Fabrication And Performance Study Of Photoelectric Synaptic Device Based On Two-dimensional Material Heterojunction

Due to the advent of the information age,computing systems with higher performance and lower energy consumption are urgently needed in the fields of AI,big data,and the IOT.The traditional von Neumann architecture has flaws in information processing and storage.Researchers turned their attention to neural mimicry computing,that is,by simulating the most efficient computing system in nature,the human brain,to greatly improve the computer's computing efficiency and achieve intelligence,such as autonomous learning and thinking skills.To realize the great concept of neural mimicry,our primary goal is to prepare a new type of device that can simulate biological synapses in structure and function-that is,synaptic devices.Since the concept of neural mimicry was proposed,synaptic devices have made some progress,but they still face problems such as insufficient bandwidth and signal crosstalk.With the introduction of optical signals,optoelectronic synaptic devices can effectively solve the above problems.As two-dimensional semiconductor materials with excellent photoelectric performance,MoS₂ and GaSe have been widely used in the field of photoelectric detection.In this paper,we first prepared a MoS₂/GaSe heterojunction and applied a pulsed laser signal to successfully simulate biological synaptic behavior.In the follow-up work,the electrical pulse signal was simultaneously applied to the back-gate photoelectric synaptic device based on the MoS₂/GaSe heterojunction to realize the biological synapse function simulation.In this paper,the MoS₂/GaSe heterojunction is used to prepare a wide-spectrum fast-responsive optoelectronic synaptic device,the main research contents are as follows:?1?ITO/MOS2/GaSe/ITO grating type photoelectric synaptic devices were prepared by mechanical lift-off,maskless laser direct writing lithography,solution etching,etc.,and were characterized using Raman,atomic force microscope,etc.,Confirming the successful stacking of the heterojunction.Through the self-built test system,the volt-ampere characteristics and photoelectric response of the device were first studied.Among them,the volt-ampere characteristic curves of a single two-dimensional material are all linear,and under a 5V bias voltage,the photocurrent is extremely small,only 10-2nA Magnitude,and the photocurrent of the heterojunction is improved by 2 to 3 orders of magnitude and exhibits rectification characteristics,in which the forward voltage is about 0.4V.The mechanism is analyzed by the electronic energy band structure of the heterojunction,and the test proves that both are in ohmic contact with ITO.Under illumination,the electrons and corresponding holes excited by the top of the valence band cross the reduced barrier under the action of the source-drain electric field to form a larger photocurrent.Later on,a laser pulse signal was applied to obtain the post-synaptic excitation current?EPSC?.Under the 520nm laser with a power of 5mW and a duration of 1s,the EPSC response time had a rise time of 33ms and a fall time of 20ms.The relationship between EPSC and the wavelength,intensity,duration,and frequency of the stimulus signal was studied by changing the corresponding pulse parameters.Among them,under 405nm,450nm,520nm,635nm,and 808nm lasers,the device has a stable photocurrent of about 60nA,and the photocurrent gradually decreases as the wavelength increases.This is related to the increase in the absorbance with the wavelength rise.As the laser intensity,duration and frequency increase,the photocurrent also gradually increases and gradually saturates,based on the explanation of the photoconductor theory,this is because the number of photogenerated carrier pairs increases with the above parameters However,the gradual increase and the gradual increase and the simultaneous increase of the compound rate cancel each other out.Furthermore,the device can simulate the filtering characteristics of biological synapses,long-term synaptic plasticity?LTP?and double pulse facilitation?PPF?.Compared with existing synapse-like devices,it has wider signal bandwidth,faster response speed and avoids crosstalk between electrical signals.?2?By mechanical stripping,reverse photolithography process,magnetron sputtering and other methods,a back-gate optoelectronic synapse device based on MoS2/GaSe van der Waals heterojunction was prepared on SiO2 substrate,and the source and drain electrodes were made of gold.By applying electrical stimulation pulse signals on the back grid and supplemented by laser irradiation,the device's transition to short-term synaptic plasticity?STP?to biological characteristics of the synaptic filter and the double pulse Facilitate the simulation of functions.The working mechanism of the device is analyzed.With the application of positive/negative bias on the back gate,the energy band at the contact interface between SiO2 and MoS2 is bent,and the accumulation/depletion of holes is caused,which in turn increases the source-drain current./Decrease.Simultaneously synaptic peak time plasticity?STDP?was simulated by applying photoelectric pulse stimulation signals simultaneously.In this section,the defect that the device can only use a single optical input signal is optimized.The photocoupled mixed input mode is more in line with the actual situation of biological synapses,and can achieve more complex prominent behaviors,such as STDP.