What is Aluminum Nitride (AlN) Technology?

Aluminum nitride (AlN) is a versatile IIIA-nitride, ceramic material known for its high thermal conductivity, electrical insulation, and piezoelectric properties. It is one of the few materials that have both wide and direct bandgap (almost twice that of SiC and GaN) and large thermal conductivity. Furthermore, it is compatible with the complementary metal oxide semiconductor (CMOS) technology. These properties make it attractive for applications in high speed and high power communication systems. Beyond, the thermal and electrical properties, AlN offers high mechanical strength, high melting point and resistance to corrosion, thus making it suitable for harsh environments.

Aluminum nitride is stable at room temperature in inert atmospheres and melts at about 2200 °C, in vacuum it decomposes at ~1800 °C. Surface oxidation in air occurs above 700 °C and even at room temperature, surface oxide layers of 5-10 nm thickness have been detected. This oxide layer provide protection to the material up to 1370 °C. Above this temperature bulk oxidation occurs. It is stable in hydrogen and carbon-dioxide atmospheres up to 980 °C. AlN dissolves slowly in mineral acids through grain-boundary attack and in strong alkalies through attack on the aluminium-nitride grains.   

Synthesis of Aluminum Nitride (AlN)

Aluminum Nitride is synthesized by the carbothermal reduction of alumina in the presence of gaseous nitrogen or ammonia or by direct nitridation of aluminum. It has a density of 3.26 gcm3, and although it does not melt, but dissociates above 2500 oC at atmospheric pressure. Sintering aids, such as Y2O3 or Cao, and hot pressing are used to produce a dense technical-grade material. The thin films of AlN can be prepared by Chemical Vapor Deposition  (CVD) method in which the aluminum containing precursors such as trimethylaluminum and nitrogen gas are introduced into a reaction chamber at high temperatures. It allows for the deposition of AlN thin films with excellent uniformity and purity, thus making them suitable for semiconductor applications and coating.  

Aluminium Nitride Powder 

Crystal Structure 

Aluminum Nitride has a hexagonal wurtzite crystal structure. The wurtzite structure is characterized by specific arrangement of atoms, the atoms form a hexagonal arrangement along the a-axis, while along the c-axis, the atoms are stacked in layers. The atoms are arranged in two interpenetrating hexagonal close-packed sublattices, where one lattice is formed by Aluminum, and the second sublattice is formed by Nitrogen. Each Aluminum atom is bonded to four neighboring atoms in tetrahedral configuration with the covalent bonding in between them. 

Aluminium Nitride crystal with a diameter of 45 mm 

The half-filled orbitals of Al and N atoms contribute one electron, resulting in the formation of three equivalent Al-N bonds known as B1 bonds, with bond length of approximately 0.1885nm, and the fully filled orbitals of N atoms form a B2 bond parallel to the c-axis direction, with bond length of about 0.1917 nm.  

Crystal structure of Aluminium Nitride and the wurtzite structure of the AlN crystal  

Properties

Aluminum Nitride (AlN) is a versatile material known for its exceptional mechanical, thermal, and electrical properties, thus making it suitable for a wide range of applications in various filed. It has a high bandgap of approximately 6 eV at room temperature and a dielectric strength of 17 volts/mils. At room temperature, it has a density of 3.26 gm/cm3 and zero porosity. AlN exhibits high structural integrity and rigidity, it has an elastic modulus of 330 GPa and compressive strength of 2100 MPa. Naturally, AlN is an insulator but doping improves its electrical conductivity. These properties along with its low dissipation factor and high volume resistivity are the reason for its growing popularity in various sectors like electronics, optics, and material science.  

Mechanical Properties

Thermal Properties

Electrical Properties

Applications of Aluminum Nitride (AlN) Semiconductor Materials

Aluminum Nitride is a versatile ceramic material known for its exceptional properties. One of its notable characteristics is the high thermal conductivity (170 – 200 W/mK), which makes it an excellent material for heat sinks and heat spreaders in electronic devices such as transistors, integrated circuits and high power diodes. It is also used as a substrate material in electronics, especially in high-power and high-frequency devices due to its strong insulation. This combination of high thermal conductivity and electrical insulation it is widely used in packaging in LED lighting, laser diodes, and RF components. Due to its low dielectric loss, high intrinsic signal-to-noise ratio, high rigidity, and high figure of material for sensitivity, Aluminum Nitride is also used in Piezoelectric MEMS based microphones and in aeroacoustics applications.