Thermal Conductivity Of AlN Research Articles

Nitride deep-ultraviolet light-emitting diodes with microlens array

We report on the fabrication of 280-nm AlGaN-based deep-ultraviolet light-emitting diodes (UV LEDs) on sapphire substrates with an integrated microlens array. Microlenses with a diameter of 12μm were fabricated on the sapphire substrate by resist thermal reflow and plasma dry etching. LED devices were flip-chip bonded on high thermal conductive AlN ceramic submounts to improve the thermal dissipation, and the emitted UV light was extracted through the sapphire substrates. With the integrated microlens array, a 55% enhancement in the output power at 20-mA dc driving was achieved compared with the same LED without microlens. The light extraction enhancement is the result of the reduced internal reflections of the light caused by the microlens surface profile.

Thermal conductivity of AlN and AlN–GaN thin films deposited on Si and GaAs substrates

Thermal properties of thin AlN, AlN–GaN films are analyzed. The investigated films are deposited on different substrates (Si and GaAs). The photothermal measuring method based on thermal wave propagation in layered structure in 3D geometry is used. A new method for experimental data analysis is proposed. The analysis is carried out after the transformation of measured dependences to the inverse space. Obtained results show that the thermal conductivity is higher for films deposited on GaAs substrates and for AlN–GaN films.

Microwave sintering of high-density, high thermal conductivity AlN

Microwave energy was used to sinter high thermal conductivity AlN ceramics (160–225 W/mK). The effects of sintering time, temperature, and amount of additive on phase composition, phase distribution, densification behavior, grain growth, and thermal conductivity were studied. The thermal conductivity of AlN was greatly improved by the addition of Y2O3, extended sintering time, and higher sintering temperatures. Thermal conductivity development in Y2O3-doped AlN showed two distinctive time regimes: (i) densification, where full densification, secondary phase formation, concentration and segregation, and rapid purification of AlN grains occur, accompanied by a large increase in thermal conductivity; (ii) postdensification, where grain growth and secondary phase sublimation/evaporation occur, yielding a further increase in thermal conductivity. Our results indicate that microwave sintering is a promising approach for synthesis of high thermal conductivity AlN ceramics.

Demonstration of an InGaN-based light-emitting diode on an AlN/sapphire template by metalorganic chemical vapor deposition

Structural, electrical, and optical properties of an InGaN-based light-emitting diode (LED) on an AlN/sapphire template have been studied and compared with the conventional LED properties on a sapphire substrate. In comparison to the LED on sapphire, the LED on AlN/sapphire template has shown better electrical and optical characteristics, which are due to a low threading dislocation density, high resistive, and thermal conductive AlN layer. An additional advantage is to grow a high-quality LED structure on an AlN/sapphire template without using low-temperature-grown GaN or an AlN buffer layer.

Second Phase Evolution in a Yttria-Sintered Aluminum Nitride Ceramic

One of the important features of the microstructure of yttria-sintered AlN ceramics is the second phase. The type, morphology, and distribution of the second phase influence the thermal conductivity. In the present research, the effects of sintering temperature, time and cooling rate on the second phase evolution were investigated. Different morphologies of second phase were detected, characterized and quantified using scanning electron microscopy and image analysis. Moreover, the thermal conductivity of the specimens representing different microstructures was measured. The major second phase present in the specimens was YAM. The second phase was present in isolated, interconnected, agglomerated morphologies the volume fractions of which change significantly by varying the sintering parameters. The total quantity of second phase(s) increases when the sintering temperature is increased. The direct effect of second phase morphology on the thermal conductivity of AlN is discussed.

Millennial Special Leading Papers on Ceramics in the 20<sup>th</sup> Century: the Best of JCerSJ Effects of Additives on Thermal Conductivity and Electrical Resistivity of SiC Ceramics

In the early 1980s, SiC ceramics with unique properties were developed by researchers in the laboratory of Hitachi, Ltd. These SiC ceramics have high thermal conductivity (>250W/mK) comparable to that of metals, as well as high electrical resistivity (about 4×1011Ωm) close to that of insulators such as alumina. This development was epoch-making, since at that time, no other materials exhibiting both high thermal conductivity and high electrical resistivity were known except BeO and the development of SiC ceramics exhibiting these properties could not be expected because SiC is naturally a semiconductor. In addition, as the thermal expansion coefficient of SiC ceramics (4×10-6/K) is nearly equal to that of Si, the application of this material in the field of semiconductors as a substrate and heat sink was anticipated.This material is commercially used at present as a heat sink for semiconductor lasers globally and commands a high share of the market.The period when this material was developed was the most active for the ceramics industry and development. Materials called “New Ceramics” or “Fine Ceramics” were attracting attention worldwide. The fact that high thermal conductivity and high electrical resistivity could be compatible in a popular material propelled ceramics researchers to try to find materials similar to these SiC ceramics. As a consequence, a remarkable increase of the thermal conductivity in AlN, which is more manageable than SiC for semiconductor packages, was subsequently achieved. The role of these SiC ceramics in promoting the development of these new materials is a major one.These SiC ceramics are also important from the point of view of grain boundary phenomena unique to ceramics research. The SiC is produced by sintering SiC powders with small amounts of BeO additives. High thermal conductivity and high electrical resistivity result from the change of the physical and chemical states of grains and grain boundaries caused by the addition of BeO. Because of the low solubility of Be into SiC grains, the purity of SiC grains is enhanced as the impurities are emitted to grain boundary regions. The resulting decrease of phonon scattering is thought to be the cause of the high thermal conductivity. At the same time, the low solubility of Be into SiC grains results in a low carrier concentration in SiC grains and the formation of high potential barriers for the carriers at the grain boundaries. This is the reason for the high electrical resistivity. ZnO varistor is an example of “grain boundary controlled ceramics” and the varistor property of SiC ceramics has also been recognized. The dramatic changes of grain boundary characteristics exhibited by these SiC ceramics have led to the recognition of the importance of grain boundary control. Technological advances for grain boundary analysis and control, including chemical composition distribution analysis and direct measurement of electrical properties at grain boundaries, were hastened. SiC contributed to these advances.Many papers have been written on these SiC ceramics. This paper details the effects of additives on thermal conductivity and electrical resistivity. The characteristics of SiC ceramics change markedly depending on the type of chemical additive. Of all the additives, only BeO results in anomalous thermal conductivity and electrical resistivity of SiC ceramics. This is due to the low solubility of Be into SiC grains. These are essential properties of SiC ceramics. This paper, describing these properties, deserves to be considered as one of “the leading papers on ceramics of the 20th century.”SiC ceramics with high thermal conductivity and high electrical resistivity are said to be the product of “serendipity.” The effect of BeO addition was discovered in the course of finding effective additives to develop SiC ceramics

The effect of carbon coating of AIN powder on sintering behavior and thermal conductivity

High thermal conductive AlN ceramics doped with Y2O3 were produced by sintering the powders obtained after applying a carbon coating to the surface of AlN powder grains. During sintering at 1800°C for 1 hour, the carbon reacts with the surface of the AlN grains by carbothermal-reduction of Al2O3, and also with the Al2Y4O9 intermediate phase to form AlN, Y2O3 and CO. By adding 0.56 mass% of carbon, almost all the Al2Y4O9 is reacted and the thermal conductivity increases from 184 W/(m · K) to 224 W/(m · K). Further carbon addition decreases the thermal conductivity and also the final sintered density.

Development of Glass Frit Free Metallization Systems for AIN

Currently only glass bonding thick film conductor systems are commercially available for metallizing AlN-ceramic. The glass phase formed between metallization and ceramic impairs the high thermal conductivity of AlN. A new glass frit free metallization system has been developed utilizing the bonding mechanism of active brazing to provide the adhesion of metallization onto the ceramic. Aspects of paste preparation range from the derivation of the metallic powder to the selection of an appropriate printing vehicle which must decompose completely during the firing process under an inert atmosphere. The adhesion strength of the new paste system with the alternative bonding mechanism has been evaluated and contrasted with that of standard thick film pastes.

Bonding mechanism and stress distribution of a glass frit free thick film metallization for AlN-ceramic

Typical thick film pastes applied for the metallization of AlN-ceramics are glass bonding systems. The glass phase responsible for adhesion onto the ceramic unfortunately also acts as a heat barrier and impairs the excellent thermal conductivity of AlN. A new glass frit free conductor paste has been especially developed for the metallization of AlN. A numerical analysis of the stress distribution within the metallized ceramic induced by a continuous as well as a pulsed mode operating heat source has been conducted for this new metallization paste and, for comparison purpose, also for a standard thick film paste by means of a finite element program. In order to determine the physical property data of the phases occurring at the interface between metallization and substrate required for numerical simulation the relevant intermetallic samples have been synthesized.

ナイロン被覆ＡｌＮ粉体の前処理が熱伝導率に及ぼす効果について

AlN powder is thermodynamically unstable in aqueous systems. Polyamide (Nylon) coating on the surface of an AlN particle can confer a great degree of water-resistability on the AlN powder. In this study, some experimental conditions in the Nylon coating process were varied and examined in relationship to thermal conductivity of the sintered AlN bodies. Thermal conductivity of a sintered body made from Nylon coated AlN powder was under the influence of coupling agents. The coupling agent containing silicon was very effective in decreasing thermal conductivity of the sintered AlN body. Al5Y3O12 was detected by XRD analysis in the low thermal conductive AlN body.

ChemInform Abstract: Specimen Size Effect of the Thermal Diffusivity/Conductivity of Aluminum Nitride.

AbstractThe thermal diffusivity and thermal conductivity of AlN, measured by the laser‐flash technique, decrease with decreasing thickness of the specimen.

Thermal conductivity, heat capacity, and thermal diffusivity of selected commercial AlN substrates

The thermal transport properties of four commercially available AlN substrates have been investigated using a combination of steady-state and transient techniques. Measurements of thermal conductivity using a guarded longitudinal heat flow apparatus are in good agreement with published room temperature data (in the range 130–170 W · m−1 · K−1). Laser flash diffusivity measurements combined with heat capacity data yielded anomalously low results. This was determined to be an experimental effect for which a method of correction is presented. Low-temperature measurements of thermal conductivity and heat capacity are used to probe the mechanisms that limit the thermal conductivity in AlN.

Ceramic Materials for Electronic Packaging

The paper reviews ceramic materials that are used or can be used in electronic packaging. Main attention is given in relatively new packaging materials such as highly thermal conductive AlN and SiC (BeO-doped) or low-firing cordierite and spodumene glass-ceramics. Application of sol-gel processes in preparation of ceramic powders is discussed.

Metallization Issues in Advanced Ceramic Substrates:- Microstructural. Microchemistry and Thermal Conductivity in Aln

AbstractMicrochemical and microstructural study has been carried out on the tungsten-aluminum nitride (W-AlN) thick film metallization interface. A reaction has been found to occur with the formation of precipitates at AlN grain boundaries and also within the AlN grains; a thin crystalline grain boundary film was also observed. The interface morphology and chemistry is compared to the molybdenum/manganese-aluminum nitride (MoMn-AlN) interface. The effects of morphology and microchemical variations upon thermal conductivity are discussed.

Chemical Etching Properties of Highly Thermal Conductive AlN Ceramics for Electroless Ni‐P Metallization

The adhesion strength between ceramics and electroless plated Ni‐P film was investigated from the viewpoint of the chemical etching behavior. It was confirmed that chemical etching proceeds in two stages. The first etching stage is the selective dissolution of the Ca atoms, which are added as a sintering aid. Since the Ca atoms are mainly concentrated at the three grain junctions of triple points, the selective etching preferably proceeds along the triple points of the grains. In this initial etching stage, the adhesion strength of the Ni‐P plated film increases with an increase in the amount of the dissolved substrate. The deposition of electroless Ni‐P plating at the triple points makes effective anchors of metal film against the substrate. At the second etching stage, the grains also begin to be etched, and thus, the spaces between the grains are widened. In this etching stage, the adhesion strength gradually decreases with an increase in the dissolved amount of the substrate. In conclusion, it is very important to consider the etching morphology and mechanism, including the process of substrate formation (i.e., sintering aid in the substrate) in order to get a higher adhesion strength for the electroless plating metallization.