Resistive switching (RS) device behavior is highly dependent on both insulator and electrode material properties. In particular, the bottom electrode (BE) surface morphology can strongly affect RS characteristics. In this work, Ru films with different thicknesses grown on a TiN layer by radical-enhanced atomic layer deposition (REALD) are used as an inert BE in TaOx-based RS structures. The REALD Ru surface roughness is found to increase by more than 1 order of magnitude with the increase in the reaction cycle number. Simultaneously, a wide range of RS parameters, such as switching voltage, resistance both in low and high resistance states, endurance, and so forth, monotonically change. A simplified model is proposed to explain the linkage between RS properties and roughness of the Ru surface. The field distribution was simulated based on the observed surface morphologies, and the resulting conducting filament formation was anticipated based on the local field enhancement. Conductive atomic force microscopy confirmed the theoretical expectations.
Keywords: ALD; RRAM; TaOx; resistive switching; ruthenium; surface roughness.