Highly Tunable Negative Differential Resistance Device Based on Insulator-to-Metal Phase Transition of Vanadium Dioxide.

Negative differential resistance (NDR) based on the band-to-band tunneling (BTBT) mechanism has recently shown great potential in improving the performance of various electronic devices. However, the applicability of conventional BTBT-based NDR devices is restricted by their insufficient performance due to the limitations of the NDR mechanism. In this study, we develop an insulator-to-metal phase transition (IMT)-based NDR device that exploits the abrupt resistive switching of vanadium dioxide (VO2) to achieve a high peak-to-valley current ratio (PVCR) and peak current density (Jpeak) as well as controllable peak and valley voltages (Vpeak/valley). When a phase transition is induced in VO2, the effective voltage bias on the two-dimensional channel is decreased by the reduction in the VO2 resistance. Accordingly, the effective voltage adjustment induced by the IMT results in an abrupt NDR. This NDR mechanism based on the abrupt IMT results in a maximum PVCR of 71.1 through its gate voltage and VO2 threshold voltage tunability characteristics. Moreover, Vpeak/valley is easily modulated by controlling the length of VO2. In addition, a maximum Jpeak of 1.6 × 106 A/m2 is achieved through light-tunable characteristics. The proposed IMT-based NDR device is expected to contribute to the development of various NDR devices for next-generation electronics.

A Systematic Review on Recent Trends, Challenges, Privacy and Security Issues of Underwater Internet of Things.

Owing to the hasty growth of communication technologies in the Underwater Internet of Things (UIoT), many researchers and industries focus on enhancing the existing technologies of UIoT systems for developing numerous applications such as oceanography, diver networks monitoring, deep-sea exploration and early warning systems. In a constrained UIoT environment, communication media such as acoustic, infrared (IR), visible light, radiofrequency (RF) and magnet induction (MI) are generally used to transmit information via digitally linked underwater devices. However, each medium has its technical limitations: for example, the acoustic medium has challenges such as narrow-channel bandwidth, low data rate, high cost, etc., and optical medium has challenges such as high absorption, scattering, long-distance data transmission, etc. Moreover, the malicious node can steal the underwater data by employing blackhole attacks, routing attacks, Sybil attacks, etc. Furthermore, due to heavyweight, the existing privacy and security mechanism of the terrestrial internet of things (IoT) cannot be applied directly to UIoT environment. Hence, this paper aims to provide a systematic review of recent trends, applications, communication technologies, challenges, security threats and privacy issues of UIoT system. Additionally, this paper highlights the methods of preventing the technical challenges and security attacks of the UIoT environment. Finally, this systematic review contributes much to the profit of researchers to analyze and improve the performance of services in UIoT applications.

Steep-Slope Gate-Connected Atomic Threshold Switching Field-Effect Transistor with MoS2 Channel and Its Application to Infrared Detectable Phototransistors.

For next-generation electronics and optoelectronics, 2D-layered nanomaterial-based field effect transistors (FETs) have garnered attention as promising candidates owing to their remarkable properties. However, their subthreshold swings (SS) cannot be lower than 60 mV/decade owing to the limitation of the thermionic carrier injection mechanism, and it remains a major challenge in 2D-layered nanomaterial-based transistors. Here, a gate-connected MoS2 atomic threshold switching FET using a nitrogen-doped HfO2-based threshold switching (TS) device is developed. The proposed device achieves an extremely low SS of 11 mV/decade and a high on-off ratio of ≈106 by maintaining a high on-state drive current due to the steep switching of the TS device at the gate region. In particular, the proposed device can function as an infrared detectable phototransistor with excellent optical properties. The proposed device is expected to pave the way for the development of future 2D channel-based electrical and optical transistors.

Enhancement of Synaptic Characteristics Achieved by the Optimization of Proton-Electron Coupling Effect in a Solid-State Electrolyte-Gated Transistor.

Presently, the 3-terminal artificial synapse device has been in focus for neuromorphic computing systems owing to its excellent weight controllability. Here, an artificial synapse device based on the 3-terminal solid-state electrolyte-gated transistor is proposed to achieve outstanding synaptic characteristics with a human-like mechanism at low power. Novel synaptic characteristics are accomplished by precisely tuning the threshold voltage using the proton-electron coupling effect, which is caused by proton migration inside the electrolyte. However, these synaptic characteristics are degraded because traps at the interface of channel/electrolyte disturb the proton-electron coupling effect. To minimize degradation, the oxygen plasma treatment is performed to reduce interface traps. As a result, symmetric weight updates and outstanding synaptic characteristics are achieved. Furthermore, high repeatability and long-term plasticity are observed at low operating power, which is essential for artificial synapses. Therefore, this study shows the progress of artificial synapses and proposes a promising method, a low-power neuromorphic system, to achieve high accuracy.

Hysteresis Modulation on Van der Waals-Based Ferroelectric Field-Effect Transistor by Interfacial Passivation Technique and Its Application in Optic Neural Networks.

2D semiconductor-based ferroelectric field effect transistors (FeFETs) have been considered as a promising artificial synaptic device for implementation of neuromorphic computing systems. However, an inevitable problem, interface traps at the 2D semiconductor/ferroelectric oxide interface, suppresses ferroelectric characteristics, and causes a critical degradation on the performance of 2D-based FeFETs. Here, hysteresis modulation method using self-assembly monolayer (SAM) material for interface trap passivation on 2D-based FeFET is presented. Through effectively passivation of interface traps by SAM layer, the hysteresis of the proposed device changes from interface traps-dependent to polarization-dependent direction. The reduction of interface trap density is clearly confirmed through the result of calculation using the subthreshold swing of the device. Furthermore, excellent optic-neural synaptic characteristics are successfully implemeted, including linear and symmetric potentiation and depression, and multilevel conductance. This work identifies the potential of passivation effect for 2D-based FeFETs to accelerate the development of neuromorphic computing systems.

Infrared Detectable MoS2 Phototransistor and Its Application to Artificial Multilevel Optic-Neural Synapse.

Layered two-dimensional (2D) materials have entered the spotlight as promising channel materials for future optoelectronic devices owing to their excellent electrical and optoelectronic properties. However, their limited photodetection range caused by their wide bandgap remains a principal challenge in 2D layered materials-based phototransistors. Here, we developed a germanium (Ge)-gated MoS2 phototransistor that can detect light in the region from visible to infrared (λ = 520-1550 nm) using a detection mechanism based on band bending modulation. In addition, the Ge-gated MoS2 phototransistor is proposed as a multilevel optic-neural synaptic device, which performs both optical-sensing and synaptic functions on one device and is operated in different current ranges according to the light conditions: dark, visible, and infrared. This study is expected to contribute to the development of 2D material-based phototransistors and synaptic devices in next-generation optoelectronics.

Ultralow Schottky Barrier Height Achieved by Using Molybdenum Disulfide/Dielectric Stack for Source/Drain Contact.

Energy barrier formed at a metal/semiconductor interface is a critical factor determining the performance of nanoelectronic devices. Although diverse methods for reducing the Schottky barrier height (SBH) via interface engineering have been developed, it is still difficult to achieve both an ultralow SBH and a low dependence on the contact metals. In this study, a novel structure, namely, a metal/transition-metal dichalcogenide (TMD) interlayer (IL)/dielectric IL/semiconductor (MTDS) structure, was developed to overcome these issues. Molybdenum disulfide (MoS2) is a promising TMD IL material owing to its interface characteristics, which yields a low SBH and reduces the reliance on contact metals. Moreover, an ultralow SBH is achieved via the insertion of an ultrathin ZnO layer between MoS2 and a semiconductor, thereby inducing an n-type doping effect on the MoS2 IL and forming an interface dipole in the favorable direction at the ZnO IL/semiconductor interfaces. Consequently, the lowest SBH (0.07 eV) and a remarkable improvement in the reverse current density (by a factor of approximately 5400) are achieved, with a wide room for contact-metal dependence. This study experimentally and theoretically validates the effect of the proposed MTDS structure, which can be a key technique for next-generation nanoelectronics.

Reduction of Threshold Voltage Hysteresis of MoS2 Transistors with 3-Aminopropyltriethoxysilane Passivation and Its Application for Improved Synaptic Behavior.

Although molybdenum disulfide (MoS2) is highlighted as a promising channel material, MoS2-based field-effect transistors (FETs) have a large threshold voltage hysteresis (Δ VTH) from interface traps at their gate interfaces. In this work, the Δ VTH of MoS2 FETs is significantly reduced by inserting a 3-aminopropyltriethoxysilane (APTES) passivation layer at the MoS2/SiO2 gate interface owing to passivation of the interface traps. The Δ VTH is reduced from 23 to 10.8 V by inserting the 1%-APTES passivation layers because APTES passivation prevents trapping and detrapping of electrons, which are the major source of the Δ VTH. The reduction in the density of interface traps ( Dit) is confirmed by the improvement of the subthreshold swing (SS) after inserting the APTES layer. Furthermore, the improvement in the synaptic characteristics of the MoS2 FET through the APTES passivation is investigated. Both inhibitory and excitatory postsynaptic currents (PSC) are increased by 33% owing to the reduction in the Δ VTH and the n-type doping effect of the APTES layer; moreover, the linearity of PSC characteristics is significantly improved because the reduction in Δ VTH enables the synaptic operation to be over the threshold region, which is linear. The application of the APTES gate passivation technique to MoS2 FETs is promising for reliable and accurate synaptic applications in neuromorphic computing technology as well as for the next-generation complementary logic applications.

Nitrogen-Induced Filament Confinement Technique for a Highly Reliable Hafnium-Based Electrochemical Metallization Threshold Switch and Its Application to Flexible Logic Circuits.

Electrochemical metallization (ECM) threshold switches are in great demand for various applications such as next-generation logic technology, future memory, and neuromorphic computing. However, the instability of operation due to inherent filamentary randomness is a severe problem that is yet to be solved. Here, we propose a specially treated hafnium oxide (HfO x:N)-based ECM threshold switch with high reliability, low-voltage operation (0.2 V), high ON/OFF ratio (5 × 108), great endurance (106), and fast switching speed (1.5 µs at 2 V). The nitrogen ions in the HfO x:N layer assist confining the path of the metallic filament, which significantly suppresses filament randomness as well as reduces power consumption and alternating current response time. The feasibility of ECM threshold switches to logic applications, AND and OR, is first introduced. The ECM threshold switch has great potential to be utilized in complementary logic circuits because of its ultralow operation power consumption, high integrability using an array structure (4 F2), and fast switching characteristics. Furthermore, we have successfully verified its applicability to flexible electronics on polyethylene naphthalate films that can retain stable operation under considerable mechanical stress. We believe that this research paves the way to fabricate highly reliable ECM threshold switches for flexible complementary logic circuits with ultralow power consumption.

Schottky Barrier Height Modulation Using Interface Characteristics of MoS2 Interlayer for Contact Structure.

Schottky barrier height (SBH) engineering of contact structures is a primary challenge to achieve high performance in nanoelectronic and optoelectronic applications. Although SBH can be lowered through various Fermi-level (FL) unpinning techniques, such as a metal/interlayer/semiconductor (MIS) structure, the room for contact metal adoption is too narrow because the work function of contact metals should be near the conduction band edge (CBE) of the semiconductor to achieve low SBH. Here, we propose a novel structure, the metal/transition metal dichalcogenide/semiconductor structure, as a contact structure that can effectively lower the SBH with wide room for contact metal adoption. A perpendicularly integrated molybdenum disulfide (MoS2) interlayer effectively alleviates FL pinning by reducing metal-induced gap states at the MoS2/semiconductor interface. Additionally, it can induce strong FL pinning of contact metals near its CBE at the metal/MoS2 interface. The technique using FL pinning and unpinning at metal/MoS2/semiconductor interfaces is first introduced in the MIS scheme to allow the use of various contact metals. Consequently, significant reductions of the SBH from 0.48 to 0.12 eV for GaAs and from 0.56 to 0.10 eV for Ge are achieved with several different contact metals. This work significantly reduces the dependence on contact metals with lowest SBH and proposes a new way of overcoming current severe contact issues for future nanoelectronic and optoelectronic applications.

Clinical significance of preoperative neutrophil-lymphocyte versus platelet-lymphocyte ratio in patients with operable colorectal cancer.

The objective of this study was to clarify whether the neutrophil-lymphocyte ratio (NLR) and the platelet-lymphocyte ratio (PLR) are significant prognostic markers in patients with resectable colorectal cancer (CRC). A total of 200 patients who underwent curative resection for CRC were enrolled. The NLR and PLR were positively correlated (p < 0.001). Both the NLR and PLR were shown to be good prognostic biomarkers of overall survival (OS) (p=0.002 and p=0.001, respectively). The PLR was an independent prognostic factor of OS based on multivariate analysis (hazard ratio, 1.971; 95% confidence interval, 1.102-3.335; p=0.021).

Clinical importance of Bcl-6-positive non-deep-site involvement in non-HIV-related primary central nervous system diffuse large B-cell lymphoma.

In several studies of primary central nervous system lymphoma (PCNSL), deep-site involvement of the brain, as well as age and performance status (PS), were found to be independent prognostic factors. In immunocompetent patients, most primary central nervous system lymphomas (PCNSL) are diffuse large B-cell lymphomas (DLBCL), and recent studies have shown that Bcl-6 would be a favorable prognostic biomarker in PCNS-DLBCL. The objective of this study is to evaluate the clinical importance of the central nervous system (CNS) involvement pattern combined with Bcl-6 expression in PCNS-DLBCL patients. This study included 65 immunocompetent patients with PCNS-DLBCL who underwent treatment with high-dose methotrexate with whole-brain radiotherapy. Immunochemistry was performed for the Bcl-6 and Ki-67 antigens. Forty-four patients were male and 21 patients were female, with median age of 59 years. During the median follow-up period of 26 months, progression-free survival (PFS) was 25% and overall survival (OS) was 31%. Of 65 cases that could be subclassified, 31 patients were Bcl-6 positive and 34 patients were negative. Deep-site involvement of the brain was observed in 31 patients. The Bcl-6-positive group and the group having non-deep-site involvement of the brain were associated with favorable progression-free survival (PFS) (P < 0.001; P < 0.001) and overall survival (OS) (P = 0.001; P < 0.001). Results of univariate analysis showed that age above 60 years, Eastern Cooperative Oncology Group (ECOG) PS above 2, elevated lactate dehydrogenase (LDH) state, complete response (CR), and Bcl-6-positive and deep-site involvement were prognostic factors associated with PFS and OS. Results of multivariate analysis revealed that age above 60 years, ECOG above 2, elevated LDH state, Bcl-6 positivity, and deep-site involvement were independent prognostic factors for prediction of outcome. According to the combined prognostic value of Bcl-6 expression and the deep-site involvement pattern, the subgroup having Bcl-6-positive non-deep-site involvement of the brain showed more favorable PFS and OS than the other subgroups (P < 0.001, P < 0.001), whereas differences of survival among the other three subgroups were not significant (P = 0.054, P = 0.056). Bcl-6 positivity was found to be an independent prognostic factor for survival. Bcl-6 expression was associated with higher PFS and OS in patients having non-deep-site involvement. However, this was counteracted in the group of patients having deep-site involvement of the brain.

Clinical value of absolute lymphocyte counts before bortezomib-dexamethasone therapy in relapsed multiple myeloma patients.

A high absolute lymphocyte count (ALC) at diagnosis is known as a surrogate marker of favorable prognosis in newly diagnosed multiple myeloma (MM). Recent studies showed tumor sensitization and enhanced cytotoxicity of bortezomib. We hypothesized that a high ALC before bortezomib treatment would contribute to tumor sensitization and activated cytotoxicity of bortezomib in relapsed MM. Ninety-seven relapsed MM patients who underwent bortezomib-dexamethasone (Vel-Dex) therapy were analyzed. Median follow-up duration was 21 months and median age was 61 years. Complete response (CR) and very good partial response (VGPR) after 2 cycles of Vel-Dex therapy were higher in the high-ALC group (>or=1.1 x 10(9)/l) (CR + VGPR 50.0% in the high-ALC group vs. 10.4% in the low-ALC group, p = 0.001), and stable disease (SD) rate was lower in the high-ALC group (SD 11.8% in the high-ALC group vs. 44.8% in the low-ALC group, p < 0.001). In the univariate analysis, the low-ALC group before therapy was associated with shorter progression-free survival (PFS) [hazard ratio (HR), 2.780; 95% confidence interval (95% CI) 1.703-4.536, p < 0.001]. Multivariate analysis revealed that a low ALC represented an independent predictive factor for PFS (HR 1.937, 95% CI 1.168-3.212, p = 0.010). A low ALC just before Vel-Dex therapy was associated with a poor prognosis in relapsed MM.

Clinical impact of bulky mass in the patient with primary extranodal diffuse large B cell lymphoma treated with R-CHOP therapy.

Although numerous studies about primary extranodal diffuse large B cell lymphoma (DLBCL) were reported sporadically, the literature of clinical value of immunophenotype and bulky diameter in rituximab era is limited. Ninety-six patients with primary extranodal DLBCL receiving R-CHOP therapy were analyzed to evaluate whether immunophenotype and size of bulky disease are significantly important. The International Prognostic Index was still an important prognostic factor for progression-free survival (PFS) and overall survival (OS; p = 0.003, p = 0.027). Difference of survival between germinal center (GC) type and non-GC type was not different (PFS: p = 0.192; OS: p = 0.197). In two separated groups according to extranodal maximum tumor diameter (EN-MTD) 7.5 cm as cutoff value for survival, the group of EN-MTD > or =7.5 cm had lower PFS and OS than <7.5 cm (PFS: p = 0.001; OS: p = 0.008). In four divided subgroups according to EN-MTD combined with immunophenotype, the subgroup of non-GC type with EN-MTD > or = 7.5 cm had lower PFS and OS compared with the other subgroups (PFS: p < 0.001; OS: p = 0.008). Multivariate analysis revealed that non-GC with EN-MTD > or = 7.5 cm was an independent prognostic parameter (PFS: HR = 5.407, 95%CI = 2.378-12.294, p < 0.001; OS: HR = 4.136, 95%CI = 1.721-9.941, p = 0.002). Bulky primary extranodal DLBCL would be associated with unfavorable outcome especially in non-GC type.