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|Improvement of Dielectric Performance of a Prototype AlN High Temperature Chip-Level Package|
|Keywords: Packaging, AlN, high temperature|
|Aluminum nitride (AlN) is an excellent electrical insulating material in the temperature range for conventional microelectronics. More importantly, this material has a very high thermal conductivity and relatively low thermal expansion coefficient, therefore, AlN has been widely used as an important substrate material for packaging power electronics. AlN has also been proposed as a packaging substrate material for reliable high temperature electronics operating in a wide temperature range. However, it was discovered in a recent study that the dielectric properties of some commercial polycrystalline AlN materials change quite significantly with temperature at high temperatures. These material properties resulted in undesired high and temperature dependent parasitic parameters of a prototype chip-level package based on AlN substrate with the yttrium oxide dopant . This paper reports a method using a coating layer of a commercial thick-film glass, which is compatible to both AlN substrate and gold thick-film conductor, on the AlN substrate surface to significantly reduce both the parasitic capacitance and parasitic conductance between neighboring I/Os of a prototype AlN chip-level package. The parasitic parameters of an 8-I/Os low power chip-level package with the insulating glass coating were characterized at frequencies from 120 Hz to 1 MHz between room temperature and 500C, and were compared with the parameters of AlN packages without the glass coating. The testing results indicate that the improvement of parasitic capacitance and conductance between I/Os of the improved prototype AlN packages are significant and stable at high temperatures. The method using a glass coating provides a feasible way to mitigate the temperature dependence of dielectric properties of AlN and further utilize AlN as a reliable packaging substrate material for high temperature applications.  L.-Y. Chen and G.W. Hunter, “Al2O3 and AlN Ceramic Chip-level Packages for 500C Operation,” 2005 High Temperature Electronics Network (HiTEN), Paris, France, September 6-8, 2005.|
|Liang-Yu Chen, Senior Scientist
Ohio Aerospace Institute/NASA Glenn Research Center