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Effect of Macro-scale Mechanical Stress of Silicon Wafer on Room Temperature Photoluminescence Signals
摘要： Mechanical stress was applied to single side polished and double side polished Si wafers in polypropylene wafer containers for different localized stress levels and durations. Room temperature photoluminescence (RTPL) spectra from Si wafers were measured before and after applying localized mechanical stress. Significant changes (up to 26% increase) in RTPL intensity were measured from areas under different stress levels even 1 year after the fixtures for mechanical stress generation were removed. Significant effects of localized mechanical stress on RTPL intensity variations were measured up to 49 days after the fixture removal. Nearly fully relaxed RTPL signatures for localized mechanical stress were measured 450 days after the fixture removal. RTPL intensity is found to be very sensitive to the externally applied macro-scale mechanical stress of Si wafers and residual (or memorized) internal stress even after removal of fixtures for external mechanical stress generation.
关键词： Silicon,room temperature photoluminescence,stress relaxation,mechanical stress
更新于2025-09-23 15:23:52
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Joining of AlN and Al with Compositional Graded Layer by Centrifugal Mixed-Powder Method
摘要： In this study, joining of AlN and Al with compositional graded layer is made by centrifugal mixed-powder method (CMPM). The mixed-powder of AlN particles and Al particles is inserted into a spinning mold with bulk-shaped AlN, and then molten Al is poured into the spinning mold with the mixed-powder and bulk-shaped AlN. As a result, the molten Al penetrates into the space between the mixed-powder by the centrifugal force, and at the same time, the Al particles can be melted by heat from the molten Al. Then AlN and Al can be joined with compositional graded layer after solidification. Micromechanics-based analysis is also employed to understand the thermal stress relaxation by the compositional graded layer.
关键词： Joining,Ceramics/metal joining,Thermal stress relaxation,Functionally graded materials (FGMs),Micro-mechanics,Centrifugal mixed-powder method (CMPM)
更新于2025-09-23 15:22:29
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Stress Relaxation in Porous GaN Prepared by UV Assisted Electrochemical Etching
摘要： This study describes the stress relaxation in porous GaN grown on Al2O3 substrates. The results indicate that the stress relaxation has taken place in the samples which increases by increasing the etching current. As compared to the as-grown GaN films, porous GaN exhibits substantial photoluminescence (PL) intensity enhancement with red-shifted band-edge peaks associated with the relaxation of the compressive stress. The red shifted phonon energy peak (E2) in the Raman spectra of the porous GaN films confirms further such a stress relaxation. Scanning electron microscopy (SEM) demonstrates that, the current density has significant effect on the size and shape of the pores.
关键词： Stress relaxation,Porous GaN,Raman spectroscopy,Red shift
更新于2025-09-19 17:15:36
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The Influence of Selected Selective Laser Sintering Technology Process Parameters on Stress Relaxation, Mass of Models, and Their Surface Texture Quality
摘要： The article presents the results of research on the impact of basic process parameters of selective laser sintering technology on the mass of the produced models (density of the sintered material—polyamide PA 2200), stress relaxation during compression determined in accordance with the ISO 3384 standard, and geometric surface structure parameters (SGPs). During the tests, the influence of process parameters such as the location of the models on the virtual construction platform (printing direction), the density of the energy supplied to the sintered layer of powder, and the layer thickness of the manufactured material layer was taken into account. The test results confirmed that the process parameters have a significant impact on the density of the model material (in the sintered state), the mechanical properties (stress relaxation during compression), and the quality of the surface texture (SGPs). The most favorable positioning variants of the models on the construction platform were determined. The most favorable thickness variants of the combined layers and the density value of the energy supplied to the sintered powder layer were selected, depending on the expected mass, strength, and SGP quality. In addition, it has been shown that it is possible to build models with reduced mass (>20%), while maintaining satisfactory mechanical and qualitative properties of the surface texture.
关键词： additive manufacturing technologies,GPS,rapid prototyping,SLS,3D printing,stress relaxation
更新于2025-09-19 17:13:59
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Fabrication of Less Bowed Light-Emitting Diodes on Sapphire Substrates with a SiO2 Thin Film on Their Back Sides
摘要： In this study, less bowed light-emitting diodes (LEDs) were fabricated by preparing a LED structure on a sapphire substrate with a SiO2 thin ?lm on its back side. The SiO2 thin ?lm with a low thermal expansion coe?cient reduced the bow of the wafer generated by the thermal expansion coe?cient di?erence. As the thickness of SiO2 was increased from 1 μm to 4 μm, the compressive stress in the GaN ?lm was reduced from 16% to 62% with respect to that without SiO2 thin ?lm. The stress reduction in multiple quantum wells also enhanced the internal quantum e?ciency of the LED by reducing the piezoelectric ?eld.
关键词： Stress relaxation,Internal quantum e?ciency,Light-emitting diodes
更新于2025-09-12 10:27:22
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High-Temperature Cycle Durability of Superplastic Al-Zn Eutectoid Solder Joints with Stress Relaxation Characteristics for SiC Power Semiconductor Devices
摘要： We have developed a new high-temperature Al-Zn lead-free soldering process that utilizes superplasticity to realize SiC power devices with high-temperature cycle durability. The joining process consists of an Al-78wt.%Zn preparation being sandwiched by a SiC die and insulation substrate, an interfacial cleaning process at approximately 250-270oC, a heating stage to reach the solid-liquid coexisting temperature of 420-430oC, the ejection of low-melting-temperature β(Zn) from the joining area by press stress, and the transformation to a superplastic composition, i.e., Al-70 wt.% Zn at 270-310oC. Many lamellar phases that enable superplasticity can be formed in this microstructure. This solder joint composition was proven to have a better stress-relaxation effect than eutectic Al-95wt.%Zn, and the composition shows a much higher damping capability at the maximum operating temperature of SiC devices (200oC) than that of other joining candidates. The outstanding temperature cycle durability was verified in temperature cycle tests from -40oC to 300oC for 5000 cycles. This durability is due to the high-stress-relaxation effect from the superplasticity transformation realized by the lamellar structures in the Al-Zn alloy solder.
关键词： lamellar structure,damping capability,power semiconductor,SiC,superplasticity,temperature cycle test,Al-Zn eutectoid solder,lead-free solder,stress relaxation
更新于2025-09-09 09:28:46