Conductivity Of Aluminum Nitride Ceramics Research Articles

High-Thermal-Conductivity AlN Ceramics Prepared from Octyltrichlorosilane-Modified AlN Powder

Aluminum nitride has been widely used as heat-management material for large-scale integrated circuits and semiconductor packages because of its excellent insulation, high thermal conductivity, low dielectric constant and loss, similar expansion coefficient to that of silicon, and non-toxicity. However, the increase of oxygen content caused by the hydration of aluminum nitride powder during storage often decreases the thermal conductivity of aluminum nitride ceramics. In this work, we propose an approach for preparing high-thermal-conductivity AlN ceramics via octyltrichlorosilane-modified AlN powder. The octyltrichlorosilane reacted with the hydroxyl group on the surface of the AlN powder forming a siloxane protective layer. The protective layer not only enhanced the water contact angle of AlN powder from 34.8° to 151°, but also ensured the phase of AlN powder did not change in the distilled water at 25 °C for 72 h. High-thermal-conductivity AlN ceramics up to 186 W·m−1·K−1 were successfully prepared based on the modified AlN powder which had been stored for one year. This work provides a simple, effective, and practical method for the stable preparation of high-thermal-conductivity AlN ceramics.

The quantitative investigation of the lattice oxygen and grain edge oxygen on the thermal conductivity of aluminum nitride ceramics

The good thermal conductivity of AlN is essential for insulation and high heat dissipation applications. However, the influence of oxygen impurities at various locations (the lattice oxygen and grain edge oxygen) on the thermal resistivity of AlN ceramics is unclear. In this study, AlN ceramics with various oxygen distributions are prepared by different methods, and the oxygen contents of different regions are distinguished. The results indicate that the lattice oxygen is the main factor affecting thermal resistivity. Meanwhile, high-temperature annealing and pre-sintering processes can lower the lattice oxygen content from 0.061 wt% to 0.038 wt% and 0.036 wt%, respectively. Additionally, when grain edge phase volume is less than 4 vol%, it does not contribute significantly to thermal resistivity. The main formation of thermal resistance changes from phonon-defect scattering to phonon-phonon scattering with increasing temperature. These results may be informative for the microstructure design of AlN ceramics with high thermal conductivity.

Influence of Microstructure and Impurities on Thermal Conductivity of Aluminium Nitride Ceramics

Abstract The microstructure of AlN ceramics, which were pressureless sintered with CaO and CaF2 as additives, was modified via an annealing process. The thermal conductivity of these samples was measured and correlated with the microstructure changes. The influence of the microstructural elements, especially content and distribution of secondary phases, is described and quantitatively related to mixture models from literature for a full understanding of the relationships between microstructure, impurity content and thermal conductivity. The main result of the investigation is that the microstructural influence on thermal conductivity is limited to at maximum 41 W/m · K. The increase of the intrinsic thermal conductivity, due to loss of impurities especially oxygen during the beginning of the annealing process, is the main effect influencing thermal conductivity of sintered samples.

Effects of adding Y(NO3)3·6H2O on the phase change behavior and thermal conductivity of Aluminum Nitride ceramics

Effects of adding Y(NO3)3·6H2O on the phase change behavior and thermal conductivity of Aluminum Nitride ceramics

Texture Control and Thermal Conductivity of Aluminum Nitride Ceramics

Texture Control and Thermal Conductivity of Aluminum Nitride Ceramics

Processing and Characterization of Aluminum Nitride Ceramics for High Thermal Conductivity

The effects of sintering additives, microstructure, and morphology of second phase on the thermal conductivity of aluminum nitride ceramics are discussed in this review. The thermal conductivity of AlN is highly dependent on the types and amount of sintering additives, second phase morphology and microstructure. The morphology of second phase in AlN ceramics could be controlled by changing the cooling rate. The amount of second phase was able to be minimized by using the transient sintering additives. The thermal conductivity of AlN could be enhanced with the inclusion of the transient sintering additives. The thermal conductivity of AlN ceramics was evaluated by Raman spectroscopy. High temperature AC impedance studies were conducted to characterize the electrical conduction mechanism of AlN ceramics.

Investigation on Thermal Conductivity of Aluminum Nitride Ceramics by FT‐Raman Spectroscopy

FT‐Raman spectroscopy was used to characterize the thermal conductivity of yttria‐doped polycrystalline aluminum nitride (AlN) ceramics. Specimens with different thermal conductivity were prepared using sintering additives of different size, content, and mixing method. The broadening of the Raman mode is caused by point defects and impurities, which affect the thermal conductivity of the AlN grains (lattice thermal conductivity). The width of the Raman line was related to the c‐axis lattice parameter contraction, which was caused by aluminum vacancies produced by various defects. A correlation is suggested between the width of the E2 (high) phonon mode and the lattice thermal conductivity of AlN ceramics.

Effect of High Pressure Annealing on Microstructure and Thermal Conductivity of Aluminum Nitride Ceramics

The thermal annealing is an effective means of structural adjustment and performance improvement for AlN ceramics.AlN ceramics prepared at high pressure with Y2O3 as sintering additive,were annealed at high-pressure(5.0GPa) in a chinese cubic anvil ultra high-pressure and high-temperature device.The effects of high pressure annealing on microstructure and thermal conductivity of aluminum nitride ceramics were studied.The results show that the grain size of the AlN ceramics annealed at 5.0GPa and 970℃ for 2h is significantly increased,the actual crystal morphology is realistic and the second phases are almost present at the grain boundaries or triple pockets compared with the samples before annealing at high pressure.Its thermal conductivity reaches 173.2W/(m·K),which is 2.2 times of the samples without heat annealing at high pressure.However,while the annealing time is extended to the 4h,the pore size of AlN ceramics is increased with anti-densification.And the thermal conductivity of AlN ceramics annealed at 5.0GPa and 970℃ for 4h is reduced to 80.9W/(m·K).

Non-Oxide Ceramic Nanocomposites with Multifunctionality

Two types of Aluminum nitride (AlN) based ceramic nanocomposite with multifunctionality were investigated to improve machinability or electrical conductivity of AlN ceramics with high thermal conductivity. The AlN/BN nanocomposite was fabricated by hot-pressing AlN-BN composite powder, which was prepared by reducing and heating AlN particles containing a mixture of boric acid, urea and carbon. The nanocomposite containing 20 vol.% BN showed high strength, good machinability and relatively high thermal conductivity. On the other hand, the sintered AlN ceramics with CeO2 as an additive indicated high thermal conductivity and electric conductivity which is possible for electric discharge machining.

Improving thermal conductivity of aluminum nitride ceramics by refining microstructure

A reheating process was developed to improve the thermal conductivity of low-temperature sintered aluminum nitride ceramics with Dy 2O 3, Li 2O and CaO as additives. After the period of reheating, the amount of secondary phase was reduced to a very low level through carbothermal reduction. Microstructural investigation showed that the better the microstructure, the higher the thermal conductivity.

Effects of binary additives B2O3–Y2O3 on the microstructure and thermal conductivity of aluminum nitride ceramics

Aluminum nitride (AIN) ceramics, with binary additives B2O3-Y2O3, were sintered at temperatures from 1700 to 1850 °C. The microstructure and sintering characteristics were studied by XRD, HREM, SEM and TEM/EDS, which showed that Y2O3 gave different yttrium aluminates through the reaction with Al2O3 under different conditions. With the increase of sintering temperature, the yttrium-to-aluminum atomic ratio Y/Al decreased in the secondary phases of the sintered bodies. It was discovered that B2O3 could dissolve in the yttrium aluminates, forming some ordered structure with a superlattice. After sintering at 1850 °C for 4 h, a specimen with a fine microstructure and a thermal conductivity of 190 W m−1 K−1 was obtained.

Radiation-induced electrical conductivity in aluminium nitride ceramic

The electrical conductivity of aluminium nitride ceramics, doped with 8 wt% Y 3O 3 and obtained from fine raw powders synthesized in plasma, was measured with and without gamma-neutron irradiation (the maximum fast neutron flux was 3×10 15 n/m 2 s and in the gamma-dose rate range of 10 3–10 6 Gy/h) in the temperature range of 40–400°C. The electrical conductivity at room temperature was 10 −12 S/m and temperature-induced increase of conductivity has an activation energy of 1.06 eV at a temperature range of above 160°C. Radiation-induced conductivity obeys the usual power law dependence on gamma-ray dose rate. The electrical conductivity at high dose rate is less than 10 −6 S/m and is little dependent on temperature.

Effect of oxygen on the thermal conductivity of aluminium nitride ceramics

Sintered aluminium nitride is a good thermal conductor which is one of the principal properties of this ceramic. Previous studies have shown that the thermal flux transfer depends strongly on the oxygen contained in the crystal lattice, and on the powder surface. An AlN ceramic containing YF 3 as additive has been fabricated by tape-casting and sintering. This study shows that binder burnout must be carried out in air at 550 °C or in nitrogen at 650 °C. Sublimation of YF 3 to YOF, and formation of yttrium aluminate occurred during calcination. The amount of YF 3 present, thermal treatment duration and the rate of temperature increase and decrease affected oxygen diffusion in the nitride lattice. However, there is no correlation between thermal conductivity and oxygen content and microstructural characteristics are more influential than total oxygen content up to a thermal conductivity value of 220 W/m K.

Influence of Powder Characteristics on Sintering Process and Thermal Conductivity of Aluminum Nitride Ceramics

The sinterability and thermal conductivity of Y203 doped AlN powders with diverse specific surface areas (42-2.9m 2 g -1 ) and oxygen contents (0.2-2 mass%) were evaluated. It was found that sintering of fine powders induces the densification at lower processing temperatures, and for raw AlN powders with specific surface area larger than 20m 2 g -1 and oxygen content higher than 1.1 mass%, densified specimens were obtained by sintering at 1650°C for 4h. However, the resultant thermal conductivity of AlN specimens fabricated from fine powders was extremely lower than the theoretical thermal conductivity of AlN, at a level of 80 Wm -1 K -1 . The deterioration of the thermal conductivity has been attributed to the agglomeration of primary particles, and to subsequent formation of oxygen-related defect in grown AlN grains occurring at an early stage of sintering.

Effect of grain boundary phase on the thermal conductivity of aluminium nitride ceramics

AIN with high thermal conductivity was fabricated by pressureless sintering with Y2O3 as the sintering aid. The thermal conductivity was observed to increase with sintering time (up to 8 h) at 1810 °C. The distribution of the sintering aid was identified as one of the major factors influencing the thermal conductivity in AIN. Non-uniform distribution of the grain boundary phase was found to be associated with a significant amount of porosity, resulting in the enhancement of phonon scattering and thereby lowering the thermal conductivity.

The conductivity of aluminum nitride ceramics

Based on the analysis of the experimental behavior of the conductivity of highly dispersed aluminum nitride ceramics on temperature and frequency, conclusions are drawn about the existence in polycrystalline AIN of electromigration hopping mechanisms. At low temperatures and for high frequencies, the conductivity can be described within the framework of a two-point model, but as the temperature increases, or as the frequency decreases, a transition is observed through multiple jumps. The electromigration activation mechanisms dominate at temperatures higher than 370 K.

Influence of the sintering additives on the phase composition and the thermal conductivity of aluminium nitride ceramics

Abstract Polycrystalline AIN ceramics have been fabricated with Y2O3, Y2O3 + CaO, CaF2 and CaC2 as additives. Using electron microscopy and microprobe analysis, several microstructural models describing the mechanism of formation of secondary phases have been proposed. The effect of the additives on the thermal conductivity of AIN has been correlated with the results of the microstructural analysis. The addition of Y2O3 has been found to result in a thermal conductivity as high as 117 W m−1 K−1 at room temperature.

ＡｌＮ‐ＹＦ３系高熱伝導性セラミックス

Improvement has been made on the thermal conductivity of aluminum nitride ceramics which is one of the hopeful candidates of substrates for semiconductor devices. The thermal conductivity has been thought to be reduced by the presence of some impurities such as oxygen and transition metal ions in the ceramics. However, much improvement was made on the thermal conductivity of aluminum nitride ceramics by using a suitable amount of yttrium oxide and calcium oxide as a sintering aid. Addition of yttrium fluoride has also brought on faily good results for improvement of its thermal conductivity.