Aluminium nitride

For the three-letter acronym, see ALN (disambiguation).

Aluminium nitride

Names
Other names Aluminium nitride
Identifiers
CAS Number	24304-00-5 Y
ChEBI	CHEBI:50884 Y
ChemSpider	81668 Y
EC Number	246-140-8
Jmol 3D model	Interactive image
PubChem	90455
RTECS number	BD1055000
InChI InChI=1S/Al.N Y Key: PIGFYZPCRLYGLF-UHFFFAOYSA-N Y InChI=1/Al.N/rAlN/c1-2 Key: PIGFYZPCRLYGLF-PXKYIXAJAH
SMILES [Al]#N
Properties
Chemical formula	AlN
Molar mass	40.9882 g/mol
Appearance	white to pale-yellow solid
Density	3.260 g/cm3
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 (powder), insoluble (monocrystalline)
Solubility	reacts in ethanol
Band gap	6.015 eV (direct)
Electron mobility	~300 cm2/(V·s)
Thermal conductivity	285 W/(m·K)
Refractive index (nD)	1.9–2.2
Structure
Crystal structure	Wurtzite
Space group	C6v4-P63mc
Coordination geometry	Tetrahedral
Thermochemistry
Specific heat capacity (C)	30.1 J/mol K
Std molar entropy (So298)	20.2 J/mol K
Std enthalpy of formation (ΔfHo298)	318 kJ/mol
Gibbs free energy (ΔfG˚)	287.4 kJ/mol
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Aluminium nitride (AlN) is a nitride of aluminium. Its wurtzite phase (w-AlN) is a wide band gap (6.01-6.05 eV at room temperature) semiconductor material, giving it potential application for deep ultraviolet optoelectronics.

History

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

Aluminium 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. Aluminium 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. Aluminium nitride is resistant to attack from most molten salts, including chlorides and cryolite.

Manufacture

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.

Applications

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, which is called a thin film bulk acoustic resonator (FBAR). This is a MEMS device that uses aluminium nitride sandwiched between two metal layers.

Aluminium 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. AlN nanotubes as inorganic quasi-one-dimensional nanotubes, which are isoelectronic with carbon nanotubes, have been suggested as chemical sensors for toxic gases.

Currently there is much research into developing light-emitting diodes to operate in the ultraviolet using gallium nitride based semiconductors and, using the alloy aluminium gallium nitride, wavelengths as short as 250 nm have been achieved. In May 2006, an inefficient AlN LED emission at 210 nm was reported.

There are also multiple research efforts in industry and academia to use aluminum nitride in piezoelectric MEMS applications. These include resonators, gyroscopes and microphones.

Among the applications of AlN are

• opto-electronics,
• 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.

See also

• Boron nitride
• Aluminium phosphide
• Indium nitride
• Aluminium oxynitride