Study Of Memristor Based On The Interface Of Conductive Oxide/Metal

The human brain system is consisting of neurons which communicate with each other through synapses,forming a network with learning and memory abilities.With the rapid development of semiconductor integrated technology and artificial intelligence,human’s requirements for devices in storage and logic operations are getting higher and higher.If we can realize the electronic device with the basic synaptic function,and use it to construct the neural network processor,it will have a revolutionary influence on the computer hardware.Based on the above requirements,memristors are considered to be the most able to achieve digital information storage and simulation of synapses of electronic components.In this study,the metal（Al,Cr,Sm,Ti,Ag,Pt）and conductive oxide（ITO,Nb:Sr TiO₃）are used as the top electrode and the bottom electrode,respectively.The metal film is deposited by DC magnetron sputtering,and the memristor with the point contact structure is formed by the metal mask.By controlling the electrical parameters,electrode size and the method of vacuum annealing can produce the different resistance switching.In addition,the coexistence of the digital and analog characteristics of the metal/conductive oxide point contact memristor is also discussed.In sum,the main contents and results are as follows:（1）The inert metal/ITO point contact memristor is prepared at room temperature using DC magnetron sputtering.Through the I-V properties test,it is found that the device shows a bipolar resistive switching after an initiation process（0 V → +5 V → 0 V）.In the Ag/ITO memristor,the resistance range is controlled by changing the compliance current（10 m A,20 m A,40 m A,100 m A）,which confirming the presence of multilevel memory characteristics.The mechanism of the inert metal/ITO memristor is the migration of oxygen ion/oxygen vacancy under the influence of voltage which is exposed by the fitting of the I-V curve.（2）The active metal/ITO point contact memristor is prepared by depositing active metal（Al,Cr,Sm）on ITO.Electrical performance of Al/ITO shows that the sample has an asymmetric bipolar resistance switching behavior after the initiation process with the same range of scan voltage（0 V→+3 V→0 V→-3 V→0 V）.In order to control the interface of Al/ITO,the sample is annealed under the vacuum.And the I-V curve shows that a symmetrical bipolar resistance switching behavior without the initiation process.Compared with the unannealed sample,the annealed sample shows a lower working current and a higher ROFF/RON.And the annealed device exhibits more stable endurance performance（>150 cycles）and data storage（>104 s）.Finally,we reveal the existence of Al Ox in Al/TO interface by XPS and TEM.So we put forward the redox model of interface caused by the transportation of oxygen vacancy/oxygen ion.（3）The single crystal substrate Nb:Sr TiO₃ are used as the bottom electrodes（doping concentration 0.7 wt%,crystal plane orientation <100>）,and the Al/Nb:Sr TiO₃ point contact memristor is prepared by DC magnetron sputtering.The study of the sample shows that the I-V characteristics exhibits hysteresis,rectifying and nonlinear resistive switching under the effect of the interface layer and the schottky contact barrier.The cycle and retention test indicated that the device after vacuum annealing treatment（650 ℃,1 h）has a more stable data storage（>100 cycles,>104s）.The Al/Nb:Sr TiO₃ memristor shows multilevel memory characteristics by limiting the size of current and voltage.The HRTEM and EDS analysis revealed that the vacuum annealing treatment can control the rearrangement of oxygen vacancies in the Al/Nb:Sr TiO₃ interface,so it can realize the optimization of device performance.（4）The analog of memristors（Ag/ITO,Al/ITO,Al/Nb:Sr TiO₃）are tested by DC and pulse test modes.In the DC test mode and triangular wave signal,the relationship between the output current and time-dependent variables（the number of sweep cycles or,sweep rate,working time）are I exp（7）tAIt（8）0（10）（28）,thus showing the short-term memory characteristics of simulated neuronal synapses.Under the retention test of pulse mode and the constant voltage effect,the relationship between the output current and the working time is in agreement with Wickelgren’s law（（7）（8）ybl-（10）（28）tI 1）,thus showing long-term memory characteristics.So we have realized the coexistence of digital and analog of metal/conductive oxide memristors by different test methods.