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Various film crack patterns: spiral cracks (a1) and crescent shape zig-zag cracks (a2) (courtesy J. Marthelot, ref. 309 ), festooned circular blisters (b1) (courtesy A. Benedetto) and blister network (b2) (courtesy J.-Y. Faou, ref. 310 ).
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... The core design of our proposed device lies in the uniquely defined W regions which are partially etched using standard photolithography and dedicated IBE methods, shown as the two slots with 2 μm length and 2 μm width on the heavy metal (HM) in the upper panel of Fig. 4a. According to the relationship of iDMI and t W unveiled in Fig. 1f, the dedicatedly etched regions hold a larger iDMI with thinner W thickness due to the ion milling introduced local compression stress at the W/CoFeB interface 60,61 , which reduces distance between 5d and 3d atoms at the interface leading to an enhanced 3d −5d orbital hybridization [62][63][64] . It is noteworthy that the DW energy density (σ DW ) is closely related to iDMI strength 65 , ...
We report a breakthrough in the hardware implementation of energy-efficient all-spin synapse and neuron devices for highly scalable integrated neuromorphic circuits. Our work demonstrates the successful execution of all-spin synapse and activation function generator using domain wall-magnetic tunnel junctions. By harnessing the synergistic effects of spin-orbit torque and interfacial Dzyaloshinskii-Moriya interaction in selectively etched spin-orbit coupling layers, we achieve a programmable multi-state synaptic device with high reliability. Our first-principles calculations confirm that the reduced atomic distance between 5d and 3d atoms enhances Dzyaloshinskii-Moriya interaction, leading to stable domain wall pinning. Our experimental results, supported by visualizing energy landscapes and theoretical simulations, validate the proposed mechanism. Furthermore, we demonstrate a spin-neuron with a sigmoidal activation function, enabling high operation frequency up to 20 MHz and low energy consumption of 508 fJ/operation. A neuron circuit design with a compact sigmoidal cell area and low power consumption is also presented, along with corroborated experimental implementation. Our findings highlight the great potential of domain wall-magnetic tunnel junctions in the development of all-spin neuromorphic computing hardware, offering exciting possibilities for energy-efficient and scalable neural network architectures.
... Fatigue in thin films within power semiconductor devices and modules poses significant challenges to their reliability and performance under demanding operating conditions [30,31]. The formation of grooves due to thermal stress, coupled with evaporation and diffusion phenomena, represents complex interdependencies that must be addressed to enhance device durability [31][32][33][34][35]. ...
This paper constituted an extension of two previous studies concerning the mathematical development of the grain boundary grooving in polycrystalline thin films in the cases of evapora-tion/condensation and diffusion taken separately. The thermal grooving processes are deeply controlled by the various mass transfer mechanisms of evaporation-condensation, surface diffusion, lattice diffusion, and grain boundary diffusion. This study proposed a new original analytical solution to the mathematical problem governing the grain groove profile in the case of simultaneous effects of evaporation-condensation and diffusion in polycrystalline thin films by resolving the corresponding fourth-order partial differential equation = − obtained from the approximation ≪ 1. The comparison of the new solution to that of diffusion alone proved an important effect of the coupling of evaporation and diffusion on the geometric characteristics of the groove profile. A second analytical solution based on the series development was also proposed. It was proved that changes in the boundary conditions of the grain grooving profile largely affected the different geometric characteristics of the groove profile.
... Accordingly, the temperatures reached on the friction surface also increase. According to many modern authors [14][15][16], the most important elements of the friction process are temperature effects and, as a result, deformation processes caused by temperature dynamics are observed in the near-surface layers. ...
... To determine the stable states of the system from the point of view of the phase plane method, it is necessary to find the coordinates of special points. Dividing (15) by (16), we find the singular points of the phase plane, that is, the points in which the direction of the tangent to the phase trajectory is not defined. To do this, we will write a system of equations: ...
... As a result, for the obtained two-parameter system (15), (16), the obtained phase portraits are shown in Figures 1 and 2. Figure 1 shows the phase portraits describing the behavior of the system in the dry friction mode (for the temperature of the friction surfaces lower than T c0 ), for different ratios of the relaxation times τ. In particular, Figure 1a corresponds to the example of τ = 0.01. ...
This paper presents the results of the study of stress relaxation fields, deformation, and temperature of the system of nanostructured multilayer coatings. In the work, a nonlinear relationship between strain and stress was used to take into account nonlinear effects in the mechanism of nanostructure formation. The paper assumes that a friction surface is provided by the self-organization of shear components: both stress and strain on the one hand, and temperature on the other. The studied objects are described in the adiabatic approximation, taking into account the fact of the evolution of stresses and strains. With the help of phase portraits of the system, the dependence of the deformation processes on the stresses arising in the system without coating and with coating is shown. It is shown that the rate of change of deformation depends on the characteristics of the mechanical impact on the coating and on the amount of stress and deformation. A conclusion is drawn regarding the transition process in the presence of two regions (Hooke and plastic deformation) in the corresponding phase portrait of the strain–stress field of the system. The results of the work can be used to determine the effective parameters of a coating in the analysis of experimental time dependences of stresses.
... Fatigue in thin films within power semiconductor devices and modules poses significant challenges to their reliability and performance under demanding operating conditions [30,31]. The formation of grooves due to thermal stress, coupled with evaporation and diffusion phenomena, represents complex interdependencies that must be addressed to enhance device durability [31][32][33][34][35]. 3 The problem of grain boundary grooving in polycrystalline thin films was studied by many researchers [14][15][16][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. The works of Mullins [14][15][16] were devoted to solve the problem governing the profile of grain boundary grooving. ...
This paper constituted an extension of two previous studies concerning the mathematical development of the grain boundary grooving in polycrystalline thins films in the cases of the evaporation/condensation and diffusion taken separately. The thermal grooving processes are deeply controlled by the various mass transfer mechanisms of evaporation–condensation, surface diffusion, lattice diffusion, and grain boundary diffusion. This study proposed a new original analytical solution to the mathematical problem governing the grain groove profile in the case of simultaneous effects of evaporation-condensation and diffusion in polycrystalline thin films submitted to thermal and mechanical stress, and fatigue effects; by resolving the corresponding fourth-order partial differential equation ∂y∂t=C∂2y∂x2-B∂4y∂x4 obtained from the approximation y'2≪1. The comparison of the new solution to that of diffusion alone proved an important effect of the coupling of evaporation and diffusion on the geometric characteristics of the groove profile. A second analytical solution based on the series development was also proposed. It was proved that change of the boundary conditions of the grain grooving profile largely affected the different geometric characteristics of the groove profile.
... Additionally, the deposited films could also be used to link the observed changes in ionised flux fraction and deposition rate to film properties. In particular, it can be expected that there will be an increase in compressive film stress at low pressure, which could introduce further optimisation constraints depending on the application [55]. ...
The influence of pulse length, working gas pressure, and peak discharge current density on the deposition rate and
ionised flux fraction in high power impulse magnetron sputtering (HiPIMS) discharges of copper is investigated experimentally using a charge-selective (electrically biasable) magnetically shielded quartz crystal microbalance (QCM)
(or ionmeter). The large explored parameter space covers both common process conditions and extreme cases. The
measured ionised flux fraction for copper is found to be in the range from ≈ 10 % to 80 %, and to increase with in-
creasing peak discharge current density up to a maximum at ≈ 1.25 A/cm^2, before abruptly falling off at even higher
current density values. Low working gas pressure is shown to be beneficial in terms of both ionised flux fraction and
deposition rate fraction. For example, decreasing the working gas pressure from 1.0 Pa to 0.5 Pa leads on average to
an increase of the ionised flux fraction by ≈ 14 pp (percentage points) and of the deposition rate fraction by ≈ 4 pp
taking into account all the investigated pulse lengths.
... Figure 7(b) shows samples S1-S3 with a thickness of about 1300 nm, the overall stress is described as the tensile part, and the residual stress decreases with the increase of the number of steps, the residual stress decreased by about 43% from 1575 MPa for S1 to 841 MPa for S3. But in the schematic diagram of the compressive stress part in Fig. 7(c), the sample S4-S6 thicknesses around 630 nm show the opposite result, the stress increases with increasing deposition steps [6,28], the residual stress increases by about 41% from −515 MPa for S4 to −884 MPa for S6. The derivation of the stress gradient schematic is from Eq. (2) [6], where f is the average stress for an AlN film of thickness t f , α fits the slope of the stress, γ is the power-law spacing of stress vs. thickness at a fixed power, β is a scale factor, and α, β, and γ are valued depending on the processing environment. ...
In this work, a unique approach in experiments was carried out by a pulsed DC sputtering for the 60/30-min process in one-step and multi-step (two- and four-step) deposition to obtain trends of residual stress and film properties of aluminum nitride (AlN). Film characteristics comparison between one-step and multi-step deposition was used to study the correlation among film crystallite orientation, residual stress, and film features. The thickness, microstructure, residual stress, and crystallite status of AlN films were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The results show that the films have different stress characteristics in different microstructures when processed at the same amount of time in different deposition intervals. The increase in the degree of ion bombardment and induced substrate temperature raised leads to the interpretation of different microstructural changes in films. In this investigation, the film with thickness about 1300 nm for one-step deposition has a surface roughness of 2.67 nm, the grain size of 65.1 nm, and residual stress of 1575 MPa. In the four-step deposition, these values were reduced to 2.46 nm, 51.4 nm, and 841 MPa, respectively. In situ optical emission spectroscopy (OES) data were collected during plasma deposition of selected dominant wavelengths of N2 (315 and 336 nm) and Al (394 and 396 nm) for large-scale data analysis. Based on a cross-validation test executed from OES data preprocessing, the methodology with the principal component analysis (PCA) and value of microstructure characteristics (VMC) algorithm demonstrated that this unique multi-step deposition technique can provide a good stress gradient control from microstructural analysis and can effectively classify film characteristics in AlN film deposition.
... Recently, considerable attention has been drawn to films and coatings based on organic materials [8][9][10]. Physical and chemical properties of thin films and coatings differ significantly from the properties of bulk materials due to the peculiarity of their geometric sizes, structure, the presence of developed surface and mechanical stresses [11,12]. Therefore, determining their properties and the relation between the technological conditions of growth and the characteristic of the final product is an urgent task. ...
... Thus, it seems that the number of cells was very high, forming a dense layer. High levels of cell-to-cell interactions likely induced large stress on the layer, causing its flaking [47]. It seems that the adhesion of cells to the surface was so strong that this flaking also caused fragmentation of the CNF membrane (SM 5). ...
In this study, we report the fabrication of carbon nanofiber (CNF) – carbon nanotube (CNT) nanofibrous composites obtained by thermal treatment of an electrospun polyacrylonitrile precursor. Four types of CNTs of similar sizes but different surface functional groups were used: highly oxidized (HO, CNT composed of carbon of mainly a +3 oxidation number) and low oxidized (LO, CNT composed of carbon of mainly a +2 oxidation number) and two types of amidized CNTs derived from the oxidized ones (HNH and LNH, respectively). CNTs affected the structure and chemical composition of the CNF composites. All of the materials were hydrophobic, and their electrical conductivities varied from 317 [S/m] (CNF+HNH) to 542 [S/m] (CNF). The obtained nanofibers were cytocompatible (at day 7, the viability of cells was above 89%) and revealed strong bactericidal properties towards Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria strains (reduction from 11% for CNF to 84% for CNF+HNH). The presence of CNTs improved the antibacterial performance and the strongest effects were observed for the HO and HNH - CNTs composed of carbon of mainly a +3 oxidation number that had the highest sharing of quaternary nitrogen atoms, suggested to have bactericidal properties. In summary, in this study highly electrically conductive, cytocompatible, and antibacterial CNF-CNT composites were obtained. These materials could serve as scaffolds for long-term in vitro cultures or as a new class of wearable electronics among numerous other biomaterial applications.
... We note that good adhesion between adjacent layers is necessary to preserve residual stress. Residual compressive stresses above 1 GPa are commonly observed in many thin films and coatings, 36 providing evidence of good bonding. Therefore, lower stress levels of $150 MPa as desired here should be readily achievable. ...
... (C) The biaxial modulus and the coefficient of thermal expansion for representative cathodes and electrolytes. Each of these materials are representative of a broader class of solid electrolytes or electrodes: LLZTO is representative of oxide electrolytes, 24,25 Li 10 GeP 2 S 12 (LGPS) is representative of crystalline sulfide electrolytes,26,27,28,29 Li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP) is representative of LISICON electrolytes, 30,31,32 and nickel manganese cobalt oxide33,34,35 (NMC) or lithium Iron phosphate (LFP)36 are representative of various classes of cathodes.33,34 (D) The residual compressive stress at the solid-electrolyte/cathode interface. ...
Metal-dendrite penetration is a mode of electrolyte failure that threatens the viability of metal-anode-based solid-state batteries. Whether dendrites are driven by mechanical failure or electrochemical degradation of solid electrolytes remains an open question. If internal mechanical forces drive failure, superimposing a compressive load that counters internal stress may mitigate dendrite penetration. Here, we investigate this hypothesis by dynamically applying mechanical loads to growing dendrites in Li6.6La3Zr1.6Ta0.4O12 solid electrolytes. Operando microscopy reveals marked deflection in the dendrite growth trajectory at the onset of compressive loading. For sufficient loading, this deflection averts cell failure. Using fracture mechanics, we quantify the impact of stack pressure and in-plane stresses on dendrite trajectory, chart the residual stresses required to prevent short-circuit failure, and propose design approaches to achieve such stresses. For the materials studied here, we show that dendrite propagation is dictated by electrolyte fracture, with electronic leakage playing a negligible role.
... Flexible electronics has manifested exploration and development of potential energy efficient technologies like ultrathin sensors, actuators, wearable electronics and new generation straintronic devices in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13] . The ability of these electronics to bend, stretch and wrap makes them advantageous over conventional electronics. ...
Flexible materials have brought up a new era of application-based research in stretchable electronics and wearable devices in the last decade. Tuning of magnetic properties by changing the curvature of devices has significant impact in the new generation of sensor-based technologies. In this work, magnetostrictive FeGa thin films have been deposited on a flexible Kapton sheet to exploit the magneto-elastic coupling effect and modify the magnetic properties of the sample. The FeGa alloy has high magnetostriction constant and high tensile strength making its properties susceptible to external stress. Tensile or compressive strain generated by the convex or concave states influence the uniaxial magnetic anisotropy of the system. Low temperature measurements show a hard magnetic behavior and the presence of exchange-bias effect after field cooling to 2 K. The results obtained in this study prove essential for the development of flexible electronics.
