Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-02-01
2002-11-05
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S512000, C362S241000
Reexamination Certificate
active
06476551
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an LED array head and a minute reflection optical elements array for use in the LED array head. In particular, the present invention relates to an LED array head used as a light source of an LED array printer and a minute reflection optical elements array for use in the LED array head. The printer includes an optical writing apparatus, such as a LED array printer utilizing an electrophotographic process. The present invention further relates to a method of making the LED array head and the minute reflection optical elements array.
2. Discussion of the Background
The LED array printer using an electrophotographic process with an LED array head as its light source has a merit that deformation of the optical system due to vibration or heat is very small compared with a laser printer using a laser raster system.
FIG. 4
shows an outline of a basic structure of such an LED array printer. In
FIG. 4
, the LED array printer is constructed so that light rays emitted from an LED array head
100
are focused on a surface of a photosensitive body
102
(e.g., a photosensitive drum) through an equal-scale focusing optical system
101
. Thereby, the photosensitive surface of the photosensitive body is exposed by the focused light rays and an electrostatic latent image is formed thereon.
One example of the LED array head
100
, which has already been proposed, is shown in FIG.
5
. In
FIG. 5
, an array of LED light-emitting portions
111
are formed so as to protrude from a surface of a silicon base plate
110
by causing the chemical compound semiconductor to grow in the low-cost silicon base plate
110
used as a head base plate (see Japanese Laid-open Patent Publication No. 9-45955/1997).
In the LED array
100
, respective LED light-emitting portions
111
include plural semiconductor layers electrically connected to individual electrodes
112
and a common electrode
113
both formed on the silicon base plate
110
. The light emitted from the respective LED light-emitting portions
111
is focused on the photosensitive body
102
through the equal-scale focusing optical system
101
.
As shown in
FIG. 6
, the light-emitting portion
111
is formed so as to protrude from the silicon base plate
110
. Thus, light is radiated directly towards the equal-scale optical system
101
. However, light is also radiated from a side surface of the respective LED light-emitting portions
111
in a direction of a surface of the base plate (hereinafter referred to as “side surface light”). This radiated light is reflected by the respective LED light-emitting portions
111
, the individual electrodes
112
, the common electrode
113
, or by a bonding wire for the individual electrodes
112
. The light reflected is radiated toward the photosensitive body
102
as light-emitting points. Therefore, a latent image is formed on the photosensitive body
102
and which includes the side surface light (i.e., a noise component). After the latent image is developed, the developed image is transferred onto paper as a toner image. Consequently, there is a deterioration of image quality, such as an unevenness of line width on the image.
For example, background art Japanese Laid-open Patent Publication No. 6-25244/1994 has already proposed that a light-intercepting film be provided on side surface portions of the respective LED light-emitting portions
111
. The light-emitting portions
111
are formed to have a protruding shape by growing and laminating (four-layer) semiconductor layers:
114
a
,
114
b
,
114
c
and
114
d
on the silicon base plate
110
(see FIG.
6
). The electric current flows from the individual electrodes
112
to the common electrode
113
. The individual electrodes
112
and common electrode
113
are respectively formed on upper and lower surfaces of the silicon base plate
110
. Thereby, the light-emitting portions
111
emit light. In this example, the essentially desired light to be emitted is emitted from the upper surface
111
a
of the respective LED light-emitting portions
111
. However, a side surface
111
b
of the LED light-emitting portion
111
also emits light. Thus, this side-surface light is suppressed by forming a reflective film (i.e., light intercepting film) with a protection film
115
. The proposed LED array head of the background art as mentioned above adopts such a structure.
However, a problem exists with this structure because a part of the light is transmitted through a reflection film
116
. Even though this transmitted light is faint, the light exerts a negative influence on an exposure pattern on a surface of the photosensitive body
102
. Therefore, it is necessary to use a thin film compound of material having a sufficient effect of intercepting the light as the reflection film
116
(e.g., metal) instead of a transparent material such as an oxide compound (oxided substance).
Here, as the method of forming the metal reflection film, a material having an anisotropic property in an film forming direction is generally used. As shown in
FIG. 6
, the shape of the side surface of the LED light-emitting portion
111
in the array direction thereof is constricted in a shape of a 90°—inclined letter V, “<”, or in the shape of a reversed mesa. Therefore, if the side surface
111
b
of the LED light-emitting portion
111
is vertical or has an overhang of a reversed-mesa shape it is inevitably necessary to adopt a film forming process of inclining and piling the base plate, etc. Thus, the process of assembling the LED array head is complicated. This is a problem to be solved.
Furthermore, to avoid a short-circuit between the conductive metal electrodes, it is necessary to insulate the individual electrodes and the light intercepting film with an insulating film. Thus, the number of processes inevitably increases.
In addition, radiated light has a property of a wide radiation angle. Therefore, it is difficult to effectively direct the radiated light into the equal-size focusing optical system
101
in FIG.
4
. In addition, the essential light is first directed into the equal-size focusing optical system
101
and then radiated to expose the photosensitive body
102
. Therefore, it is desired to narrow the radiation angle thereof so that the light can be easily directed into the equal size-focusing optical system as incident light, and thereby a light combining efficiency can be improved.
In recent years, personal and office information apparatus have been largely developed. Therefore, a demand for a high resolution, compact, and inexpensive apparatus has been considerably raised, such as a printer using an electrophotographic process. As an apparatus satisfying such a demand, for instance, there exists an LED array printer using an LED array head having a large number of very small (miniature-sized) LED light-emitting elements arranged in a state of an array on a base plate. Since an LED array printer is a solid-state scanning type printer using the LED array head as the writing light source, it is possible to easily make the apparatus small-sized, compared the raster scanner type laser printer utilizing the semiconductor laser. Furthermore, because the respective LED light-emitting elements in the LED array head perform the writing operation in parallel, it is possible to have high-speed output, especially compared with the raster scanner type laser printer. The LED array printer has the merits as mentioned above.
Another example of an LED array head has been proposed in Japanese Laid-open Patent Publication No. 6-125,1114/1994. For example, referring to
FIG. 10
, the reference numeral
201
represents an LED array chip, in which an LED light-emitting element
202
, a bonding pad
203
, etc. are formed. The LED array chip is mounted on a base plate
204
together with a driver IC (not shown), etc. The LED array chip
201
is constructed such that an electric current is supplied so as to flow between the bonding pad
203
on the LED array chip
201
and a bonding pad
205
dis
Akiyama Shoichi
Osawa Yasuhiro
Saito Tetsuro
Patel Vip
Ricoh & Company, Ltd.
Williams Joseph
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