$\hbox {HfO}_{x}/\hbox {TiO}_{x}/\hbox {HfO}_{x}/ \hbox {TiO}_{x}$ Multilayer-Based Forming-Free RRAM Devices With Excellent Uniformity

In this letter, a significantly improved uniformity of device parameters (for cycle-to-cycle uniformity within one device and device-to-device uniformity), such as set voltage, reset voltage, and HRS and LRS resistance distributions, is successfully demonstrated on HfO_x/TiO_x multilayer (ML)-based resistive switching devices, as compared with HfO_x-based single-layer device. In addition, the reported ML devices are free from forming process, which is greatly beneficial from the viewpoint of RRAM circuit operation. It is believed that both the Ti doping effect and the confinement of conduction filament within different dielectrics layers contribute to the improvement.