Composite materials aluminum nitride

This chapter considers the properties of ceramics used in microelectronic apphcations, including aluminum oxide (alumina, AljOj), beryUium oxide (beryUia, BeO), aluminum nitride (AIN), boron nitride (BN), diamond (C), and silicon carbide (SiC). Several composite materials, aluminum silicon carbide (AlSiC) and Dymalloy , a diamond/copper structure, are also described. Although the conductive nature of these materials prevents them from being used as a conventional substrate, they have a high thermal conductivity and may be used in applications where their relatively low electrical resistance is not a consideration. 

The combination of toxic hazard and high price (itself in part due to the extra measures needed in production processes to ensure the workers safety) has been an effective brake on commercial development of beryllium chemistry. Where possible substitute, albeit less effective, materials are often used titanium as an alternate lightweight metal or carbon fiber composites, phosphor-bronzes in place of beryllium alloys, aluminum nitride in place of BeO (1). 

Metals and ceramics (claylike materials) are also used as matrices in advanced composites. In most cases, metal matrix composites consist of aluminum, magnesium, copper, or titanium alloys of these metals or intermetallic compounds, such as TiAl and NiAl. The reinforcement is usually a ceramic material such as boron carbide (B4C), silicon carbide (SiC), aluminum oxide (A1203), aluminum nitride (AlN), or boron nitride (BN). Metals have also been used as reinforcements in metal matrices. For example, the physical characteristics of some types of steel have been improved by the addition of aluminum fibers. The reinforcement is usually added in the form of particles, whiskers, plates, or fibers. 

Results on other composite materials are similar to those obtained by Morrell and Ashbee.56 Creep asymmetry has been demonstrated for two grades of siliconized silicon carbide,35,60,61 SiC whisker-reinforced silicon nitride,53 HIPed silicon nitride,29 and vitreous-bonded aluminum oxide.29 Again, stresses required to achieve the same creep rate were at least a factor of two greater in compression than in tension. In two grades of siliconized silicon carbide,35,58-61 the stress exponent changed from 4 at creep rates below... 

Aluminum nitride is most commonly used for its high thermal conductivity. Recently, a poreless composite material, TiAl-TiB2-AlN, was obtained by reacting a Ti-F(0.7-0.95)A1+(0.05-0.50)8 mixture at 30- to 100-atm nitrogen pressure (Yamada, 1994). The use of high-pressure nitrogen gas was found to be effective for simultaneous synthesis and consolidation of nitride ceramics with dispersed intermetallic compounds (e.g., TiAl). Dense, crack-free products with uniform grains (approximately 10 mm in size) were obtained. 

Based on sturdy composite materials comprising metallic tungsten and aluminum nitride, we fabricated a AIN/W FGM approximately 0.5 mm thick in which the amount of metallic tungsten added was changed in stages by a normal sintering method in a nitrogen gas atmosphere ( at 1 atm ). 

For attenuated phase shift lithography, light blocking materials, which have phase shifting characteristic, such as molybdenum silicide (MoSi), aluminum/aluminum nitride cermet, understoichiometric silicon nitride, tantalum silicon oxide composite, are used. All these materials record 4 15 % transmission at UV light... 

Aluminum nitride may be used in composite structures containing aluminum for either structural or electronic applications, due to its attractive thermal, electronic, and mechanical properties [176-178]. AlN ceramics are also known to have a sufficiently high-temperature compatibility with refractory metals. Finally, AlN is an ecologically safe material. The structure of AlN as a ceramics layer of the multilayer Al/AlN composites has been investigated to only a limited degree [179]. 

The previous chapter was a review of the structure and composition of the three refractory covalent nitrides boron nitride, aluminum nitride, and silicon nitride. This chapter is an assessment of the properties and a suimnary of the fabrication processes and applications of these three materials. 

The term sialon was adopted in the seventies to describe solid-solution compositions containing the elements Si-Al-O-N. The crystal lattice of P-Si3N4 can readily accommodate other atoms such as A1 and 0, and the Sialons are formed by the addition of alumina (AI2O3) or aluminum nitride (AIN) to P-Si3N4- An empirical formula for this family of materials is Si5.jjAlxOxNg.. The sialons show promise as high-temperature engineering materials. 

Aside from diamond, cubic boron nitride B4N (CBN), boron carbide B4C, silicon carbide SiC, aluminum oxide AI2O3, and aliuninum oxide/zirconium oxide mixtures are used as abrasives for ceramics and composite materials. 

The sur ce FT-IR stey of a nanosize aluminum nitride powder definitely brought evidence of the specific chemical composition of its first atomic layer. The unavoidable contamination, mainly by atmospheric water, implies the presence of oxygen and hydrogen in this first layer. As a result, a comparison with the alumina sur ce appeared quite reasonable. Indeed, methanol and pyridine used as probe molecules showed the same behavior on both material sur ces. The acidity of the AIN sur ce was proven by the presence of two types of Al Lewis sites. However for AIN, a specific dissociative adsorption mechanism of acidic methanol could be possibly explained by the presence of weakly basic AI3N sites. Besides, the isotopic exchange... 

ABSTRACT. The reaction of tris-ethylaminoborane with diethyl aluminum amide was used to obtain a precursor containing B, Al, and N. Heating of the precursor to 1000 under ammonia yields a homogeneous composite of tuibostratic boron nitride and crystalline aluminum nitride. This material was studied by TEM, X-ray diffraction, IR, solid state NMR, and elemental analysis. The characterization of intermediates during the pyrolysis process is also discussed. 

In order to achieve high thermal conductance, aluminum nitride, silicon nitride, silicon carbide and the like which have high thermal conductance are being tried as ceramic ingredients. However whatever the type, it is difficult to exceed that of the alumina used in HTCCs. However, compared with resin materials, glass/alumina composites can achieve thermal conductivity more than ten times higher. 

The selection of a binding material is strongly dependent on the substrate material. For example, the most common glass composition used with alumina is a lead/bismuth borosU-icate composition. When this glass is used in conjunction with aluminum nitride, however, it is rapidly reduced at firing temperatures. Alkdine earth borosihcates must be used with AIN to promote adhesion. 

Ceramic-glass composite materials may be used to economically fabricate very complex multilayer interconnection structures. The materials in powder form are mixed with an organic binder, a plasticizer, and a solvent and formed into a slurry by ball or roll milling. The slurry is forced under a doctor blade and dried to form a thin sheet, referred to as green tape or greensheet. Further processing depends on the type of material. There are three basic classes of materials high temperature cofired ceramic (HTCC), low temperature cofired ceramic (LTCC), and aluminum nitride. 

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