Material For High Temperature Devices Research Articles

Ablation behavior and mechanisms of high-entropy rare earth titanates (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 coating deposited by plasma spraying technology

High-entropy rare earth titanates (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 (YHT) have great application potential in the thermal protection coating field. In this work, the YHT coating was successfully prepared by atmospheric plasma spraying. The influence of different spraying powers and coating ablation behavior by plasma flame on the phase composition and microstructure morphology of the coating surface, cross-section and fracture surface were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscope. Results show that the YHT powder has a sufficiently melted state before impacting the metal substrate and the coating can be effectively deposited through optimizing the plasma spraying power. And the YHT coatings undergo slight sintering, leading to the formation and growth of a spherical structure at 1200 °C, while the grain preferential growth, mechanical failure and water-like structure occurred due to strong thermal shock at 1400 °C. In addition, when the coating surface temperatures are 1200 °C and 1400 °C, the corresponding heat insulation temperatures are 590 °C and 620 °C, respectively, indicating that YHT coating has good thermal insulation ability. This study provides a powerful theoretical basis and technical support for the application of high-entropy rare earth titanates YHT as a thermal protection material for high temperature devices.

Graphene, a material for high temperature devices--intrinsic carrier density, carrier drift velocity, and lattice energy.

Heat has always been a killing matter for traditional semiconductor machines. The underlining physical reason is that the intrinsic carrier density of a device made from a traditional semiconductor material increases very fast with a rising temperature. Once reaching a temperature, the density surpasses the chemical doping or gating effect, any p-n junction or transistor made from the semiconductor will fail to function. Here, we measure the intrinsic Fermi level (|EF| = 2.93 kBT) or intrinsic carrier density (nin = 3.87 × 106 cm−2K−2·T2), carrier drift velocity, and G mode phonon energy of graphene devices and their temperature dependencies up to 2400 K. Our results show intrinsic carrier density of graphene is an order of magnitude less sensitive to temperature than those of Si or Ge, and reveal the great potentials of graphene as a material for high temperature devices. We also observe a linear decline of saturation drift velocity with increasing temperature, and identify the temperature coefficients of the intrinsic G mode phonon energy. Above knowledge is vital in understanding the physical phenomena of graphene under high power or high temperature.

Nanoindentation of Porous Die Attach Materials as a Means of Determining Mechanical Attributes

A die attach nanopaste for high temperature use on silicon carbide (SiC) based power semiconductor devices was developed utilizing silver (Ag) and aluminium (Al) nanoparticles as well as organic additives. Total nanoparticle content was varied at 84.7, 85.5, 86.2 and 87 wt%, while the Ag to Al ratio was fixed to 80:20. The die attach nanopaste was sintered in open air at 380 °C for 30 minutes to create an Ag-Al inter-metallic compound between the SiC die and substrate. To determine the mechanical attributes of the post-sintered die attach interlayer, nanoindentation was performed on the samples. It was found that, a low Young modulus of elasticity, E, between 9.3-9.8 GPa was obtained. This was followed by a reduction in hardness as well as stiffness for the post-sintered Ag80-Al20 die attach material when compared against that of solder alloys or bulk metals. The formation of pores in the die attach material as it underwent sintering is believed to have contributed to this decrease in mechanical properties. The findings of this research enables the possibility of introducing a much cheaper die attach material for high temperature devices, which also has excellent mechanical properties to alleviate thermal mismatch issues between the semiconductor die and substrate.

Determination of the electrical conductivity of heat-resistant concretes

The problem of the electrical conductivity of heat-resistant concretes and bonding agents is considered and a method for determining this parameter is suggested. In addition to the thermal resistivity, the electric conductivity is a factor affecting the lifetime of lining materials for high-temperature devices. The problem is especially urgent in electric heaters.