Abstract Aluminum Nitride Research Articles

Preparation of aluminium nitride powder from a (hydroxo)(succinato)aluminium(III) complex

Aluminium nitride (AIN) powder was prepared by using a (hydroxo)(succinato)aluminium(III) complex as a new precursor. The AIN powder was obtained by calcining the complex without mixing any carbon source under a flow of nitrogen in the temperature range 1200–1500 °C and then burning out the residual carbon. The complex began to decompose at ca. 400 °C and turned into γ-alumina at temperatures >600 °C. Carbothermal reduction and nitridation of the γ-alumina, resulting in the formation of AIN, commenced at ca. 1200 °C without γ–α alumina transition. A short time at the higher calcination temperature was more likely to favour complete nitridation than a long time at the lower calcination temperature. The AIN powders prepared were ultrafine, and their particle size depended on the calcination temperature and duration of calcination.

Columnar microstructures of preferred oriented Aluminum Nitride films prepared by reactive sputtering

Aluminum nitride (AIN) thin films have drawn much attention as piezoelectric materials for generation and detection of surface acoustic wave (SAW) owing to high ultrasonic velocity and fairly large piezoelectric coupling factors. Since the piezoelectric properties are strongly dependent upon the c-axis orientation of AIN films, it is important to control the crystallographic orientation with deposition parameters. Though many reports have been presented, the mechanism of crystallographic orientation change with deposition parameters still remains unknown and the microstructure analysis of AIN films have been scarcely carried out. In this paper, we present the effect of sputtering pressure on thecrystallographic orientation and the microstruclure of the deposited AIN films, using X-ray diffraction (XRD) and transmission electron microscopy (TEM) study.AIN films have been deposited on Si (100) wafers by reactive RF magnetron sputtering in Ar-N2 gas mixture without substrate heating. The base pressure of vacuum chamber was below 1.5X10-6 Torr, RF power was 200 W and the ratio of gas flow rate (Ar:N2) was 3:1. Processing pressures ranged from 5 to 12 mTorr. Crystal structure of as-deposited films examined with XRD (Rigaku, D/MAX-RC, 12 kW) and microstructure analyses were carried out using crosssectional and plan-view TEM (JEOL 4000FX, 400 kV).

Compatibility between molybdenum and aluminium nitride

Abstract Molybdenum and aluminium nitride sintered discs are strongly bonded after hot pressing at 1850°C under 20 MPa in flowing argon. If aluminium nitride discs are pre-sintered with lime or yttria additive, the bonding is only achieved when the dopant content is weak (1 to 3%). By comparison with the behaviour of tungsten under the same conditions, the bonding is supposed to be due to the reaction of the secondary oxide phase of molybdenum with its analogue in aluminium nitride, providing a complex interfacial phase, able to exist at the grain boundaries of both the materials near the interface, and making the bonding strong after cooling. If the interfacial phase is too great in volume and too liquid (when AlN is doped with important amounts of lime or yttria) it is expelled from the interfacial zone and no bonding is observed.

Some properties of aluminium nitride powder synthesized by low-pressure chemical vapour deposition

Aluminium nitride (AIN) powders were synthesized by a low-pressure chemical vapour deposition, i.e. reactions of vaporized aluminium with various compositions of NH3-N2 gases at 1050°C under a pressure of 0.1–1.3 kPa. The properties of the resulting powders were divided into three categories, according to the NH3 content in the NH3-N2 gases: (i) 0 ⩽ NH3 < 40%, (ii) 40⩽NH3⩽60%, and (iii) 60<NH3⩽100%. In Region (i), the unreacted aluminium adhered to the AIN crystallites to form spherical primary particles; in Region (ii), the spherical agglomerates with diameters of 0.2–0.5 μm, composed of primary particles, were present as minimum units of secondary particles; in Region (iii), the crystal growth of AIN was enhanced with increasing NH3 contents. The primary particles formed by the reaction of aluminium vapour with NH3-N2 gases containing NH3⩾40% were single crystals.

Light-induced defects in aluminum nitride ceramics

Aluminum nitride (AlN) ceramic samples exhibit a dramatic photo-darkening when exposed to UV radiation. In this paper, this phenomenon has been investigated utilizing photo-induced absorption measurements, where the transmission of a visible probe beam is monitored before and after exposure to a UV pump beam. Changes in the probe transmission as large 60% have been observed. The results of this study show that the center responsible for the photo-induced absorption process is an aluminum vacancy-oxygen impurity complex which resides in the AlN lattice. An energy level diagram is constructed which is consistent with these experimental findings.

Thermal conductivity of calcium-doped aluminium nitride ceramics

Aluminium nitride ceramics were prepared with the addition of up to 12wt% of calcium oxide as a sintering aid. Both the oxygen and the calcium content of the samples decreased during sintering with increasing sintering temperature and soaking time. Higher amounts of calcium oxide resulted in higher thermal conductivities, with values up to 142 W m−1 K−1. Moderate sintering temperatures, short temperature soaking times and the use of inexpensive Ca-based sintering additives should enable the production of aluminium nitride ceramics with sufficiently high thermal conductivity at relatively low cost.

Gas-phase synthesis of AlN powders from AlCl3-NH3-N2

Aluminium nitride powders were synthesized by the gas-phase reaction of AlCl3-NH3-N2 system. The yield of AlN powders from AlCl3 and their crystallinity increased as the reaction temperature and the mole ratio of NH3/AlCl3 were increased. AlN powders were also formed outside the reactor and their crystallinity was amorphous. The yield of AlN powders was as high as 80% when the reactor temperature was 1000 °C and the mole ratio of NH3/AlCl3 was 8. Most of the HCl by-product was recovered as NH4Cl outside the reactor. Powder characteristics, such as shape, size distribution and crystallinity, were also studied.

Preparation of AlN thin films by reactive sputtering and optical emission spectroscopy during sputtering

Abstract Aluminum Nitride (AlN) thin films were prepared by reactive rf-magnetron sputtering in a mixed gas atmosphere composing of argon and nitrogen. The deposition rate, electrical resistivity and crystal structure were studied as a function of partial pressure of nitrogen (P N2). Total pressure(P N2+Ar) was controlled to maintain a constant pressure of 6.0 ×10−2 Pa. The structure of as-prepared films can be divided into three regions from X-ray diffraction analysis: (1) P N2 ≤ 6.0 ×10−3 Pa, Al, (2) P N2 = 1.2 ×10−2 Pa ∼ 2.4 ×10−2 Pa, a mixed phase of Al and AlN, (3) P N2 ≥ 3.0 ×10−2 Pa, AlN. With increase of P N2, the deposition rate of the films decreased drastically around P N2 = 2.4 ×10−2 Pa, and finally approached to a constant value of 25 A/min around P N2 = 6.0 ×10−1 Pa. This is proved from the measurement of optical emission spectroscopy to occur by the formation of nitride on the surface of aluminum target. AlN thin films deposited in higher P N2 exhibited a higher crystallity and a higher ref...

Chemical and electronic properties of aluminium nitride on GaAs(110)

Aluminium nitride was synthesized on GaAs(110) at room temperature by a reaction of aluminium evaporated from a Knudsen cell with ammonia. Chemical and electronic properties were studied by using photoemission spectroscopy excited with MgKα, ZrMζ as well as monochromatic He I and He II radiation and by the use of low-energy electron energy-loss spectroscopy (LEELS). AIN was found to reduce signals from cation and anion dangling bonds of the GaAs(110) surface and to induce surface states of donor- as well as acceptor-type. Deposition of 1 ML of AIN decreases the ionization energy by 1 eV. The Ga(3d) clean-surface core-level component is completely removed at this coverage. This decrease in intensity for coverages below one monolayer is correlated with the attenuation observed with the Ga(3d) surface exciton in LEELS. No chemically shifted components of Ga(3d) and As(3d) core levels were observed when AIN was deposited on GaAs(110). For AIN coverages above one monolayer, the intensity of Ga(3d) and As(3d) core-level emission excited with ZrMζ radiation fall off exponentially. This indicates homogeneous growth and abrupt interfaces. For AIN, with x < 1, on the other hand, the intensity decrease deviates from this behavior. This is caused by exchange reactions similar to those observed for Al on GaAs(110).

Binder chemistry, adhesion and structure of interfaces in thick-film metallized aluminium nitride substrates

Aluminium nitride substrates from three different sources were metallized by standard thick film processing using gold conductor pastes, Pd-Ag paste, and a ruthenium oxide resistor paste. Screen printed pastes were fired in a typical three-zone furnace to obtain metallized AIN substrates. Interfacial reaction zones were studied by microscopic (optical and scanning electron microscopy) and electron beam microprobe analysis techniques. The elements in the binder materials in thick film pastes form amorphous phases at the interface which influence the adhesion of thick films to the AIN substrate. The lack of certain elements (Cd, Zn, Ca) in the binder of the gold thick-film paste led to weaker adhesion and severe degradation of the thick-film adhesion during thermal cycling.

Brazing of aluminum nitride substrates

Aluminum nitride (AlN) is currently under investigation as a potential candidate for replacing aluminum oxide (Al2O3) as a substrate material for electronic circuit packaging. The requirements for such a material are that it can be metallized and joined to produce hermetic enclosures for semiconductor devices. A technique for brazing AlN using a nonactive metal braze has been investigated. The process involves the in situ decomposition of an active metal hydride. This process improves the wetting of the AlN and led to the development of strong bonding between braze and ceramic. The ceramic-braze interface was studied using scanning electron microscopy (SEM). The nature of the interfacial reactions and the reaction products have been identified using x-ray diffraction (XRD). The progress of the reaction has been followed using differential thermal analysis (DTA). The experimental results have been correlated with thermodynamic predictions of the reaction processes. In addition to joining ceramic to ceramic, braze joints of AlN to copper and to a low expansion iron-nickel lead frame alloy were made. Residual stress resulting from a mismatch of thermal expansion coefficients between AlN and copper caused cracking in the ceramic upon cooldown from the brazing temperature. No cracking occurred in the ceramic when joined to the iron-nickel alloy. The results obtained are important for the realization of AlN as a ceramic packaging material for semiconductor devices.

Thermodynamic considerations in the thick-film metallization of aluminium nitride substrates

Aluminium nitride (A1N) is currently under investigation as a substrate material for use in microcircuit applications, in particular where high thermal conductivity is required. Metallization of the substrate is required for mounting of the integrated circuit and to provide interconnection to other circuit components. A widely used technique to metallize substrates is thick-film technology. There are two primary methods used to achieve adhesion between a thick-film conductor and the ceramic substrate. These are frit bonding and reactive bonding. The reactive bonders are generally oxides which, during firing, form mixed oxide phases or liquid eutectic phases at the interface, which provide adhesion of the metal film. Bonding to the metallization occurs by reduction and solid solution

Characterization of Gold—Aluminum Nitride and Gold—Silicon Carbide Interfaces

Aluminum nitride and silicon carbide substrates were screen‐printed with fritless gold and fired at 850°C in air. Interfacial diffusion zones up to 7 αm thick were observed, in which the concentrations of Au, Na impurities, and combined O varied together. Secondary ion mass and photoelectron spectroscopy revealed oxidized Al in the gold conductor supported by AIN. It is suggested that enhanced oxidation accompanies the diffusion of Au into the ceramics.

Surface oxygen artifacts on aluminum nitride

Aluminum nitride (AlN)is an increasingly important electronic ceramic with oxygen as an important bulk impurity. Quantitative microanalysis of oxygen to determine its precise distribution is a necessary step in characterization of the ceramic that may be complicated due to surface oxidation. AlN is thermodynamically unstable compared to the oxide (Al2O3) at room temperature in the presence of environmental oxygen or water and may thus be expected to form a thin, possibly passive oxide film similar to the oxide layer of pure aluminum metal. Such an oxide layer has been used to explain anomalies in oxygen quantification in AlN by neutron activation methods [1] but reflecteion high energy electron diffraction studies [2] failed to reveal either crystalline or amorphous oxide phases forming at room temperature.Electron diffraction techniques in the transmission electron microscope were used to examine thin AlN sections for possiblecrystalline surface layers. A ceramic AlN sample was prepared using conventional techniques for the preparation of thin foils with final thinning accomplished by ion milling.

Planar defects in AIN

Aluminum nitride has recently become the subject of much interest as a technologically useful ceramic. The mechanical strength, high thermal conductivity and large electrical resistivity and a relatively small thermal expansion coefficient, make this material extremely well suited as a semiconductor substrate material. AlN has the hexagonal, wurtzite structure rather than the cubic structure of the more common semiconductors. It is also a polar material. The characterization of microstructural defects in this material is obviously necessary to the understanding of the materials properties.In sintered AlN material, several different planar defects have previously been examined. Anti-phase boundaries (which produce the same configuration as basal twins in this structure) and stacking-faults have been identified in this material. A defect described as a “dome-like defect” has also been reported. The association of oxygen impurities with these extended defects has also been proposed. In this paper we report the observation of a defect (which may be the same as the “dome-like defect”) consisting of a flat, planar, basal fault and a curved, planar fault (rather than a spherical one) which join together to enclose a region of AlN, and separate it from the rest of the grain.

Characterisation of Aluminium Nitride Ceramic Substrates

Aluminium nitride (AlN) is currently under investigation as a substrate material for use in microcircuit applications in particular where high thermal conductivity is required. Three commercially available substrate materials have been characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The differences in thermal conductivity between the materials and also the difference from the theoretical thermal conductivity have been correlated to the presence of low thermal conductivity second phase regions between grains, defects within the crystal structure, the presence of oxygen impurities and poor sintering behaviour. The highest thermal conductivity substrate obtainable during this study was 140 W7m K. The substrates were identified as comprising hexagonal AIM having a wurtzite type structure. In addition, oxide and oxynitride phases were detected. The surface morphology of the substrates was also investigated, as it is the nature of the surface that will be of importance in determining the adhesion of applied films.

Microstructural characterization of AIN sintered with Y2O3

Aluminum nitride's high thermal but low electrical conductivity make it a potential ceramic packaging material. Processing history, however, can have significant effects on these properties and studies aimed at correlating them to the processing and microstructure are sparse.Pure AIN cannot be readily sintered without additives. Addition of Y2O3 significantly improves its densification behavior and the results presented here concern microstructural analysis of AIN sintered with Y2O3.High-purity AIN powder (containing 1.24% oxygen impurity) with 3 or 9 weight% Y2O3 added was sintered in N2 at 1850°C for 1 hour followed by a further 3 hours at 1900°C. Samples made using this treatment were &gt;95% dense. Specimens for microstructural investigation were prepared using standard techniques and examined using a JEOL 200 CX AEM.The general microstructure of all specimens consists of AIN grains with pockets of intergranular phase(s) located at triple points and some grain boundaries (FIG. 1).

Hot-Pressing of Shock-Activated Aluminum Nitride

Aluminum nitride powders were subjected to explosive shock treatment at 17 and 22 GPa and then hot-pressed. The ram pressure required to obtain equivalent densification behavior in hot-pressing was 16 MPa lower in shocked powders than in unshocked powders in the pressure regime in which deformation is attributed to dislocation motion. Transmission electron microscopy on hot-pressed samples confirmed that dislocation processes were active in both shocked and unshocked powders. The higher densification rates in shocked material are related to dynamic recrystallization which is promoted by the high dislocation densities and results in enhanced dislocation motion.

Sintering behaviour and properties of SiCAION ceramics

Silicon carbide (SiC), aluminium oxycarbide (AI2OC), and aluminium nitride (AlN) all have the same wurtzite crystal structure and can be processed so as to form SiCAION, an acronym for the solid solution. This paper describes processing of SiC-Al2OC ceramics by pressureless reactive sintering and gives mechanical property data on the same. Experiments showed that densification occurred by a liquid-phase sintering mechanism. Both alpha and beta SiC up to a particle size of 5μm were used to form the solid solution, boron additions were not necessary to promote densification, and densities greater than 97% of the theoretical were achieved by pressureless sintering. SiC-Al2OC ceramics, containing minor amounts of AIN, were fabricated from conventional raw materials. Phase identification by X-ray diffraction and metallography showed that the materials consisted of two phases: SiCAION and SiC. Mechanical property data were obtained on pressureless sintered and hot-pressed materials. Hot-pressed materials had room-temperature strengths in excess of 600 MPa, hardness greater than 25 G Pa, and fracture toughness greater than 4 M Pa m−1/2. Pressureless sintered bars had bend strengths in excess of 300 M Pa.

ALNx thin films produced by d.c. reactive magnetron sputtering

Aluminium nitride is the very promising thin film material for piezoelectric /2,3/ and microelectronic /4,5/ applications. The high microhardness of AlNX films, verified in our experiment, opens new possibilities of practical utilization of these films.