Impact of device size and thickness of Al₂O₃ film on the Cu pillar and resistive switching characteristics for 3D cross-point memory application

Impact of the device size and thickness of Al₂O₃ film on the Cu pillars and resistive switching memory characteristics of the Al/Cu/Al₂O₃/TiN structures have been investigated for the first time. The memory device size and thickness of Al₂O₃ of 18 nm are observed by transmission electron microscope image. The 20-nm-thick Al₂O₃ films have been used for the Cu pillar formation (i.e., stronger Cu filaments) in the Al/Cu/Al₂O₃/TiN structures, which can be used for three-dimensional (3D) cross-point architecture as reported previously Nanoscale Res. Lett.9:366, 2014. Fifty randomly picked devices with sizes ranging from 8 × 8 to 0.4 × 0.4 μm² have been measured. The 8-μm devices show 100% yield of Cu pillars, whereas only 74% successful is observed for the 0.4-μm devices, because smaller size devices have higher Joule heating effect and larger size devices show long read endurance of 10⁵ cycles at a high read voltage of -1.5 V. On the other hand, the resistive switching memory characteristics of the 0.4-μm devices with a 2-nm-thick Al₂O₃ film show superior as compared to those of both the larger device sizes and thicker (10 nm) Al₂O₃ film, owing to higher Cu diffusion rate for the larger size and thicker Al₂O₃ film. In consequence, higher device-to-device uniformity of 88% and lower average RESET current of approximately 328 μA are observed for the 0.4-μm devices with a 2-nm-thick Al₂O₃ film. Data retention capability of our memory device of >48 h makes it a promising one for future nanoscale nonvolatile application. This conductive bridging resistive random access memory (CBRAM) device is forming free at a current compliance (CC) of 30 μA (even at a lowest CC of 0.1 μA) and operation voltage of ±3 V at a high resistance ratio of >10⁴.