Light emitting diode array

Details Light emitting diode array Light emitting diode array

1998-12-23

2001-06-26

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Solid-state type

Reexamination Certificate

active

06252351

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a light emitting diode (hereinafter referred to simply as “LED”) array, and more particularly to an LED array providing a high light output and a uniform distribution of light intensity.
BACKGROUND OF THE INVENTION
There is a GaAlAs LED as one of the LEDs, and since such LED exhibits high intensity, they are arrayed to provide an LED array which has been utilized as a light source for LED printer.
FIG. 1
is a plan view showing an example of conventional LEEDs, and
FIG. 2
is a plan view showing another example of conventional LEDs.
LED array has a fine structure, and it is classified into two types. One of them is peripheral electrode type LED array (
FIG. 1
) wherein an electrode (peripheral electrode)
30
is disposed on a side (peripheral part) of a light take-out region
20
in a light emitting dot
10
, and the other type is a central electrode type LED array (
FIG. 2
) wherein an electrode (central electrode)
31
is disposed at an central portion of a light take-out region
21
in a light emitting dot
11
. In either of the LEDs, the electrode
30
or
31
is disposed through a contact layer
40
or
41
for electrode, and the electrode
30
or
31
is connected to a metal interconnection
50
or
51
.
In the peripheral electrode type LED shown in
FIG. 1
, since the peripheral electrode
30
is disposed on a peripheral portion of the light take-out region
20
, it is very difficult to uniformly expand an input current over the whole area of the light take-out region
20
. As a result, the light which can be taken out from the light take-out region
20
decreases with increase in a distance from the peripheral electrode
30
, because the light output decreases, resulting in unevenness of light output in the light take-out region
20
, besides, high light output cannot be obtained in this case. Furthermore, there is a possibility of variations in a mode of expanding an input current depending upon a slight difference in crystallizability of each LED, so that variations of each LED in an LED array become also remarkable.
Moreover, since distribution of light intensity is biased toward the peripheral electrode
30
, there has been such a problem that a light emitting region effective for printing of an LED printer is not arranged horizontally in a straight line, but staggered, even in the light take-out regions
20
of adjacent LEDs are arranged horizontally in a straight line.
On the other hand, in the central electrode type LED shown in
FIG. 2
, since the central electrode
31
is positioned in a central portion of the light take-out region
21
, this type of LEDs can overcome the above-mentioned disadvantage involved in peripheral electrode type LEDs. In other words, the input current can be extended over the whole area of the light take-out region
21
in the central electrode type LEDs.
However, in the case where a finer structure of LED is required as, for example, in a high density LED array of 600 DPI or more, when a central electrode type structure is used, a size of the central electrode cannot be reduced further because of assuring reliability. For this reason, a ratio of LED covered by electrode (hereinafter referred to as “electrode covering ratio”) increases, so that it becomes difficult to obtain an LED of high output. In addition, as a result of providing the remarkably narrow light take-out region
21
, a problem arises also in a shape of light emitting spot.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an LED array affording a high light output and a uniform distribution of light intensity.
According to the invention, an LED array, comprises: a light take-out region provided on a pn junction structured by a cladding layer of a first conductivity type and an active layer of a second conductivity type, the light take-out region having a predetermined area; a contact layer provided on the cladding layer, the contact layer being extended from an inside edge of the light take-out region beyond a central position of the light take-out region; and an electrode provided on the contact layer, the electrode being extended from an inside edge of the light take-out region not to reach the central position thereof.
This invention is concerned with an LED array containing an electrode disposed on a part of each of a plurality of light emitting dots, and an interconnection drawn out alternatively with respect to the direction perpendicular to the aligned direction of the light emitting dots (referred also as “reference straight line”), wherein the electrodes in adjacent light take-out regions are staggered relative to the reference straight line.
In addition to the above described constitution, a light emitting pattern formed by light take-out regions may be arranged in a straight line in the present invention.
According the present invention, a contact layer having a low resistance and made of GaAs or a GaAlAs layer having a low Al mixed crystal ratio is extended from an inside edge of a light take-out region in a light emitting dot to a central position thereof, whereby an input current in the light take-out region expands, and on the other hand, an electrode is extended from an inside edge of a light take-out region to the center of the light take-out region so as to shape like substantially a letter T with a length which is not over the center, whereby increase in an electrode covering ratio in the light take-out region can be suppressed. In other words, the electrode and the contact layer contribute significantly for expanding an input current in the light take-out region. Thus, a uniform light output in the light take-out region can be attained, and the light output can be remarkably improved.
Furthermore, when electrodes in the light take-out regions in adjacent light emitting dots are staggered relative to the direction perpendicular to an aligned direction of the light take-out regions (reference straight line), the light take-out regions are arranged horizontally in substantially a straight line, so that a light emitting pattern in the aligned direction of the light take-out regions are not so staggered, even if light emitting regions effective for printing of an LED printer deviate to a peripheral electrode side.


REFERENCES:
patent: 5067809 (1991-11-01), Tsubota
patent: 5821567 (1998-10-01), Ogihara et al.
patent: 5977565 (1999-11-01), Ishikawa et al.
patent: 5994739 (1999-11-01), Nakagawa et al.

Affiliated with

Also associated with

Rating

Light emitting diode array does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Light emitting diode array, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light emitting diode array will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2439241