[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Memristive devices are electrical resistance switches that can retain a state of internal resistance based on the history of applied voltage and current. These devices can store and process information, and offer several key performance characteristics that exceed conventional integrated circuit technology. An important class of memristive devices are two-terminal resistance switches based on ionic motion, which are built from a simple conductor/insulator/conductor thin-film stack. These devices were originally conceived in the late 1960s and recent progress has led to fast, low-energy, high-endurance devices that can be scaled down to less than 10 nm and stacked in three dimensions. However, the underlying device mechanisms remain unclear, which is a significant barrier to their widespread application. Here, we review recent progress in the development and understanding of memristive devices. We also examine the performance requirements for computing with memristive devices and detail how the outstanding challenges could be met.

Memristive devices for computing

http://sces.phys.utk.edu/mostcited/mc1_1114.pdf

Colossal Magnetoresistant Materials: The Key Role of Phase Separation

A wide variety of experimental results and theoretical investigations in recent years have convincingly demonstrated that several transition metal oxides and other materials have dominant states that are not spatially homogeneous. This occurs in cases in which several physical interactions-spin, charge, lattice, and/or orbital-are simultaneously active. This phenomenon causes interesting effects, such as colossal magnetoresistance, and it also appears crucial to understand the high-temperature superconductors. The spontaneous emergence of electronic nanometer-scale structures in transition metal oxides, and the existence of many competing states, are properties often associated with complex matter where nonlinearities dominate, such as soft materials and biological systems. This electronic complexity could have potential consequences for applications of correlated electronic materials, because not only charge (semiconducting electronic), or charge and spin (spintronics) are of relevance, but in addition the lattice and orbital degrees of freedom are active, leading to giant responses to small perturbations. Moreover, several metallic and insulating phases compete, increasing the potential for novel behavior.

http://science.sciencemag.org/content/sci/309/5732/257.full.pdf

Complexity in Strongly Correlated Electronic Systems

Organic semiconducting oligomers for use in thin film transistors.

Hole mobility in organic ultrathin film field-effect transistors is studied as a function of the coverage. For layered sexithienyl films, the charge carrier mobility rapidly increases with increasing coverage and saturates at a coverage of about two monolayers. This shows that the first two molecular layers next to the dielectric interface dominate the charge transport. A quantitative analysis of spatial correlations shows that the second layer is crucial, as it provides efficient percolation pathways for carriers generated in both the first and the second layers. The upper layers do not actively contribute either because their domains are smaller than the ones in the second layer or because the carrier density is negligible.

Spatially correlated charge transport in organic thin film transistors

We introduce a model that accounts for the bipolar resistive switching phenomenon observed in transition-metal oxides. It qualitatively describes the electric-field-enhanced migration of oxygen vacancies at the nanoscale. The numerical study of the model predicts that strong electric fields develop in the highly resistive dielectric-electrode interfaces leading to spatially inhomogeneous oxygen vacancies distribution and a concomitant resistive switching effect. The theoretical results qualitatively reproduce nontrivial resistance hysteresis experiments that we also report providing key validation to our model.

/pdf/mechanism-for-bipolar-resistive-switching-in-transition-3q5c9y8u92.pdf

Mechanism for bipolar resistive switching in transition-metal oxides

/pdf/mechanism-for-bipolar-resistive-switching-in-transition-3mthsk4r0j.pdf

Mechanism for bipolar resistive switching in transition metal oxides

A systematic study of phase separation effects in polycrystalline ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ obtained under different thermal treatments is reported. Samples with average grain size ranging from 200 to 1300 nm were studied. Magnetic and electrical measurements show quantitative differences among samples in their low-temperature behavior, indicating that the fraction of the ferromagnetic (FM) phase gradually decreases as the grain size increases. Percolation of the FM phase in samples with a small fraction of this phase suggests that grain boundaries play a distinctive role in the spatial distribution of coexisting phases. The defective structure at the grain surface could explain the local inhibition of the antiferromagnetic charge ordered phase, an effect that is gradually removed with increasing grain size. Qualitative agreement of the data with this description is found. This effect is also found to be highly dependent on the oxygen content of the samples and its spatial distribution.

Controlled phase separation in La 0.5 Ca 0.5 MnO 3

We investigate the electric-pulse-induced resistance switching in manganite systems. We find a "complementarity" effect where the contact resistance of electrodes at opposite ends show variations of opposite sign and is reversible. The temperature dependence of the magnitude of the effect reveals a dramatic enhancement at a temperature T*, below the metal-insulator transition. We qualitatively capture these features with a theoretical model, providing evidence for the physical mechanism of the resistance switching. We argue that doping control of the electronic state of the oxide at the interfaces is the mechanism driving the effect.

Pablo Levy

Papers

Spatially correlated charge transport in organic thin film transistors

Mechanism for bipolar resistive switching in transition-metal oxides

Mechanism for bipolar resistive switching in transition metal oxides

Controlled phase separation in La 0.5 Ca 0.5 MnO 3

Mechanism of electric-pulse-induced resistance switching in manganites.