The Fabrication And Properties Of Hf_0.5Zr_0.5O₂ Thin Film Resistive Switching Memory Devices

As one of the most potential candidates for the next-generation nonvolatile memory,the resistive random access memory?RRAM?has received increasing attention in recent years.Since the resistive switching storage medium plays an important role in the performance of RRAM,the switching properties and mechanisms of various thin film materials have been intensively investigated.However,the lack of relevant mechanisms remains obstacles for the applications of RRAM devices.In this work,the Hf_xZr_1-xO₂?HZO?-based thin film RRAM devices and the crossbar array were fabricated on various substrates by pulsed laser deposition?PLD?.The influence of the thin films deposition conditions on the resistive switching properties have been investigated,and the resistive switching mechanisms also have been analyzed.The main results are as follows:1 The influence of deposition conditions of the HZO thin films fabricated on Pt/Ti/SiO₂/Si substrates by PLD on the microstructure was studied.The results show that the HZO thin films deposited at room temperature were amorphous with a flat surface and dense structure.The HZO thin films were polycrystalline with the deposition temperature from 450?to 650?.The AFM image shows that the film with a flat surface and dense structure at 550?.Oxygen partial pressure also has significant influence on the crystallization of HZO thin films,and the films tend to formed a monoclinic phase of HfO₂ with lower oxygen partial pressure.2 The resistive switching characteristics of HZO thin films were investigated,and the I-V behavior,endurance,retention,operating voltage?current?,and operating speed were analyzed.It was found that the deposition temperature hardly have the influence on the resistive switching behavior,while the oxygen partial pressure and thickness had a great influence on it.With the decrease of oxygen partial pressure,the initial resistance of the films was getting lower,leading to a small ON/OFF ratio.Although the thickness of the films has no obvious effect on the resistive switching behaviors of the thin films,it has a great influence on switching properties.In the optimized process conditions,HZO thin film RRAM device shows a high ON/OFF ratio of over 1000 with no obvious degradation during 25,000 endurance cycles.3 The conduction mechanisms of HZO thin films fabricated with various oxygen partial pressure were analyzed.Although the devices fabricated with various oxygen partial pressure demonstrate the different conduction mechanisms,the resistive switching behaviors can be explained by the formation and rupture of the conductive filaments.The resistive switching behaviors are strongle dependent on the rupture of the conductive filaments,leading to the different Reset processes under unipolar and bipolar mode.The multi-level resistive switching in HZO thin films also has been studied.Although the multi-level resistive switching has different behaviors in unipolar and bipolar mode,that can be explained by the uniform multiple conduction filaments model.4 The flexible HZO thin film resistive switching devices on PET and paper substrates were fabricated,and their resistive switching characteristics were analyzed.The results show that the deposition process of HZO films at room temperature can be transferred to the flexible substrates,realizing the fabrication of flexible HZO thin film RRAM devices.The resistive switching characteristics of the flexible HZO thin films were related to the oxygen partial pressure during the deposition processes.The devices demonstrated the typical bipolar and unipolar resistive switching behaviors with low and high oxygen partial pressure,respectively.The flexible RRAM devices revealed good electrical performance and switching properties,which can meet the requirements for application.5 Application potentials of HZO thin film RRAM devices were studied.The RRAM devices based on crossbar array and 1-diode-1-resistor?1D1R?integrated structure were fabricated with MEMS process.The sneak path has an obvious effect on the resistive switching performance of the device cells in the crossbar array structure,which significantly reduce the switching ratio.The diode in the 1D1R structure also has a very important effect on the device switching ratio.The high access resistance significantly degrades the resistive switching properties.The results indicate the direction for the application of HZO thin film RRAM devices.