In recent years, due to advances in technology and efficiency, the application of LEDs has become more and more widespread; with the upgrading of LED applications, the market demand for LEDs is also toward higher power and higher brightness, which is known as the development of high-power LEDs. .
For the design of high-power LEDs, most of the current large-scale manufacturers mainly use large-size single low-voltage DC LEDs. There are two methods, one is the traditional horizontal structure and the other is the vertical conductive structure. In the first approach, the process is almost the same as the general small-size die. In other words, the cross-sectional structure of the two is the same, but unlike the small-sized die, high-power LEDs often need to operate at high currents. Underneath, a little unbalanced P and N electrode design can lead to serious current crowding. The result is that the LED chip can not meet the brightness required by the design, which will also damage the reliability of the chip. (Reliability).
Of course, for upstream wafer makers/wafers, this process has high process compatibility and eliminates the need to purchase new or special machines. On the other hand, for downstream systems, the surrounding mix, Such as the design of the power supply, etc., the difference is not big. However, as mentioned above, it is not easy to spread the current evenly on large-size LEDs. The larger the size, the more difficult it is. At the same time, due to the geometric effect, the light extraction efficiency of large-size LEDs tends to be smaller and smaller. .
Figure: Differences in the driving methods of low-voltage diodes, AC diodes and high-voltage diodes (click on the image to enlarge).
The second method is much more complicated than the first one. Since the commercialized blue LEDs are almost all grown on the sapphire substrate, the vertical conductive structure must be bonded to the conductive substrate before being electrically non-conductive. The sapphire substrate is removed, and then the subsequent process is completed; in terms of current distribution, since the lateral conduction is less considered in the vertical structure, the current uniformity is better than the conventional level structure; otherwise, the basic In terms of physical processing, materials with good electrical conductivity also have high thermal conductivity. By replacing the substrate, we also improve heat dissipation and lower the junction temperature, which indirectly improves the luminous efficiency. However, the biggest disadvantage of this approach is that due to the increased complexity of the process, the yield is lower than the traditional horizontal structure, and the production cost is much higher.
Basic structure and key technology of high voltage light-emitting diode (HV LED)
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