Nanoscale resistive switching in ultrathin PbZr0.2Ti0.8O3-La0.7Sr0.3MnO3 bilayer

Abstract

Electric switching of ultrathin ferroelectric films is vital for electronic elements such as multiferroic tunnel junctions, but the large required field may induce ionic motions as addressed here. Unipolar current–voltage (I–V) characteristics of ultrathin (3 nm) PbZr0.2Ti0.8O3 (PZT) grown on La0.7Sr0.3MnO3 (LSMO) by pulsed laser deposition have been investigated in an ambient-condition force microscope. Topographic changes have been recorded after the I–V measurements. No ferroelectric switching is found, but resistive switching with features in agreement with earlier work on similar perovskite titanates. The onset of hysteretical I–V loops is correlated with a clear height increase in the contacted area under the Pt-covered tip. The onset voltage of 4.5 V (−2.5 V) for positive (negative) tip bias is clearly different for the two voltage polarities. The observed height changes after applying electrical voltage reveal a volume expansion that must be attributed to chemical changes in both the PZT and the LSMO layers. A fast and a slow process of ionic motion or electrochemical reaction contributing to the observed features is identified. The slow one occurs at negative voltage, causes very large height increase, and is hypothetically attributed to processes following the electro-splitting of the adsorbed surface water.