Highly conductive Cu–Cu interconnections of SiC die with Ti/Ni/Cu metallization and direct bonded copper substrate for high-power semiconductor devices are achieved by the low-temperature sintering ...of Cu nanoparticles with a formic acid treatment. The Cu–Cu joints formed via a long-range sintering process exhibited good electrical conductivity and high strength. When sintered at 260 °C, the Cu nanoparticle layer exhibited a low resistivity of 5.65 μΩ·cm and the joints displayed a high shear strength of 43.4 MPa. When sintered at 320 °C, the resistivity decreased to 3.16 μΩ·cm and the shear strength increased to 51.7 MPa. The microstructure analysis demonstrated that the formation of Cu–Cu joints was realized by metallurgical bonding at the contact interface between the Cu pad and the sintered Cu nanoparticle layer, and the densely sintered layer was composed of polycrystals with a size of hundreds of nanometers. In addition, high-density twins were found in the interior of the sintered layer, which contributed to the improvement of the performance of the Cu–Cu joints. This bonding technology is suitable for high-power devices operating under high temperatures.
Ultrafast control of vortex microlasers Huang, Can; Zhang, Chen; Xiao, Shumin ...
Science (American Association for the Advancement of Science),
02/2020, Letnik:
367, Številka:
6481
Journal Article
Recenzirano
Odprti dostop
The development of classical and quantum information-processing technology calls for on-chip integrated sources of structured light. Although integrated vortex microlasers have been previously ...demonstrated, they remain static and possess relatively high lasing thresholds, making them unsuitable for high-speed optical communication and computing. We introduce perovskite-based vortex microlasers and demonstrate their application to ultrafast all-optical switching at room temperature. By exploiting both mode symmetry and far-field properties, we reveal that the vortex beam lasing can be switched to linearly polarized beam lasing, or vice versa, with switching times of 1 to 1.5 picoseconds and energy consumption that is orders of magnitude lower than in previously demonstrated all-optical switching. Our results provide an approach that breaks the long-standing trade-off between low energy consumption and high-speed nanophotonics, introducing vortex microlasers that are switchable at terahertz frequencies.
This paper describes a method to achieve rapid pressureless low-temperature sintering of Ag nanoparticles for bonding. Organic shells adsorbing on the surface of Ag nanoparticles to stabilize them ...were thinned to create a sparse protecting layer. The numerous coherent twin boundaries formed in sintered Ag nanoparticles with a grain size of 21nm induce ultrahigh thermal conductivity (229Wm−1K−1), which overcomes the intrinsic defect that metals with nanosized grains generally exhibit a significantly reduced thermal conductivity because of the grain boundary scattering effect.
•Cu@Ag nanoparticles were successfully sintered at low temperature by ultrasonic.•Ag shells dewetting, dense and crystallized Cu cells were formed in the joints.•Abrupt high temperature generated by ...ultrasonic attributed to the deep sintering.•Void-free and dense sintered microstructure contributes the joint with good property.
Sintering of low-cost Cu nanoparticles (NPs) for interconnection of chips to substrate at low temperature and in atmosphere conditions is difficult because they are prone to oxidation, but dramatically required in semiconductor industry. In the present work, we successfully synthesized Cu@Ag NPs paste, and they were successfully applied for joining Cu/Cu@Ag NPs paste/Cu firstly in air by the ultrasonic-assisted sintering (UAS) at a temperature of as low as 160 °C. Their sintered microstructures featuring with dense and crystallized cells are completely different from the traditional thermo-compression sintering (TCS). The optimized shear strength of the joints reached to 54.27 MPa, exhibiting one order of magnitude higher than TCS at the same temperature (180 °C) under the UAS. This ultra-low sintering temperature and high performance of the sintered joints were ascribed to ultrasonic effects. The ultrasonic vibrations have distinct effects on the metallurgical reactions of the joints, resulting in the contact and growth of Cu core and the stripping and connection of Ag shell, which contributes to the high shear strength. Thus, the UAS of Cu@Ag NPs paste has a great potential to be applied for high-temperature power device packaging.
In this study, composite solder pastes with different sizes of Sn and Cu particles were prepared. A large fraction of solid/liquid interfacial contacts adjusted by the Cu particle sizes contributed ...to an ultra-rapid metallurgical reaction at a high in-situ temperature of 437.1 °C under ultrasonic waves. Thus, the sole IMC of high-melting-point Cu3Sn joints with a tiny proportion of residual Cu were obtained in air at 250 °C for 10 s under the ultrasonic-assisted transient liquid phase (TLP). The intermetallic joints exhibited the average shear strength of 49.96 MPa at ambient temperature. In particular, a promising shear strength of 46.54 MPa was obtained at the high temperature of 350 °C, which exhibits significant potential for the high temperature electronic devices.
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•Solder pastes with different sizes of Sn and Cu particles were prepared.•The sole intermetallic of Cu3Sn joints were obtained under ultrasonic for 10 s.•The joint exhibited promising shear strength of 46.54 MPa at 350 °C.•The joints exhibit great potential in high temperature packaging.
The effects of Ag content on the interfacial reactions between Sn–Ag–Cu (SAC) solders and Cu substrates during soldering were studied based on an experiment in which the liquid solder is removed ...after a long exposure time. This removal of the solder allows for the capture and visualization of the interfacial IMCs formed during soldering and avoids the influence of Cu6Sn5 precipitated from the solder matrix during cooling. The results showed that a Cu6Sn5 scallop type layer with round grains having a strong texture was formed at the interface of the SAC solders/Cu systems. The addition of Ag decreased the IMC/liquid SAC solder interfacial energy and improved the wettability of the solder on the Cu. In addition to the reaction energy, the interfacial microstructure also affected the interfacial IMC growth extent. By changing the growth environment near the interface, Ag affected the orientation of Cu6Sn5 grains formed at the interface, leading to the evolution of a microstructure that generates more Cu6Sn5 grain boundaries at the interface. Consequently, under the same reflow conditions, SAC solders with a higher Ag content in contact with the Cu substrate form thicker IMCs interfacial layers.
•We design an experiment to obtain IMCs formed at molten solder/Cu interface.•Round Cu6Sn5 grains with strong texture form at SAC solders/Cu interface.•Interfacial IMC microstructure evolution affects its growth extent.•Ag promotes interfacial IMC growth by affecting growth orientation of Cu6Sn5 grains.
We report a Cu-to-Cu interconnects fabrication process based on the pressureless low temperature sintering of Ag nanoparticles for electronic packaging. The organic shells of citrates covering the ...nanoparticles stabilize the Ag nanoparticles. It is not necessary for organic shells to be completely decomposed for sintering to take place. Instead, it is sufficient that the chemical bonds that connect the organic shells with Ag nanoparticles are broken. This new point of view leads to a way to lower bonding temperature. A novel pinecone-like recrystallization morphology of sintered Ag nanoparticles is obtained, which results from the residuals of organic shells by the sintering process. The effect of recrystallization morphology on the thermal conductivity of sintered Ag nanoparticles is discussed. The shear strength of joints reaches 17–25MPa at temperatures ranging from 423K to 473K.
► Pressureless sintered joints are achieved at low bonding temperatures of 423–473K. ► Sintering can take place so long as the chemical bonds on nanoparticles are broken. ► We find a novel pinecone-like recrystallization morphology of Ag nanoparticles. ► Thermal conductivity of sintered Ag layers is reduced due to the scattering effect.
•Sn/Ni composite solder pastes with different sizes of Ni particles were prepared.•The joints of sole Ni3Sn4 IMC and residual Ni were obtained by U-TLP for 10 s.•The kinetics, microstructure, and ...property were systemically investigated.•The mechanism of growth-stripping-recycling by ultrasonic was proposed and proved.
The high-melting-point joints by transient-liquid-phase are increasingly playing a crucial role in the die bonding for the high temperature electronic components. In this study, three kinds of Sn/Ni composite solder pastes composed of different sizes of Ni particles were synthesized to accelerate metallurgical reaction among Sn/Ni interfaces under the ultrasonic-assisted transient liquid phase (U-TLP) soldering. The temperature evolution, microstructure and mechanical property in joints composed by these composite solder pastes with or without ultrasonic energy were systemically investigated. The intermetallic joint consisted of high-melting-point sole Ni3Sn4 intermetallic compound with a little residual Ni was obtained under the conditions of no pressure and lower power (200 W) in a high-temperature duration of only 10 s, its shear strength was up to 45.3 MPa. Ultrasonic effects significantly accelerated the reaction among the interfaces of liquid Sn and solid Ni, which attributed to the temperature rise caused by acoustic cavitation because of large number of liquid/solid interfaces during U-TLP, resulting in accelerated solid/liquid interfacial diffusion and growth of intermetallic compounds. This intermetallic joint formed by U-TLP soldering has a promising potential for applications in high-power device packaging.
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•Four different flow behaviors and deformation mechanisms of PM superalloy with high γ′ content under isothermal compression were revealed.•The microstructure evolution for different ...flow behaviors were systematic analysis.•The effects of γ′ on the microstructure under different hot deformation conditions were demonstrated.•The evolution mechanisms of abnormally growing grains with high deformation storage energy were revealed.
This study examines the flow behavior and deformation mechanism of a FGH4113A superalloy with high γ′ content for different strain rates (0.01–1 s−1) at sub-solvus (1030, 1080 °C), near-solvus (1130 °C), and sup-solvus temperatures (1180 °C). The results indicated that the alloy exhibits four different flow behaviors: rapid softening after reaching peak stress (at 1030–1080 °C), slow softening after reaching peak stress (at 1130–1180 °C/0.1–1 s−1), steady state flow (at 1130 °C/0.01 s−1), and continuous hardening (at 1180 °C/0.01 s−1). The strain rate sensitivity exponent decreases as the flow behavior transforms from dynamic softening to continuous hardening. Moreover, the dynamic recrystallization (DRX) fraction decreases with increasing strain rate at sub-solvus temperatures, where an inverse trend was observed at near- or sup-solvus temperatures. These observations are influenced by the interplay of continuous original grain boundary migration (COBM), DRX, and grain growth. Meanwhile, the primary γ′ phase has different roles under distinct deformation conditions. At sub-solvus temperature, the primary γ′ phase facilitates DRX, grain refinement, and coordinated plastic deformation. At near-solve temperature, the primary γ′ phase predominantly contributes to coordinated plastic deformation. At the sup-solvus temperature, the γ′ phase entirely dissolves, with the grains coarsened by COBM continuously undergoing compressed, exhibiting continuous hardening.
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•High-quality bonding of highly (111)-oriented nanotwinned Ag films was achieved at 200 °C in air.•The void closure model based on diffusion, plastic deformation, and power-law creep ...mechanism was proposed.•The (111) texture significantly increased the interfacial bonding ratio by accelerating surface source diffusion.
Low-temperature bonding of nanotwinned (NT-) metals holds great potential for enhancing the performance and reliability of electronic interconnections. In this study, we performed low-temperature bonding of (111)-oriented nanotwinned silver (NT-Ag) films and thoroughly investigated the influence of (111) texture on the interfacial microstructure and bonding strength of the joints. The results demonstrated that high-quality bonding of highly (111)-oriented NT-Ag films was achieved even at 200 °C in air. The defect-free, coherent Ag(111)Ag(111) bonding interface was formed via face-to-face bonding of the highly (111)-oriented columnar grains. The shear strength of the joints significantly increased with the rise in (111) texture intensity. Moreover, we developed the void closure model to quantitatively elucidate the contribution of (111) texture to void closure and bonding ratio. Modeling results revealed that the (111) texture, with the highest surface diffusion coefficient, greatly increased the interfacial bonding ratio by accelerating surface source diffusion, thereby enabling high-strength bonding at low temperatures. The experimental validation and modeling results presented here contribute a novel perspective for optimizing interfacial microstructure and bonding strength by regulating the surface texture in the solid-state bonding of metals.
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