Further enhancement of thermal conductivity through optimal uses of h-BN fillers in polymer-based thermal interface material for power electronics

Due to the demand of miniaturization and increasing functionality in power electronics, thermal dissipation becomes a challenging problem for thermal management and reliability. To enable effective heat transfer across the interconnect interfaces, thermal interface materials (TIMs) are required. Electrically insulating TIMs are primarily polymer-based composites which use conductive fillers to enhance thermal conductivity (TC). In this study, the optimal hybrid filler constituents, achieved through mixing spherical and platelet h-BN particles with different ratios, in polymer-based TIM was predicted using finite element (FE) simulations. The underpinning mechanisms of the variation in TC of the TIMs were analyzed from the temperature distribution patterns and micro heat flux paths. Results showed that with the same total volume fraction of h-BN, mixed spherical and platelet h-BN fillers of a certain ratio can further improve the thermal properties of the TIMs compared with those with spherical or platelet h-BN particles alone

Effect of bias voltage on microstructure and mechanical properties of nanocomposite ZrCN films deposited by filtered cathodic vacuum arc

Nanocomposite ZrCN films consisting of nanocrystalline ZrCN grains embedded in nitrogen-doped amorphous carbon film are deposited by filtered cathodic vacuum arc technology under different bias voltages ranging from 50 to 400 V. The influence of bias voltage on the characterization and the mechanical properties of the ZrCN films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and nano-indentation. The bias voltage has a subtle effect on the ZrCN grain size, which is around 9.5 nm and keeps almost constant. A slight increase of the bias voltage induces a relatively high sp 3 fraction about 40% in N-doped amorphous C films but leads to the graphitization of the films under a higher voltage. The best mechanical property of the ZrCN film with the hardness of 41 GPa is obtained under the bias voltage of 200 V, indicating the positive effect of slight increase of ion bombardment on the hardness of the films

Tribological behavior of diamond-like carbon coatings with patterned structure deposited by the filtered cathodic vacuum arc

Patterned diamond-like carbon (DLC) coatings were deposited on a Si (100) substrate using the filtered cathodic vacuum arc technique. The effects of the patterning and of the coating thickness on tribological behavior of DLC coating were investigated using a ball-on-disk tribometer under dry and oil-lubrication conditions. The results suggest that 1 mm2 patterned structures delimited by 100-μm grooves can enhance the tribological properties. The coefficients of friction of the tested patterned films were 0.123 and 0.067 under dry and oil lubrication conditions, respectively, 10% and 21% lower than the coefficients of friction of the continuous DLC films with the same thickness. Raman spectroscopy measurements showed graphitized wear particles for both the continuous and patterned DLC films, but the debris of patterned DLC films having a greater degree of graphitization under dry sliding. The grooves of the patterned coatings could serve as a lubricant reservoir and trap the wear debris, which was beneficial for the tribological properties. The effect of the thickness of the patterned DLC films on their tribology behavior was also investigated. The 0.4-μm-thick patterned samples exhibited the lowest coefficients of friction of 0.105 and 0.058 under dry and oil lubrication conditions, respectively, while the 0.8-μm-thick patterned samples showed the lowest specific wear rate. In addition, the coefficients of friction of the patterned samples increased with an increase in the film thickness under oil lubrication conditions

Preparation of mesoporous carbon nitride structure by the dealloying of Ni/a-CN nanocomposite films

The preparation of mesoporous carbon nitride (p-CN) structure by the selective dealloying process of Ni/a-CN nanocomposite films is investigated. The composition and structure of the Ni/a-CN nanocomposite films and porous carbon nitride (p-CN) films are determined by scan electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Phase separated structure including nickel carbide phase and the surrounding amorphous carbon nitride (a-CN) matrix are detected for the as-deposited films. Though the bulk diffusion is introduced in the film during the annealing process, the grain sizes for the post-annealed films are around 10 nm and change little comparing with the ones of the as-deposited films, which is associated with the thermostability of the CN surrounding in the film. The p-CN skeleton with its pore size around 12.5 nm is formed by etching the post-annealed films, indicative of the stability of the phase separated structure during the annealing process