Field-induced resistive switching in metal-oxide interfaces

Abstract

We investigate the polarity-dependent field-induced resistive switching phenomenon driven by electric pulses in perovskite oxides. Our data show that the switching is a common occurrence restricted to an interfacial layer between a deposited metal electrode and the oxide. We determine through impedance spectroscopy that the interfacial layer is no thicker than 10 nm and that the switch is accompanied by a small capacitance increase associated with charge accumulation. Based on interfacial I − V characterization and measurement of the temperature dependence of the resistance, we propose that a field-created crystalline defect mechanism, which is controllable for devices, drives the switch.Recent observation of room-temperature resistive switching driven by electric fields in various perovskite oxides has garnered attention due to the potential for nonvolatile memory applications. This fieldinduced resistive switch has been reported in several compounds. 1,2,3,4,5,6 The switching observed shares several features: a moderate switch speed; an altered resistance inconsistent with the well-accepted bulk resistivity; and a sensitivity to surface treatments. Various models have been put forth, but inconsistencies remain. For instance, bulk charge ordering in Pr 0.7 Ca 0.3 MnO 3 (PCMO) has been suggested, but this creates an apparent conflict with both the spatial symmetry and the reported bulk properties.1 Although interface models have been proposed involving either lattice defects or carrier concentration, 2,5,7 the exact nature of this interface remains vague. We therefore investigate the interface properties associated with the resistive switch and have observed: a) the switching is a common phenomenon to the metal-oxide interfacial layer; b) the interfacial transport properties are rather different from that of the bulk; c) the interfacial resistance is dominated by the carrier trapping with no indication of Schottky barriers; and d) the capacitance of the interfacial layer, on the order of 1000 nF/cm 2 , changes with switching, which is indicative of a change in the space-charge. These observations can be self-consistently understood using a carrier-trapping model and suggest that the field-induced switch is not restricted to a small class of materials. Therefore, the potential for controlling this phenomenon for device applications is considerable.Ceramic samples synthesized by standard solid-state reactions were determined to be single-phase based on X-ray powder diffraction patterns taken on a Rigaku DMAX-IIIB diffractometer. PCMO thin films were ac sputtered on LaAlO 3 substrates at 760• C in an Ar:O 2 = 2 : 3 mixed atmosphere at 140 mTorr. The films were found to be highly epitaxial. Pt leads were attached to the ceramic samples using Ted Pella Leitsilber 200 Ag paint. The thin film samples received sputtered Ag electrodes to which Pt leads were also attached using Ag paint.Ceramic LaCoO 3 , La 0.7 Ca 0.3 MnO 3 , Pr 0.7 Ca 0.3 MnO 3 , SrFeO 2.7 , RuSr 2 GdCu 2 O 3 , and YBa 2 Cu 3 O 7 were tested. We adopted ...

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