Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-05-27
2002-05-14
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S237000, C257S088000
Reexamination Certificate
active
06388696
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an LED array constituted by forming a plurality of LEDs (light emitting diodes) on a single semiconductor substrate, and an LED printer head constituted by employing this LED array, and in particular, it relates to an LED array that is capable of supporting a high density printer head of 1200 DPI (dots per inch) or higher.
Light emitting diode (hereafter referred to simply as LED) arrays are employed as exposure light sources (print heads) for the photosensitive drums in electrophotographic printers.
FIG. 1
illustrates an example of an LED structure in the prior art, with FIG.
1
(
a
) presenting its top view and FIG.
1
(
b
) presenting a cross section through line A-A′ in FIG.
1
(
a
). The LED array illustrated in
FIG. 1
supports a low density printer head with a resolution of 600 DPI or lower, and is constituted by simply providing LEDs
10
in a single row on an n-type semiconductor substrate
2
.
In
FIG. 1
, a plurality of p-type semiconductor layers
13
are formed on the n-type semiconductor substrate
2
, with a layer insulating film
12
having opening portions
16
formed at the surface of the n-type semiconductor substrate
2
. On the layer insulating film
12
, a plurality of p-side electrodes (discrete electrodes)
14
that are individually connected to a p-type semiconductor layer
13
at an opening portion
16
are formed. In addition, an n-side electrode (common electrode)
15
is formed over the entire rear surface of the n-type semiconductor substrate
2
. When a voltage is applied between a p-side electrode
14
and the n-side electrode
15
at an LED
10
, a phenomenon of light emission occurs at the bonding surface of the n-type semiconductor substrate or interface of the n-type semiconductor layer
13
, and the emitted light is radiated to the outside through the surface of the p-type semiconductor layer
13
. The p-side electrodes
14
are each constituted of an aluminum (Al) film or an Al alloy film, whereas the n-side electrode
15
is constituted an Au alloy film.
However, in a super-high density LED array of 1200 DPI or higher, the pitch of the p-side electrodes becomes narrower and the wiring space for the p-side electrodes becomes reduced, making it difficult to provide a bonding pad (p-side pad electrode) for each p-side electrode. Thus, an LED array supporting a high density of 1200 DPI or higher designs the structure illustrated in
FIG. 2
to reduce the number of p-side pad electrodes. FIG.
2
(
a
) is a top view illustrating an example of an LED array in the prior art the supports a high density of 1200 DPI. FIG.
2
(
b
) presents a cross section through line A-A′ in FIG.
2
(
a
), and FIG.
2
(
c
) presents a cross section through line B-B′ in FIG.
2
(
a
).
The LED array illustrated in
FIG. 2
is achieved by providing a plurality of LEDs at each of a plurality of n-type semiconductors blocks
11
with the elements isolated from one another by a high resistance semiconductor substrate
32
and separating grooves
3
. In each n-type semiconductor block
11
, a plurality of p-type semiconductor layers
13
, p-side electrodes
44
to be individually connected to the p-type semiconductor layers
13
, an n-type contact electrode
45
a
to be connected to the n-type semiconductor block
11
and an n-side pad electrode
45
b
to be connected to the n-side contact electrode
45
a
are formed. Among the plurality of p-side electrodes
44
provided in the block, only a specific number of p-side electrodes are provided with a p-side pad electrode
44
b
(in
FIG. 2
, one p-side pad electrode
44
b
is formed in each block). An n-side electrode
45
constituted of the n-side contact electrode
45
a
and the n-side pad electrode
45
b
is a common electrode shared by all the LEDs within the block.
When a voltage is applied between a p-side electrode
44
and the n-side electrode
45
, an LED causes a light emission phenomenon at the bonding surface of the n-type semiconductor substrate
32
and the p-type semiconductor layer
13
, and this emitted light is radiated to the outside through the surface of the p-type semiconductor layer
13
. The p-side electrodes
44
are each constituted of an aluminum (Al) film or an Al alloy film, whereas the p-side electrode
45
is constituted of an Au alloy film.
Furthermore, p-side common wirings
4
which connect with specific p-side electrodes
44
in the individual blocks at via holes
21
are formed, and through the p-side common wirings
4
, p-side electrodes
44
that are not provided with a p-side pad electrode in a given block are connected to p-side electrode
44
having a p-side pad electrode in another n-type semiconductor block
11
. A first layer insulating film
12
is formed between the n-type semiconductor blocks
11
and the p-side common wirings
4
, and a second layer insulating film
48
is formed between the p-side common wirings
4
and the p-side electrodes
44
.
However, in LED arrays in the prior art, since it is necessary to separately form the p-side electrodes and the n-side electrodes using different conductive film materials, the number of manufacturing steps is high, presenting a problem in that the production cost is high also. In particular, in the LED array illustrated in
FIG. 2
, which necessitates the n-side contact electrodes and the n-side pad electrodes to be formed separately, the number of manufacturing steps is further increased, to result in a further increase in production cost.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a new and improved LED array, whose n-side contact electrodes and p-side electrodes, n-side contact electrodes and n-side pad electrodes or n-side contact electrodes, n-side pad electrodes and p-side electrodes can be formed using a single conductive film through a single manufacturing step to simplify the manufacturing process, to achieve a reduction in production cost and also to achieve a reduction in the inconsistency in characteristics among the individual substrates (wafers), and an LED printer head employing the LED array.
Another object of the present invention is to provide a new and improved LED array that achieves higher yield with peeling of the n-side pad electrodes prevented by forming the n-side pad electrodes at the n-side semiconductor substrate in close adherence, and an LED printer head employing the LED array.
Yet another object of the present invention is to provide a new and improved LED array that achieves a simplification in the manufacturing process and reduced production cost by constituting the n-side electrodes in a single-layer structure, and an LED printerhead employing the LED array.
A still further object of the present invention is to provide a new and improved LED array that achieves a reduction in the chip size by constituting the n-side electrodes in a simple graphic shape and the entire n-side electrodes as n-side pad electrodes, and an LED printer head employing the LED array.
A still further object of the present invention is to provide a new and improved LED array that can be achieved as an end surface light emitting LED array by providing the p-side pad electrodes and the n-side electrodes at the same side relative to the row of the light emitting portions that are formed at high density, to facilitate mounting at a printer head and to achieve a reduction in the width of the LED array, and an LED printer head employing the LED array.
A still further object of the present invention is to provide a new and improved LED array, and an LED printer head through which the head size of the printer head can be reduced by constituting the printer head employing the LED array described above.
In order to achieve the objects described above, in the LED array in a first aspect of the present invention, which is constituted by forming a second conductive-type semiconductor layer at a first conductive-type semiconductor substrate and forming a first conduction-side contact electrode to be co
Hamano Hiroshi
Ogihara Mitsuhiko
Shimizu Takatoku
Taninaka Masumi
Kunitz Norman N.
Nguyen Lamson D.
Oki Electric Industry Co,. LTD
Venable
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