognition rate can reach～90%.In terms of multifunctional optoelectronic regulation,we fabricate a three-terminal memristor based on MoS₂/p-Si vertical heterojunction and implement synergetic optoelectronic modulation of synaptic behavior.The device shows a stable volatile resistive switching under electrical stimuli,then versatile synaptic functions are successfully mimicked.Meanwhile,the device exhibits persistent photoconductivity（PPC）behavior under photonic stimuli and photonic synaptic functions are realized.Furthermore,optical-write electric-erase and photonic potentiation and electric habituation are successfully emulated through synergetic optoelectronic modulation.It is found that the volatile resistive switching originates from electrons trapping/detrapping at the MoS₂/Si O₂ interface.And it is confirmed that random localized potential fluctuations（RLPF）is the mechanism for PPC in the device,and the trap sites for the RLPF mechanism may come from the defects at the MoS₂/Si O₂ interface and sulfur vacancies in MoS₂.Furthermore,we fabricate a four-terminal device based on WO₃-WSe₂ planar heterojunction and implement multi-terminal optoelectronic modulation of synaptic behavior.The device shows a volatile resistive switching and two neuron-based synaptic functions are successfully emulated.Furthermore,the back gate and light can regulate the conductance of the device,which can be used to mimic the modulation effect of astrocytes on synaptic weight.Detailed electrical measurements,atmosphere experiment and Raman spectroscopy provide insights into the mechanism of memristive behavior,revealing that the protons insertion/extraction in the intermediate transition layer of WO_3-yaccount for the memristive behavior.