JP3231893B2 - Image sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor for reading an image with a photoelectric conversion element having a photoconductive layer using an organic photoconductive material.

[0002]

2. Description of the Related Art Several types of line image sensors for use in image input devices such as facsimile machines and image scanners have been proposed with the aim of achieving higher performance and lower cost. Sensor materials used for these image sensors are a-Si (amorphous silicon), C
dS, CCD (Charge Coupled Dev)
ice) and an organic photoconductive material, but an image sensor using an organic photoconductive material is easy to form a film, excellent in productivity, and easy to increase in area. It has several advantages. For this reason, some examples of image sensors using an organic material are known. (For example, JP-A-61-285262, JP-A-61-291657, and JP-A-1-184961.
In addition, when image sensors are classified according to their structure, a non-matrix type in which a driving switch is provided for each element of the sensor, and a matrix type in which all elements of the sensor are divided into a plurality of blocks and subjected to matrix wiring. And divided into In particular, a photoconductive matrix image sensor is excellent in that the number of driving ICs can be reduced and cost can be reduced, but a plurality of elements are connected to one matrix wiring. Therefore, a current spills between the elements.
For this reason, a blocking diode for preventing current from flowing around is often added to each element. The optical signal detection method of this sensor is to use a resistor as a load, apply a photocurrent to this, detect the voltage generated at this resistor, or store the charge flowing from the sensor in the stray capacitance of the wiring, etc. There are detection methods and the like, but when the sensor current is small, the latter, which is more resistant to noise, is more advantageous.

[0003]

However, the addition of a blocking diode for preventing current from flowing into each element of the image sensor increases the number of manufacturing steps and causes a reduction in yield. In addition, if this is removed, current sneak around between the elements occurs, which causes a problem that the SN ratio deteriorates and accurate image information cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is an object of the present invention to provide a semiconductor device in which a reverse bias voltage is applied during light irradiation compared with a device resistance value when a forward bias voltage is applied during light signal detection. By using a photoelectric conversion element made of an organic photoconductive material having a sufficiently large resistance value for the element in a matrix image sensor, a blocking diode is added to each element when reading a signal from this image sensor. It is another object of the present invention to obtain an image sensor capable of preventing an electric current from flowing between the elements of the sensor without causing the current to circulate, thereby obtaining an accurate image.

[0005]

In the image sensor according to the present invention, the resistance value when a reverse bias voltage is applied during light irradiation as each photoelectric conversion element is smaller than the resistance value when a forward bias voltage is applied. It has an organic photoconductive layer that is 100 times or more larger.

[0006]

In the present invention, since an organic photoconductive material is used for the photoconductive layer of the photoelectric conversion element, an optical signal is detected by applying a forward bias voltage to lower the resistance of each photoelectric conversion element. When a reverse bias voltage is applied at the time of irradiation, the resistance value of the photoelectric conversion element becomes 100 times or more larger than the resistance value of the photoelectric conversion element when a forward bias voltage is applied, and the sneak current between the photoelectric elements is suppressed. .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a so-called sandwich type element among photoelectric conversion elements used in an image sensor according to the present invention will be described with reference to FIG.

FIG. 1A is a plan view showing a configuration example of a photoelectric conversion element used in the image sensor of the present invention.
FIG. 2B is a cross-sectional view taken along line II of FIG. In FIG. 1, a blocking layer 2 and a photoconductive layer 3 are formed on a support 4 on which individual electrodes 1 are provided, and a common electrode 5 is further provided thereon. In this case, the blocking layer 2
Is provided directly in contact with the individual electrode 1 serving as a positive electrode. One photoelectric conversion element is constituted by one of the individual electrodes 1, an electrode pair facing the individual electrode, and the photoconductive layer 3 and the blocking layer 2 interposed between the pair of electrodes, and corresponds to the light of the individual photoelectric conversion element. Signal can be taken out. The photoconductive layer 3 and the blocking layer 2 may be common to each photoelectric conversion element. Further, at least one of the electrodes, that is, the individual electrode 1 (or the common electrode 5) is required to be a transparent electrode that sufficiently transmits light because it serves as a light incident path. Examples of the transparent electrode include metal oxides such as indium oxide, tin oxide, and indium tin oxide films, and thin films of metals such as gold and aluminum. Various metals can be used for the other opposing electrode, that is, the common electrode 5 (or the individual electrode 1), and examples thereof include aluminum, titanium, gold, silver, copper, nickel, chromium, molybdenum, tantalum, and tungsten. . When exposure is performed from the side of the support 4, it is necessary that the support 4 also sufficiently transmits light. As the charge generating substance of the organic photoconductive layer 3, azo pigments, phthalocyanine pigments, polycyclic quinone pigments, perylene pigments, merocyanine pigments, squarium pigments, etc., and as the charge transfer substances, hydrazone derivatives, pyrazoline derivatives, carbazole, Examples include heterocyclic derivatives such as indole and oxadiazole, derivatives such as triphenylamine, stilbene derivatives, and high molecular compounds having the above compound in the side chain or main chain. Among them, hydrazone derivatives, arylamines, and stilbenzene derivatives are more preferable charge transfer materials. A layer configuration in which the above-described charge generation material is dispersed in a binder as the organic photoconductive layer 3;
A layer configuration in which a charge generation material and a charge transfer material are contained as effective components, and both materials are dispersed in a binder resin, and a layer configuration in which a charge generation layer and a charge transfer layer are laminated are exemplified.
Above all, a photoconductive layer comprising at least a charge generation layer containing a charge generation substance and a charge transfer layer containing a charge transfer substance is preferable.

Each photoelectric conversion element of the image sensor of the present invention
Is made of an organic photoconductive material and a forward bias voltage of 7 is applied.
To detect the optical signal and apply a reverse bias voltage during light irradiation.
The resistance value of the photoelectric conversion element when applied increases the forward bias voltage.
Sufficiently larger than the resistance value of the photoelectric conversion element when applied
Although the characteristic is sufficiently large here, for example,
Light irradiation (normally 15μW / cm^TwoAbout), reverse bias voltage
The resistance value of the photoelectric conversion element at
Forward bias voltage applied to photoelectric conversion element when optical signal is detected
(Usually about 10V to 40V)
It is 100 times or more the resistance value, more preferably 2 times.
This is a characteristic having 000 times or more. Therefore, like this
Layer with charge generation layer and charge transfer layer that can provide various characteristics
A configuration is particularly preferred. Also, the optical signal of the photoelectric conversion element
Detection is usually performed by applying a voltage (normally 10 V to 4
0V ), The photocurrent (light current)
Current) is sufficiently larger than the photocurrent (dark current) when light is not irradiated.
(50 times or more) is possible, but this optical signal detection
Sometimes the voltage applied to the device is a forward bias voltage, which is positive and negative
The reverse voltage is defined as a reverse bias voltage.

Next, the charge storage of the image sensor of the present invention will be described. product
In the scheme A driving example will be described. FIG. 2 shows an image sensor according to the present invention.
FIG. 3 is a driving circuit diagram of the circuit shown in FIG.
FIG. In FIG. 2, S11 to SMN are the photoelectric converters of FIG.
It is a conversion element, and a photoelectric conversion element row is formed by arranging N × M pieces.
And is divided into M blocks.
Are connected to the common electrode side wirings K1 to KM. Ma
The individual electrode 1 side of the photoelectric conversion element is a matrix wiring.
L1 to LN. C11 to CMN are element capacitors
R11 to RMN are element resistances, and LC1 to L-CN are
The stray capacitance and VS of the trix lines L1 to LN are the sensor drive
Power supply (in this example, the forward bias voltage of the sensor is negative
X1 to XM are power switches, and Y1 to YN are power switches.
Load reset switch, A1 to AN are impedance conversion
Amplifiers, Z1 to ZN are read-side switches, GND is
Source ground.

In FIG. 3, power source switches X1 to XM
Indicates that the pulse is in the “H” state on the sensor drive power supply VS side,
The state of “L” is the power ground (GND) side. In addition, the charge reset switches Y1 to YN output pulses "H".
State is turned on.

First, the charge reset switches Y1 to YN are all turned on, the power supply switches X1 to XM-1 are all turned to the power ground GND, XM is the sensor drive power supply VS, and the reading switches Z1 to ZN are all turned off. In this state, the power switch X1 is switched from the power ground GND to the sensor driving power VS, and the power switch XM is switched from the sensor driving power VS to the power ground GNA. Then, a voltage is applied to the photoelectric conversion elements S11 to S1N, and the element capacitors C11 to C1N are charged. Next, the charge reset switches Y1 to YN are sequentially turned off every clock. Since the photoelectric conversion elements S11 to S1N generate photocurrents corresponding to the respective light amounts, the element capacitors C11 to C1N are charged according to the photocurrents immediately after the charge reset switches Y1 to YN are turned off. The discharged charges are discharged, and the charges are accumulated in the floating capacitances L-C1 to L-CN of the wiring. Therefore, a voltage is generated in the matrix wirings L1 to LN.

On the other hand, the photoelectric conversion elements S11 to S1N are connected to corresponding elements from the second block to the Mth block on the individual electrode 1 side by matrix wirings L1 to LN, respectively. Since the fifth side is the power ground GND side, a reverse bias voltage is applied to each of the photoelectric conversion elements S21 to SMN of the second to Mth blocks by the voltage generated in the matrix wirings L1 to LN. A current flows through S21 to SMN. This is the sneak of the current between the sensor elements, and when the time t elapses, the matrix wirings L1 to L1.
A voltage expressed by the following equation is generated in LN according to the amount of each charge.

[0014]

Vout = VS１ (r2 / (r1 + r2)) ・ (1-exp (-t / τ)) where r = 1 / (1 / r1 + 1 / r2), c = c1 +
c 2 + c 3 τ (time constant) = c · r [Equation 1], r 1 is a selected element resistance (the selected element is a sensor signal detection target element) in the sensor drive power supply VS, and r 2 is connected to the selected element by matrix wiring. The parallel resistance at the reverse bias voltage Vout of all the non-selected element resistances, c1 is the selection element capacitance, c2 is the parallel capacitance of all the non-selection element capacitances connected to the selection element and the matrix wiring on the individual electrode 1 side, c3 Is the stray capacitance of the matrix wiring, VS is the sensor drive power supply, and t is the accumulation time.

The photoelectric conversion element S used in the present invention
Since the element resistances of 11 to SMN are non-linear resistances at the time of irradiating a constant amount of light, the element resistance value is a function of the element applied voltage. For example, when the selection element is S12, the non-selection elements connected to the selection element S12 by matrix wiring are S22 to SM2, and the selection element resistance r1 is the resistance of R12 and the non-selection element resistance R22 to RM2 in the sensor drive power supply VS. Reverse bias voltage Vou
At t, the total parallel resistance is r2, the selected element capacitance c1 is C12,
The total parallel capacitance of the unselected element capacitances C22 to CM2 is c2, and the stray capacitance LC2 of the wiring is the stray capacitance c3 of the matrix wiring.

In Equation (1), the sneak current between the photoelectric conversion elements S11 to SMN of the sensor occurs due to the presence of the parallel resistor r2. In the case of r2 >> r1, equation (1) is expressed by the following equation. Can be approximated as follows.

[0017]

Vout = VS２ (1-exp (-t / τ)) where τ (time constant) = cr1 and c = c1 + c2 +
c3 Since [Equation 2] does not include r2, in this case, the current wraparound can be ignored. Also, in [Equation 1], when the time constant τ (τ = cr, where r is the parallel resistance of r1 and r2) is sufficiently larger than the accumulation time t, Equation (1) can be approximated as the following equation.

[0018]

Vout = Vs · t / (c · r1) Here, c = c1 + c2 + c3 Since r2 is not included in [Equation 3], the sneak current can be ignored in this case as well. .

Each of the photoelectric conversion elements S11 to SMN of the image sensor according to the present invention has a characteristic that the element resistance value when applying a reverse bias voltage Vout during light irradiation is sufficiently larger than the element resistance value when applying a forward bias voltage. When the selected element is bright (light irradiation) and all non-selected elements connected to the selected element by matrix wiring are bright (in this case, the value of the parallel resistance r2 is minimum and the current sneak is maximum). , Normal sensor drive conditions (normal sensor drive power supply VS
R2 >> r1), the reverse bias voltage Vout can be approximated by [Equation 2] regardless of the value of the time constant τ, and the sneak current between the elements can be ignored. On the other hand, in a sensor which does not have such characteristics, for example, in which each element resistance is a linear resistance when irradiating a constant amount of light, under the same condition, r2 >> r1 is not satisfied, and the current sneak can be ignored. Disappears. When the selected element is dark (no light irradiation) and all the non-selected elements connected to the selected element by matrix wiring are light (light irradiation), r2 >> r1 does not hold under normal sensor driving conditions. , [1], the values of r1 and r2 are sufficiently large, and the time constant τ is the accumulation time t (typically several hundred μsec to 100 m in the present driving method).
sec). For this reason, the output in this case can be approximated by [Equation 3], and the wraparound of the current can be ignored. On the other hand, in a sensor in which each element resistance has a linear resistance value when irradiating a constant amount of light, the time constant τ in [Equation 1] does not become sufficiently larger than the accumulation time t under the same condition. For this reason, the current wraparound cannot be ignored. After all, in the image sensor of the present invention, when the current sneak is maximum, that is, even when all the non-selected elements connected to the selected element by the matrix wiring are clear, the current sneak is ignored regardless of the state of the selected element. Can be done.

The reverse bias voltage Vout generated in the matrix wiring becomes a signal output of the photoelectric conversion elements S11 to S1N, which is subjected to impedance conversion by the amplifiers A1 to AN.
These signal outputs are read by sequentially switching the charge reset switches Z1 to ZN. Here, immediately after the signal output of each of the photoelectric conversion elements S11 to S1N is read, the charge reset switches Y1 to YN are sequentially turned on every clock so that the accumulation time t (period when the reset switch is OFF) of each element becomes constant. Switch on and reset the stored charge. Next, these charge reset switches Y1 to Y
After all N are turned on, the power switch X1 is switched from the sensor driving power source VS to the power ground GND,
At the same time, connect the power switch X2 to the power ground GND.
Is switched to the sensor drive power supply VS side, and the signal output of the element in the second block is read by the same operation as the reading of the signal output of the element in the first block. Thereafter, the same operation is performed for all blocks, and the signal outputs of all elements are read. Specific Example 1 Copolymerized nylon (manufactured by Daicel Co., Ltd., trade name: Daiamide T1)
71) was dissolved in n-propanol, and a transparent electrode of indium tin oxide (ITO) was used as the individual electrode 1 of FIG.
8 elements per unit (8dot / mm, area per element is 0.01m
m ² ) A total of 1728 devices were dried and dip-coated to a thickness of 0.3 μm on a glass plate on which a one-dimensionally patterned 1728 element was formed. Next, 10 g of oxytitanium phthalocyanine as a charge generating substance was dispersed with dimethoxyethane by a sand grinder, and mixed with a solution of 5 g of polyvinyl butyral resin (trade name: Slek BH-3, manufactured by Sekisui Chemical Co., Ltd.) in dimethoxyethane. Then, a coating solution was obtained. This coating solution was applied on the two blocking layers composed of the nylon layer by an immersion method and dried to provide a 0.4 μm charge generation layer. Next, polycarbonate (product name Novalex 7025A, Mitsubishi Kasei
100 g, 160 g of the compound represented by Chemical Formula 1 and 40 g of the compound represented by Chemical Formula 2 were dissolved in dioxane, dip-coated on the charge generating layer, dried, and dried to a thickness of 0.5 μm. A charge transfer layer was provided. Further, aluminum was vacuum-deposited thereon to provide a counter electrode, and the sandwich-type photoelectric conversion element shown in FIG. 1 was produced.

[0021]

Embedded image

[0022]

Embedded image FIG. 4 shows an example of voltage and current characteristics of a photoelectric conversion element having a pair of electrodes manufactured by the same method as above for measurement. FIG.
(A) shows an LED (manufactured by Stanley Electric Co., Ltd .; HPY5566, peak wavelength 570 nm) having a photoelectric conversion element surface with a diameter of 4 mm having a diameter of 15 mm.
FIG. 4B is a diagram showing a relationship between a device applied voltage (in this case, a forward bias voltage is a positive voltage) and a photocurrent (bright current) when light is irradiated so as to be μW / cm ² , and FIG. FIG. 4 (a)
FIG. 6 is a diagram illustrating a relationship between an element applied voltage and a photocurrent (dark current) when an LED is turned off under the same conditions as in FIG.

When a forward bias voltage of 20 V, a reverse bias voltage of 6.0 V, a reverse bias voltage of 4.6, and a reverse bias voltage of 2.0 V were applied to the photoelectric conversion element, the measured bright current was 1.3 × 10 ⁻⁶ A. , -5.8 × 10 ^-11 A, -3.1 × 10
^-11 A, and -3.2 is × 10 ^-12 A, measurements respectively 8.8 × 10 ^-10 A dark ^{current, -5.6 × 10 -11 A, -2.8} × 10 -11 A and -3.0 × 10 ^{- It is 12} A, and the element area is 0.
After calculating the element resistance value per 01mm ^2, respectively 1.9
× 10 ¹⁰ Ω, 1.3 × 10 ¹⁴ Ω, 1.9 × 10 ¹⁴ Ω, and 7.9 × 1
0 ¹⁴ Ω. Therefore, in this photoelectric conversion element, the element resistance value when applying a reverse bias voltage (6.0 V or less) at the time of light irradiation is sufficiently larger than the element resistance value at a forward bias voltage of 20 V normally applied at the time of detecting an optical signal (about 7,000 times or more). ) The thing was confirmed. Specific Example 2 It is assumed that the photoelectric conversion element (8 dots / mm, the area per element is 0.01 mm ² ) of Example 1 is used for a matrix type image sensor composed of 18 blocks to read signals by the above-described driving method. Then, r1 and r2 in the equation (1) are obtained by using the measurement result of the specific example 1.

When the selection element is bright (irradiated with light) and dark (not irradiated with light), r1 is defined as r1 (bright) and r1 respectively.
(Dark), when the sensor drive power supply VS is -20 V (the forward bias voltage of the sensor is a negative voltage in the above-described drive method), r
1 (bright) is 1.9 × 10 ¹⁰ Ω and r1 (dark) is 2.9 × 10 ¹³ Ω. Also, the case where the current wraparound between the elements of the sensor is the largest is when all the non-selected elements connected to the selected element by the matrix wiring are bright (light irradiation), and in this case, r2 is replaced by r2 ( And the current wraparound is the smallest when all non-selected elements connected to the selected element by matrix wiring are dark (light is not irradiated).
Assuming that r2 in this case is r2 (dark), Vout is -4.6V
In the case of, r2 (bright) is 1.1 × 10 ¹³ Ω and r2 (dark) is 1.2
× 10 ¹³ Ω, when Vout is -2.0V, r2 (bright) is 4.6 ×
10 ¹³ Ω and r2 (dark) are 4.9 × 10 ¹³ Ω. When the reverse bias voltage applied to the sensor was 1.0 V or less, measurement was impossible because the photocurrent value was very small. Therefore, Vout is -1.0V
In the following case, the value of r2 is the same as r2 when Vout is -2.0V.

Next, the calculated r1 (bright), r1
(Dark), r2 (bright), and r2 (dark), the ratio of r2 to r1 (r2 / r1) in equation (1) in the above assumption,
The time constant τ and the output Vout are calculated for the following cases A, B and C, respectively, and the comparison is performed.

A: In the case of using the image sensor of the present invention B: In the case of A, when there is no current sneak between the elements of the image sensor (when r 2 is made infinite in [Equation 1], [Equation 2] C: When the element resistance is a linear resistance (r1 (bright)), r1
(Dark) uses the values calculated above, and r2 (bright) and r2
The values of (dark) are r1 (bright) / 17 and r1 respectively.
(Dark) / 17.

Here, Vs is -20 V, and the accumulation time t is 100 ms.
c and c are set to 20PF. (1) When the selected element is bright (light irradiation) and all the non-selected elements connected to this by matrix wiring are bright: A: r2 / r1: 570, τ: 380 msec, V
out: In the case of -4.6V B; r2 / r1: infinity, τ: 380msec, V
out: at -4.6V C; r2 / r1: 5.9 × 10 ^-2 , τ: 21 msec,
Vout: -1.1 V (2) When the selected element is bright, and all non-selected elements connected to this by matrix wiring are dark (no light irradiation) In the case of A: r2 / r1: 610, τ: 380 msec , Vo
ut: -4.6V B; r2 / r1: infinity, τ: 380msec, Vo
ut: -4.6V at C; r2 / r1: 90, τ: 380msec, Vo
ut: -4.6V (3) When the selected element is dark and all the non-selected elements connected to it by matrix wiring are light: In the case of A; r2 / r1: 1.6, τ: 350sec, V
out: In the case of -3.5mV B; r2 / r1: infinity, τ: 570sec, V
out: In the case of -3.5mV C; r2 / r1: 3.9 × ^10-5 , τ: 22msec,
Vout: -0.8 mV (4) When the selected element is dark and all non-selected elements connected to this by matrix wiring are dark: A: r2 / r1: 1.7, τ: 360 sec, V
out: In the case of -3.5mV B; r2 / r1: infinity, τ: 570sec, V
out: -3.5mV C; r2 / r1: 5.9 × 10 ^-2 , τ: 32msec,
As a result of Vout: -0.5 mV or more, in the case of using the sensor of the present invention A, in the cases of (1) and (2), r2 >> r1. Therefore, regardless of the value of the time constant τ as described above, The effect of the current wraparound is negligible, and in the cases of (3) and (4), r2
>> r1, but the time constant τ is sufficiently larger than the accumulation time, and in this case also, the influence of the current sneak can be ignored as described above. As a result, in the cases (1) to (4), the influence of the current sneak was negligible, and almost the same output as in the case where the current sneak did not occur was obtained.

When the element resistance of C is a linear resistance, (1)
In the case of (2), it is not r2 >> r1, and the time constant τ is smaller than the accumulation time (100 msec). Therefore, the influence of the current sneak cannot be ignored, and the output largely decreases as compared with the case of B. In the case of 2), r2 >> r1, and substantially the same output as in the case of B is obtained. In the case of (3), the time constant τ is smaller than the accumulation time, and since it is not r2 >> r1, the influence of the current sneak cannot be ignored, and the output is greatly reduced as compared with the case of B. , (4), the time constant τ was sufficiently larger than the accumulation time, and almost the same output as in the case of B was obtained.

After all, when the element resistance of C is a linear resistance, the influence of the current sneak depends on the state of the non-selected element connected to the selected element and the matrix wiring regardless of whether the selected element is bright or dark. Varies depending on the light / dark state of the non-selected element. However, in the case of using the image sensor of the present invention A, the selected element is connected to the selected element by a matrix wiring regardless of whether the selected element is light or dark. Irrespective of the state of light and darkness, it was confirmed that the influence of the current wraparound between the elements of the sensor was negligible and the output was hardly reduced. Comparative Example 1 In the photoelectric conversion element of the specific example 1, when the organic photoconductive layer in the element was only a charge generation layer (thickness: 0.9 μm), the electrodes consisted of a pair of voltage and current of the photoelectric conversion element for measurement. FIG. 5 shows an example of the characteristic. FIG. 5 (a) shows a LED (manufactured by Stanley Electric Co., Ltd .; HPY5566, peak wavelength 570 nm) having a diameter of 4 m from a light source.
The element applied voltage when light is irradiated so that the element surface of m becomes 15 μW / cm ² (in this case, the forward bias voltage is a positive voltage)
FIG. 5 is a diagram showing the relationship between the light current and the light current (bright current).
FIG. 6B is a diagram showing the relationship between the element applied voltage and the photocurrent (dark current) when the LED is turned off under the same conditions as in FIG.

When the forward bias voltage of 20 V, the reverse bias voltage of 6.0 V, the reverse bias voltage of 4.6 V, and the reverse bias voltage of 2.0 V were applied to the photoelectric conversion element, the measured bright current was 2.9 × 10 ^−7. A, -8.0 × 10 ^-8 A, -5.0 × 10
^-8 A and -1.5 × 10 ^-8 A, and the element area in this case
The element resistance per 0.01 mm ² is 8.8 × 10 ¹⁰ Ω,
The values are 9.4 × 10 ¹⁰ Ω, 1.2 × 10 ¹¹ Ω, and 1.7 × 10 ¹¹ Ω. Therefore, in this photoelectric conversion device, the device resistance value when applying a reverse bias voltage (6.0 V or less) at the time of light irradiation is not sufficiently larger than the device resistance value at a forward bias voltage of 20 V normally applied at the time of detecting a light signal (less than 2 times). ).

Next, the same layer structure as that of the photoelectric conversion element is used.
Assuming a case where a signal is read by the above-described driving method using eight photoelectric conversion elements per 1 mm (8 dots / mm, the area per element is 0.01 mm ² ) in a matrix type image sensor composed of 18 blocks. , R1 in equation (1) at the time of light irradiation
When r and r2 are obtained, r1 (bright) is 8.8 × 10 ¹⁰ Ω when the sensor driving power supply VS is -20 V, and r is obtained when Vout is -2 V.
2 (bright) is 9.6 × 10 ⁹ Ω. In this case, r2 <r1
Vout cannot be approximated as in the equation (2), and the current wraparound between the sensor elements cannot be ignored.

[0032]

As described above, according to the present invention, the resistance value when a reverse bias voltage is applied to the photoconductive layer of each photoelectric conversion element during light irradiation is smaller than the resistance value when a forward bias voltage is applied. Since this photoelectric conversion element is used for a matrix type image sensor, when reading with this image sensor, the sneak current between each element of the image sensor is obtained. Therefore, deterioration of the SN ratio can be prevented, and accurate image information can be obtained. In addition, there is no need to add a blocking diode for each element, so that the manufacturing process of the image sensor can be simplified and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a photoelectric conversion element used for an image sensor according to the present invention.

FIG. 2 is a drive circuit diagram of the image sensor of the present invention.

FIG. 3 is a diagram illustrating drive timings of the drive circuit of FIG. 2;

FIG. 4 is a voltage and current characteristic diagram of a photoelectric conversion element in which an organic photoconductive layer in the photoelectric conversion element used in the image sensor of the present invention is laminated on a charge generation layer and a charge transfer layer.

FIG. 5 is a voltage and current characteristic diagram of a photoelectric conversion element in which an organic photoconductive layer in the photoelectric conversion element has only a charge generation layer.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 individual electrode 2 blocking layer 3 photoconductive layer 4 support 5 common electrode S11 to SMN photoelectric conversion element C11 to CMN element capacitance R11 to RMN element resistance K1 to KM common electrode side wiring L1 to LN individual electrode side matrix wiring L- C1 to L-CN Stray capacitance of matrix wirings L1 to LN VS Sensor driving power supply X1 to XM Power supply side switch Y1 to YN Charge reset switch A1 to AN Impedance conversion amplifier Z1 to ZN Reading side switch GND Power supply ground

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kei Ishihara 1000 Kamoshita-cho, Midori-ku, Yokohama-shi, Kanagawa Prefecture Inside Mitsubishi Chemical Research Institute (72) Inventor Masatoshi Kato 2--14-40 Ofuna, Kamakura-shi, Kanagawa 3 Ryo Denki Co., Ltd., Living Systems Laboratory (72) Inventor Tadahiko Hamaguchi 2--14-40, Ofuna, Kamakura City, Kanagawa Prefecture Mitsui Electric Co., Ltd., Living Systems Laboratory (72) Inventor, Takeshi Takeda 2-14, Ofuna, Kamakura City, Kanagawa Prefecture No. 40: Mitsubishi Electric Corporation Living System Laboratory (56) References JP-A-2-155270 (JP, A) JP-A-1-184496 (JP, A) JP-A-61-271868 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 27/146 H04N 1/028 H04N 5/335

Claims (1)

(57) [Claims] 1. A photoelectric conversion element array in which a plurality of photoelectric conversion elements for performing optical signal detection by applying a forward bias voltage are arranged in a line, and one end of each of the photoelectric conversion elements is provided on a common electrode side.
In the image sensor in which the other end is connected to the individual electrode side by a matrix wiring, each of the photoelectric conversion elements has a resistance value when a reverse bias voltage is applied during light irradiation, compared with a resistance value when a forward bias voltage is applied. An image sensor comprising an organic photoconductive layer that is at least 100 times as large as an organic photoconductive layer.