Robust Group III light emitting diode for high reliability in standard packaging applications

DETAILED DESCRIPTION The present invention is a physically robust light emitting diode that offers high reliability in standard packaging and will withstand high temperature and high humidity conditions.
As noted in the background, ohmic contacts must be protected from physical, mechanical, environmental and packaging stresses to prevent degradation of Group III nitride LEDs.
In this regard, FIG.
1 is a photograph of an entire LED ("die").
In the device of FIG.
1 the passivation layer of silicon dioxide (glass) has been removed except around the outside edge of the die.
The portions where glass is still present are generally indicated by the spotted or stained-appearing portions around the perimeter of the generally square die.
This mottled appearance results from a varying gap of air under the glass as it delaminates from the die.
In the die illustrated in FIG.
1, the delamination begins at about the three o'clock position (moving clockwise) and reaches approximately the 11:00 o'clock position.
The passivation layer is absent from the center of the die and the wire ball bond can be seen at the very center of the die still attached to the bond pad.
In this particular example, the center portion of the passivation layer was removed while the die was being de-encapsulated after testing.
The passivation layer of the die illustrated in FIG.
1 had delaminated in the package during testing, and allowed moisture to penetrate beneath the passivation layer.
The resulting delamination reduced the initial light output of this particular device by about 20%.
Subsequently the moisture, which tends to permeate through the epoxy lens of an LED lamp and around the leads coming out of the bottom of the lamp package, causes the thin semi-transparent ohmic contact to degrade and eventually fail completely.
This failure in turn causes the light output to continue to fall and eventually increase the forward voltage of the device.
In the device photographed in FIG.
1, the failure of the contact appears as the dark or rough areas just to the right of the center of the die