Aluminum Nitride (Al N), a covalently bonded ceramic is synthesized from abundantly available elements Al and N. The ceramic does not occur naturally. AlN has a Wurtzite crystal structure and is stable in inert atmospheres at temperatures in excess of 2000°C. It exhibits high thermal conductivity property while remaining a strong dielectric. This unusual combination of properties is what makes Al N a critical advanced materials for many future applications in Optics, lighting, electronics and green environmental technologies.

Surmet is the only supplier in the US with the ability to synthesize, process and treat the AlN powder to the required surface area and particle size characteristics. Surmet stands alone also the only company in the US with capacity to synthesize tonnage quantities of high quality AlN powder. Surmet is capable of fabricating sintered Al N components in complex shapes for electronic and industrial customers. With over 75,000 square feet of manufacturing and R&D space, Surmet's Buffalo, NY facility has been a leading supplier of high purity Aluminum Nitride to international customers for over 20 years.

Surmet's Aluminum Nitride (AlN) Manufacturing Capabilities:

Surmet's AlN Powder:

For over twenty years Surmet's Buffalo facility with over 75,000 square feet of well-equipped manufacturing and R&D capabilities, has been a supplier of high purity AlN powder to its customers worldwide. Surmet is now one of only a handful of companies globally that has the capacity to synthesize high quality AlN powder in tonnage quantities and its Buffalo operations is the only one in the US to synthesize, process and treat the AlN powder to the required surface and particle size characteristics.

Powder Features:

  • Competitive Cost
  • Suitable for tape making, sintering, hot pressing or as thermally conductive fillers in polymers.
  • High chemical purity with low oxygen (<1.5%) and carbon (<0.15%).
  • Compositionally homogenous for high thermal conductivity.
  • Powders are not agglomerated, facilitating easier processing.
  • Surmet produces AlN using both direct nitridation and carbothermal reduction methods. Multiple grades are available for best economics for various applications.
  • Water-resistant "WR" grade of powders available.

Sintered AlN Products:

In addition to powder production, Surmet is capable of producing and supplying sintered AlN products. In order to meet the growing demand for the thermal management applications, Surmet is developing copper metalized Aluminum Nitride tapes, net-shaped complex 3-D device structures and composites. Advanced products such as AlN micro-channel reactors and AlN substrates with novel embedded metallic structures are also under development at Surmet.

Advantages of AlN:

  • Uniform microstructure
  • High thermal conductivity* (70-180 Wm-1K-1)
  • High electrical resistivity
  • Thermal Expansion Coefficient close to that of Silicon
  • Resistance to corrosion and erosion
  • Excellent thermal shock resistance
  • Chemically stable up to 980°C in Hydrogen and Carbon dioxide atmospheres, and in air up to 1380°C (surface oxidation typically occurs around 780°C and the oxide layer at the surface protects the bulk up to 1380°C).

*Tailored via processing conditions and additives.

Surmet's Aluminum Nitride (AlN) Analytical Capabilities:

X-Ray Diffraction (XRD):

XRD is an important tool for characterizing powders and bulk samples. XRD analysis is typically used to find out composition, phase, crystal structure, lattice parameters. Our engineers and scientists who are experts in materials characterization utilize XRD for AlN quality control as well as developmental work.

Furnaces:

Surmet has multiple vacuum, controlled atmosphere and air furnaces that are capable of synthesizing and and heat treating AlN in tonnage quantities. Some of the furnaces are designed and custom built for manufacturing and R&D operations.

Particle size & distribution:

PSD is also an important tool for quality control of powder production. Surmet's PSD is capable of measuring powders all the way from few nanometers to hundreds of microns. PSD is extensively used for AlN powder production and developmental work.

Microscopy:

Surmet's optical microscopy lab has several stereomicroscopes and compound microscope that have been very useful for AlN production as well as other R&D work.

Why AlN is a preferred choice for substrate and thermal management applications:

Aluminum Nitride is a unique ceramic material that is highly thermally conductive as well as electrically insulating. AlN, cubic-BN and BeO are the only ceramic materials that possess high thermal conductivity. Though BeO and c-BN conducts better than AlN, use of BeO is restricted in many applications because of its toxicity and c-BN is very difficult to produce. Moreover, thermal expansion coefficient of AlN is closely matched to Silicon over a wide range of temperatures.

Intrinsic (single crystals) thermal conductivities (Wm-1K-1) of various materials.1-4

Thermal conductivity basics:

Thermal conductivity (k) is the ability of a material to transport thermal energy due to temperature gradient. Steady state k is a proportionality constant of the heat flux (time rate of heat flow per unit area) through a solid and the imposed temperature gradient. In dielectric materials, heat is transferred in the form of lattice vibrations (phonons) also known as phonon conduction. In single crystals, this transfer is limited by the energy loss resulting from anharmonic phonon-phonon scattering also known as Umklapp Scattering. Materials with simple structure, covalent bonding and low atomic mass generally possess high thermal conductivity.

Anything that impinges on the phonon propagation through the solid has negative influence on thermal conductivity of the solid. Temperature, impurities, pore size and distribution, grain size, compositional homogeneity and orientation affect mean free path for phonon conduction. This is the reason why typical k values of polycrystalline materials are normally significantly lower than the intrinsic numbers.

Theoretical thermal conductivity of AlN is about 280 Wm-1K-1; however, typical values for polycrystalline AlN are significantly lower and vary depending upon the processing conditions and purity. Oxygen content is known to be one of the major contributors for this variation and lower values. Presence of oxygen in nitrogen sites creates an aluminum vacancy. This vacancy results in a considerable difference in mass between the original site occupant (i.e. Aluminum) and the new site occupant (vacancy) leading to increased scattering cross section thus to decrease thermal conductivity.

1. G.A. Slack, Thermal Conductivity of Pure and Impure Silicon, Silicon Carbide, and Diamond, J. Appl. Phys. 35 (1964) 3460.
2. G.A. Slack, R.A. Tanzilli, R.O. Pohl and J.W. Vandersande, The Intrinsic Thermal Conductivity of AlN, J. Phys. Chem. Solids 48 (1987) 641.
3. E.K. Sichel, and J.I. Pankove, Thermal Conductivity of GaN, 25 - 360 K, J. Phys. Chem. Solids 38 (1977) 330.
4. G.A. Slack and S.B. Austerman, Thermal Conductivity of BeO Single Crystals, J. Appl. Phys. 42 (1971) 4713.