Microscopic Evolution Research Articles

Thermal-Aware EM Reliability for Advanced Metal Interconnects of Complementary FET

Electromigration (EM) of metal interconnects is the continuous reliability concern for high-density integration beyond 5-nm technology, especially for the buried power rails in vertically stacked device structure. In this work, EM reliability of alternative metal interconnects based on complementary FET (CFET) is investigated by kinetic Monte Carlo (KMC) method. The microscopic evolutions of void formation in power rails can be well reproduced by considering the coupled effects of thermal and stress distribution during the EM simulation. The influences of grain boundary in different metal materials on EM lifetime are analyzed to provide the optimal strategy of process integration. Thermal-aware EM reliability is further predicted, indicating the importance of self-heating on EM evaluation of power rails in CFET.

Investigation on Water Transformation and Pore Structure of Cement-Stabilized Dredged Sediment Based on NMR Technology.

Cement-stabilized dredged sediment (CDS) when used as a new road construction material cannot only solve the problem of abandoned sediment disposal, but also effectively save natural soil resources. This study aimed to evaluate the strength and permeability of CDS and establish corresponding prediction models from the perspective of a stabilization mechanism. The soil–water composition and pore size distribution were investigated by the nuclear magnetic resonance (NMR) technique. The results demonstrated that more liquid pore water inside the CDS specimen transformed into combined water with cement hydration. The amount of combined water, which essentially characterized the hydration process of cement, presented a linear relationship with log (t). The cementation and filling action of hydrates resulted in the transformation of large pores into smaller ones, hence the optimal pore size decreased with an increasing curing period and cement content. The stress–strain curves and hydraulic conductivity were determined based on unconfined compression and flexible wall penetration tests, respectively. The unconfined compressive strength increased exponentially with the amount of combined water, and the functional correlations of hydraulic conductivity and micropore parameters were established. The reliability of the NMR technique as a new method to study the microscopic evolution mechanism of the strength and permeability of CDS was further verified by scanning electron microscopy and mercury intrusion porosimetry tests.

Metrics for Quantification of By-Process Segregation in Ge-Rich GST

Ge-rich GST alloys are the most promising materials for phase-change memory (PCM) to fulfill the soldering compliance and the tough data retention requirements of automotive applications. Significant efforts have been made to engineer those materials and optimize their integration inside the fabrication process of PCM. In this perspective, the physical characterization of the device and the material is instrumental in understanding the underlying physics, improving the process, and optimizing the interactions between the device, the process, and the material itself. Especially, microscopic investigations have gathered increasing interest, giving detailed descriptions of local material modulations that have a crucial role in cell programming and reliability performances. In this work, a deep analysis of Ge-rich GST microscopic alloy evolution during the integration process has been performed, exploiting analysis by EELS with TEM supported by a novel statistical data post-processing method. The new proposed statistical-based methodology also introduces new simple metrics for elemental compositional evaluations that have been exploited for process engineering.

Understanding high-temperature cycling-induced crack evolution and associated atomic-scale structure in a Ni-rich LiNi0.8Co0.1Mn0.1O2 layered cathode material

X-ray nano-computed tomography (nano-CT) and deep learning combined with Cs-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy were employed to investigate the atomic to microscopic structural evolution of LiNi0.8Co0.1Mn0.1O2 (NCM) upon cycling at 55 °C. Two types of intergranular cracks were clearly distinguished by nano-CT for cycled cathode particles; denoted open and closed cracks depending on whether or not the cracks reach the surface of the NCM secondary particles. The volume of high-temperature cycling-induced cracks quantified by deep learning increased drastically, particularly for the open cracks, and this phenomenon was accompanied by rapid degradation of capacity retention. Further precise STEM analysis of the crack regions revealed that migration of transition metal (TM) ions to the Li layer forms a rocksalt-like structure, and the associated reduction of TM ions, e.g., Ni3+ to Ni2+, predominately occurred in the open crack regions in the presence of penetrated electrolyte, even for regions extending to the center of the secondary particle. In contrast, in the closed crack regions, no significant atomic-scale structure distortion and limited reduction of TM ions was observed. Thus, our results provide fundamental guidance for improving the electrochemical performance of Ni-rich layered cathode materials for cycling at elevated temperatures.

Microscopic origins of anisotropy for the epitaxial growth of 3C-SiC (0001) vicinal surface: A kinetic Monte Carlo study

In order to investigate the microscopic evolution of the step flow growth process and reveal the microscopic origins of crystalline anisotropy during the epitaxial growth of 3C-SiC (0001) vicinal surface, a three-dimensional Kinetic Monte Carlo model is established, in which Si and C are considered individually. The helicoidal boundary condition is applied to the direction perpendicular to the step, and the periodic boundary condition is used in the direction along the step. Then, the effects of crystalline anisotropy on lateral growth rate, morphologies of step patterns, and growth mode are studied. The results show that the lateral growth rate in [1−210] is larger than that in ⟨1−100⟩, and the zigzag and meandering patterns of step are constructed in [1−210] and ⟨1−100⟩ directions, respectively, which is consistent with the experimental observations. Two possible origins of anisotropy are also revealed: one is the higher concentration of the edge sites of the step and the larger bonding energy in the [1−210] direction and another is the adatom diffusion along the edge of the step. Finally, a larger area of pure step flow growth mode is obtained in the [1−210] direction, which is good for lowering the cost for 3C-SiC epitaxial layers.

A new method to determine the crack closure stress based on stress difference

Crack closure stress is a key stress threshold of rocks under compression, the determination of which is of great significance to the evaluation of macroscopic deformation behavior and microscopic fracture evolution characteristics of rocks. Based on the applicability and analysis of the existing methods, a novel method called axial stress difference (ASD) method on the basis of axial stress - axial strain curve is proposed. This method reduces the dependence on the elastic modulus which restricts the promotion of previous methods, and can objectively acquire the crack closure stress by the identification of the onset point of linearly elastic stage of axial stress - axial strain curves. Then, the crack closure stress of rock materials under uniaxial and triaxial compression obtained by the ASD method is compared with the counterparts from other methods. The results obtained by the ASD method are close to that by other methods, which can also be verified by the small standard deviation and coefficient of variation. Since the International Society for Rock Mechanics and Rock Engineering (ISRM) has not yet recommended standard methods for solving the crack closure stress, this method can be an effective supplement to the existing methods.

Crystallization insights revealed by simulation solidification study of Fe63Ni33Co4 alloy melt at subcritical cooling rate

The rapid solidification of Fe63Ni33Co4 alloy at the subcritical cooling rate (1×1013 K/s) has been investigated by molecular dynamics (MD) simulation. The macroscopic phase transitions were analyzed in terms of the variation of potential energy and the related microscopic structure evolutions were depicted by the largest standard cluster analysis (LaSCA). It was found that such Fe63Ni33Co4 melt experiences liquid-liquid transition, liquid-solid transition, and solid-solid transition, which are respectively linked with the evolutions of amorphous local structures with 3-, 4- and 5-fold symmetries, BCC structures and FCC/HCP clusters. These findings shed new light on the complicated solidification mechanism of alloys from local cluster structural evolution features.

Visualization and analysis of mapping knowledge domains for coal pores studies

The structure and quantity of coal pores determine the adsorption capacity of CO2, CH4, O2, N2 and other multi-element mixed gases, which is an important link connecting coal spontaneous combustion and gas disasters. To better grasp developments and trends in research on spontaneous combustion and gas disasters around the world and to promote theoretical research into their prevention and control, research progress on coal pores is reviewed and analyzed using bibliometrics based on a total of 5515 publications collected from the Web of Science Core Collection database. Yearly quantitative distribution of literature, country/region distribution, organization distribution, main source journal distribution, subject category distribution, research knowledge bases, research hotspots and frontiers are all analyzed, CiteSpace and Vosviewer are used to plot knowledge domain maps. The results show that the number of papers on spontaneous combustion studies has grown exponentially, that China, USA, Australia, France, Canada, Russia, Japan, Germany, and Poland are the most active countries in coal pores, but results from USA are the most influential, and that Fuel, E&F, IJCG, JNGSE, JLPPI and FPT are the main sources of published research on coal pores. At present, a framework for the basic theory and research methods is complete, but the research network is too centralized, and there are few frontier branches. Structure and quantity of coal pores research, Intrinsic mechanism of pore development, Influencing factors of pore development and microscopic chemical group evolution law are the main knowledge bases for coal pores studies. Research on coal pores has expanded from the macro level to the micro scale. Molecular simulation, pore structure characterization, methane reservoir and methane adsorption have become research frontiers.

Multiscale study on the microstructural evolution and macromechanical deterioration of expansive soil under dry–wet cycles

Abstract To explore the influence law of dry–wet cycles on the microstructure of expansive soil and the deterioration effect of macroscopic shear strength, the correlation between the change in the soil internal structure and the deterioration of the mechanical properties is analysed. The expansive soil in the test section of the slope support project in Hanzhong city, Shaanxi Province, China, is selected for sample preparation, three groups of different dry–wet cyclic water content variation paths are defined. The volume damage rate of the soil sample caused by dry–wet cycles is tested, and the microscopic evolution law of soil sample structure was analyzed. On the basis of the conclusion of microscopic analysis, the deterioration effect of macro shear strength of soil samples is further elaborated. The results show that expansive soil is rich in hydrophilic minerals such as illite and montmorillonite. The larger the amplitude of the dry–wet cycle, the more significant the volume change is. With the alternating dry–wet cycle treatment, the microscopic analysis shows that the water migration channels gradually become larger until a new balance is reached. The T2 spectra of the NMR test also show that the overall internal structure develops from stable to unstable. With dry–wet cycles, the unstable change in the soil internal structure leads to the attenuation of the macroscopic shear strength. These micro- and macroscopic research results show that the deterioration effect of drying and wetting on expansive soil cannot be ignored.

Microscopic Evolution of Pore Characteristics and Particle Orientation of Granite Residual Soil in One-Dimensional Compression

This study investigates the microstructural changes of granite residual soil (GRS) upon compression, the aim being to understand further the deformation mechanism from a microscopic perspective and establish the relationship between the mechanical behavior and microstructural characteristics of GRS. By means of (i) experimental compression tests with different loadings and (ii) scanning electron microscopy (SEM), the structural evolution of GRS during compression tests is investigated systematically from both macroscopic and microscopic perspectives. Microstructural characteristics including particle morphology, pore size distribution, and particle preferred orientation are investigated specifically through SEM quantification methods. With an obvious turning point, thee–log σv′curve for natural GRS approaches the intrinsic compression line gradually when the vertical pressure exceeds the preconsolidation pressure, which indicates the significant influence of cementation bonding on the mechanical behavior of intact GRS. At the microscopic scale, the deformation of natural GRS is attributed to the compression and transformation of large pores, while the deformation of remolded GRS is also related to the transformation from mesopores to small pores. Upon compression loading, particles show higher preferred direction angle perpendicular to vertical loading, thereby facilitating the preferred orientation. With increasing vertical loading, the microfabric can no longer sustain the initial alignment pattern and tends to be rearranged and reoriented into a more stable and stronger structure. This study offers guidance for the deformation analysis of subgrade related to GRS.

Role of interface on irradiation damage of Cu−diamond composites using classical molecular dynamics simulations

Cu−diamond composites have been proposed as a candidate thermal management material for spacecraft electronics. Nevertheless, irradiation effects on the composites remain poorly understood at present. Here we focus on investigating the influence of Cu−diamond interfaces (CDIs) on energetic displacement cascades using atomistic simulations. Results show that a primary knock-on atom of Cu (PKA-Cu) can induce more significant damage than a PKA-C. Under almost all circumstances, the statistically averaged fraction of surviving interstitials is not only lower than that of vacancies but also no more than 1. Because of the unique nature in the mobility and interactions with CDIs, Cu interstitials exhibit the lowest concentration among all defects in most cases. The high residual rate of displaced defects in diamond makes it relatively difficult to heal. The structural damage is mainly manifested in a short-range disorder of diamond and a long-range disorder of Cu after irradiation. At elevated temperatures, the atomic displacement region may form compact chain-like defects to restrain lattice loosening. Despite the above, CDIs could act as effective sinks to facilitate the recombination and/or annihilation of irradiation-induced defects in all scenarios. This study provides an important insight into the understanding of the microscopic evolution of irradiation defects for the composites.

Aggregate shape effect on fracture and breakage of cementitious granular materials

To assess the aggregate shape influences on the cementitious granular material fracture and breakage behaviors, mortar samples containing two types of aggregates with same material but different shapes, namely, irregular glass particles and rounded glass particles, are compressed under quasi-static to high strain rate (1000–3500 s−1) loadings. Experimental results reveal that the extent of aggregate shape effect on the mortar stiffness is significantly enhanced with the increase of strain rate or cement strength. Although the critical strain energy is discovered to be aggregate shape independent, different microscopic fracture evolutions induced by the aggregate shape influences still exist and are effectively reflected by the corresponding coupled evolution of fragment size and shape. Meanwhile, the fracture locality preference within the aggregate particles is also validated by the associated microscopic evidence. This study sheds light on the future high strength granular composite material design, in particularly, upon high strain rates.

Mechanical evolution of bubble structure and interactive migration behaviors of two particles in flowing wet foam

Multiparticle migration in a wet foam fluid is increasingly found in relevant engineering applications. The microscopic reciprocal influence between the flowing foam and the settling multiparticle has not been fully understood. In this study, we mainly analyze the rheological and mechanical behaviors of this multiphase transport system based on the microscopic structural morphology. The settling behaviors of two particles, as well as the mechanical variation of bubbles influenced by the particles, are mainly explored. We find that the entrance of a bubble into the distance between the two particles positioned vertically causes significantly different bubble pressure components of the drag force for the two particles. In the process of bubble entering the distance, the bubble pressure, as well as the maximum principal stress of the bubble, rises; as the bubble leaves the distance, its pressure and the maximum principal stress decrease. For the two particles positioned horizontally, we mainly analyze the bubble pressure component of the lift force, as well as the pressure evolution of bubbles when the bubble–bubble separation and contact occur in the distance between the particles. This study assists in understanding the microscopic structural and mechanical evolution of wet foam in this multiphase transport system.

BEOL Process Effects on ePCM Reliability

The effect of back-end of line (BEOL) process on cell performance and reliability of Phase-Change Memory embedded in a 28nm FD-SOI platform (ePCM) is discussed. The microscopic evolution of the Ge-rich GST alloy during process is the focus of the first part of the paper. A new metric for quantification of active material modifications is introduced to better follow its evolution with process sequence. Ge clustering has been shown to occur during the fabrication, impacting the pristine resistance and the after forming cell performance. Two different BEOL processes are then benchmarked in terms of key performance. An optimized process is identified, and an extensive electrical characterization of array performance and reliability is done on the full 16MB chip. The optimized BEOL process results in a memory cell fully compatible with the requirements for demanding automotive applications.

Analysing the Interaction between Microscopic Deformation, Microstructure and Void Evolution of Near-α Titanium Alloys during Non-Superplastic Hot Deformation by an Integrated Crystal Plasticity Finite Element Model.

High-efficiency and low-cost hot forming technologies for titanium alloys have been developed for producing complex-shaped, thin-walled tubular components under non-superplastic forming conditions. Under these forming conditions, there exist complex and highly integrated material evolution processes including microscopic heterogeneous deformation, microstructure evolution and damage behaviour. This paper presents an integrated crystal plasticity finite element model of near-α titanium alloys during non-superplastic hot deformation conditions considering grain boundary sliding (GBS), dynamic recrystallisation (DRX), as well as void evolution. The polycrystalline model of a near-α TA15 titanium alloy was established, containing α phase, β phase and grain boundary (GB) regions, in which the GB region was a visualised representation of GBS. The quantitative strength ratio between the GB regions and α phase was calculated according to the Zener–Holloman parameter Z and grain size, which determined the microscopic deformation behaviour. There were found to be two high microscopic strain regions in the α phase: intragranular deformation bands through the most favourable slipping and near the GBs through multiple slipping, which promoted continuous and discontinuous DRX, respectively. With the decrease in parameter Z or grain size, the activated dislocations accommodating GBS were found to no longer pile up inside the grain, but instead travel across the grain interior. Finally, methods to improve the macroscopic plastic formability were proposed for the difficult-to-form titanium alloys experiencing non-superplastic hot deformation.

Macroscopic Behavior and Microscopic Structure Evolution of Marine Clay in One-Dimensional Compression Revealed by Discrete Element Simulation

Marine clay has been attracting in-depth research on its mechanical behavior and internal structure evolution, which are crucial to marine infrastructure safety. In the formation process of marine clay, including the sedimentation and consolidation stages, the compression behavior and internal structure evolution are highly dependent on the pore water salinity. Discrete element method (DEM) simulation is a powerful tool to study the microscopic mechanics behind the complicated macroscopic mechanical behavior of marine clay. In this study, a DEM simulation scheme is systematically proposed to numerically study the macroscopic beahvior and microscopic structure evolution of marine clay in one-dimensional compression that mimics the marine clay formation process. First, the proposed calculation scheme for double layer repulsive interaction and van der Waals interaction is introduced. Then, the developed DEM simulation scheme is validated by satisfactorily reproducing the experimentally observed one-dimensional compression curves and internal structure transition from an edge-to-edge/edge-to-face flocculated structure to a face-to-face dispersed structure. Finally, evolutions of coordinate number and fabric anisotropy are quantitatively evaluated in the microscopic view. The noticeable effects of ion concentration on the internal structure evlotion and mechanical behavior of marine clay have been examined and discussed.

On the evolution of residual stresses due to cooling considering martensitic phase transformation

AbstractThe direct consideration of residual stresses can positively influence the properties of a component and offers a new perspective compared to the typical strategy of avoiding residual stresses. Instead of minimizing residual stresses in forming processes, their consideration can positively influence the properties of the final component. For instance, the targeted adjustment of residual stresses can extend the service life or durability and improve the manufacturability of metal components. This is investigated in current research using experimental and numerical analyses on a cylindrical component with eccentric hole made of steel 100Cr6. Here, the cooling process after hot bulk forming is simulated to analyze the influence of microscopic phase evolution on the macroscopic stress distribution. For this purpose, different variants of the microstructural evolution described by a random process are compared.

Minewater deep transfer and storage

Subjected to the environmental influence of minewater drainage, a new method of minewater deep transfer and storage (MWDTS) was proposed and trialed in the eastern margin of Ordos basin, China. Based on the scientific issue, why, where, how, what and the consequence of MWDTS were presented in this paper. Two target geological mediums, including Baotashan coarse sandstone (BCS) in Yan'an Formation of Jurassic and Liujiagou Formation (LFm) of Triassic, were compared and analyzed to acquire the ideal aquifer as the groundwater reservoir. LFm was eventually selected as the final minewater reservoir and the scientific well named MC-1 was constructed, and the permeability of LFm reservoir was enhanced by artificial hydraulic fracturing. The laboratory tests including SEM, XRD, mercury injection, mechanical strength, microscopic permeability evolution and hydrochemical composition, as well as the field tests covering groundwater table recovery and different pressure water injection, revealed that the deep LFm was the optimal minewater reservoir. The original LFm was low porosity at 7.5% and lower permeability at 5.31 × 10−6 m/d to 6.19 × 10−6 m/d. The space with natural & artificial hydraulic fracture and pores was the main storage space. The pressure of hydraulic fracturing should be greater than 31.5 MPa, the continuous MWDTS would change the mechanical strength, and the whole permeability of the screening section was shown 1788 to 2858 times greater than natural. As the continued reinjection of minewater, the total amount of 1.00 million cubic meters had conducted. The capacity of MWDTS in the rejection well was predicted at 2.85 to 3.68 million cubic meters. On the basis of technical and economic evaluation, it would reduce the environmental pollution caused by minewater drainage and be one option method for minewater management of coal mine enterprises in the Ordos Basin.

Particle Flow Analysis of Macroscopic and Mesoscopic Failure Process of Salt Rock under High Temperature and Triaxial Stress

In order to reveal the mechanism of thermal-induced deformation and fracture development of salt rock under high temperature, the particle flow program PFC2D was used to study the triaxial compression failure process of salt rocks under different temperatures; at the same time, a combination model of Burge and Linearpbond was proposed to simulate plastic deformation and heat conduction of salt rock. Finally, the simulation results were compared with the experimental results to verify the validity of the conclusion. The simulation results show that the elastic limit points of rock gradually descend, the dilatancy points rise gradually, and the plastic deformation characteristics of salt rock become more obvious with the increase of temperature. Due to the damage of the sample, the strong chains break and disappear, increasing the proportion of the weak chains, and the high temperature intensifies the rupture of the contact between the particles in the salt rock. As the temperature increases from 50°C to 120°C, the strong chains in the rock sample decrease significantly, and the damage gradually increases; when the temperature is 150°C, the contact force decreases sharply, and the damage of salt rock is significant. According to the particle displacement cloud diagrams, it is found that the expansion direction from the middle part of the rock sample to the left and right ends is 12.08°, 9.55°, 8.2°, 6.33°, and 0°, respectively. The displacement directions of the rock sample show obvious radial expansion tendency, and the higher the temperature, the more obvious the “drum-shaped” failure phenomenon in the middle of the rock sample. During the heating process, the thermal cracks are mainly tensile cracks, and transverse cracks are gradually formed in the middle of the model. The cementation failure points at the top and bottom of the model expand in an oblique direction and form oblique cracks of about 45°. From the three different mathematical models of macroscopic and mesoscopic views, it is concluded that the effect of temperatures on salt rock is more significant after 90°C. This research is important for exploring the macroscopic and microscopic mechanics evolution of salt rock and provides a reference for determining the long-term mechanical strength of salt rock.

A topological view on microscopic structural evolution for granular material under loading and unloading path

Granular materials demonstrate complex mechanical behaviors due to the irreversible rearrangements at particle scale. The irreversible behaviors of granular materials can be observed after unloading the granular assembly. In this study, biaxial tests of dense and loose granular assemblies are conducted using discrete element method (2D DEM). We investigate the multiscale behaviors of granular materials under loading–unloading-reloading path. Both dense and loose granular assemblies show hysteresis loops, but their underlying mechanisms and meso-structural evolutions are different. The hysteretic behavior of the dense sample is relevant to the dynamics of contact force network and the evolution of contact loops. The approximate linearity of stress–strain relation during unloading and reloading stages is attributed to the robustness of strong contact network, while the nonlinearity of stress–strain relation is related to the evolution of contact topology. Specifically, loops of 4-sides within the contact network play an important role by transforming into smaller or larger loops by losing and joining particles during the unloading and reloading path. The loose compactness of granular media results in the unapparent evolution of structures at the mesoscale. Besides, the roles of strong and weak subnetworks are not distinguished. The fewer changes in contact loops may cause unconspicuous nonlinear deformation.