GOALI: Core/Shell Sinterable Advanced Ceramic Materials Using Particle Atomic Layer Deposition

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

A recent Department of Energy analysis concluded that the adoption of light-emitting diodes (LEDs) in 2013 was correlated with a one-year energy cost savings of $1.8 billion, which is less than 5 percent of the expected savings with complete adoption of LEDs. A key driver in the cost and performance of LEDs is the heat sink as LED lumen efficiency decreases by 0.3-0.5 percent for each 1°C increase in operating temperature. However, the costs of manufacturing the desired heat sink material, aluminum nitride (AlN), are substantial as a result of the high sintering temperature required to form dense AlN parts and the proclivity for AlN to degrade in the presence of water. The benefits of atomic layer deposition (ALD) for densification and processing of AlN are expected to be transformative in enabling lower-cost production of AlN parts and present a domestic route to manufacturing ceramic thermal packages, an area currently dominated by foreign manufacturers. This Grant Opportunity for Academic Liaison with Industry (GOALI) research program will promote collaboration between university and industry and enable the education of both graduate and undergraduate students. The densification of AlN with yttria (Y2O3) currently requires temperatures in excess of 1700°C, mandating the use of expensive graphite furnaces. Through ALD of the sintering aid, Y2O3, onto AlN substrate particles, it is expected that a conformal and pinhole-free Y2O3 film will protect the AlN particles from degradation by water, allowing processing in water instead of more expensive solvent-based processing. Further, the precisely thick and uniform ALD Y2O3 films around primary AlN substrate particles, are expected to provide for beneficial liquid phase sintering in the intergranular region of the densifying matrix - promoting low temperature densification. A decrease in densification temperature not only lowers the energy input required to form dense AlN parts but may also enable the use of more inexpensive alumina furnaces in lieu of graphite furnaces. For gel-casting, the ALD Y2O3 coatings will also simplify the processing of colloidal gels since only one surface (i.e. Y2O3) will be present, not two - AlN and Y2O3. The uniform nature of ALD coatings should be a substantial improvement over conventional ball milling techniques where the incorporation of Y2O3 is not uniform with respect to each AlN particle, leading to inconsistencies in densification behavior and the properties of dense AlN parts. The combination of AlN particles resistant to hydrolysis and lower temperature densification may dramatically decrease the costs of manufacturing the AlN heat sink and thus, LEDs.