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

美国能源部最近的一项分析得出结论，2013年采用发光二极管（led）与一年节省18亿美元的能源成本相关，这还不到完全采用led预期节省的5%。LED成本和性能的关键驱动因素是散热片，因为工作温度每增加1°C， LED流明效率就会下降0.3- 0.5%。然而，制造所需的散热材料氮化铝（AlN）的成本很高，因为形成致密AlN部件所需的烧结温度很高，而且AlN在存在水的情况下容易降解。原子层沉积（ALD）用于AlN的致密化和加工的好处有望在实现AlN部件的低成本生产方面具有变革性，并为目前由国外制造商主导的陶瓷热封装制造领域提供了一条国内路线。这项与工业界学术联络的资助机会（GOALI）研究计划将促进大学与工业界之间的合作，并使研究生和本科生的教育成为可能。用钇（Y2O3）致密化AlN目前需要超过1700℃的温度，这就要求使用昂贵的石墨炉。通过烧结助剂Y2O3在AlN衬底颗粒上的ALD，预计一层保形且无针孔的Y2O3薄膜将保护AlN颗粒不被水降解，从而允许在水中加工而不是更昂贵的溶剂基加工。此外，在初生AlN衬底颗粒周围精确厚且均匀的ALD Y2O3薄膜有望在致密化基体的晶间区域提供有利的液相烧结，从而促进低温致密化。致密化温度的降低不仅降低了形成致密AlN部件所需的能量输入，而且还可以使用更便宜的氧化铝炉来代替石墨炉。对于凝胶铸造，ALD Y2O3涂层也将简化胶体凝胶的处理，因为只有一个表面（即Y2O3）将存在，而不是两个- AlN和Y2O3。ALD涂层的均匀性应该比传统的球磨技术有很大的改进，在传统的球磨技术中，Y2O3的加入对于每个AlN颗粒来说都是不均匀的，导致致密化行为和致密AlN部件的性能不一致。耐水解和低温致密化的AlN颗粒的组合可能会大大降低制造AlN散热器的成本，从而降低led的成本。

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.