Discipline: Technology and Engineering
Subcategory: Materials Science
Session: 2
Room: Virginia B
Kirsten A. Lovelace - Howard University
Co-Author(s): Sonya T. Smith, Howard University, Washington, DC
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. The importance of low thermal expansion materials is useful in their widespread use in electronic devices, heat-engine components, aircraft materials and aerospace equipment. Thermal expansion mismatch causes substantial problems in operating device reliability because of the various stresses imposed on the joint materials undergoing temperature changes. Theory supports the advantage of utilizing Sapphire (Al2O3) and Silicon Nitride (Si3N4) within microchip configuration. However, there is limited data available that confidently supports this assertion beyond theory. Sapphire with a coefficient of thermal expansion (CTE) of 4.0 ppm/K 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 electro-mechanical 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 1.08 1/K for sapphire at 5.7 K. There is a maximum mean relative deviation in comparison to NIST data of 4.2% and 5.8% for silicon nitride and sapphire, respectively. The results from this validation have an overall mean error percentage of less than 6%. These results indicate that the coefficient of thermal expansion values at cryogenic temperatures for silicon nitride and sapphire are substantially closer than traditional printed circuit board and substrate materials, copper and silicon. The use of these favorable materials can ultimately reduce thermal expansion mismatch within microelectronic packaging, increasing the thermal management within the overall system. Future research involves experimentally testing the Residual Resistivity Ratio (RRR) and electrical resistivity at cryogenic temperatures. References: Touloukian, Y S. Thermophysical Properties of High Temperature Solid Materials. New York: Macmillan, (1967). Tang, K., Sha, L., Li, Y., Liu, S., “Measurement of thermal expansion at low temperatures using the strain gage method” Journal of Zheijiang University (Applied Physics & Engineering) 15(50), pp. 323-330, (2014). Corruccini, R.J., Gniewek, J.J., “Thermal Expansion of Technical Solids at Low Temperatures: A Compilation from the Literature” US Department of Commerce, National Bureau of Standards. (1961). Funder Acknowledgements: The authors would like to acknowledge Northrop Grumman for their support of this project under P.O. 8200178647. Also acknowledged are the Applied Fluids Thermal Research Laboratory (@FTERLab) for providing experimental and computational support as well as technicians T. Brown and T. Crawford from the Howard University Nanotechnology Facility (HUNF). Faculty Advisor/Mentor: Sonya T. Smith, Ph.D., ssmith@howard.edu
Funder Acknowledgement(s): Northrop Grumman Corporation
Faculty Advisor: Sonya T. Smith, Ph.D., ssmith@howard.edu
Role: I have conducted all of the research.