Jason Posselt, vice president of marketing at American BridgELux, promoted the company's GaN-type LEDs that can be mass-produced on 8-inch substrates.
Jason Posselt pointed out that the company has previously built 135 lumens per watt of GaN-On-Silicon LEDs, which grow on the germanium substrate. The biggest significance of this method is to reduce the cost of large-size wafers when producing LEDs. At the same time, the price of the ruthenium substrate is lower than the price of the sapphire substrate. The reason why this technology has not received much attention in the past is the yield, cost and technology threshold. Today, the company has succeeded in creating products that are competitive enough and are also available to many market customers. Bridgelux's latest achievement is 614mW, <3.1V@350mA 1.1mm size LED, which is the highest efficiency of current 8-inch LED. The company emphasizes that it will continue to publish progress and development in this area.
In terms of production capacity, tantalum substrate is already the most common substrate material in the semiconductor industry. Among them, 8å‹ wafer fab equipment is old, and the LED of the germanium substrate can be easily utilized for the original production capacity. Bridgelux's strategy is to cooperate with Japanese manufacturer Toshiba. The two companies will use the latest modified GaN-On-Silicon technology to produce 8 å‹çŸ½ substrate LEDs with Toshiba's 8 å‹ fab capacity in Asia. The impact of production may not be small, and it is expected to reduce the cost by 75%.
In fact, it affects most of the existing LED chip industry based on sapphire substrates. The technical progress expected in the market is not so fast, but Bridgelux's breakthrough is likely to change the existing competitive landscape and trigger different technological progress paths. Intense confrontation.
Substrate materials are the cornerstone of the technological development of the semiconductor lighting industry. Different substrate materials require different epitaxial growth techniques, chip processing techniques, and device packaging technologies. Substrate materials determine the development path of semiconductor lighting technology. The choice of substrate materials depends on the following nine aspects:
[1] The structural characteristics are good, the crystal structure of the epitaxial material and the substrate are the same or similar, the lattice constant mismatch is small, the crystallization property is good, and the defect density is small;
[2] The interface characteristics are good, which is beneficial to the nucleation of the epitaxial material and strong adhesion;
[3] Good chemical stability, not easily decomposed and corroded in the temperature and atmosphere of epitaxial growth;
[4] good thermal performance, including good thermal conductivity and low thermal mismatch;
[5] good electrical conductivity, can be made into upper and lower structures;
[6] The optical performance is good, and the light emitted by the fabricated device is absorbed by the substrate;
[7] Good mechanical properties, easy to process, including thinning, polishing and cutting;
[8] low price;
[9] Large size, generally requires a diameter of not less than 2 inches.
Sapphire/Al2O3
The most common substrate currently used for gallium nitride growth is Al2O3, which has the advantages of good chemical stability, no absorption of visible light, moderate price, and relatively mature manufacturing technology. Although there are many inadequacies, they are all overcome one by one. The lattice mismatch is overcome by the transition layer growth technique. The poor conductivity is overcome by the same side P and N electrodes. The poor mechanical properties are difficult to cut by laser dicing. A large thermal loss pairing the epitaxial layer forms compressive stress. Will not crack. However, the poor thermal conductivity does not reveal significant defects in the device under low current operation, but the problem is very prominent in the high current operation of the power device.
Some manufacturers use flip-chip to prepare power devices to overcome this problem. The future research and development of Al2O3 substrates on the international market is to grow large-diameter Al2O3 single crystals, which will develop in the direction of 4-6 inches, and reduce impurity contamination and improve surface polishing quality. At present, mainstream sapphire substrate manufacturers are able to achieve 6-inch batch delivery. Hanfang Samsung LED has converted most of its production capacity to 6å‹. However, at present, the mainstream chip factory in China is still using two films, mainly based on cost considerations.
Tantalum carbide / SiC
In addition to the Al2O3 substrate, the substrate currently used for GaN growth is SiC, which ranks second in the market. It has many outstanding advantages, such as good chemical stability, good electrical conductivity, and good thermal conductivity. It does not absorb visible light, etc., but the shortage is also very prominent. For example, the price is too high, the crystal quality is difficult to reach Al2O3 and Si, and the machining performance is poor. In addition, the SiC substrate absorbs ultraviolet light below 380 nm and is not suitable for the development of ultraviolet LEDs below 380 nm.
Due to the excellent electrical conductivity and thermal conductivity of the SiC substrate, it is not necessary to use the flip-chip bonding technology to solve the heat dissipation problem on the power GaN LED device on the Al2O3 substrate, but the upper and lower electrode structures can be used to solve the power nitriding. The heat dissipation problem of gallium LED devices plays an important role in the development of semiconductor lighting technology. At present, only the American CREE company can provide commercial high-quality SiC substrates. Cree announced on April 12, 2012 that its white light power LED light efficiency has once again set a new record in the LED industry, reaching 254 lm/W. This record is nearly a hundred lm higher than the highest light efficiency record achieved by the Al2O3 substrate. The future development of SiC substrates is to significantly reduce manufacturing costs and improve crystal quality.
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