Wide-Range Synaptic Current Responses with a Liquid Ga Electrode via a Surface Redox Reaction in a NaOH Solution at Different Molar Concentrations.

A liquid Ga-based synaptic device with two-terminal electrodes is demonstrated in NaOH solutions at 50 °C. The proposed electrochemical redox device using the liquid Ga electrode in the NaOH solution can emulate various biological synapses that require different decay constants. The device exhibits a wide range of current decay times from 60 to 320 ms at different NaOH mole concentrations from 0.

Plasma Nitridation Effect on -GaO Semiconductors.

The electrical and optoelectronic performance of semiconductor devices are mainly affected by the presence of defects or crystal imperfections in the semiconductor. Oxygen vacancies are one of the most common defects and are known to serve as electron trap sites whose energy levels are below the conduction band (CB) edge for metal oxide semiconductors, including -GaO. In this study, the effects of plasma nitridation (PN) on polycrystalline -GaO thin films are discussed.

Synaptic Current Response of a Liquid Ga Electrode via a Surface Electrochemical Redox Reaction in a NaOH Solution.

An ionic device using a liquid Ga electrode in a 1 M NaOH solution is proposed to generate artificial neural spike signals. The oxidation and reduction at the liquid Ga surface were investigated for different bias voltages at 50 °C. When the positive sweep voltage from the starting voltage ( ) of 1 V was applied to the Ga electrode, the oxidation current flowed immediately and decreased exponentially with time.

Enhanced third harmonic generation in ultrathin free-standing β-GaO nanomembranes: study on surface and bulk contribution.

Third harmonic generation (THG) has proven its value in surface and interface characterization, high-contrast bio-imaging, and sub-wavelength light manipulation. Although THG is observed widely in general solid and liquid substances, when laser pulses are focused at nanometer-level ultra-thin films, the bulk THG has been reported to play the dominant role. However, there are still third harmonics (TH) generated at the surface of the thin-films, not inside the bulk solid - so-called surface TH, whose relative contribution has not been quantitatively revealed to date.

Impact of Al doping on a hydrothermally synthesized β-GaO nanostructure for photocatalysis applications.

Aluminum (Al)-doped beta-phase gallium oxide (β-GaO) nanostructures with different Al concentrations (0 to 3.2 at%) are synthesized using a hydrothermal method. The single phase of the β-GaO is maintained without intermediate phases up to Al 3.

Fast-Response Colorimetric UVC Sensor Made of a GaO Photocatalyst with a Hole Scavenger.

A fast-response colorimetric ultraviolet-C (UVC) sensor was demonstrated using a gallium oxide (GaO) photocatalyst with small amounts of triethanolamine (TEOA) in methylene blue (MB) solutions and a conventional RGB photodetector. The color of the MB solution changed upon UVC exposure, which was observed using an in situ RGB photodetector. Thereby, the UVC exposure was numerically quantified as an MB reduction rate with the value of the photodetector, which was linearly correlated with the measured spectral absorbance using a UV-Vis spectrophotometer.

Highly Aligned Polymeric Nanowire Etch-Mask Lithography Enabling the Integration of Graphene Nanoribbon Transistors.

Graphene nanoribbons are a greatly intriguing form of nanomaterials owing to their unique properties that overcome the limitations associated with a zero bandgap of two-dimensional graphene at room temperature. Thus, the fabrication of graphene nanoribbons has garnered much attention for building high-performance field-effect transistors. Consequently, various methodologies reported previously have brought significant progress in the development of highly ordered graphene nanoribbons.

Ultrathin ZrO-Organic Hybrid Dielectric (EOT 3.2 nm) via Initiated Chemical Vapor Deposition for High-Performance Flexible Electronics.

A one-step synthesis method is introduced and used to form an ultrathin, homogeneous organic-inorganic hybrid dielectric film with a high dielectric constant (high-), based on initiated chemical vapor deposition. The hybrid dielectric is synthesized from tetrakis-dimethyl-amino-zirconium and 2-hydroxyethyl methacrylate, which are a high- inorganic material and a soft organic material, respectively. A detailed material analysis on the synthesized ZrO-organic hybrid (Zr-hybrid) is performed.

Influence of Self-Heating Effect on Interface Trap Generation in Highly Flexible Single-Crystalline Si Nanomembrane Transistors.

We analyze the interface trap states generated by the self-heating effect in flexible single-crystalline Si nanomembrane (sc-Si NM) transistors. Despite the excellent device performance (: ~61 mV/dec, : ~10, Nit: ~5 × 10 cm, eff: ~250 cm²/V·s) and mechanical flexibility ( ═ 1 mm) of sc-Si NM transistors on a polymer substrate, they are vulnerable to thermal reliability issues due to the poor thermal conductivity ( < 1 W/m·K) of the polymer substrate. Understanding the detailed mechanism driving heat-related device degradation is key to improving device reliability, life expectancy, and overall device performance.

Mechanical and Electrical Reliability Analysis of Flexible Si Complementary Metal-Oxide-Semiconductor Integrated Circuit.

A flexible Si complementary metal-oxide-semiconductor (CMOS) integrated circuit (IC) with multi-level interconnects is realized by thinning down and transferring the CMOS IC onto a polymer substrate. A detailed mechanical and electrical reliability analysis of the flexible Si CMOS IC is carried out in relation to the neutral mechanical plane (NMP) that is extracted from both analytical and numerical modeling. To enhance the reliability by optimizing the NMP position, the thicknesses of all the layers in the CMOS IC on the polymer substrate are carefully adjusted.

Novel Vapor-Phase Synthesis of Flexible, Homogeneous Organic-Inorganic Hybrid Gate Dielectric with sub 5 nm Equivalent Oxide Thickness.

Organic-inorganic hybrid dielectrics have attracted considerable attention for improving both the dielectric constant ( k) and mechanical flexibility of the gate dielectric layer for emerging flexible and wearable electronics. However, conventional solution-based hybrid materials, such as nanocomposite and self-assembled nanodielectrics, have limitations in the dielectric quality when the thickness is deep-scaled, which is critical to realizing high-performance flexible devices. This study proposes a novel vapor-phase synthesis method to form an ultrathin, homogeneous, high- k organic-inorganic hybrid dielectric.

High-Aspect Ratio -Ga₂O₃ Nanorods via Hydrothermal Synthesis.

High-aspect ratio -Ga₂O₃ nanorods consisting of prism-like crystals were formed using gallium oxyhydroxide and ammonia hydroxide via a hydrothermal synthesis followed by the subsequent calcination process. The formation of high-aspect ratio -Ga₂O₃ nanorods was attributed to the oriented attachment mechanism that was present during the hydrothermal synthesis. A field-effect transistor was fabricated using the high-aspect ratio -Ga₂O₃ nanorod, and it exhibited the typical charge transfer properties of an n-type semiconductor.

Preparation of Wrinkled Graphene Oxide Using Solution Method.

Wrinkled graphene oxide (WGO) is formed using the solution method. The sub-μm-sized wrinkles are generated on the GO surface, with more wrinkles forming as the GaCl3 in the solution increases. The wrinkles are observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) methods.

A High-Performance Top-Gated Graphene Field-Effect Transistor with Excellent Flexibility Enabled by an iCVD Copolymer Gate Dielectric.

A high-performance top-gated graphene field-effect transistor (FET) with excellent mechanical flexibility is demonstrated by implementing a surface-energy-engineered copolymer gate dielectric via a solvent-free process called initiated chemical vapor deposition. The ultrathin, flexible copolymer dielectric is synthesized from two monomers composed of 1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane and 1-vinylimidazole (VIDZ). The copolymer dielectric enables the graphene device to exhibit excellent dielectric performance and substantially enhanced mechanical flexibility.

Impedance Spectroscopy Analysis and Equivalent Circuit Modeling of Graphene Oxide Solutions.

The optical and electrical characteristics of a graphene oxide solution (GS) with different graphene oxide (GO) concentrations in de-ionized water are investigated via the electrochemical impedance spectroscopy (EIS) method. The measurement results produced by the EIS for the GS are represented with both Bode and Nyquist plots in a frequency range from 1 kHz to 10 MHz. Using these results, we develop an equivalent circuit model as a function of the GO concentration, representing the GS as a mixed circuit of two-dimensional (2D) GO dispersed in parallel in de-ionized (DI) water.

Compliment Graphene Oxide Coating on Silk Fiber Surface via Electrostatic Force for Capacitive Humidity Sensor Applications.

Cylindrical silk fiber (SF) was coated with Graphene oxide (GO) for capacitive humidity sensor applications. Negatively charged GO in the solution was attracted to the positively charged SF surface via electrostatic force without any help from adhesive intermediates. The magnitude of the positively charged SF surface was controlled through the static electricity charges created on the SF surface.

Vertically Formed Graphene Stripe for 3D Field-Effect Transistor Applications.

A 100-nm wide, vertically formed graphene stripe (GS) is demonstrated for three-dimensional (3D) electronic applications. The GS forms along the sidewall of a thin nickel film. It is possible to further scale down the GS width by engineering the deposited thickness of the atomic layer deposition (ALD) Ni film.

Dependence of Grain Size on the Performance of a Polysilicon Channel TFT for 3D NAND Flash Memory.

We investigated the dependence of grain size on the performance of a polycrystalline silicon (poly-Si) channel TFT for application to 3D NAND Flash memory devices. It has been found that the device performance and memory characteristics are strongly affected by the grain size of the poly-Si channel. Higher on-state current, faster program speed, and poor endurance/reliability properties are observed when the poly-Si grain size is large.

Hybrid Integration of Graphene Analog and Silicon Complementary Metal-Oxide-Semiconductor Digital Circuits.

We demonstrate a hybrid integration of a graphene-based analog circuit and a silicon-based digital circuit in order to exploit the strengths of both graphene and silicon devices. This mixed signal circuit integration was achieved using a three-dimensional (3-D) integration technique where a graphene FET multimode phase shifter is fabricated on top of a silicon complementary metal-oxide-semiconductor field-effect transistor (CMOS FET) ring oscillator. The process integration scheme presented here is compatible with the conventional silicon CMOS process, and thus the graphene circuit can successfully be integrated on current semiconductor technology platforms for various applications.

Valley-engineered ultra-thin silicon for high-performance junctionless transistors.

Extremely thin silicon show good mechanical flexibility because of their 2-D like structure and enhanced performance by the quantum confinement effect. In this paper, we demonstrate a junctionless FET which reveals a room temperature quantum confinement effect (RTQCE) achieved by a valley-engineering of the silicon. The strain-induced band splitting and a quantum confinement effect induced from ultra-thin-body silicon are the two main mechanisms for valley engineering.

Improved Drain Current Saturation and Voltage Gain in Graphene-on-Silicon Field Effect Transistors.

Graphene devices for radio frequency (RF) applications are of great interest due to their excellent carrier mobility and saturation velocity. However, the insufficient current saturation in graphene field effect transistors (FETs) is a barrier preventing enhancements of the maximum oscillation frequency and voltage gain, both of which should be improved for RF transistors. Achieving a high output resistance is therefore a crucial step for graphene to be utilized in RF applications.

A Gallium Oxide-Graphene Oxide Hybrid Composite for Enhanced Photocatalytic Reaction.

Hybrid composites (HCs) made up of gallium oxide (GaO) and graphene oxide (GO) were investigated with the intent of enhancing a photocatalytic reaction under ultraviolet (UV) radiation. The material properties of both GaO and GO were preserved, even after the formation of the HCs. The incorporation of the GO into the GaO significantly enhanced the photocatalytic reaction, as indicated by the amount of methylene blue (MB) degradation.

A Robust Highly Aligned DNA Nanowire Array-Enabled Lithography for Graphene Nanoribbon Transistors.

Because of its excellent charge carrier mobility at the Dirac point, graphene possesses exceptional properties for high-performance devices. Of particular interest is the potential use of graphene nanoribbons or graphene nanomesh for field-effect transistors. Herein, highly aligned DNA nanowire arrays were crafted by flow-assisted self-assembly of a drop of DNA aqueous solution on a flat polymer substrate.