氧分压对Ni/HfO_x/TiN阻变存储单元阻变特性的影响

采用射频磁控溅射的方法,基于不同氧分压制备的氧化铪构建了Ni/HfO_x/TiN结构阻变存储单元.研究发现,随着氧分压的增加,薄膜表面粗糙度略有降低;另一方面,阻变单元功耗降低,循环耐受性能可达10~3次,且转变电压分布的一致性得到改善.结合电流-电压曲线线性拟合结果及外加温度测试探究了器件的转变机理,得出在低阻态的传导机理为欧姆传导机理,在高阻态的传导机理为肖特基发射机理,并根据氧空位导电细丝理论,对高低阻态的阻变机理进行了详细的理论分析.

Influneces of different oxygen partial pressures on switching properties of Ni/HfOx/TiN resistive switching devices

The HfO_x-based resistive random access memory (RRAM) has been extensively investigated as one of the emerging nonvolatile memory (NVM) candidates due to its excellent memory performance and compatibility with CMOS process. In this study, the influences of deposition ambient, especially the oxygen partial pressure during thin film sputtering, on the resistive switching characteristics are discussed in detail for possible nonvolatile memory applications. The Ni/HfO_x/TiN RRAMs are fabricated, and the HfO_x films with different oxygen content are deposited by a radio frequency magnetron sputtering at room temperature under different oxygen partial pressures. The oxygen partial pressures in the sputter deposition process are 2%, 4% and 6% relative to engineer oxygen content in the HfO_x film. Current-voltage (I-V) measurements, X-ray photoelectron spectroscopy, and atomic force microscopy are performed to explain the possible nature of the stable resistive switching phenomenon. Through the current-voltage measurement, typical resistive switching behavior is observed in Ni/HfO_x/TiN device cells. It is found that with the increase of the oxygen partial pressure during the preparation of HfO_x films, the stoichiometric ratio of O in the film is improved, the root mean square (RMS) of the surface roughness of the film slightly decreases due to the slower deposition rate under a higher oxygen partial pressure, and the high resistance state (HRS) current decreases. In addition, by controlling the oxygen content of the device, the endurance performance of the device is improved, which reaches up to 10³ under a 6% oxygen partial pressure. The HfO_x films prepared at a higher oxygen partial pressure supply enough oxygen ions to preserve the switching effect. As the oxygen partial pressure increases, the uniformity of the switching voltage is improved, which can be attributed to the fact that better oxidation prevents the point defects (oxygen vacancies) from aggregating into extended defects. Through the linear fitting and temperature test, it is found that the conduction mechanism of Ni/HfO_x/TiN RRAM device cells in low resistance state is an ohmic conduction mechanism, while in high resistance state it is a Schottky emission mechanism. The interface between TE and the oxide layer (HfO_x) is expected to influence the resistive switching phenomenon. The activation energy of the device is investigated based on the Arrhenius plots in HRS. A switching model is proposed according to the theory of oxygen vacancy conductive filament. Furthermore, the self-compliance behavior is found and explained.