JP6543565B2 - PHOTOELECTRIC CONVERSION ELEMENT AND PHOTOELECTRIC CONVERSION MODULE - Google Patents

Description

  The present invention relates to a photoelectric conversion element and a photoelectric conversion module.

  Patent Document 1 discloses a radiation image reading apparatus. The radiation image reading apparatus includes a photoelectric conversion element for reading image information obtained by scanning excitation light on a stimulable phosphor layer in which a radiation image is recorded. The photoelectric conversion element has a photodiode and a silicon photomultiplier. Then, the photoelectric conversion element for reading the image information is switched between the photodiode and the silicon photomultiplier according to the light amount of the photostimulable light read by the photoelectric conversion element.

JP, 2008-287165, A

  In recent years, as a photoelectric conversion element for detecting weak light, one in which pixels formed of an avalanche photodiode (hereinafter, APD) are two-dimensionally arranged is known. In such a photoelectric conversion element, a weak bias light quantity to the photodiode array is obtained by supplying a common bias voltage to each pixel and collecting the output current from each pixel collectively and performing photon counting. It can measure accurately. As such a photoelectric conversion device, there is, for example, MPPC (registered trademark) manufactured by Hamamatsu Photonics.

  However, as the application range of such photoelectric conversion elements is expanded, it is desired to be able to cope with a wide light amount range from a weak light amount to a relatively large light amount. This invention is made in view of such a subject, and it aims at providing the photoelectric conversion element and photoelectric conversion module which can respond to a wide light volume range.

  In order to solve the problems described above, the photoelectric conversion device according to the present invention is formed on a common semiconductor substrate, a plurality of pixels each including an avalanche photodiode operated by a common bias voltage, and formed on the semiconductor substrate A plurality of first wirings electrically connected to two or more first pixels included in the plurality of pixels and collectively extracting output currents from the two or more first pixels, and a plurality of wirings formed on the semiconductor substrate A second wiring electrically connected to the two or more second pixels included in the pixel and collectively taking out the output current from the two or more second pixels, the first wiring and the constant potential line, Between the second wiring and the constant potential line, and connected between the second wiring and the constant potential line, and connected between the second resistor and the constant potential line. Second pixe And a second resistor for converting the second voltage signal output current from the resistance value of the second resistor is smaller than the resistance value of the first resistor.

  The photoelectric conversion module according to the present invention is a photoelectric conversion module including a photoelectric conversion element and a readout circuit for reading out the output current from the photoelectric conversion element, wherein the photoelectric conversion element is formed on a common semiconductor substrate and is common And a plurality of pixels each including an avalanche photodiode operated by the bias voltage of the semiconductor device, and two or more first pixels electrically connected to two or more first pixels formed on the semiconductor substrate and included in the plurality of pixels. Two or more second pixels which are electrically connected to a first wiring for collectively extracting output current from the pixels, and to two or more second pixels formed on the semiconductor substrate and included in the plurality of pixels. And the second circuit for taking out the output current from the circuit at one time, and the read out circuit or the photoelectric conversion element is connected between the first wiring and the constant potential line, An output from two or more second pixels, which is connected between a first resistor converting an output current from the first pixel above to a first voltage signal, a second wire and a constant potential line And a second resistor that converts current into a second voltage signal, wherein the resistance of the first resistor is greater than the resistance of the second resistor.

  In these photoelectric conversion elements and photoelectric conversion modules, the resistance value of the first resistor that converts the output current from the first pixel into a voltage signal converts the output current from the second pixel into a voltage signal. Greater than the resistance value of the resistance of. Thereby, even when the amount of incident light is weak, the output currents from the two or more first pixels can be converted into voltage signals with a relatively large amplification factor. In other words, since the voltage signal can be output with high gain with respect to the incident light quantity, photon counting can be performed with high accuracy. On the other hand, even when the amount of incident light is relatively large, the output currents from the two or more second pixels can be converted into voltage signals with a relatively small amplification factor. In other words, since the voltage signal can be output with a low gain with respect to the amount of incident light, the upper limit of the amount of incident light at which the output is saturated can be further increased. Therefore, according to the above-described photoelectric conversion element and photoelectric conversion module, by selecting the first voltage signal or the second voltage signal according to the amount of incident light, a wide range of light amounts can be supported from weak light amounts to relatively large light amounts. can do.

  The photoelectric conversion module described above has the same configuration as that of the conventional photoelectric conversion element except that two types of wiring (first and second wiring) are provided for extracting the output current from the pixel at one time. It can be adopted. Therefore, the design of the photoelectric conversion element is extremely easy, and the change in the characteristics from the conventional photoelectric conversion element can be suppressed to a small level.

  In the photoelectric conversion module described above, the readout circuit corresponds to a photon counting circuit that counts current pulses output from two or more first pixels based on the first voltage signal, and a second voltage signal. And an A / D converter for generating a digital signal. Thereby, signals corresponding to a wide light amount range can be suitably read out from a weak light amount to a relatively large light amount.

  According to the present invention, it is possible to provide a photoelectric conversion element and a photoelectric conversion module that can correspond to a wide light amount range.

It is a top view of the photoelectric conversion element concerning one embodiment of the present invention. It is a top view which expands and shows a part of light-receiving surface. It is a figure which shows roughly the cross-sectional structure of a photoelectric conversion element. It is a figure showing roughly the example of composition of an external circuit. It is a top view of the photoelectric conversion element concerning the 1st modification. It is a top view which expands and shows a part of light-receiving surface. It is a figure which shows roughly the cross-sectional structure of a photoelectric conversion element. It is a figure showing roughly the example of composition of the external circuit concerning the 2nd modification.

  Hereinafter, embodiments of the photoelectric conversion element and the photoelectric conversion module according to the present invention will be described in detail with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

  FIG. 1 is a plan view of a photoelectric conversion element 1A according to an embodiment of the present invention. The photoelectric conversion element 1A includes a semiconductor substrate 30, and the main surface of the semiconductor substrate 30 is a light receiving unit 3A that receives light. In the light receiving unit 3A, the plurality of pixels 10 are two-dimensionally arranged. Each of the plurality of pixels 10 is configured to include an APD that operates with a common bias voltage.

  The plurality of pixels 10 includes two or more first pixels 11 and two or more second pixels 12. The light receiving area (effective sensing area) of the first pixel 11 and the light receiving area of the second pixel 12 are substantially equal to each other. In one example, the pitch (center spacing) between adjacent first pixels 11 is 50 μm, and the pitch between adjacent second pixels 12 is also 50 μm. In the present embodiment, a first pixel row 11A in which the first pixels 11 are aligned in the column direction, and a second pixel row 12A in which the second pixels 12 are aligned in the column direction Are alternately arranged in the row direction.

  The photoelectric conversion element 1A further includes a first wiring 21 and a second wiring 22 for signal readout. The first wires 21 are electrically connected to the two or more first pixels 11, and the output current from these first pixels 11 is taken out collectively. The second wiring 22 is electrically connected to the two or more second pixels 12, and the output current from these second pixels 12 is taken out collectively.

  FIG. 2 is a plan view showing a part of the light receiving section 3A in an enlarged manner. As shown in FIG. 2, the APD of the first pixel 11 and the first wiring 21 are electrically connected via the quenching resistor 23. In other words, one end of the quenching resistor 23 is electrically connected to the APD of the first pixel 11, and the other end is electrically connected to the first wiring 21. Similarly, the APD of the second pixel 12 and the second wiring 22 are electrically connected via the quenching resistor 24. In other words, one end of the quenching resistor 24 is electrically connected to the APD of the second pixel 12, and the other end is electrically connected to the second wiring 22. The resistance values of the quenching resistors 23 and 24 are substantially equal to each other. In one example, the resistance value of the quenching resistors 23 and 24 is 250 kΩ. In the example shown in the drawings, the quenching resistors 23 and 24 are disposed in a spiral shape, but the quenching resistors 23 and 24 can be disposed in various shapes, for example, linearly disposed. It may be set. The quenching resistors 23 and 24 are made of, for example, a light transmitting (semitransparent) conductive material.

  FIG. 3 is a view schematically showing a cross-sectional configuration of the photoelectric conversion element 1A. The photoelectric conversion element 1A includes a semiconductor substrate 30 made of, for example, n-type Si. The plurality of pixels 10 described above are formed on the common semiconductor substrate 30. Specifically, the semiconductor substrate 30 has a main surface 30a and a back surface 30b, and a lower surface electrode (cathode) 31 is provided on the entire surface of the back surface 30b. In the semiconductor substrate 30 including the main surface 30a, the p-type semiconductor region 32a constituting the first pixel 11 and the p-type semiconductor region 32b constituting the second pixel 12 are spaced apart from each other. It is formed side by side. The p-type semiconductor regions 32a and 32b are made of, for example, p-type Si. The APD of the first pixel 11 is configured by the p-type semiconductor region 32 a and the semiconductor substrate 30 forming a pn junction. Similarly, the APD of the second pixel 12 is configured by forming a pn junction between the p-type semiconductor region 32 b and the semiconductor substrate 30.

A first insulating film 33 is provided on the entire surface of the main surface 30a. The first insulating film 33 may be preferably made of, for example, an insulating silicon compound such as SiO ₂ or SiN. A contact electrode (anode) 34 a is provided on the p-type semiconductor region 32 a and the first insulating film 33. The contact electrode 34 a is in contact with the p-type semiconductor region 32 a through the opening formed in the first insulating film 33. Similarly, a contact electrode (anode) 34 b is provided on the p-type semiconductor region 32 b and the first insulating film 33. The contact electrode 34 b is in contact with the p-type semiconductor region 32 b through an opening formed in the first insulating film 33.

  The first wiring 21 and the second wiring 22 are made of metal and are formed on the semiconductor substrate 30. In the present embodiment, the first wiring 21 and the second wiring 22 are first insulating films located on the region of the semiconductor substrate 30 in which neither the p-type semiconductor region 32 a nor the p-type semiconductor region 32 b is formed. It is provided on 33.

The first wiring 21, the second wiring 22, the first insulating film 33, and the contact electrodes 34 a and 34 b are covered with a second insulating film 35. The second insulating film 35 covers the entire surface of the semiconductor substrate 30 and may be preferably made of an inorganic insulator such as SiO ₂ or SiN. The quenching resistors 23 and 24 described above are provided on the second insulating film 35. One end and the other end of the quenching resistor 23 are electrically connected to the contact electrode 34 a and the first wiring 21 through an opening formed in the second insulating film 35. One end and the other end of the quenching resistor 24 are electrically connected to the contact electrode 34 b and the second wire 22 through an opening formed in the second insulating film 35.

  Here, a configuration of a photoelectric conversion module including the photoelectric conversion element 1A and a reading circuit that reads the output current from the photoelectric conversion element 1A will be described. FIG. 4 is a view schematically showing a configuration example of the photoelectric conversion module 2A. As shown in FIG. 4, a common bias voltage HV is applied to the cathode or lower surface electrode 31 (see FIG. 3) of each APD of the plurality of pixels 10.

  The readout circuit 5A includes a first resistor 41, a second resistor 42, a photon counting circuit 60, an amplification circuit 70, a peak hold circuit 71, an A / D converter 72, and a signal processing unit 80. The resistance value of the second resistor 42 is smaller than the resistance value of the first resistor 41. In one example, the resistance of the first resistor 41 is 1 MΩ to several MΩ, and the resistance of the second resistor 42 is 50 Ω (ie, a normal 50 Ω termination).

  The first resistor 41 is connected between the first wiring 21 and the reference potential (GND) line 51, which is a constant potential line, and converts the output current from the first pixel 11 into the first voltage signal V1. Convert. Specifically, one end of the resistor 41 is connected to the anode of the APD of the first pixel 11 via the first wire 21 and the quenching resistor 23. The other end of the resistor 41 is connected to a reference potential (GND) line 51. One end of the resistor 41 is connected to the photon counting circuit 60, and the voltage drop across the resistor 41 is input to the photon counting circuit 60 as a first voltage signal V1.

  The photon counting circuit 60 includes a comparator 61 and a counter 62. The comparator 61 compares the reference voltage generated by the D / A converter 63 with the first voltage signal V1. Then, when the first voltage signal V1 exceeds the reference voltage (ie, when a current pulse exceeding the threshold is output from the first pixel 11), a signal is sent to the counter 62. The counter 62 counts the number of times the signal is sent from the comparator 61. The count value corresponds to the amount of light incident on all the first pixels 11.

  The second resistor 42 is connected between the second wiring 22 and the reference potential (GND) line 51 which is a constant potential line, and the output current from the second pixel 12 is converted to the second voltage signal V2. Convert. Specifically, one end of the resistor 42 is connected to the anode of the APD of the second pixel 12 via the second wire 22 and the quenching resistor 24. The other end of the resistor 42 is connected to a reference potential (GND) line 51. One end of the resistor 42 is connected to the A / D converter 72 via the amplifier circuit 70 and the peak hold circuit 71. The second voltage signal V2 is amplified by the amplifier circuit 70 and then held by the peak hold circuit 71. Then, the held voltage is input to the A / D converter 72. The A / D converter 72 converts the input voltage signal (analog signal) into a digital signal. The digital value corresponds to the amount of light incident on all the second pixels 12.

  The count value output from the counter 62 and the digital value output from the A / D converter 72 are sent to the signal processing unit 80. The signal processing unit 80 adopts one of the count value and the digital value having a significant value, and specifies the amount of incident light based on the value.

  The effects obtained by the photoelectric conversion module 2A of the present embodiment described above will be described. In the photoelectric conversion module 2A, the resistance value of the resistor 41 that converts the output current from the first pixel 11 into the first voltage signal V1 converts the output current from the second pixel 12 into the second voltage signal V2. Larger than the resistance value of the resistor 42. Thereby, even when the amount of incident light is weak, the output currents from the two or more first pixels 11 can be converted into the first voltage signal V1 with a relatively large amplification factor. In other words, since the first voltage signal V1 can be generated with a high gain with respect to the amount of incident light, photon counting can be performed with high accuracy. On the other hand, even when the amount of incident light is relatively large, the output currents from the two or more second pixels 12 can be converted into the second voltage signal V2 with a relatively small amplification factor. In other words, since the second voltage signal V2 can be generated with a low gain with respect to the amount of incident light, the upper limit of the amount of incident light at which the output is saturated can be further increased. Therefore, according to the photoelectric conversion module 2A of the present embodiment, comparison is made from weak light amount by selecting the count value based on the first voltage signal V1 or the digital value based on the second voltage signal V2 according to the incident light amount It is possible to cope with a wide light amount range up to a very large light amount.

  Moreover, in the present embodiment, the same as the conventional photoelectric conversion element except that two types of wiring (first and second wirings 21 and 22) are provided for simultaneously extracting the output current from the plurality of pixels. The configuration can be adopted. Therefore, the design of the photoelectric conversion element 1A is extremely easy, and the change in the characteristics from the conventional photoelectric conversion element can be suppressed to a small level.

  Further, according to the present embodiment, it is possible to cope with both the case where the amount of incident light is weak and the case where the amount of light is relatively large, with one device in which the light detection principle of each pixel is common. As a result, it is possible to expect a common operating voltage, cost reduction by configuring on the same substrate, and uniform characteristics. Moreover, according to the present embodiment, it is possible to arrange a large number of pixels 10 in a two-dimensional manner, and a large light receiving surface can be easily realized. Further, the degree of freedom in the arrangement of the plurality of pixels 10 is high, and it is easy to change the light receiving unit 3A into a shape suitable for the application or optical system, such as a square, a rectangle, a circle, and a polygon. Furthermore, compared to the configuration of Patent Document 1, even when the amount of incident light is relatively large, shot noise becomes extremely small, and high gain and high S / N ratio can be compatible in a wide light amount range.

  Further, as in the present embodiment, the readout circuit 5A counts the current pulses output from the two or more first pixels 11 based on the first voltage signal V1, and the second counting circuit 60A. And an A / D converter 72 for generating a digital signal corresponding to the voltage signal V2. Thereby, signals corresponding to a wide light amount range can be suitably read out from a weak light amount to a relatively large light amount.

(First modification)
FIG. 5 is a plan view of a photoelectric conversion element 1B according to a first modification of the present invention. The difference between the photoelectric conversion element 1B and the above embodiment is the arrangement of the first pixel 11 and the second pixel 12 on the light receiving surface. In the light receiving unit 3B of this modification, a plurality of first regions A1 each including the first pixels 11 of K ₁ pieces (K ₁ is an integer of 2 or more, and the case of K ₁ = 16 is illustrated in the figure) A plurality of second areas A2 each including the second pixels 12 of K ₂ (K ₂ is an integer of 2 or more, and the case of K ₂ = 16 is illustrated in the figure) are mixed in the light receiving unit 3B. It is arranged in a two-dimensional form (matrix form). In the example shown in FIG. 5, the first area A1 and the second area A2 are arranged in a checkered pattern.

FIGS. 6A and 6B are plan views showing the first area A1 and the second area A2 in an enlarged manner, respectively. FIG. 7 is a view schematically showing the cross-sectional configuration of the photoelectric conversion element 1B. In one example, in the first area A1, the first pixels 11 are arranged in a two-dimensional form of M ₁ rows N ₁ columns (M ₁ and N ₁ are integers of 1 or more, provided that M ₁ × N ₁ = K ₁ ) ing. Then, the first wirings 21 are disposed every two rows, and the first pixels 11 located on both sides of each of the first wirings 21 are connected to the first wirings 21 via the quenching resistance 23. It is electrically connected. Similarly, in the second area A2, the second pixels 12 are arranged in a two-dimensional form of M ₂ rows and N ₂ columns (M ₂ and N ₂ are integers of 1 or more, provided that M ₂ × N ₂ = K ₂ ) ing. Then, the second wirings 22 are disposed every two rows, and the second pixels 12 located on both sides of each second wiring 22 are connected to the second wirings 22 via the quenching resistance 24. It is electrically connected.

  The arrangement of the first and second pixels in the present invention is not limited to the above embodiment, and various forms are possible, such as the photoelectric conversion element 1B of the present modification. And the same effect as photoelectric conversion element 1A and photoelectric conversion module 2A of an embodiment mentioned above can be suitably produced regardless of what kind of pixel arrangement.

(2nd modification)
FIG. 8 is a plan view of a photoelectric conversion module 2B according to a second modification of the present invention. The difference between the photoelectric conversion module 2B and the above embodiment is the arrangement of the resistors 41 and 42. That is, although the resistors 41 and 42 are included in the readout circuit 5A in the above embodiment, in the photoelectric conversion module 2B, the readout circuit 5B does not have the resistors 41 and 42, and the photoelectric conversion element 1C is a resistor 41, Having 42. The configurations of the photoelectric conversion element 1C and the readout circuit 5B excluding the arrangement of the resistors 41 and 42 are the same as those of the photoelectric conversion element 1A and the readout circuit 5A of the above embodiment.

  As in the present modification, the photoelectric conversion element 1C may have the resistors 41 and 42. Even in such a case, the same effects as those of the photoelectric conversion module 2A of the above-described embodiment can be suitably achieved.

  The photoelectric conversion element and the photoelectric conversion module according to the present invention are not limited to the embodiments described above, and various other modifications are possible. For example, the embodiments and the modifications described above may be combined with each other as needed. Moreover, although several M ohms and 50 ohms were illustrated as resistance value of resistance 41 and 42 in the said embodiment, resistance value is not limited to these, A various resistance value is employable. In the above embodiment, Si is exemplified as a constituent material of the semiconductor substrate 30 and the p-type semiconductor regions 32a and 32b. However, in the present invention, various semiconductor materials can be adopted for the semiconductor substrate and each p-type semiconductor region.

  1A to 1C: photoelectric conversion element, 3A, 3B: light receiving unit, 10: pixel, 11: first pixel, 11A: first pixel row, 12: second pixel, 12A: second pixel row, 21 ... first wiring, 22 ... second wiring, 23, 24 ... quenching resistance, 30 ... semiconductor substrate, 31 ... lower surface electrode, 32a, 32b ... p-type semiconductor region, 33 ... first insulating film, 34a, 34b: contact electrode 35: second insulating film 41: first resistor 42: second resistor 60: photon counting circuit 61: comparator 62: counter 63: D / A converter 70: 70 Amplifier circuit 71: peak hold circuit 72: A / D converter 80: signal processing unit A1: first area A2: second area.

Claims (3)

A plurality of pixels formed on a common semiconductor substrate, each including an avalanche photodiode operating with a common bias voltage;
A first wiring formed on the semiconductor substrate and electrically connected to two or more first pixels included in the plurality of pixels, and collectively extracting output currents from the two or more first pixels When,
A second wiring formed on the semiconductor substrate and electrically connected to two or more second pixels included in the plurality of pixels, and collectively taking out an output current from the two or more second pixels When,
A first resistor connected between the first wiring and the constant potential line and converting output current from the two or more first pixels into a first voltage signal;
A second resistor connected between the second wiring and the constant potential line and converting an output current from the two or more second pixels into a second voltage signal;
The photoelectric conversion element whose resistance value of said 2nd resistance is smaller than the resistance value of said 1st resistance. A photoelectric conversion module comprising: a photoelectric conversion element; and a readout circuit for reading out an output current from the photoelectric conversion element,
The photoelectric conversion element is
A plurality of pixels formed on a common semiconductor substrate, each including an avalanche photodiode operating with a common bias voltage;
A first wiring formed on the semiconductor substrate and electrically connected to two or more first pixels included in the plurality of pixels, and collectively extracting output currents from the two or more first pixels When,
A second wiring formed on the semiconductor substrate and electrically connected to two or more second pixels included in the plurality of pixels, and collectively taking out an output current from the two or more second pixels And
The readout circuit or the photoelectric conversion element is
A first resistor connected between the first wiring and the constant potential line and converting output current from the two or more first pixels into a first voltage signal;
A second resistor connected between the second wiring and the constant potential line and converting output current from the two or more second pixels into a second voltage signal;
The photoelectric conversion module whose resistance value of said 2nd resistance is smaller than the resistance value of said 1st resistance. The read circuit
A photon counting circuit that counts current pulses output from the two or more first pixels based on the first voltage signal;
The photoelectric conversion module according to claim 2, further comprising: an A / D converter that generates a digital signal corresponding to the second voltage signal.

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