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In this work, the effect of thermal annealing on the resistance switching behavior of Nb2O5 films was investigated in conjunction with an analysis of the chemical bonding states and crystal structure. The Nb2O5 films were deposited via reactive sputtering, and annealed via rapid thermal annealing at various temperatures up to 650°C. The crystal structure of the as-deposited Nb2O5 films transformed from amorphous to a hexagonal Nb2O5 crystalline phase with tetragonal NbO2 following thermal annealing at 500°C. The conductivity of the Nb2O5 films increased drastically as the annealing temperature increased. An increase in the non-lattice oxygen in the Nb2O5 films was also observed with thermal annealing. Pt/Nb2O5/Pt stacks with the as-deposited Nb2O5 showed typical unipolar resistance switching behaviors after electro-forming; however, the Nb2O5 film devices annealed at 500°C showed RESET-first resistance switching behavior without prior electro-forming. The RESET-first resistance switching in annealed Nb2O5 is believed to be due to the nano-scale conductive path formed in the annealed Nb2O5 films. [ABSTRACT FROM AUTHOR]

In this manuscript, we study the problem of detecting coordinated free text campaigns in large-scale social media. These campaigns--ranging from coordinated spam messages to promotional and advertising campaigns to political astro-turfing--are growing in significance and reach with the commensurate rise in massive-scale social systems. Specifically, we propose and evaluate a content-driven framework for effectively linking free text posts with common "talking points" and extracting campaigns from large-scale social media. Three of the salient features of the campaign extraction framework are: (i) first, we investigate graph mining techniques for isolating coherent campaigns from large message-based graphs; (ii) second, we conduct a comprehensive comparative study of text-based message correlation in message and user levels; and (iii) finally, we analyze temporal behaviors of various campaign types. Through an experimental study over millions of Twitter messages we identify five major types of campaigns--namely Spam, Promotion, Template, News, and Celebrity campaigns--and we show how these campaigns may be extracted with high precision and recall. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effect of thermal annealing on both the physical properties and the resistive switching properties of ZrO2 films deposited by atomic layer deposition (ALD) method were investigated for its potential application to non-volatile memory devices. The ZrO2 films in the Pt/ZrO2/TiN structure exhibited unipolar and bipolar resistance switching behaviors depending on the nature of the bias applied to Pt top electrodes for the electro-forming process. For unipolar switching, the resistance of the high resistance state (HRS) was reduced with increasing annealing temperature, accompanied with the increase of metallic Zr in the annealed ZrO2 films. In contrast, the HRS resistance in the bipolar switching was increased while the low resistance state (LRS) resistance was decreased with increasing annealing temperature, producing a greater change in resistance. SIMS and EDX showed that the thickness of interfacial TiO x N y layer between the ZrO2 and the TiN bottom electrode was enlarged with annealing. The enlarged TiO x N y layer was expected to produce the reduction of LRS resistance with the increase of HRS resistance in the bipolar resistance switching. [Copyright &y& Elsevier]

In our study, the physical properties of (TiO)(SiO), including band-gap, band-offset, and thermal stability and the electrical properties of band-engineered SiO/(TiO)(SiO) tunnel barrier stacks, including the tunneling current and charge-trapping characteristics for applications to nonvolatile memory devices were investigated. It was observed that the band-gap and band-offset of (TiO)(SiO) can be controlled by adjustment in the composition of the (TiO)(SiO) films. Ti-silicate film with TiO:SiO cycle ratio of 1:5 was maintained in an amorphous phase, even after annealing at 950 °C. The tunneling current of the band-engineered SiO/(TiO)(SiO) stacked tunnel barrier was larger than that of a single SiO barrier under a higher external bias, while the tunneling current of a SiO/(TiO)(SiO) stacked tunnel barrier under a lower external bias was smaller. Charge-trapping tests showed that the voltage shift for SiO/(TiO)(SiO) is slightly larger than that for single SiO. [ABSTRACT FROM AUTHOR]

The process window for the high etching selectivity of silicon nitride to silicon oxide was investigated in CF4/CH4 inductively coupled plasma. This work showed that the etching selectivity could be controlled by modulating the thickness of the fluorocarbon film with the flow rates of CH4 gas. The carbon content in the fluorocarbon by-product layers on the etched films was observed to play a critical role in determining the etching selectivity of silicon nitride to silicon oxide. The increase in the carbon content in the fluorocarbon films with increasing CH4 gas caused the etch rates of both silicon oxide and silicon nitride films to be reduced, eventually leading to the etch stops. The minimum effective thickness of the fluorocarbon films was estimated to be 20 Å for the etch stop. The infinite etching selectivity of the silicon nitride to the silicon oxide on the blanket wafers could be achieved for the CH4 flow rate above 30 SCCM (SCCM denotes cubic centimeters per minute at STP) for the CF4 flow rate of 10 SCCM. NF3/CH4 and SF6/CH4 plasma showed etch behavior similar to CF4/CH4 plasma. [ABSTRACT FROM AUTHOR]

Understanding the Solution-State Doping of Donor-Acceptor Polymers Through Tailored Side Chain Engineering for Thermoelectrics (Adv. Funct. Keywords: aggregations; donor-acceptor polymers; organic thermoelectrics; side chain engineering; solution-state dopants EN aggregations donor-acceptor polymers organic thermoelectrics side chain engineering solution-state dopants 1 1 1 12/20/22 20221215 NES 221215 B Donor-Acceptor Polymers b In article number 2207886, Jaeyoung Jang, Hwan Jung, Yong Jin Jeong, and co-workers demonstrate the aggregation effects of donor-acceptor polymers during solution-state doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquino dimethane (F4TCNQ) for organic thermoelectrics. Aggregations, donor-acceptor polymers, organic thermoelectrics, side chain engineering, solution-state dopants. [Extracted from the article]

Highlights: [•] Migration of oxygen anions between HfO2 and Ti during the switching. [•] Effect of the redox reaction on initial conductivity and switching. [•] RESET-first resistive switching engineered by redox reaction with annealing. [ABSTRACT FROM AUTHOR]

Highlights: [•] Thermal SiO2 tunnel layer on poly-Si exhibits breakdown at low electric field. [•] Defect assisted tunneling current exhibits in LP-TEOS SiO2 tunnel layer. [•] Fast program/erase characteristics are observed in LP-TEOS SiO2 tunnel layer device. [•] Program and endurance fail, which are related with IV characteristic, exhibit in thermal SiO2 device. [•] Stable memory characteristics can be observed in radical SiO2 tunnel layer device. [Copyright &y& Elsevier]

The development of n -type conjugated polymers (CPs) forming an acceptor–acceptor (A–A)-type structure are quite challenging due to the synthetic limitation of imposing a functional group on the electron deficient aromatic structure. The diketopyrrolopyrroles (DPP) structure exhibits n -type characteristics; however, the extended π-structure enables stannylation at the terminal position. The stannylated DPP is beneficial for making n -type CPs, but its use in the development of n -type CPs and their application in n -type organic thin-film transistors and organic thermoelectric devices have been not extensively studied. In the present study, we synthesized the A–A-type conjugated polymer, poly [((2,5-bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo [3,4- c ]pyrrole-1,4-dione)-5,5′-diyl)- alt -((2,7-bis(2-ethylhexyl)benzo [lmn] [3,8]phenanthroline-1,3,6,8(2 H ,7 H)-tetraone)-4,9-diyl))] (PDPP-NDI), by Stille coupling of distannylated DPP and dibrominated naphthalene diimide (NDI). The alternating copolymerization of DPP and NDI moieties led to a low-lying LUMO energy level of −4.4 eV, suitable for electron transport. The n -type organic thin-film transistors were fabricated with PDPP–NDI, and a substantial average electron mobility of 3.78 × 10−2 cm2 V−1 s−1 was obtained after thermal annealing. The n -type organic thermoelectric devices were developed via n -doping, and PDPP–NDI exhibited n -type thermoelectric properties, with an average power factor of 1.82 × 10−3 μW m−1 K−2. Image 1 • An acceptor–acceptor-structured n -type alternating copolymer, PDPP–NDI, was developed. • A small bandgap of 1.03 eV and deep LUMO energy level of −4.4 eV were achieved. • The n -type characteristics of PDPP–NDI were successfully utilized in n -type OTFTs and OTE devices. • The device characteristics of both OTFT and OTE devices were fully studied and discussed. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Nb doping on the resistance switching characteristics of NiO x films was investigated. Pt/Nb-doped NiO x /Pt metal–insulator–metal stacks were fabricated using NiO x films with various Nb contents sputtered by reactive dc magnetron sputtering. The resistance switching behaviors of the metal–insulator–metal stacks were then examined in conjunction with a study on the physical properties such as the chemical bonding of NiO x films. Nb doping of NiO x at a Tdep of 400°C and an O2 partial pressure of 5% resulted in an improved endurance of SET/RESET processes with a narrower distribution of VSET, and a larger memory window compared to un-doped NiO x films. NiO x with 5.47% Nb deposited at an O2 partial pressure of 15% showed bistable resistance switching behavior while undoped NiO x material, deposited under the same condition did not. A study of the chemical bonding states by X-ray photoelectron spectroscopy showed that the Nb-doping of NiO x films produced an increase in the density of Ni0 and a reduction in the density of Ni3+, compared to corresponding values for undoped NiO x films deposited under the same condition. The resistive switching behavior of NiO x was enhanced by defect engineering with metal impurity with different oxidation valence. [Copyright &y& Elsevier]

Abstract: High-k dielectric material stacks are considered to be a good candidate for tunnel barrier, replacing single SiO2 tunnel dielectrics in non-volatile flash memory. The use of low-k/high-k tunnel barriers was expected to enhance the electric field sensitivity with possibility of the reduction in operation voltage for Flash devices. In this work, we investigated the physical properties of (HfO2) x (SiO2)1−x with various compositions in conjunction with the tunneling characteristics of (HfO2) x (SiO2)1−x /SiO2 double dielectric structure for the application to charge trap flash memory(CTF) devices. The band-engineered (HfO2) x (SiO2)1−x /SiO2 double dielectric structure showed enhanced tunneling current above 2 V, while showed smaller tunneling current below 2 V because of increasing physical thickness of designed double layer structures. The band-engineered charge trap (CTD) device with (HfO2) x (SiO2)1−x /SiO2 double dielectric structure showed faster program/erase speed and larger memory window at same time and voltage compared to the CTD with a single SiO2 tunnel barrier. [Copyright &y& Elsevier]

Zinc pnictides, particularly Zn 3 As 2 , hold significant promise for optoelectronic applications owing to their intrinsic p-type behavior and appropriate bandgaps. However, despite the outstanding properties of colloidal Zn 3 As 2 nanocrystals, research in this area is lacking because of the absence of suitable precursors, occurrence of surface oxidation, and intricacy of the crystal structures. In this study, a novel and facile solution-based synthetic approach is presented for obtaining highly crystalline p-type Zn 3 As 2 nanocrystals with accurate stoichiometry. By carefully controlling the feed ratio and reaction temperature, colloidal Zn 3 As 2 nanocrystals are successfully obtained. Moreover, the mechanism underlying the conversion of As precursors in the initial phases of Zn 3 As 2 synthesis is elucidated. Furthermore, these nanocrystals are employed as active layers in field-effect transistors that exhibit inherent p-type characteristics with native surface ligands. To enhance the charge transport properties, a dual passivation strategy is introduced via phase-transfer ligand exchange, leading to enhanced hole mobilities as high as 0.089 cm 2 V -1 s -1 . This study not only contributes to the advancement of nanocrystal synthesis, but also opens up new possibilities for previously underexplored p-type nanocrystal research., (© 2024 Wiley‐VCH GmbH.)

In this study, a two-dimensional electron gas (2DEG), which is a conductive layer formed at the interface of Al 2 O 3 and TiO 2 , was used as an electrode for resistive random access memory (RRAM) and implemented in a cell size down to 30 nm. For an RRAM device comprising W/2DEG/TiO 2 /W, we confirmed that the dominant switching mechanism changed from interfacial to filamentary as the cell size decreased from 500 nm to 30 nm. Through analyses of changes in forming characteristics and conduction mechanisms in the low resistive state depending on the cell size, it was identified that the 2DEG acted as an oxygen-scavenging layer of TiO 2 during the resistive switching process. By comparing the switching characteristics of RRAM devices with and without 2DEG for a 30 nm cell size, we confirmed that a high-performance 2DEG RRAM was realized, with highly uniform current-voltage characteristics, a low operating voltage (∼1 V), and a high on/off ratio (>10 2 ). Finally, the applicability of the proposed device to a crossbar array was validated by evaluating 1S1R operation with an NbO 2 -based selector. Considering the improved switching uniformity, the 2DEG RRAM shows promise for high-density memory applications., (© 2023 IOP Publishing Ltd.)

Advanced materials and device engineering has played a crucial role in improving the performance of electrochemical random access memory (ECRAM) devices. ECRAM technology has been identified as a promising candidate for implementing artificial synapses in neuromorphic computing systems due to its ability to store analog values and its ease of programmability. ECRAM devices consist of an electrolyte and a channel material sandwiched between two electrodes, and the performance of these devices depends on the properties of the materials used. This review provides a comprehensive overview of material engineering strategies to optimize the electrolyte and channel materials' ionic conductivity, stability, and ionic diffusivity to improve the performance and reliability of ECRAM devices. Device engineering and scaling strategies are further discussed to enhance ECRAM performance. Last, perspectives on the current challenges and future directions in developing ECRAM-based artificial synapses in neuromorphic computing systems are provided., (© 2023 Wiley-VCH GmbH.)

In this study, we developed two novel conjugated polymers that can easily be doped with F4TCNQ organic dopants using a sequential doping method and then studied their organic thermoelectric (OTE) properties. In particular, to promote the intermolecular ordering of OTE polymers in the presence of the F4TCNQ dopant, alkylthiazole-based conjugated building blocks with highly planar backbone structures were synthesized and copolymerized. All polymers showed strong molecular ordering and edge-on orientation in the film state, even in the presence of the F4TCNQ organic dopant. Thus, the sequential doping process barely changed the molecular ordering of the polymer films while making efficient molecular doping. In addition, the doping efficiency was improved in the more π-extended polymer backbones with thienothiophene units due to the emptier space in the polymer lamellar structure to locate ionized F4TCNQ. Moreover, the study of organic thin-film transistors (OTFTs) revealed that higher hole mobility in OTFTs was the key to increasing the electrical conductivity of OTE devices fabricated using the sequential doping method.

Benzo[1,2-d:4,5-d']bis(oxazole) (BBO) is a heterocyclic aromatic ring composed of one benzene ring and two oxazole rings, which has unique advantages on the facile synthesis without any column chromatography purification, high solubility on the common organic solvents and planar fused aromatic ring structure. However, BBO conjugated building block has rarely been used to develop conjugated polymers for organic thin film transistors (OTFTs). Three BBO-based monomers, BBO without π-spacer, BBO with non-alkylated thiophene π-spacer and BBO with alkylated thiophene π-spacer, were newly synthesized and they were copolymerized with a strong electron-donating cyclopentadithiophene conjugated building block to give three p-type BBO-based polymers. The polymer containing non-alkylated thiophene π-spacer showed the highest hole mobility of 2.2 × 10 -2 cm 2 V -1 s -1 , which was 100 times higher than the other polymers. From the 2D grazing incidence X-ray diffraction data and simulated polymeric structures, we found that the intercalation of alkyl side chains on the polymer backbones was crucial to determine the intermolecular ordering in the film states, and the introduction of non-alkylated thiophene π-spacer to polymer backbone was the most effective to promote the intercalation of alkyl side chains in the film states and hole mobility in the devices.

In this study, we investigated the effect of an Al 2 O 3 barrier layer in an all-solid-state inorganic Li-based nano-ionic synaptic transistor (LST) with Li 3 PO 4 electrolyte/WO x channel structure. Near-ideal synaptic behavior in the ultralow conductance range (∼50 nS) was obtained by controlling the abrupt ion migration through the introduction of a sputter-deposited thin (∼3 nm) Al 2 O 3 interfacial layer. A trade-off relationship between the weight update linearity and on/off ratio with varying Al 2 O 3 layer thickness was also observed. To determine the origin of the Al 2 O 3 barrier layer effects, cyclic voltammetry analysis was conducted, and the optimal ionic diffusivity and mobility were found to be key parameters in achieving ideal synaptic behavior. Owing to the controlled ion migration, the retention characteristics were considerably improved by the Al 2 O 3 barrier. Finally, a highly improved pattern recognition accuracy (83.13%) was achieved using the LST with an Al 2 O 3 barrier of optimal thickness., (© 2021 IOP Publishing Ltd.)

In this study, the optical and electrical properties of a transparent conductive oxide (TCO) film synthesized via the radio frequency (RF) magnetron co-sputtering of Al-doped ZnO (AZO) and ZnO targets on a glass substrate were investigated. In the visible region, the resistivity, transmittance, and carrier concentration of the TCO film are influenced by the ratio of Al doping. The samples were prepared using two targets with the same deposition condition, except several different power levels on an AZO target to obtain different Al compositions in the film. The power range was 100-160 W in 20 W steps on the AZO target with a constant 50 W power level on the ZnO target. The electrical and optical characteristics of the film were measured using several apparatuses. The cross-section of the films was measured with via field emission scanning electron microscopy (FESEM) to determine the thickness of the film. The electrical and optical properties of the AZO films were measured via Hall measurement and UV-visible spectroscopy. The structural characteristics of the AZO films were confirmed by Raman spectroscopy.