Resistive switching characteristics of sol-gel derived La₂Zr₂O₇ thin film for RRAM applications

Amorphous La₂Zr₂O₇ thin films were fabricated using the sol-gel method and the bipolar resistive switching behavior of the metal(Al or Ti)/LZO/ITO devices were systematically investigated. The effect of film thickness, top electrodes, and post-annealing treatment conditions on the RS characteristics of the La₂Zr₂O₇ thin films were also discussed. The film thickness increases significantly as the number of spin-coating layers increases, leading to a higher operation voltage and fewer switching cycle times. In addition, the RS properties of the devices are affected by the work function difference between the top and the bottom electrodes. All devices exhibited similar conduction mechanisms, which are described by the ohmic conduction in the low resistance state and space-charge limited current in the high resistance state. Moreover, the RS performance can be profoundly improved by the post-annealing treatment because of the formation of a thicker AlO_x interface layer between the Al and LZO thin films, which was revealed via TEM images. The optimized RRAM performances are 1971 cycle times and high stable retention time for over 10⁵ with a R_on/R_off ratio of around 10¹ at a post-annealing temperature of 300°C. The multilevel RS performances are also observed. Besides, this device maintained a large enough memory window in the retention test at 85°C thermal stress. The longer life is to be expected.