Sidewall Materials Research Articles

Solving the issue of increasing forming voltage during device miniaturization in hafnium oxide-based resistive access memory using high-k sidewall material

An electrothermal coupling model of resistive random access memory (RRAM) was established based on the oxygen vacancy conduction mechanism. By resolving the partial differential equation for the coefficients, the variation process of the device resistance was simulated. In our studies, a device model was proposed which can accurately simulate the whole process of RRAM forming, reset, and set. Based on the established model, a new high dielectric constant (high-k) material (La2O3) is introduced as the sidewall material. The La2O3 sidewall material can concentrate the electric field and helps to speed up the formation of conductive filaments. The La2O3 sidewall can effectively reduce the forming voltage increase during the miniaturization process. Then, the influence of sidewall thermal conductivity on forming voltage is studied, and it is discovered that low thermal conductivity helps to reduce the model’s forming voltage and increase the temperature concentration. These findings serve as a foundation for more studies on the choice of sidewall materials.

Experimental studies on sidewall pool fire for assessing green façades hazard

Fire hazard assessment on green façade used to be carried out by a window plume. Large amount of fuel was burnt. A small pool fire placed adjacent to the façade can give similar effect on assessing the hazardous consequences. Fire plume characteristics provide important information of fire hazards adjacent to façade. The average flame height of rectangular source fire located against different sidewall materials were investigated in this study.Burning tests were conducted with rectangular burners of different dimensions with adjacent walls of different thermal properties, including steel plate and calcium silicate board. Experimental results of fire source with sidewall were compared with those in open space. Due to sidewall blockage, a deep necking-in structure was observed at the flame base and entrained air for combustion. Effect of aspect ratio of the fire pool and effect of heat loss through a sidewall on the average flame height were investigated. Convection lost would decrease the temperature of the fuel-air mixture and should not be ignored. On average, the mean flame height of the fire source with steel plate was 1.08 times that with calcium silicate board. A model for estimating the average flame height was developed by modifying the mirror model.

Extremely high corrosion resistance of ZnxNi1–xCr2O4 spinel as sidewalls in the aluminum electrolyte

The sidewall material is a key component in new electrolytic cell with an inert electrode for the aluminum electrolysis industry. The continuous development of novel sidewall materials with excellent corrosion resistance in molten salts electrolyte is an important topic. Herein, a new system of sidewall material, spinel structured ZnxNi1–xCr2O4 (x = 0 – 1), is prepared by solid-phase reaction and the corrosion-resistance enhancement is investigated. The results prove that Zn2+ plays two roles in the ZnxNi1–xCr2O4 spinels. Firstly, Zn2+ tunes the surface energies of spinels resulting in the octahedral grains, which suppresses the cation diffusion in the corrosion process. Secondly, Zn2+ stabilizes the Cr3+ in the spinels. As a result, the Zn0.5Ni0.5Cr2O4 spinel displays an extremely low corrosion rate ∼0.007 cm·a–1 in NaF-KF-AlF3 bath at 800 °C comparing with other sidewall materials. The as-obtained spinel shows great potential as a novel sidewall material for the new electrolytic cell.

A comparative study on high pulse energy femtosecond laser drilling of high-aspect-ratio holes under different pressure conditions

Laser drilling of high-aspect-ratio holes is gradually on the agenda in the field of aerospace manufacturing. We present a comparative study of high pulse energy femtosecond laser micro-hole machining of thermal barrier coated superalloys under different pressure conditions. The ablation results showed that severe contaminative ablation patterns occurred near the geometric focus position, which is related to the remarkable refraction of the plasma near the geometric focus. Adopting negative defocus positions can restrain the plasma defocusing effect and eliminate these ablation defects. As compared to the case in the atmospheric pressure condition, the drilled holes had good retention in diameters, and the aperture size as small as 30 μm can be achieved in the low-pressure environment, which is attributed to a good suppression of the plasma defocusing effect. The drilled samples have convergent and divergent shapes struck within the hole in the low-pressure condition while the hole profiles show good collimation along the thickness direction in the atmospheric pressure environment. This can be attributed to the fact that the pulse energy can be well dispersed to the hole sidewall because of the plasma defocusing effect in the atmospheric pressure environment, and the sidewall materials can be effectively removed. The maximum aspect ratio of the hole can reach 15.7 based on the drilling results. The presented results provide some guidance for the machining of micro-holes with high aspect ratios on other occasions.

Driver's visual luminance model considering the reflection characteristics of a tunnel’s inner wall: Theory and practice I

A driver's visual luminance value under one-time stopping sight distance is the basic value for highway tunnel lighting design and quality evaluation. Currently, the driver's visual luminance value is obtained using the pavement reflection coefficient method with or without considering the diffuse reflection coefficient of the sidewall. This does not fully consider the influence of the reflection characteristics of the tunnel’s sidewall and pavement materials, potentially resulting in a large discrepancy between the measured and theoretically calculated values of driver’s visual luminance, which significantly affects the lighting design and quality evaluation of highway tunnels. Therefore, this study first establishes a driver's visual luminance theoretical model considering the reflection characteristics of the tunnel sidewall and pavement and uses the five-parameter model to fit the measured eigenvalues of the tunnel sidewall and pavement reflection to obtain a bidirectional reflectance distribution function. Theoretical calculation and actual measurement verification are performed using a 1:10 tunnel simulation model. Finally, the theoretically calculated value of visual luminance and the calculated values of the JTG and IESNA specifications are compared with the measured data of the tunnel simulation model. The results show that the mean error between the theoretically calculated value of visual luminance and the measured data remains at 6.0%, which is significantly lower than the corresponding errors in the JTG and IESNA specifications. After calculation, when a high diffuse reflection coating is applied to the sidewall of the tunnel, the driver's visual luminance can be increased by 16.8% on average.

Reduction in RF sheath rectification with insulating antenna enclosure walls

Radiofrequency (RF) sheath rectification is one of the most prominent deleterious effects associated with ion cyclotron range of frequencies (ICRF) heating in fusion plasmas. RF sheaths and associated effects, such as impurity generation and convective cell generation, need to be mitigated to ensure that ICRF is a viable option for heating in future fusion devices. Experiments were performed on the Large Plasma Device (LAPD) at UCLA to explore the effects of using electrically-insulating antenna enclosures on RF rectified sheaths. Three different enclosure side-wall materials were used, including copper, MACOR (electrically insulating), and MACOR over copper. In the case of the MACOR–copper side walls, the non-conductive MACOR material was exposed to the bulk plasma but a layer of copper was added below to allow for image currents to flow. All three of the experiments had similar plasma density, temperature, and background magnetic field. In the case of the copper enclosure, RF rectified potentials, many times the local electron temperature, and associated formation of convective cells were observed and reported Martin M. et al (2017 Phys. Rev. Lett. 119 205002). In the experiments with MACOR and MACOR–copper enclosures, RF rectification was significantly reduced. Additionally, these latter two experiments showed no evidence of convective cell formation. Although the results from the MACOR experiment are reminiscent of the results obtained in ASDEX-U with a three-strap antenna optimized to reduce image currents on the antenna limiters Bobkov V. et al (2016 Nucl. Fusion 56 084001), the MACOR–copper experiment seems to suggest that insulating plasma facing materials have at least an equally strong impact on reducing potential rectification.

Evaluation of the Effects of Tunnel Lighting Environment on Energy Consumption and Drivers’ Reaction Time

The 24-hour artificial lighting of the tunnels consumes a large amount of electricity, which means increased environmental damage and carbon footprint for China, which is dominated by thermal power. In order to alleviate the above problems, the effects of the tunnel lighting environment on energy consumption and drivers’ reaction time were evaluated by the finite element method and laboratory test to optimize the lighting environments. In this study, based on the Wanxichong extra-long tunnel in Yunnan Province, a 3D tunnel model using DIALux software is established first. Then, the effects of climate conditions, layout method of the lamps, and layout height and reflection of the sidewall material on the average luminance and uniformity on the pavement, the efficiency ratio per unit length, and the actual energy efficiency value were investigated. Finally, the indoor lighting environment simulation experiments were conducted to examine the effect of the type of sidewall materials, contrast, background luminance, and eccentricity on drivers’ reaction time. Simulation results show that, under the same climate condition and layout method of lamps, the average luminance and luminance uniformity on the road surface are positively correlated with the reflectivity of the sidewall material. On the clear days, the efficiency ratio per unit length corresponding to the 2 m high sidewall material is the largest, while the efficiency ratio per unit length on cloudy days and mixed days corresponding to the 2.5 m high sidewall material is the largest. In addition, the staggered layout of the lamps at the entrance of the tunnel consumes less power, which is more conducive to energy saving. Experimental results show that, with the increase of background luminance, the reaction time of drivers decreases. Meanwhile, applying energy-storage reflective coating on the sidewalls of the tunnel has a better visual performance than using light yellow ceramic tiles and cement mortar on the sidewalls. This conclusion would provide a lower energy consumption lighting design method and higher drive comfortable for highway tunnels.

Thermal Field Effect in Resistive Random Access Memory With Sidewall Structures of Different Thermal Conductivity

The effect of different pulse rise time in resistive random access memory (RRAM) is presented in this study. The result shows that the length of pulse rise time will lead to variations in RRAM OFF-state resistance that occur due to which of two distinct effects governs the reaction, either the electric field or the thermal field. Different sidewall materials are adopted in RRAM devices to verify these phenomena, and a physical model supplemented with COMSOL simulation is proposed.

Enhanced lighting on the road surface with TIR-PA optical element on tunnel sidewall.

Both the lighting quality and driving safety inside the tunnel have been quite a concern around the world. In this study, a plate with prism array of total internal reflection (TIR-PA) has been designed to enhance the lighting on the road surface inside the tunnel in adherence to traffic safety as well as energy savings. Such optical elements, above the tunnel sidewall, can redirect the rays emitted from both the headlight and lighting devices to the road surface, which supports higher flux on the road. Simultaneously, the simulation is conducted with consideration of practical factors based on the mathematical model and edge-ray principle to attain the effect of the TIR-PA plates. On the one hand, for the rays from the lighting devices, the enhancement rate of illuminance has reached 12.60%-16.58%, which is attributed to TIR-PA plates above the different sidewalls of the Lambertian scattering property. TIR-PA can be suitable for various sidewall materials due to the small effect of illumination reduction. On the other hand, 30.2%-32.2% rays of the headlight source received by the sidewall, due to the effect of TIR-PA plates, are redirected to the driving distance for 27.3-71.9 m, which makes 15.9-31.1m2 of road surface brighter. It makes contributions to the improvement of illuminance distribution and drivers' pre-judgment. In the future, broader applications regarding the TIR-PA plates will be explored widely in tunnel lighting systems due to the low production cost.

A novel tunnel lighting method aided by highly diffuse reflective materials on the sidewall: Theory and practice

Interior surfaces of tunnels can reflect light when a highly diffuse reflective material is used on the sidewalls. This study introduces a novel energy-saving method that uses the reflected light effectively. To validate the proposed method, the brightening effect of a highly diffuse reflective material is measured based on the bidirectional reflection distribution function (BRDF) of the sidewall materials. The BRDF specifies the reflective properties of the sidewall materials, and the incremental reflection is then quantified. The proposed method offers better computational certainty and sidewall material adaptability than those of existing methods. For different materials selected as test objects, the error between the calculated and measured values was controlled to be less than 5.35%. In addition, the relative error between the calculated and measured values, obtained using the proposed method, was 3.62% on average, and the corresponding errors obtained using China's lighting design rules and the Recommended Practice for Tunnel Lighting presented by the Illuminating Engineering Society of North America (IESNA) were 18.02% and 7.98%, respectively. Overall, the proposed method provides a theoretical basis to help realize the unification of tunnel lighting with safety, energy savings, and comfort.

Simulation of temperature management inside rubber smokehouses of perspex, steel, and ash-brick materials

In a rubber smokehouse, the material properties of the wall of the room along with the flow, velocity and temperature distributions affect the drying process of rubber sheets. Simulation is carried out for a smokehouse of perspex, steel, and ash-brick sidewall materials with air velocities of 0.45–0.7 m/s and temperatures of 328–348 K varying the heat inputs. The result showed that the smokehouse made from the ash-brick is most efficient to reduce the heat loss and faster the drying of the sheets. The simulation matches excellently with the published experimental result.

Carbide formation and accumulation in SiMn furnaces

Recent excavations of Norwegian medium size SiMn furnaces have revealed spectacular amounts of carbide-rich materials accumulating on the sidewalls. In an excavated furnace from Eramet Kvinesdal, producing a 19%Si silicomanganese alloy prior shutdown, the sidewall materials contained silicon carbide in addition to SiMn alloy, slag and carbon. This contrasts with the large amounts of titanium carbides found in a furnace from Ferroglobe (Glencore then) which was producing 16%Si silicomanganese. The significant volume occupied by the carbides is likely to affect the flow of materials as well as furnace operation. It is therefore meaningful to understand how and when those carbides can form, especially concerning titanium carbide given the low content of titanium (about 0.3%) in the raw materials. The present study investigates the conditions under which TiC and SiC can appear in the furnace. Slag, alloy, and gas compositions were chosen to mimic industrial charges and were reacted between 1450 and 1650 °C. The reacted samples were further analysed by electron probe microanalysis with wavelength-dispersive X-ray spectroscopy (EPMA/WDS). Thermodynamic calculations were conducted using FactSage 8.0 and used for further reflection. The results indicate that TiC was formed by both precipitation and chemical reaction.

Sub-nanosecond pulse programming and device design strategy for analog resistive switching in HfOx-based resistive random access memory

The analog switching behavior of resistive random access memory (RRAM) is crucial for its application in neuromorphic computing. This paper investigates the switching mechanism of RRAM under sub-nanosecond and nanosecond pulse programming, with selected device materials and structures, using the kinetic Monte Carlo simulation method. The microscopic distribution of oxygen vacancies is simulated in all three spatial dimensions and in the time dimension (four-dimensional). According to the simulation results, thermal effects are a critical factor affecting the switching behavior. The thermal effects inside the HfOx switching layer can be almost completely eliminated by using sub-nanosecond pulses with low voltage, finally leading to good analog behavior. When nanosecond pulses are applied, effective heat insulation is the key to realizing analog characteristics. In general, the switching process is proposed to involve three stages. Having the lowest energy consumption, the first stage shows the greatest potential for achieving analog behavior. The use of heat-isolating structures, like capping layers and side wall materials with lower thermal conductance, could be a solution to improve the analog behavior of RRAM at the first stage when down-scaling the device size.

Fabrication of MgO-NiO-Fe2O3 materials and their corrosion in Na3AlF6-AlF3-K3AlF6 bath

Ledge-free sidewall is preferred because it probably reduces the energy requirement of aluminum production by about 30%. However, such approach poses great material challenge since the sidewall materials would be in direct contact with corrosive electrolytes. In the present study, MgO-NiO-Fe2O3 materials were fabricated using fused magnesia, nickel oxides and ferric oxide powders as starting materials. All the specimens were corroded in a Na3AlF6-AlF3-K3AlF6 bath to estimate the corrosion resistance. The results revealed that reaction sintering occurs in the MgO-NiO-Fe2O3 system during firing process. After firing at 1400 to 1600○C, all the specimens prepared are composed of single-phase NixMg1-xFe2O4 composite spinel, whose lattice parameter decreases and chemical stability improves with increasing Ni2+ ion concentration. And densification of the MgO-NiO-Fe2O3 specimens can be enhanced by increasing the NiO content. The corrosion results show that the increase of NiO content has an obvious positive effect on corrosion resistance of the specimens due to the improved chemical stability of the NixMg1-xFe2O4 phase. However, the incorporation of high MgO content into the specimens is favorable for formation of a dense and stable ceramic layer on their surface during the corrosion process, which effectively promotes the electrolyte penetration resistance of the specimens as it functions as the blocking layer between the specimens and electrolyte.

Reduced Lateral Confinement and Its Effect on Stability in Patterned Strong Polyelectrolyte Brushes.

The stability of strong polyelectrolyte brushes (PEBs) was studied in bulk and in patterned structures. Thick PEBs of poly([(2-methacryloyloxy)ethyl]trimethylammonium chloride) with thicknesses >100 nm were synthesized using single electron transfer living radical polymerization. Brush patterning was identified using deep-ultraviolet photolithography by means of either a top-down (TD) or bottom-up (BU) method, with features as small as 200 nm. The brushes were soaked in water under a range of pH or temperature conditions, and the hydrolysis was monitored through dry-state ellipsometry and atomic force microscopy measurements. BU patterns showed reduced degrafting for smaller patterns, which was attributed to increased stress relaxation at such dimensions. In contrast to the already relaxed BU-patterned brush, a TD-patterned brush possesses perpendicular structures that result from the use of orthogonal lithography. It was found that the TD process induces cross-linking on the sidewall, which subsequently fortifies the sidewall materials. This modification of the polymer brushes hindered the stress relaxation of the patterns, and the degrafting trends became irrelevant to the pattern sizes. With proper tuning, the cross-linking on the sidewall was minimized and the degrafting trends were again relaxation-dependent.

Thermal conductivity of the sideledge in aluminium electrolysis cells: Experiments and numerical modelling

During aluminium electrolysis, a ledge of frozen electrolytes is generally formed, attached to the sides of the cells. This ledge acts as a protective layer, preventing erosion and chemical attacks of both the electrolyte melt and the liquid aluminium on the side wall materials. The control of the sideledge thickness is thus essential in ensuring a reasonable lifetime for the cells. The key property for modelling and predicting the sideledge thickness as a function of temperature and electrolyte composition is the thermal conductivity. Unfortunately, almost no data is available on the thermal conductivity of the sideledge. The aim of this work is to alleviate this lack of data. For seven different samples of sideledge microstructures, recovered from post-mortem industrial electrolysis cells, the thermal diffusivity, the density, and the phase compositions were measured in the temperature range of 423 K to 873 K. The thermal diffusivity was measured with a laser flash technique and the average phase compositions by X-ray diffraction analysis. The thermal conductivity of the sideledge is deduced from the present experimental thermal diffusivity and density, and the thermodynamically assessed heat capacity. In addition to the present experimental work, a theoretical model for the prediction of the effective thermal transport properties of the sideledge microstructure is also proposed. The proposed model considers an equivalent microstructure and depends on phase fractions, porosity, and temperature. The strength of the model lies in the fact that only a few key physical properties are required for its parametrization and they can be predicted with a good accuracy via first principles calculations. It is shown that the theoretical predictions are in a good agreement with the present experimental measurements.

Piezoelectric energy harvester using mechanical frequency up conversion for operation at low-level accelerations and low-frequency vibration

In this paper, we propose a modified frequency up-conversion mechanism to lower the operational acceleration level for energy harvesting devices using a snap-through buckling phenomenon. The proposed device consists of a buckled bridge beam clamped on flexible sidewalls with a proof mass and cantilever beams attached to the bridge. When subject to a vibration, the buckled bridge beam snaps through between two stable states, inducing impulsive acceleration on the attached piezoelectric cantilevers. During the snap-through transition, the flexible sidewalls deflect outward, thus lowering the threshold acceleration value for the state transition. Various sidewall materials with different flexibilities were tested to determine the maximum output power, bandwidth, and output characteristics for various input acceleration values. The minimum acceleration value for snap-through transition was 0.5g (g = 9.8 m/s2) when using latex sidewalls. A maximum output power of 0.4 mW Hz/cm2--that is 10 μW for test sample at an excitation frequency of 15 Hz--was generated by using the proposed device with latex sidewalls.

Preparation of MgO–NiFe2O4–TiO2 materials and their corrosion in Na3AlF6–AlF3–K3AlF6 bath

The development of new electrolysis technology in aluminum industry requires a new generation of refractory materials to replace the Si3N4 bonded SiC refractories, which are currently used widely as sidewall materials in Hall-Héroult cells. In the present paper, the MgO based materials are considered as potential candidates for this type of application and are prepared using fused magnesia, pre-synthesized nickel ferrite and anatase powder as starting materials. The reaction sintering process of the MgO–NiFe2O4–TiO2 materials is investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM). All the specimens are corroded in a Na3AlF6–AlF3–K3AlF6 bath to assess the electrolyte corrosion resistance and the results are compared with those for nickel ferrite materials. The results show that reaction sintering occurs in the MgO–NiFe2O4–TiO2 system in the range of 1000–1600°C. Firstly MgO reacts with TiO2 to produce the Mg2TiO4 phase at 1000°C, which in turn reacts with NiFe2O4 to form the NiχTi1−χFe2χMg2−2χO4 composite spinel at temperatures above 1000°C. As a result, the mass transfer and densification in the MgO–NiFe2O4–TiO2 specimens are enhanced. All the specimens are composed of the composite spinel and periclase phases. As the amount of NiFe2O4 added increases, more composite spinel phase precipitates inside MgO grains at high temperatures. The MgO–NiFe2O4–TiO2 refractories prepared exhibit good corrosion resistance to the electrolyte melts. And their corrosion resistance increases with the increase in the NiFe2O4 addition. When the amount of NiFe2O4 added is 30wt%, the refractory shows a corrosion resistance comparable to that of the pure NiFe2O4 refractory; the reasons for this much improved corrosion resistance are investigated and discussed.

Thermal Conductivity of Porous Si3N4‐Bonded SiC Sidewall Materials in Aluminum Electrolysis Cells

A thorough analysis of the thermal conductivity of virgin and spent porous Si3N4‐bonded SiC sidewall materials in the Hall–Héroult electrolysis cell is reported. The thermal conductivity, measured by the laser flash method, was observed to vary significantly among the virgin materials and also within a single block of the same material. A significant reduction of the thermal conductivity in both the bottom and top part of the spent blocks was observed, which could be correlated with significant changes in the microstructure in both regions due to chemical degradation. The thermal conductivity was correlated with the phase composition, apparent porosity, and microstructure related parameters like grain‐boundary resistance, pore‐shape, and pore‐orientation factor. Analytical models were used to analyze the influence of these factors on the thermal conductivity of the Si3N4‐bonded SiC porous composites. Two different explanations for the significant reduction in the thermal conductivity in the bottom and the top parts of the spent block were proposed, and both were related to the microstructure evolution caused by the chemical degradation.

Research on Reaction Mechanism of Si<sub>3</sub>N<sub>4</sub> and AlF<sub>3</sub> in CO Atmosphere

The reaction between Si3N4 and AlF3 had been investigated in CO atmosphere at high temperature. Experimental results are shown that the reaction between Si3N4 and AlF3 is accelerated with the rise of temperature. At the temperature of 950 (aluminum electrolytic operation temperature is 935±15), there is obvious reaction between Si3N4 and AlF3; under this experiment condition, Si3N4 converted into Si2N2O partly, Si2N2O can also react with AlF3. The reaction products of Si3N4 with AlF3 are SiF4 (g) and AlN, while the reaction products of Si2N2O with AlF3 are SiF4 (g) and Al8O3N6. So, during the usage of Si3N4-bonded SiC sidewall brick in aluminum electrolysis cells, the content of Si3N4 in Si3N4-SiC block are reduced which can bring down the corrosion of aluminum electrolyte to the sidewall materials.