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After the Paris Agreement was signed in 2015, many countries worldwide focused on the hydrogen economy, aiming for eco-friendly and renewable energy by moving away from the existing carbon economy, which has been the primary source of global warming. Hydrogen is the most common element on Earth. As a light substance, hydrogen can diffuse quickly; however, it also has a small risk of explosion. Representative explosion accidents have included the Muskingum River Power Plant Vapor Cloud Explosion accident in 2007 and the Silver Eagle Refinery Vapor Cloud Explosion accident in 2009. In addition, there was an explosion in a hydrogen tank in Gangneung, Korea, in May 2019, and a hydrogen refueling station (HRS) in Norway exploded in 2018. Despite this risk, Korea is promoting the establishment of HRSs in major urban centers, including downtown areas and public buildings, by using the Regulatory Sandbox to install HRSs. This paper employed the Hydrogen Risk Assessment Model (HyRAM) of Sandia National Laboratories (SNL), a quantitative risk assessment (QRA) program specialized in hydrogen energy for HRSs installed in major urban hubs. A feasibility evaluation of the site conditions of an HRS was conducted using the French land use planning method based on the results obtained through evaluation using the HyRAM and the overpressure results of PHAST 8.0. After a risk assessment, we confirmed that an HRS would be considered safe, even if it was installed in the city center within a radius of influence of jet fires and overpressure. [ABSTRACT FROM AUTHOR]

In this article, we investigate dynamics of electrically driven abrupt and volatile resistive switching characteristics, which are called threshold switching (TS) characteristics, in insulator-to-metal transition NbOx switch, BTex-based ovonic threshold switch, and Ag-based atomic switch by adopting field-induced nucleation theory. To verify field-induced nucleation phenomena in the initial electroforming and electrically driven TS processes of the TS devices, we apply constant square voltage pulses with various voltage magnitudes and measure the delay time required for the electrical switching process. During both the forming and switching processes, it is observed that all the TS devices exhibit switching delay time exponential in 1/voltage with different nucleation barrier energies (W0). In addition, we find that the W0 for the first forming process appears to be larger than that for the subsequent switching process and the difference is observed to be greater if the formed device is crystallized and smaller if not. Moreover, we find that the effective barrier energy and the fastest speed that a device can have (τ0) are closely related to switching speed of the TS devices. Also, we reveal that the hold voltage characteristics are affected by the W0 and carrier concentration of the solid electrolyte. [ABSTRACT FROM AUTHOR]

In this study, we investigate the initial electroforming and electrically driven threshold switching characteristics of a binary boron-tellurium-based ovonic threshold switch (OTS) device using field-induced nucleation theory and related material parameters. First, an analysis of the current-voltage characteristics of devices with various electrode areas shows that the OTS device exhibits filamentary switching, consistent with the field-induced nucleation framework. Further, we find that the OFF-state current depends on the device area, whereas the hold current remains constant regardless of the device area, indicating that the ON-state current flows through a local conduction path. For verifying field-induced nucleation phenomena in the forming and subsequent switching of the OTS device, we apply constant voltage pulses and measure the delay time required for electrical switching of the device. During both forming and switching processes, the switching time is exponential in inverse voltage with different nucleation energy (W0) values; W0 for forming is larger than that for switching. To verify this analysis, incremental voltage pulses with various pulse widths are also applied to confirm the relation between the threshold voltage and time. The W0 values for the two types of switching in this analysis are consistent, solidifying our understanding of the critical contribution of nucleation phenomena in OTS. The smaller W0 for switching can be explained by the generation of clusterlike nucleation sites during forming with lower nucleation energy than in the surrounding matrix. [ABSTRACT FROM AUTHOR]

This paper examines network prominence in a co-prescription network as an indicator of opioid doctor shopping (i.e., fraudulent solicitation of opioids from multiple prescribers). Using longitudinal data from a large commercially insured population, we construct a network where a tie between patients is weighted by the number of shared opioid prescribers. Given prior research suggesting that doctor shopping may be a social process, we hypothesize that active doctor shoppers will occupy central structural positions in this network. We show that network prominence, operationalized using PageRank, is associated with more opioid prescriptions, higher predicted risk for dangerous morphine dosage, opioid overdose, and opioid use disorder, controlling for number of prescribers and other variables. Moreover, as a patient's prominence increases over time, so does their risk for these outcomes, compared to their own average level of risk. Results highlight the importance of co-prescription networks in characterizing high-risk social dynamics. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate a new concept of threshold selector by combining Ag-based selector with NbOx insulator metal transition (IMT) selector. To overcome intrinsic limits of slow turn-off speed ( $> 1\mu \text{s}$ ) of the Ag-based selector, we adopted NbOx IMT selector with fast turn-off speed. The hybrid device exhibits excellent selector characteristics, such as extremely low off-current (<1 pA) and fast turn-off speed ( $< 1~\mu \text{s}$ ). It shows excellent read-out margin (>75% at >210 word lines) in a fast sequential operation of cross point memory array. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a volatile atomic switch that can be utilized for obtaining steep subthreshold swing (SS) (<5 mV/dec) characteristics in FETs. We propose a CMOS-compatible atomic switch (W/Cu2S/W) that demonstrates volatility and immunity to the voltage–time dilemma. Furthermore, we enhance the device characteristics by examining the composition control, scaling of device size, and film thickness. Then, the atomic switch is integrated with a conventional transistor that has a large SS (>60 mV/dec). The result shows an improvement in the SS, which results from the transition of the atomic switch between the ON and OFF states, which is caused by the formation and rupture of a conductive filament. As a result, excellent switching characteristics are obtained for the FETs, such as low IOFF (∼10−5μA/μm), high ION/IOFF ratio (∼105), low VDD (∼0.25 V), and steep SS (<5 mV/dec). [ABSTRACT FROM AUTHOR]

In this research, we investigate an electroforming and electrically driven insulator-metal transition (E-IMT) characteristic of the NbOx film that follows the framework of nucleation theory. First, we carry out the electroforming process to form the crystalline NbO2 phase, and it separated to nucleation and grain-growth according to external electric field degree. During the electroforming process, we also study the field-induced nucleation that occurred selectively according to the crystallinity of films. We conclude that the E-IMT process was the result of Peierls transition between the tetragonal and the rutile NbO2 phases, and we experimentally deduce the minimum energy pathway for transition. [ABSTRACT FROM AUTHOR]

This study demonstrates an integrate and fire (I&F) neuron using threshold switching (TS) devices to implement spike‐based neuromorphic system. An I&F neuron can be realized using the hysteric voltage switch characteristics of a TS device. To investigate the effects of various TS devices on neuron behavior, neurons are compared using three different types of TS device: NbO2‐based insulator‐to‐metal transition (IMT) device, B–Te‐based ovonic threshold switching device, and Ag/HfO2‐based atomic‐switching TS device. The results show that the off‐state resistance and switching time of the TS devices determine the leaky/nonleaky characteristics and types of activation function of neuron, respectively. In addition, it is confirmed that the threshold voltage and on‐state resistance of the TS device determine the total power consumption of neuron. Furthermore, the feasibility of the TS devices in a spiking neural network is verified by simulation program with integrated circuit emphasis (SPICE) simulation. This work indicates applicability of TS‐based I&F neuron in neuromorphic hardware application. [ABSTRACT FROM AUTHOR]

The development of selector devices is essential for the implementation of dense memory arrays. Ovonic threshold switch (OTS) devices have gained interest as high‐performance selectors, but their material complexity and low thermal stability remain concerns. The effect of element compositions and its types on binary telluride‐based OTS are investigated to develop selectors that meet the simple material composition and high thermal stability requirements while ensuring low OFF‐state leakage current (IOFF). Through a careful control of Te composition in binary tellurides, binary OTS devices with low IOFF (≈5 nA) and fast switching speed (<10 ns) are obtained. In addition, high endurance (108) and thermal stability (450 °C) are achieved by adopting tellurides including small elements. The high thermal stability of the developed OTS devices results from the strong covalent bonds between Te and small elements that prevent crystallization of the tellurides, which is revealed by performing first‐principles calculations. The binary OTS are also compatible with a 3D stacking technology, which is confirmed by fabricating a 3D B‐Te‐based device that shows good OTS characteristics. In addition, the OTS device successfully suppresses the leakage current in half‐selected cells when it is integrated with a resistive random access memory (ReRAM) device. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate a new binary ovonic threshold switching (OTS) selector device scalable down to ø30 nm based on C-Te. Our proposed selector device exhibits outstanding performance such as a high switching ratio (I on /I off  > 10 5 ), an extremely low off-current (∼1 nA), an extremely fast operating speed of <10 ns (transition time of <2 ns and delay time of <8 ns), high endurance (10 9 ), and high thermal stability (>450 °C). The observed high thermal stability is caused by the relatively small atomic size of C, compared to Te, which can effectively suppress the segregation and crystallization of Te in the OTS film. Furthermore, to confirm the functionality of the selector in a crossbar array, we evaluated a 1S-1R device by integrating our OTS device with a ReRAM (resistive random access memory) device. The 1S-1R integrated device exhibits a successful suppression of leakage current at the half-selected cell and shows an excellent read-out margin (>2 12 word lines) in a fast read operation.

NbO 2 has the potential for a variety of electronic applications due to its electrically induced insulator-to-metal transition (IMT) characteristic. In this study, we find that the IMT behavior of NbO 2 follows the field-induced nucleation by investigating the delay time dependency at various voltages and temperatures. Based on the investigation, we reveal that the origin of leakage current in NbO x is partly due to insufficient Schottky barrier height originating from interface defects between the electrodes and NbO x layer. The leakage current problem can be addressed by inserting thin NiO y barrier layers. The NiO y inserted NbO x device is drift-free and exhibits high I on /I off ratio (>5400), fast switching speed (<2 ns), and high operating temperature (>453 K) characteristics which are highly suitable to selector application for x-point memory arrays. We show that NbO x device with NiO x interlayers in series with resistive random access memory (ReRAM) device demonstrates improved readout margin (>2 9 word lines) suitable for x-point memory array application.

In this paper, we investigate the quantized conduction behavior of conductive bridge random access memory (CBRAM) with varied materials and ramping rates. We report stable and reproducible quantized conductance states with integer multiples of fundamental conductance obtained by optimizing the voltage ramping rate and the Ti-diffusion barrier (DB) at the Cu/HfO 2 interface. Owing to controlled diffusion of Cu ions by the Ti-DB and the optimized ramping rate, through which it was possible to control the time delay of Cu ion reduction, more than seven levels of discrete conductance states were clearly observed. Analytical modeling was performed to determine the rate-limiting step in filament growth based on an electrochemical redox reaction. Our understanding of the fundamental mechanisms of quantized conductance behaviors provide a promising future for the multi-bit CBRAM device.