Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
1999-08-09
2003-01-28
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S054000, C257S072000, C257S291000, C250S370140, C250S370090, C349S041000
Reexamination Certificate
active
06512279
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric converter, its driving method, and a system including the photoelectric converter. More particularly, the present invention relates to a one-dimensional or two-dimensional photoelectric converter, its driving method, and a system including the photoelectric converter which can read the same size of original copies such as, for example, a facsimile, a digital copying machine, or an X-ray camera.
2. Related Background Art
Conventionally, a read system having a condensed optical system and a CCD-type sensor has been used as a read system such as a facsimile, a digital copying machine, or an X-ray camera. In recent years, however, a development of photoelectric converting semiconductor materials represented by hydrogenated amorphous-silicon (hereinafter “a-Si”) has contributed to an advancement of developing so-called a contact-type sensor in which a photoelectric converting element and a signal processor are formed on a large-sized substrate to read the same size of copies as for an information source by using a photoelectric system, and it has been or is being put to practical use. Particularly, a-Si can be used not only as photoelectric converting materials, but also as semiconductor materials for thin film electric field effect type transistor (hereinafter “TFT”), therefore, photoelectric converting semiconductor layer and a TFT semiconductor layer can be formed at a time conveniently.
FIGS. 1A and 1B
are typical sectional views each of which is used to show an example of a structure of a conventional optical sensor, in other words, an example of a layer structure of the optical sensor, and
FIG. 1C
is a schematic circuit diagram used to describe a driving method, which shows an example of a typical driving method available for both
FIGS. 1A and 1B
. Each of
FIGS. 1A and 1B
shows a photodiode type optical sensor; the structure in
FIG. 1A
is called a PIN type, and that in
FIG. 1B
is called a Schottky type. In
FIGS. 1A and 1B
, reference numerals
1
,
2
,
3
,
4
, and
5
indicate an insulating substrate, a lower electrode, a p type semiconductor layer (hereinafter “p-layer”), an intrinsic semiconductor (hereinafter “i-layer”), an n type semiconductor (hereinafter “n-layer”), and a transparent electrode, respectively. In the Schottky type structure in
FIG. 1B
, materials for the lower electrode
2
are appropriately selected to form a Schottky barrier layer so that unnecessary electrons will not be injected from the lower electrode
2
to the i-layer
4
.
In
FIG. 1C
, reference numerals
10
,
11
, and
12
indicate the symbolized above optical sensor, a power supply, and a detector of a current amplifier or the like, respectively. In the optical sensor
10
, a direction shown by C indicates a side of the transparent electrode
6
in
FIGS. 1A and 1B
, a direction shown by A indicates a side of the lower electrode
2
, and the power supply
11
is set so that a positive voltage is applied to side C against side A. Now, the operation is roughly described below.
As shown in
FIGS. 1A and 1B
, light is incident from a direction shown by an arrow. When the light reaches the i-layer
4
, it is absorbed and electrons and holes are generated. Since an electric field is applied to the i-layer
4
by the power supply
11
, the electrons move to the side C, in other words, they move to the transparent electrode
6
after passing through the n-layer
5
, and the holes move to the side A, in other words, to the lower electrode
2
. Accordingly, optical current is fed to the optical sensor
10
. If light is not incident on the layer, electrons and holes are not generated on the i-layer
4
; for the holes in the transparent electrode
6
, the n-layer
5
acts as a hole injection blocking layer, and for electrons in the lower electrode
2
, the p-layer
3
in the PIN type structure in
FIG. 1A
or the Schottky barrier layer in the Schottky type structure in
FIG. 1B
acts as an electron injection blocking layer, therefore, both the electrons and holes cannot move and no current is applied. As described above, the presence or absence of the incident light varies the current fed to a circuit. If the change is detected by the detector
12
in
FIG. 1C
, the layers act as an optical sensor.
For the above conventional optical sensor, however, it is difficult to produce a high signal-to-noise ratio and low cost photoelectric converter. The reasons are described below.
The first reason is that the injection blocking layer is required at two portions both in the PIN type structure in FIG.
1
A and the Schottky type structure in FIG.
1
B.
In the PIN type structure in
FIG. 1A
, the n-layer
5
which is an injection blocking layer requires characteristics of not only introduce electrons to the transparent electrode
6
and but also inhibiting holes from being injected to the i-layer
4
. If the layer loses one of the characteristics, the optical current may be reduced or increased due to current generated without incident light (hereinafter “dark current”), which leads to lowering the signal-to-noise ratio. The dark current itself can be considered as a noise and also includes fluctuation called a shot noise, in other words, a quantization noise, therefore, the quantization noise in the dark current cannot be reduced even if the dark current is removed by the detector
12
.
Generally, to improve the characteristics, it is required to optimize conditions of creating films for the i-layer
4
and n-layer
5
and conditions of annealing after the creation. Also for the p-layer
3
which is another injection blocking layer, however, the equivalent characteristics are required though electrons and holes are reversed, and the both conditions must be optimized in the same manner. In general, the optimizing conditions for the former n-layer are not the same as for the p-layer, and it is hard to satisfy the both conditions simultaneously.
In other words, if the injection blocking layer is required at two portions in the same optical sensor, it is difficult to form an optical sensor having high signal-to-noise ratio.
It can also be said to the Schottky type structure in FIG.
1
B. Additionally, in the Schottky type structure in
FIG. 1B
, a Schottky barrier layer is used for one injection blocking layer, in which a difference between work functions of the lower electrode
2
and the i-layer
4
is used, therefore, materials for the lower electrode
2
are restricted or the characteristics are largely affected by localized levels of an interface and it is further difficult to satisfy the conditions.
It is also reported that approx. 100 Å of a thin silicon or a metal oxide or nitride film is formed between the lower electrode
2
and the i-layer
4
to further improve the characteristics of the Schottky barrier layer. In this method, however, holes are introduced to the lower electrode
2
by using a tunneling effect to enhance an effect of inhibiting electrons from being injected to the i-layer
4
and a difference between work functions is also used, therefore, materials for the lower electrode
2
must be restricted. In addition, since it uses contrary characteristics, i.e., blocking injection of the electrons and movement of the holes caused by the tunneling effect, the oxide or nitride film must be extremely thin, i.e., approx. 100 Å. The control of the thickness and layer features is difficult and reduces productivity.
Further, the requirement of two portions of the injection blocking layer not only reduces productivity, but also increases cost. This is because desired characteristics as an optical sensor cannot be obtained if a trouble is caused by dust even at a single portion of the injection blocking layer since the injection blocking layer is important as its characteristics.
By using
FIG. 2
, the second reason is described below.
FIG. 2
shows a layer structure of an electric field effect type transistor (TFT) formed by thin semiconductor films. The TFT is sometimes used a
Itabashi Satoshi
Kaifu Noriyuki
Kobayashi Isao
Mizutani Hidemasa
Takeda Shinichi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Jackson, Jr. Jerome
LandOfFree
Photoelectric converter, its driving method, and system... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photoelectric converter, its driving method, and system..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoelectric converter, its driving method, and system... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3052611