7 September 2001 Aluminum nitride coatings by reactive pulsed dc magnetron sputtering
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Abstract
Aluminum nitride (AIN) has the potential to meet the requirements of hypersonic-seeker windows that operate in the visible to mid-wave infrared and rf frequencies. With dielectric properties and thermal-shock resistance similar to those of hot-isostatic-pressed silicon nitride, but with a thermal conductivity eight times higher, AIN is a primary candidate for high-power-microwave windows and for high- speed radomes. The true potential of AIN has yet to be demonstrated because single crystals of AIN with purities high enough to be considered intrinsic have never been fabricated. Carbon and oxygen are the two most significant impurities and are the most difficult to eliminate. Impurities and voids present in AIN fabricated from nanocrystalline powders degrade the thermal-mechanical properties and produce optical scatter that limits the useful wavelength range. A large amount of scatter could be removed by eliminating the carbon and oxygen impurities and by reducing the crystallite size in polycrystalline AIN to sub-micron and nanometer sizes. Oxygen incorporation has yet to be avoided using conventional powder processing techniques because the newly formed AIN powders react spontaneously with trace amounts of oxygen. Over the past 50 years, the solid-state-chemistry approach has been used by several research groups and has produced useful material for electronic heat-sink applications but never the high- optical-quality material needed for 2-mm-thick missile domes and windows. This suggests that research aimed at producing high-quality-microcrystalline-AIN coatings and freestanding films would be productive. This paper will present results for films of AIN deposited using reactive asymmetric- bipolar-pulsed-dc-magnetron sputtering.
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Mark B. Moran, Mark B. Moran, Linda F. Johnson, Linda F. Johnson, } "Aluminum nitride coatings by reactive pulsed dc magnetron sputtering", Proc. SPIE 4375, Window and Dome Technologies and Materials VII, (7 September 2001); doi: 10.1117/12.439188; https://doi.org/10.1117/12.439188
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