JP2007208008A - Optical detection module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical detection module capable of precisely compensating a dark current component from a photodiode. <P>SOLUTION: A light shielding photodiode having been light-shielded is arranged in the region adjoining one side of a square light receiving photodiode 1 for detecting light to form a unit 3. Multiple units are arranged to constitute a photodetector. A subtraction circuit 32 is provided which subtracts the output current of the light-shielding photodiode, multiplied with area ratio of the light receiving photodiode and light shielding photodiode from the output current of the light receiving photodiode to constitute a optical detection module. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light detection module capable of compensating a dark current component from a photodiode with high accuracy.

  2. Description of the Related Art Conventionally, so-called multi-division photometry, which divides an object scene into a plurality of areas and performs photometry using a luminance signal for each area, is used in many cameras. In the multi-division photometry method, in order to obtain more accurate luminance information from the object field, it is more advantageous that the number of divisions of the photodiode is larger.

  FIG. 8 is a circuit configuration diagram showing a configuration of a signal processing circuit in a photoelectric conversion apparatus that can be applied to, for example, a multi-division photometry sensor disclosed in JP-A-2002-199292. In FIG. 8, 101a, 101b, and 101c are input terminals, 102a, 102b, and 102c are integration circuits including an operational amplifier, an integration capacitor, a reset switch, and a reference voltage source, and 103a, 103b, and 103c are integration circuits 102a, 102b, and 102c. Sampling switches 104a, 104b, 104c are holding circuits composed of a hold capacitor and a buffer amplifier, 105a, 105b, 105c are readout switches for sequentially reading out the outputs of the holding circuits 104a, 104b, 104c, 106 A read switch driving shift register, 107 is an output buffer amplifier, 108 is an output terminal, and 109 is an A / D converter for A / D converting the output signal.

In the signal processing circuit configured as described above, the input terminals 101a, 101b, and 101c are connected to the photoelectric conversion elements of the photometric sensors arranged in a matrix, respectively, and input to the input terminals 101a, 101b, and 101c. The photocurrent Ip detected by the photoelectric conversion element is converted into a voltage signal by the integrating circuits 102a, 102b, and 102c, and held in the hold circuits 104a, 104b, and 104c via the sampling switches 103a, 103b, and 103c. The voltage signals held in the hold circuits 104a, 104b, and 104c are sequentially output to the output terminal 108 via the read switches 105a, 105b, and 105c driven by the shift register 106. When the integration capacity of the integration circuit is C and the integration time is T, the output voltage Vout is expressed by the following equation (1). Incidentally, Id is a dark current flowing out from the photoelectric conversion element.
Vout = (Ip + Id) × T / C (1)

  On the other hand, the following method is known as a method for compensating the dark current component from the output of the photoelectric conversion element. FIG. 9 is a schematic plan view showing a configuration of a pixel portion having a light-shielding portion of a solid-state imaging device disclosed in Japanese Unexamined Patent Publication No. 9-238287. In FIG. 9, reference numeral 201 denotes a pixel area of a pixel portion, and a plurality of pixels 202 are arranged in a matrix in the pixel area 201. The central portion of the pixel region 201 is a light receiving portion effective pixel region 203, which is formed by a plurality of effective pixels 202A. On the other hand, an optical black portion (hereinafter referred to as OB portion) region 204 is disposed on the outer periphery of the light receiving portion effective pixel region 203. The OB portion pixel 202B formed in the OB portion region 204 has the same configuration as that of the effective pixel 202A, but an OB portion metal light shielding film 205 is formed on the entire upper surface thereof. In FIG. 9, 206 is a readout circuit, 207 is a peripheral circuit region, and 208 is an output terminal.

In the pixel portion configured as described above, the effective pixel 202A formed inside the light receiving portion effective pixel region 203 receives light from the subject and photoelectrically converts the light into an image signal (signal charge). , Output photocurrent and dark current. On the other hand, the OB portion pixel 202B outputs only dark current. Therefore, the dark current can be compensated by subtracting the output of the OB portion pixel 202B from the output of the effective pixel 202A.
JP 2002-199292 A JP-A-9-238287

  By the way, in the conventional signal processing circuit shown in FIG. 8, when the light quantity is large, the photocurrent Ip generated by the photoelectric conversion element is Ip >> Id, so that an output signal proportional to the light quantity is obtained. However, when the amount of light is weak, the photocurrent Ip approaches the dark current Id, so that the output signal is not proportional to the amount of light, and therefore there is a problem that weak light cannot be detected.

  On the other hand, FIG. 9 discloses a dark current compensation method using an OB portion pixel as a method for solving the above-described problem. However, when the effective pixels are arranged away from the OB portion pixels formed on the outer peripheral portion, the element characteristics of both pixels vary relatively, and therefore the dark current value between the OB portion pixels and the effective pixels does not vary. It will be different. Further, when there is a temperature gradient in the pixel portion, the dark current value similarly differs between the OB portion pixel and the effective pixel. Therefore, there is a problem that dark current cannot be sufficiently compensated even if the output of the OB portion pixel is subtracted from the output of the effective pixel.

  The present invention has been made to solve the above-described problems in the conventional dark current compensation method for photoelectric conversion elements, and provides a photodetection module capable of highly accurately compensating for the dark current component from the photodiode. For the purpose.

  In order to solve the above-mentioned problem, the invention according to claim 1 is directed to a first photodiode that receives incident light, and a second photodiode that is formed adjacent to the first photodiode and that blocks incident light. A photodetecting section in which a plurality of units made of diodes are arranged on the same substrate; and a subtracting circuit for subtracting the output of the second photodiode from the output of the first photodiode in the same unit. This constitutes a light detection module.

  According to a second aspect of the present invention, in the optical detection module according to the first aspect, the second photodiode is formed so as to surround at least a part of an outer edge of the first photodiode. Is.

  According to a third aspect of the present invention, in the light detection module according to the second aspect, the second photodiode surrounds an outer edge of the first photodiode and is formed by closing an end portion thereof. It is characterized by.

  According to a fourth aspect of the present invention, in the light detection module according to the first aspect, the first unit and the second unit adjacent to each other among the plurality of units share the second photodiode. It is characterized by being.

  According to the first aspect of the present invention, since the first photodiode that receives incident light and the shielded second photodiode are formed adjacent to each other, variation in electrical characteristics of each photodiode is reduced. The dark current component can be compensated with higher accuracy. According to the second aspect of the present invention, the shielded second photodiode is formed so as to surround at least a part of the outer edge of the first photodiode that receives incident light. Variations in electrical characteristics can be reduced, and dark current components can be compensated with higher accuracy. According to the invention of claim 3, since the light-shielded second photodiode is formed by surrounding the outer edge of the first photodiode that receives incident light and closing its end. Variations in the electrical characteristics of each photodiode can be further reduced, and the dark current component can be compensated with higher accuracy. According to the invention of claim 4, among the plurality of units, the adjacent first unit and the second unit share the light-shielded second photodiode. The unit interval can be narrowed, and the size of the first photodiode that receives incident light per unit area can be increased to increase the aperture ratio.

  Next, the best mode for carrying out the present invention will be described.

  First, Example 1 will be described. FIG. 1 is a diagram showing a configuration of a first embodiment of a light detection module according to the present invention. In the case of a photodetection module used as a photometric sensor or the like, detailed resolution as required for a solid-state imaging device is not required, so that the pixel size is large and there may be a space between pixels. Therefore, in the first embodiment of the light detection module according to the present invention, as shown in FIG. 1, light is shielded in a rectangular light-receiving photodiode 1 for detecting light and a region adjacent to one side of the light-receiving photodiode 1. A light-shielding photodiode 2 is arranged, and the light-receiving and light-shielding photodiodes 1 and 2 constitute a photodiode unit 3. In the first embodiment shown in FIG. 1, the photodetection unit is configured with the photodiode unit 3 having a 3 × 3 configuration, and the light-shielding photodiodes 2 are arranged between the photodiode photodiodes arranged in the row direction. The thing of the form which is shown is shown.

2A is a diagram showing a cross-sectional structure of two photodiode units (a first photodiode unit and a second photodiode unit) along the line AA ′ in FIG. In FIG. 2, 11 is an N-type substrate, 12 is an N-well formed on the N-type substrate 11, 13, 14, 15, 16 are first to fourth P ⁺ -types formed on the N-well 12. diffusion layer, N ⁺ -type diffusion layer formed on the N-well12 17, 18 is a LOCOS oxide film for the photodiode separating selectively formed on the N-well12 region, a first P ⁺ type diffusion The light receiving photodiode PD1p of the first unit is composed of the layer 13 and the N-well 12, and the light-shielding photodiode PD1d of the first unit is composed of the second P ⁺ diffusion layer 14 and the N-well 12 is the third P ^+. The light-receiving photodiode PD2p of the second unit is formed by the type diffusion layer 15 and the N-well 12, and the light-shielding photodiode PD2d of the second unit is formed by the fourth P ⁺ -type diffusion layer 16 and the N-well 12. Yes.

Reference numeral 19 denotes a first interlayer film formed in the wiring region, and reference numeral 20 denotes a first interlayer formed by connecting to the first P ⁺ -type diffusion layer 13 through a contact hole formed in the first interlayer film 19. The anode terminal 21 of the light receiving photodiode PD1p of the unit is for light shielding the first unit formed by connecting to the second P ⁺ type diffusion layer 14 through the contact hole formed in the first interlayer film 19 The anode terminal 22 of the photodiode PD1d is connected to the third P ⁺ -type diffusion layer 15 through a contact hole formed in the first interlayer film 19, and is connected to the second unit light-receiving photodiode PD2p. An anode terminal 23 is connected to the fourth P ⁺ -type diffusion layer 16 through a contact hole formed in the first interlayer film 19, and is connected to the fourth unit light-shielding photodiode PD2d. 24 Is formed in the first interlayer film 19 This is a cathode terminal common to each photodiode formed by connecting to the N ⁺ type diffusion layer 17 through the contact hole. Reference numeral 25 denotes a second interlayer film formed on the first interlayer film 19, and 26 denotes a light shielding metal formed on the second interlayer film 25. The configuration of each photodiode in the cross-sectional configuration portion shown in FIG. 2A is the circuit configuration shown in FIG.

  In the two photodiode units shown in FIG. 2A, the wiring for transmitting the signals output from the respective light receiving photodiodes and the light shielding photodiodes has a one-layer configuration arranged on the light shielding photodiode region. However, the signal transmission wiring in the case of the photodetecting section composed of a large number of units may be provided on the light-shielding photodiode region in a multilayer wiring configuration.

  Next, the configuration of the signal processing circuit for the photodetection unit configured as described above will be described together with the operation thereof. As shown in FIG. 1, the region of the light receiving photodiode 1 in the light detection unit of the first embodiment is larger than the region of the light shielding photodiode 2, and their areas are different. Therefore, the output current from the light shielding photodiode 2 is A current amplifying circuit 31 for doubling the area ratio of the light receiving photodiode 1 and the light shielding photodiode 2 is provided, and the light shielding photodiode 2 obtained by multiplying the output current from the light receiving photodiode 1 by the area ratio. Are subtracted by the subtracting circuit 32, and the subtracted current is integrated by the integrating circuit 33 and held by the holding circuit. Then, the held outputs of the respective units are sequentially output to the output terminal 36 by the multiplexer 35.

Here, the photocurrent of the light receiving photodiode 1 is Ip, its dark current is Id1, the dark current of the light blocking photodiode 2 is Id2, and the area ratio of the light receiving photodiode 1 and the light blocking photodiode 2 is k. Then, the output voltage Vout is expressed by the following equation (2).
Vout = {(Ip + Id 1) −kId 2} × T / C (2)

Here, since the light-receiving photodiode 1 and the light-shielding photodiode 2 are arranged adjacent to each other, variation is small and equivalent electric characteristics can be obtained. Therefore, Id 1 = kId 2 can be set, Is expressed as in equation (3).
Vout = Ip x T / C (3)

  In this way, a photodetection module capable of compensating for dark current with high accuracy is realized by arranging a light-receiving photodiode and a light-shielding photodiode adjacent to each other to equalize the electrical characteristics. be able to.

  Next, Example 2 will be described. In the first embodiment shown in FIG. 1, the light-shielding photodiode is arranged along one side of the rectangular light-receiving photodiode. However, the light detection module according to the second embodiment is as shown in FIG. In addition, a light-shielding photodiode 2a is arranged around the square-shaped light-receiving photodiode 1, that is, adjacent to the four sides, and the light-receiving photodiode 1 is placed in this wiring area with the light-shielding photodiode area as a wiring area. And a wiring for transmitting an output signal from the light-shielding photodiode 2a is arranged in a multilayer wiring structure to constitute a light detection section.

The signal processing circuit for the light detection unit of the light detection module according to the second embodiment is the same as the signal processing circuit in the light detection module according to the first embodiment shown in FIG. In Example 2, the photocurrent of the light-receiving photodiode 1 is Ip, the dark current is Id1, the dark current of the light-shielding photodiode 2a is Id2, and the area ratio of the light-receiving photodiode 1 and the light-shielding photodiode 2a. If m is m, the output voltage Vout is expressed by the following equation (4).
Vout = {(Ip + Id 1) −mId 2} × T / C (4)
Here, the light-receiving photodiode 1 is surrounded by the light-shielding photodiode 2a and adjacent to each other, and has the same electrical characteristics with less variation. Therefore, Id 1 = mId 2 can be obtained. , (4) is represented as (5).
Vout = Ip x T / C (5)

  In this way, dark current can be compensated with higher accuracy by arranging the light receiving photodiodes adjacent to each other so that the light receiving photodiodes are surrounded by the light shielding photodiodes, and equalizing the electrical characteristics of both. A simple light detection module can be realized.

  In the second embodiment, a rectangular light-receiving photodiode 1 is formed by arranging light-shielding photodiodes 2a adjacent to the periphery of the four sides and having a rectangular outer edge, and a large number of such units. Although the photodetection module in which the photodetection unit is configured by arranging the photodetection unit is shown, another arrangement is provided as a mode in which the light shielding photodiode is arranged adjacent to the photodetection photodiode so as to surround the photodetection photodiode. The modes are shown in FIGS. 4A to 4E as modified examples of the light detection unit of the second embodiment.

  FIG. 4A shows a unit in which a light shielding photodiode 2b having a rectangular outer edge is disposed adjacent to the circular outer edge of the circular light receiving photodiode 1a. is there. FIG. 4B shows a light-receiving photodiode 1a having a rectangular shape on both the inner and outer edges similar to that of the second embodiment shown in FIG. Are arranged so as to surround the unit. FIG. 4C shows a unit configured by arranging an annular light-shielding photodiode 2c adjacent to the circular outer edge of the circular light-receiving photodiode 1a. FIG. 4D shows a unit configured by arranging a light-shielding photodiode 2d adjacent to its four sides and having a circular outer edge with respect to the rectangular light-receiving photodiode 1. FIG. FIG. 4E shows a unit in which an annular light shielding photodiode 2c is arranged so as to surround the light receiving photodiode 1 with respect to the square light receiving photodiode 1. Also in the modified example, the same effects as those of the second embodiment shown in FIG. 3 can be obtained.

  Further, in the second embodiment and the modification example, the unit is configured by arranging the light shielding photodiode having a shape closed so as to surround the light receiving photodiode with respect to the light receiving photodiode. For example, as shown in FIG. 5, the light-shielding photodiode has a shape adjacent to two connected sides of the rectangular light-receiving photodiode 1, that is, the outer edge of the light-receiving photodiode. The unit may be configured by forming a light-shielding photodiode 2 'so as to surround a part of the light-emitting diode. In this case, although not as shown in the second embodiment or its modification, The dark current can be compensated with higher accuracy than that shown in the first embodiment shown in FIG.

  Next, Example 3 will be described with reference to FIG. The external structure itself of the light detection section of the light detection module according to this embodiment is the same as the light detection section in the light detection module according to the first embodiment shown in FIG. The difference is that, in the third embodiment, the light shielding photodiodes arranged between the rectangular light receiving photodiodes arranged in the row direction are shared between two units adjacent in the column direction. Therefore, each unit 3 in the light detection unit of the third embodiment has two light receiving photodiodes 1 and two adjacent ones on the upper and lower sides so as to sandwich the light receiving photodiode 1. It is composed of light-shielding photodiodes 2-1, 2-2.

In the thus configured light detection section, output currents (dark currents) from two light shielding photodiodes 2-1 and 2-2 that are shared between adjacent units arranged so as to sandwich the light receiving photodiode 1 therebetween. ) Is copied using the current mirror circuit 37 and is used in the adjacent unit. An output current output from the two light shielding photodiodes 2 sandwiching the light receiving photodiode 1 via the current mirror circuit 37 is output from the light receiving photodiode 1 and the two light shielding photodiodes 2 by the current amplification circuit 31. The signal is amplified by the area ratio and is subtracted from the output current from the light receiving photodiode 1 by the subtracting circuit 32. The subtracted current is similarly integrated by the integration circuit 33, held by the hold circuit 34, and sequentially output to the output terminal 36 by the multiplexer 35. Here, the photocurrent of the light receiving photodiode 1 is Ip, the dark current is Id 1, the dark current of one light shielding photodiode 2-1 is Id 2a, and the dark current of the other light shielding photodiode 2-2 is dark current. The output voltage Vout is expressed by the following equation (6) where Id is 2b and the area ratio between the light-receiving photodiode 1 and the two light-shielding photodiodes 2-1 and 2-2 is n.
Vout = {(Ip + Id 1) -n (Id 2a + Id 2b)} * T / C (6)

In this embodiment, since the two light-shielding photodiodes are arranged adjacent to the light-receiving photodiode so as to sandwich the light-receiving photodiode as described above, the electric characteristics are small and the same electric characteristics are obtained. 1 = n (Id 2a + Id 2b). Therefore, the equation (6) is expressed as the following equation (7).
Vout = Ip x T / C (7)

  In this way, by arranging two light-shielding photodiodes adjacent to the light-receiving photodiode so as to sandwich the light-receiving photodiode, and making the electrical characteristics of the two equal, dark current can be further increased. It is possible to compensate with high accuracy, and the light shielding photodiode is shared between adjacent units, so that the unit interval can be reduced and the size of the light receiving photodiode per unit area can be reduced. The aperture ratio can be increased and the aperture ratio can be increased.

  In the third embodiment, two light-shielding photodiodes are arranged so as to sandwich a rectangular light-receiving photodiode from one direction, and the light-shielding photodiodes are shared in units adjacent to each other in the column direction to be sandwiched. As shown in FIG. 7, four light-shielding photodiodes 2-1 and 2-2 are arranged so as to sandwich a rectangular light-receiving photodiode 1 from two directions. , 2-3, 2-4, and the units adjacent to each other in the two directions of the matrix can share the light-shielding photodiodes. By adopting such a configuration, Furthermore, the variation can be reduced to achieve the same electrical characteristics, and the dark current can be compensated with higher accuracy.

  In the first to third embodiments, the light detection unit is shown as an area sensor type in which light receiving photodiodes are two-dimensionally arranged. However, a line sensor type in which light receiving photodiodes are one-dimensionally arranged. The configurations of the first to third embodiments according to the present invention can also be applied to the photodetecting section, and the same operational effects can be obtained.

It is a figure which shows the structure of Example 1 of the photon detection module which concerns on this invention. FIG. 1 is a schematic cross-sectional view showing a cross-sectional structure taken along the line AA ′ in the light detection unit of the light detection module according to the first embodiment shown in FIG. 1 and an equivalent circuit of each photodiode shown in the cross-sectional structure portion. FIG. It is a figure which shows the structure of the photon detection module which concerns on Example 2 of this invention. It is a figure which shows the structure of 1 unit in the modification of the photon detection part of the photon detection module which concerns on Example 2 shown in FIG. It is a figure which shows the further another modification of the photon detection part in Example 2 shown in FIG. It is a figure which shows the structure of the photon detection module which concerns on Example 3 of this invention. It is a figure which shows the modification of the photon detection part in the photon detection module which concerns on Example 3 shown in FIG. It is a figure which shows the structural example of the signal processing circuit in the photoelectric conversion apparatus applicable to the conventional multi-division photometry photometric sensor. It is a figure which shows the structure of the pixel part which has the light-shielding part of the conventional solid-state imaging device.

Explanation of symbols

1, 1a Light-receiving photodiode 2, 2a, 2b, 2c, 2d, 2'2-1, 2-2, 2-3, 2-4 Light-shielding photodiode 3 units
11 N-type substrate
12 N-well
13 First P ⁺ type diffusion layer
14 Second P ⁺ type diffusion layer
15 Third P ⁺ type diffusion layer
16 Fourth P ⁺ type diffusion layer
17 N ⁺ type diffusion layer
18 LOCOS oxide film
19 First interlayer film
20, 21, 22, 23 Anode terminal
24 Common cathode terminal
25 Second interlayer film
26 Shading metal
31 Current amplifier circuit
32 Subtraction circuit
33 Integration circuit
34 Hold circuit
35 multiplexer
36 Output terminal
37 Current mirror circuit

Claims (4)

  A plurality of units each including a first photodiode that receives incident light and a second photodiode that is formed adjacent to the first photodiode and shields incident light are arranged on the same substrate. A light detection module comprising: a light detection unit; and a subtraction circuit that subtracts the output of the second photodiode from the output of the first photodiode in the same unit.   The photodetection module according to claim 1, wherein the second photodiode is formed so as to surround at least a part of an outer edge of the first photodiode.   The photodetection module according to claim 2, wherein the second photodiode is formed by surrounding an outer edge of the first photodiode and closing an end portion thereof.   2. The photodetection module according to claim 1, wherein among the plurality of units, adjacent first units and second units share the second photodiode.

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