Takahiro Namazu

Dual-composition Al/Ni multilayer thin films with various architectural designs were fabricated to investigate curling motion driven by volume shrinkage and to assess their potential to enhance the direct bonding of Al busbars. The reacted films exhibited pronounced, composition-dependent curling deformation, with a higher Al fraction yielding a smaller radius. In contrast, total film thickness and bilayer period had only a minor influence. A theoretical curvature analysis was conducted to compare predicted deformation with experimental results, and to estimate the mismatch strain and the bending-generated energy. Bonding between two Al busbars was demonstrated. Larger curvature led to increased cracking in the reacted layer, which is expected to facilitate easier removal of the reacted interlayer after bonding. These results demonstrate that tailoring the Al/Ni film’s multilayer architecture provides effective control of curvature after reaction, offering a promising pathway for reactive bonding systems that require simple post-bonding removal of the reacted NiAl film or reduced mechanical damage.

Neutral-density (ND) filters that attenuate light without spectral distortion are essential for imaging and sensing systems. We examine self-assembled sub-100 nm SiO ₂ nanoparticle structures in ultrapure water (UPW) as a model platform for color-preserving ND filters. Nanoparticles are synthesized by a Stöber-type process, varying ammonia content, UPW fraction, and stirring rate to control size and monodispersity. Three representative films are selected: Sample A is an ideal monodisperse assembly, Sample B contains small-particle impurities that fill voids, and Sample C contains large-particle impurities that cause crowding. Angle-resolved reflectance shows Bragg peaks whose intensity and sharpness reflect in-plane order. Time-resolved transmittance during drying in UPW indicates that Sample A maintains higher transparency, whereas Samples B and C deteriorate more rapidly. Scanning electron microscope images, size histograms, and radial distribution functions connect these optical trends to impurity-driven changes in interparticle spacing, guiding future polymer-embedded, tunable ND filters for broadband, color-neutral attenuation in thin-film devices.

This paper describes the effects of Al/Ni rapid heating on the mechanical reliability of sintered Ag die-attach assemblies. The sintered Ag layer, which includes multiple voids, undergoes degradation, such as cracking and aging, due to temperature fluctuations. After the sintered Ag die-attach process, Al/Ni rapid heating was adopted into the sintered layer. The porosity of the sintered Ag film prepared under low-pressure conditions was drastically reduced by applying Al/Ni post-heating. Uniaxial tensile testing revealed that Al/Ni-treated low-pressure sintered films had a Young’s modulus of 63 GPa and a tensile strength of 240 MPa, respectively, which is comparable to that of untreated high-pressure sintered Ag. In the thermal shock test, the crack propagation rate after 60 MPa sintering was similar whether or not Al/Ni treatment was applied. In contrast, the positive effect of the post-heating was observed on the degradation rate after 5 MPa sintering. Cracking phenomena are discussed based on cross-sectional scanning electron microscopy results, which describe the pore distribution in the sintered Ag layer after Al/Ni post-heating.

Raman spectroscopy is a powerful tool to analyze materials. The demand for analyzing materials in a smaller analytical region is increasing as technology advances. Tip-enhanced Raman spectroscopy (TERS) is an option. However, measuring the surface of three-dimensional bulk materials is quite challenging, since simultaneously excited micro-Raman signals hide the enhanced nano-Raman signals. In 2024, another approach of using a porous gold membrane was reported to dedicate solid surface analysis. However, this method, for example, sacrifices the lateral analytical spot size because nanopores distribute throughout the membrane. Here, 70-nm thick gold microplates with nano-through-holes in the center are fabricated. The gold microplates provide a smaller analytical spot because nano-through-holes are fabricated only in a spatially limited region. The microplates and the surrounding structures are clearly visible under optical microscopes. We moved gold microplates to another location on a silicon substrate using a manipulator and successfully demonstrated nano-Raman measurements of silicon surface via nano-through-holes. The finite-difference time-domain calculations confirmed that enhanced electric fields are available by the nano-through-holes and revealed that the nano-Raman signals come from the surface of silicon within a depth of 5.4 nm.

The strengthening mechanisms of sintered silver (s-Ag) films, including copper oxide (CuO) nanoparticles (NPs), were investigated to enhance their mechanical and thermal reliability for power semiconductor device packaging applications. CuO NPs, synthesized via a chemical washing method, were incorporated into the s-Ag matrix at a 0.5 wt% ratio. In-situ SEM tensile testing at room temperature (RT) and 300°C revealed significant improvements in the mechanical performance of the CuO included s-Ag films. Although CuO inclusion had little effect on strength and fracture mechanisms at RT, it significantly enhanced mechanical performance at 300°C compared to pure s-Ag films. The reduction of oxygen content in CuO NPs during sintering, as analyzed by energy-dispersive X-ray spectroscopy (EDX), facilitated stronger interatomic bonding between CuO and Ag particles. Furthermore, the reduced CuO NPs acted as barriers to grain boundary degradation, reducing void growth and maintaining microstructural stability under elevated temperatures. The findings obtained in this study demonstrate the potential of CuO inclusion to improve the reliability of s-Ag films in power semiconductor die-attach applications.

In this paper, the influence of O content on the exothermic and self-propagating characteristics of Ti/SiOx films is reported. 2 μm-thick multilayer films with various atomic ratios and bilayer thicknesses are prepared using a tertiary-source magnetron sputtering system with DC/RF multifunction cathodes. DC, DC, and RF modes are used for depositing Ti, Si, and SiO2 films, respectively, where cosputtering of Si and SiO2 is conducted to control O content in SiOx film layers. Threshold powers for exothermic reaction estimated by electric spark and laser irradiation depend on the Ti to Si ratio and bilayer thickness, whereas reaction propagation speed and maximum temperature mainly depend on the bilayer thickness and the Ti to Si ratio, respectively. The three characteristics are influenced by O content. The heat of reaction also shows both bilayer thickness and Ti to Si ratio effects, and it decreases with increasing O content. In the Ti/Si films, the exothermic reaction propagates completely into the films, whereas in the Ti/SiOx films, self-propagation of the exothermic reaction becomes difficult with increasing O content. The cause of the influence of O content on reaction propagation characteristics is discussed from the viewpoint of a change of heat balance with increasing O content in the Ti/SiOx films.

This paper reviews sintered silver (s-Ag) die-attach materials for wide band gap (WBG) semiconductor packaging. WBG devices that die-attach with s-Ag have attracted a lot of attention owing to their low energy loss and high temperature operation capabilities. For their practical operation, a reliability design should be established based on the failure of physics of the s-Ag die layer. This paper first focuses on the material characteristics of the s-Ag and tensile mechanical properties. Then, the s-Ag die-attach reliability is assessed with high-temperature storage, power cycling, and thermal shock tests. Each fracture mode was discussed by considering both the fracture surface analysis results and its mechanical properties. Finally, the effective reliability design parameters of the s-Ag die layer are introduced.