Impedance spectroscopic analysis on effects of partial oxidation of TiN bottom electrode and microstructure of amorphous and crystalline HfO2 thin films on their bipolar resistive switching

Abstract

The electrical resistance switching (RS) properties of amorphous HfO₂ (a-HfO₂) and crystalline HfO₂ (c-HfO₂) thin films grown on a TiN substrate via atomic layer deposition were examined using DC current–voltage (I–V) sweep and AC impedance spectroscopic (IS) analyses. The rapid thermal annealing of the a-HfO₂ film at 500 °C under a N₂ atmosphere for 5 min crystallized the HfO₂ film and induced an interfacial TiON barrier layer. The a-HfO₂ sample showed fluent bipolar RS performance with a high on/off ratio (∼500), whereas the c-HfO₂ sample showed a much lower on/off ratio (<∼10), but its switching uniformity was better than that of a-HfO₂. Such critical differences can be mainly attributed to the absence and presence of the TiON barrier layer in the a-HfO₂ and c-HfO₂ samples, respectively. The AC IS especially enabled the resistance states of the HfO₂/Pt interface and the HfO₂/TiN interface to be separately examined during one complete switching cycle of each sample. Although the Pt/c-HfO₂ interface has a Schottky barrier in the pristine state, it disappeared once the c-HfO₂ was electroformed and was not recovered even after the reset step. In contrast, the Pt/a-HfO₂ interface partly recovered the Schottky barrier after the reset.