Forming-Free, Low-Voltage, and High-Speed Resistive Switching in Ag/Oxygen-Deficient Vanadium Oxide(VO)/Pt Device through Two-Step Resistance Change by Ag Filament Formation.

Forming-free, low-voltage, and high-speed resistive switching is demonstrated in an Ag/oxygen-deficient vanadium oxide (VO)/Pt device via the facilitated formation and rupture of Ag filaments. Direct current (DC) voltage sweep measurements exhibit forming-free switching from a high-resistance state (HRS) to a low-resistance state (LRS), called SET, at an average V of +0.23 V.

Enhanced linear and symmetric synaptic weight update characteristics in a Pt/p-LiCoO/p-NiO/Pt memristor through interface energy barrier modulation by Li ion redistribution.

Artificial synaptic devices have been extensively investigated for neuromorphic computing systems, which require synaptic behaviors mimicking the biological ones. In particular, a highly linear and symmetric weight update with a conductance (or resistance) change for potentiation and depression operation is one of the essential requirements for energy-efficient neuromorphic computing; however, it is not sufficiently met. In this study, a memristor with a Pt/p-LiCoO/p-NiO/Pt structure is investigated, where a low interface energy barrier between the Pt electrode and the NiO layer makes for a more linear and symmetric conductance change.

Nanoscale Vertical Resolution in Optical Printing of Inorganic Nanoparticles.

Direct optical printing of functional inorganics shows tremendous potential as it enables the creation of intricate two-dimensional (2D) patterns and affordable design and production of various devices. Although there have been recent advancements in printing processes using short-wavelength light or pulsed lasers, the precise control of the vertical thickness in printed 3D structures has received little attention. This control is vital to the diverse functionalities of inorganic thin films and their devices, as they rely heavily on their thicknesses.

Linear and symmetric synaptic weight update characteristics by controlling filament geometry in oxide/suboxide HfO bilayer memristive device for neuromorphic computing.

Memristive devices have been explored as electronic synaptic devices to mimic biological synapses for developing hardware-based neuromorphic computing systems. However, typical oxide memristive devices suffered from abrupt switching between high and low resistance states, which limits access to achieve various conductance states for analog synaptic devices. Here, we proposed an oxide/suboxide hafnium oxide bilayer memristive device by altering oxygen stoichiometry to demonstrate analog filamentary switching behavior.

Electroforming-free threshold switching of NbO -based selector devices by controlling conducting phases in the NbO layer for the application to crossbar array architectures.

Bipolar threshold switching characteristics, featuring volatile transition between the high-resistance state (HRS) at lower voltage than threshold voltage ( ) and the low-resistance state (LRS) at higher voltage irrespective of the voltage polarity, are investigated in the Nb(O)/NbO /Nb(O) devices with respect to deposition and post-annealing conditions of NbO layers. The device with NbO deposited by reactive sputtering with 12% of O gas mixed in Ar shows threshold switching behaviors after electroforming operation at around +4 V of forming voltage ( ). On the other hand, electroforming-free threshold switching is achieved from the device with NbO deposited in the reduced fraction of 7% of O gas and subsequently annealed at 250 °C in vacuum, thanks to the increase of the amount of conducting phases within the NbO layer.

Wide range modulation of synaptic weight in thin-film transistors with hafnium oxide gate insulator and indium-zinc oxide channel layer for artificial synapse application.

Wide range synaptic weight modulation with a tunable drain current was demonstrated in thin-film transistors (TFTs) with a hafnium oxide (HfO2-x) gate insulator and an indium-zinc oxide (IZO) channel layer for application to artificial synapses in neuromorphic systems. The drain current in these TFTs was reduced significantly by four orders of magnitude on application of a negative gate bias, then could be restored to its original value by applying a positive bias. The reduced drain current under negative biasing is interpreted as being caused by voltage-driven oxygen ion migration from the HfO2-x gate insulator to the IZO channel, which reduces the oxygen vacancy concentration in the IZO channel.

Analog Memristive Characteristics of Square Shaped Lanthanum Oxide Nanoplates Layered Device.

Square-shaped or rectangular nanoparticles (NPs) of lanthanum oxide (LaO) were synthesized and layered by convective self-assembly to demonstrate an analog memristive device in this study. Along with non-volatile analog memory effect, selection diode property could be co-existent without any implementation of heterogeneous multiple stacks with ~1 μm thick LaO NPs layer. Current-voltage (I-V) behavior of the LaO NPs resistive switching (RS) device has shown an evolved current level with memristive behavior and additional rectification functionality with threshold voltage.

Effect of the Bilayer Period of Atomic Layer Deposition on the Growth Behavior and Electrical Properties of the Amorphous In-Zn-O Film.

This study reports on the effect of a bilayer period on the growth behavior, microstructure evolution, and electrical properties of atomic layer deposition (ALD) deposited In-Zn-O (IZO) films, fixing the ALD cycle ratio of In-O/Zn-O as 9:1. Here, the bilayer period is defined as the total number of ALD cycles in one supercycle of In-O and Zn-O by alternately stacking Zn-O and In-O layers at a temperature of 220 °C. IZO films with a bilayer period from 10 to 40 cycles, namely, IZO[In-O/Zn-O = 9:1] to IZO[36:4], result to form an amorphous phase with a resistivity of 4.

Enhancement of cortisol measurement sensitivity by laser illumination for AlGaN/GaN transistor biosensor.

In this study, high electron mobility transistor (HEMT) device was used as an immuno biosensor to measure concentration of a stress hormone, cortisol, by using selective binding on cortisol monoclonal antibody (c-Mab). Also, the HEMT sensor was enhanced in its sensitivity through light illumination to generate photocurrent. The optical pumping could assist the biosensor to discriminate more detailed change, which could result in an increment of limit of detection (LOD) to 1.

Effect of nitrogen-doping on drain current modulation characteristics of an indium-gallium-zinc oxide thin-film transistor.

The effect of nitrogen-doping (N-doping) in an indium-gallium-zinc oxide (IGZO) channel layer on the analog, linear, and reversible drain current modulation in thin-film transistors (TFTs) with Al-top-gate/SiO/TaO/IGZO stack is investigated for potential application to artificial synaptic devices. The N-doped devices exhibit a more linear increase of drain current upon repeating positive gate biasing, corresponding to synaptic potentiation, while the undoped device shows a highly non-linear and abrupt increase of drain current. Distinct from the increase of drain current at positive biasing for potentiation, the decrease of drain current for depression behavior at negative biasing is found to be the same.

Analog Memristive Characteristics of Mesoporous Silica-Titania Nanocomposite Device Concurrent with Selection Diode Property.

A threshold resistive switching (RS) device concurrently demonstrating analog memristive property with mesoporous silica-titania (m-ST) nanocomposites is introduced in this study. The nanostructured m-ST layer in an Al/m-ST/Pt device was constructed by facile soft templating of evaporation-induced self-assembly (EISA) method to demonstrate nonlinear threshold RS behaviors accompanying with discrete synaptic characteristics along with adaptive motions. The EISA layer was composed of well-ordered mesopores (∼10 nm), where paths of electrical currents could be controllably guided and sequentially activated by repeated voltage sweeps.

Single- and double-gate synaptic transistor with TaO gate insulator and IGZO channel layer.

We demonstrate single- and double-gate synaptic operations of a thin-film transistor (TFT) with double-gate stack consisting of an Al-top-gate/SiO /TaO /n-IGZO on a SiO/n-Si-bottom-gate substrate. This synaptic TFT exhibits a tunable drain current, mimicking synaptic weight modulation in the biological synapse, upon repeatedly applying gate and drain voltages. The drain current modulation features are analog, voltage-polarity dependently reversible, and strong with a dynamic range of multiple orders of magnitude (∼10).

Synaptic behaviors of thin-film transistor with a Pt/HfO /n-type indium-gallium-zinc oxide gate stack.

We report a variety of synaptic behaviors in a thin-film transistor (TFT) with a metal-oxide-semiconductor gate stack that has a Pt/HfO /n-type indium-gallium-zinc oxide (n-IGZO) structure. The three-terminal synaptic TFT exhibits a tunable synaptic weight with a drain current modulation upon repeated application of gate and drain voltages. The synaptic weight modulation is analog, voltage-polarity dependent reversible, and strong with a dynamic range of multiple orders of magnitude (>10).

Synaptic characteristics with strong analog potentiation, depression, and short-term to long-term memory transition in a Pt/CeO/Pt crossbar array structure.

A crossbar array of Pt/CeO/Pt memristors exhibited the synaptic characteristics such as analog, reversible, and strong resistance change with a ratio of ∼10, corresponding to wide dynamic range of synaptic weight modulation as potentiation and depression with respect to the voltage polarity. In addition, it presented timing-dependent responses such as paired-pulse facilitation and the short-term to long-term memory transition by increasing amplitude, width, and repetition number of voltage pulse and reducing the interval time between pulses. The memory loss with a time was fitted with a stretched exponential relaxation model, revealing the relation of memory stability with the input stimuli strength.

A study on the resistance switching of AgSe and TaO heterojunctions using structural engineering.

The resistive random access memory (RRAM) devices with heterostuctures have been investigated due to cycling stability, nonlinear switching, complementary resistive switching and self-compliance. The heterostructured devices can modulate the resistive switching (RS) behavior appropriately by bilayer structure with a variety of materials. In this study, the bipolar resistive switching characteristics of the bilayer structures composed of TaO and AgSe, which are transition-metal oxide (TMO) and silver chalcogenide, were investigated.

Artificial synaptic characteristics with strong analog memristive switching in a Pt/CeO/Pt structure.

Artificial synaptic potentiation and depression characteristics were demonstrated with Pt/CeO/Pt devices exhibiting polarity-dependent analog memristive switching. The strong and sequential resistance change with its maximum to minimum ratio >10, imperatively essential for stable operation, as repeating voltage application, emulated the potentiation and depression motion of a synapse with variable synaptic weight. The synaptic weight change could be controlled by the amplitude, width, and number of repeated voltage pulses.

Synaptic transistor with a reversible and analog conductance modulation using a Pt/HfOx/n-IGZO memcapacitor.

A synaptic transistor emulating the biological synaptic motion is demonstrated using the memcapacitance characteristics in a Pt/HfOx/n-indium-gallium-zinc-oxide (IGZO) memcapacitor. First, the metal-oxide-semiconductor (MOS) capacitor with Pt/HfOx/n-IGZO structure exhibits analog, polarity-dependent, and reversible memcapacitance in capacitance-voltage (C-V), capacitance-time (C-t), and voltage-pulse measurements. When a positive voltage is applied repeatedly to the Pt electrode, the accumulation capacitance increases gradually and sequentially.

Enhancement of Emission Lifetime of CNT Emitters by Coating ZnO on the CNT Surface.

Carbon nanotubes (CNTs) have been investigated as field-emission sources owing to their high electrical conductivity and high aspect ratio. However, practical applications demand that the emission lifetime of CNTs be further improved. Since ZnO demonstrates impressive electrical and thermal conductivity, when coated on the surface of CNTs, it can allow the CNT field emitters to endure high electrical stress and high temperature.

Resistive Switching Characteristics of Tantalum Oxide Thin Film and Titanium Oxide Nanoparticles Hybrid Structure.

The fabrication of hybrid structure with TiO2 nanoparticle assembly and Ta2O5 thin film layer was demonstrated. The close-packed nanoparticles could influence the resistive switching behaviors due to the huge numbers of interface states and vacancies in the nanoparticle assembly. The device with hybrid structure presented the typical bipolar resistive switching characteristics in the structure of Ti/TiO2/Ta2O5/Au on SiO2/Si substrate.

Investigation of Switching Phenomenon in Metal-Tantalum Oxide Interface.

To investigate the nature of the switching phenomenon at the metal-tantalum oxide interface, we fabricated a memory device in which a tantalum oxide amorphous layer acted as a switching medium. Different metals were deposited on top of the tantalum oxide layer to ensure that they will react with some of the oxygen contents already present in the amorphous layer of the tantalum oxide. This will cause the formation of metal oxide (MOx) at the interface.

Service-Oriented Security Framework for Remote Medical Services in the Internet of Things Environment.

Objectives: Remote medical services have been expanding globally, and this is expansion is steadily increasing. It has had many positive effects, including medical access convenience, timeliness of service, and cost reduction. The speed of research and development in remote medical technology has been gradually accelerating.

Implementation of hospital examination reservation system using data mining technique.

Objectives: New methods for obtaining appropriate information for users have been attempted with the development of information technology and the Internet. Among such methods, the demand for systems and services that can improve patient satisfaction has increased in hospital care environments.

Methods: In this paper, we proposed the Hospital Exam Reservation System (HERS), which uses the data mining method.

Resistive switching characteristics of ZnO nanowires.

Binary transition metal oxides such as ZnO, TiO2, and MnO; and their various structures such as thin film, nanowire, and nanoparticle assembly; have been widely investigated for use in insulators in resistive random access memory (ReRAM), considered a next-generation nonvolatile memory device. Among the various driving mechanisms of resistive switching in insulating materials, the conductive filament model is one of the most widely accepted. Studies on spatially confined structures such as one-dimensional nanostructures and zero-dimensional nanoparticles to reveal the detailed filament constructing mechanism are warranted because low-dimensional nanostructures can provide more localized properties with a narrow dispersion of operational parameter values compared with thin-film structures.

Resistive switching characteristics of manganese oxide nanoparticle assembly with crossbar arrays.

The fabrication of 3 x 3 crossbar arrays measuring 20 μm in width was demonstrated. The bipolar resistive switching characteristics in manganese oxide nanoparticles were investigated in the crossbar structure of top electrode (Au)/nanoparticle assembly/bottom electrode (Ti) on SiO2/Si substrate. The monodisperse manganese oxide nanoparticles measuring 13 nm in diameter were chemically synthesized by thermal decomposition of manganese acetate in the presence of oleic acid at high temperature.

Therapeutic effect of repetitive magnetic stimulation combined with speech and language therapy in post-stroke non-fluent aphasia.

Objective: To investigate the therapeutic effect of repetitive transcranial magnetic stimulation (rTMS) and speech and language therapy (SLT) on the improvement of performance on the Korean-version of the Western Aphasia Battery (K-WAB) in post-stroke non-fluent aphasic patients.

Methods: Twenty post-stroke, non-fluent aphasic patients were enrolled and assigned to one of two groups: a case group (n = 10) or a control group (n = 10). Participants were recruited from the inpatient clinic of the Physical and Rehabilitation Medicine Department of Bundang Jesaeng General Hospital from March 2011 to January 2012.