The Study Of Three Dimensional (3D)Vertical Resistive Switching Memory: Characteristics, Mechanisms And Integration

Three-dimensional (3D) integration and multi-level cell(MLC) are two attractive technologies to achieve ultra-high density for mass storage applications. In the first part study of this paper, a three layer 3D vertical AlOδ/Ta2O5-x/TaOy resistive random access memory are fabricated and characterized. The vertical cells in three layers show good uniformity and high performance:more than 1000×HRS/LRS windows, more than 1010 endurance cycles, longer than 104s retention times at 125℃.Meanwhile, four level MLC is demonstrated with two operation strategies, current controlled scheme (CCS) and voltage controlled scheme (VCS).The switching mechanism of 3D vertical RRAM cells is studied based o temperature-dependent transport characteristics.After the success of fabrication 3D RRAM device unites, the realization of 3D RRAM arrays will be directly used in the industrial product applications. There are two critical challenges which determine the array density of 3D RRAM:1)the scaling limit in both horizontal and vertical directions;2)the integration of selector devise in 3D structure. In the second part study of this paper, we present novel 3D RRAM structure using one dimensional material-carbon nanotube(CNT), as one electrode is demonstrated. The electrical results reveal that the RRAM devices could switch normally with a CNT integrated electrode at nanometer scale. Especially, due to metal Sc and CNT contact forms near-ohm contact, the Ⅰ-Ⅴ curve of this TaOy-CNT-Sc device is nearly similar to that of the same type normal device. Simultaneously, benefited from the asymmetric carrier transport induced by Schcottky barrier at metal/CNT and oxide/semiconducting CNT interfaces, a selector built-in 3D RRAM structure using semiconducting CNT as one side electrode is successfully fabricated and characterized.