23.3 Light-Emitting Diodes
651
(a)
(b)
(c)
(d)
Barracuda
(1998)
Transparent
substrate
(1994)
Prometheus
(2000)
Absorbing
substrate
(1991)
Fig. 23.11 Optimization of light exit by 3D design of the LED chip, a scheme, b emission pattern comparison and c
SEM image of the ATON chip. Reprinted with permission from [1948]. d Development stages towards the truncated
inverted pyramid (Prometheus) chip. From [1949]
0.5–2 W and 10–100 lm). An epoxy-free technique for encapsulation also enhances the color uniformity
and maintains the brightness.
Thin-Film LED
In the thin-film LED design [1950], as schematically shown in Fig. 23.12a, a metal mirror is evaporated on the LED layers. In a flip-chip design, subsequently the metal side is wafer bonded to another
metallized substrate and the original substrate is removed. Additionally, the LED surface can be patterned (before bonding) into an (hexagonal) array of (hexagonal) microprism mesas with an insulating
(e.g. silicon nitride) layer with openings in order to optimize the current path. The microprisms are
optimized to allow efficient reflection of light towards the emitting surface. This technology is scalable
to large areas without loss in efficiency.
In order to avoid bonding from the top which leads to partial shielding of the emitted radiation and
is a mechanical process, contact schemes for flip-chip LEDs have been devised for contacting both the
n- and the p-layer from the same side [1952]. In Fig. 23.13 a schematic cross-section and an emission
651
(a)
(b)
(c)
(d)
Barracuda
(1998)
Transparent
substrate
(1994)
Prometheus
(2000)
Absorbing
substrate
(1991)
Fig. 23.11 Optimization of light exit by 3D design of the LED chip, a scheme, b emission pattern comparison and c
SEM image of the ATON chip. Reprinted with permission from [1948]. d Development stages towards the truncated
inverted pyramid (Prometheus) chip. From [1949]
0.5–2 W and 10–100 lm). An epoxy-free technique for encapsulation also enhances the color uniformity
and maintains the brightness.
Thin-Film LED
In the thin-film LED design [1950], as schematically shown in Fig. 23.12a, a metal mirror is evaporated on the LED layers. In a flip-chip design, subsequently the metal side is wafer bonded to another
metallized substrate and the original substrate is removed. Additionally, the LED surface can be patterned (before bonding) into an (hexagonal) array of (hexagonal) microprism mesas with an insulating
(e.g. silicon nitride) layer with openings in order to optimize the current path. The microprisms are
optimized to allow efficient reflection of light towards the emitting surface. This technology is scalable
to large areas without loss in efficiency.
In order to avoid bonding from the top which leads to partial shielding of the emitted radiation and
is a mechanical process, contact schemes for flip-chip LEDs have been devised for contacting both the
n- and the p-layer from the same side [1952]. In Fig. 23.13 a schematic cross-section and an emission