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

The influence of electrodes on unipolar switching characteristics of a Pt/HfO
₂
/Pt resistor with symmetric electrodes is investigated by comparing the reset voltage (V
_R
), set voltage (V
_S
), current at low resistance state (I
_LRS
) and high resistance state (I
_HRS
), and I
_LRS
/I
_HRS
with positive and negative voltage polarities. The values of ±V
_R
and ±V
_S
of the Pt/HfO
₂
/Pt resistor for respective positive and negative polarities are very similarly distributed. Concerning current levels at two resistance states (I
_LRS
and I
_HRS
), however, unexpected asymmetric current characteristics of the Pt/HfO
₂
/Pt symmetric resistor are observed. The asymmetric current behavior at the symmetric Pt/HfO
₂
/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/HfO
₂
and HfO
₂
/Pt, are analyzed using X-ray photoelectron spectroscopy. The bottom interface of HfO
₂
/Pt, postprocessed with insulating HfO
₂
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.