JP2002247287A - Image reading element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading element which is superior in an optical sensitivity characteristic, high in brightness/darkness current ratio, and high in light response speed. SOLUTION: In the image reading element having a photoconductive layer and a transparent electrode, the transparent electrode is formed of a transparent conduction film consisting of zinc oxide containing aluminum oxide. The photoconductive layer contains a photoconductive material consisting of a porphyrin compound. The photoconductive material consisting of the porphyrin compound is the Y-type crystal material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus suitably used for an image sensor having, for example, a photoconductive layer, converting image information by light into an electric signal, and outputting the electric signal to an image forming apparatus or the like. It relates to an element.

[0002]

2. Description of the Related Art For example, in an image sensor mounted on a facsimile or the like, an image reading element is used as an element for converting image information into an electric signal.

FIG. 1 is a schematic sectional view showing an example of the structure of an image sensor. In this figure, 91 is an image reading element, 92 is a rod lens array, 93 is a light source,
Reference numeral 94 denotes an original. As shown in FIG. 1, light from a light source 93 is applied to a document 94 traveling in the direction of the arrow, and light having an intensity corresponding to the image density is reflected from the document 94. Incident on the image reading element 91, and in the image reading element 91,
It is converted into a signal current of a magnitude corresponding to the light intensity.

FIG. 2 is a schematic diagram showing a process until image information due to a change in intensity of light incident on an image reading element is output as a time-dependent change of a signal current, that is, a time-series signal. The process shown in FIG. 2 is a photocurrent type process in which a change in signal current is read out as it is. A signal current obtained by photoelectric conversion is, for example, a counter electrode (not shown) composed of individual electrodes arranged for each pixel. , Are sequentially transmitted to an exposing unit including, for example, a light emitting diode in the image forming apparatus.

FIG. 3 is an explanatory sectional view showing the basic structure of the image reading element. This image reading element is
A photoconductive layer 9 containing a photoconductive substance (a substance that generates charges by light) is provided between a counter electrode 96 formed for each pixel and a transparent electrode 95 common to all the counter electrodes 96.
7 are interposed. Reference numeral 98 denotes a transparent support. In the image reading device having such a structure, the transparent electrode 95 is usually made of indium oxide (In ₂ O).
₃ ), a NESA film made of tin oxide (SnO ₂ ) (registered trademark of PPG, USA), or an ITO film made of indium oxide-tin oxide (In ₂ O ₃ —SnO ₂ ). It is formed of a transparent conductive film. On the other hand, as a photoconductive substance constituting the photoconductive layer 97, a film can be formed by a simple method such as a printing method or a coating method, and a device having a large area can be economically manufactured. Therefore, those composed of organic substances are being studied.

Until now, the following techniques have been introduced with respect to an image reading element constituted by using a photoconductive substance made of an organic substance. (A) A technique using an azo pigment as a photoconductive substance constituting an image reading element (for example, Japanese Patent Application Laid-Open No. 61-2 / 1986)
No. 85262, JP-A-61-291657,
See JP-A-1-184951. (B) A technique using a titanyl phthalocyanine pigment as a photoconductive substance constituting an image reading element (see, for example, JP-A-4-62476). (C) A technique in which a quinacridone pigment is used as a photoconductive substance constituting an image reading element and a charge transporting substance is used as necessary (for example, Japanese Patent Application Laid-Open No. 6-326290).
Reference).

By the way, the following characteristics are required for the image reading element mounted on the image sensor. (1) High photocurrent and low dark current. This means that it has excellent light sensitivity characteristics and a high light-dark current ratio. Specifically, excellent light sensitivity characteristics means that, for example, when an image reading element is irradiated with light at an illuminance of 1000 lux while applying a voltage of about several volts to several tens of volts, 10 ³ nA
/ 10 mm ² or more (1 nA / dot or more) means that a photocurrent flows, and a high light-to-dark current ratio means that a dark current in an electric field of at least one polarity is extremely small and a ratio of a photocurrent value to a dark current value Means greater. (2) High light response speed. Specifically, the rise time (Tr) and the fall time (Td) of the photocurrent are short.

[0008]

However, the conventional image reading device does not sufficiently satisfy both of the above-mentioned characteristics, and in particular, the light-to-dark current ratio which affects the resolution and gradation of an image is not sufficient. Improvements in the photoconductive layer have been desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide an image reading element having excellent light sensitivity characteristics, a high light / dark current ratio, and a high light response speed. It is in.

[0010]

According to the present invention, there is provided an image reading element having a photoconductive layer and a transparent electrode, wherein the transparent electrode is formed of a transparent conductive film made of zinc oxide containing aluminum oxide. It is characterized by having been done. In the image reading element of the present invention, it is preferable that the photoconductive layer contains a photoconductive substance made of a porphyrin compound. In the image reading element of the present invention, the photoconductive substance composed of the porphyrin compound is preferably a Y-type crystal substance of titanyl phthalocyanine.

[0011]

According to the above-described image reading element, the transparent electrode constituting the image reading element is formed of a transparent conductive film made of zinc oxide containing aluminum oxide, and this transparent conductive film is transparent. Since the work function is small and the Schottky barrier is high, the dark current when light is not irradiated can be made low. As a result, a high light-to-dark current ratio is obtained, and the transparent electrode is formed in the photoconductive layer. As a result of the formation of the high electric field portion on the side, the filter effect due to absorption of light by the photoconductive substance itself of the photoconductive layer becomes small, and therefore, excellent photosensitivity characteristics,
Both high light response speeds can be achieved.

By using a porphyrin-based compound such as a Y-type crystal substance of titanyl phthalocyanine as a photoconductive material for forming the photoconductive layer, the above-mentioned effects can be surely obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image reading device according to the present invention will be described in detail. FIG. 4 is a sectional view showing an example of the configuration of the image reading element of the present invention. This image reading element is configured such that a photoconductive layer 3 is interposed between a transparent electrode 1 and a counter electrode 2. That is, the film-shaped transparent electrode 1 is formed on the insulating support 4,
An image reading element is constituted by providing the photoconductive layer 3 and the counter electrode 2 on top of each other in this order.

As the insulating support 4 constituting the image reading element, glass (for example, float glass, soda glass), quartz (quartz), transparent resin (for example, polyethylene terephthalate, polybutylene terephthalate, polyether sulfone, polycarbonate), etc. It is formed of an insulating and transparent material.

Transparent electrode 1 constituting image reading element
Is zinc oxide containing aluminum oxide (hereinafter referred to as “A
ZO ”. ). This AZO contains, for example, 10% by mass or less, preferably 1 to 5% by mass of aluminum oxide in zinc oxide. The film thickness of AZO forming the transparent electrode 1 is usually, for example, 1 μm or less, preferably 0.1 to 0.1 μm.
5 μm.

As a method for forming the transparent electrode 1 made of AZO, an evaporation technique such as a vacuum evaporation method or a sputtering method can be adopted. For example, using a sintered body obtained by adding aluminum oxide in an appropriate ratio to powder of zinc oxide as a target, the AC power is set to 100 W by sputtering magnetron sputtering under an atmosphere of Ar gas pressure of 1 Pa, It is preferable to perform sputtering at a temperature of 100 ° C. Further, film formation can also be performed by an evaporation method such as laser ablation.

The photoconductive layer 3 interposed between the transparent electrode 1 and the counter electrode 2 contains a porphyrin compound as a photoconductive substance. Specifically, among porphyrin-based compounds, it is particularly preferable to use a Y-type crystal substance of titanyl phthalocyanine (oxytitanium phthalocyanine). Here, titanyl phthalocyanine is a compound represented by the following structural formula.

[0018]

Embedded image

"Y-type crystal" of titanyl phthalocyanine
Are stable A-type crystals (monoclinic and also referred to as “β type”) and stable B-type crystals (triclinic and “α
Also called a "type." ) Exists as an intermediate stable phase. The crystal structure of this Y-type crystal is a monoclinic crystal of a space group P2 ₁ / c, and its lattice constant is a ≒ 1.38 nm, b ≒.
1.39 nm, c ≒ 1.51 nm, β ≒ 120.2 °. The twist angle of the packing in the ab plane of the Y-type crystal is 4 °, which is smaller than the twist angle (19 °) of the A-type crystal having a similar crystal structure.

FIG. 5 is an X-ray diffraction diagram of a titanyl phthalocyanine Y-type crystal material [powder X-ray diffraction (CuK
α)]. As shown in the figure, 9.6 °, 24.1 ° and 2
Characteristic peaks are observed around 7.2 °, and by confirming the presence of these peaks in the diffractogram, Y
Identification of the type crystal material can be performed.

The Y-type crystal substance is much more excellent in improving the image reading characteristics, particularly the light response characteristic, than the substance having another crystal structure (A type, B type) of titanyl phthalocyanine. By including the Y-type crystal substance as a photoconductive substance in the photoconductive layer 3, the obtained image reading device has excellent photosensitivity characteristics, a high light-dark current ratio, and a high photoresponse speed. .

The method of forming the photoconductive layer 3 includes: (1) a method of depositing the Y-type crystal substance on the transparent electrode 1;
The Y-type crystal substance and the binder resin are dissolved or dispersed in an organic solvent to prepare a coating solution, and the coating solution is applied to the transparent electrode 1 by, for example, a bar coater method, a spinner method, a printing method, or a dipping method. A method of applying and drying the coating film can be used, and the method (2) is preferably used. The thickness of the photoconductive layer 3 thus formed is generally 0.1 to 10 μm, preferably 0.5 to 10 μm.
3.0 μm.

As the binder resin used for forming the photoconductive layer 3, those known as binder resins for electrophotographic photosensitive members can be used as they are, for example, polyethylene, polypropylene, vinyl chloride, vinyl acetate. Consisting of polymers of addition polymerization type or polycondensation type such as vinyl butyral, vinyl formal, acrylic resin, methacrylic resin, epoxy resin, polyurethane resin, phenolic resin, polyester resin, alkyd resin, polycarbonate resin, silicone resin and melamine resin. Resins; copolymer resins such as vinyl chloride-vinyl acetate copolymer and vinyl chloride-vinyl acetate-maleic anhydride copolymer; and high-molecular organic semiconductors such as poly-N-vinyl carbazole. Of these, polycarbonate is preferred There. The ratio of the binder resin constituting the photoconductive layer 3 to the Y-type crystal substance of titanyl phthalocyanine is, for example, a ratio of 10 to 100 parts by mass of the Y-type crystal substance to 100 parts by mass of the binder resin.

The photoconductive layer 3 may contain a P-type or N-type charge transport material (CTM), if necessary. The content ratio of CTM is set to 0 to 100 parts by mass with respect to 100 parts by mass of the binder resin.

The counter electrode 2 can be formed by depositing or sputtering a metal such as aluminum, tin, lead, nickel, palladium, gold or platinum on the surface of the photoconductive layer 3. Although only one counter electrode is shown in FIG. 4, the counter electrode constituting the image reading element of the present invention is generally formed of individual electrodes arranged for each pixel.

AZO is transparent and has a small work function.
NESA film used as a conventional transparent conductive film, I
A Schottky barrier larger than the TO film is formed,
The dark current at the time of non-irradiation of light can be reduced, and as a result, a high light-to-dark current ratio can be obtained, and a high electric field portion is formed in the photoconductive layer 3 on the transparent electrode 1 side. In addition, the filter effect due to the photoconductive substance itself of the photoconductive layer 3 absorbing light is small, and therefore, both excellent photosensitivity characteristics and high photoresponse speed can be achieved.

The image reading element having the above-described configuration is used by applying a voltage between both electrodes so that the polarity of the counter electrode 2 with respect to the transparent electrode 1 becomes positive or negative.
Since this image reading element has a single configuration in which only the photoconductive layer 3 is interposed between the transparent electrode 1 and the counter electrode 2, a voltage (drive voltage) applied between both electrodes is provided.
Can be set low. Note that the configuration of the image reading element of the present invention is not limited to the configuration shown in FIG. 4, and various configurations as described below can be employed.

<Structure in the case of using the polarity of the counter electrode side as (positive)> (1) Transparent electrode / photoconductive layer / N-type charge transport layer (N-type CT
L) / counter electrode (2) transparent electrode / p-type charge transport layer (p-type CTL) / photoconductive layer / counter electrode (3) transparent electrode / electron injection blocking layer / photoconductive layer / counter electrode (4) transparent electrode / Electron injection blocking layer / Photoconductive layer / N-type CT
L / counter electrode (5) Transparent electrode / P-type CTL / photoconductive layer / hole injection blocking layer / counter electrode

<Configuration when using the polarity of the counter electrode side as (negative)> (1) Transparent electrode / photoconductive layer / P-type CTL / counter electrode (2) Transparent electrode / N-type CTL / photoconductive layer / Counter electrode (3) Transparent electrode / hole injection blocking layer / photoconductive layer / counter electrode (4) Transparent electrode / hole injection blocking layer / photoconductive layer / P-type C
TL / counter electrode (5) Transparent electrode / N-type CTL / photoconductive layer / electron injection blocking layer / counter electrode

In the above, the “hole injection blocking layer”
The generation of dark current is suppressed by blocking the flow of holes, and can be formed of a resin such as a polyamide resin having a resistivity of, for example, about 10 ⁶ to 10 ¹⁴ Ω · cm. Also, "Electron injection blocking layer"
Is to suppress the generation of dark current by blocking the flow of electrons, and is formed of, for example, a resin such as an ethylene copolymer having a resistivity of about 10 ⁶ to 10 ¹⁴ Ω · cm. Can be.

In the above, P-type CTL or N-type CT
As a method for forming L, for example, 10 to 10,000 parts by mass of CT with respect to 100 parts by mass of a binder resin
M may be dissolved in an organic solvent to prepare a coating solution, and the coating solution may be applied and dried.

[0032]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited by these examples. <Example 1> 0.3 g of titanyl phthalocyanine Y-type crystal substance (Y-TiOPc) [manufactured by Sanyo Dyeing Co., Ltd.] and polycarbonate resin "K1300" [manufactured by Teijin Chemicals Ltd.]
1.0 g was dissolved in 30 ml of 1,2-dichloroethane to prepare a coating solution for forming a photoconductive layer. On one surface of a glass substrate, zinc oxide (AZO) containing aluminum oxide at a ratio of 3% by mass is vapor-deposited to form a transparent electrode having a thickness of 0.2 μm. The prepared coating solution was applied using a bar coater and dried at room temperature for 24 hours to form a photoconductive layer having a dry film thickness of 1.4 μm. Next, a vacuum deposition of aluminum was performed on the surface of the photoconductive layer to form a counter electrode composed of an aluminum vapor-deposited film, thereby producing an image reading device having the configuration shown in FIG.

<Comparative Example 1> The procedure of Example 1 was repeated, except that a transparent electrode was formed using ITO instead of AZO.
An image reading device for comparison was manufactured.

Example 2 An image reading element for comparison was manufactured in the same manner as in Example 1 except that "PS (polystyrene)" was used instead of the polycarbonate resin "K1300" as a binder. .

<Comparative Example 2> The procedure of Example 2 was repeated, except that a transparent electrode was formed using ITO instead of AZO.
An image reading device for comparison was manufactured.

<Evaluation of Image Reading Element> Examples 1 and 2
Table 1 shows the respective constituent materials constituting the image reading devices manufactured according to Comparative Examples 1 and 2. Further, for each of the image reading elements manufactured in Examples 1 and 2 and Comparative Examples 1 to 3, the electric field strength of 5 V / μm was formed between the transparent electrode and the counter electrode, with the polarity on the counter electrode side being positive. Voltage was applied so as to be in a state of being closed. In this state, pulse-type repetitive exposure (blinking cycle 200 msec) as shown in FIG. 6A is performed, and the rise time (Tr) and fall time (Td) are measured to evaluate the optical response characteristics. The photocurrent when the light amount of 3000 μW / cm ² was irradiated was measured to evaluate the photosensitivity characteristics, and the dark current without light irradiation was measured to calculate the light-dark current ratio. The results are shown in Table 2. Here, the “rise time (Tr)” means that when exposure is started (ON),
The time from when the output value of the signal current reaches 10% to 90% of the saturation value is referred to as “fall time (Td)”. It means the time from 90% to 10% of the value [FIG.
(B)).

[0037]

[Table 1]

[0038]

[Table 2]

From the results shown in Tables 1 and 2, from Example 1
It can be understood that the image reading device according to Comparative Example 1 has a significantly lower dark current and a higher light-dark current ratio than the image reading device according to Comparative Example 1, and has excellent light sensitivity characteristics. It is noteworthy that such an excellent light / dark current ratio is exhibited without providing a carrier injection blocking layer. Moreover, it is clear that the image reading device according to Example 1 has shorter Tr and Td and higher light response speed than the image reading device according to Comparative Example 1.

Similarly, the image reading device according to Example 2 has a higher light-dark current ratio than the image reading device according to Comparative Example 2, and has excellent light sensitivity characteristics. Moreover, it is clear that the light response speed is high.

[0041]

According to the image reading device of the present invention, the transparent electrode constituting the image reading device is formed of a transparent conductive film made of AZO, and this transparent conductive film is transparent and has a small work function. Since the Schottky barrier is high, the dark current when light is not irradiated can be reduced. As a result, a high light-to-dark current ratio can be obtained, and in the photoconductive layer, a high electric field portion is provided on the transparent electrode side. Is formed, the photoconductive substance itself of the photoconductive layer itself has a small filter effect by absorbing light,
Therefore, both excellent light sensitivity characteristics and high light response speed can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of the structure of an image sensor.

FIG. 2 is a schematic diagram showing a process until image information is output as a temporal change of a signal current.

FIG. 3 is an explanatory cross-sectional view showing a basic structure of an image reading element.

FIG. 4 is a cross-sectional view illustrating an example of the configuration of the image reading element of the present invention.

FIG. 5 is an X-ray diffraction diagram of titanyl phthalocyanine in a Y-type crystal substance.

FIGS. 6A and 6B are charts showing (a) the amount of exposure to the image reading element and (b) the change over time in the signal current from the image reading element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent electrode 2 Counter electrode 3 Photoconductive layer 4 Insulating support 91 Image reading element 92 Rod lens eye 93 Light source 94 Document 95 Transparent electrode 96 Counter electrode 97 Photoconductive layer 98 Transparent support

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M118 AA02 AA05 AB01 BA07 CA06 CA14 CB20 FB09 5C051 AA01 BA02 DA03 DB01 DB08 DC02 DC07 5F088 AA11 AB11 BA02 BA04 BB03 FA02 FA05

Claims (3)

[Claims] 1. An image reading device having a photoconductive layer and a transparent electrode, wherein the transparent electrode is formed of a transparent conductive film made of zinc oxide containing aluminum oxide. 2. The image reading element according to claim 1, wherein the photoconductive layer contains a photoconductive substance made of a porphyrin compound. 3. The image reading device according to claim 2, wherein the photoconductive substance comprising a porphyrin compound is a Y-type crystal substance of titanyl phthalocyanine.