Kirsten A. Lovelace
Howard University, Washington, DC 20059, USA
Sonya T. Smith
Howard University, G-048, 2300 Sixth St, Washington, D.C, 20059, USA
This research investigates the effects of thermal cycling from room to cryogenic temperatures (300K - 4K) on
the thermal expansion coefficient of two ceramic substrates of Silicon Nitride (Si3N4) and alpha-Alumina/Sapphire (α-Al2O3). Due to the shortage of available data, a comparative study with reference materials, Copper, Carbon Steel 1008 and Molybdenum, are compared to NIST property data as a proof of concept. Accurate thermal contraction data of materials at low temperatures are important in material selection
and thermal design of engineered systems. Low thermal expansion materials are widely used in electronic devices such as, heat-engine components, aircraft materials and aerospace equipment. Thermal expansion mismatch causes substantial problems in device operating reliability because of induced thermal stresses imposed on the joint materials undergoing temperature changes. Theory supports the advantage of utilizing Sapphire (Al2O3) and Silicon Nitride (Si3N4) within microchip configurations to mitigate this issue. However, there are limited data available that confidently support this assertion beyond theory. Sapphire with a 4.0 ppm/K coefficient of thermal expansion (CTE) and Silicon Nitride with a CTE of 3.3 ppm/K share closer values than traditional Silicon (2.7 ppm/K) and Copper (17 ppm/K) at room temperature. An electromechanical method for in-situ strain measurements is presented as a tool to characterize thermomechanical behavior of Sapphire and Silicon Nitride. The calculated coefficient of thermal expansion for silicon nitride is 1.35 1/K and 0.994 1/K for sapphire at 5.7 K. The results from this validation have a mean error percentage of
less than 6 %.