Abstract
We report here on the presence of two different nonvolatile resistive switching mechanisms in Pt-Pr0.67Ca0.33MnO3-Pt sandwich structures based on pulsed electrical transport measurements. As a function of pulse length, amplitude and temperature, the devices show two different switching regimes. The first is positive switching (PS) where a high resistance state (HRS) evolves at positive bias at the top electrode in the voltage range of U ≈ 0.5–1.2 V and pulse lengths tp ≈ 10−7 s. In addition, we observe a cross over to negative switching (NS) for U > 1 V and tp ≈ 10−3 s. Here, the HRS evolves at negative bias applied at the top electrode. We present strong evidence that both switching mechanisms take place at the interface between Pr0.67Ca0.33MnO3 and the top electrode. Based on finite element simulations of the temperature evolution during the electrical pulses, we show that the onset of Joule heating is characteristic of the PS regime, whereas drastic temperature increases of several hundred Kelvin evolve during NS. Based on the observed different timescales, pulse amplitudes and temperature dependences of PS and NS, respectively, we suggest that two different switching mechanisms are involved: a fast, short range exchange of oxygen at the interface with the metallic electrode for PS and a slower, long range redistribution of oxygen in the entire PCMO film for the NS.
Highlights
A large variety of transition metal oxides embedded in metal electrodes exhibit nonvolatile resistance changes under external electric stimulation
The final resistance after each cycle is the sum of all previous switching processes and is, remarkably, almost constant for switching sequences which are symmetric with respect to the increase and decrease of applied pulse amplitude/length
The qualitative same R+/R− characteristics can be observed for alternating pulses with variable pulse length at fixed stimulation amplitude Uapp (figure 2(b))
Summary
A large variety of transition metal oxides embedded in metal electrodes exhibit nonvolatile resistance changes under external electric stimulation. This makes them possible candidates for resistive random access memory (R-RAM) applications [1, 2]. Pr1−xCaxMnO3 manganite thin films sandwiched by precious Pt electrodes exhibit both volatile and nonvolatile resistance changes Volatile resistance reductions are observed in electric fields due to driven polaron states with enhanced conductivity, both in bulk single crystals [5] as well as in lateral thin films geometry [6].The small polaron mobility is thermally activated. Due to Joule heating, can significantly reduce the resistance
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