|Jmol-3D images||Image 1|
|Molar mass||40.9882 g/mol|
|Appearance||white to pale-yellow solid|
|Melting point||2,200 °C (3,990 °F; 2,470 K)|
|Boiling point||2,517 °C (4,563 °F; 2,790 K) decomposes|
|Solubility in water||reacts|
|Band gap||6.2 eV (direct)|
|Electron mobility||~300 cm2/(V·s)|
|Thermal conductivity||285 W/(m·K)|
|Refractive index (nD)||1.9–2.2|
heat capacity C
|30.1 J/mol K|
|20.2 J/mol K|
|Std enthalpy of
|Gibbs free energy ΔG||287.4 kJ/mol|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
AlN was first synthesized in 1877, but it was not until the middle of the 1980s that its potential for application in microelectronics was realized due to its relative high thermal conductivity for an electrical insulating ceramic (70–210 W·m−1·K−1 for polycrystalline material, and as high as 285 W·m−1·K−1 for single crystals).
Stability and chemical properties
Aluminum nitride is stable at high temperatures in inert atmospheres and melts at 2800 °C. In a vacuum, AlN decomposes at ~1800 °C. In the air, surface oxidation occurs above 700 °C, and even at room temperature, surface oxide layers of 5-10 nm have been detected. This oxide layer protects the material up to 1370 °C. Above this temperature bulk oxidation occurs. Aluminum nitride is stable in hydrogen and carbon dioxide atmospheres up to 980 °C.
The material dissolves slowly in mineral acids through grain boundary attack, and in strong alkalies through attack on the aluminium nitride grains. The material hydrolyzes slowly in water. Aluminum nitride is resistant to attack from most molten salts, including chlorides and cryolite.
AlN is synthesized by the carbothermal reduction of aluminium oxide or by direct nitridation of aluminium. The use of sintering aids, such as Y2O3 or CaO, and hot pressing is required to produce a dense technical grade material.
Epitaxially grown thin film crystalline aluminium nitride is used for surface acoustic wave sensors (SAWs) deposited on silicon wafers because of AlN's piezoelectric properties. One application is an RF filter which is widely used in mobile phones, including called a thin film bulk acoustic resonator (FBAR). This is a MEMS device that uses aluminium nitride sandwiched between two metal layers.
Aluminum nitride is also used to build piezoelectric micromachined ultrasound transducers, which emit and receive ultrasound and which can be used for in-air rangefinding over distances of up to a meter.
Metallization methods are available to allow AlN to be used in electronics applications similar to those of alumina and beryllium oxide.
Currently there is much research into developing light-emitting diodes to operate in the ultraviolet using the gallium nitride based semiconductors and, using the alloy aluminum gallium nitride, wavelengths as short as 250 nm have been achieved. In May 2006, an inefficient AlN LED emission at 210 nm has been reported.
Among the applications of AlN are
- dielectric layers in optical storage media,
- electronic substrates, chip carriers where high thermal conductivity is essential,
- military applications,
- as a crucible to grow crystals of gallium arsenide,
- steel and semiconductor manufacturing.
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