Construction Of Memristor Based On Hafnium Oxide And Its Conduction Mechanism

The human brain consists of many neurons connected by synapses that can perform sensory,learning and memory functions at the same time.Therefore,synapses are the main unit of biological brain,and the synthesis of artificial synapses similar to biological synapses is very important for the development of neural morphological computing system.Neural morphological computing system is a large-scale parallel system,which has been deeply studied and is expected to replace the traditional digital computing system.The memristor has the characteristics of high speed,low power consumption and easy compatibility with CMOS,so it has a wide application prospect in the fields of synapses simulation and realizing the integration of storage and calculation.This thesis focuses on the sandwich structure device Ta/HfOx/TiN,focusing on the effects of titanium intercalation and the preparation process of each functional layer on the performance of the device,and exploring the mechanism of conductance modulation.The main contents are as follows:First,the growth process of HfO₂ thin film is optimized by RF magnetron sputtering process,by changing the parameters such as oxygen partial pressure,sputtering power,sputtering film thickness and so on.The DC characteristics which are most consistent with the characteristics of the memristor are obtained by studying the step-by-step control variables.The surface morphology and growth thickness of the thin films were characterized and analyzed by means of atomic force microscope,ellipsometer and four-probe test system,and the electrical and synaptic properties of the devices were analyzed by semiconductor parameter analyzer.The results show that the process of synaptic excitation inhibition can be simulated in the pulse test,and the forward enhancement process is nonlinear,but the linearity of the reverse inhibition process can reach 98.4%;the tolerance of the device using ITO as electrode can reach6000 times.Second,on the basis of the initial simulation characteristics of the single-layer intercalation device,a new two-layer intercalation device structure,Ta/Ti/HfOx/Ti/HfOx/TiN,is further designed to obtain a better oxygen vacancy concentration distribution and more optimized device simulation characteristics.1.For hafnium oxide devices with different upper and lower thickness ratios,their properties are compared and analyzed,and better electrical characteristics are obtained:the device can simulate a good excitation suppression process;the linearity of conductance modulation is significantly improved,up to 98.4% in the positive direction and 98.1% in the negative direction.At the same time,the device symmetry and modulation amplitude have also been effectively improved.2.Combined with the electrical properties of the devices,the working mechanism of the multilayer devices is studied by means of high resolution transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).The double logarithm fitting of the device and the filament growth model of the device are completed,and the conduction process of the device is guessed reasonably,which proves the feasibility of improving the simulation characteristics of the device by changing the oxygen vacancy distribution in the device.