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.

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.