Reversible modification of electrical properties at the nanoscale level in bilayer oxide systems

Abstract

We report the results of experimental study of resistive switching effects in heterogeneous oxide systems based on bilayers with different sequences of two oxide layers (TiO2 and Al2O3) by means of tunnelling atomic-force microscopy (AFM). These systems demonstrate a bipolar resistive switching. Moreover, the resistance state of metal-insulator-metal capacitors with TiO2/Al2O3 bilayers can be electrically tuned over seven orders of magnitude. To elucidate a possible influence of nanoscale characteristics of these bilayers on the parameters of both bipolar resistive switching and electrical tuning of the resistance state, electrical properties of TiO2/Al2O3 bilayers with different thicknesses of the top Al2O3 layer and Al2O3/TiO2 bilayers were investigated. The presence of more conductive anatase crystallites in the amorphous phase of TiO2 layer was experimentally observed only for TiO2/Al2O3 bilayers. Measurements of the current distribution justify the reversible formation of conductive areas in the top Al2O3 layer located directly above the anatase crystallites, under the voltage application between the AFM tip and the bottom electrode of the structure. These conductive areas could be switched back into the high resistive state by application of bias voltage of reverse polarity.