industry LEDmanufacturing
Wafer bonding: selecting the right process for making powerful, vertical LEDs
LEDs with a vertical geometry are promising candidates for deployment in solid-state lighting products because they can handle the high drive currents needed to deliver a high luminous output. Manufacturing this form of LED requires a wafer-to-wafer bonding process,which involves many variables that need to be optimised for the specific device design, say Thomas Uhrmann, Eric Pabo,Viorel Dragoi and Thorsten Matthias from EV Group.
W
Figure 1: A key features of the vertical LED is its highly reflective
sub-structure that excels at conducting the heat away. This allows the device to
operate at high currents, and consequently high luminous output
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www.compoundsemiconductor.net July 2011
hite LEDs are already impacting the general lighting market, and their
penetration in this sector is widely expected to rise. The rate of adoption will be governed by three factors: luminous efficiency, cost per lumen installed, and lumens per socket.
One way to improve all three areas simultaneously is to increase LED efficiency. But even greater gains to the lumen output of the luminaire and its cost-per- lumen are possible by combining gains in efficiency with a higher drive current for the device. Cranking this up, however, increases LED heating. And to cope with this, the system designer must carefully
manage heat that flows from the device junction to the package, fixture and surrounding environment.
It is possible to increase the rate that heat flows out of the LED by using metal wafer bonding for transfer of the epistructure to another substrate. Take this step and the LED benefits on two fronts: it can rapidly conduct heat away through a metal bond with a low thermal resistance, and it can dissipate heat through a substrate with low thermal resistance.
This approach can not only enhance the electrical properties of the nitride-based white LED, but also its blue variant and its red, orange and yellow cousins
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