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The amorphous carbon-based resistive memory has recently attained vast attention due to its non-volatility, fast switching speed, long data retention, and multilevel recording. However, the memory switching mechanism of amorphous carbon media remains mysterious and thus severely restricted its application prospect. To resolve this issue, a comprehensive three-dimensional model by simultaneously solving the current continuity equation, heat transfer equation, and mass concentration equation, is developed to model the physical conversions between sp2 and sp3 clusters. According to simulations, electric field was considered as the sole critical factor that determines the formation of conductive sp2 filament during the `SET' process, whereas the `RESET' process is mainly attributed to the induced high temperature that accelerates the growth of sp3 cluster and causes the rupture of the sp2 filament. It was additionally found that the sp2 filament was preferably formed inside the region having larger sp2 concentrations, and its rupture usually initiates from the filament center. The threshold voltages of carbon resistive memory for different thickness and different sp2 fractions were also calculated and exhibited good agreement with experimental measurements.

A phase-change memory (PCM) model for robust and efficient simulations of circuits including neuromorphic ones is reported in this work. The features of a hysteretic dynamic resistance in the voltage domain, and the incubation in the crystallization, are covered in the model. The Landau–Khalatnikov (LK)-type equation for ferroelectric is used to develop the PCM hysteresis module. A voltage-controlled relaxation oscillation is successfully simulated for the Ge2Sb2Te5 (GST) PCM. A technique of direct evaluation (DE) is then developed to reformulate the PCM model without any internal node. A significant enhancement of simulation efficiency is achieved compared with the traditional approach without sacrificing the accuracy. The functional correctness of the PCM device model and the acceleration effect in circuit simulations are verified. [ABSTRACT FROM AUTHOR]

A major challenge for glass X-ray tube makers is the reduction in the tube size for portable or handheld applications. Size reduction is difficult mainly due to contact size restrictions for glass-to-metal welding. In high-voltage (60–70 kV) portable applications such as dental imaging, a distance of at least 5 mm should be maintained between the anode and the glass envelope to prevent the latter from burnout, which further limits reduction in the tube’s diameter. In this study, reduction in the size of a dental X-ray tube by approximately 43% is achieved by replacing the glass envelope with ceramic. Instead of welding, the ceramic body permits the use of brazing, which supports extremely small contact sizes. Additionally, due to the higher dielectric constant of ceramic, even less than 1 mm spacing is permissible between the envelope and the anode, enabling further size reduction. Despite the 43% reduction in size, limiting spatial resolutions of approximately 8 and 7 lines per mm are obtained for the ceramic and glass sealed tubes, respectively. Moreover, the two tubes obtain similar X-ray images of human teeth, verifying the potential of the compact-size ceramic X-ray tube in dental imaging. [ABSTRACT FROM AUTHOR]

Using chlorophyll-a observational data from the Geostationary Ocean Color Imager (GOCI) satellite operated by the Korean Satellite Center, thousands of high chlorophyll belts are found along the coast of East China Sea (ECS). These belts extend tens to hundreds of kilometers offshore with an average length of roughly 90 km and 18.3% occurrence probability. Through statistical analysis, appearance of these belts is characterized with a band oriented along the coastline direction around 100-km offshore with a maximum likely occurrence near 28.5°N. The instability of the coastal front plays an important role in the formation of the high-appearance band, and the eastward current associated with the estuarine front contributes to the maximum occurrence region around 28.5°N. These chlorophyll belts not only provide additional nutrients for phytoplankton growth but also are an important factor for the healthy coastal ecosystems. [ABSTRACT FROM AUTHOR]

This article reviews the resistive random-access memory (ReRAM) technology initialization back in the 1960s and its heavily focused research and development from the early 2000s. This review goes through various oxygen/oxygen vacancy and metal-ion-based ReRAM devices and their operation mechanisms. This review also benchmarks the performance of various oxygen/oxygen vacancy and metal-ion-based ReRAM devices with general trend drawn. Being a semiconductor memory and storage technology, the commercialization attempts for both stand-alone mass storage/storage-class memory and embedded nonvolatile memory are also reviewed. Looking toward the coming era, the potential of using ReRAM technology to improve machine learning efficiency is discussed. [ABSTRACT FROM AUTHOR]

High-resistance state (HRS) current has significant effect on the reliability and power consumption of resistive switching memories. Low HRS current is helpful for obtaining ultra-low power and for high ON/OFF ratio nonvolatile memory application. The reduced HRS current of a sol-gel magnesium titanate nickelate-based resistive random access memory by using nickel (II) acetylacetone as substitute for acetylacetone in magnesium titanate (MTO) was presented. Forming-free, high ON/OFF ratio of over 106, excellent current distribution and good retention at 85 °C were achieved. Moreover, the effect of nickel (Ni) on the surface roughness, operation voltage, switching cycles, HRS current, ON/OFF ratio, current distribution, and switching behavior was explored. These results indicate that the incorporation of Ni in sol-gel MTO is an effective way to achieve high-performance memory devices.

A novel hydrogen sensor has been developed by using an optimized 0.18- $\mu \text{m}$ resistive random access memory process with a Pt/Ta2O5/TaOx/TaN stack. This resistive hydrogen sensor (ReHsensor) conforms to the ISO26142 standard in which it exhibits exceptional sensing capabilities, including a short response time (about 20 s for 1 vol.% hydrogen gas), high sensitivity, wide hydrogen concentration detection range (up to 4 vol.%) in air and N2 ambient, high gas selectivity (no reaction with CH4, CO, CH3OH, or CH3COCH3) and is immune to poisoning by SO2 and hexamethyl disiloxane. As it does not require a heater, the power consumption of the ReHsensor is very low, at 0.4 mW. [ABSTRACT FROM AUTHOR]

Nanoscale filament is the active area in oxygen vacancy type resistance random access memory (ReRAM), which is formed stochastically during electric test after being fabricated in a clean room. That is, the filament dimension cannot be controlled with a designed mask pattern. Here, we introduce a formula to describe the current cycle-to-cycle trajectories based on a stochastic differential equation (SDE) with microscopic structure parameters: filament dimension and oxygen vacancy concentration. Since ReRAM conduction follows hopping, the filament can be described by a random resistance network (RRN). The stochastic configuration of an RRN follows the Brownian motion, which is the key parameter in the diffusion of SDE. The formula provides a practically quantitative filament characterization method, which is verified by direct observation of the filament in actual devices. Based on the formula, we can predict ReRAM endurance with the given microscopic structure parameters. [ABSTRACT FROM AUTHOR]

The unidirectional bipolar resistance switching in GaN/InGaN-based light-emitting diode (LED) was discovered to explore optically readable resistive random access memory (RRAM) device. The device displays stable resistance window in both endurance and retention tests, showing good nonvolatility for memory application. The light-emitting state of this device can also be tuned by the resistance switching. Such phenomenon is illustrated as the switching between conventional light-emitting rectifying behavior and nonlight-emitting metal-like ohmic behavior. Large amount of structural and point defects in the epitaxial wafer were considered as the main contributor to the resistance switching in LED device. [ABSTRACT FROM AUTHOR]

Molecular communication is a nanoscale communication method in which information is encoded in molecules. Molecular communication using microtubules in free space is one of the realistic scenarios proposed for this type of nanocommunication. Based on this technique, molecular communication via filaments using nano-relays is proposed in this paper to improve the performance of the system in terms of delay and bit error probability. An analytical model using jump diffusion processes is proposed for molecular propagation in this scenario. It is shown that the proposed mathematical model is capable of tracking molecular propagation in molecular communication via filaments using nano-relays. Also, the model is used to investigate effects of different parameters on delay and bit error probability. [ABSTRACT FROM PUBLISHER]

Since thermal effects play a major role in filamentary RRAM devices, we compare the two localized thermometry methods developed for such devices. One method is based on short-pulsed measurements and the other on the measurement of minority-carrier injection from the filament into a semiconductor electrode by thermionic emission. We carried out and compared the measurements on the same functional oxide layer. Both methods indicate that the filament temperature is at least \sim 550 K during device operation. Furthermore, comparison between the measured thermal resistance and the thermal simulations of both techniques shows that under the conditions of low forming current compliance ( \sim 10~\mu \text{A} ), the filament dimensions are below \sim 5 nm. We show that the thermionic emission method is useful for high-resistance ( >100~\textk\Omega ) devices operating at low-power conditions ( <10~\mu \textW ), whereas the pulsed thermometry is more suitable for lower resistance devices ( <500~\textk\Omega ) operated above 1 \mu \textW . The average thermal resistance measured by the pulse technique decreases with applied power. Our simulations indicate that the expansion of the heated zone surrounding the filament can explain the observed reduction in thermal resistance with applied power. The underlying physics of the two methods is discussed. [ABSTRACT FROM AUTHOR]

Computer investigations devoted to hot filaments of streamer microwave (MW) discharge features and to shock wave (SW) ( $M\approx 1.5$ ) propagation through the MW filaments area have been made. Analysis of SW propagation through the hot filaments showed that there is a strong influence on SW, which leads to SW destruction at some filament forms and displacement. This shows a possibility of MW discharge hot filament applicability for technologies. [ABSTRACT FROM PUBLISHER]

The device size-dependent resistive memory switching and improvement in the switching performance in a CMOS compatible W/TiN contact device is reported as compared to W/W, Al/TiN, and Ir/TiN contacts, due to oxygen-rich layer formation at the W/filament interface. A small device area of 0.15 × 0.15 μm ^2 and interface between the electrodes has been observed from the transmission electron microscopy images. The fabricated small size devices have shown improved switching endurance with a small current compliance of 50 μA without separate forming process. The reactivity of electrode materials and its interface play an important role in obtaining the stable resistive switching behavior in W/TiN contact-formed W/TiOx/TiN structure. This device has shown long consecutive switching cycles (>10^3), read endurance of >10^5 times, good uniformity, and data retention of >10 ^4 s at 85 °C under low-current compliance of 50 μA. [ABSTRACT FROM PUBLISHER]

An analysis of the plasma front velocities during turnoff of a power diode is used to explain the differences between the formation and the behavior of cathode-side and anode-side filaments. Device simulations show, how cathode-side filaments may trigger a thermal runaway at the end of a reverse-recovery period of diodes turned off with extremely high current rates operating the diode in a regime far away from the safe operating area. From the transient voltage curve, the analysis of the reverse-recovery charge as a function of the dc-link voltage and an analysis of the turnoff transients in the current-voltage phase space, it is, however, deduced that the appearance of a cathode-side filament by itself does not necessarily lead to diode destruction. The transformation of the initially avalanche-generated filaments into filaments that are essentially driven by thermal mechanism seems to be a further important condition for device destruction. [ABSTRACT FROM PUBLISHER]

This paper gives an overview about different failure mechanisms which limit the safe operating area of power devices. It is demonstrated how the device internal processes can be investigated by means of device simulation. For instance, the electrothermal simulation of high-voltage diode turn-off reveals how a backside filament transforms into a continuous filament connecting the anode and cathode and how this can be accompanied with a transition from avalanche-induced into thermally driven carrier generation. A similar current destabilization may occur during insulated-gate bipolar transistor turn-off with a high turn-off rate, when the channel is closed quickly leading to strong dynamic avalanche. It is explained how the current filamentation depends on substrate resistivity, device thickness, channel width, and switching conditions (gate resistor and overcurrent). Filamentation processes during short-circuit events are discussed, and possible countermeasures are suggested. A mechanism of a periodically emerging and vanishing filament near the edge of the chip is presented. Examples on current destabilizing effects in gate turn-off thyristors, integrated gate-commutated thyristors, and metal–oxide–semiconductor field-effect transistors are given, and limitations of current device simulation are discussed. [ABSTRACT FROM PUBLISHER]

We developed a non-destructive testing (NOT) system utilizing multi-channel high-temperature superconductor (HTS) SQUID gradiometers in order to examine rare earth (RE)-123 coated conductors striated into multi-filamentary lines. The 5-channel HTS SQUID gradiometer array was composed of ramp-edge junctions with LaErBaCuO and SmBaCuO electrode layers, and fabricated by using an HTS multilayer fabrication technique. The parallel gradiometers detected the vertical element of magnetic field gradient induced around defects by an eddy current. It was demonstrated that we can detect macroscopic defects in each filamentary superconducting line at high speed up to 30 m/h. [ABSTRACT FROM AUTHOR]

Printed circuit board (PCB) specimens containing three different IPC-B-25 test structures were exposed to temperature/humidity/bias conditions in order to evaluate the effects of conformal coating, conductor spacing, voltage bias, flux chemistry, and test environment on surface insulation resistance (SIR). Results indicate that conformal coatings improve reliability, provided that sources of contamination on the PCB and within the coating are minimized. The presence of fibrous contaminants within the coating represented a preferential medium for moisture adsorption and ion transport, leading to accelerated reduction of SIR. In the absence of contamination, PCBs with conformal coatings were found to be less susceptible to SIR degradation than uncoated PCBs, with silicone providing better protection than urethane, and acrylic providing the least protection of the three coating materials evaluated. Conductor spacing was observed to represent a factor in the electrochemical migration (ECM) process independent of electric field, indicating that updated test structures are required to predict reliability of today's high-density assemblies. The SIR failure rate with rosin-based no-clean flux was observed to be greater than that with aqueous-based no-clean flux. A higher failure rate was also observed for tests conducted at 40 degC/93% RH than for 85 degC/85% RH. Due to the more rapid evaporation of weak organic acids in the flux residues at higher temperatures, test results obtained at 85 degC/85% RH will not accurately predict reliability at lower temperatures for PCBs processed using no-clean flux. PCB specimens were exposed to temperature/humidity/bias conditions in order to evaluate the effects of conformal coating, conductor spacing, voltage bias, flux chemistry, and test environment on reduction of surface insulation resistance. Results indicate that, in the absence of contamination, conformal coatings improve reliability [ABSTRACT FROM PUBLISHER]

Precursor filaments of Dy-Ba-Cu-O super-conductor were prepared by a solution spinning method and partially melting in an atmosphere gas with various Oxygen concentrations, It was found that the transport Jc value at 77 K and 0 T of the filamentary sample was strongly dependent on the partial-melting temperature and gas atmosphere. The samples partially melted under flowing 1%O2 + Ar gas exhibited Jc values larger than 104 A/cm² over a wide temperature range of 980-1040° C and a dense microstructure, The filamentary sample with the starting composition of Dy : Ba : Cu = 1.18 : 2.12 : 3.09 treated at 1020° C under flowing 1%O2+Ar showed a transport Jc value greater than 4.3 × 104 A/cm² at 77 K and 0 T, and the Jc value of 2.0 × 10³ A/cm² was maintained up to the magnetic fields of 14 T. The samples partially melted in 20% O2 + Ar gas and 100% O2 gas showed relatively low Jc value of 6.0 × 10³ A/cm² and 1.2 × 10² A/cm² at most. [ABSTRACT FROM AUTHOR]

Sub-1-nA operating current conductive-bridge resistive memory devices showing pronounced rectifying behavior have been demonstrated in a cell structure consisting of Cu top electrode, atomic layer deposition Al2O3 switching film and polysilicon bottom electrode as an in-cell resistor. This ultralow current provides energy savings by minimizing write, erase, and read currents. Despite having such low currents, excellent retention, ON/OFF ratio, and endurance have been demonstrated. Devices programmed with <1-nA peak current pass 6 h retention test at 85 °C and show no significant degradation after 10 000 write/erase cycles. Due to the partially formed filament, the devices at ON-state exhibit pronounced nonlinear $I$ – $V$ and current rectification—both factors are very beneficial for RRAM array operation. Multilevel storage can be obtained by controlling the filament shape through compliance current. [ABSTRACT FROM AUTHOR]

Traditionally, a large number of silicon oxide materials are extensively used as various dielectrics for semiconductor industries. In general, silicon oxide cannot be used as resistance random access memory (RRAM) due to its insulating electrical properties. In this letter, we have successfully produced resistive switching and forming-free behaviors by zinc doped into silicon oxide. The current–voltage fitting data show that current transport mechanism is governed by Poole–Frenkel behavior in high-resistance state and Ohm's law in low-resistance state, consisting with filament theory. Additionally, good endurance and retention reliabilities are exhibited in the zinc-doped silicon oxide RRAM. [ABSTRACT FROM AUTHOR]

The forming stage characteristics of electrochemical-metallization resistive-switching-random-access-memory cells are studied with an improved kinetic Monte Carlo simulator. The filament topographies obtained at different forming voltage levels and the relationship between forming time and filament topographies are investigated in detail. The so-called “voltage–time dilemma” is simulated and studied. In addition, the various chemical and physical processes that produce these results are discussed. Finally, the simulated pattern is compared with experiments conducted on \Cu/H2\O and \Ag/Ag2\S systems. [ABSTRACT FROM AUTHOR]

Memory-state [low-resistance state (RL) and high-resistance state (RH)] dependence of random telegraph noise (RTN) of \Ta2\O5/\TiO2 resistive random access memory is investigated. The conduction mechanism of both memory states and a limit of resistance controllability are also investigated to clarify the difference in the RTN mechanism of both states. The boundary between the RL and RH states was found at 5–20 \k\Omega, and the conduction mechanism much depended on the memory state. The noise also depended on the memory state. The noise amplitude in the RH state was larger than that in the RL state. In the RH state, a tunnel barrier was generated to cut off a conduction path (filament), and traps inside the tunnel barrier were supposed to increase the noise amplitude. Moreover, the composition of the following degraded the noise distribution in the RH state: 1) capture and emission of charges with traps and 2) instability of these traps against the bias temperature stress. [ABSTRACT FROM PUBLISHER]

The controllability of resistance in the set (low resistance) and reset (high resistance) states of Ta2O5/TiO2 resistive random access memory (ReRAM) was investigated to achieve low-voltage and multilevel operation. Since resistance in a set state tended to decrease due to the history effect of the lowest resistance, multilevel operation with a controlled set resistance was found to be difficult to achieve. On the other hand, the reset resistance could be controlled accurately by varying the reset voltage. The switching mechanism, the tunnel barrier of which is regenerated to cut off the filament, obtains the high repeatability of the reset resistance. As a result, a four-level storage ReRAM was successfully demonstrated with multireset level operation. In addition, the set voltage was found to strongly depend on reset resistance. Preventing reset resistance from exceeding 1 GΩ achieved a low-set-voltage operation below 5 V. [ABSTRACT FROM AUTHOR]

In this letter, we investigated the current-dependent switching characteristics of Al/6F-HAB-diphenyl carbamyl (PI-DPC)/Al devices fabricated by spin coating. The current required to switch off the device increased with an increase in the current compliance, limiting the ON-state current, whereas the on and off voltages were almost constant. In addition, the turn-off current and the on and off voltages remained almost constant at the constant current compliance. The observed phenomenon indicates that the bistability of the PI-DPC device that is induced by controlling the current is attributed to filament formation and repulsive Coulomb interaction by charge trapping. [ABSTRACT FROM AUTHOR]

Formation of multifilaments in dielectric barrier discharge (DBD) excimer lamp has been simulated using two dimensional fluid model. The simulation had started from a small cluster of electron-ion pair in the middle of discharge gap. After the first streamer arrived at the cathode, the discharge expanded on the surface of the dielectric toward the lateral direction until the polarity of the discharge voltage change. The edges of this surface discharge become the start point of next second and third filaments. Within one and half cycles of the discharge voltage waveform, five filaments are formed in stably in 3-cm discharge space. [ABSTRACT FROM AUTHOR]