Chip shaping for flip-chip light emitting diode

Details Chip shaping for flip-chip light emitting diode Chip shaping for flip-chip light emitting diode

2002-10-10

2004-08-31

Flynn, Nathan J. (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Incoherent light emitter structure

With heterojunction

C257S081000, C257S098000, C257S099000, C257S100000

Reexamination Certificate

active

06784460

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to the field of light sources. More specifically, the present invention relates to a method of improving light extraction from a light emitting diode (“LED”) of flip-chip design through geometrical shaping of the chip.
DESCRIPTION OF THE RELATED ART
An LED is a semiconductor chip or die that emits light when a forward current flows through the LED.
FIG. 1
illustrates a known LED
30
of flip-chip design, where the LED
30
includes a transparent substrate
31
having a cuboidal shape (e.g., a rectangular prism), a negatively doped layer
32
, an active p-n junction layer
33
, and a positively doped layer
34
. A pair of ohmic contacts
35
and
36
are employed to forward bias LED
30
whereby light is generated and emitted from the active p-n junction layer
33
into the substrate
31
. Typically, a refractive index of the substrate
31
will be different than a refractive index of the surrounding environment (e.g., air or a medium employed to encapsulate the substrate
31
). As illustrated in
FIG. 2
, such a difference in the refractive indices establishes a critical angle that results in a partitioning of the substrate
31
into escape cones
31
a
,
31
c
and
31
e
and total internal reflection cones (“TIRC”)
31
b
and
31
d
. It is well known in the art that the substrate
31
will emit light from the escape cones
31
a
,
31
c
and
31
e
as exemplified by the arrows therein, because an angle of incidence of the emitted light will be less than the critical angle. Conversely, the substrate
31
will not emit light from the TIRC cones
31
b
and
31
d
as exemplified by the arrows therein, because an angle of incidence of the trapped light will be equal to or greater than the critical angle for each internal reflection of the trapped light by the substrate
31
.
The present invention advances the art by a contribution of an improved light extraction from a LED of flip-chip design.
SUMMARY OF THE INVENTION
A flip-chip design of a LED is constructed in accordance with various embodiments of the present invention. The LED comprises a light emitting region including a negatively doped layer, a positively doped layer, and an active p-n junction layer between the negatively doped layer and the positively doped layer. The LED further includes a transparent substrate overlying the light emitting region, wherein the transparent substrate has a pyramidal shape determined by (1) the composition of electrically conductive or electrically non-conductive material, (2) the number of side surfaces, (3) the degree of offset of an apex or top surface, and (4) the slope angle of each side surface.
The features and advantages of the present invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.


REFERENCES:
patent: 6024455 (2000-02-01), O'Neill et al.
patent: 6323063 (2001-11-01), Krames et al.
patent: 6610598 (2003-08-01), Chen
patent: 2002/0153835 (2002-10-01), Fujiwara et al.

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