Formula AlN Melting point 2,200 °C Boiling point 2,517 °C | Molar mass 40.9882 g/mol Density 3.26 g/cm³ | |
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Appearance white to pale-yellow solid | ||
Aluminium nitride
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.
Contents
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 relatively high thermal conductivity for an electrically 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 in the presence of gaseous nitrogen or ammonia 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