Resistive switching characteristics of HfO<sub><i>x</i></sub>-based resistance random access memory under photoelectric synergistic regulation

Abstract

Cu/HfO<sub><i>x</i></sub>/Pt and Cu/HfO<sub><i>x</i></sub>-ZnO/Pt resistance random access memory (RRAM) devices are prepared by magnetron sputtering. The results show that the Cu/HfO<sub><i>x</i></sub>/Pt device has the stable bipolar resistive switching characteristics, good retention (as long as 10<sup>4</sup> s), and a switching ratio greater than 10<sup>3</sup>. The current conduction mechanism of HfO<sub><i>x</i></sub> device is ohmic conduction at low resistance, while space charge limited current (SCLC) mechanism dominates at high resistance, and the conductive filament is composed of oxygen vacancies. Owing to the low content and random distribution of oxygen defects in the HfO<sub><i>x</i></sub> film, the endurance and uniformity of the device are poor. Compared with HfO<sub><i>x</i></sub> device, HfO<sub><i>x</i></sub>-ZnO device exhibits lower operating voltage and better uniformity and stability. The main reason is that ZnO material has smaller formation energy of oxygen vacancy, which can produce more oxygen defects under electric field to participate in the resistive switching behavior of the device, thereby reducing the operating voltage and improving the uniformity of the device. In addition, owing to the existence of the interface between HfO<sub><i>x</i></sub> and ZnO film, the random distribution of oxygen defects is inhibited, that is, the random fracture and formation of conductive filament are inhibited, which is beneficial to improving the uniformity of the device. In addition, the resistive switching behaviors of Cu/HfO<sub><i>x</i></sub>/Pt and Cu/HfO<sub><i>x</i></sub>-ZnO/Pt RRAM devices under different intensities of 255 nm ultraviolet illumination are studied. For Cu/HfO<sub><i>x</i></sub>/Pt device, the light of 255 nm wavelength shows little effect on its resistive switching characteristics. For the Cu/HfO<sub><i>x</i></sub>-ZnO/Pt RRAM device, the operating voltage and stability of the device can be improved by increasing the light intensity. Although the switching ratio of the device decreases with the increase of light intensity, the device can exhibit multiple resistance states by adjusting different light intensities to achieve multi-level storage. Finally, the analysis of the <i>I</i>-<i>V</i> curves of the devices indicates that the two types of devices show similar resistive switching mechanisms under the illumination of light or no light, which can be explained by the resistive switching mechanism of oxygen vacancy conductive filament. Therefore, a physical model based on the oxygen vacancy conductive filament is established to explain the resistive switching behavior of the device in this paper.