| dc.description.abstract | In crystal growth, Kyrupoulos method applies to grow large size crystal. During the large size sapphire crystal growth, it’s hard to observe temperature and flow inside the high temperature furnace. According to this reason, we need numerical simulation to calculate crystal growth, to improve the yield and to cost down. The thesis simulates 90kg large size sapphire crystal growth by Kyrupoulos method. In Kyrupoulos furnace, we use three heaters to avoid the high temperature gradient in crystal, crucible melting and thermal waste.
This study uses the COMSOL Multiphysics software to simulate large size sapphire crystal. We simulate three types of heater power ratios, 0.8:1.0:0.4(case1), 1.0:1.0:0.4(case2), 1.2:1.0:0.4(case3), differ from top and middle heater relative magnitude. The result shows top heater power effect the strength of cell. The strong cell makes crystal grow in radial direction and suppress its axial direction growth. Then produce different interface shape.
With melt reduce, upper cell gets weak. It accelerates crystal growth in axial direction, and the crystal diameter is less than crystal shoulder length. In the KY method growth large sapphire crystal, top heater power can control crystal shape effectively. We compare interface temperature gradient, total power and crystal shape. We find that heater power ratio 1.2:1:0.4 has better result, though it has solidification phenomena. We use case3 be the initial value to modify heater power ratio. Decreasing top heater power to be the same with middle heater power, then decrease top and middle heater power at the same time. The simulation result has good temperature gradient, lower total power and crystal ingot grow in same diameter. We also simulate thermal stress field distribution of every crystal growth stage. And get thermal stress variation in large sapphire crystal growth process. The result shows that the thermal stress of crystal is smaller than the maximum tensile strength of sapphire crystal (414MPa). | en_US |