[Source: "High-tech LED - Technology and Applications" June issue]
LED light-emitting diodes have the advantages of small size, high luminous efficiency, long life, no pollution in the manufacturing process, etc. It is a true energy-saving and environment-friendly light source, with the further improvement of LED light efficiency and further reduction of production cost plus global With the promotion of energy-saving technologies within the scope, LEDs are developing at an unprecedented speed, and it is expected to gradually replace traditional light sources in the next few years (except for a few special applications).
The LED is composed of a doped GaN-based crystal, but it is very difficult to directly prepare a gallium nitride crystal. The current LED chip converts a material constituting a gallium nitride component into a gaseous state by epitaxial technology, and deposits a layer on a certain layer. Different doped gallium nitride crystals are formed on the prefabricated substrate, and further processed to form a light emitting diode. At present, LED substrate materials used in large-scale commercial use are aluminum oxide crystals (commonly known as sapphire) and silicon carbide crystals. Although silicon carbide is superior to sapphire in lattice mismatch, thermal expansion coefficient and thermal conductivity, sapphire is better. Chemical stability, non-absorption of visible light, high mechanical strength, good processing performance, stable devices, relatively mature manufacturing technology, especially the manufacturing cost is only one-tenth of that of silicon carbide, so the LED with the largest market share The substrate material is the first to push the sapphire crystal.
The rapid development of the LED industry has promoted the huge demand for substrate-level sapphire crystals, which has promoted the demand for sapphire crystal growth equipment. Since the beginning of 2010, more than ten companies in China have been involved in sapphire crystal growth and crystal equipment development, investment. The scale ranges from tens of millions to billions of yuan. The selected technical solutions are basically the crystal growth process of the bubble method.
The core technology of the bubble growth crystal growth furnace lies in the design of the thermal field. The material, shape, structure and size of the four thermal fields are formed by the heating body, the heat protection layer, the upper seed crystal heat exchanger and the lower crucible support. The comprehensive design of the distribution, such as the high-purity Al2O3 raw material in the crucible, shows a distribution pattern of high temperature at the lower part of the upper part and high temperature at the lower part of the radial axis. When the crystal grows, it is from the center of the upper surface of the melt ( Cold-hearted) Introduce pre-selected high-quality seed crystals (seeds) so that the melt grows from the top to the bottom of the crucible with the seed crystal as the core until the melt is completely consumed to form a single crystal.
Among the four major factors that form the thermal field of a bubble furnace, the design of the crucible support is critical and is one of the keys to the sequential temperature gradient required to influence the thermal field to form a single crystal. In this paper, based on the 85 kg-class bubble sapphire crystal growth furnace designed and developed by ourselves, the experimental research on the crucible support was carried out.
I. Design and test
1.1 Basic requirements for support
a. High temperature resistance: The melting point of sapphire crystal is 2050 degrees. The temperature of the upper surface of the inner surface of the melt is not lower than this temperature, and the temperature of the lower part of the crucible is generally required to reach 2150 degrees. Under the same temperature gradient and the same aspect ratio, the larger the crystal, the higher the temperature reached in the lower part of the crucible. If the temperature gradient is larger, the lower temperature will be higher. In fact, considering the purification needs of the degassing and degassing of the melt before seeding, it is generally necessary to artificially raise the temperature of the melt to a higher temperature and keep it for a while after the raw material is melted. Therefore, for a large-sized crystal, if a temperature gradient is designed Also large, during the actual crystal growth period, the temperature of the lower part of the crotch will reach 2350 degrees, which puts higher requirements on the temperature resistance of the crucible support;
b. High temperature compressive strength: The growth process of the sapphire crystal is generally made of tungsten ruthenium. The tungsten ruthenium used for the growth of a 85 kg sapphire crystal weighs 245 kg, plus the weight of the raw material and the support base. The weight is about 400 kg. In order to reduce the heat loss of the lower part of the crucible through the support, the axial temperature gradient of the melt is reversed (the lower temperature is lower than the upper temperature). The general design orientation is to minimize the cross-sectional area of ​​the crucible support. Therefore, the crucible support material is required to be 2500 degrees. The continuous compressive strength at temperature is not less than 20MPA;
c. Low thermal conductivity: the purpose is to reduce the loss of heat in the lower part of the crucible through the support seat, causing the axial temperature gradient of the lower part of the crucible to be reversed;
d. The material has less gas storage: it is beneficial to form a high vacuum quickly;
e. Less volatiles: to avoid contamination of the crystal growth environment;
f. cheaper;
Almost no material can be found while meeting the above requirements.
For more information, please refer to the June issue of "High-tech LED-Technology and Applications" magazine.
LED light-emitting diodes have the advantages of small size, high luminous efficiency, long life, no pollution in the manufacturing process, etc. It is a true energy-saving and environment-friendly light source, with the further improvement of LED light efficiency and further reduction of production cost plus global With the promotion of energy-saving technologies within the scope, LEDs are developing at an unprecedented speed, and it is expected to gradually replace traditional light sources in the next few years (except for a few special applications).
The LED is composed of a doped GaN-based crystal, but it is very difficult to directly prepare a gallium nitride crystal. The current LED chip converts a material constituting a gallium nitride component into a gaseous state by epitaxial technology, and deposits a layer on a certain layer. Different doped gallium nitride crystals are formed on the prefabricated substrate, and further processed to form a light emitting diode. At present, LED substrate materials used in large-scale commercial use are aluminum oxide crystals (commonly known as sapphire) and silicon carbide crystals. Although silicon carbide is superior to sapphire in lattice mismatch, thermal expansion coefficient and thermal conductivity, sapphire is better. Chemical stability, non-absorption of visible light, high mechanical strength, good processing performance, stable devices, relatively mature manufacturing technology, especially the manufacturing cost is only one-tenth of that of silicon carbide, so the LED with the largest market share The substrate material is the first to push the sapphire crystal.
The rapid development of the LED industry has promoted the huge demand for substrate-level sapphire crystals, which has promoted the demand for sapphire crystal growth equipment. Since the beginning of 2010, more than ten companies in China have been involved in sapphire crystal growth and crystal equipment development, investment. The scale ranges from tens of millions to billions of yuan. The selected technical solutions are basically the crystal growth process of the bubble method.
The core technology of the bubble growth crystal growth furnace lies in the design of the thermal field. The material, shape, structure and size of the four thermal fields are formed by the heating body, the heat protection layer, the upper seed crystal heat exchanger and the lower crucible support. The comprehensive design of the distribution, such as the high-purity Al2O3 raw material in the crucible, shows a distribution pattern of high temperature at the lower part of the upper part and high temperature at the lower part of the radial axis. When the crystal grows, it is from the center of the upper surface of the melt ( Cold-hearted) Introduce pre-selected high-quality seed crystals (seeds) so that the melt grows from the top to the bottom of the crucible with the seed crystal as the core until the melt is completely consumed to form a single crystal.
Among the four major factors that form the thermal field of a bubble furnace, the design of the crucible support is critical and is one of the keys to the sequential temperature gradient required to influence the thermal field to form a single crystal. In this paper, based on the 85 kg-class bubble sapphire crystal growth furnace designed and developed by ourselves, the experimental research on the crucible support was carried out.
I. Design and test
1.1 Basic requirements for support
a. High temperature resistance: The melting point of sapphire crystal is 2050 degrees. The temperature of the upper surface of the inner surface of the melt is not lower than this temperature, and the temperature of the lower part of the crucible is generally required to reach 2150 degrees. Under the same temperature gradient and the same aspect ratio, the larger the crystal, the higher the temperature reached in the lower part of the crucible. If the temperature gradient is larger, the lower temperature will be higher. In fact, considering the purification needs of the degassing and degassing of the melt before seeding, it is generally necessary to artificially raise the temperature of the melt to a higher temperature and keep it for a while after the raw material is melted. Therefore, for a large-sized crystal, if a temperature gradient is designed Also large, during the actual crystal growth period, the temperature of the lower part of the crotch will reach 2350 degrees, which puts higher requirements on the temperature resistance of the crucible support;
b. High temperature compressive strength: The growth process of the sapphire crystal is generally made of tungsten ruthenium. The tungsten ruthenium used for the growth of a 85 kg sapphire crystal weighs 245 kg, plus the weight of the raw material and the support base. The weight is about 400 kg. In order to reduce the heat loss of the lower part of the crucible through the support, the axial temperature gradient of the melt is reversed (the lower temperature is lower than the upper temperature). The general design orientation is to minimize the cross-sectional area of ​​the crucible support. Therefore, the crucible support material is required to be 2500 degrees. The continuous compressive strength at temperature is not less than 20MPA;
c. Low thermal conductivity: the purpose is to reduce the loss of heat in the lower part of the crucible through the support seat, causing the axial temperature gradient of the lower part of the crucible to be reversed;
d. The material has less gas storage: it is beneficial to form a high vacuum quickly;
e. Less volatiles: to avoid contamination of the crystal growth environment;
f. cheaper;
Almost no material can be found while meeting the above requirements.
For more information, please refer to the June issue of "High-tech LED-Technology and Applications" magazine.
With Sdec Engine Diesel Generator
With Sdec Engine Diesel Generator,Sdec Diesel Generator,Sdec Diesel Generator Set,Sdec Power Generator
Shanghai Kosta Electric Co., Ltd. , https://www.generatorksd.com