JP3445407B2 - Solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device for identifying the wavelength of incident light. 2. Description of the Related Art Attention has been focused on solid-state imaging devices that can identify the wavelength of incident light, that is, the color of incident light. As a light receiving element used for this purpose, a two-color separation type color sensor is commercially available. FIG. 2 is a configuration diagram of the two-color separation type color sensor 100. 2A is a cross-sectional configuration diagram of the two-color separation type color sensor 100, and FIG. 2B is an equivalent circuit configuration diagram of the two-color separation type color sensor 100. As shown in FIG. 2A, in the two-color separation type color sensor, the p-type silicon semiconductor layer 130, the n-type silicon semiconductor layer 120, and the p-type silicon semiconductor
It has an np sandwich structure, in which an electrode 111 is formed on the surface of the p-type silicon semiconductor layer 110, an electrode 121 is formed on the surface of the n-type silicon semiconductor layer 120, and an electrode 131 is formed on the surface of the p-type silicon semiconductor layer 130. Have been. Then, as shown in FIG. 2B, it can be considered that the two photodiodes PD1 and PD2 are connected in series to face each other. [0003] The light absorption coefficient of silicon is highly wavelength-dependent, and the depth of reaching the inside of silicon varies depending on the wavelength.
Therefore, when a reverse bias voltage is applied between the electrode 111 and the electrode 121 and a reverse bias voltage is applied between the electrode 121 and the electrode 131, the p-type silicon semiconductor layer 110 and the n-type Light quantity absorbed by the depletion layer near the boundary with the type silicon semiconductor layer 120, and n
-Type silicon semiconductor layer 120 and p-type silicon semiconductor layer 13
The light quantity absorbed by the depletion layer near the boundary with 0 is different. By utilizing this phenomenon, the electrode 111 and the electrode 1
The photoelectric flow generated between the electrodes 121 and 131 (the photoelectric flow generated at the PD1) and the photoelectric flow generated between the electrodes 121 and 131 (the photoelectric flow generated at the PD2) are extracted.
A solid-state imaging device that discriminates the color of incident light from the ratio of the two current amounts has been proposed. FIG. 3 is a circuit configuration diagram of such a solid-state imaging device. [0005] As shown in FIG.
A logarithmic conversion circuit 910 having an operational amplifier A1 and a diode D1 for inputting a current signal I _SC1 generated by the color separation type color sensor 100 and (b) PD1 for logarithmic conversion.
(C) a logarithmic conversion circuit 920 having an operational amplifier A2 and a diode D2 for inputting and logarithmizing the current signal I _SC2 generated by the PD2, and (d) a logarithmic conversion circuit 910.
(E) a difference operation circuit 930 for calculating the difference between the output signal of the logarithmic conversion circuit 920 and the output signal of
And a processing unit 940 that collects the output signal of the received light and identifies the wavelength of the received light. According to this device, the output V ₀ of the difference calculation circuit 930 is as follows: V ₀ = (kT / q) · [log (I _SC2 / I _SC1 )] · (R2 / R1) (1) , K: Boltzmann constant T: absolute temperature q: electron charge In this apparatus, a two-color separation type color sensor 1
The current signal I _SC1 and the current signal I _SC2 generated as a result of the light reception at 00 are signal-processed by the logarithmic conversion circuits 910 and 920 and the difference calculation circuit 930 to generate a signal having a value represented by the equation (1). The processing unit 940 collects this signal,
The value of (I _SC2 / I _SC1 ) is obtained by inverse logarithmic conversion, and (I _SC2 / I _SC1 ) is obtained.
The color of the received light is identified based on the value of _SC2 / _ISC1 ). [0008] Since the conventional solid-state imaging device is configured as described above, it has the following problems. Due to the temperature dependence of the diodes D1 and D2 used in the logarithmic conversion circuits 910 and 920, the output V ₀ of the difference calculation circuit 930 is equal to the temperature T, as shown in equation (1).
And the measurement result varies depending on the temperature at the time of light reception. The logarithmic conversion circuit 910 and the logarithmic conversion circuit 920 have their own offsets. The offset value of the logarithmic conversion circuit 910 is Vα, and the logarithmic conversion circuit 92
When the offset value of 0 and V?, The value of V _{0 is, V 0 = (kT / q} ) · [log (I SC2 / I SC1) + (Vβ-Vα)] · (R2 / R1) ... (2) Becomes Therefore, when the value of V ₀ is subjected to antilogarithmic conversion, the offset variation (Vβ−Vα) is further enlarged, so that accurate measurement cannot be expected. SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has as its object to provide a solid-state imaging device capable of reducing temperature dependency and performing accurate color identification. According to the present invention, there is provided a solid-state imaging device comprising: (a) (1) a first semiconductor layer having a first conductivity type; and (2) a surface of the first semiconductor layer. And (3) a third semiconductor layer having the first conductivity type and formed on a part of the surface of the second semiconductor layer. A semiconductor layer; (4) a first electrode formed on a part of the surface of the first semiconductor layer where the second semiconductor layer is not formed; and (5) a third semiconductor of the second semiconductor layer. A second electrode formed on a part of the surface on which the layer is not formed, and (6) a third electrode formed on a part of the surface of the third semiconductor layer, and the first semiconductor The layer, the second semiconductor layer, and the third semiconductor layer are mainly formed of a semiconductor material whose light absorption has wavelength dependence, and receive light from the surface side of the third semiconductor layer. An optical device, and (b) a first photocurrent generated between the first electrode and the second electrode due to light reception during application of a reverse bias voltage between the first electrode and the second electrode. A signal, and a charge corresponding to the input first photocurrent signal
Is stored in the first capacitive element, and the amount of the stored charge is
A first integration circuit that outputs a corresponding first integration signal ;
(C) inputting a second photocurrent signal generated between the second electrode and the third electrode due to light reception during application of a reverse bias voltage between the second electrode and the third electrode; , Its entered number
Charge corresponding to the second photocurrent signal is stored in the second capacitive element.
And outputs a second integration signal corresponding to the amount of the accumulated electric charge.
And a second integrating circuit for inputting the information. Further, the solid-state imaging device of the present invention is provided with (d) a first integration signal output from a first integration circuit,
A first analog-to-digital converter that converts the input first integrated signal into a first digital signal, and outputs the first digital signal; and (e) a second integrated circuit that outputs the first integrated signal. A second analog-to-digital converter that receives the second integrated signal, converts the input second integrated signal into a second digital signal, and outputs the second digital signal. It is further characterized by being provided. Further, in the solid-state imaging device according to the present invention, the first digital signal output from the first analog-to-digital converter and the second digital signal output from the second analog-to-digital converter are input. And a first digital value indicated by the first digital signal and a second digital value indicated by the second digital signal.
And a calculator for outputting a third digital signal indicating a third digital value corresponding to the ratio of the digital value to the digital value. In the solid-state imaging device according to the present invention, the arithmetic unit inputs the first digital signal and the second digital signal to the address input terminal, and outputs the data output terminal according to the data written in the storage unit. And a read-only memory element for outputting a third digital signal from the memory. In the solid-state imaging device according to the present invention, first, a reverse bias voltage is applied between the first electrode and the second electrode, and between the second electrode and the third electrode. Apply a reverse bias voltage. In this state, when light is received from the third semiconductor layer side by the light receiving section, the first electrode and the first electrode are connected at a ratio corresponding to the wavelength of the received light due to the wavelength dependence of the light absorption of the semiconductor material. An electric current is generated between the second electrode and between the second electrode and the third electrode. The current signal (I1) generated between the first electrode and the second electrode is input to a first integration circuit, integrated, and output as a first integration signal. Since the integration circuit is configured without using a portion having a large temperature dependency, the integration output has a small fluctuation due to temperature. Therefore, the first integrated signal has a small temperature fluctuation. The current signal (I2) generated between the second electrode and the third electrode is input to a second integrating circuit, integrated and output as a second integrated signal. Also in this case, similarly to the case of the first integrator, the second integration signal has a small temperature fluctuation. The thus obtained first integrated signal and the second integrated signal
By determining the ratio between I1 and I2 based on the integrated signal of (1) and (2), the temperature dependency can be reduced and accurate color identification can be performed. The first integrated signal is converted to a first digital signal by a first analog-to-digital converter, and the second integrated signal is converted to a second digital signal by a second analog-to-digital converter. By converting the subsequent processing into a digital signal that is highly resistant to external noise,
Measurement accuracy can be improved. By providing an arithmetic unit for calculating the ratio of I1 to I2 from the first digital signal and the second digital signal in consideration of the offset value of each integrating circuit measured in advance, it is possible to reduce the variation in offset. Deterioration in measurement accuracy can be reduced, and measurement accuracy can be further improved. Embodiments of the present invention will be described below with reference to the accompanying 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 configuration diagram of a solid-state imaging device according to an embodiment of the present invention. As shown in FIG. 1, this device comprises (a)
The two-color separation type color sensor 100 and (b) a current signal I1 (ie, PD1) generated between the electrode 111 and the electrode 121 due to light reception during application of a reverse bias voltage between the electrode 111 and the electrode 121. The generated current signal I1) is input and integrated, and (c) light is generated between the electrodes 121 and 131 by light reception during application of a reverse bias voltage between the electrodes 121 and 131. An integrating circuit 220 for receiving and integrating the current signal I2 (that is, the current signal I2 generated by the PD2); and (d) the integrating circuit 21
An analog-to-digital converter 310 for inputting the integrated signal output from 0 and performing analog-to-digital conversion; (e) an analog-to-digital converter 320 for inputting the integrated signal output from the integration circuit 220 and performing analog-to-digital conversion;
(F) The digital signal output from the analog-to-digital converter 310 and the digital signal output from the analog-to-digital converter 320 are input, and after removing each preset offset amount from both digital signals, the ratio of An arithmetic circuit 400 for calculating the value; and (g) a processing unit 500 for collecting the arithmetic result output from the arithmetic circuit 400, identifying the color of the received light, and notifying the integration circuits 210 and 220 of an integration operation instruction. And The integrating circuit 210 includes an amplifier A1 for inputting the current signal I1, an input terminal for the current signal I1 of the amplifier A1 and one terminal, and a capacitive element C1 connected to the output terminal and the other terminal of the amplifier A1. The input terminal and one terminal of the current signal I1 of the amplifier A1 are connected to the output terminal of the amplifier A1, and the other terminal is connected. When the integration operation instruction signal notified from the processing unit 500 is significant, it is opened. Switch element S1 that closes when the operation instruction signal is insignificant
And The integration circuit 220 has the same configuration as the integration circuit 210. Further, the capacitance value C2 of the capacitance value C1 and the capacitance element C2 of the capacitor C1, when the same amount is given to the PD1 and PD2, the current value generated by the PD1 at I _10, PD2 Assuming that the generated current value is I _20, the current value is selected so as to satisfy I ₁₀ / I ₂₀ = C2 / C1 (3). The arithmetic circuit 400 inputs the digital signal output from the analog-to-digital converter 310 and the digital signal output from the analog-to-digital converter 320 through an address input terminal, and stores the digital signal in the storage unit corresponding to the designated address in advance. A read-only memory (ROM) for outputting written data from a data output terminal is provided. The solid-state imaging device according to the present embodiment operates as follows to identify the color of the received light. First, while applying a reverse bias voltage between the electrode 111 and the electrode 121,
31 and a reverse bias voltage is applied. At the beginning, the processing section 500 outputs the integration operation signal in a non-significant manner. That is, the switch elements S1 and S2 of the integration circuits 210 and 220 are set to a closed state. At the start of the measurement, the processing section 500 makes the integration operation instruction signal significant. As a result, the switching elements S1 and S2 are opened, and the integrating circuits 210 and 220 are turned off.
Starts the integration operation. In this state, the two-color separation type color sensor 10
When 0 is received, a current signal I1 is generated between the electrode 111 and the electrode 121 and a current signal I2 is generated between the electrode 121 and the electrode 131 at a ratio according to the wavelength distribution of the received light. The current signal I1 is input to the integration circuit 210,
Electric charges are stored in the capacitor C1. A voltage signal corresponding to the amount of the accumulated charge is output as an integration signal of the integration circuit 210. As a component of the integration circuit 210, there is no component whose operating characteristic has a large temperature dependency unlike a single diode, and therefore, this integration signal has a small fluctuation due to temperature. The integrated signal output from the integrating circuit 210 is converted into a digital signal by the analog-to-digital converter 310 and then input to the arithmetic circuit 400. Similarly to the current signal I1, the current signal I2 is also input to the integration circuit 220, integrated, and output as an integrated signal. The integrated signal is digitized by the analog-to-digital converter 320. input.
The integration signal output from the integration circuit 220 is also
As in the case of the integration signal output from 10, the temperature fluctuation is small. In the arithmetic circuit 400, the digital signal output from the analog-to-digital converter 310 and the digital signal output from the analog-to-digital converter 320 are input to the address input terminal of the ROM. The storage section corresponding to the designated address of the ROM stores digital data of a ratio value relating to a value obtained by removing each offset value from the digital value indicated by both digital signals, and stores the digital data in a data output terminal. Output from A digital signal reflecting the digital data is output from the arithmetic circuit 400 to the processing section 500. The processing section 500 collects the data of the digital signal output from the arithmetic circuit 400 when it is determined that the predetermined measurement time has elapsed, identifies the color of the received light from the collected data value, and , The integration operation instruction signal is set to be insignificant and the next measurement is prepared. Thus, the color of the received light is identified with high accuracy. The present invention is not limited to the above embodiment, but can be modified. For example, the capacitive elements C1, C
The selection of the capacitance value of 2 can be simply made to be the same capacitance value instead of the relationship of the expression (3). In such a case, it is necessary to change the configuration of the arithmetic circuit (for example, the write data in the storage unit of the ROM) or the method of color identification of the processing unit (for example, the value of the collected data in the color comparison table). . As described above in detail, according to the solid-state imaging device of the present invention, the operation characteristics can be reduced without using a logarithmic conversion circuit using a single diode whose operation characteristics are highly temperature-dependent. Has decided to use an integrating circuit having low temperature dependency, so that the temperature dependency can be reduced and the received light can be accurately identified. Further, if an arithmetic circuit for performing an arithmetic operation by removing the offset at the preceding stage after digitizing the integrated signal from the integrating circuit is provided, the received light can be identified with higher accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a solid-state imaging device according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a two-color separation type color sensor. FIG. 3 is a configuration diagram of a conventional solid-state imaging device. 100: two-color separation type color sensor, 110, 120, 1
30 ... semiconductor layer, 111, 121, 131 ... electrode, 21
0, 220: integrating circuit, 310, 320: analog-to-digital converter, 400: arithmetic circuit, 500: processing unit.

Continuation of the front page (56) References JP-A-3-144325 (JP, A) JP-A-4-3588 (JP, A) JP-A-6-105069 (JP, A) JP-A-4-248756 (JP) JP-A-2-271223 (JP, A) JP-A-62-26282 (JP, A) JP-A-55-26467 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H01L 27/146 G01J 3/50 H01L 27/14 H04N 5/335 JICST file (JOIS)

Claims (1)

(57) Claims 1. A first semiconductor layer having a first conductivity type, and a second conductivity type formed on a part of the surface of the first semiconductor layer. A second semiconductor layer having a first conductivity type formed on a part of the surface of the second semiconductor layer; and a second semiconductor layer having the first conductivity type.
A first electrode formed on a part of the surface where the third semiconductor layer is not formed, and a second electrode formed on a part of the surface of the second semiconductor layer where the third semiconductor layer is not formed. And a third electrode formed on a part of the surface of the third semiconductor layer, and the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer A light receiver formed mainly of a semiconductor material having a wavelength dependency of light absorption and receiving light from a surface side of the third semiconductor layer; and a light receiver between the first electrode and the second electrode. The first electrode and the second electrode are received by receiving light during application of a reverse bias voltage.
A first photocurrent signal generated between the first and second electrodes is input, a charge corresponding to the input first photocurrent signal is stored in a first capacitor, and the first photocurrent signal is calculated according to the amount of the stored charge. A first integration circuit for outputting a first integration signal, and a second integration circuit configured to receive the second electrode and the third electrode by receiving light during application of a reverse bias voltage between the second electrode and the third electrode.
A second photocurrent signal generated between the first and second electrodes is input, a charge corresponding to the input second photocurrent signal is stored in the second capacitor, and the second photocurrent signal is calculated according to the amount of the stored charge. A second integration circuit that outputs the second integration signal, and the first integration signal that is output from the first integration circuit, and converts the input first integration signal into a first digital signal. A first analog-to-digital converter that converts the analog-to-digital signal into a digital signal and outputs the first digital signal; and the second integrated signal that is output from the second integration circuit. A second digital-to-analog converter that converts the integrated signal of the second digital signal into a second digital signal, and outputs the second digital signal; and the first analog-digital converter that is output from the first analog-digital converter. A digital signal and the second The second digital signal output from the log digital converter is input, and the ratio of the ratio of the first digital value indicated by the first digital signal to the second digital value indicated by the second digital signal is calculated. And a computing unit that outputs a third digital signal indicating a third digital value according to the value. The computing unit inputs the first digital signal and the second digital signal to an address input terminal. Then, according to the data written in the storage unit, a third
A solid-state imaging device, comprising: a read-only storage element that outputs a digital signal.