JP2006318947A - Light-receiving device and electronic equipment using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-receiving device capable of achieving desired spectral sensitivity characteristics by combining a plurality of photodiodes. <P>SOLUTION: In the light-receiving device 100, the plurality of photodiodes 10 are arranged flat on the same semiconductor substrate 30 and are designed so that the spectral sensitivity characteristics differ. The photodiodes 10 are formed by using a diffusion layer, having a profile whose concentration and depth are each different. The photodiodes 10 are arranged flat at different positions, and anode and cathode electrodes 50, 52 are provided independently. A photoelectric current Ip flowing in each photodiode 10 is synthesized by a synthesis circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light receiving device that detects light incident on a photodiode and outputs it as an electrical signal.

  In various electronic devices such as small information terminals and cameras such as mobile phones and PDAs (Personal Digital Assistance), a light receiving device that measures the illuminance around the electronic device is used. For example, in a notebook personal computer, a mobile phone, and the like, it is conceivable that the ambient illuminance is measured by a light receiving device and the brightness of a liquid crystal backlight is adjusted according to the illuminance.

  In such a light receiving device, a photocurrent flowing according to the amount of light received by a light receiving element such as a photodiode or a phototransistor is detected and detected as a digital or analog signal. Here, when the light receiving device is used as an illuminance sensor, the spectral sensitivity characteristic of the photodiode becomes a problem. In general, the spectral sensitivity characteristics of a photodiode formed on a semiconductor substrate depend on the device structure such as the concentration profile and the depth of the PN junction, and the spectral sensitivity characteristics required for the light receiving device are always included. is not. That is, since the photodiode has a wide sensitivity characteristic from the visible region to the near infrared, there is a problem that the light intensity detected by the photodiode does not necessarily correspond to the brightness perceived by the human eye.

  Patent Document 1 discloses a technique for realizing a desired spectral sensitivity characteristic by forming an optical filter on the upper surface of a photodiode. In Patent Document 2, in order to obtain a desired spectral sensitivity characteristic, photodiodes having different spectral sensitivity characteristics are formed at different depths in an overlapping manner, and currents flowing through the photodiodes are synthesized. Thus, a technique for realizing a desired spectral sensitivity characteristic is disclosed.

JP-A-6-77507 JP 2004-119713 A

  In the technique described in Patent Document 1, since it is necessary to form a multilayer film or the like, there is a problem that the manufacturing cost becomes higher than that of a normal semiconductor manufacturing process. Further, according to the technique described in Patent Document 2, the cathode terminals of the two photodiodes are necessarily connected structurally, and there is a problem that there are many restrictions on the photocurrent combining process.

  The present invention has been made in view of such problems, and an object thereof is to provide a light receiving device capable of realizing a desired spectral sensitivity characteristic by combining a plurality of photodiodes.

  One embodiment of the present invention relates to a light receiving device. This light receiving device includes a plurality of photodiodes arranged in a plane on the same semiconductor substrate and having different spectral sensitivity characteristics, and a combining circuit that combines currents flowing through the plurality of photodiodes.

  According to this aspect, by arranging the photodiodes having different spectral sensitivity characteristics on the plane, the anode and the cathode of each photodiode can be provided independently, so that the synthesis process can be performed with a high degree of freedom by the synthesis circuit. it can. In addition, since the area of each photodiode can be adjusted independently, the spectral sensitivity characteristics can be finely adjusted.

  The light receiving device may include a wiring layer on the upper surface of the plurality of photodiodes, and the pattern of the wiring layer may be formed so that the light receiving area of each photodiode can be adjusted. In this case, characteristics closer to the desired spectral sensitivity characteristics are obtained by changing the mask of the wiring layer or shifting the mask position during exposure according to the performance of the photodiode during the semiconductor manufacturing process. be able to.

  The plurality of photodiodes may have PN junctions formed at different depths. The plurality of photodiodes may have PN junctions having different concentration profiles. Spectral sensitivity characteristics can be controlled by adjusting the concentration and depth of the diffusion layers of the P layer and the N layer.

  The plurality of photodiodes includes two photodiodes in which anodes and cathodes are connected to each other, and the anode is connected to a predetermined power source, and a current obtained by synthesizing currents flowing from the cathode to the two photodiodes is taken out. Good. Further, the cathodes connected to each other may be grounded, and the sum of the currents flowing from the anode to the two photodiodes may be taken out. In this case, the spectral sensitivity characteristics of the two photodiodes can be added with the light receiving area of each photodiode as a parameter.

  The plurality of photodiodes may include two photodiodes connected in series between a predetermined power source and the ground, and a difference current between currents flowing through the two photodiodes may be extracted from a connection point between the two photodiodes. In this case, the spectral sensitivity characteristics of the two photodiodes can be subtracted using the light receiving area of each photodiode as a parameter.

  The combining circuit may include a current mirror circuit that replicates the current flowing through one photodiode, and may combine the output current of the current mirror circuit with the current flowing through another photodiode. In this case, the spectral sensitivity characteristic can be adjusted using the mirror ratio of the current mirror circuit as a parameter in addition to the light receiving area of the photodiode.

  The synthesis circuit may be integrated on the semiconductor substrate. A reduction in size can be achieved by integrating the photodiode and the synthesis circuit.

  Another embodiment of the present invention is an electronic device. This electronic apparatus includes the above-described light receiving device and a liquid crystal panel. The light receiving device controls the luminance of the backlight of the liquid crystal panel according to the amount of received light.

  According to this aspect, the visibility of the liquid crystal panel can be increased or the power consumption can be reduced by controlling the luminance of the backlight of the liquid crystal panel according to the ambient illuminance in which the electronic device is used.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the light receiving device of the present invention, desired spectral sensitivity characteristics can be realized by combining a plurality of photodiodes.

  FIG. 1 is a cross-sectional view of a semiconductor substrate on which a light receiving device 100 according to the present embodiment is formed. FIG. 2 is a block diagram illustrating a configuration of an electronic device 200 in which the light receiving device 100 is mounted. 2 is, for example, a mobile phone terminal, a digital still camera, a digital video camera, or the like. The electronic apparatus 200 includes a liquid crystal panel 90, an LED 92, a constant current circuit 94, a power source 96, a control circuit 98, and a light receiving device 100. The liquid crystal panel 90 is driven by a liquid crystal driver (not shown) and displays image information. The LED 92 is installed on the back surface of the liquid crystal panel 90 and operates as a backlight. The power supply 96 supplies the battery voltage or a voltage obtained by stepping up and down the battery voltage to each block of the electronic device 200. One of the output voltages of the power supply 96 is supplied to the anode of the LED 92. The constant current circuit 94 is provided between the cathode of the LED 92 and the ground, and controls the current flowing through the LED 92 to adjust the light emission luminance. The constant current generated by the constant current circuit 94 is controlled by the control circuit 98.

  The light receiving device 100 detects the illuminance around the electronic device 200 and outputs it to the control circuit 98. The light receiving device 100 includes a plurality of first to third photodiodes 10 a to 10 c collectively called a photodiode 10, a synthesis circuit 20, and an IV conversion circuit 22. The first photodiode 10a to the third photodiode 10c are arranged so that light incident from the outside of the electronic device 200 can be received, and photocurrents Ip1 to Ip3 corresponding to the amount of received light respectively flow. The combining circuit 20 performs a combining process of adding and subtracting the photocurrents Ip1 to Ip3 flowing through the first photodiode 10a to the third photodiode 10c, and generates a detection current Iout. This detection current Iout is output to the IV conversion circuit 22.

  The IV conversion circuit 22 converts the detection current Iout to current and outputs the detection voltage Vout. The control circuit 98 converts the detection voltage Vout from analog to digital, and instructs the constant current circuit 94 for a constant current value necessary for adjusting the light emission luminance of the LED 92 in accordance with the magnitude of the detection voltage Vout.

  In the electronic device 200 according to the present embodiment, the control circuit 98 performs the following control as the light emission luminance control of the LED 92 based on the detection current Iout (detection voltage Vout). That is, in the electronic device 200, when the surroundings are bright, that is, when the detection current Iout is large, the light emission luminance of the LED 92 is set high so that the image displayed on the liquid crystal panel 90 becomes clearer. Conversely, when the surroundings are dark, that is, when the detection current Iout is small, control is performed to set the light emission luminance low and reduce the power consumption.

  Here, the relationship between the photocurrent flowing through the photodiode 10 and the brightness perceived by human vision will be described. The human eye is sensitive to light in the visible region and has little sensitivity to ultraviolet or infrared light. On the other hand, the spectral sensitivity characteristic of the photodiode 10 depends on the semiconductor manufacturing process and device structure, but has a broad spectrum from the near ultraviolet to the near infrared. Since sunlight and fluorescent light incident on the photodiode 10 includes light of wavelengths other than visible light, if all wavelengths of the incident light are detected, the brightness and difference felt by human vision are different. Will occur. Therefore, it is necessary to approximate the spectral sensitivity characteristic of the photodiode 10 to a so-called visual sensitivity characteristic.

  Hereinafter, a configuration of the light receiving device 100 for bringing the spectral sensitivity characteristic of the photodiode 10 close to the visibility characteristic will be described. Returning to FIG. As shown in FIG. 1, the first photodiode 10 a to the third photodiode 10 c are formed on the same semiconductor substrate 30. The first photodiode 10 a to the third photodiode 10 c are formed so as to have different spectral sensitivity characteristics, and are arranged in a plane on the semiconductor substrate 30.

FIG. 3 is a diagram showing the spectral sensitivity characteristics of the photodiode 10. In FIG. 3, the horizontal axis indicates the wavelength, and the vertical axis indicates the relative light receiving sensitivity. Three curves indicated by solid lines represent the spectral sensitivity characteristics of the first to third photodiodes 10a to 10c in FIG. 1, respectively. Moreover, what is indicated by a broken line in FIG.
Returning to FIG. The spectral sensitivity characteristics of the photodiode 10 are determined using the material of the semiconductor substrate 30, the impurity concentration and thickness of each diffusion layer, the depth of the PN junction surface, and the like as parameters. In the light receiving device 100 according to the present embodiment, the semiconductor substrate 30 is a P-type silicon substrate. The first photodiode 10 a forms a PN junction by diffusing an N layer 32 in the semiconductor substrate 30 and diffusing a P layer 34 on the upper surface thereof. The concentration and diffusion depth of each diffusion layer are designed so as to have spectral sensitivity characteristics indicated by 10a in FIG. An anode electrode 50a and a cathode electrode 52a are drawn from the P layer 34 and the N layer 32, respectively. An insulating film 54 is formed on the upper surface of the semiconductor substrate 30.

  In the second photodiode 10b, a P layer 36 is formed with a slightly higher impurity concentration than the semiconductor substrate 30, and an N layer 38 is formed thereon. The PN junction surface of the second photodiode 10 b is formed at a shallow position with respect to the other photodiodes 10. In general, the spectral sensitivity characteristic of the photodiode 10 has a spectrum on the ultraviolet light side as it is formed at a position where the depth from the surface of the semiconductor substrate is shallow, and has a spectrum on the infrared side as it is formed at a position deeper from the surface. become. Therefore, the spectral sensitivity characteristic of the second photodiode 10b has a peak on the short wavelength side. An anode electrode 50b and a cathode electrode 52b are drawn from the P layer 36 and the N layer 38, respectively.

  The third photodiode 10 c forms an N layer 40 deep in the semiconductor substrate 30 and forms a PN junction with the P-type semiconductor substrate 30. A cathode electrode 52c and an anode electrode 50c are drawn out from the N layer 40 and the P layer of the semiconductor substrate 30, respectively. The third photodiode 10c has a peak on the long wavelength side as shown in FIG. 3 because the N layer 40 is formed in a region deeper than the first photodiode 10a and the second photodiode 10b.

  In FIG. 3, in order to obtain the visibility characteristic indicated by REF using the three spectral sensitivity characteristics indicated by 10a to 10c, the following arithmetic processing may be performed. When each spectral sensitivity characteristic is written as fa (λ), fb (λ), fc (λ), and fref (λ) as a function of wavelength, fref (λ) = C1 × fa (λ) + C2 × fb ( λ) + C3 × fc (λ) can be approximated. Here, C1 to C3 are variables that take positive or negative values (hereinafter, these variables are also referred to as synthesis coefficients). In the present embodiment, C1 is positive, C2 and C3 are negative, and the spectral components in the infrared and ultraviolet regions are removed from fa (λ) having the widest spectrum, so that characteristics close to the visibility characteristic are obtained. Obtainable.

  The synthesis circuit 20 in FIG. 2 performs a synthesis process corresponding to fref (λ) = C1 × fa (λ) + C2 × fb (λ) + C3 × fc (λ). The combining process can be realized by adding and subtracting the photocurrent Ip flowing through each photodiode 10, and when the combining coefficient is positive, the current is added, and when the combining coefficient is negative, the current is subtracted. 4A to 4D show circuit configuration examples of the synthesis circuit 20. FIG. 4A shows a configuration of the synthesis circuit 20 that adds the photocurrents of the photodiodes PD1 and PD2. In the photodiodes PD1 and PD2, the anodes and the cathodes are connected to each other, the anode is connected to a predetermined power supply Vcc, and the cathode is connected to the output terminal 60. From the output terminal 60, the sum current Iout = Ip1 + Ip2 of the currents flowing through the two photodiodes PD1 and PD2 can be extracted. Here, the current value of the photocurrent Ip flowing through the photodiodes PD1 and PD2 is proportional to the light receiving areas S1 and S2. Therefore, by adjusting the light receiving area, the spectral sensitivity characteristics of the photodiodes PD1 and PD2 can be multiplied by the synthesis coefficients C1 and C2 proportional to the light receiving area. In contrast to FIG. 4A, the anodes of the photodiodes PD1 and PD2 may be grounded, and the sum current Iout = Ip1 + Ip2 may be extracted from the cathode.

  FIG. 4B shows a configuration of the synthesis circuit 20 that subtracts the photocurrents of the photodiodes PD1 and PD2. The photodiodes PD1 and PD2 are connected in series between a predetermined power supply Vcc and the ground. A connection point between the two photodiodes is connected to the output terminal 60. From the output terminal 60, the difference current Iout = Ip1-Ip2 between the photocurrents Ip1 and Ip2 flowing through the two photodiodes PD1 and PD2 can be extracted. Similar to FIG. 4A, by adjusting the area ratio of the photodiodes PD1 and PD2, the spectral sensitivity characteristic can be multiplied by the synthesis coefficient and subtracted.

  FIG. 4C shows a configuration of the synthesis circuit 20 that adds the photocurrents of the photodiodes PD1 and PD2. This synthesis circuit includes a current mirror circuit including transistors Q1 and Q2. A photodiode PD1 is connected to the transistor Q1, and a photocurrent Ip1 flows. A current Ip1 ′ = MRR × Ip1 obtained by multiplying the photocurrent Ip1 by the mirror ratio MRR flows through the transistor Q2. The collector of the transistor Q2 and the anode of the photodiode PD2 are connected to the output terminal 60. The output terminal 60 outputs a sum current Iout = MRR × Ip1 + Ip2 of the current Ip1 ′ and the photocurrent Ip2. As described above, according to the synthesis circuit 20 in FIG. 4C, addition processing can be performed using the mirror ratio of the current mirror circuit as a parameter in addition to the area ratio of the photodiodes PD1 and PD2.

  FIG. 4D shows a configuration of the synthesis circuit 20 that subtracts the photocurrents of the photodiodes PD1 and PD2. The synthesis circuit 20 includes a current mirror circuit composed of transistors Q3 and Q4. A photodiode PD1 is connected to the transistor Q3, and a photocurrent Ip1 flows. A current Ip1 ′ = MRR × Ip1 obtained by multiplying the photocurrent Ip1 by the mirror ratio MRR flows through the transistor Q4. The collector of the transistor Q4 and the anode of the photodiode PD2 are connected to the output terminal 60. The output terminal 60 outputs a difference current Iout = Ip2−MRR × Ip1 between the current Ip1 ′ and the photocurrent Ip2. As described above, according to the synthesis circuit 20 in FIG. 4D, the subtraction process can be performed using the mirror ratio of the current mirror circuit as a parameter in addition to the area ratio of the photodiodes PD1 and PD2.

  The synthesis circuit 20 performs the photocurrent synthesis process of the first photodiode 10a to the third photodiode 10c of FIG. 1 using the circuit configuration shown in FIGS. 4A to 4D as a basic block. Wirings and transistors constituting the synthesis circuit 20 can be integrally formed on the semiconductor substrate 30 on which the photodiode 10 is formed.

According to the light receiving device 100 according to the present embodiment, it is possible to obtain a spectral sensitivity characteristic close to the visual sensitivity characteristic by combining the photocurrents of a plurality of photodiodes having different spectral sensitivity characteristics arranged on a plane.
Since the light receiving device 100 of the present embodiment can independently form the anode terminal and the cathode terminal of each photodiode as shown in FIG. 1, as illustrated in FIGS. 4 (a) to 4 (d). In addition, various connection forms are possible, and the degree of freedom of the composition process can be set high. When the spectral sensitivity characteristics of the photodiodes 10 are multiplied by a coefficient and synthesized, the coefficient can be finely adjusted by adjusting the area of the photodiode 10. In addition, when combining using a current mirror circuit, there is an advantage that the coefficient ratio can be set large. By combining these synthesis circuits, a spectral sensitivity characteristic closer to the visual sensitivity characteristic can be obtained.

  In the light receiving device 100 according to the present embodiment, each photodiode 10 performs spectral sensitivity characteristics by adding and subtracting current. Therefore, it is possible to reduce the circuit scale as compared with the case where the current-voltage conversion is performed for each photodiode and the voltage is added or subtracted using an operational amplifier or the like, or the digital signal processing is performed after analog-digital conversion. it can.

  Furthermore, the light receiving device 100 can realize more excellent spectral sensitivity characteristics by adding the configuration described below. In general, the spectral sensitivity characteristics of the photodiode may shift the wavelength peak or change the relative sensitivity of each photodiode due to variations in the semiconductor manufacturing process. Therefore, if the spectral sensitivity characteristic of each photodiode 10 is evaluated in the intermediate process of the semiconductor manufacturing process and the synthesis coefficients C1 to C can be adjusted based on the spectral sensitivity characteristic, the spectral sensitivity characteristic with reduced process variation can be achieved. Can be obtained.

  For this purpose, the light receiving device 100 may be provided with a wiring pattern such as aluminum wiring on the upper surface of the photodiode 10 so that the light receiving area of each photodiode 10 can be adjusted. That is, several types of aluminum wiring patterns in which the light receiving portion of the photodiode 10 can be shielded are prepared, and an aluminum wiring pattern mask is selected based on the spectral sensitivity characteristics of the photodiode measured in the middle of the semiconductor manufacturing process. As a result, spectral sensitivity characteristics with reduced process variations can be obtained, and the yield can be improved. In addition, the light receiving area of each photodiode may be adjusted by shifting the mask during exposure of the aluminum wiring.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment, the case where three photodiodes are combined to reproduce the visibility characteristic has been described. However, the present invention is not limited to this, and the spectral sensitivity characteristics of more photodiodes are combined to improve the visibility characteristic. It may be reproduced. In addition, according to the light receiving device 100 according to the present embodiment, spectral sensitivity characteristics other than the visibility characteristics can also be realized.

  Moreover, although the mobile phone terminal etc. were illustrated as the electronic device 200, it is not limited to this, It can use for the various apparatuses which change the operation | movement according to the brightness around the apparatus.

  As described in the embodiment, the elements constituting the light receiving device 100 may be integrated as a whole or may be divided into different integrated circuits. Furthermore, a part thereof may be composed of discrete parts. Which part is integrated may be determined according to cost, occupied area, application, and the like.

It is sectional drawing of the semiconductor substrate in which the light-receiving device based on this Embodiment is formed. It is a block diagram which shows the structure of the electronic device carrying the light-receiving device of FIG. It is a figure which shows the spectral sensitivity characteristic of a photodiode. 4A to 4D are circuit diagrams illustrating configuration examples of the synthesis circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Photodiode, 10a 1st photodiode, 10b 2nd photodiode, 10c 3rd photodiode, PD1 photodiode, PD2 photodiode, 20 Synthesis circuit, 22 IV conversion circuit, 30 Semiconductor substrate, 32 N layer, 34 P layer 36 P layer, 38 N layer, 40 N layer, 50 anode electrode, 52 cathode electrode, 54 insulating film, 100 light receiving device, 200 electronic device, 90 liquid crystal panel, 92 LED, 94 constant current circuit, 96 power supply, 98 control circuit.

Claims (10)

A plurality of photodiodes having different spectral sensitivity characteristics arranged in a plane on the same semiconductor substrate;
A synthesis circuit for synthesizing currents flowing through the plurality of photodiodes;
A light receiving device comprising:   The light receiving device according to claim 1, wherein a wiring layer is provided on an upper surface of the plurality of photodiodes, and a wiring pattern of the wiring layer is formed so that a light receiving area of each photodiode can be adjusted.   The light receiving device according to claim 1, wherein the plurality of photodiodes have PN junctions formed at different depths.   The light receiving device according to claim 1, wherein each of the plurality of photodiodes has a PN junction having a different concentration profile.   The plurality of photodiodes include two photodiodes in which anodes and cathodes are connected to each other. The anodes are connected to a predetermined power source, and a sum current of currents flowing from the cathodes to the two photodiodes is taken out. The light receiving device according to claim 1 or 2.   The plurality of photodiodes include two photodiodes in which anodes and cathodes are connected to each other, the cathode is grounded, and a sum current of currents flowing from the anodes to the two photodiodes is extracted. The light receiving device according to claim 1 or 2.   The plurality of photodiodes include two photodiodes connected in series between a predetermined power source and a ground, and a difference current flowing between the two photodiodes is extracted from a connection point of the two photodiodes. The light receiving device according to claim 1, wherein the light receiving device is a light receiving device.   3. The synthesis circuit includes a current mirror circuit that replicates a current that flows through one photodiode, and synthesizes an output current of the current mirror circuit and a current that flows through another photodiode. The light receiving device described in 1.   The light receiving device according to claim 1, wherein the synthesis circuit is integrated on the semiconductor substrate. The light receiving device according to claim 1 or 2,
LCD panel,
And the light receiving device controls the luminance of the backlight of the liquid crystal panel in accordance with the amount of received light.

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