Leakage current behaviors of Al/ZrO2/Al and Al/YSZ/Al devices

The leakage current behaviors of Al/ZrO2/Al and Al/yttria stabilized zirconia (YSZ)/Al devices are investigated for resistive random access memory (RRAM) applications. A silicon oxide layer (450 nm) is first formed on a Si wafer by thermal oxidation. Onto it an Al bottom electrode (270 nm), a ZrO2 or YSZ nano-film (75 nm), and an Al top electrode (270 nm) are sequentially deposited by sputtering. These RRAM devices exhibit ohmic behaviors in the low-field region, while Schottky and Poole-Frenkel emissions take over in the high-field regions. Both the Schottky and trap barrier levels are decreased when monoclinic ZrO2 is replaced by cubic YSZ in the metal/oxide/metal structure. This is attributed not only to the higher symmetry crystal structure and lower binding energy of YSZ, but also to the formation of more oxygen vacancies and their re-distribution associated with yttria doping.