Neuromorphic engineering, a methodology for emulating synaptic functions or neural systems, has attracted tremendous attention for achieving next-generation artificial intelligence technologies in the field of electronics and photonics. However, to emulate human visual memory, an active pixel sensor array for neuromorphic photonics has yet to be demonstrated, even though it can implement an artificial neuron array in hardware because individual pixels can act as artificial neurons. Here, we present a neuromorphic active pixel image sensor array (NAPISA) chip based on an amorphous oxide semiconductor heterostructure, emulating the human visual memory. In the 8 × 8 NAPISA chip, each pixel with a select transistor and a neuromorphic phototransistor is based on a solution-processed indium zinc oxide back channel layer and sputtered indium gallium zinc oxide front channel layer. These materials are used as a triggering layer for persistent photoconductivity and a high-performance channel layer with outstanding uniformity. The phototransistors in the pixels exhibit both photonic potentiation and depression characteristics by a constant negative and positive gate bias due to charge trapping/detrapping. The visual memory and forgetting behaviors of the NAPISA can be successfully demonstrated by using the pulsed light stencil method without any software or simulation. This study provides valuable information to other neuromorphic devices and systems for next-generation artificial intelligence technologies.
The technological ability to detect a wide spectrum range of illuminated visible-to-NIR is substantially improved for an amorphous metal oxide semiconductor, indium gallium zinc oxide (IGZO), without employing an additional photoabsorber. The fundamentally tuned morphology via structural engineering results in the creation of nanopores throughout the entire thickness of ∼30 nm. See-through nanopores have edge functionalization with vacancies, which leads to a large density of substates near the conduction band minima and valence band maxima. The presence of nanoring edges with a high concentration of vacancies is investigated using chemical composition analysis. The process of creating a nonporous morphology is sophisticated and is demonstrated using a wafer-scale phototransistor array. The performance of the phototransistors is assessed in terms of photosensitivity (S) and photoresponsivity (R); both are of high magnitudes (S = 8.6 × 10 4 at λ ex = 638 nm and P inc = 512 mW cm 2− ; R = 120 A W 1− at P inc = 2 mW cm 2− for the same λ ex ). Additionally, the 7 × 5 array of 35 phototransistors is effective in sensing and reproducing the input image by responding to selectively illuminated pixels.
The silicon nitride (SiNx) atomic layer deposition with bis(dimethylaminomethylsilyl)-trimethylsilyl amine precursor and N2 remote plasma was investigated. The process window ranged from 250 to 400 °C, and the growth rate was about 0.38 ± 0.02 Å/cycle. The physical, chemical, and electrical characteristics of the SiNx thin films were examined as a function of deposition temperature and plasma power. Based on the results of spectroscopic ellipsometry and x-ray photoelectron spectroscopy, the growth rate and state of binding energy showed little difference depending on the plasma power. The better film properties such as leakage current density and etch resistance were obtained at higher deposition temperatures and higher plasma power. High wet etch resistance (wet etch rate of ∼2 nm/min) and low leakage current density (∼10−8 A/cm2) were obtained. The step coverage, examined by transmission electron microscopy, was about 80% on a trench with an aspect ratio of 4.5.
The fabrication of Hf 0.5 Zr 0.5 O 2 -ferroelectric negative capacitor using solution combustion is presented for the first time. The starting materials used for the solution combustion to form equimolar Hf 0.5 Zr 0.5 O 2 are to act as both combustible elements and cation sources. Jain's method, which is used for estimating the stoichiometric quantities of precursors in propellant chemistry, has also been modified and applied. The conventional assumption for this method that molecular oxygen does not take part in the reaction is refuted and stoichiometric combustion in the presence of molecular oxygen is proposed. This reaction is followed by post-rapid thermal processing to stabilize the metastable, non-centrosymmetric orthorhombic phase. The thin film stacks, Hf 0.5 Zr 0.5 O 2 /HfO 2 , are used to achieve sub-thermionic swing (forward sweep: 25.42 ± 8.05 mV dec −1 , reverse sweep: 42.56 ± 4.87 mV dec −1 ) in MoS 2 negative capacitance field effect transistors with a hysteresis of ≈40 mV at 1 nA, resulting in ultra-low-power operation.
Silicon nitride (SiNx) thin films using 1,3-di-isopropylamino-2,4-dimethylcyclosilazane (CSN-2) and N2 plasma were investigated. The growth rate of SiNx thin films was saturated in the range of 200–500 °C, yielding approximately 0.38 Å/cycle, and featuring a wide process window. The physical and chemical properties of the SiNx films were investigated as a function of deposition temperature. As temperature was increased, transmission electron microscopy (TEM) analysis confirmed that a conformal thin film was obtained. Also, we developed a three-step process in which the H2 plasma step was introduced before the N2 plasma step. In order to investigate the effect of H2 plasma, we evaluated the growth rate, step coverage, and wet etch rate according to H2 plasma exposure time (10–30 s). As a result, the side step coverage increased from 82% to 105% and the bottom step coverages increased from 90% to 110% in the narrow pattern. By increasing the H2 plasma to 30 s, the wet etch rate was 32 Å/min, which is much lower than the case of only N2 plasma (43 Å/min).
This study explores a class of resistive memory candidatessimple binary halidesand demonstrates their efficacy in switching between high- and low-resistive states. Herein, copper halide, particularly copper iodide (CuI), is investigated for its resistive switching efficacy when sandwiched between indium tin oxide (ITO) and silver electrodes on flexible polyethylene terephthalate (PET) substrates. CuI is deposited on ITO-coated PET using an innovative dissolution-recrystallization technique, in which a deposition temperature of 80 °C is sufficient to eliminate the carrier solventacetonitrileand impart considerable densification of CuI for effective memory characteristics. The PET/ITO/CuI is transparent (>90%), and the PET//ITO/CuI/Ag devices display states of notably low- and high-resistive states with a ratio of more than 10 within a voltage biasing range of −2.5 to +2.5 V. Additionally, the devices exhibit similar resistive states under bending stress. Halides (in particular, CuI) are, thus, introduced as a class of active materials for transparent and flexible resistive memories.
Water sensors are a type of level sensor that can be used in various applications requiring the sensing of water levels, such as in dams, nuclear power plants, water pipes, water tanks, and dehumidifiers. In particular, water sensors in water ingress monitoring systems (WIMS) protect lives and property from disasters caused by water leakage and flooding. Here, a resistive water sensor for WIMS that incorporates poly(3,4-ethylenedioxythinophene):poly(styrene sulfonate) (PEDOT:PSS) grafted with poly(ethylene glycol) methyl ether (PEGME) (PEDOT:PSS-g-PEGME copolymer) as high-conductivity electrodes and laser-treated PEDOT:PSSg-PEGME copolymer as the low-conductivity resistive component is reported. The configuration of the water sensor is modeled as two parallel resistors (R laser treated PEDOT:PSS || R water ) when water comes into contact with the sensor surface. The two-resistor configuration exhibits a better performance in comparison with single-resistor configurations comprising only PEDOT:PSS-g-PEGME copolymer or laser-treated PEDOT:PSS-g-PEMGE copolymer. Moreover, PEDOT:PSS-g-PEGME copolymer is applied to the sensor to improve the stability of PEDOT:PSS in water. We demonstrate that the sensor can detect the water level in real time with high sensitivity and accuracy, and thus has potential in applications for monitoring water-related hazards.
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