In-plane Values Research Articles

Oriented Bi2Te3-based films enabled high performance planar thermoelectric cooling device for hot spot elimination

Film-thermoelectric cooling devices are expected to provide a promising active thermal management solution with the continues increase of the power density of integrated circuit chips and other electronic devices. However, because the microstructure-related performance of thermoelectric films has not been perfectly matched with the device configuration, the potential of planar devices on chip heat dissipation has still not been fully exploited. Here, by liquid Te assistant growth method, highly (00 l) orientated Bi2Te3-based films which is comparable to single crystals are obtained in polycrystal films in this work. The high mobility stem from high orientation and low lattice thermal conductivity resulting from excess Te induced staggered stacking faults leads to high in-plane zT values ~1.53 and ~1.10 for P-type Bi0.4Sb1.6Te3 and N-type Bi2Te3 films, respectively. The planar devices basing on the geometrically designed high orientation films produce a remarkable temperature reduction of ~8.2 K in the hot spot elimination experiment, demonstrating the great benefit of Te assistant growth method for oriented planar Bi2Te3 films and planar devices devices design, and also bring great enlightenment to the next generation active thermal management for integrated circuits.

Wrinkled layers lead to high in-plane zT values in hexagonal CaAgSb

Layered thermoelectric materials (LTMs) have attracted great attention due to their anisotropic transport behaviors that provide an opportunity to disentangle the interrelated electrical and thermal conductivities. In this study, we found that hexagonal CaAgSb (h-CaAgSb) possesses a lower lattice thermal conductivity and a higher electrical conductivity simultaneously along the in-plane direction when compared with the out-of-plane direction. The low in-plane lattice thermal conductivity mainly originates from the low group velocity of longitudinal acoustic phonon modes. Meanwhile, strong anharmonicity is discovered for the low-lying optical phonon modes. On the other hand, the high in-plane electrical conductivity relies on the small effective mass. Thus, both p-type and n-type h-CaAgSb exhibit a high zT over 2.0 along the in-plane direction at the optimal carrier concentrations. The anisotropic transport properties of h-CaAgSb reported in this work may provide guidance to the experiments. More importantly, the physical insights revealed for the disentangled electrical and thermal transport properties may pave the way for finding other excellent LTMs and optimizing the thermoelectric performance through structure engineering.

Stretchable and Skin-Conformal Thermoelectric Generator with Highly Flexible and Plastically Bendable Silver Selenide Films.

Among inorganic thermoelectric materials, flexible thermoelectric materials have attracted considerable attention. In this study, highly flexible and plastically bendable silver selenide films with excellent thermoelectric performance at room temperature are presented. The flexibility of the freestanding silver selenide films was significantly improved through a simple annealing treatment. The highly flexible silver selenide films with a thickness of 26.0 μm displayed outstanding n-type thermoelectric performance, achieving an in-plane zT value of 0.38 at room temperature. Because silver selenide films are plastically bendable with a bending radius of less than 1 mm, they can be shaped into various forms. To achieve stretchability and skin-conformality in the thermoelectric generator, S-shaped silver selenide strips were used as an n-type thermoelectric element. Effective harvesting of electricity from heat of the human body was successfully demonstrated.

A strain acceleration method to identify the onset of diffuse necking

This paper presents an innovative ‘strain acceleration method’ for determining the onset of diffuse necking in sheet forming tests using data obtained from digital image correlation (DIC). The method identifies the onset time of diffuse necking and provides the corresponding in-plane principal strain values by detecting a local extreme in the second derivative of the minor principal in-plane strain with respect to time at the edges of the sheet surface region where diffuse necking occurs. Results obtained from applying the method to tensile testing on two different materials and comparisons with available methods based on force-time or principal strain rate evolutions confirm its accuracy and validity. The new method was implemented in a computer software to be used for research and education that also enables determination of localized necking and fracture and plotting the strain loading paths in principal strain space.

Optical intensity figures of merit of insulator-metal-insulator and metal-insulator-metal thin-film stacks

This paper discusses the quality factors Q and the intensity figures of merit (IFoM) evaluating the intensity and leakage of modes of the reflection flux and of the plane-wave and locally excited transmitted fluxes of insulator-metal-insulator (IMI) and metal-insulator-metal (MIM) 2D planar thin-film stacks, here air-Au-glass and air-Au-SiO2-Au-glass stacks respectively. These thin film stacks sustain a single surface plasmon polariton (SPP) and multiple planar waveguide (PWG) modes. The Q and IFoM of the 3D dispersion graph (in-plane wave vector k ρ /k 0 ∈ [0, 1.52]/frequency ω ∈ [0.5, 2.7] eV/observable dispersion) are calculated and analyzed along 2D cuts where either the in-plane wave vector k ρ /k 0 or the frequency ω are varied the other independent variable being kept fixed. Here these two cuts are called spatial (ω fixed) and frequency (k ρ /k 0 fixed) domains. Due to a lower leakage, the Q and IFoM of the IMI and MIM thin film stack modes are significantly larger in the spatial domain than in the frequency domain. In the spatial domain the IMI and MIM stack modes dominate at low and high frequencies respectively. In the frequency domain, the Q and IFoM of a MIM stack mode is always larger than that of an IMI stack. Our results span a large domain of frequencies in the SPP and RPP region and of the in-plane wave vector whereas the results in the literature presented above concern only particular laser frequencies and limited in-plane wave vector values. Our Q and IFoM of the 2D planar thin film stack modes, obtained with optimized independent variables, are larger than those of other planar thin film stacks but smaller than some 2D/3D nano scale samples with an involved geometry. The simplicity of producing these simple IMI and MIM stacks permit their use in the applications.

Multifunctional polyimide/boron nitride nanosheet/Ti3C2Tx MXene composite film with three-dimensional conductive network for integrated thermal conductive, electromagnetic interference shielding, and Joule heating performances

With the demand for further miniaturization and higher frequency operation of electronic devices, polymer films with high thermal conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) are urgently required. Herein, polyimide (PI)/boron nitride nanosheets (BNNS) aerogels with oriented porous structure are fabricated by unidirectional-freezing and freeze-drying methods. Subsequently, hierarchical PI/BNNS/Ti3C2Tx composite films with consecutively electrically and thermally conductive networks are successfully prepared via a unidirectional PI/BNNS aerogels-assisted immersion and hot-pressing strategy. Owing to the three-dimensional conductive dual networks of BNNS and Ti3C2Tx, the composite film exhibits excellent thermal conductivity with the maximum in-plane value of 4.73 W/(m·K), increased by 456 % compared to pure PI film. Moreover, the conductive network of Ti3C2Tx is conducive to the excellent EMI shielding performance, endowing the PI/BNNS/Ti3C2Tx composite film with an outstanding EMI SE value of 49.2 dB at 8.2 GHz with a low MXene content of 6 wt% and thickness of 300 μm. Furthermore, the composite film shows the superior Joule heating performance with fast thermal response and sufficient reliability. Therefore, the resulting composite film exhibits excellent thermal conductive, EMI shielding and Joule heating performance, which enables the potential application of multifunctional composites for thermal management and EMI shielding.

The engineering elastic constants of bio-inspired sandwich cores with wavy cylinders

Beetle Elytron Plates (BEPs) represent a new class of biomimetic sandwich cores with excellent mechanical properties and inspired by the internal structure of the beetle elytra. The cores have a hexagonal centre-symmetric configuration with through-thickness cylinders in the unit cell. The present work describes the behaviour of the engineering elastic constants of an evolution of these BEP topologies that feature cylinders with waviness. These BEP core configurations are simulated using Finite Element models, with periodic boundary conditions for volumetric homogenization. The models are then used to perform a parametric analysis against the geometry characteristics of the new cellular configurations. This work further explores the potential design space of BEP cellular metamaterials by altering the geometry of the trabeculae and facilitates further investigation into the mechanical properties of these new BEP topologies with wave-shaped units. Although – and as expected - the specific nondimensional out-of-plane tensile modulus has values here close to unity, BEP topologies with out-of-plane wave-shaped cylinders show enhanced in-plane moduli values than classical straight cylinder configurations, except for the Young's modulus of MBEP cores with only one semi-wave. The same trend is observed for the nondimensional Young's modulus of EBEP configurations, whereas the situation is opposite for the MBEP topologies. The nondimensional out-of-plane shear modulus decreases for both EBEP and MBEP configurations compared to the straight cylinder cores.

Unsaturated out-of-plane permeability measured with three-dimensional flow monitoring by etched optical fiber sensors

In our work, the three-dimensional flow in stacks of biaxial E-glass fiber non-crimp fabrics (NCF) and unidirectional carbon fiber layers was monitored by the etched optical fiber sensors embedded inside the fabric stack. The influence of embedding sensors with a diameter of 200 µm on the flow was experimentally illustrated and discussed. The out-of-plane permeability of the two fabric materials was estimated with a radial infusion model using the in-plane permeability values as the prior knowledge. The assumed radius of the semi-ellipsoidal flow was derived and showed a good agreement with the results obtained by the best fit of the exact solution, which provides an approximate solution that simplifies the calculation process. The asymptotic form and the modified semi-ellipsoidal inlet radius method for the case of a non-negligible radius of injection tube compared to the fabric sample thickness were verified. The uncertainties related to the unknown flow pattern near the inlet were also demonstrated. The presented results facilitate the further development and standardization of out-of-plane permeability measurement methods with embedded sensors.

Mixed-Dimensional (1D-2D) Carbon as a Conductive Additive and Enabler for Next Generation Lithium-Ion Batteries

The race to develop the next generation of lithium-ion batteries with higher performance metrics (e.g. energy density, power density, cyclability) has spurred interest in carbon allotropes, such as carbon nanotubes (1D) and graphene (2D). Herein, a new multi-dimensional carbon material, comprised of long and entangled 1D nanotubes that unfurl into a spanning network of 2D sheetlets, is investigated as a conductive additive in lithium-ion battery cathodes. Compared to conventional conductive additives, this so-called 1.5D carbon material improves both electrical and thermal pathways between battery active materials within the electrode.In this presentation, the electrical, thermal, and electrochemical properties of the mixed-dimensional (1.5D) carbon are compared to conventional additives such as carbon black and graphite. Higher active material loadings, less heat generation, and more energy-dense cells can be enabled by the improved electrical conductivity, where three times less carbon black results in one order of magnitude higher electrode conductivity. The thermal conductivity of these cathodes is also enhanced in both the through- and in-plane directions, which is beneficial for battery thermal management. For instance, using a third of the carbon amount results in more than 30% and 240% higher through- and in-plane thermal conductivity values, respectively. The combination of these properties translates to overall improvements in electrochemical performance metrics including rate capability, lower cell impedance, and higher achievable capacities. Compared to cells with conventional carbon black, there is a 20% reduction in ohmic resistance determined by electrochemical impedance spectroscopy. In terms of capacity retention and rate capability, full cells cycled at a 2C charge and 0.5C discharge rate demonstrated 2.5% higher initial capacity than carbon black with a retention of 95% vs 94.4% after 120 cycles.

Experimental Study on In-plane Stiffness of Track in a Turnout of the Railway in Vietnam

Aims: This study aims to determine the in-plane stiffness of the track in a turnout of the railway in Vietnam. Background: Track stiffness is a basic parameter of railway tracks that influences the bearing capacity of the track, the dynamic behavior of passing vehicles, the quality of track geometry, and the life of track components. Objective: The objective of this research is to determine the in-plane stiffness of the track based on substructure modulus, and rail pad stiffness at a track section in a turnout. Methods: Various tests which included the field tests of the substructure modulus, and rail pad stiffness tests in the laboratory were done. Substructure modulus was investigated at ten locations in the field. Rail pad stiffness was tested with five samples in the laboratory. In-plane stiffness of the track was calculated through substructure modulus and rail pad stiffness. The finite element method was used to evaluate the bearing capacity of bearings with different in-plane stiffness values. Results: Based on the results obtained, the substructure modulus was from 0.49 N/mm3 to 1.48 N/mm3. The rail pad stiffness is from 32.99 kN/mm to 34.92 kN/mm. These results are used to calculate the in-plane stiffness of the track. The in-plane stiffness of a track section in a turnout in Vietnam is from 25.18 kN/mm to 30.19 kN/mm. According to the finite element method, it is possible to determine the maximum value of forces transmission to the supports from 37.743 kN to 38.989 kN corresponding to the above stiffness values with the axle load of train 14 tons and rail P60. Conclusion: The stiffness of the supporting is proportional to the value of the force transmitted to the supporting. This study clearly showed that the substructure (soil and ballast) properties had the most impact on the total in-plane stiffness of the track. The results will be a tool for the track maintenance engineer to implement correct maintenance activities.

Covalently modified graphene and 3D thermally conductive network for PEEK composites with electromagnetic shielding performance

Polyetheretherketone (PEEK) has inferior interfacial compatibility due to its rigid structure. Hence, achieving the desired thermal conductivity (TC) of PEEK composites is challenging. Covalently bonded amino-graphene (NH2-GnPs) and polybenzoxazine (PBZ) can reduce interfacial thermal resistance (ITR). Hybrid NH2-GnPs and multi-walled carbon nanotubes (MWCNTs) were applied synergistically to refine the TC pathways. Additionally, the 3D thermally conductive network was constructed from electrospun NH2-GnPs&MWCNTs/ketimine-biphenyl polyetheretherketone (PEBEKt) and freeze-dried MWCNTs/[email protected] composites arranged in a sandwich structure. The oriented fillers could improve the heat diffusion network by increasing heat flow conveyance. The optimal in-plane and through-plane TC values were 21.0 and 6.9 Wm−1K−1, respectively, 90 and 29 times those of pure PEEK. The composites also exhibited excellent electromagnetic shielding (80.4 dB, 21.1%), thermal stability, and thermal management capabilities. Consequently, the 3D thermally conductive composites can provide a viable idea for thermal management and electromagnetic shielding materials.

Design of PGM-Free Cathode Catalyst Layers for PEMFC Applications: The Impact of Electronic Conductivity

The impact of the electronic resistance of platinum-group-metal-free cathode catalyst layers (PGM-free CCLs) for proton-exchange-membrane fuel cells (PEMFCs) was systematically investigated. Here we selected two different PGM-free catalysts (having high and low electronic conductivity) and integrated them into CCLs without and with conductive carbon fiber additives. To investigate the impact of the electronic resistivity () of PGM-free catalysts and CCLs, their through-plane values were quantified by an in situ electrochemical impedance spectroscopy (EIS) approach based on a one-dimensional transmission line model. The results indicate that the electronic conductivity of PGM-free CCLs can be increased by adding carbon additive, resulting in a significant improvement of the fuel cell performance (by ∼60 mV at 1 A cm−2 in H2/O2 configuration). Ex situ four-point probe measurements of the in-plane values of some of the CCLs were found to differ vastly from the through-plane values. This difference is attributed to the anisotropic morphology of the CCLs, caused by preferential fiber orientation and/or cracks in the CCLs. In the end, we suggest guidelines for the design and evaluation of PGM-free CCLs and for assessing and improving their electronic resistance.

Temperature and p-doping dependence of the power factor in SnS: The role of crystalline symmetry

Temperature and doping dependence of the power factor of p-type SnS, and their dependence on space-group symmetry (Pnma(62)-SnS and C2mb(39)-SnS), were investigated by density functional theory calculation combined with the Boltzmann transport theory. Our results show that the anisotropy in electrical conductivity of C2mb-SnS (Pnma-SnS) in its in-plane value is six orders (one order) of magnitude greater than its corresponding out-of-plane value. The thermopower in C2mb-SnS is about eight times as large as that of in Pnma-SnS at high temperatures, and the maximum Power Factor for C2mb-SnS is two times as large as that of Pnma-SnS, being this difference considerably greater at high temperatures. Our findings indicate that the role of effective masses and bandgap characteristics are critical in reducing the impact of the bipolar transport effect at high temperatures, contributing to our predicted better performance of the C2mb-SnS as a thermoelectric device compared to Pnma-SnS.

A novel two-dimensional reflective coherent gradient sensor and its applications in residual deformation measurement of laser repaired metal components

Directed Energy Deposition (DED), known as an important branch of additive manufacturing, are becoming increasingly crucial in different industrial fields. However, this extreme manufacturing process may bring about quality issues for the DED product, and in-situ monitoring for characterizing mechanical parameters of thick DED products still needs to be improved. In this manuscript, for the convenient in-situ bidirectional residual deformation measurement of thick DED metal components, a novel two-dimensional coherent gradient sensor (2D-CGS) is established based on crossed Ronchi gratings. Firstly, the diffraction characteristic of the crossed Ronchi grating used in 2D-CGS is analyzed, and then the principles of 2D-CGS are analyzed in detail for bidirectional out-of-plane displacement gradient measurement. Furthermore, two temporal phase-shifting techniques: plane-parallel plate rotating (PPR) method and prism translation (PT) method, are extended from one dimension to 2D for improving the accuracy of 2D-CGS post-processing, named as 2D-PPR method and 2D-PT method. Verification experiment shows that the 2D-CGS system can synchronously measure the bidirectional curvature fields of the standard spherical reflector with the maximum relative error of 3.80%, which is equivalent to the accuracy of typical CGS. Finally, in the application of zig-zag deposited DED process, the bidirectional residual deformation fields of repaired components are in-situ monitored by portable 2D-CGS system, and the relationship of dwell time between adjacent tracks and the residual deformation is analyzed based on bidirectional centerline curvature on the bottom surface of substrate. A new parameter named as the orthotropic symmetry coefficient is defined based on curvature to analyze the full-field in-plane orthogonal anisotropy. Results show that both the degree of in-plane orthogonal anisotropy and value of residual deformation decreases with the increase of dwell time from 0 to 5 s, while varying a little with the dwell time exceeding 5 s, which also indicates the proposed parameter could well evaluate the degree of full-field orthotropic anisotropy. Meanwhile, the position of maximum curvature also gradually moves from the end toward the beginning in deposition direction. In summary, the proposed 2D-CGS method can measure the full-field bidirectional deformation in high efficiency, which may be promising in future in-situ monitoring applications.

Micro Computed Tomography based stochastic design and flow analysis of dry fiber preforms manufactured by automated fiber placement

The effective design of channels in dry tape preforms is crucial for achieving desired preform permeability for successful resin injection for composites manufacturing using Automated Fiber Placement (AFP) process. Achieving target gaps and their locations in the AFP layup is extremely challenging. This work investigates the correlation between the spatial variability of the preforms and the in-plane permeability using an X-ray Computed Tomography (XCT) based characterization framework. The tomographic images of two different dry carbon tape preforms with different tape widths were used to generate realistic and XCT based stochastic models to be used for numerical permeability predictions. The variability in the tape placement by the robotic head and its effect on preform permeability was also examined through stochastic geometric modeling of the laid preform. A benchmark transient permeability measurement set-up was utilized to obtain experimental in-plane preform permeability through 2D radial mold filling. The in-plane numerical permeability values showed significant scatter, with a coefficient of variance of 75%–130%, which deviated from the experimental measurements by approximately one order of magnitude. These findings strongly re-affirm that the experimental permeability measurement technique based on transient mold filling of dry fiber AFP preforms is complex however, the XCT based stochastic modeling technique is an effective way to estimate the permeability of dry fiber AFP preforms virtually.

Mechanical property-enhanced thermally conductive self-healing composites: preparation using designed self-healing matrix phase and hyBNNSs.

Polymer composites with good thermal conductivity are gaining more and more attention in the current electronics sector, due to their superior heat management capabilities. However, conventional thermally conductive polymer composites are usually subject to interruptions in heat transfer because of physical damage. The present study prepared mechanical property-enhanced thermally-conductive self-healing composites through compositing a self-healing polyurethane matrix with hydroxylated boron nitride (hyBNNSs). The self-healing polyurethane was obtained by incorporating ligands and cerium(III) triflate [Ce(SO3CF3)3] as the metal center into the polyurethane elastomer. An optimal sample (PUp2C) with high tensile strength (6.8 MPa) and stretchability (1053%), ideal toughness (49.2 MJ m-3), and remarkable healing efficiency (97% healing after 48 h at 35 °C) was obtained. An increase in the content of hyBNNSs from 10% to 30% led to a significant increase in the mechanical performance of hyBNNSs20%/PUp2C, which manifested as the increase in the elongation at break (from 1053% to 1302.5%) and stress (from 6.8 MPa to 16.4 MPa). The XRD results revealed that combining PU with hyBNNSs through coordination bonds could significantly promote the crystallization of PUp2C, which was beneficial to enhancing the mechanical properties of the composites. The through-plane (λ⊥) and the in-plane (λ∥) values of the BNNSs30%/PUp2C composite reached 0.41 and 1.42 W mK-1, respectively, which were 195.2% and 507.1% higher than those of the original PUp2C, respectively.

Effect of fiber orientation and loading direction on the compressive response of E-glass/Epoxy laminated composites used in modern helicopter blades submitted to high strain rate

In this investigation, the dynamic behaviour of glass fibre reinforced poly- mer under in-plane and out-of-plane dynamic compression tests was studied experimentally and numerically under varying the fibres orientation and the loading conditions. The composites consist of unidirectional E-glass fibers reinforced epoxy polymer composites used in modern helicopter blade application as inner surface. Specimens, with a cylindrical shape, are impacted at a constant strain rate subjected to SHPB and Ls Dyna program. The numerical results are in good agreement with experimental results. The results show that the out-of-plane stress values for different fiber orientation are close to each other, but the in-plane stress value is far lower for the fibers direction of ±45◦. This study will facilitate fiber orientation selection for dynamic effects during the helicopter blade production phase. Not only simple tests but also practical ideas make this study stand out. Considering results, the use of ±90◦ fiber direction in helicopter blades seems to be more advantageous against dynamic effects.

Coherent Spin Dynamics of Electrons in Two-Dimensional (PEA)2PbI4 Perovskites.

The versatile potential of lead halide perovskites and two-dimensional materials is merged in the Ruddlesden-Popper perovskites having outstanding optical properties. Here, the coherent spin dynamics in Ruddlesden-Popper (PEA)2PbI4 perovskites is investigated by picosecond pump-probe Kerr rotation in an external magnetic field. The Larmor spin precession of resident electrons with a spin dephasing time of 190 ps is identified. The longitudinal spin relaxation time in weak magnetic fields measured by the spin inertia method is as long as 25 μs. A significant anisotropy of the electron g-factor with the in-plane value of +2.45 and out-of-plane value of +2.05 is found. The exciton out-of-plane g-factor of +1.6 is measured by magneto-reflectivity. This work contributes to the understanding of the spin-dependent properties of two-dimensional perovskites and their spin dynamics.

(Digital Presentation) Prediction of an in-Plane Anomalous Current Using Numerical Simulation and Machine Learning

Even normally shipped batteries may contain disturbing factors such as very small amounts of foreign matter or structural inhomogeneity, which can cause serious accidents such as thermal runaway or explosions. Since dismantling and identifying the cause is time-consuming and costly, nondestructive techniques for identifying the cause are required. A method for detecting abnormal current distribution by magnetic field inverse analysis has been proposed as one such method, but it is difficult to directly elucidate the factors that cause the abnormal current distribution itself. In this study, we first focused on the effect of different separator structures and analyzed the in-plane directional current distribution using machine learning in order to construct a non-destructive model for estimating the causes.A one-dimensional model based on porous electrode theory [1] was used. Constant current charging, homogeneous electrode layer structure, uniform Li concentration in active material particles, and isothermal conditions were assumed. The electrode layer was assumed to be a porous body consisting of active material, electrolyte, and auxiliary materials (conductivity assistant and binder). Using the previously reported structural information and physical properties [2], [3], Case 1 was a coin cell using LiNi1/3Co1/3Mn1/3O2 as the cathode active material, and Case 2 was a laminated cell using LiCoO2 as the cathode active material. The anode active material was graphite and the electrolyte was 1.0 M LiPF6 solution in EC・DEC solvent for both Case 1 and 2. The degree of flexure of the cathode and anode was determined using the formulas from previous studies [4]. Cross-sectional images of the actual biaxially oriented separator were obtained using a focused ion beam scanning electron microscope, and the three-dimensional simulated structure was reproduced based on these images (Sep. A). Similarly, a nonwoven fabric structure (Sep. B) and a foam structure (Sep. C) were also reproduced.Since the collector foils are connected in-plane, the potentials at both ends of the cell must be uniform. Under this constraint, the ion current distribution can be estimated depending on the in-plane structure distribution of the separator. In this study, the correlation between the local porosity (ε) of the separator and the local ion current (denoted as C-rate) was determined using a nonlinear regression method called Support Vector Regression (SVR) [5]. 100 points were taken randomly from 0.4~1.0 and 5~10 for ε and C-rate, respectively, and used as explanatory variables. Each charging curve was compared with the charging curve at the in-plane mean value of (ε, C) = (0.545, 7.5), and the RMSE (root mean square error) of the voltage was calculated as the objective variable.The in-plane reaction distribution was obtained from the voltage error predicted from ε and C-rate by SVR and the porosity distribution of the separator. The mesh size was 40 nm/pixel. For each separator, the difference between high and low reaction profiles was more clearly observed in Case 2. The reaction overvoltage distribution at a certain point in Case 2 was acquired, and it was confirmed that the reaction was concentrated near the separator of the negative electrode. This also made it possible to estimate the Li deposition point, which is the starting point of degradation.Using machine learning to analyze the in-plane current distribution, it was found that the current distribution differs depending on the electrode conditions even for the same separator. We will use this technology to develop a technique for identifying factors based on the current distribution obtained by nondestructive measurement.

Compressive Strained Si1-XGex Channel for High Performance Gate-All-Around Nanosheet Transistors

As scaling of conventional FinFET architecture to achieve target transistor density and performance becomes more complex and difficult, it is essential to attain a next generation transistor architecture. Horizontal Gate-All-Around (hGAA) nanosheet (NS) devices have attracted attention as a candidate to replace FinFETs at the 5nm technology node and beyond due to their excellent electrostatics and short channel control. Compared to scaled FinFET, stacked GAA NS offers circuit performance improvements with increased effective width per active footprint while also enabling gate length scaling. Exploring performance improvement techniques, such as channel strain engineering, is important for next generation CMOS technologies. It is difficult, however, to effectively induce strain into the channel region using source/drain stressors in scaled GAA NS structures due to reduction of the stressor (embedded SiGe in source/drain region) volume as transistor dimension shrinks. In addition, strain relaxation of source/drain stressors caused by introduction of crystalline defects decreases effectiveness to induce strain into the channel region. This is more pronounced by the fact that achieving superior epitaxial growth is more difficult on the GAA NS device structure due to the presence of inner spacer dielectric. Therefore, we proposed a stacked GAA NS pFET device with compressively strained SiGe channel. The SiGe channel NS devices were fabricated using Si NS channel trimming by selective isotropic dry etch and selective SiGe epitaxial growth techniques after the Si NS channel release (Fig. 1). This is the preferable scheme in terms of strain retention in the SiGe channel NS region since there are no patterning processes that cause strain relaxation during downstream processing.To investigate the device characteristics of SiGe NS devices, we fabricated strained Si1-xGex (x = 0.2, 0.25, 0.3, and 0.35) channel NS pFET and investigated the crystallinity and strain in the channel region. Fig. 2 contains cross-sectional TEM images across the gate after Si0.7Ge0.3 channel formation. We observed no visible crystalline defects in the 4 nm-thick Si0.7Ge0.3 layer grown on the 2 nm-thick trimmed Si NS, indicating superior crystallinity of Si0.7Ge0.3 layer. To investigate strain in the nanoscale strained SiGe NS channel structures, Precession Electron Diffraction (PED) characterization was performed to evaluate lattice deformation of the stacked SiGe NS channel with 4 nm-thick Si0.7Ge0.3 epitaxial growth. Lattice deformation values are defined as the difference between in-plane lattice constants and the Si lattice constant, normalized by the Si lattice constant. Fig. 3 shows in-plane lattice deformation contour maps in the region of the stacked SiGe NS channel obtained from both X-cut (across the gate) and Y-cut (along the gate) for the SiGe NS structure with sheet width of 20 nm. The in-plane lattice deformation values were extracted from the middle of the SiGe NS channel as shown in Fig. 4. Preservation of half the amount of strain along the channel direction ([110]) was confirmed whereas strain along the NS width direction ([1-10]) was found to be almost fully relaxed due to elastic relaxation. This results in the Si0.7Ge0.3 channel being uniaxially stressed. The compressive stress along the channel direction estimated from the [110] lattice deformation is ~1 GPa.Normalized hole mobility in the representative Si1-xGex channel NS pFET as a function of inversion carrier density (Ninv) is shown in Fig. 5. The hole mobility of Si1-xGex channel (x = 0.35) with Si cap is almost 100% higher than that of Si NS channel. The mobility benefit of Si1-xGex channel is attributed to reduced effective hole mass along the transport direction caused by a high compressive strain in the Si1-xGex channel.The technique demonstrated in this study for forming compressively strained SiGe channel NS has great potential to improve pFET device performance for next generation of CMOS logic in GAA Nanosheet technology. Figure 1