Potential Fluctuation in RRAM Based on Non-Stoichiometric Hafnium Sub-Oxides

Abstract

We study the structure of nonstoichiometric HfOx films with variable composition using methods of XPS, spectroscopic ellipsometry, and ab initio calculations. According to XPS and optical absorption experiment data HfOx consists of metal Hf and ~10-15% of nonstoichiometric hafnium sub-oxide HfOy (y<2). HfOy can be placed between HfO2 and Hf, inside HfO2, inside Hf. According to this model space fluctuations of chemical composition cause space fluctuations of bandgap in HfOx. We found that transport in such electronic systems is described by percolation theory. This approach can be applied to explain LRS transport of HfOx-based RRAM.