Young Jin Choi

Resistive Switching Behavior in Organic–Inorganic Hybrid CH3NH3PbI3−xClx Perovskite for Resistive Random Access Memory Devices

The CH3 NH3 PbI3- x Clx organic-inorganic hybrid perovskite material demonstrates remarkable resistive switching behavior, which can be applicable in resistive random access memory devices. The simply designed Au/CH3 NH3 PbI3- x Clx /FTO structure is fabricated by a low-temperature, solution-processable method, which exhibits remarkable bipolar resistive switching and nonvolatile properties.

Bifunctional resistive switching behavior in an organolead halide perovskite based Ag/CH3NH3PbI3−xClx/FTO structure

Organolead halide perovskite materials open up a new era for developing low-cost and high efficiency solar cells due to their simple and inexpensive fabrication process, superior light absorption coefficient, and excellent charge mobility. In addition to solar cells, hybrid perovskites have also seen dynamic advances with rapidly expanded applications to many other exciting fields including electronic and optical devices. Here, we demonstrate a new type of bifunctional resistive switching memory device based on a very simple bilayer structure of Ag and a CH3NH3PbI3−xClx perovskite material on an FTO substrate with both digital and analog resistive switching characteristics. The bi-stable resistive switching behavior with reliable endurance over 103 times and a retention time of 4 × 104 s demonstrates that the Ag/CH3NH3PbI3−xClx/FTO device can be a promising candidate for RRAM. In the low voltage sweeping region, surprisingly, analog resistive switching behavior with potentiation and depression characteristics was also observed, which can be useful in neuromorphic computing device applications. The possible Ag conducting filaments formed by redox reactions of the Ag electrode may play a key role in this newly observed resistive switching phenomenon.

Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters

We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.

Resistive switching characteristics of a compact ZnO nanorod array grown directly on an Al-doped ZnO substrate

ZnOs resistive switching properties have drawn much attention because ZnO has a simple chemical composition and is easy to manipulate. The propulsion mechanism for resistive switching in ZnO is based on a conducting filament that consists of oxygen vacancies. In the case of film structure, the random formation of the conducting filaments occasionally leads to unstable switching characteristics. Limiting the direction in which the conducting filaments are formed is one way to solve this problem. In this study, we demonstrate reliable resistive switching behavior in a device with an Au/compact ZnO nanorod array/Al-doped ZnO structure with stable resistive switching over 105 cycles and a long retention time of 104 s by confining conducting filaments along the boundaries between ZnO nanorods. The restrictive formation of conducting filaments along the boundaries between ZnO nanorods is observed directly using conductive atomic force microscopy.

Analog Memristive and Memcapacitive Characteristics of Pt-Fe 2 O 3 Core-Shell Nanoparticles Assembly on p + -Si Substrate

Analog memristive and memcapacitive switching characteristics were investigated in Pt-Fe2O3 core-shell nanoparticles (NPs) assembly on p+-Si substrate. The Ti/NPs/p+-Si structure exhibited gradually changing resistance (memristive) and capacitance (memcapacitive) at the same time as repeating the application of voltage with respect to the polarity of voltage. As applying negative voltage at top Ti electrode, the resistance decreased and the capacitance increased due to the increase of diffusion capacitance at n-NPs/p+ -Si junction. On the other hand, applying the positive voltage increased resistance and decreased capacitance by increasing depletion width at the junction. The polarity-dependent resistance and capacitance changes are thought to be ascribed to the charging of the NPs assembly that alters the potential of the assembly. The concurrent analog memristive and memcapacitive characteristics also emulated the biological synaptic potentiation and depression motions, which is indicative of potential application to neuromorphic devices as well as analog nonvolatile memory and circuits.

Memory Devices: Resistive Switching Behavior in Organic–Inorganic Hybrid CH3NH3PbI3−xClx Perovskite for Resistive Random Access Memory Devices (Adv. Mater. 40/2015)

Y. J. Choi, L. Wang, and co-workers report on page 6170 a new application of an organic-inorganic hybrid perovskite (CH3 NH3 PbI3-x Clx ) in a resistive random-access-memory device. The memory device has a very simple structure consisting of Au/CH3 NH3 PbI3-x Clx on conductive substrates, which exhibits a typical resistive-switching behavior and non-volatile properties with a low operating voltage, as well as good stability and reproducibility. This finding adds another important potential application of hybrid perovskites to their functionality library.

Resistive switching effect at boundary between film like grown ZnO nanorods

In this study, we demonstrate that the resistive switching phenomena mainly occur at the boundary between ZnO nanorods by forming conducting filaments along the boundary in Au/ZnO nanorods/AZO structure. Conducting atomic force microscope study was conducted to confirm the location of conducting path between ZnO nanorods. Furthermore, the reliable resistive switching behavior was obtained from well-aligned boundary by vertically and compactly grown ZnO nanorods on the Al doped ZnO substrate.