Photoelectric Neuromorphological Device Based On Molybdenum Disulfide

Today,with the high development of information technology,big data,artificial intelligence,Internet of things and other technologies are widely used in people’s daily life,and the information transmission between various terminals is becoming more and more frequent.In the face of such huge information processing,the traditional computer based on von Neumann architecture memory computing separation mode has faced great challenges.Its disadvantages of slow speed and high power consumption are becoming increasingly prominent.The neuromorphological device based on memory computing integration is expected to solve this problem.As a representative of transition metal chalcogenides,molybdenum disulfide has excellent electrical and optical properties and low power consumption.In recent years,it has also been used in the research of neuromorphological devices.Based on molybdenum sulfide,a transition metal chalcogenide compound,molybdenum sulfide back gate field effect transistor was prepared on hafnium oxide substrate.Its electrical and optical properties were studied.An artificial synaptic device based on molybdenum sulfide transistor structure was prepared,and the plasticity of synapse was simulated.The main contents of this paper include the following aspects.(1)Through the chemical vapor deposition system,the preparation method of large-size molybdenum sulfide single crystal film was explored.A single-layer molybdenum sulfide crystal with the size of 70 microns was prepared in a one inch quartz tube with molten glass as the substrate.The results show that the molybdenum sulfide grown by chemical vapor deposition system is a high-quality monolayer.A new dry transfer process is developed:the dry transfer technology of PMMA photoresist is used to realize the transfer technology which is nondestructive and efficient for materials and can be applied to any substrate.Hafnium oxide dielectric films with a thickness of 18.8 nm were prepared by atomic layer deposition system.The dielectric constant is about 18.The hafnium oxide dielectric films have good withstand voltage.The back gate device of molybdenum sulfide was prepared by laser direct writing lithography on a single-layer molybdenum sulfide transfer hafnium oxide substrate.Under the condition of vacuum and room temperature,the corresponding channel length is 4 microns,the carrier mobility is 16.2 cm~2/V·s,and the switching ratio of the device is as high as 10~8.The optical performance of molybdenum disulfide is further studied.The optical test is carried out with visible light with different power densities with wavelengths of 450 nm and 532 nm in vacuum and normal temperature environment.From the transfer characteristic curve,it can be seen that the device has obvious photocurrent after applying light.This research also lays a foundation for the next work.(2)A transistor based on hafnium oxide gate dielectric and molybdenum sulfide was prepared,and the function of neural synapse was simulated.Firstly,the short-term plasticity of synapse was simulated.Using visible light with wavelength of450 nm and optical power density of 0.107 m W/cm~2,the time of light pulse was changed by 10,20,30,50,100,200,300,500,800 and 100 ms.the excitatory postsynaptic current EPSC increased with the increase of pulse time.Changing the optical power density of 0.193,0.318,1.43,3.50 and 39.0 m W/cm~2,the excitatory postsynaptic current EPSC of the device gradually increased with the increase of light intensity.The double pulse facilitation behavior of synapse was simulated.The light pulse time was 200 ms.the time interval between the two pulses was changed by 200,600,800,3000 and 4000 ms.the difference between the two pulse peaks became smaller and smaller with the increase of time interval.The values of double pulse facilitation(PPF)were 80.11%,41.95%,37.79%,23.53%and 21.81%,which reflected the dependence of short-range synaptic plasticity on time interval.In addition,the variable synaptic plasticity is simulated.By changing the number of light pulses to 5,20 and 30,with the increase of the number of light pulses,the device simulates the transformation of synapse from short-range plasticity to long-range plasticity,reflecting the dependence of synaptic plasticity on the number of light pulses.These research works not only improve our understanding of the growth of two-dimensional materials and two-dimensional material devices,provide help for exploring new materials and technologies to continue Moore’s law,but also show the development prospect of two-dimensional materials in the field of brain like neural networks in the future.