Suzhu Yu

Thermal conductivity of polystyrene–aluminum nitride composite

Abstract The thermal conductivity of polymer composites having a matrix of polystyrene (PS) containing aluminum nitride (AlN) reinforcement has been investigated under a special dispersion state of filler in the composites: aluminum nitride filler particles surrounding polystyrene matrix particles. Data for the thermal conductivity of the composites are discussed as a function of composition parameters (aluminum nitride concentration, polystyrene particle size) and temperature. It is found that the thermal conductivity of composites is higher for a polystyrene particle size of 2xa0mm than that for a particle size of 0.15xa0mm. The thermal conductivity of the composite is five times that of pure polystyrene at about 20% volume fraction of AlN for the composite containing 2xa0mm polystyrene particle size. The relationship between thermal conductivity of composites and AlN filler concentrations has been compared with the predictions of two theoretical models from the literature.

Dielectric properties of polystyrene–aluminum-nitride composites

For polymer composites to be used in electronic packaging, they must have a good combination of thermal and dielectric properties. A composite of aluminum-nitride (AlN) particles dispersed around polystyrene matrix particles has been synthesized in this study. The purpose of using this microstructure is to improve the thermal properties of the polymer at the low-filler content with a minimal increase in the dielectric constant of the polymer composite. The dielectric relaxation behavior of polystyrene–AlN composites has been investigated with broadband dielectric relaxation spectroscopy. The experimental results indicate that the dielectric property of polystyrene–AlN composites is a function of polystyrene particle size, AlN filler concentration, temperature, and frequency under this dispersion state. The dependence of Maxwell–Wagner–Sillars or interfacial polarization of polystyrene–AlN composites on AlN volume fraction has also been studied. The Davidson–Cole equation is used to fit the experimental Co...

Surface modified silica mesoporous films as a low dielectric constant intermetal dielectric

Silica mesoporous films with low dielectric constant were successfully fabricated by a multiple-step sol–gel process. Various surface modifications were conducted to make the surface of the films hydrophobicity, which was proved very effective to maintain the low dielectric properties of the films. The basic properties of the silica films were evaluated by atomic force microscopy, specular x-ray reflectivity, Fourier transform infrared, and thermal gravimetric and differential thermal analysis. An inherent low dielectric constant of around 2.0 was realized for about 56% porosity of the silica film with pore size less than 40 nm and the leakage current was at a level of 10−6u2009A/cm2 after two months of fabrication. Preliminary results of the silica films prepared here present a very positive prospective to intermetal dielectric applications.

The effect of TEOS/MTES ratio on the structural and dielectric properties of porous silica films

This paper presents the results of the characterization of porous silica films used as intermetal dielectrics. The films were fabricated via sol-gel process using tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) as precursors with acid and base as catalysts. Several advanced techniques such as transmission electron microscopy, specular X-ray reflectivity, Fourier transform infrared spectroscopy, nitrogen adsorption, thermal gravimetric, and differential thermal analysis have been employed to obtain information on the structural properties of the films and reaction mechanisms involved in the sol-gel process of such dielectrics. The characterization results show the effects of the TEOS/MTES ratio on the development of the porosity, pore size, and pore interconnectivity of the films, which reflects the influence of different mechanisms of hydrolysis and condensation of silica precursors in different pH conditions and the existence of covalently bonded organic ligands on the pore structure. An inherently low dielectric constant of around 2.0 was realized for about 60% porosity in the silica films. The pore sizes were less than 10 nm with majority of pores being closed-cells.

Thermal expansion behaviour of polystyrene-aluminium nitride composites

The thermal expansion behaviour of polymer composites having a matrix of polystyrene containing aluminium nitride (AlN) reinforcement has been investigated under a special dispersion state of filler in the composite: AlN filler particles surrounding polystyrene matrix particles. It is found that the coefficient of thermal expansion (CTE) of the composite is about 0.3 of that of polystyrene at about 20% volume fraction of AlN. The particle size of the polymer matrix is also found to have an effect on the thermal expansion of the polymer composite under this dispersion state. The dependence of the transition temperatures of the polystyrene on the AlN concentration and polystyrene particle size has also been studied. The experimental CTEs of composites have been compared with Kerner, Turner and Thomas models. The Thomas expression more closely matches the behaviour of polystyrene-AlN composites.

Synthesis of organically modified mesoporous silica as a low dielectric constant intermetal dielectric

Silica mesoporous films with low dielectric constant were successfully fabricated by a multiple step sol-gel process. The employment of inorganic/organic precursors proved very useful in preventing the film from cracking. The acid/base two-step catalysis could adjust the refractive index or porosity of the silica films effectively and easily. The basic properties of the silica films were evaluated by transmission electron microscopy, specular x-ray reflectivity, Fourier transform infrared spectroscopy, and thermal gravimetric and differential thermal analysis. An inherently low dielectric constant of around 2.0 was realized for about 57% porosity in the silica film with a pore size less than 10 nm. The leakage current was at a level of 10−6u2002A/cm2 one month after fabrication. The dependencies of the dielectric properties of the films on the relative amount of the components in the starting solution and on the processing temperature were investigated in detail. Preliminary results of the silica films prepar...

Dynamic mechanical properties of polystyrene–aluminum nitride composite

A composite of aluminum nitride (AlN) particles dispersed around polystyrene matrix particles was synthesized in this study. The purpose of using this microstructure is to improve the thermal properties of a polymer at a low filler content with a minimal increase in the dielectric constant of the polymer composite to meet the material requirements for electronic packaging. The dynamic mechanical properties of this type of polystyrene-AlN composite were investigated here. The experimental results indicate that the dynamic mechanical property of the polystyrene-AlN composite is a function of the polystyrene particle size, AlN filler concentration, and temperature under this dispersion state. The addition of an AlN concentration into polystyrene increases both the storage modulus and the α-transition temperature. The smaller polystyrene particle size gives a higher storage modulus and damping peak.

Synthesis and Characterization of Templating Low Dielectric Constant Organosilicate Films

The porous hydrogen methyl silsesquioxane films have been successfully synthesized by the incorporation of poly(amidoamine) (PAMAM) which is thermally decomposed to form nanometer-scale voids within the films. A coupling agent was used to prevent the phase separation of the sacrificial material and the matrix by chemically bonding them together. The decomposition behavior of PAMAM was studied in different atmospheres, and it was found that PAMAM degraded more effectively in air than in nitrogen. Atomic force microscopy and transmission electron microscopy micrographs provided information about the structure of the hybrid films, and specular X-ray reflectivity was used to evaluate the density and porosity of the films. A dielectric constant as low as 2.2 was achieved for closed-cell mesoporous film with PAMAM loading of 15 wt %.

Low Dielectric Constant Organosilicate Films Prepared by Sol-Gel and Templating Methods

Low dielectric constant organosilicate films with controllable microstructure have been successfully synthesized by multiple-step sol-gel process and templating method, which are the two basic methods to establish porous network in the films. Ultra-low dielectric constant (k) of around 2.0 can be achieved for both films. The microstructure such as porosity, pore interconnection and pore size of the two types of the films have been studied and compared. It has been found that the sol-gel films have a higher level of porosity comparing to the templating films to obtain the same k value. The sol-gel film has a majority of closed pores with pore size around 5 nm. The templating film has a closed pore structure with pore size around 10 nm. Preliminary results present a very positive prospective for intermetal dielectric applications.