Looking at LED Chip Size

 
 

We do need to consider another factor, and that is LED chip size. For our calculations we’ve used 45×45-mil high-brightness LEDsrectangles, including the street width, or spaces between the chips. This size – around one square millimeter – is typical for high-brightness LEDs and is therefore a good comparison. However, as chip sizes increase the advantage for large diameter wafers also increases slightly. For example, if you use a 60×60-mil rectangle, the advantage for 6-in wafers increases to 58%.

So far we have focused on comparing 2-in to 6-in wafers, but we should discuss other sizes as well. Today’s LEDs are also made on 3- and 4-in wafers in large numbers. What is the relationship with these other sizes? Moving from 2-in to 4-in only gives 14.7% advantage, using a standard layout of 14 4-in wafers in the reactor. The gain from 4-in to 6-in is much more significant at 35.2%.

For 8-in substrates, the advantage is a very large – 77% more LED chips over 2-in – and that is only from the five 8-in wafers that can fit in a typical MOCVD reactor. Comparing a move from 6-inch to 8-in directly, there is a 14% gain.

We now have an accurate view of the advantage large diameter brings to the LED chip count: 55% more for 6-in and 77% for 8-in. While these are impressive numbers, one factor we haven’t taken into account in our LED chip simulation is LED chip yield. We will look at this important factor next.


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