JPH03225957A - Image sensor and its manufacture - Google Patents

Abstract

PURPOSE:To easily manufacture an image sensor by forming the following: a voltage source used to supply sawtooth waves which are increased or decreased continuously or in stages with the time; and a circuit in which a plurality of first diodes provided respectively with a first electrode and a second electrode are connected in series. CONSTITUTION:When sawtooth waves are generated from a voltage source 1, first diodes Da1 to Da3 turn on sequentially. When an inclined voltage of the sawtooth waves is increased gradually, a potential Vp0 at a point P0 is increased gradually. Thereby, when the potential Vp0 at the point P0 becomes a forward voltage Vf of a second diode Db0 in a unit circuit K0, the diode Db0 turns on, and the potential Vp0 at the point P0 becomes a nearly definite value (nearly Vf), i.e., a saturation voltage value. When potentials Vp0 to Vp3 at points P0 to P3 are changed sequentially, photodiodes S0 to S3 connected between the individual points P0 to P3 and the ground via a current-voltage conversion circuit 2 are driven sequentially. That is to say, the photodiodes S0 to S3 are scanned electrically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image sensor in which a plurality of photodiodes are sequentially scanned based on a sawtooth voltage, and a method for manufacturing the same.

[Prior art and problems to be solved by the invention] Image sensors include multiple photoelectric conversion elements for converting optical information into electrical signals, and select electrical signals by electrically scanning the multiple photoelectric conversion elements. It has an analog switch for obtaining For example, the analog switch is disclosed in Japanese Patent Application Laid-Open No. 1983-
As disclosed in Japanese Patent No. 2377, it is made of a field effect transistor and is placed near the photoelectric conversion element. By the way, in an image sensor having an integrated circuit configuration, the width of one photoelectric conversion element, that is, one pixel (for example, 12
One field effect transistor must be placed to fit within 5 μm).

However, it is not easy to form a field effect transistor within such an extremely narrow width. Furthermore, when three wiring conductor layers for the drain, source, and gate of a field effect transistor are provided within a predetermined width on the substrate, the width of the three wiring conductor layers inevitably becomes narrower, and the image sensor The manufacturing yield has become low.

In order to solve this type of problem, Japanese Patent Application No. 1-198279 discloses a method of scanning photodiodes using a series circuit of diodes. However, the specific configuration and manufacturing method of this image sensor are not disclosed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image sensor that can be easily manufactured and a method for manufacturing the same.

[Means for Solving the Problems] To achieve the above object, the present invention provides a sawtooth wave that increases or decreases continuously or stepwise with time. It is a circuit in which a voltage source 1 for controlling the voltage and a plurality of first diodes Da1 to Da3 each having a first electrode and a second electrode are connected in series, one end of which is connected to the voltage source 1. and each of the first diodes Da1 to Da3 has a directionality such that the forward current of each of the first diodes Da1 to Da3 flows based on the sawtooth wave, and ~ a first electrode in which the first electrode of Da3 is arranged on the voltage source 1 side;
, each with a first resistor or capacitor R
a1 to Ra3 or Ca1 to Ca3 and the second diode D
b1 to Db3 connected in series, each connected between the second electrode of each of the first diodes Da1 to Da3 and the other end of the voltage source 1, and each of the second a plurality of second series circuits in which each of the second diodes Db1 to Db3 has a directionality such that the forward current of the diodes Db1 to Db3 flows based on the sawtooth wave; Diode D
a plurality of second resistors or capacitors Rb1 to Rb3 or C1 to C3 connected between the second electrodes of a1 to Da3 and the other end of the voltage source 1, respectively, and the first resistor or capacitor Ral; Connection points P1 to P between ~Ra3 or Ca1 to Ca3 and the second diodes Db1 to Db3
3 and the common current output line 3, a plurality of photodiodes 81 to S3 each connected in a reverse biased direction between the common current output line 3 and the voltage source 1;
a current-voltage conversion circuit 2 connected to the other end; and a plurality of blocking diodes connected between each of the photodiodes 81 to S3 to electrically isolate the photodiodes 81 to S3. DC1~Dc
3, wherein the first diodes Da1 to Da3 and the second diode Db1
-Db3, the photodiodes 81-S3, and the blocking diodes Dc1-Dc3 are the same insulating substrate 1
The present invention relates to an image sensor characterized in that it is a diode of the same junction type formed on the top of the image sensor.

Note that each diode is preferably a PIN type diode made of hydrogenated amorphous silicon.

Furthermore, when manufacturing the image sensor, a common semiconductor layer and an upper electrode layer 17 are provided for each diode on the same insulating substrate 11, and after bonding, the diodes are separated. desirable.

[Function] When a sawtooth wave is generated in the image sensor of the present invention, the photodiodes 81 to S3 are sequentially scanned. 0 First and second diodes Da1 to Da3, Db1 to D included in this image sensor
b3, the photodiodes S1 to S33, and the blocking diodes Dc1 to Dc3 are diodes of the same junction type, so that they can be easily manufactured and a low-cost image sensor can be provided.

Further, by providing a common semiconductor layer and an upper electrode layer and then separating each diode, the number of photolithography steps can be reduced.

[Embodiment 1] The one-dimensional image sensor according to the embodiment of the present invention shown in FIG. It has a conversion circuit 2.

This -dimensional image sensor is configured to be able to detect more than four pixels. but,
Since it is difficult to show the entire configuration of this -dimensional image sensor in the drawing, only the -part thereof is shown in FIG.

The three unit circuits 1, K2, and K31 that are the same as each other are the first diodes Da1, Da2, and Da3, and the second diodes Da1, Da2, and Da3.
diodes Dbl, Db2, Db3 and the first resistor R
a1, Ra2, Ra3, and second resistors Rb1, Rb2,
Rb3 and photodiodes S1, S2, S for light detection
3, Boo q Daioh 1eDcl, Dc2,
It consists of DC3. Another unit circuit KO placed between the voltage source 1 and the unit circuit 1 includes a second diode DbO, a first resistor RaO, and a photodiode SO.
and a blocking diode DcO. The unit circuit KO is connected to another unit circuit 1, K2, and the first in K3.
It does not have anything corresponding to the diodes Dal, Da2, Da3 and the second resistors Rb1, Rb2, Rb3. However, the unit circuit KO also has 1, K2,
The first diode of K3 and the corresponding second resistor can be connected. Furthermore, the first stage unit circuit KO can be omitted from the image sensor shown in FIG. 1 if necessary. Anode (first electrode) and cathode (second electrode)
three first diodes Da1, Da2, D having
One end (left end) of a circuit in which a3 are connected in series (first series two circuit) is connected to one end of voltage source 1. The first diodes Dal, Da2, and Da3 have directionality that is biased in the forward direction by the voltage of the voltage source 1. That is, the anodes (first electrodes) of the first diodes Da1 to Da3 are arranged on the voltage source 1 side.

Note that when the upper terminal of the voltage source 1 is negative, the cathodes of the first diodes Da1 to Da3 are arranged on the voltage source 1 side. First diode Da1, Da2, D
First resistors Ral, Ra2, Ra3 and second diodes Db1, Db2, Db3 were connected in series between the cathode (second electrode) of a3 and the other end (ground) of the voltage source 1, respectively. The circuits (second series circuits) are connected to each other. In the unit circuit KO, a first resistor RaO and a second diode D are connected between one end and the other end of the voltage source 1.
A series circuit with bO is connected. The second diodes DbO1, Db1, Db2, and Db3 have directionality that is biased in the forward direction by the voltage of the voltage source 1.

Interconnection point P between the third first resistor Ra01Ra1, Ra2, Ra3 and the second diode DbO1Db1, Db2, Db3 in each unit circuit KO, K1, K2, K3
O1P1, P2, P3 have photodiodes So,
31, S2, S3 and blocking diode DCO1D
Series circuit with C1, DC2, and Dc3 (third series circuit)
is connected. That is, the cathodes of the photodiodes SO to S3 are connected to the points PO to P3 via the blocking diodes DCO to DC3, and the anodes of the photodiodes SO to S3 are connected to the common current output line 3.

The current-voltage conversion circuit 2 has a common current output line 3 and a voltage source 1.
A resistor R connected between the other @ (ground) and a capacitor C connected between the current output line 3 and the output terminal 4
It consists of Therefore, the photodiodes SO to S3 are substantially connected in parallel to the second diodes DbO to Db3. Further, the photodiodes SO to S3 are connected to the voltage source 1
It is connected so that it is reverse biased at a voltage of . Therefore, the current flowing through the photodiodes SO to S3 is extremely small.

Details of each part of the image sensor shown in Figure 1 are as follows. It is.

Voltage source 1 consists of a sawtooth wave generating circuit, which periodically generates the sawtooth wave or sweep signal shown in FIG. The maximum amplitude of the sawtooth wave in FIG. 2 is set to a value that can turn on all the first and second diodes Da1 to Da3 and DbO to Db3 in FIG. 1.

Photodiodes SO to S3, first diode Da1
~Da3, the second diodes DbO~Db3, and the blocking diodes DCO~Dc3 are PIN junction diodes of the same type, and are connected to a hydrogenated amorphous silicon semiconductor layer and one of the blocking diodes provided below this semiconductor layer. It consists of an electrode layer and another electrode layer provided above the semiconductor layer.

Since the photodiodes SO to S3 are reverse-biased, they are represented isometrically by a parallel circuit of a capacitance CS shown in FIG. 3 and a current source Is proportional to the light intensity. In addition,
Equivalent capacitance CS of photodiode SO~S3
The value of the current flowing through is extremely small.

5. When the first diodes Da1 to Da3 and the second diodes DbO to Db3 are turned on, the voltage across them, that is, the forward voltage Vf is approximately 1. First resistance RaO~R
a3 are each 100Ω, and the second resistors Rb1~
Rb3 is 1 to Ω, respectively, and these are TiO2, T
It is formed from a material such as a-8i02 or NiCr.

[Operation] In the image sensor shown in FIG. 1, when the sawtooth wave shown in FIG. 2 is generated from the voltage source 1, the first diode Da
1 to Da3 become conductive in sequence.

As the slope voltage of the sawtooth wave gradually increases, the potential VpO at point PO gradually increases as shown in FIG. 4(A). As a result, the potential VpO at point PO becomes the second potential of the unit circuit KO.
When the forward voltage of the diode DbO becomes f, the diode DbO turns on, and the potential VpO at the point PO becomes a substantially constant value (approximately Vf), that is, a saturation voltage value. Almost at the same time as the second diode DbO of the unit circuit KO is turned on, the first diode Da1 of the unit circuit 1 is also turned on. During the period when the first diode Da1 in the unit circuit is non-conducting (off state), the cathode of the first diode Da1 is at approximately zero volts, but the first diode Da1 is at approximately zero volts.
1 turns on and the voltage Vd of the voltage source 1 further increases, the cathode voltage of the first diode Da1 becomes the voltage V
It increases following d.

That is, when the first diode Dal is turned on, the voltage across it is almost fixed to the forward voltage Vf, so a voltage obtained by subtracting the forward voltage Vf of the diode Da1 from the power supply voltage Vd is applied across the resistor Rbl. . Further, during a period in which the second diode Db1 in the unit circuit is non-conductive, the unit of the point P1 becomes approximately equal to the voltage across the second resistor Rb1. Therefore, after the first diode Dal is turned on, the potential Vp1 at the point P1 gradually increases as shown in FIG. 4(A). When the potential Vp1 at point P1 reaches the forward voltage Vf of the second diode Db1, this becomes an on state, and the potential Vp1 at point P1 becomes an almost constant value (Vf
)become. Almost at the same time as the second diode Db1 in the unit circuit is turned on, the seventh diode Da2 in the unit circuit is turned on, and the point P2 is turned on as shown in FIG. 4(A). A potential Vp2 is obtained.

When the slope voltage of the sawtooth wave supplied from the voltage source 1 further increases, the first diode Da3 of 3 is connected to the unit circuit.
turns on, and the potential Vp of FIG. 4(A) is applied to point P3.
3 is obtained. When the potentials VpO to Vp3 of points PO to P3 change sequentially as shown in FIG. 4(A), each point PO to
Photodiodes SO to S3 connected between P3 and the ground via the current-voltage conversion circuit 2 are sequentially driven. That is, the photodiodes SO to S3 are electrically scanned.

In the circuit of FIG. 1, photodiodes SO to S3 are arranged one-dimensionally. This photodiode SO
~ When reading optical information in S3, first, the first diodes Da1 to Da3 and the second diodes DbO to Db
Voltage source 1 is the voltage that can turn on all of 3.
Generate from. Note that the first diodes Da1 to Da
The voltage 8 for turning on all of the diodes DbO to Db3 and the second diodes DbO to Db3 can be given in the form of a sawtooth wave as shown in FIG. In other words, the maximum value of the sawtooth wave and the voltage value in this vicinity are the first
and second diodes Da1 to Da3 and DbO to Db
You can turn on all 3.

During the period when all of the first diodes Da1 to Da3 and the second diodes DbO to Db3 are in the on state, the point P
Each photodiode SO to S3 is
is reverse biased, charging a capacitance CS shown isometrically in FIG. Note that since the equivalent capacitance Os is extremely small, the blocking diodes DcO~D
The equivalent capacitance Cs can be charged by a small current in the region before the point where the forward current of c3 rises steeply.

When an optical signal obtained from an object (not shown) such as a facsimile document placed opposite to the image sensor in Fig. 1 is input to the photodiodes SO to S3, the presence or absence and size of the optical signal are detected. As a result, the amount of charge in the equivalent capacitance Cs of the photodiodes SO to S3 changes. That is, among the photodiodes SO to S3, the equivalent capacitance Cs is discharged in the one to which the optical signal is input, and the equivalent capacitance Cs is not discharged in the one to which the optical signal is not input. The amount of discharge of the equivalent capacitance Cs changes depending on the amount of light.

There are two methods for providing optical input to the photodiodes SO to S3. One of them is photodiode SO~S
One method is to always provide optical input to the voltage source 1, and the other is to provide optical input only during a predetermined period (for example, a period when the voltage Vd of the voltage source 1 is 0 volts).

When the voltage Vd of the voltage source 1 increases linearly with time as shown in FIG. 2, potentials VpO1Vp1, Vp2, ■p3 are obtained at points PO to P3 as shown in FIG. 4(A),
As a result, the photodiodes SO to S3 are sequentially reverse biased. In other words, the voltage for charging the equivalent capacitance Cs shown in FIG.
It is applied to O to S3. At this time, the photodiode SO
~0 of S3 A charging current flows to those of the equivalent capacitance C8 that are discharged due to optical input, but no charging current flows to those that are not discharged due to no optical input. Since the charging current of the equivalent capacitance Cs of the photodiodes SO to S3 flows through the current-voltage conversion circuit 2, the voltage vout at the output terminal 4 changes depending on the presence or absence of the charging current.

In a state where each equivalent capacitance C8 is discharged because optical input is given to all four photodiodes SO to S3, the potentials VpO to Vp shown in FIG. 4(A)
3 is sequentially applied to the photodiodes SO to S3, the voltage vout at the output terminal 4 changes each time a charging current flows through the photodiodes SO to S3, as shown in FIG. 4(B). That is, the potentials VpO to Vp3 at each point PO to P3
As the charging current increases, the charging current of the equivalent capacitance CS increases, and when the potentials VpO to Vp3 at each point PO to P3 are saturated, the charging current decreases, and an output voltage vout corresponding to this change in the charging current is obtained.

In Fig. 4 <C>, no optical input is given to 82 of the four photodiodes SO11 Sl, S2, and S3, and 5
A change in the voltage Vout at the output terminal 4 when optical input is applied only to O1S1 and S3 is shown. In this case, when the potentials VpO to Vp3 shown in FIG. 4A are sequentially applied to the photodiodes SO to S3, no charging current flows through the photodiode S2. That is, Fig. 4 (A
) does not cause a change in the output voltage Vout corresponding to the potential Vp2.

[Manufacturing method] This image sensor has first diodes Da1 to Da3 and second diodes DbO to Db3 on a common insulating substrate 11 made of glass as shown in FIG. 5(A) and FIG.
, photodiodes SO to S3, blocking diodes DcO to Dc3, first resistors RaO to Ra3, and second resistors Rb1 to Rb3. Their geometric arrangement is as shown in FIGS. 5(A) and 5(B).

Next, a manufacturing method for these will be explained in order of steps with reference to FIG. 6. Note that since unit circuits KO to 3 are formed at the same time by the same method, the manufacturing method for unit circuits 1 and 2 will be explained as an example.

As shown in FIG. 6(A), a resistor pA 12, a lower electrode layer 13, and an N-type hydrogenated amorphous silicon film (hereinafter referred to as an N-type film) 14 are formed on an insulating substrate 11 made of a glass substrate. , an I-type (intrinsic semiconductor) hydrogenated amorphous silicon film (hereinafter referred to as ■-type film) 15, and a P-type hydrogenated amorphous silicon film (hereinafter referred to as P-type film) 16. , and a transparent electrode layer (upper electrode layer) 17 were sequentially formed. To explain in more detail, Resistance II! 12 is T a SiO2 1000
The lower electrode layer 13 is formed by sputtering to a thickness of 1 to 100% chromium (Or>1).
It was formed by sputtering to a thickness of 0,000 angstroms. The N-type film 14, I-type film 15, and P-type film 16 were each formed by a glow discharge method.

More specifically, the N-type film 14 includes SiH4, PH3 and H2.
A film with a thickness of about 300 angstroms was formed using the mixed scum of the above, and the amount of P (phosphorus) doped was 0.6%. The type I film 15 was formed to a thickness of about 5000 Å by using a mixed residue of S I Ht, H2, and H2, and of course no conductivity type determining impurities were added. The P-type film 16 is formed using a mixed gas of SiH, B2H6, and H2 to have a film thickness of about 300 oz.
The doping amount of boron) was set to 0.6%. The transparent electrode layer 17 is made of ITO (indium tin oxide) by electron beam evaporation.
The film was formed by vapor deposition to a film thickness of 9°O angstroms. Note that the resistive film 12 is connected to the first and second resistors Ra.
1, formed in common to Ra2, lower electrode layer 13, N
A type film 14, a type film 15, a P type film 16, and a transparent electrode layer 17 were formed commonly for each diode.

Next, as shown in FIG. 6(A), a first resist layer 17 is formed.
was provided and patterned by a photolithography process to obtain what is shown in FIG. 6(B). That is,
A first mask (not shown) consisting of a resist layer 17 was provided, and the transparent electrode layer 17 was patterned by a wet etching method. The amorphous semiconductor layer consisting of the N-type film 13, the ■-type film 14, and the P-type film 15 is dry-etched using a mixed gas of 5% CF gas and 02 gas. Next, after this dry etching, the transparent electrode layer 17 was etched again by wet etching using the same mask to reduce the surface area of the transparent electrode layer 17. 6th
Although the pattern of each part is shown in principle in Figure (B), in reality, each part becomes trapezoidal due to lateral etching, and the transparent electrode layer 17 protrudes in the lateral direction, but wet etching is performed again. This protrusion is removed.

The pattern in FIG. 6(B) corresponds to the final pattern of the resistive film 12.

Next, after peeling off the first mask, a second resist layer 18 is provided as shown in FIG. 6(C), and the second mask (
), wet etching the transparent electrode layer 17, and forming a P-type l! By dry etching the semiconductor layer consisting of the semiconductor layer 16, the ■-type film 15, and the N-type film 14, the sixth
What is shown in Figure (D>) was obtained. As a result, the first and second
The diodes Dal and Dbl, the booging diode Del, and the photodiode S1 are separated from each other.

Next, a protective and separating film 19 made of an I-type film made of a hydrogenated amorphous semiconductor is formed by a glow discharge method.
A third resist layer 20 is provided thereon, and a third mask (not shown) based on this resist layer 20 is used as shown in FIG. 6(F). A pattern protection and separation film 19 was obtained. In this way, if the protection and separation film 19 is a type II film, the type I film 1 in the diode portion
It becomes possible to form the semiconductor layer with the same equipment as the semiconductor layer No. 5, etc., and it becomes possible to simplify the manufacturing equipment.

Next, after peeling off the third mask, the chromium layer 1 for the extraction electrode (wiring conductor) is removed as shown in FIG.
9 and an aluminum layer 20 are formed by sputtering, a fourth resist layer 23 is formed thereon, a fourth mask (not shown) made of this resist layer 23 is provided, and this is used to form a chromium layer 20. An extraction electrode layer consisting of a layer 19 and an aluminum layer 20, and a lower electrode layer 13 consisting of chromium.
was etched as shown in FIG. 6(H).

After that, a protective film (not shown) and a photodiode SO
~The part excluding the light receiving area of S3 and the other 6 diodes Da1~Da3, DbO~Db3, DCO~
A light shielding film (not shown) was formed on DC3 to complete the image sensor.

When the relationship between the PH3 doping amount and film thickness of the I-type film 15 and the electrical characteristics was investigated in connection with this example, the results shown in FIG. 7 were obtained. That is, in the method for manufacturing the I-type film 15 described above, only the doping amount of PH3 is 0120.40.8.
When the leakage current Id of the completed diode was changed to 01111ra, the leakage current Id of the completed diode when a reverse voltage of 3 sq. The series resistance Rs of
It changed as shown in As is clear from this, it is desirable that the amount of phosphorus doped is in the range of 0 to 401) pH.

Figure 8 shows the thickness of the ■-type film 15 and the leakage current I of the diode.
The relationship between d and series resistance Rs is shown. That is, in the manufacturing method of the ■-type film 15 explained in the example, when only this film thickness was changed in the range of 1000 to 5000 angstroms, the leakage current Id of the diode at 73V was as shown by characteristic line A. The series resistance Rs is now as shown by characteristic line B. The series resistance Rs of the diode increases rapidly when it exceeds 3000 angstroms. However, when the thickness of the ■-shaped film 15 increases, the equivalent capacitance decreases and the time constant in the scanning circuit decreases.

Taking these into consideration, it is desirable to determine the thickness of the I-type film 15 so that the series resistance Rs/I-type film thickness is at or near the maximum. This desirable film thickness is 2000 to 5000 angstroms.

This embodiment has the following advantages.

(1) First diodes Da1 to D on the same substrate 11
a3, second diode DbO to Db3, blocking diode DcO to Dc3, photodiode SO to S
3 are formed into the same type (PIN type), making it easier to manufacture the image sensor.

(2) Since all the diodes are made of hydrogenated amorphous silicon and are formed simultaneously, they can be obtained extremely easily with a small number of photolithography steps. Note that no problem occurs even if the upper electrodes of the diodes other than the photodiodes SO to S8 and S3 are transparent electrodes.

(3) As shown in FIG. 6(A), the resistive film 12 and the lower electrode layer 13 are formed on the entire surface of the substrate 11, and then the sixth
After patterning as shown in Figure (B), Figure 6 (D
), each diode Da1, Dbl, Dcl,
Since Sl is separated, each diode can be formed under the same conditions.

Note that although the first resistor Ral and the second resistor Rbl are continuous with each other, no problem arises in terms of the electrical circuit.

(4) By etching the transparent electrode layer 17 twice using the same mask, unnecessary lateral protrusions can be easily removed.

(5) Since the protection and separation layer 19 is an I-type film, it can be easily formed.

(6) As shown in FIG. 5(B), the first resistor Ra1
By arranging ~Ran and the second resistors Rb1 to Rbn on one straight line, the width of the unit circuit (bit) can be reduced. Moreover, the connection of the ground wiring conductors 40 of the second resistors 9 Rb1 to Rbn to the voltage source 1 becomes easy, and the power supply terminals 41 can be arranged rationally. Note that FIG. 5B shows an image sensor configured by a group (block) of n unit circuits (bits).

[Modifications] The present invention is not limited to the above-described embodiments, and, for example, the following modifications are possible.

(1) A P-type film, an I-type film, and an N-type film can be formed in this order on the lower electrode layer 13. However, in the case of the NIP configuration described in the example, the forward current If at 1■ is 0.18A/-, and the leakage current Id at -5V is 2X10-''A/aJ. On the other hand, when the PIN configuration is reversed, If is 0.1OA/afl and Id is IX
It becomes 10-10A/-. First diode Da1-D
It is desirable that the forward current of a3 and the second diodes DbO to Db3 is large, and the blocking diode DcO
It is desirable that the leakage current Id of ~Dc3 and the photodiode SO~S3 is 10xlo'A/- or less, but it is possible to keep the forward current and leakage current within an allowable range with either the NIP elliptical configuration or the IN configuration. can.

(2) Blocking diodes DcO to DC3 for preventing mutual interference of photodiodes SO to S3 are connected in series to first resistors RaO to Ra3, or second resistors Rb1 to Rb3 and first resistors Ra1 to It is possible to connect with Ra3. It is also possible to reverse the positions of the photodiodes SO to S3 and the blocking diodes DcO to DC3.

(3) If the number of read pixels of the image sensor according to the embodiment is increased, the driving voltage Vd must be increased accordingly. Therefore, it is desirable to set the maximum number of read pixels to about several dozen. When increasing the number of pixels, the image sensor may be divided into a plurality of blocks and driven.

In FIG. 9, the unit circuit in FIG. 1 is divided into n unit circuits corresponding to numbers 1 to 3, or m circuit blocks B1 to 1 B2 . . . B+n. Each circuit block B1 to Bn+ includes several to several dozen units corresponding to unit circuits 1 to 3 in FIG. 1, and corresponds to the image sensor circuit in FIG. 1 with voltage source 1 omitted. It is something to do. Each circuit block 81 to BP is connected to a voltage source 1a via a multiplexer 10. Each circuit block B
The output terminals of 1 to BIIl are commonly connected via amplifiers A1 to Am.

The voltage source 1a repeatedly generates a sawtooth wave (triangular wave) shown in FIG. 10(A). The multiplexer 10 distributes the sawtooth wave shown in FIG. 10(A) to circuit blocks B to BF, as shown in FIGS. 10(B) and 10(C). Optical input to each photodiode of each circuit block B1 to B1m is always given as shown in FIG. 10<D>.

FIGS. 11 and 12 show another method of driving the image sensor. In FIG. 11, just as in FIG. 9, n unit circuits corresponding to unit circuits 1 to 3 in FIG. 1 are divided into m circuit blocks 81 to B111.

Each of the circuit blocks B1 to B2 (2) is connected to the voltage source 1, respectively. The voltage source 1 in FIG. 9 generates the sawtooth wave shown in FIG. 12(A), similar to that in FIG. 1. The sawtooth wave is shown in Figure 12 (B) < C)
As shown in FIG. 3, the signals are simultaneously supplied to circuit blocks B1 to Bm. As a result, scanning starts at the same time in each of the circuit blocks B1 to BIIl, and outputs are generated at the same time. The output of each circuit block B1-Bl is sent to a signal processing circuit 30 including a memory.

The signal processing circuit 30 arranges the outputs of the circuit blocks B1 to BIn on a common time axis so as to correspond to the arrangement order of the circuit blocks B1 to Bn. In the image sensor shown in FIG. 11, as shown in FIG. 12(D), the optical output to the photodiode is given during the period when the drive voltage Vd is zero.

(4) The sawtooth wave can be a stepped sawtooth wave as shown in FIG. 11, or a sawtooth wave that increases in a quadratic curve as shown in FIG.

(5) The polarity of each diode and the polarity of the voltage source 1 can also be reversed.

3 (6) Diodes Da1 to Da3, DbO to Db3,
Various types of junction diodes can be used in place of DcO-Dc3 and photodiodes SO-S3.

(7) A voltage may be applied to the cathode terminals of the diodes DbO to Db3. That is, the dynamic range can be expanded by applying a bias voltage between the diodes DbO to Db3 and the ground.

(S) In FIG. 1, the value of the second resistor may be set to gradually increase from Rb1 to Rb3. That is, it may be set to RbO<Rbl<Rb2<Rb3.

(10) As shown in FIG. 15, capacitors C1 to C may be connected in place of the second resistors Rb1 to Rb3 in FIG. Further, the capacitors C1 to C3 in FIG. 15 can be replaced with diodes connected to be reverse biased. This diode acts as a capacitor.

(11) As shown in FIG. 16, the first resistors RaO to Ra3 in FIG. 1 can be replaced with capacitors CaO to Ca3. Also, capacitor CaO~Ca
3 can be replaced by a diode connected in the reverse bias direction. However, in this case, it is necessary to increase the leakage current and current of the second diodes DtlO to DI+3 to form a discharge circuit for the capacitor.

(12) As shown in Figures 15 and 16, the current -
The voltage conversion circuit 2 can be configured with an operational amplifier 31, a feedback resistor Rf, and a capacitor Cf. Operational amplifier 3
The inverting input terminal of No. 1 is connected to the common current output line 3, and the non-inverting input terminal is connected to ground. Note that an inverting amplifier 32 is connected to the operational amplifier 31.

(13) It is possible to create a circuit in which DbO, DaOlSo, and DcO in the first stage are omitted.

[Effects of the Invention] As described above, according to each claimed invention, the first and second diodes, the blocking diode, and the photodiode are all of the same type, so that the image sensor can be manufactured easily. 5 things become possible.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an image sensor according to an embodiment of the present invention, Figure 2 is a waveform diagram showing a sawtooth wave, Figure 3 is an equivalent circuit diagram of a photodiode, and Figure 4 (A).
is a diagram showing the potential change at each point PO to P3 of the circuit in Figure 1, and Figure 4 (B) is a diagram showing the voltage change at the output terminal of the circuit in Figure 1.
Figure 4 (C) shows the voltage change at the output terminal of the circuit in Figure 1 when all three photodiodes receive optical input.
Figure 5 (A) is a plan view showing the arrangement of each part of the image sensor in Figure 1; A circuit diagram showing the image sensor considering the arrangement of each element and wiring of the image sensor in Figure 1, Figures 6 (A) to (H) are the image sensor's Vl-Vl line in Figure 5 (A). A cross-sectional view showing the corresponding parts in the order of steps, Figure 7 is a diagram showing the relationship between the PH3 doping amount of the I-type film of the diode, leakage current, and series resistance, and Figure 8 is a diagram showing the relationship between the thickness of the I-type film of the diode and the leakage current. FIG. 9 is a block diagram showing the principle of a photodiode drive method when there are many unit circuits, FIG. 10 is a diagram showing the state of each part in FIG. 9, FIG. 11 is a block diagram showing the principle of another driving method for the photodiode when there are many unit circuits, similar to FIG. 9. FIG. 12 is a diagram showing the state of each part in FIG. 11, and FIG. 14 and 14 are waveform diagrams showing modified examples of the sawtooth wave, and FIG. 15 and FIG. 16 are circuit diagrams showing modified examples of the image sensor, respectively. 1... Voltage source, 2... Current-voltage conversion circuit, 3...
- Common current output line, 4... Output terminal, 11... Insulating substrate, 12... Resistance film, 13... Lower electrode layer, 14
... N type film, 7 15... I type film, 16... P type film, 17... Transparent electrode layer, Da1 to Da3... First diode, Db
O~Db3... second diode, DcO~Dc3・
...Blocking diode, SO~S3...Photodiode, RaO~Ra3...First resistor, Rb1
~Rb3...Second resistance.

Claims (1)

[Claims] [1] A plurality of voltage sources each having a voltage source (1) for supplying a sawtooth wave that increases or decreases continuously or stepwise with time, and a first electrode and a second electrode. A circuit in which first diodes (Da1 to Da3) are connected in series, one end of which is connected to the voltage source (1),
In addition, each of the first diodes (Da1 to Da3) has a directionality such that the forward current of each of the first diodes (Da1 to Da3) flows based on the sawtooth wave.
has, and each first diode (Da1 to D
a3) a first series circuit in which the first electrode is placed on the side of the voltage source (1), each connected to a first resistor or capacitor (Ra1 to Ra3
or Ca1 to Ca3) and the second diode (Db1 to D
b3) connected in series, each connected between the second electrode of each first diode (Da1 to Da3) and the other end of the voltage source (1), and a plurality of second series circuits in which each second diode (Db1 to Db3) has a directionality such that the forward current of the second diode (Db1 to Db3) flows based on the sawtooth wave; , a plurality of second resistors or capacitors (Rb1 to Rb1 to Rb2) connected between the second electrode of each of the first diodes (Da1 to Da3) and the other end of the voltage source (1);
Rb3 or C1-C3), the first resistor or capacitor (Ra1-Ra3 or Ca1-Ca3), and the second resistor or capacitor (Ra1-Ra3 or Ca1-Ca3).
Connection points (P1 to P
3) and a common current output line (3), a plurality of photodiodes (S1 to S3) each connected with reverse bias directionality between the common current output line (3) and the common current output line (3); A current-voltage conversion circuit (2) connected between the other end of the voltage source (1) and the photodiode (S1-S3) in order to electrically isolate the photodiode (S1-S3). Multiple blocking diodes (
Dc1 to Dc3), the first diode (Da1 to Da3), the second diode (Db1 to Db3), the photodiode (S1 to S3), and the blocking diode (Dc1
-Dc3) are diodes of the same junction type formed on the same insulating substrate (11). [2] The first diode (Da1 to Da3), the second diode (Db1 to Db3), the photodiode (S1 to S3), and the blocking diode (
2. The image sensor according to claim 1, wherein each of Dc1 to Dc3) is a PIN type diode made of hydrogenated amorphous silicon. [3] A voltage source (1) for supplying a sawtooth wave that increases or decreases continuously or stepwise with time; and a plurality of first diodes each having a first electrode and a second electrode ( Da1 to Da3) are connected in series, one end of which is connected to the voltage source (1),
In addition, each of the first diodes (Da1 to Da3) has a directionality such that the forward current of each of the first diodes (Da1 to Da3) flows based on the sawtooth wave.
has, and each first diode (Da1 to D
a3) a first series circuit in which the first electrode is disposed on the voltage source (1) side, each connected to a first resistor or capacitor (Ra1 to Ra3
or Ca1 to Ca3) and the second diode (Db1 to D
b3) connected in series, each connected between the second electrode of each first diode (Da1 to Da3) and the other end of the voltage source (1), and a plurality of second series circuits in which each second diode (Db1 to Db3) has a directionality such that the forward current of the second diode (Db1 to Db3) flows based on the sawtooth wave; , a plurality of second resistors or capacitors (Rb1 to Rb1 to Rb2) connected between the second electrode of each of the first diodes (Da1 to Da3) and the other end of the voltage source (1);
Rb3 or C1-C3), the first resistor or capacitor (Ra1-Ra3 or Ca1-Ca3), and the second resistor or capacitor (Ra1-Ra3 or Ca1-Ca3).
Connection points (P1 to P
3) and a common current output line (3), a plurality of photodiodes (S1 to S3) each connected with reverse bias directionality between the common current output line (3) and the common current output line (3); A current-voltage conversion circuit (2) connected between the other end of the voltage source (1) and the photodiode (S1-S3) in order to electrically isolate the photodiode (S1-S3). Multiple blocking diodes (
Dc1 to Dc3), in which the first
diodes (Da1 to Da3), the second diodes (Db1 to Db3), and the photodiodes (S1 to Db3).
S3) and the blocking diodes (Dc1 to Dc3
) with a common junction to the semiconductor layers (14, 15,
16) and an upper electrode layer (17), respectively, the first diode (Da1 to Da3), the second diode (Db1 to Db2), the photodiode (S1 to S3), and the blocking step. Diode (Dc1
~ Dc3) The upper electrode layer (17) and the semiconductor layer (14, 15) correspond to the desired pattern of the upper electrode.
, 16). , 16).