Non-Volatile Giant Resistance Switching in Metal-Insulator-Manganite Junctions
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Non-Volatile Giant Resistance Switching in Metal-Insulator-Manganite Junctions
Rickard Fors, Sergey I. Khartsev and Alexander M. Grishin Condensed Matter Physics, Royal Institute of Technology SE-164 40 Stockholm-Kista, SWEDEN ABSTRACT Heteroepitaxial CeO2(80nm)/L0.67Ca0.33MnO3(400nm) film structures have been pulsed laser deposited on LaAlO3(001) single crystals to fabricate two terminal resistance switching devices. Ag/CeO2/L0.67Ca0.33MnO3 junctions exhibit reproducible switching between a high resistance state (HRS) with insulating properties and a semiconducting or metallic low resistance state (LRS) with resistance ratios up to 105. Reversible electrical switching is a polar effect achievable both in continuous sweeping mode and in the pulse regime.
INTRODUCTION In 2000, Liu et al. reported that Pr0.7Ca0.3MnO3/YBa2Cu3O7-δ heterostructures with Ag electrodes exhibited reversible, polarity dependent switching by application of short voltage pulses [1]. Subsequent work showed that most any perovskite could replace Pr0.7Ca0.3MnO3 (PCMO), that multilevel switching was feasible and that conventional CMOS technology could be used in fabrication [2-4]. The actual switching mechanism was later shown to be located on the Ag/PCMO interface, possibly due to ion migration, ruling out the initial idea that this is a bulk PCMO effect [5]. By introducing a doped insulating layer between the top metal and the conducting oxide, Beck et al. showed switching by pulsed, as well as by continuously applied voltage in junctions where the insulator is a perovskite. [6]. In our view, apart from their memory capabilities, all these structures thus involve oxide materials and have a metal-insulator-oxide build-up. To elucidate the roles of the conducting bottom layer and the insulating barrier in the family of two-terminal Resistance Random Access Memory (RRAM) devices we have fabricated and characterized novel metal/oxideinsulator/oxide-conductor (MOC) three-layer Ag/CeO2/La0.67Ca0.33MnO3/LaAlO3(001) structures exhibiting reproducible switching between a low resistance state (LRS) and a high resistance state (HRS) with resistance ratios up to 105. By inserting a very thick insulating CeO2 layer, 80 nm, we have succeeded to differentiate between interface and bulk effects in the insulator.
PROCESSING AND STRUCTURAL CHARACTERIZATION The fabrication of the test structures was carried out according to the outline below. Ceramic targets with the compositions La0.67Ca0.33Mn03 and CeO2 were ablated using a 248 nm KrF excimer Lambda Physik-Compex-102 laser with a radiation energy density of 5 J/cm2, a pulse repetition rate of 20 Hz and a substrate-to-target distance of 60 mm. The deposition onto the LaAlO3(001) (LAO) single crystal was carried out at an oxygen pressure of 250 mTorr, with a substrate temperature of 730 °C for LCMO and 750 °C for CeO2. The structure was finally post-
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annealed in situ at 400 mTorr oxygen for 10 minutes. Measured layer thicknesses were approximately 400 nm and 80 nm for LCMO and CeO2 respectiv
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