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Diameter Controlling Method of Large Size Sapphire Single Crystal Grown by Kyropoulos Method

To obtain high quality crystals,a precision diameter-constant controlling method was required in the growth process of large size sapphire single crystal by Kyropoulos method.Based on the weight of the crystal to control the thermal field,and to achieve diameter-constant growth of crystals.a generalized minimum variance principle base on online adjusting polynomial weights(RAPW_GMV) control method is introduced,and establishing model of system.Its main idea is based on the online estimation of the parameters of controlled object and RAPW_GMV output,online adjusting polynomial weights,fulfill the controlling of thermal field and diameter-constant growth of crystals.The emulator and experimental results confirm that the controlling method achieve precision diameter-constant controlling of Sapphire Single Crystal and effectively improve the quality of sapphire single crystal.

For an inductively heated Czochralski furnace used to grow sapphire single crystal, influence of the inner (wall-to-wall) and crystal internal (bulk) radiation on the characteristics of the growth process such as temperature and flow fields, structure of heat transfer and crystal-melt interface has been studied numerically using the 2D quasi-steady state finite element method. The obtained results of global analysis demonstrate a strong dependence of thermal field, heat transport structure and crystal-melt interface on both types of radiative heat transfer within the growth furnace.


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