Growth Of Interfacial Layer Research Articles

Interfacial characteristics and thermal stability of polymer-derived SiCf/Ti composite fabricated by powder hot isostatic pressing

The novel SiCf/Ti composite is prepared by hot isostatic pressing (HIP) with polymer-derived (PD) SiC fiber and powder titanium alloy as raw materials in this work. The interfacial characteristics and thermal stability of the PD SiCf/Ti composite have been systematically investigated. The interfacial properties of the PD SiCf/Ti composites are quantified to discuss the interfacial reaction mechanisms and kinetics. The results show that with the proposed HIP process, the powder matrix can be near-fully dense, and the matrix and SiC fiber are well bonded with a uniform interfacial layer. The major interfacial products are C-Ti compounds and Si-Ti compounds, which are formed by atomic diffusion reaction. During subsequent thermal exposure conditions, the interfacial layer growth is temperature-dependent and diffusion-controlled, following the parabolic relation and Arrhenius law. The frequency factor k0 is 102–103 times lower than that in the chemical vapor deposition (CVD) SiCf/Ti composites, showing better interfacial thermal stability. After thermal exposure, the element diffusion becomes significant, and the microhardness of the near-interface zone is noticeably greater than the matrix microhardness because of the atomic diffusion of C. The microhardness of both the matrix and near-interface zone reaches the highest value after 900 °C/9 h thermal exposure. It is concluded that the PD SiCf/Ti composites with good thermal stability can be successfully fabricated by powder HIP.

Evaluation of Solidification and Interfacial Reaction of Sn-Bi and Sn-Bi-In Solder Alloys in Copper and Nickel Interfaces

Although there are studies devoted to lower Indium (In) addition, Sn-Bi alloys containing 10 wt.% In or more have been barely investigated so far. Higher In contents may offer the potential for improved joint production, better control over the growth of interfacial layers, and enhanced mechanical strength. The present article focuses on the solidification, wettability, adhesion strength, and interfacial intermetallic growth in the Sn-40%Bi-10%In alloy soldered on Cu and Ni pads. SEM-EDS, wettability tests, and tensile tests were performed. The contact angles were measured in Cu and Ni as 24° and 26°, respectively. Indium addition promoted coarsening of the as-solidified microstructure due to an increase in the alloy solidification range. The Bi spacing was increased at least three times, with a strong segregation of Bi towards the interface. The formation and growth of alloy/Cu reaction layers were also evaluated under the different aging conditions of the as-soldered joints, simulating real service. A growth kinetics model of the reaction layer showed that In increases the activation energy, thereby reducing the layer growth. The adhesions of the formed intermetallics films in Cu and Ni were analyzed using tensile tests. It was observed that the alloy/Ni couple exhibited better adhesion. Premature fracturing appears to happen in the alloy/Cu joint due to the higher intermetallic compound’s (IMC) thickness, rough morphology, and coarser microstructure. Both ductile fracture features with dimples and cleavage zones associated with Bi, Cu6(Sn,In)5, and Ni3Sn4 intermetallics were observed.

Influence of Biaxial Strain and Interfacial Layer Growth on Ferroelectric Wake-Up and Phase Transition Fields in ZrO2.

Investigations on fluorite-structured ferroelectric HfO2/ZrO2 thin films are aiming to achieve high-performance films required for memory and computing technologies. These films exhibit excellent scalability and compatibility with the complementary metal-oxide semiconductor process used by semiconductor foundries, but stabilizing ferroelectric properties with a low operation voltage in the as-fabricated state of these films is a critical component for technology advancement. After removing the influence of interfacial layers, a linear correlation is observed between the biaxial strain and the electric field for transforming the nonferroelectric tetragonal to the ferroelectric orthorhombic phase in ZrO2 thin films. This observation is supported by applying the principle of energy conservation in combination with ab initio and molecular dynamics simulations. According to the simulations, a rarely reported Pnm21 orthorhombic phase may be stabilized by tuning biaxial strain in the ZrO2 films. This study demonstrates the significant influence of interfacial layers and biaxial strain on the phase transition fields and shows how strain engineering can be used to improve ferroelectric wake-up in ZrO2.

Hydrated WO3.0.33H2O nanorod for an excellent anode materials enables high performance and long-cycle stability for aqueous Zn-ion batteries

Metal dissolution and solid electrolyte interface layer growth are the most challenging issues in a reversible aqueous Zn-ion battery. To address this issue, an electrolyte-material marriage must be devise. Herein, we have develop the unique hydrate WO3.0.33H2O nanorods that integrate the layers and hexagonal tunnel structures for an aqueous Zn-ion battery. However, the one-dimensional morphology and confinement of the hydrate molecules of WO3.0.33H2O nanorods enable the superhighway and sub-second electron transport. Owing to this unique property, WO3.0.33H2O nanorods exhibit a capacity of 91 mAh g−1, which is two-fold higher than the three-dimensional WO3 cube in 1 M ZnCl2 electrolyte. Additionally, WO3.0.33H2O nanorods exhibit excellent durability and coulombic efficiency of 94 % and 99 % after 3000 cycles, respectively. To further examine the electrolyte suitability, the WO3.0.33H2O nanorods show excellent reversibility of the insertion and deinsertion of the Zn2+ ion in 1 m ZnCl2 compares to 1 M ZnSO4 and 1 M Zn(CH3COO)2 electrolytes. Therefore, this unique construction of hydrates WO3.0.33H2O nanorods would be a new avenue for designing the anode materials for a reversible aqueous Zn-ion battery.

Modeling and Analysis of Temperature-Dependent Capacity Degradation in Large Format Lithium-Ion Batteries

The large-format lithium-ion batteries, widely used for electric vehicle applications, are generally characterized by spatial non-uniformities in temperature. The presence of thermal gradients and temperature-dependence of cell parameters are responsible for non-uniform degradation within the battery that leads to poor performance of the battery packs and also poses safety risks. In this work, we aim to develop a detailed physics-based simulation framework to model non-uniform, temperature-dependent capacity degradation within these large format batteries based on the classical pseudo two-dimensional (p2D) battery model. The electrochemical model will be coupled with degradation mechanisms to capture solid-electrolyte interface layer growth, reversible lithium plating, structural disintegration, and volume change within the electrodes on the cell level signatures and usable capacity over charge/discharge cycles. The effects of temperature inhomogeneities will be accounted in the multi-cell simulations at different operating temperatures for individual cells with dynamic currents and temperature and concentration dependent battery parameters as the model inputs.Overall, the primary focus of this study is to capture the effect of spatial temperature variation on battery capacity over cycles and help identify an improved design for the battery module. The model is implemented in an efficient equation-based form for the p2D model and degradation mechanisms with dynamic cell inputs using the mathematical modules in the finite element based solver, COMSOL Multiphysics. This approach enables an easier model development and analysis of the detailed physics and allows an easier implementation of any additional side reaction. The relative contributions of various fade modes have also been compared to understand their competitive interplay over cell cycles. The model predictions are validated with the available experimental data and in-house codes for each case. We believe that this simple yet detailed model can be further developed to be computationally feasible for adoption and implementation in a battery thermal management system.

Metal-organic decomposed cerium oxide thin film in mixed ambient at different temperatures for MOS capacitor

Post-deposition annealing of CeO2 thin films in nitrogen/oxygen/nitrogen ambient from 400 until 1000 °C successfully transformed the films from oxygen poor to oxygen-rich state, in which an excess of oxygen was detected at higher temperatures as the oxygen interstitials. The adsorbed nitrogen attaching to oxygen vacancies in the CeO2 thin films would inhibit further oxidation of the films, and thus controlling the film thickness in addition to expanding the lattice. The increase of temperature has enhanced adsorption and diffusion of nitrogen and oxygen, decreasing the attachment of nitrogen to the oxygen vacancies. The dissociated nitrogen would reside as dangling bonds that caused a difficulty in controlling the oxidation and hence interfacial layer growth was expected. An exaggerated film growth dominated by interfacial layer happened at the highest temperature, surpassing the CeO2 layer thickness. The lowest interface trap density was attained but a degradation in the current-voltage characteristic happened due to the presence of excess oxygen and nitrogen as the scattering center for the incoming electrons during forward bias operation. A better performance was achieved by the film annealed at 800 °C via the demonstration of the lowest leakage current level, surpassing other films. Detailed explanation was discussed in this work.

Impact of Ni-coated carbon fiber on the interfacial (Cu,Ni)6Sn5 growth of Sn-3.5Ag composite solder on Cu substrate during reflow and isothermal aging

In this work, a novel composite solder was fabricated by mechanically incorporating Ni-coated carbon fiber (Ni-CF) into the Sn-3.5Ag solder paste in an effort to improve the overall service capability, where the intermetallic compound (IMC) formation and growth is a fundamental issue for consideration. General findings indicated that the addition of Ni-CF did not significantly impact the processing properties of the base alloy, such as melting temperature and wettability, when the reinforcement fraction was less than 2 wt%. Isothermal aging tests were carried out to study the formation and growth of interfacial IMC layers between the composite solder and Cu substrate. The addition of Ni-CF into Sn-3.5Ag solder could effectively promote the formation of interfacial (Cu, Ni)6Sn5 phase during reflow but retard its growth in the solid-state aging. The addition of 1 wt% Ni-CF was believed to be more effective to restrict and reduce the subsequent growth rate of the IMCs during solid-state aging due to the initial formation of a thicker (Cu, Ni)6Sn5 layer after reflow.

Enhanced Ferroelectric and Piezoelectric Properties in Graphene-Electroded Pb(Zr,Ti)O3 Thin Films.

While using ferroelectric polarization to tune the functional properties of 2D materials has been extensively studied recently, the effects of 2D materials on the ferroelectricity and piezoelectricity of ferroelectrics are much less explored. In this work, we report markedly enhanced ferroelectric and piezoelectric properties of graphene/Pb(Zr0.52Ti0.48)O3/SrRuO3 (GR/PZT/SRO) capacitors. Compared with conventional metal-electroded ferroelectric capacitors, the GR/PZT/SRO capacitors exhibit more abrupt polarization switching, larger switchable polarization, lower leakage current, and smaller coercive voltage. Moreover, with graphene electrodes, the ferroelectric properties of PZT capacitors are much more stable against aging. The enhanced ferroelectric behaviors in GR/PZT/SRO capacitors can be attributed to an improved interface with fewer defects and inhibited growth of defective interfacial layer resulting from the graphene protection. Because of the atomic thickness and extraordinary mechanical flexibility of graphene, the piezoelectric response in PZT with graphene electrode is about four times larger than the one with an Au electrode. Our findings on the enhanced ferroelectric and piezoelectric properties of PZT with 2D electrodes advance the understanding of the 2D/PZT interface and provide solutions for developing high-performance ferroelectrics devices.

Impact of annealing on electric and elastic properties of 10-nm Hf0.5Zr0.5O2 films prepared on Si by sputtering

HfO2-based films are important materials used in broad range of electronic applications from high-performance transistors and memory cells, to thermoelectric and energy harvesting elements. By employing scanning probe methods, we made nanoscale comparison of chemical composition, surface morphology, the elastic modulus and the surface potential of bare 10-nm thick Hf0.5Zr0.5O2 films prepared on Si by a carbon-free sputtering process. The composition mapping confirmed uniform distribution of Hf and Zr in the film along wafer size. Suppression of the monoclinic phase in films annealed at 600 - 800 °C had strong impact on spatial variations of film properties. Small surface roughness, large electric domain sizes (50–200 nm at 700 °C) and small fluctuations of the surface potential (40–50 meV) in Si coated with the films are appealing for gate-stack applications. Films annealed at 600-700 °C showed the elastic modulus of about 169 GPa and the ferroelectric polarization reversal at a field of ~1 MV/cm as observed by nanoscale poling with a Pt-coated scanning probe. In contrast, properties of films annealing at 800 °C were affected by growth of thick interfacial oxide layer. The presented nanoscale approach is beneficial in optimizing of physical and mechanical properties of thin dielectric films.

Effect of SiO2 nanoparticle addition on growth of interfacial Ag3Sn intermetallic compound layers between lead-free solder and silver conductor

This study investigated the effects of silver powder modification on intermetallic compound (IMC) formation and silver leaching during soldering at high temperatures. Silica nanoparticles (NPs) were deposited onto a silver powder surface to inhibit silver leaching, which can lead to soldering joint failure during high-temperature soldering. The NPs were deposited through hydrolysis and a condensation reaction of tetraethyl orthosilicate (TEOS) based on the Stöber method. Fourier transform infrared spectroscopy and scanning electron microscopy were used to observe the microstructures of silver powders after the deposition of silica NPs with various TEOS concentrations and various deposition times. As the deposition time increased, the amount of silica NPs on the surface of the silver powder increased. The transmission electron microscopy results show that silica NPs were located at the IMC grain boundaries, which can hinder the dissolution of IMCs by lead-free solder melt along grain boundaries during soldering, retarding silver leaching. The growth kinetics and mechanism of IMCs during soldering were investigated. The results show that the growth of IMCs is mainly dominated by bulk diffusion. The activation energy for IMC growth increased and the growth rate decreased with increasing silica NP addition and deposition time.

Study of SiO2 Interfacial Layer Growth during Fabrication Process of Ferroelectric HfxZr1−XO2-Based Metal-Ferroelectric Semiconductor

Recently, ferroelectric HfxZr1−xO2 (HZO) thin films have attracted much attention towards high-density and low-power ferroelectric memories such as ferroelectric field-effect transistors (FeFETs) for artificial intelligence (AI). [1] An annealing process at ≥ 300 °C is typically required to form the ferroelectric orthorhombic (O) phase of HZO films. [2, 3] It remains a big issue of an abnormal SiO2 interfacial layer (SiO2-IL) growth at the HZO/Si interface during metal-ferroelectric-semiconductor (MFS) fabrication process. It has been reported that a SiO2-IL growth led to degradation of remanent polarization (2P r) and reliability of MFS capacitors. [4] However, it is unclear how the process conditions of MFS structures, such as an atomic layer deposition (ALD) of HZO films and annealing process, affect the SiO2-IL formation in detail. In this work, we investigated a SiO2-IL growth as a function of the process temperature of ALD and annealing processes and a SiO2-IL growth of TiN/HZO/Si structures.P+-Si substrate was first cleaned using a buffered hydrofluoric acid to remove native oxide, and then an HZO film was deposited by ALD using H2O gas and (Hf/Zr)[N(C2H5)CH3]4 (Hf:Zr = 1:1) cocktail precursor. The ALD growth temperature was varied from 200 to 300 °C. A 100-nm-thick TiN film was then fabricated as gate electrode by DC sputtering. Finally, the post-metallization annealing (PMA) was carried out at 300–600 °C in an N2 atmosphere. A 3-nm-thick HZO film was used to evaluate the SiO2-IL growth using XPS analysis. On the other hand, TiN-gated MFS capacitor with a 10-nm-thick HZO film was prepared to examine electrical properties.First, the formation of the SiO2-IL was found to be negligible small at HZO (3 nm)/Si interface regardless of the ALD growth temperatures because no significant peak originating from Si-O bonds was observed in XPS spectra of Si 2p. Therefore, we employed 300 °C as an ALD temperature of HZO films for the fabrication of MFS capacitors. Next, the SiO2-IL growth as a function of PMA temperature was evaluated. The SiO2-IL growth increased as PMA temperature increased from 400 to 600 °C. Therefore, the annealing process at a lower temperature suppressed a SiO2-IL growth for the fabrication of MFS structures.Finally, polarization–electric field (P– E) measurements were conducted to evaluate the ferroelectricity of TiN/HZO (10 nm)/p+-Si MFS capacitors after the PMA process at 300–600 °C. The MFS capacitors after the PMA process at 500 and 600 °C showed breakdown during the P– E measurement due to a large leakage current. The MFS capacitor after the PMA process at 400 °C showed significantly higher 2P r value of 26 µC/cm2 compared to that (7.6 µC/cm2) after the PMA process at 300 °C. This is because the HZO films of the MFS capacitor after the PMA process at 400 °C were crystallized with the ferroelectric O phase while the HZO films had an amorphous-like structure after the PMA process at 300 °C, evaluated by X-ray diffraction (XRD). These experimental results indicated that the PMA temperature significantly affects the growth of the SiO2-IL at the HZO/Si interface while almost no difference was observed between the ALD temperature conditions.This work was partially supported by JSPS KAKENHI (JP18J22998 and JP20H02189).[1] J. Y. Kim et al., APL Mater. 9, 021102 (2021).[2] T. Onaya et al., Microelectron. Eng. 215, 111013 (2019).[3] S. J. Kim, et al., S. J. Kim et al., Appl. Phys. Lett. 111, 242901 (2017).[4] J. Mohan et al., Appl. Phys. Lett. 118, 102903 (2021).

Study of SiO2 Interfacial Layer Growth during Fabrication Process of Ferroelectric HfxZr1−XO2-Based Metal-Ferroelectric Semiconductor

We studied a SiO2 interfacial layer (SiO2-IL) growth between a ferroelectric HfxZr1−xO2 (HZO) film, which fabricated by atomic layer deposition (ALD) using a Hf/Zr cocktail precursor, and p-type Si substrate during the metal-ferroelectric-semiconductor (MFS) fabrication. For the annealing process, two types of a post-deposition annealing (PDA) and post-metallization annealing (PMA) were employed before and after the fabrication of the TiN top-electrodes, respectively. An ultra-thin SiO2-IL of one or two monolayers at the HZO/Si interface was achieved using a 300°C fabrication process of ALD, and PDA or PMA. In contrast, PDA and PMA processes at ≥ 400°C led to an unexpected SiO2-IL formation, which increased with the annealing temperature, regardless of the formation of TiN top-electrodes. Therefore, we found that a suppressed SiO2-IL of HZO-based MFS structures can be obtained using the 300°C fabrication process.

Origins of the change in mechanical strength of silicon/gold nanocomposites during irradiation

Silicon-based layered nanocomposites, comprised of covalent-metal interfaces, have demonstrated elevated resistance to radiation. The amorphization of the crystalline silicon sublayer during irradiation and/or heating can provide an additional mechanism for accommodating irradiation-induced defects. In this study, we investigated the mechanical strength of irradiated Si-based nanocomposites using atomistic modeling. We first examined dose effects on the defect evolution mechanisms near silicon-gold crystalline and amorphous interfaces. Our simulations reveal the growth of an emergent amorphous interfacial layer with increasing dose, a dominant factor mitigating radiation damage. We then examined the effect of radiation on the mechanical strength of silicon-gold multilayers by constructing yield surfaces. These results demonstrate a rapid onset strength loss with dose. Nearly identical behavior is observed in bulk gold, a phenomenon that can be rooted to the formation of radiation-induced stacking fault tetrahedra which dominate the dislocation emission mechanism during mechanical loading. Taken together, these results advance our understanding of the interaction between radiation-induced point defects and metal-covalent interfaces.

Interface Behavior of Brazing between Zr-Cu Filler Metal and SiC Ceramic

The interface behavior of brazing between Zr-Cu filler metal and SiC ceramic was investigated. Based on the brazing experiment, the formation of brazing interface products was analyzed using OM, SEM, XRD and other methods. The stable chemical potential phase diagram was established to analyze the possible diffusion path of interface elements, and then the growth behavior of the interface reaction layer was studied by establishing relevant models. The results show that the interface reaction between the active element Zr and SiC ceramic is the main reason in the brazing process the interface products are mainly ZrC and Zr2Si and the possible diffusion path of elements in the product formation process is explained. The kinetic equation of interfacial reaction layer growth is established, and the diffusion constant (2.1479 μm·s1/2) and activation energy (42.65 kJ·mol−1) are obtained. The growth kinetics equation of interfacial reaction layer thickness with holding time at different brazing temperatures is obtained.

Pre-deposition growth of interfacial SiO2 layer by low-oxygen-partial-pressure oxidation in the Al2O3/4H-SiC MOS structure

A novel thermal oxidation method for growing a thin SiO2 layer is proposed for improving the Al2O3/4H-SiC-based MOS structure characteristics. The method combines low oxygen partial pressure and high temperature oxidation during the SiO2 layer growth process. Compared with the conventional thermal oxidation method, the experimental results show that the proposed method can effectively reduce the density of trapped charges in the oxide and at the gate dielectric/4H-SiC epilayer interface, and improve the breakdown characteristic of the MOS structure. The interface trap density (Dit) at energy level of 0.2 eV below the conduction band edge (EC) of 4H-SiC in the sample by our proposed method is reduced to 6.6 × 1012 cm−2 eV−1, which is about 4 times lower than the as deposited Al2O3/4H-SiC sample. The core reason underlying the improvement is the reduced SiO2 layer thickness and lower SiCxOy component concentration, as shown by X-ray photoelectron spectroscopy measurements.

Graphene-induced positive shift of the flat band voltage in recessed gate AlGaN/GaN structures

In this work, a layer of graphene is inserted into Al2O3/recessed gate AlGaN/GaN structures to realize the positive shift of flatband voltage VFB. With a chemically inert surface and a high work function, graphene suppresses the interfacial layer growth, reduces the donor-like interface defects during the growth of Al2O3 gate dielectrics, provides a potential well to confine electrons from AlGaN and the interface defects, lifts the conduction band of GaN, leads to the disappearance of 2DEG at recessed AlGaN/GaN interface, and positively shifts VFB from 1.4 V to 5.2 V. This method provides a promising solution to fabricate E-mode AlGaN/GaN high electron mobility transistor.

Performance of Sn-3.0Ag-0.5Cu Composite Solder with Kaolin Geopolymer Ceramic Reinforcement on Microstructure and Mechanical Properties under Isothermal Ageing.

This paper elucidates the effect of isothermal ageing at temperature of 85 °C, 125 °C and 150 °C for 100, 500 and 1000 h on Sn-3.0Ag-0.5Cu (SAC305) lead-free solder with the addition of 1 wt% kaolin geopolymer ceramic (KGC) reinforcement particles. SAC305-KGC composite solders were fabricated through powder metallurgy using a hybrid microwave sintering method and reflowed on copper substrate printed circuit board with an organic solderability preservative surface finish. The results revealed that, the addition of KGC was beneficial in improving the total thickness of interfacial intermetallic compound (IMC) layer. At higher isothermal ageing of 150 °C and 1000 h, the IMC layer in SAC305-KGC composite solder was towards a planar-type morphology. Moreover, the growth of total interfacial IMC layer and Cu3Sn layer during isothermal ageing was found to be controlled by bulk diffusion and grain-boundary process, respectively. The activation energy possessed by SAC305-KGC composite solder for total interfacial IMC layer and Cu3Sn IMC was 74 kJ/mol and 104 kJ/mol, respectively. Based on a lap shear test, the shear strength of SAC305-KGC composite solder exhibited higher shear strength than non-reinforced SAC305 solder. Meanwhile, the solder joints failure mode after shear testing was a combination of brittle and ductile modes at higher ageing temperature and time for SAC305-KGC composite solder.

Effect of Ni on the Suppression of Sn Whisker Formation in Sn-0.7Cu Solder Joint.

The evolution of internal compressive stress from the intermetallic compound (IMC) Cu6Sn5 growth is commonly acknowledged as the key inducement initiating the nucleation and growth of tin (Sn) whisker. This study investigates the effect of Sn-0.7Cu-0.05Ni on the nucleation and growth of Sn whisker under continuous mechanical stress induced. The Sn-0.7Cu-0.05Ni solder joint has a noticeable effect of suppression by diminishing the susceptibility of nucleation and growth of Sn whisker. By using a synchrotron micro X-ray fluorescence (µ-XRF) spectroscopy, it was found that a small amount of Ni alters the microstructure of Cu6Sn5 to form a (Cu,Ni)6Sn5 intermetallic layer. The morphology structure of the (Cu,Ni)6Sn5 interfacial intermetallic layer and Sn whisker growth were investigated by scanning electron microscope (SEM) in secondary and backscattered electron imaging mode, which showed that there is a strong correlation between the formation of Sn whisker and the composition of solder alloy. The thickness of the (Cu,Ni)6Sn5 IMC interfacial layer was relatively thinner and more refined, with a continuous fine scallop-shaped IMC interfacial layer, and consequently enhanced a greater incubation period for the nucleation and growth of the Sn whisker. These verification outcomes proposes a scientifically foundation to mitigate Sn whisker growth in lead-free solder joint.

Structural, Thermal and Wetting Characteristics of Novel Low Bi-Low Ag Containing Sn–x.Ag–0.7Cu–1.0Bi (x = 0.5 to 1.5) Alloys for Electronic Application

Low drop failure tendency and reduced cost of low silver SAC alloys has provoked researchers to exploit their potential for portable electronics. Low Bi addition in near-eutectic SAC alloys has proven confinement of IMC layer. In order to exploit potential of Ag variation (0.5–1.5 wt%) on structural, thermal, wettability and IMCs layers growth during thermal aging in low Bi-low Ag, Sn–xAg–0.7Cu–1.0Bi alloys were investigated. The resulting microstructure were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Furthermore, structure–property correlations were established. This study signifies that 1.5 wt% Ag is responsible for lower melting point (220.18 °C) and lower contact angle (33°) in low Bi-low Ag, Sn–xAg–0.7Cu–1.0Bi alloys. Moreover, increment in Ag content restricted the interfacial IMC layer growth during thermal aging making them reliable for use in portable electronics. The microstructural investigations inferred that 0.5 wt% Ag solder joint with Cu substrate had the highest growth rate (0.34 μm/h1/2) of IMC layer thickness while 1.5 wt% Ag solder joint had lowest growth rate (0.17 μm/h1/2).

Electrode interface optimization advances conversion efficiency and stability of thermoelectric devices

Although the CoSb3-based skutterudite thermoelectric devices have been highly expected for wide uses such as waste heat recovery and space power supply, the limited long-term service stability majorly determined by the degradation of electrode interface obstructs its applications. Here, we built up an effective criterion for screening barrier layer based on the combination of negative interfacial reaction energy and high activation energy barrier of Sb migration through the formed interfacial reaction layer. Accordingly, we predicted niobium as a promising barrier layer. The experimental results show the skutterudite/Nb joint has the slowest interfacial reaction layer growth rate and smallest interfacial electrical resistivity. The fabricated 8-pair skutterudite module using Nb as barrier layer achieves a recorded conversion efficiency of 10.2% at hot-side temperature of 872 K and shows excellent stability during long-time aging. This simple criterion provides an effective guidance on screening barrier layer with bonding-blocking-conducting synergetic functions for thermoelectric device integration.