Resistive Switching in Semimetallic SrIrO₃ Thin Films

Abstract

Local electrical properties, measured by conductive atomic force microscopy, of semimetallic SrIrO3 thin films are reported. The appearance of an Anderson-type metal-insulator transition (MIT) triggered by disorder and spatial localization due to film thickness reduction is analyzed, as well as their influence on the resistive switching behavior. For thin enough films (below ~3nm) samples are insulating with hysteretic I-V curves indicative of reversible resistive switching behavior between two states of clearly different resistance at room temperature. A Table of Contents entry: Disorder and spatial localization due to thickness reduction allow generating a metal-insulator transition in semimetallic SrIrO3 thin films. Below about 3 nm films are insulating with hysteretic I-V curves indicative of resistive switching behavior at room temperature. Current maps allow demonstrating the writing/erasing processes making evident the feasibility of the system for the implementation of Re-RAMs

Resistive switching in Strontium iridate based thin films

“…The nature of the MIT induced by reducing the film thickness has been previously elucidated by analyzing the temperature dependence of the resistivity of the fully insulating 2 nm thick sample. 27,40 The low temperature regime, up to about 40-45 K, is well described by using the Mott's variable range hopping (VRH) model: Lnσ ∝ 1/T 1/3 ,σ being the conductivity, 41 while the high temperature range is properly described by using the Arrhenius equation for thermal activation conduction ρ(T) = ρ 0 e (∆/k 𝐵 T) , ∆ being an activation energy (a value of 123 ~ 6 meV was obtained from the fit) and kB the Boltzmann's constant. Figure 2(b) shows, in typical Arrhenius plot, the quality of this fitting.…”

“…On the other hand, SrIrO3 thin films were grown by rf sputtering at 900ºC in 140 mTorr oxygen atmosphere as described elsewhere. 27 In order to achieve single Titerminated substrates with well-defined atomic steps, all STO substrates in this work were treated before the film deposition. The treatment consisted of a 10 min bath of ultrasounds in deionized water and a post-annealing of 2h at 1000ºC.…”

“…34 It has been observed that thin films of iridates, such as Sr2IrO4 or SrIrO3 possess a very sensitive surface. 26,27,35 The poor surface stability turns the C-AFM measurements more challenging since high electric fields should be applied between the tip and the iridate surface to obtain the desired switching. With the aim of protecting the films and stabilize the current, Pt nanoparticles were deposited in situ on some of the films after their growth.…”

“…21 Nevertheless, in this latter case, a MIT can be also triggered by tuning the compressive strain induced by the substrate or by reducing the film thickness, [22][23][24][25][26] although recent studies indicate the coexistence of disorder effects and electronic correlations leading to either disorder driven Anderson MIT or unconventional Mott-Anderson transition. 23,27 In this work we present a study of RS behavior in Srn+1IrnO3n+1 thin films of the n=1 phase ( hereafter SIO-214) and of the n=∞ phase (SIO-113) by means of local I-V curve measurements and current mapping, by using conductive atomic force microscopy (C-AFM). While SIO-214 films are insulating, SIO-113 films present semimetallic behavior but, for film thickness below ~ 3 nm an Anderson-type MIT i.e., induced by disorder, is triggered.…”

Low-temperature emergent neuromorphic networks with correlated oxide devices

“…Manganites ( 53 ) and cobaltates ( 54 ) also display properties that could potentially be tuned via light-ion doping, which could then be turned into random networks. Furthermore, recent work on 5 d iridates with strong spin−orbit coupling have displayed resistive switching ( 55 ), which could be used in spin-torque oscillators that also provide neuromorphic functionalities ( 56 ).…”