Research On Characteristics Of H-BN-Based Memristors

A memristor is a passive electronic device with a memory function.It has the dimension of resistance,but its memristance is closely related to the application history of the input current or voltage.The memristor is regarded as the fourth basic circuit element in addition to the resistor,the capacitor and the inductor.The memristor can play a huge role in many fields,especially in the research of computation and storage,and neural synaptic network.Therefore,it attracts increasing attention of researchers.As a new type of wide bandgap semiconductor materials,hexagonal boron nitride(h-BN)is one of the preferred materials for preparing memristors due to the excellent characteristics of high thermal conductivity and thermal expansion coefficient,strong thermal and chemical stability,and extremely high resistivity.However,so far,the hexagonal boron nitride has been seldom used in the fabrications of memristors,and there are relatively few reports in the literature.In this paper,we have developed two aspects of research,one deals with the simulations of the memristor characteristics;the other involves the fabrications of memristors based on h-BN two dimensional thin films,and the investigations of resistive switching mechanisms of the fabricated h-BN-based memristors.As for the simulations of memristor characteristics,firstly,the electrical characteristics of the HP memristor were analyzed and deduced,and the relationship between the memristance M(t)and the charge q(t) was obtained.According to this model,memristive characteristics were simulated based on matlab,and the I-V characteristic curve of the memristor was obtained.The I-V curve of the memristor exhibited hysteresis characteristics.As the frequency of the input signal increased,the hysteresis characteristic of the memristor became inconspicuous.Next,the equivalent circuit model of the memristor was designed based on the HP memristor model,and the I-V characteristic of the equivalent circuit model corresponds to that of the HP memristor.The designed equivalent circuit model was simulated based on PSPICE,and the I-V curve of the circuit was obtained.As the frequency of the input signal increased,the hysteresis characteristic of the equivalent circuit became insignificant,which was consistent with the results obtained by matlab simulation.Finally,based on the "Lab of electronics intelligence" platform,we carried out the simulation of analog circuit model for the HP memristor and the construction of the actual circuit,and the study in a nonlaboratory environment was developed combining the virtual instruments and actual devices.The other important research in this paper is the fabrications of h-BN-based memristor prototypes and the investigations of their memristive characteristics and resistive switching mechanisms.A metal-insulating layer-metal(MIM)vertical structure memristor was designed,and the semiconductor processes including evaporation and thermal annealing were used to prepare top electrodes.The circular electrode array was used as the top electrodes with two materials,Al and Au.The copper foil substrate of the h-BN thin film was used as the bottom electrode,which made the device preparation easier and reduced the influence of the process steps on the thin film.The experimental research of the memristive characteristics and the analysis of resistive switching mechanisms for the fabricated memristors were performed.Firstly,the sample with the structure of Al/h-BN/Cu was tested.The pre-forming process occurred at a bias voltage of1.09 V,and the I-V curve of the unipolar switching characteristic was obtained through the test.Based on many measurements,we have found that the reset voltage of the device was relatively stable,centered around 0.4V,while the set voltage was slightly unstable in comparison,and the floating range was 2.2V-2.8V.The memristive properties of the unipolar type were mainly related to the formation of conductive filaments in the dielectric material and the breakage of the conductive filaments caused by Joule heat.Next,the sample with a structure of Au/h-BN/Cu was tested,and the forming process occurred at an applied bias voltage of 4.7 V.The I-V curve of the bipolar switching characteristics was obtained by the subsequent tests,and the tested results showed good repeatability of the fabricated device.The fitted curves of I-V characteristics for the bipolar switching memristors were in good agreement with space charge limited current(SCLC)effect.According to the SCLC theory,it could be inferred that the bipolar resistive switching characteristics of the prepared memristors were mainly due to the process of electron capture and release by defects formed in the h-BN thin film.