JPH0779155B2 - Image sensor and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image sensor of a type in which a plurality of photodiodes are sequentially scanned based on a sawtooth voltage, and a manufacturing method thereof.

[Problems to be Solved by Related Art and Invention] An image sensor selects a plurality of photoelectric conversion elements for converting optical information into electric signals and an electric signal by electrically scanning the plurality of photoelectric conversion elements. And an analog switch for obtaining the same. The analog switch is composed of a field effect transistor, for example, as disclosed in JP-A-63-2377, and is arranged in the vicinity of 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 pixels).
One field effect transistor must be arranged so that it fits within 5 μm. However, it is not easy to form a field effect transistor so as to fit in such an extremely narrow width. Further, when the three wiring conductor layers for the drain, the source and the gate of the field effect transistor are provided within a predetermined width on the substrate, the width of the three wiring conductor layers is inevitably narrowed. Yield of manufacturing was low.

In order to solve this kind of problem, a method of scanning a photodiode by using a series circuit of diodes is a patent application.
No. 1-198279. However, no specific configuration and manufacturing method of this image sensor are disclosed.

Then, the objective of this invention is providing the image sensor which can be manufactured easily, and its manufacturing method.

[Means for Solving the Problems] The present invention for achieving the above object will be described with reference to the reference numerals of the drawings showing an embodiment. A sawtooth wave that increases or decreases continuously or stepwise with time is supplied. Is a circuit in which a plurality of first diodes D _{a1 to} D _a3 each having a first electrode and a second electrode are connected in series, and one end of which is the voltage source 1 Each of the first diodes D _{a1 to} D _a3 has a directionality such that the forward current of each of the first diodes D _{a1 to} D _a3 flows based on the sawtooth wave, and A first series circuit in which the first electrodes of the first diodes D _{a1 to} D _a3 are arranged on the side of the voltage source 1 and a first resistor or a capacitor R _{a1 to} R _a3 or C, respectively. _{a1 to} C _a3 and the second
Each of the diodes D _{b1 to} D _b3 of the first diode D _{a1 to} D _a3 is connected in series between the second electrode and the other end of the voltage source 1.
And second respective diodes D _b1 of to D _b3 forward current the sawtooth wave directional flowing based on the respective second diode D _b1 to D _b3 is a plurality which second has Series circuit and respective first diodes D _{a1 to} D _a3
A plurality of second resistors or capacitors R _{b1 to} R _b3 respectively connected between the second electrode and the other end of the voltage source 1.
Or C1 to C3 and the first resistor or capacitor R _{a1 to} R _a3
Alternatively, the connection points P _{1 to} P ₃ between the C _{a1 to} C _a3 and the second diodes D _{b1 to} D _b3 and the common current output line 3 are reverse biased and are respectively connected. a voltage conversion circuit 2, - a plurality of photodiodes S ₁ to S _3, which are the common current output line 3 and connected to a current between the other end of the voltage source 1
And the photodiode S ₁ to S ₃ electrically said to separate photodiode S1~S3 plurality of blocking diodes respectively connected between each other D _c1 to D _c3, an image sensor consisting of, the first The diode of D _a1
~ D _a3 and the second diodes D _{b1 to} D _b3 , the photodiodes S _{1 to} S ₃ and the blocking diodes D _{c1 to} D _c3
Is a diode of the same junction type formed on the same insulating substrate 11, and relates to an image sensor.

It is desirable that each diode is a PIN diode made of hydrogenated amorphous silicon.

Further, when manufacturing the image sensor, it is desirable to provide a common semiconductor layer and an upper electrode layer 17 for each diode on the same insulating substrate 11, and then separate each diode.

When generating a sawtooth wave in the image sensor of [Operation] The present invention, photodiode S ₁ to S ₃ are sequentially scanned. First and second diodes included in this image sensor
Since D _{a1 to} D _a3 , D _{b1 to} D _b3 , photodiodes S _{1 to} S ₃ , and blocking diodes D _{c1 to} D _c3 are diodes of the same junction type, they can be easily manufactured,
It is possible to provide a low cost image sensor.

If a common semiconductor layer and an upper electrode layer are provided and then each diode is separated, the number of photolithography steps can be reduced.

[Embodiment] The one-dimensional image sensor according to the embodiment of the present invention shown in FIG. 1 has a voltage source 1 and four unit circuits K ₀ , K ₁ , K ₂ and K corresponding to 4 pixels or bits. ₃ and the current-voltage conversion circuit 2. This one-dimensional image sensor is configured to be able to detect a number of pixels greater than four. However, since it is difficult to show the entire structure of this one-dimensional image sensor in the drawing, only a part thereof is shown in FIG.

The three unit circuits K ₁ , K ₂ , and K ₃ that are identical to each other include a first diode D _a1 , D _a2 , and D _a3 and a second diode D _b1 , D _b2 , and D 3.
_b3 , the first resistors R _a1 , R _a2 , R _a3 , and the second resistors R _b1 , R a
_b2 , R _b3 and photodiodes S ₁ , S ₂ , S for light detection
₂ and blocking diodes D _c1 , D _c2 , D _c3 . Another unit circuit K ₀ arranged between the voltage source 1 and the unit circuit K ₁ includes a second diode D _b0 and a first resistor R 0.
_a0 , photodiode S ₀ , blocking diode
It consists of D _c0 . Unit circuit K ₀ is another unit circuit K ₁ , K ₂ , K ₂
Of the first diode D _a1 , D _a2 , D _a3 and the second resistor R _b1 , R _b2 , R _b3 in. However, the unit circuit K0 can also be connected to the unit circuits K1, K2, and K3 corresponding to the first diode and the second resistor. Further, the unit circuit K0 at the first stage can be omitted from the image sensor of FIG. 1 if necessary. One end of a circuit (first series circuit) in which three first diodes D _a1 , D _a2 , and D _a3 each having an anode (first electrode) and a cathode (second electrode) are connected in series ( The left end is the voltage source 1
Is connected to one end of. The first diodes D _a1 , D _a2 ,
D _a3 has a directivity that is biased in the forward direction by the voltage of the voltage source 1. That is, the first diodes D _{a1 to} D _a3
The anode (first electrode) of is disposed on the voltage source 1 side. When the upper terminal of the voltage source 1 is negative, the cathodes of the first diodes D _{a1 to} D _a3 are arranged on the voltage source 1 side. Between the cathode (second electrode) of the first diode D _a1 , D _a2 , D _a3 and the voltage source 1 and the other end (ground) there are first resistors R _a1 , R _a2 , R _a3 and a second resistor R _a3 . Diode D
Circuits (second series circuits) in which _b1 , D _b2 , and D _b3 are respectively connected in series are connected. In the unit circuit K ₀ , the first resistor R _{a0 is provided} between one end and the other end of the voltage source 1.
And a second diode D _b0 connected in series. The second diodes D _b0 , D _b1 , D _b2 and D _b3 have a directionality in which they are forward biased by the voltage of the voltage source 1.

The first resistance R _a0 in each unit circuit K ₀ , K ₁ , K ₂ , K ₃
R _a1 , R _a2 , R _a3 and the second diode D _b0 , D _b1 , D _b2 , D _b3
At the interconnection points P ₀ , P ₁ , P ₂ , P ₃ of the photodiode S ₀ ,
S ₁ , S ₂ , S ₃ and blocking diodes D _c0 , D _c1 , D _c2 , S
A series circuit (third series circuit) with _c3 is connected.
That is, the cathodes of the photodiodes S _{0 to} S ₃ are connected to the points P _{0 to} P ₃ via the blocking diodes D _{c0 to} D _c3 , and the anodes are connected to the common current output line 3.

The current-voltage conversion circuit 2 includes a common current output line 3 and a voltage source 1.
Consisting connected to the capacitor C during the other end resistance R _L and a current output line 3 which is connected between the (ground) and the output terminal 4. Therefore, photodiode S0~S3 are substantially connected in parallel with the second diode D _b0 to D _b3. The photodiodes S _{0 to} S ₃ are connected so as to be reverse biased by the voltage of the voltage source 1. Therefore, the current flowing through the photodiodes S _{0 to} S ₃ is extremely small.

Details of each part of the image sensor of FIG. 1 are as follows.

The voltage source 1 is composed of a circuit that generates a sawtooth wave, and periodically generates a sawtooth wave, that is, a sweep signal shown in FIG. The maximum amplitude width of the sawtooth wave in FIG. 2 is set to a value capable of turning on all the first and second diodes D _{a1 to} D _a3 and D _{b0 to} D _b3 in FIG.

Photodiodes S _{0 to} S ₃ , first diodes D _{a1 to} D _a3 ,
Second diodes D _{b0 to} D _b3 , blocking diode D
_{c0 to} D _c3 are PIN junction diodes of the same type, each of which is a hydrogenated amorphous silicon semiconductor layer, one electrode layer provided below the semiconductor layer, and the other provided above the semiconductor layer. And an electrode layer.

Since the photodiodes S _{0 to} S ₃ are reverse biased,
It is equivalently shown by the parallel circuit of the capacitance Cs and the current source Is proportional to the light intensity shown in FIG. The value of the current flowing through the equivalent capacitance Cs of the photodiodes S _{0 to} S ₃ is extremely small.

The first diodes D _{a1 to} D _a3 and the second diodes D _{b0 to} D
_The voltage across both ends when _b3 is turned on, that is, the forward voltage V _f is approximately 1V. The first resistors R _{b1 to} R _b3 each have a resistance of 100 kΩ, and the second resistors R _{b1 to} R _b3 each have a resistance of 1 kΩ, which are made of a material such as TiO2, Ta-SiO2 or NiCr.

[Operation] In the image sensor of FIG. 1, when the sawtooth wave shown in FIG. 2 is generated from the voltage source 1, the first diode D _a1
~ D _a3 becomes conductive sequentially. When the sawtooth ramp voltage gradually increases, the potential V _{p0 at} the point P ₀ gradually increases as shown in FIG. 4 (A). As a result, the potential V at the point P _0
p0 is the forward voltage Vf of the second diode D _b0 of the unit circuit K ₀
Then, the diode D _b0 is turned on, and the potential V _{p0 at} the point P ₀ becomes a substantially constant value (approximately V _f ), that is, the saturation voltage value.
At the same time as the second diode D _b0 of the unit circuit K ₀ is turned on, the first diode D _a1 of the unit circuit K ₁ is also turned on. While the first diode D _a1 of the unit circuit K ₁ is non-conducting (off state), the first diode D _a1
The cathode of the first diode is near zero volts
When D _a1 is turned on and the voltage V _d of the voltage source 1 further increases, the cathode voltage of the first diode D _a1 follows the voltage V _d and increases. That is, when the first diode D _a1 is turned on, the voltage across this is almost fixed to the forward voltage Vf, so the voltage obtained by subtracting the forward voltage Vf of the diode D _a1 from the power supply voltage Vd is the resistance R _b1 . Join both ends. Further, the potential at the point P ₁ becomes substantially equal to the voltage across the second resistor R _b1 while the second diode D _b1 of the unit circuit K ₁ is non-conducting. Therefore, after the first diode D _a1 is turned on, the potential V _p1 at the point P ₁ gradually rises as shown in FIG. 4 (A). The potential V _{p1 at the} point P ₁ is the second diode D
_At the forward voltage V _f of _b1 , this turns on and
The electric potential V _{p1 of} P ₁ becomes almost constant (V _f ). At about the same time that the second diode D _b1 of the unit circuit K ₁ is turned on, the first diode D _a2 of the unit circuit K2 is turned on, and the point P2 is turned on as shown in FIG. 4 (A). A potential V _p2 is obtained. When the ramp voltage of the sawtooth wave supplied from the voltage source 1 further increases, the first diode D _a3 of the unit circuit K ₃
Is turned on, and the potential V _p3 of FIG. 4 (A) is obtained at the point P ₃ . When the potentials V _{p0 to} V _{p3 at} the points P _{0 to} P ₃ sequentially change as shown in FIG. 4 (A), the current-voltage conversion circuit 2 is interposed between the points P _{0 to} P ₃ and the ground. The connected photodiodes S _{0 to} S ₃ are sequentially driven. That is, the photodiodes S _{0 to} S ₃ are electrically scanned.

In the circuit of FIG. 1, the photodiodes S _{0 to} S ₃ are arranged one-dimensionally. When reading optical information with the photodiodes S _{0 to} S ₃ , first of all, the first diode D _a1
~ D _a3 and the second diodes D _{b0 to} D _b3 are all generated from the voltage source 1 so that the voltage can be turned on. The first diodes D _{a1 to} D _a3 and the second diode D a
voltage for all of the _b0 to D _b3 to the ON state is given by the sawtooth wave shown in Figure 2. That is, the maximum value of the sawtooth wave and the voltage value in the vicinity thereof can turn on all of the first and second diodes D _{a1 to} D _a3 and D _{b0 to} D _b3 .

The first diodes D _{a1 to} D _a3 and the second diodes D _{b0 to} D
all of _b3 is in a period in the ON state, the photodiodes S ₀ to S ₃ by the forward voltage V _f of the second diode D _b0 to D _b3 obtained point P ₀ to P ₃ are reverse biased, The capacitance C _s equivalently shown in FIG. 3 is charged. Since the equivalent capacitance C _s is extremely small, the charging of the equivalent capacitance C _s can be achieved by the minute current in the region before the point where the forward current of the blocking diodes D _{c0 to} D _c3 steeply rises.

When an optical signal obtained from a subject (not shown) such as a facsimile document arranged opposite to the image sensor of FIG. 1 is input to the photodiodes S _{0 to} S ₃ ,
Photodiode S ₀ ~
The charge amount of the equivalent capacitance C _s of S ₃ changes. That, in discharge occurs in equivalent capacitance C _s in what optical signal enters in the photodiode S ₀ to S _3, in which the optical signal is not inputted does not occur discharge of the equivalent capacitance C _s. The amount of discharge of the equivalent capacitance C _s changes depending on the amount of light. There are two methods of giving an optical input to the photodiodes S _{0 to} S ₃ . One of them is a method of always applying an optical input to the photodiodes S _{0 to} S ₃ , and the other is to apply an optical input only during a predetermined period (for example, a period when the voltage V _d of the voltage source 1 is zero volt). How to give.

When the voltage Vd of the voltage source 1 linearly increases with time as shown in FIG. 2, the potentials V _p0 , V _p1 , V _p2 , and V are shown at points P _{0 to} P ₃ as shown in FIG. 4 (A). _p3 is obtained, which sequentially reverse biases the photodiodes S ₀ -S ₃ . In other words, the voltage for charging the equivalent capacitance Cs shown in FIG. ₃ is applied to the photodiodes S _{0 to} S ₃ . At this time, the photodiode S ₀ to S charging current flows in the _three of the equivalent capacitance Cs relative to that light input is discharged, but the charge current relative to that light input did not discharged without Does not flow. Since the charging current of the equivalent capacitance Cs of the photodiodes S _{0 to} S ₃ flows through the current-voltage conversion circuit 2, the voltage V _{out of the} output terminal 4 changes depending on the presence or absence of the charging current. Since each of the four photodiodes S _{0 to} S ₃ receives an optical input, each equivalent capacitance C _s
In the state where There has been discharged, the potential V _p0 ~V _p3 as shown in FIG. 4 (A) is sequentially applied to the photodiode S ₀ to S _3, the voltage V _out of the output terminal 4 4 As shown in the figure (B), it changes every time the charging current flows through the photodiodes S _{0 to} S ₃ . That is, the charging current increases the equivalent capacitance Cs with increasing potential V _p0 ~V _p3 of the points P ₀ to P _3, the points P ₀
When the potential V _p0 ~V _p3 of to P ₃ is saturated, the charging current decreases,
An output voltage V _out corresponding to this change in charging current is obtained.

FIG. 4C shows four photodiodes S ₀ , S ₁ , S ₂ ,
Without optical input is given to S2 of the S _3, S _0, the change in S _1, S ₃ only to the voltage V _out of the output terminal 4 when the optical input is given is shown. In this case, the potential V shown in FIG.
_{When p0 to} V _p3 are sequentially applied to the photodiodes S _{0 to} S ₃ , no charging current flows in the photodiode S ₂ . That is, the output voltage V corresponding to the potential V _p2 shown in FIG.
_No change in _out occurs.

[Manufacturing Method] This image sensor includes first diodes D _{a1 to} D _a3 and second diodes D _{b0 to} D _b on a common insulating substrate 11 made of glass shown in FIGS. 5 (A) and 6. _b3 , photodiodes S0 to S3, blocking diodes D _{c0 to} D _c3 , first resistors R _{a0 to} R _a3 , and second resistors R _{b1 to} R _b3 . These geometrical arrangements are as shown in FIGS. 5 (A) and 5 (B).

Next, a method for manufacturing these will be described in the order of steps with reference to FIG. Since the unit circuits K _{0 to} K ₃ are formed simultaneously by the same method, the manufacturing method of the unit circuit K ₁ will be described as an example.

As shown in FIG. 6 (A), a resistance film 12, a lower electrode layer 13, and an N-type hydrogen 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 an I-type film) 15, a P-type hydrogenated amorphous silicon film (hereinafter referred to as a P-type film) 16, The transparent electrode layer (upper electrode layer) 17 was sequentially formed. More specifically, the resistance film 12 is made of TaSi.
It was formed by sputtering O ₂ to a thickness of 1000 Å. The lower electrode layer 13 is made of chromium (Cr)
It was formed by sputtering to a thickness of 1000 Å. The N-type film 14, the I-type film 15, and the P-type film 16 were formed by the glow discharge method. More specifically, the N-type film 14 is made of Si.
A mixed gas of H ₄ , PH ₃ and H ₂ was used to form a film having a thickness of about 300 Å, and the doping amount of P (phosphorus) was set to 0.6%. The I-type film 15 has a thickness of about 50 using a mixed gas of SiH ₄ and H _2.
It was formed to have a thickness of 00 angstrom, and conductivity type determining impurities were not added. The P-type film 16 is formed to have a film thickness of about 300 Å using a mixed gas of SiH ₄ , B ₂ H ₆ and H ₂ , and B
The doping amount of (boron) was set to 0.6%. The transparent electrode layer 17 was formed by depositing ITO (indium tin oxide) with a film thickness of 900 angstrom by an electron beam vapor deposition method. The resistance film 12 is commonly formed for the first and second resistors R _a1 and R _a2 , and the lower electrode layer 13, the N-type film 14, and the I-type film are formed.
15, the P-type film 16, and the transparent electrode layer 17 were formed commonly to each diode.

Next, as shown in FIG. 6 (A), a first resist layer 17 was provided, and patterning was performed by a photolinography process to obtain the one shown in FIG. 6 (B). That is, a first mask (not shown) made of the resist layer 17 is provided,
The transparent electrode layer 17 was patterned by a wet etching method. The amorphous semiconductor layer composed of the N-type film 13, the I-type film 14 and the P-type film 15 was dry-etched by a mixed gas of CF ₄ gas and 5% of O ₂ gas. Next, after this dry etching, the transparent electrode layer 17 is etched again by the wet etching method using the same mask,
Surface area was reduced. In FIG. 6 (B), the pattern of each part is shown in principle, but in reality, each part becomes trapezoidal by lateral etching, and the lateral protrusion of the transparent electrode layer 17 occurs. Wet etching removes this protrusion. The pattern of FIG. 6 (B) corresponds to the final pattern of the resistance film 12.

Next, after peeling off the first mask, a second resist layer 18 is provided as shown in FIG. 6C, a second mask (not shown) is formed, and the transparent electrode layer 17 is wet. By etching, the semiconductor layer composed of the P-type film 16, the I-type film 15 and the N-type film 14 was dry-etched to obtain the one shown in FIG. 6 (D). Thereby, the first and second diodes
D _a1 , D _b1 , blocking diode D _c1 , and photodiode S1 are isolated from each other.

Next, a protection / separation film 19 made of an I-type film made of a hydrogenated amorphous semiconductor is formed by a glow discharge method as shown in FIG. 6 (E), and a third resist layer 20 is formed thereon. A third mask (not shown) based on the resist layer 20 provided was used to obtain a protection and separation film 19 having a pattern shown in FIG. 6 (F). If the protection / separation film 19 is an I-type film in this way, it can be formed in the same device as the semiconductor layer such as the I-type film 15 in the diode portion, and the manufacturing device can be simplified. become.

Next, after removing the third mask, as shown in FIG. 6 (G), the chromium layer 21 for the extraction electrode (wiring conductor) is formed.
And an aluminum layer 22 are formed by a sputtering method, and a fourth resist layer 23 is formed thereon, and the resist layer 23
A fourth mask (not shown) made of chrome is provided, and using this, a lead electrode layer made of a chromium layer 21 and an aluminum layer 22 and a lower electrode layer 13 made of chrome are formed in FIG. 6 (H).
Etched as shown in FIG.

After that, a protective film (not shown) and photodiodes S ₀ to
Except for the light receiving area of S ₃ and other diodes D _a1 ~
A light-shielding film (not shown) was formed on D _a3 , D _{b0 to} D _b3 , and D _{c0 to} D _c3 to complete the image sensor.

When the relationship between the PH ₃ doping amount and the film thickness of the I-type film 15 and the electrical characteristics was examined 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, when only the doping amount of PH ₃ was changed to 0, 20, 40, and 80 ppm, the leakage current I _d of the completed diode when a reverse voltage of 3 V was applied was Changes as shown by characteristic line A, and
The series resistance R _s during forward operation when a voltage of 0.7 V or higher was applied changed as shown by the characteristic line B in FIG. As is clear from this, it is desirable that the doping amount of phosphorus is in the range of 0 to 40 ppm.

FIG. 8 shows the relationship between the thickness of the I-type film 15, the leakage current I _{d of the} diode, and the series resistance Rs. That is, in the method for manufacturing the I-type film 15 described in the embodiment, only this film thickness is 1000 to 50
When changed in the range of 00 angstrom, the leakage current I _d of the diode at 3V becomes as shown by the characteristic line A,
Further, the series resistance Rs is shown by the characteristic line B. The series resistance Rs of the diode increases sharply above 3000 angstroms. However, as the film thickness of the I-type film 15 increases, the equivalent capacitance decreases and the time constant in the scanning circuit decreases. In consideration of these, it is desirable to determine the film thickness of the I-type film 15 so that the series resistance R _s / I-type film thickness becomes maximum or in the vicinity thereof. This desired film thickness is 2000-5000 Angstroms.

This embodiment has the following advantages.

(1) First diode D _{a1 to} D _a3 , second diode D _{b0 to} D _b3 , blocking diode D _c0 on the same substrate 11.
Since ~ D _c3 and the photodiodes S _{0 to} S ₃ are formed in the same type (PIN type), the image sensor can be easily manufactured.

(2) Since each diode is made of hydrogenated amorphous silicon and is formed at the same time, it can be obtained very easily by a small number of photolithography steps. No problem occurs even if the upper electrodes of the diodes other than the photodiodes S _{0 to} S ₃ 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 patterned as shown in FIG. (D)
Since the diodes D _a1 , D _b1 , D _c1 , and S ₁ are separated as shown in (3), it is possible to form each diode under the same condition. Although the first resistor R _a1 and the second resistor R _b1 are continuous with each other, no problem occurs in the electric circuit.

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

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

(6) As shown in FIG. 5 (B), the first resistors R _{a1 to} R a
The width of the unit circuit (bit) can be reduced by arranging _an and the second resistors R _{b1 to} R _bn on one straight line. Further, the connection of the ground wiring conductor 40 of the second resistors R _{b1 to} R _{bn to} the voltage source 1 becomes easy, and the power supply terminal 41 can be rationally arranged. Note that FIG. 5B shows that the image sensor is 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 embodiment, the forward current I _f at 1 V is 0.18 A / cm ²
And the leakage current Id at −5V is 2 × 10 ⁻⁹ A / cm ² , while I _f is 0.10 A / cm ² , I _d when the PIN configuration is reversed.
Is 1 × 10 ^-10 A / cm ² . The forward currents of the first diodes D _{a1 to} D _a3 and the second diodes D _{b0 to} D _b3 are preferably large, and the leakage currents I _d of the blocking diodes D _{c0 to} D _c3 and the photodiodes S _{0 to} S ₃ are It is preferably 1 × 10 ⁻⁸ A / cm ² or less, but the forward current and the leakage current can be set within the allowable range in both the NIP configuration and the PIN configuration.

(2) The blocking diodes D _{c0 to} D _c3 for preventing mutual interference of the photodiodes S _{0 to} S ₃ are connected to the first resistors R _{a0 to} R a.
_a3 be connected in series or may be connected between the second resistor R _b1 to R _b3 and the first resistor R _a1 to R _a3.
Further, the positions of the photodiodes S _{0 to} S ₃ and the blocking diodes D _{c0 to} D _c3 can be reversed.

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

In FIG. 9, n unit circuits corresponding to the unit circuits K _{1 to} K ₃ in FIG. ₁ are divided into _m circuit blocks B _{1 to} B ₂ ... B _m . Each circuit block B _{1 to} B _m includes a unit circuit K ₁ shown in FIG.
Includes several to several tens the equivalent of a ~K _3, it is equivalent to the circuit obtained by omitting the voltage source 1 from the image sensor circuit of FIG. 1. Each circuit block B _{1 to} B _m is connected to the voltage source 1 a via the multiplexer 10. Each circuit block B ₁ ~
The output terminals of B _m are commonly connected via amplifiers A _{1 to} A _m . The voltage source 1a repeatedly generates the sawtooth wave (triangular wave) shown in FIG. Multiplexer 10 is as shown in Figure No. 10 (B) (C), distributes FIG. 10 the sawtooth wave (A) to the circuit block B~B _m. Each circuit block B ₁ ~
The light input to each photodiode of B _m is shown in Fig. 10 (D).
Always give as shown.

11 and 12 show another driving method of the image sensor. Also in FIG. 11, just as in FIG. 9, n unit circuits corresponding to the unit circuits K _{1 to} K ₃ in FIG. ₁ are divided into _m circuit blocks B _{1 to} B _m . Each circuit block B ₁ ~
_Bm is connected to the voltage source 1, respectively. The voltage source 1 shown in FIG. 9 generates the sawtooth wave shown in FIG. 12 (A) similarly to that shown in FIG. The sawtooth wave is simultaneously supplied to the circuit blocks B _{1 to} B _m as shown in FIGS. As a result, scanning is simultaneously started in each of the circuit blocks B _{1 to} B _m , and outputs are simultaneously generated. The outputs of the circuit blocks B _{1 to} B _m are sent to the signal processing circuit 30 including a memory. Signal processing circuit 30
Is arranged on a common time axis so as to correspond to the output of the circuit block B ₁ .about.B _m in sequence order of the circuit block B ₁ ~B _m. In the image sensor of FIG. 11, the light output to the photodiode is given during the period when the drive voltage Vd is zero, as shown in FIG. 12 (D).

(4) The sawtooth wave can be a stepwise sawtooth wave as shown in FIG. 13 and a sawtooth wave increasing quadratically as shown in FIG.

(5) The polarities of the diodes and the voltage source 1 can be reversed.

(6) Various types of junction diodes can be used in place of the diodes D _{a1 to} D _a3 , D _{b0 to} D _b3 , D _{c0 to} D _c3 , and the photodiodes S _{0 to} S ₃ .

(7) A voltage may be applied to the cathode terminals of the diodes D _{b0 to} D _b3 . That is, a bias voltage can be applied between the diodes D _{b0 to} D _b3 and the ground to expand the dynamic range.

(8) In FIG. 1, change the value of the second resistor from R _b1 to R _b3.
You may set so that it may become large gradually toward. That is, R _b0 <R _b1 <R _b2 <R _b3 may be set.

(10) As shown in FIG. 15, the second resistance R _{b1 of} FIG.
Capacitors C _{1 to} C may be connected instead of ~ R _b3 . Further, the capacitors C _{1 to} C ₃ in FIG. 15 can be replaced with diodes connected so as to be reverse-biased. This diode functions as a capacitor.

(11) As shown in FIG. 16, the first resistance R _{a0 of} FIG.
~ R _a3 can be replaced by capacitors C _a0 ~ C _a3 . Further, the capacitors C _{a0 to} C _a3 can be replaced with diodes connected in the reverse bias direction. However,
In this case, it is necessary to increase the leakage current of the second diodes D _{b0 to} D _b3 to form a capacitor discharge circuit.

(12) As shown in FIGS. 15 and 16, the current-voltage conversion circuit 2 includes an operational amplifier 31, a feedback resistor Rf, and a capacitor Cf.
It can be composed of and. The inverting input terminal of the operational amplifier 31 is connected to the common current output line 3, and the non-inverting input terminal is connected to the ground. The inverting amplifier 32 is an operational amplifier.
Connected to 31.

(13) The circuit can be made by omitting D _b0 , R _a0 , S ₀ , and D _c0 in the first stage.

[Effects of the Invention] As described above, according to the inventions of the respective claims, the first and second diodes, the blocking diode, and the photodiode are all of the same type, so that the image sensor is easily manufactured. It will be possible.

[Brief description of drawings]

1 is a circuit diagram showing an image sensor according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing a sawtooth wave, FIG. 3 is an equivalent circuit diagram of a photodiode, and FIG. 4 (A) is FIG. Showing potential changes at respective points P _{0 to} P ₃ of the circuit of FIG. 4, and FIG. 4 (B) shows voltage changes of the output terminal of the circuit of FIG.
FIG. 4 (C) is a diagram showing a state in which all the two photodiodes have an optical input, and FIG.
FIG. 5 (A) is a plan view showing the arrangement of each part of the image sensor in FIG. 1, and FIG. 5 (B) is a view showing a state where light is input to only three of the two photodiodes. A circuit diagram showing the image sensor in consideration of the arrangement of each element and wiring of the image sensor of FIG. 1, FIGS. 6 (A) to 6 (H) correspond to line VI-VI of the image sensor of FIG. 5 (A). FIG. 7 is a cross-sectional view showing a portion to be processed in the order of steps, FIG. 7 is a diagram showing the relationship between the PH ₃ doping amount of the diode I-type film, the leak current, and the series resistance, and FIG. 8 is the thickness of the diode I-type film and the leak current. FIG. 9 is a block diagram showing in principle the driving method of the photodiode when the number of unit circuits is large, and FIG. 10 is a diagram showing the state of each part of FIG. FIG. 11 shows another method of driving the photodiode when the number of unit circuits is large as in FIG. FIG. 12 is a block diagram showing the principle, FIG. 12 is a diagram showing the state of each part of FIG. 11, FIGS. 13 and 14 are waveform diagrams showing a modified example of a sawtooth wave, and FIGS. 15 and 16 are image sensors. FIG. 7 is a circuit diagram showing each modified example of FIG. 1 ... Voltage source, 2 ... Current-voltage conversion circuit, 3 ... Common current output line, 4 ... Output terminal, 11 ... Insulating substrate, 12 ...
Resistive film, 13 ... Lower electrode layer, 14 ... N-type film, 15 ... I-type film, 16 ... P-type film, 17 ... Transparent electrode layer, D _{a1 to} D _a3 ...... First diode, D _{b0 to} D _b3 ...... Second diode, D _c0
~ D _c3 ... blocking diode, S ₀ ~ S ₃ ... photo diode, R _a0 ~ R _a3 ... first resistance, R _b1 ~ R _b3 ... second resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Owada Toru Owada 6-16-20 Ueno Taito-ku, Tokyo Within Taiyo Denki Co., Ltd. (56) Reference JP-A-2-124679 (JP, A) JP-A 3-148177 (JP, A) JP-A-3-220973 (JP, A)

Claims (3)

[Claims] 1. A plurality of first electrodes each having a voltage source (1) for supplying a sawtooth wave which continuously or stepwise increases or decreases with time, and a first electrode and a second electrode. A circuit in which diodes (D _{a1 to} D _a3 ) are connected in series, one end of which is connected to the voltage source (1), and the forward current of each first diode (D _{a1 to} D _a3 ) is Each of the first diodes (D _{a1 to} D _a3 ) has a directivity such that it flows based on the sawtooth wave, and the first electrodes of the respective first diodes (D _{a1 to} D _a3 ) are A first series circuit arranged on the side of the voltage source (1) and a first resistor or capacitor (R _{a1 to} R _a3 or C respectively)
_{a1 to} C _a3 ) and a second diode (D _{b1 to} D _b3 ) connected in series, and the second electrode of each of the first diodes (D _{a1 to} D _a3 ) and the voltage source. Each of the second diodes (D _{b1 to} D _b3 ) is connected between the other end of (1) and the second diode (D _{b1 to} D _b3 ) so that the forward current flows based on the sawtooth wave. A plurality of second series circuits included in the diodes (D _{b1 to} D _b3 ), the second electrodes of the respective first diodes (D _{a1 to} D _a3 ), and the other of the voltage source (1) A plurality of second resistors or capacitors (R _{b1 to} R _b3 or C ₁ respectively connected between the terminals and
~ C ₃ ) and the first resistor or capacitor (R _a1 ~ R _a3 or C _a1 ~
C _a3 ) and the second diode (D _{b1 to} D _b3 ) connecting points (P _{1 to} P ₃ ) and the common current output line (3) are reverse-biased and have directivity, respectively. A plurality of connected photodiodes (S _{1 to} S ₃ ) and a current-voltage conversion circuit (2) connected between the common current output line (3) and the other end of the voltage source (1). And a plurality of blocking diodes (D _c1 to D _c1 ) respectively connected between the photodiodes (S _{1 to} S ₃ ) to electrically isolate the photodiodes (S _{1 to} S ₃ ).
D _c3 ), and the first diode (D _{a1 to} D _a3 ), the second diode (D _{b1 to} D _b3 ), the photo diode (S _{1 to} S ₃ ), and the blocking. An image sensor characterized in that diodes (D _{c1 to} D _c3 ) are diodes of the same junction type formed on the same insulating substrate (11). 2. The first diode (D _{a1 to} D _a3 ), the second diode (D _{b1 to} D _b3 ), the photodiode (S _{1 to} S ₃ ) and the blocking diode (D _{c1 to} D). _c3 )
The image sensor according to claim 1, wherein each is a PIN diode made of hydrogenated amorphous silicon. 3. A plurality of first sources each having a voltage source (1) for supplying a sawtooth wave that continuously or stepwise increases or decreases with time, and a first electrode and a second electrode. A circuit in which diodes (D _{a1 to} D _a3 ) are connected in series, one end of which is connected to the voltage source (1), and the forward current of each first diode (D _{a1 to} D _a3 ) is Each of the first diodes (D _{a1 to} D _a3 ) has a directivity such that it flows based on the sawtooth wave, and the first electrode of each of the first diodes (D _{a1 to} D _a3 ) is the A first series circuit arranged on the voltage source (1) side and a first resistor or capacitor (R _{a1 to} R _a3 or C, respectively).
_{a1 to} C _a3 ) and a second diode (D _{b1 to} D _b3 ) connected in series, and the second electrode of each of the first diodes (D _{a1 to} D _a3 ) and the voltage source. Each of the second diodes (D _{b1 to} D _b3 ) is connected between the other end of (1) and the second diode (D _{b1 to} D _b3 ) so that the forward current flows based on the sawtooth wave. A plurality of second series circuits included in the diodes (D _{b1 to} D _b3 ), the second electrodes of the respective first diodes (D _{a1 to} D _a3 ), and the other of the voltage source (1) A plurality of second resistors or capacitors (R _{b1 to} R _b3 or C ₁ respectively connected between the terminals and
~ C ₃ ) and the first resistor or capacitor (R _a1 ~ R _a3 or C _a1 ~
C _a3 ) and the second diode (D _{b1 to} D _b3 ) connecting points (P _{1 to} P ₃ ) and the common current output line (3) are reverse-biased and have directivity, respectively. A plurality of connected photodiodes (S _{1 to} S ₃ ) and a current-voltage conversion circuit (2) connected between the common current output line (3) and the other end of the voltage source (1). And a plurality of blocking diodes (D _c1 to D _c1 ) respectively connected between the photodiodes (S _{1 to} S ₃ ) to electrically isolate the photodiodes (S _{1 to} S ₃ ).
And D _c3), in the method for manufacturing an image sensor comprising, on the same insulating substrate (11), said first diode (D _a1 to D _a3) and said second diode (D _b1 to D _b3) respectively the semiconductor layer (14, 15, 16) the upper electrode layer (17) and a having a common junction with said photodiode (S ₁ to S ₃₎ and said blocking diode (D _c1 to D _c3) And the first diode (D _{a1 to} D _a3 ), the second diode (D _{b1 to} D _b2 ), the photodiode (S _{1 to} S ₃ ), and the blocking diode (D _{c1 to} D _c3 ). The upper electrode layer (17) so as to correspond to the desired pattern of the upper electrode of
And a step of respectively etching the semiconductor layers (14, 15, 16), the method of manufacturing an image sensor.