Introduction of high tensile strain into Ge-on-Insulator structures by oxidation and annealing at high temperature

It is demonstrated in this work that a high temperature thermal process including oxidation and N2 annealing at 850 oC can provide tensile strain of ~0.58 % at maximum into Ge-on-Insulator (GOI) structures without any special patterning or external stressors. The different impacts of oxidation and annealing on tensile strain generation, surface roughness and crystal qualities in the GOI structures fabricated by Ge condensation and wafer bonding are systematically examined. Tensile strain of 0.47 % is achieved without severe thermal damages under the optimal thermal process condition, which indicates the high potential of the present method for improving the performance of GOI n-channel MOSFETs. The influence of thermal expansion mismatch between Ge and SiO2 are suggested as a possible physical origin of high amount of tensile strain into GOI structures.

Instant, multiscale dry transfer printing by atomic diffusion control at heterogeneous interfaces

Transfer printing is a technique that integrates heterogeneous materials by readily retrieving functional elements from a grown substrate and subsequently printing them onto a specific target site. These strategies are broadly exploited to construct heterogeneously integrated electronic devices. A typical wet transfer printing method exhibits limitations related to unwanted displacement and shape distortion of the device due to uncontrollable fluid movement and slow chemical diffusion. In this study, a dry transfer printing technique that allows reliable and instant release of devices by exploiting the thermal expansion mismatch between adjacent materials is demonstrated, and computational studies are conducted to investigate the fundamental mechanisms of the dry transfer printing process. Extensive exemplary demonstrations of multiscale, sequential wet-dry, circuit-level, and biological topography-based transfer printing demonstrate the potential of this technique for many other emerging applications in modern electronics that have not been achieved through conventional wet transfer printing over the past few decades.

Grain Refinement Of Magnesium and Az19E Magnesium Alloy By Addition Of MgB2 Inoculant

The increased use of magnesium alloys with improved mechanical properties is a prominent strategy towards increasing fuel efficiency of vehicles and decreasing emissions. This study investigates the grain refining efficiency and fading of MgB2 micro- and nano-particle added Pure Mg and AZ91E. Addition of micro and nano-sized MgB2 provided a reduction in grain size for Pure Mg and AZ91E. Enhanced heterogeneous nucleation and grain growth restriction was believed to be the source of refinement. Fading was observed for both Pure Mg and AZ91E, with the nano-particle added castings showing an increased resistance. The elongation of the Pure Mg samples showed improvements, whereas no improvements for UTS and YS was seen. The improved ductility was believed to be due to the grain refinement and coefficient of thermal expansion mismatch. The AZ91E samples did not show improvements in mechanical properties. This was believed to be due to stress concentration from Al-Mn intermetallics.

Grain Refinement Of Magnesium and Az19E Magnesium Alloy By Addition Of MgB2 Inoculant

The increased use of magnesium alloys with improved mechanical properties is a prominent strategy towards increasing fuel efficiency of vehicles and decreasing emissions. This study investigates the grain refining efficiency and fading of MgB2 micro- and nano-particle added Pure Mg and AZ91E. Addition of micro and nano-sized MgB2 provided a reduction in grain size for Pure Mg and AZ91E. Enhanced heterogeneous nucleation and grain growth restriction was believed to be the source of refinement. Fading was observed for both Pure Mg and AZ91E, with the nano-particle added castings showing an increased resistance. The elongation of the Pure Mg samples showed improvements, whereas no improvements for UTS and YS was seen. The improved ductility was believed to be due to the grain refinement and coefficient of thermal expansion mismatch. The AZ91E samples did not show improvements in mechanical properties. This was believed to be due to stress concentration from Al-Mn intermetallics.

The Influence of La and Ce on Microstructure and Mechanical Properties of an Al-Si-Cu-Mg-Fe Alloy at High Temperature

The effect of lanthanum (La)+cerium (Ce) addition on the high-temperature strength of an aluminum (Al)–silicon (Si)–copper (Cu)–magnesium (Mg)–iron (Fe)–manganese (Mn) alloy was investigated. A great number of plate-like intermetallics, Al11(Ce, La)3- and blocky α-Al15(Fe, Mn)3Si2-precipitates, were observed. The results showed that the high-temperature mechanical properties depended strongly on the amount and morphology of the intermetallic phases formed. The precipitated tiny Al11(Ce, La)3 and α-Al15(Fe, Mn)3Si2 both contributed to the high-temperature mechanical properties, especially at 300 °C and 400 °C. The formation of coarse plate-like Al11(Ce, La)3, at the highest (Ce-La) additions, reduced the mechanical properties at (≤300) ℃ and improved the properties at 400 ℃. Analysis of the strengthening mechanisms revealed that the load-bearing mechanism was the main contributing mechanism with no contribution from thermal-expansion mismatch effects. Strain hardening had a minor contribution to the tensile strength at high-temperature.

Unravelling thermal stress due to thermal expansion mismatch in metal–organic frameworks for methane storage

Thermal stress is present in metal–organic frameworks undergoing temperature changes during adsorption and desorption. We computed the thermal pressure coefficient as a proxy for this phenomenon and discuss the impact of thermal expansion mismatch.

Minimized thermal expansion mismatch of cobalt-based perovskite air electrode for solid oxide cells

The mismatch of thermal expansion coefficients (TECs) between cobalt-containing perovskite air electrode and electrolyte is a great challenge for the development of thermo-mechanically durable solid oxide cell (SOC). In this...

Additive Fabricated Compliant Interconnects: Design, Fabrication and Reliability Effects

Electronics packaging development is greatly dependent on the magnitude of interconnect and on-chip stress that ultimately limits the reliability of electronic components. Thermomechanical strains occur because of the coefficient of thermal expansion mismatch from different conjoined materials being assembled to manufacture a device. To curb the effect of thermal expansion mismatch, studies have been done in integrating compliant structures between dies, solder balls, and substrates. Initial studies have enabled the design and manufacturing of these structures using a photolithography approach which involves an increased number of fabrication steps depending on the complexity of the structures. This current study involves the fabrication of these structures using a different approach, utilizing additive manufacturing that reduces the number of fabrication steps required to obtain compliant geometries, while also providing a platform for unique compliant structures. This paper discusses the method of fabrication and analyzes the properties and effects of these interconnect structures on a die. Structural finite element thermal cycling simulations between −40 to 125°C show about a 115% increase in the solder joint fatigue life. Additionally, fabricated test structures created directly on a PCB were experimentally characterized for compliance using a micro-indenter tester, showing a mechanical compliance range of 265.95 to 656.78 μ/N for selected design parameters to be integrated into a test vehicle.

Surface Rumpling Behavior of Hf/Zr Single-Doped and Co-Doped β-NiAl Coatings during High-Temperature Cyclic Oxidation

Reactive elements like Hf- and Zr-doped β-NiAl are considered to be promising candidate materials for protective coatings used at ultra-high temperatures. However, the role of reactive element co-doping on cyclic oxidation behavior and the surface rumpling of β-NiAl coatings remains unclear. Thus, in this paper, Hf and Zr single-doped and co-doped β-NiAl coatings were deposited on a single crystal superalloy by electron beam physical vapor deposition and the cyclic oxidation at 1150 °C was investigated. The coatings yielded a similar oxidation rate during cyclic oxidation. Obvious surface rumpling appeared in the single-doped coatings, whereas it was effectively alleviated in the co-doped coating. Related mechanisms were discussed, including thermal expansion mismatch, martensitic transformation and phase transformation from β-NiAl to γ′-Ni3Al. The non-uniform phase transformation from β to γ′ was finally believed to be responsible for the discrepancy in the rumpling extents between the single-doped and co-doped coatings.