Study On Preparation And Device Properties Of Tantalum Oxide-based Thin Films By Reactive Magnetron Sputtering

Memristor,as an up-and-coming technology,is to achieve neuromorphic computing in hardware systems.As a memristor,resistive random access memory（RRAM）has begun to gradually take the place of the status of other memories in recent years,with rapid development,excellent performance and extensive research.With the appearance of the digital information era,information storage technology has developed rapidly,the resistive memory material in RRAM has also developed rapidly.RRAM has become the research focus in the storage field,owing to the advantages of lower power consumption,faster access speed,and stronger durability.Tantalum oxide（TaO_x）thin film has always been one of the best resistive switching（RS）layer materials for RRAM with the advantages of high dielectric constant,low leakage current density,high breakdown voltage and compatibility with current silicon processes.The oxygen concentration（O/Ta）,crystal structure and microscopic morphology of TaO_x film have a great influence on its RS performance,and the TaO_x-based bilayer structure exhibits excellent RS properties.In this paper,through the preparation of TaO_x thin film and its RRAM,the structure optimization of TaO_x film and the improvement of device performance are achieved from the the aspects of oxygen concentration,crystallinity,microstructure,electrode material,and double-layer structure,as well as the analysis of the RS mechanism.This paper mainly includes the following points:（1）TaO_x film with multiple crystal orientations was grown on Si substrate via reactive magnetron sputtering（RMS）,and the process parameters were constantly optimized.By changing the oxygen partial pressure in the coating atmosphere,TaO_x thin film with different O/Ta and microstructures was successfully prepared.The thin film characterization results show that the prepared crystalline TaO_x thin film has uniform distribution of elements,smooth and dense surface and high crystallinity.In addition,ITO film with different crystal orientations was prepared on Si substrates according to altering the oxygen partial pressure and the target-to-base distance.Then,the effect of ITO film on the growth of TaO_x film was investigated.The results show that ITO film would further increase the O/Ta of the TaO_x thin film,and also affect its element distribution and microstructure.（2）The Ta/TaO_x/ITO structure was prepared via RF-RMS,and the effect of TaO_x layers with different O/Ta on the RS performance of the device was studied.The results indicate that the TaO_xfilm with 25%oxygen partial pressure has the best crystallinity,and the Ta/TaO_x/ITO structure fabricated on this basis has the best electrical properties.Specifically,the thickness of the TaO_x layer is approximately 200 nm,the RS window size reaches 1.8×10³,and the turn-on voltage is 3.0 V.In order to further enhance the RS characteristics,different RS structures had been manufactured and researched.It was found that the Ta/TaO_x/ITO structure has lower switching voltage and power consumption,while the Ta/TaO_x/Pt/Ti structure has a larger switching window,according to different bottom electrodes.The conduction mechanism of the Ta/TaO_x/ITO structure is mainly attributed to the space charge limited current（SCLC）conduction mechanism and the conductive filament model formed by the abundant Ta⁵⁺in the top electrode and TaO_x layer.（3）Study on RMS preparation and performance optimization based on TaO_x-based bilayer structures.The set voltage and reset voltage of the Ta/Hf O₂/TaO_x/ITO structure is 2.0 V and-1.8 V respectively,and the switching window is only 10.However,the set and reset voltage of the Ta/Zn O/TaO_x/ITO structure is 2.0 V and-1.0 V respectively,and the switching window reaches about48.Therefore,the RS performance of the Ta/Zn O/TaO_x/ITO structure is better.In addition,The Ta/Zn O/TaO_x/Pt/Ti structure can reduce the set voltage to 0.5 V,and its storage window is about 10.The TaO_x dielectric layer thickness of the Ta/Zn O/TaO_x/Pt/Ti structure is reduced to 50 nm,and the structure shows excellent RS characteristics,with the set voltage of 1.6 V and switching window of10².The conduction mechanism of the Ta/Zn O/TaO_x/BE bilayer film structure is mainly based on the coupling between the oxygen vacancy filaments in the Zn O layer and the Ta⁵⁺conductive filaments in the TaO_x layer,as well as the conduction mechanism of SCLC.