Asymmetric Current Behavior on Unipolar Resistive Switching in Pt/HfO2/Pt Resistor With Symmetric Electrodes

Abstract

The influence of electrodes on unipolar switching characteristics of a Pt/HfO2/Pt resistor with symmetric electrodes is investigated by comparing the reset voltage ( $V_{R})$ , set voltage ( $V_{S})$ , current at low resistance state ( $I_{\mathrm{ LRS}}$ ) and high resistance state ( $I_{\mathrm{ HRS}})$ , and $I_{\mathrm{ LRS}}/I_{\mathrm{ HRS}}$ with positive and negative voltage polarities. The values of $\pm V_{R}$ and $\pm V_{S}$ of the Pt/HfO2/Pt resistor for respective positive and negative polarities are very similarly distributed. Concerning current levels at two resistance states ( $I_{\mathrm{ LRS}}$ and $I_{\mathrm{ HRS}}$ ), however, unexpected asymmetric current characteristics of the Pt/HfO2/Pt symmetric resistor are observed. The asymmetric current behavior at the symmetric Pt/HfO2/Pt resistor indicates the role of different environments at top and bottom interfaces, although they are formed with the same electrode material using the same deposition method. Two types of interfaces, Pt/HfO2 and HfO2/Pt, are analyzed using X-ray photoelectron spectroscopy. The bottom interface of HfO2/Pt, postprocessed with insulating HfO2 film deposition, is probed nonstoichiometric HfO x and weak oxidation of Pt electrode and is influenced by the variation of the current levels and the current ratio at both high and low resistance states.