Long-term Reliability Research Articles

Single-layer graphene based resistive humidity sensor enhanced by graphene quantum dots

Graphene is broadly applied as sensitive sensing material results from its superb features. Concurrently, as a derivative of graphene with 0D structure, graphene quantum dots (GQDs) offer more possibilities as a supportive sensing material due to its adjustable size and functional group modification. In this work, GQDs are introduced to single-layer graphene (SLG) based humidity sensor to enhance the sensing performance. Specifically, consistent resistance response to relative humidity (RH) is extended from the range of 10%–60% to 10%–90% by contrary to original SLG based sensor. Parallelly, effect of the amount of GQDs is investigated by means of multiple GQDs deposition. As the resultant higher binding efficiency between water molecules and the functional groups of GQDs, improved response rate is observed. For the case of 4-time deposition of GQDs, the response rate ( ΔR/R ) reaches ∼130% in RH range of 10%–90%. Besides, the response time and recovery time are ∼0.7 s and ∼1.1 s, respectively. The fluctuation of the resistance change of the sensor under constant humidity is less than 5% over a month which demonstrates long-term reliability.

Thermodynamically extended symplectic numerical simulation of viscoelastic, thermal expansion and heat conduction phenomena in solids

AbstractSymplectic numerical schemes for reversible dynamical systems predict the solution reliably over large times as well, and are a good starting point for extension to schemes for simulating irreversible situations like viscoelastic wave propagation and heat conduction coupled via thermal expansion occuring in rocks, plastics, biological samples etc. Dissipation error (artificial nonpreservation of energies and amplitudes) of the numerical solution should be as small as possible since it should not be confused with the real dissipation occurring in the irreversible system. In addition, the other well-known numerical artefact, dispersion error (artificial oscillations emerging at sharp changes), should also be minimal to avoid confusion with the true wavy behavior. The continuum thermodynamical aspects (respect for balances with fluxes, systematic constitutive relationships between intensive quantities and fluxes, the second law of thermodynamics with positive definite entropy production, and the spacetime-based kinematic viewpoint) prove valuable for obtaining such extended schemes and for monitoring the solutions. Generalizing earlier works in this direction, here, we establish and investigate such a numerical scheme for one-dimensional viscoelastic wave propagation in the presence of heat conduction coupled via thermal expansion, demonstrating long-term reliability and the applicability of thermodynamics-based quantities in supervising the quality of the solution.

Power Cycling Reliability with Temperature Deviation of Pressureless Silver Sintered Joint for Silicon Carbide Power Module

SiC devices can enhance power conversion in electric vehicles. However, traditional soldering techniques are limited by their low melting temperatures. Therefore, we used pressureless Ag sintering to assemble a 1200 V/200 A SiC metal-oxide-semiconductor field-effect transistor power module and compared the long-term reliability, electrical properties, and driving performance of the module with those of a similar module assembled using the solder Sn-3.0Ag-0.5Cu (SAC305). To assess sinter joint reliability, we performed power cycling tests over two temperature ranges, 50–150°C and 50–175°C, for 15,000 cycles. Subsequently, we compared the breakdown voltage (BVDSS) and drain-source on-resistance (RDS(ON)) of the SiC power modules and performed cross-sectional analyses of the device bonding interfaces. No difference in BVDSS was found between the Ag-sintered and SAC305-soldered joints. However, the RDS(ON) exhibited minimal variation for the Ag-sintered module but significantly varied for the SAC305-soldered module, suggesting that the former better maintained its characteristics. Furthermore, the electrical characteristics of the SAC305-soldered module underwent more significant alterations with increasing temperature change during power cycling, indicating that cracks propagated throughout the SAC305 soldered joint over time. Therefore, Ag sintering was quantitatively validated as the superior die attachment technology compared to soldering for long-term reliability.

Assessment of the Performance and Defect Investigation of PV Modules after Accelerated Ageing Tests

Photovoltaic (PV) modules' degradation behaviour, together with outdoor field condition and fault diagnostics, consist valuable data in evaluating efficiency and establishing long-term reliability of a PV system. However, since PV modules commonly come with 25 (even over) years of warranty, testing modules in field for that long period is not feasible. Thus, due to time constraints, many accelerated aging tests have been recently introduced for testing reliability and durability of PV modules. Scope of the presented study is the assessment of the performance degradation and fault (defect) propagation mechanisms with regard to three monocrystalline silicon (mc-Si) PV modules, through a specific thermal cycle accelerated ageing test. The parameters that were experimentally evaluated towards the accelerated ageing process of this study, were: i) the thermal signature evolution and/or propagation of any diagnosed defects, especially in two modules, by means of infrared (IR) thermographic measurements, ii) the overall performance degradation of each module, by means of electrical I-V measurements, together with iii) specific morphological characteristics, by means microscopy imaging. The intended study gave useful and promising results in assessing the effect of the applied thermal cycles upon the modules’ thermal behaviour, electrical efficiency and morphology.

Overview of the research work of Prof. Koyanagi and the composite materials laboratory

Materials at the quantum scale are highly unpredictable, making it impossible to predict certain measurements. There are also limitations to numerical simulations and modelling techniques for understanding advanced materials at the molecular scale. Professor Jun Koyanagi, Koyanagi Laboratory, Tokyo University of Science, Japan, is working to establish a quantitative link that connects the nanoscale simulations to the metre scale. This involves developing methods and techniques that accurately relate the behaviour observed at the molecular level to the macroscopic properties of the material. In order to do this, a comprehensive understanding of the underlying physics and mechanics at each scale is required. Koyanagiâ–™s team is hoping to apply multiscale numerical simulations that will help to ensure the long-term reliability of a range of advanced materials. A key focus of the research is carbon fibre reinforced plastic (CFRP) and Koyanagi wants to pave the way for the widespread use of CFRP in aerovehicles in the near future. The team will conduct multiscale numerical simulations and advanced material development to ensure the reliability and long-term durability of CFRP. This will allow them to confidently incorporate CFRP into the construction of aerovehicles and these will be more sustainable and environmentally friendly as the lightweight nature of CFRP will significantly contribute to enhancing fuel efficiency and reducing emissions. The researchers are using analytical and experimental methods to evaluate the thermal and mechanical properties of composite materials.

Residual life prediction of lithium battery based on hybrid model of WOA–VMD and attention mechanism

Abstract In order to improve the long-term reliability of lithium battery and ensure the safe operation of the system, a forecasting method combining whale optimization algorithm (WOA), variational mode decomposition (VMD) and the Gated Recurrent Unit model with Attention mechanism (GRU-Attention) was proposed. WOA–VMD was used to decompose the battery capacity data into the intrinsic mode component and residual component, which were, respectively, predicted by GRU-Attention, and finally effectively integrated to obtain accurate capacity prediction results. Through the experiments of the Li-ion battery data set of the Advanced Life Cycle Engineering Center of the University of Maryland, the proposed Li-ion battery combination prediction model has high prediction accuracy and stability. This method is a novel combination of advanced technologies and algorithms, and its effectiveness in improving the long-term reliability of lithium batteries has been verified by experiments. This research is of great significance for promoting the development and application of lithium battery technology.

Flexible MXene-based Janus film with superior heat dissipation capability for ultra-efficient electromagnetic interference shielding and Joule heating

The incorporation of polymers into MXene-based functional materials has been proven to be an effective strategy for improving their flexibility and mechanical properties. However, insulating polymers inevitably sacrifice the conductivity of MXene, resulting in a deterioration of electromagnetic interference (EMI) shielding performance. In this work, inspired by Janus structure, an asymmetric flexible film composed of the carboxylated styrene-butadiene rubber (XSBR) with magnetic boron nitride nanosheets (mBNNS) layer and the MXene layer is developed through a casting plus spraying approach. The resulting mBNNS/XSBR@MXene (BXM) Janus film demonstrates the characteristic of “one side insulation, one side conductivity”, with the conductivity of 2746 S cm−1 on the MXene side and surface resistivity of 4.9 × 1013 Ω on the mBNNS/XSBR side. Profit from the designed Janus architecture, the EMI shielding effectiveness and in-plane thermal conductivity of the BXM Janus film reach 74.55 dB and 8.45 W m−1 K−1 when the total mass fraction of mBNNS and MXene is 50 wt%, which is 148 % and 43.46 % higher than that of the BXM blend film without Janus structure. Moreover, the BXM Janus film exhibits low applied voltage (∼3.0 V) driven Joule heating performance with a response time of less than 10 s, a saturation temperature of 133.7 °C, and long-term steady reliability. Meanwhile, the BXM Janus film possesses good mechanical properties and excellent EMI shielding stability. Therefore, this work provides an effective strategy to fabricate flexible MXene-based multifunctional film for EMI shielding, heat dissipation, and thermal management applications.

Leakage Mechanism and Cycling Behavior of Ferroelectric Al0.7Sc0.3N.

Ferroelectric scandium-doped aluminum nitride (Al1-xScxN) is of considerable research interest because of its superior ferroelectricity. Studies indicate that Al1-xScxN may suffer from a high leakage current, which can hinder further thickness scaling and long-term reliability. In this work, we systematically investigate the origin of the leakage current in Al0.7Sc0.3N films via experiments and theoretical calculations. The results reveal that the leakage may originate from the nitrogen vacancies with positively charged states and fits well with the trap-assisted Poole-Frenkel (P-F) emission. Moreover, we examine the cycling behavior of ferroelectric Al0.7Sc0.3N-based FeRAM devices. We observe that the leakage current substantially increases when the device undergoes bipolar cycling with a pulse amplitude larger than the coercive electric field. Our analysis shows that the increased leakage current in bipolar cycling is caused by the monotonously reduced trap energy level by monitoring the direct current (DC) leakage under different temperatures and the P-F emission fitting.

Proposition of optimal self-curing method in horizontal-floating gate FET-type gas sensors for reliability improvement

Gas sensing technology has seen rapid advancements in recent years, finding applications in air quality monitoring, food freshness inspection, and medical diagnosis. However, to successfully integrate gas sensors into these applications, it is crucial to ensure their stability and long-term reliability. While previous studies have primarily focused on improving response, sensitivity, and selectivity, there has been limited research on enhancing their reliability. This study aims to address this gap by proposing a method to improve the reliability of horizontal floating-gate FET-type gas sensors using a self-curing approach. When the sensor is exposed to the repetitive program/erase operation, the FET transducer used as a sensor platform is damaged by the Fowler-Nordheim tunneling-induced stress. A significant increase in the trap density inside the gate oxide is observed after the P/E cycling. The parasitic bipolar junction (PBJT) inherent to the FET transducer flows a large current via the entire channel, generating a Joule heat. The trap is decreased by the annealing effects of the Joule heat, and the damaged gate oxide is fully recovered by the curing. The proposed PBJT curing can effectively improve the reliability of the sensor using the internal operation of the FET transducer without using bulky external equipment.

Ti4+ substitution suppressing P2-O2 phase transition to construct stable P2-Na0.67Ni0.33Mn0.67O2 cathode for long-term durable sodium-ion batteries

Due to high safety and cost-effective resources, sodium-ion batteries show great prospect in large-scale energy storage systems. Owing to wide structural framework and high theoretical capacity, Na-based layered oxide with prismatic P2-type structure is an ideal cathode candidate for sodium-ion batteries. However, Na-based layered compounds always suffer from detrimental multiple phase transitions during cycle period, resulting in structure deterioration and rapid capacity decay. Herein, stable P2-Na0.67Ni0.33Mn0.67-xTixO2 cathodes are constructed through substituting Mn with Ti. In-situ XRD demonstrates that Ti substitution effectively successfully suppresses the undesired phase transition of P2-O2, and in turn appears a stable Z-symbiotic intermediate phase with minimal volume change. Hence, designed P2-Na0.67Ni0.33Mn0.37Ti0.3O2 cathode shows better structural stability and long-term cycling reliability, yielding a high reversible capacity of 123 mAh g−1 and a high capacity retention of 89 % after 100 cycles at 0.2C. More importantly, a high working voltage of 3.5 V and a boosted energy density of 400 Wh kg−1 is achieved in the NNMTO-3 || HC full cell, which further strengthens the competence of Ti-substituted Na-based layered oxide cathodes. This work provides a feasible design insight for long-life, high-voltage sodium-ion batteries, which can be applied to construct more stable layered compounds and further improves their electrochemical properties.

Combining polynomial regression with unsupervised machine learning on wafer-level packaging reliability prediction

ABSTRACT The benefits of wafer-level packaging include better thermal dissipation, lower latency and reduced space consumption. Accelerated thermal cycling test (ATCT) is a regulation that determines whether a product is ready for mass production, but it takes a long time and is costly to perform. The design-on-simulation approach can reduce the number of ATCT experiments and shorten the design cycle. However, the simulation method must be verified before it can be treated as an experiment; if the simulation consistently matches experiments at close range, it can also be treated as an experiment. In addition, the verified simulation method can be used to develop a machine learning (ML) database and obtain an artificial intelligence model for long-term reliability prediction. Due to its effectiveness in solving nonlinear problems with relatively short computation times, polynomial regression (PR) is used in this study as ML model. Results show combining PR with an unsupervised learning algorithm, K-means, can produce more accurate predictions.

A whole service time SHM damage quantification model hierarchical evolution mechanism

Accurate damage quantification for an individual aircraft by using structural health monitoring (SHM) technology poses a persistent challenge in practical engineering. Existing damage quantification models typically rely on prior data acquired from ground design and tests. However, an individual aircraft is subject to diverse uncertainties throughout its whole service time, such as time-varying environmental and operational conditions, different flight missions, and different damage morphologies. Consequently, employing a prior trained model for damage quantification inevitably introduces errors, thereby limiting the engineering applicability of SHM. To improve the damage quantification accuracy for individual aircraft under the influence of uncertainty, a new whole lifetime data-based damage quantification model hierarchical evolution mechanism is proposed in this paper. Multi-source data from the design, service, and maintenance stages of individual aircraft are adopted to continuously evolve the probabilistic damage diagnosis model, enabling it to characterize the specific data distribution and track the damage propagation. The proposed method is validated through fatigue tests of a landing gear beam structure, which is an important aircraft load-carrying component, with guided wave monitoring based hidden Markov model quantifying its crack propagation. The validation result demonstrates the effectiveness of the proposed method in ensuring the long-term reliability of the model and achieving more accurate damage quantification for an individual aircraft.

Using NEMSIS to report annual air medical transport statistics

The objective of this study was to use the National Emergency Medical Services Information System (NEMSIS) dataset to generate national air medical transport statistics. Retrospective review of the 2021 NEMSIS dataset to identify all air medical transfers, both fixed- and rotor-wing. Transfers where then subcategorized into interfacility and scene responses. Frequencies for each category were generated and reported. A total of 317,267 air medical transfers were completed in 2021. These included 19,421 (6 %) with missing incident location code data. Of the 297,706 transfers with valid location codes, 208,689 (70%) were interfacility transfers, and 89,016 (30%) were scene responses. These preliminary results are consistent with other national estimates and achieve representation of all states and territories. Future work will include longitudinal analysis of NEMSIS datasets and direct survey of transport programs to establish long-term reliability.

Implantable Neural Electrodes Fabrication Based on Perfluoroalkoxyalkane Film.

In this paper, the fabrication of perfluoro-alkoxy alkane (PFA) film-based planar neural electrodes was proposed. The fabrication of PFA-based electrodes started with cleaning of PFA film. The argon plasma pretreatment was performed on the PFA film surface and attached to a dummy silicon wafer. Metal layers were deposited and patterned using the standard Micro Electro Mechanical Systems (MEMS) process. Electrode-sites and pads were opened using reactive ion etching (RIE). Lastly, the electrode patterned PFA substrate film was thermally laminated with the other bare PFA film. Electrical-physical evaluation tests were conducted along with in vitro tests, ex vivo tests and soak tests to evaluate the electrode performance and biocompatibility. The electrical and physical performance of PFA-based electrodes had better performances compared to other biocompatible polymer-based electrodes. Also, the biocompatibility and longevity were verified by cytotoxicity test, elution test, and accelerated life test. The PFA film-based planar neural electrode fabrication was established and evaluated. The PFA based electrodes showed excellent benefits such as long-term reliability, low water absorption rate, and flexibility using the neural electrode. For implantable neural electrodes, hermetic sealing is required for in vivo durability. PFA fulfilled a low water absorption rate with relatively low Young's modulus to increase the longevity and biocompatibility of the devices.

Factor analysis and evaluation of one-year test-retest reliability of the 33-item Childhood Trauma Questionnaire in Chinese adolescents.

The 33-item Childhood Trauma Questionnaire (CTQ-33) is a recently developed tool expanded from the 28-item Childhood Trauma Questionnaire (CTQ-28) to assess childhood trauma events, which showed good test-retest reliability over 2 weeks. However, little is known regarding the factor structure and long-term test-retest reliability of the CTQ-33. To fill such a gap, this study investigated the factorial validity of the CTQ-33 and test-retest reliability of the scale over a relatively long interval of 1 year. Data on demographics, the CTQ-33 scores, and mental health statuses such as depressive/anxiety symptoms were collected in Chinese adolescents (n = 188) twice across a one-year period. Results of the confirmatory factor analysis (CFA) revealed that the Chinese version of CTQ-33 has close factor validity when compared to the original CTQ-28 in college students. Furthermore, the total and most subscale scores of the CTQ-33 have fair to good test-retest reliability (intra-class correlation coefficients >0.6 for the total score, and > 0.4 for most subscales), except for the physical abuse subscale. Moreover, we replicated previous findings of significant positive relationships between levels of different childhood trauma subtypes using the CTQ-33. These findings provide initial evidence supporting that the CTQ-33 is overall reliable to assess childhood traumatic events in adolescents over relatively long intervals.

STUDY OF THE STRUCTURAL FEATURES OF STRING-CONCRETE SPAN STRUCTURES

Summary. The analysis of inspection results and experience in the operation of transport facilities show that bridges with string-concrete girders according to the standard designs VTP-16 and VTP-15 are in the worst condition. The wire prestressing reinforcement of these beams, which has a small diameter of 3 mm or 5 mm, loses its cross-section over time and breaks due to corrosion. This leads to the exhaustion of the residual service life of string-concrete girders on many bridges, which has caused several collapses in Ukraine in recent years. The structural features of string-concrete girders, including the use of small-diameter prestressed wire reinforcement, play a key role in their long-term operation and reliability. The number of such structures on Ukrainian roads of national importance reaches about 500 units, and their service life is more than 60 years. Lack of proper maintenance can lead to serious economic and safety problems. Analysing the technical condition of bridge span elements and identifying defects helps to improve traffic safety, extend the service life of bridges and reduce overall costs. Effective repair and strengthening of bridge structures ensure the normal functioning of the transport infrastructure, which is critical for the economic development and security of the country. This article investigates various aspects of the operation of bridges with string-concrete girders. The causes of defects are analysed and proposals are made to temporarily preserve the stability of structures prior to major repairs or reconstruction. The structural features of bridges with string-concrete girders reveal significant shortcomings that eventually lead to serious problems. Small-diameter wire prestressing reinforcement is prone to corrosion, which reduces its cross-section and leads to rupture. This, in turn, can lead to a complete collapse of the bridge span. Keywords: bridge, span structure, string-concrete, technical condition, defects, recommendations.

Topographic analysis of layer erosion in abrasive media

This article delves into the critical role of abrasive wear on the surface of plates in determining the long-term performance and reliability of pressing equipment utilized in the machinery industry. Operating within environments saturated with abrasive particles, these machines face challenges that impact their durability. The rate of deterioration is intricately linked to factors such as collision error, mechanical properties of materials, abrasive particle pressure, and the magnitude of impact loads. The separation of corrosive particles unfolds on a micro-scale, driven by the decomposition of metals resulting from mechanical fatigue, multi-cycle stresses, and repeated loading. By comprehensively examining these factors, this research aims to provide insights that contribute to the development of strategies for mitigating abrasive wear, thereby enhancing the overall operational longevity and reliability of pressing equipment crucial to the production of various machinery components.

Investigating chemical and cracking processes in cement paste exposed to a low external sulfate attack with emphasis on the contribution of gypsum

Durability of concrete exposed to an external sulfate attack is a great concern for the long-term reliability of nuclear waste containment. This paper presents experimental results obtained on cement paste subjected to a low concentration (30 ×10−3 mol/L) external sulfate attack. Samples were characterized with complementary methods (XRD, SEM-EDS, microtomography, microindentation, autoradiography) to follow the evolution of chemical, mineralogical, microstructural and mechanical properties during 8 months. Cement pastes of different C3A contents were used to boost either ettringite or gypsum formation during the sulfate attack to assess their respective impact on the degradation. Cracks parallel to the attacked surface occurred in the zone of gypsum formation and portlandite dissolution, which suggests that gypsum has a key effect on the expansion. Reactive transport modeling supported the discussion on the competition between hydrolysis, gypsum and ettringite precipitation as well as the analytical homogenization to estimate Young’s moduli.

Evaluating Mechanical Strength in Vertical-Axis Tidal Turbines: A Comparative Study of Internal Blade Structure and Material Selection through CFD Simulation

Due to the density of water, tidal turbine blades are subject to significantly greater stresses than wind turbine blades. Multiple blade failures occurred during prototype testing as a result of loading conditions and protracted exposure to seawater, which created a severe work environment. The structural integrity of tidal turbine blades is essential for long-term reliability and performance. Numerous investigations into structural performance have been conducted. However, previous research has centred on horizontal-axis tidal turbines, while research on small-scale vertical-axis tidal turbines is limited. This paper aims to compare the Vertical-Axis Tidal Turbine (VATT) structural performance of hollow and solid blade structures in an identical NACA profile using three distinct materials. Finite element analysis (FEA) is employed to construct a model and simulate the mechanical characteristics of VATT blades. The use of static analysis simulation is employed in order to evaluate many parameters, including stress distribution and deflection. Parametric studies are conducted to explore the impact of internal blade structure and materials on mechanical strength. The use of computational fluid dynamics (CFD) simulations is employed for the purpose of analyzing the interaction between blades of vertical axis tidal turbines (VATT) and tidal currents, thereby enabling the assessment of structural loading. According to the simulation results, the hollow profile is subject to significant deflections and stresses. Other data indicates that the utilization of stiffeners in porous structures improves material efficiency and results in lighter blades, although further analysis is needed to investigate fatigue life prediction in optimizing structural design.

Thermal Analysis of System in Package Considering Boundary Conditions for Long-Term Reliability Studies

Thermal Analysis of System in Package Considering Boundary Conditions for Long-Term Reliability Studies