Chemical insight into origin of forming-free resistive random-access memory devices

We demonstrate the realization of a forming-step free resistive random access memory (RRAM) device using a HfO(x)/TiO(x)/HfO(x)/TiO(x) multilayer structure, as a replacement for the conventional HfO(x)-based single layer structure. High-resolution transmission electron microscopy (HRTEM), along with electron energy loss spectroscopy (EELS) analysis has been carried out to identify the distribution and the role played by Ti in the RRAM stack. Our results show that Ti out-diffusion into the HfO(x) layer is the chemical cause of forming-free behavior. Moreover, the capability of Ti to change its ionic state in HfO(x) eases the reduction-oxidation (redox) reaction, thus lead to the RRAM devices performance improvements. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3645623]