Brain-like synapse thin-film transistors using oxide semiconductor channels and solid electrolytic gate insulators

Human brain has astonishing advantages such as tolerance to system faults, low power consumption, and adaptive learning ability from pre-obtained data unlike conventional computer system with Von Neumann architecture. One of the most attractive benefits of human brain is an ability of parallel processing. Considering these advantages, new types of devices featured to emulate the human brain are quite demanding. These artificially designed systems are called neuromorphic systems, in which neurons are inspired by electronic signals applied to synapses. They can be useful components in artificial perception and action systems. Recently, many types of electronic devices mimicking the functions of human brain have been energetically studied [1-2]. However, these devices have following limitations. First, it needs additional external memories for storing synapse information because CMOS devices cannot work as nonvolatile memories. Second, conventional Si-based electronic technology is not compatible with large-area electronics implemented on glass or flexible substrates. In this work, we propose new type of synapse device with thin-film transistor (TFT) configuration for realizing simple device structure and operation for synaptic learning, in which oxide semiconductor In-Ga-Zn-O (IGZO) and solid electrolytes, such as poly(4-vinylphenol) - sodium β-alumina (PVP-SBA) and polypropylene carbonate (PPC), are employed as active channel and solid-electrolytic gate insulators for TFT operations, respectively. Solid electrolytes can be promising for controlling the synaptic weights by exploiting the movements of charged ions within the electrolytes. Lithium and sodium ions are transported in PPC and PVP-SBA, respectively. Synaptic weights can be determined as the modulated channel conductance and be estimated from the gradual variations in drain currents. Figs. 1(a) and 1(b) show cross-sectional view of fabricated synapse TFT using PVP-SBA gate insulator and schematic structures of biological synapse & neuron, respectively. Figs. 2(a) and 2(b) showed the variations in output drain currents as functions of two input pulse parameters, amplitude and width. First, the voltage pulses were repeatedly applied to the gate terminal one-hundred times with a fixed pulse width of 50 ms. The output drain current gradually increased with increasing the number of pulses [Fig. 2(a)]. When the pulse amplitude was varied to 10 and 20 V at ten-time applications, the value of obtained output drain current markedly increased and the current ratio for two conditions were calculated to be approximately 2.6. These results clearly suggest that the synaptic weights could be more fortified when larger voltage signals (20 V) were employed for synaptic operations. In other words, it means that the quantity of residual memory or response significantly increased with stronger stimuli. When pulse signals with a fixed amplitude of 10 V were applied with variations in pulse widths of 10, 50, and 100 ms. The output drain currents more quickly increased for longer pulses [Fig. 2(b)]. The obtained current ratios of 100-ms conditions to 10-ms condition at ten- and one-hundred-time applications were estimated to be approximately 3.1 and 2.1, respectively. These results emulate the changes in learning time at a single event. Our proposed synapse TFTs can be a suitable candidate for the next-generation low-power large-area electronics such as neuromorphic systems and flexible bio-mimicking devices. Please click Additional Files below to see the full abstract

Enhancement of carbamazepine removal rate using Tetradesmus obliquus KNUA061 and NaOCl and utilization of the resulting biomass

Pharmaceutical and personal care products (PPCPs) are discharged into receiving water bodies mainly from sewage treatment plants. Due to the inefficient removal in conventional wastewater treatment facilities, PPCPs have become a major concern to aquatic ecosystems, water quality, and public health worldwide since they cause harmful effects on aquatic life and human even at low doses. Among the PPCPs, carbamazepine (CBZ) is one of the most commonly prescribed anticonvulsant drugs and consumed more than 1,000 tons per year. Due to its structural complexity, CBZ is known as recalcitrant compound highly stable during wastewater treatment. Consequently, it has become one of the most frequently detected pharmaceuticals in waste water, surface water, and even drinking water. In this study, Korean indigenous microalgae strains were tested as eco-friendly and cost-effective solutions for CBZ removal. Based on the preliminary biological CBZ degradation tests, Tetradesmus obliquus KNUA061 demonstrating the best CBZ removal rate was selected for further experiments. In order to increase strain KNUA061's CBZ removal efficiency, NaOCl, which is widely accepted in the water purification process, was used as an additional stimulus to induce stress conditions. At around 20 μg L−1 CBZ, addition of 1.0 mg NaOCl resulted in approximately 20% of removal rate increase without suppressing cells growth. Roughly 90% of CBZ remained its original form and the composition of the transformed secondary metabolites was less than 10% during the biodegradation process by the microalga. Based on the results of the antioxidant enzyme activities, degree of lipid oxidation, and amino acid contents, it was concluded that the redox-defence system in microalgal cells may have been activated by the NaOCl treatment. Biomass analysis results showed that higher heating value (HHV) of strain KNUA061 biomass was higher than those of lignocellulosic energy crops suggesting that it could be utilized as a possible renewable energy source. Even though its biodiesel properties were slightly below the international standards due to the high PUFA contents, the biodiesel produced from T. obliquus KNUA061 could be used as a blending resource for transportation fuels. It was also determined that the microalgal biomass has acceptable feasibility as a sustainable dietary supplement feedstock due to its high essential amino acid contents

Integration of waveguide-type wavelength demultiplexingphotodetectors by the selective intermixing of an InGaAs-InGaAsPquantum-well structure

Abstract—Using the selective intermixing of an InGaAs–In- GaAsP multiquantum-well (MQW) structure, a wavelength demultiplexing photodetector which can demultiplex two widely separated wavelengths was fabricated. An InGaAs–InGaAsP MQW with a u-InP cladding layer and a u-InGaAs cap layer, grown by metal organic chemical vapor deposition was used. Selective area intermixing of the InGaAs–InGaAsP MQW structure was done by a rapid thermal annealing after the deposition and patterning of the SiO2 dielectric layer on the InGaAs cap layer. The integrated structure consists of shorter and longer wavelength sections, separated by an absorber section. Shorter wavelength and absorber sections were intermixed with the SiO2 dielectric layer. At a wavelength of 1477 nm, the output photocurrent ratio was enhanced as the length of the absorber region increased and a ratio of over 30 dB was observed, while at a wavelength of 1561 nm, an output photocurrent ratio of 18.9 dB was observed

Adult Hippocampal Neurogenesis Can Be Enhanced by Cold Challenge Independently From Beigeing Effects

In this study, we investigated the effects of cold challenge on adult hippocampal neurogenesis (AHN) and hippocampal gene expression and whether these are mediated by beigeing of peripheral fat tissues. Cold challenge (6 ± 2°C) for 1 and 4 weeks was found to induce beigeing effects in inguinal white adipose tissue based on hematoxylin and eosin staining as well as uncoupled protein-1 immunohistochemical staining. In the hippocampus, cold challenge for 1 or 4 weeks increased dentate gyrus neurogenesis and expression of genes related to AHN, including notch signaling, G protein-coupled receptor signaling, and adrenergic beta receptor-1. However, this enhancement of neurogenesis and gene expression by cold challenge was not shown by administration of CL 316,243, which induces peripheral beigeing similar to cold challenge but does not cross the blood–brain barrier. These results suggest that cold challenge promotes AHN and central expression of AHN-related, signaling, and β1-adrenergic receptors genes, and that peripheral beigeing by itself is not sufficient to mediate these effects. Considering the increase in AHN and gene expression changes, cold challenge may offer a novel approach to hippocampal modulation