| The memristor has attracted extensive attention since its emergence,which is expected to open a new era for neuromorphic computing and digital logic.However,in the development process of memristor,devices in the fields of neurobionics,biomedicology and wearable electronics need to meet the requirements of small size,low power consumption and flexibility,which puts higher requirements on functional materials.In terms of materials,two-dimensional materials,as the representative of new materials,have many advantages such as optics,electronics,machinery,etc.,which is expected to solve the problems faced by memristors.Herein,different structures of memristors based on two-dimensional materials WS2 and MoTe2are fabricated and their memristor characteristics and physical switching mechanism are studied in this paper.Details are as follows:Firstly,A Pd/WS2/Pt structure is prepared by WS2.The device has good stability,the switching speed of the device is 13 ns（ON）and 14 ns（OFF）,the operating current is less than1μA and the switching energy reaching the level of femtojoules,which shows the excellent low-power characteristics of the device.In addition,the device successfully simulated the biological synaptic functions of spike timing dependent plasticity and paired pulse facilitation.Importantly,it is proposed that the generation of sulfur and tungsten vacancies and electron hopping between vacancies are dominantly responsible for the resistance switching performance.Through the calculation of density functional theory,it is shown that the defect states formed by sulfur and tungsten vacancies are in deep level,which can prevent the charge leakage,so it is beneficial to the application of this device in the field of low-power neuromorphic calculation.Secondly,the Pd/MoTe2/Pt device is prepared by using MoTe2.The device has a retention time of more than 6.4×104 s and I-V curves of 100 cycles are repeated.The ON voltage is concentrated between 0.28 V and 0.33 V,and the OFF voltage is concentrated between-0.12 V and-0.16 V,showing excellent storage performance.On this basis,Pd/MoTe2/Pd/PET devices with flexible substrate PET were fabricated.It was found that the devices still have excellent storage performance,and the bending radius of the devices reached 3 mm,the bending times were more than 5000 times,indicating that the devices had great application potential in the field of flexible wearable electronics.Finally,the Pd/HfO2/MoTe2/Pd/PET memristor was prepared by combining MoTe2 and HfO2.The device has gradual current characteristics,operating current with microampere-level,stable storage performance and can realize bidirectional conductance modulation.Importantly,the conductance of the device can still be modulated after a series of bending operations,and the biological synaptic functions such as PPF and STDP are simulated.In addition,X-ray photoelectron spectroscopy analysis showed that under the action of the electric field,HfO2film produced more oxygen vacancies and MoTe2 changed from the 2H phase to the highly conductive 1T′phase.Therefore,the electrons hopping between oxygen vacancies and the phase transition in MoTe2 are the main reasons for the conductance change of the device.This research shows that the combination of two-dimensional materials and oxides provides a platform to realize flexible and low-power memristors,and promotes the development of wearable artificial neuromorphic systems. |
