8 January 2010


Hitachi Cable develops 1mm x 1mm high-power 55lm red LED chips

Japan’s Hitachi Cable Ltd says that it has developed a high-power red LED chip offering a maximum luminous flux of 55 lumens (at a current of 500mA). The firm says that this luminous flux was enabled by increasing the size of the LED chip and the use of a fine-line electrode structure.

In response to demand for LEDs with higher luminous efficiency, Hitachi Cable has already developed high-brightness red ‘MR-LED’ chips (measuring 0.33mm x 0.33mm) that form a metal reflector (MR) under the light-emitting layer (yielding 2.6lm at a current of 20mA). This product is currently being supplied to LED package manufacturers and other customers.

Figure 1: Problems caused by enlarged chip size.

However, recognizing the growing demand for higher output LED chips, the firm has also now incorporated fine electrode structures and enlarged the chip dimensions to 1mm x 1mm in order to develop high-power red LED chips offering outputs as high as 55lm.

Figure 2: Structure of new high-power red LED.

Increasing the chip's dimensions is one of the methods of improving per-chip light output. However, larger chips increase the difficulty of distributing a uniform current across the entire light-emitting layer. On the other hand, if large electrodes are positioned in the upper layer of the chip for more uniform current dispersion, light from the light-emitting layer will be blocked, reducing the light extraction efficiency.

To resolve these problems in developing a new LED chip, instead of using larger electrodes Hitachi Cable has used two pad electrodes for receiving power, a backbone electrode connecting the two electrodes, and multiple fine-line electrodes that extend from the backbone electrode on the upper chip layer.

By employing fine-line electrodes, Hitachi Cable says that it has succeeded in achieving uniform dispersion of current across the entire chip surface without blocking light from the light-emitting layer, attaining a maximum luminous flux of 55 lumens in a large LED chip of 1mm x 1mm—equivalent to the combined output of 21 MR-LED chips (of 0.33mm x 0.33mm). With its higher output, the new LED chip is expected to find applications not only in display applications but also as a light source for devices such as projectors.

Figure 3: External views of high-power red LED.

Hitachi Cable says that it will continue to pursue active development of higher-power LED chips while expanding its lineup, including yellow and infrared LED chips.

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