JPH04298078A - Solid-state image pick-up element - Google Patents

Abstract

PURPOSE:To detect a storage charge amount of a photodetecting part with no mediation of CCD. CONSTITUTION:When charge is stored in an n-type diffusion layer 8, potential changes. Since the n-type diffusion layer 8 is connected to a gate 20 of a storage charge detection FET through a metal wiring 21, the gate 20 generates a similar potential change. A charge amount of the n-type diffusion layer 8 can be known by monitoring source potential of this storage charge FET. An exposure time can be optimized by detecting a photodetecting part having the largest storage charge by means of a peripheral circuit so as to control an electron shutter according to its storage charge amount without reading the storage charge amount.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensing device, and more particularly to a structure in which the light receiving portion thereof is improved.

0002

2. Description of the Related Art FIG. 4 shows a planar structure of a conventional solid-state image sensor. In the figure, 1 is proportional to the light amount and light reception time,
A light receiving section has a structure for accumulating signal charges, and is arranged in large numbers on a semiconductor substrate. 2 is a CCD section for reading signal charges, and 3 is a readout MOSFET, which is arranged between the light receiving section 1 and the CCD section 2. Its source is connected to the light receiving section 1, and its drain is connected to the CCD section 2. There is. An amplifier 4 is connected to the output side of the CCD section 2 and outputs a voltage proportional to the signal charge to the outside. 5 is light receiving part 1
6 is a sweep drain for sweeping out excess signal charges accumulated in the FET, and its source is the
The drain is connected to the sweep drain 5.
are connected to each.

FIG. 3 is a sectional view of a portion indicated by the dotted line α in FIG. In the figure, 7 is a P-type silicon substrate, and 8 is an n-type layer formed on one main surface of the P-type silicon substrate 7.
The boundary between the n-type layer 8 and the n-type layer 8 corresponds to the light receiving section 1. Further, 9 represents an oxide film, and 10 represents a protective film.

FIG. 5 is a timing chart showing the operation of the solid-state image sensor. In the figure, the horizontal axis represents the passage of time. 11 is a clock applied to the gate of the read MOSFET 3, and 12 indicates the time width tR of the "H" state of the clock 11. 13 is a clock applied to the gate of the sweep MOSFET 6, and 14 indicates the time width tS of the "H" state of the clock 13. Reference numeral 15 indicates the operation of the CCD section 2, and reference numeral 16 indicates the transfer status. 17 indicates one cycle time TC. In addition, 18 is the time tn until the sweep MOSFET 6 is turned on after the read MOSFET is turned off, and 19 is the time tn of the sweep MOSFET 6.
The time ta until the read MOSFET turns on after T6 turns off is shown in each case.

Next, the operation will be explained. Read MO
By turning the SFET 3 into the on state 12, signal charges are transferred to the CCD section 2. The CCD section 2 sequentially transfers all the transferred signal charges to the amplifier 4. Also, during this time, the sweep MOSFET 6 is turned on, and the charges accumulated during tn are swept out and discharged to the outside through the drain 5.

Next, using FIG. 6, the light receiving section 1 is connected between the TC
The change in the amount of signal charge accumulated in will be explained. In the figure, the horizontal axis represents the passage of time, and the vertical axis represents the amount of accumulated charge. 12, 14, 18, and 19 indicate the same parts as in FIG. First, during tR, all the signal charges accumulated before that are CC
Transfer to D section 2. Next, charges are accumulated during tn, but are discharged as excess charges through the drain 5 during tS. Therefore, the charges accumulated during ta are transferred to the CCD section 2 as signal charges.

The above-mentioned operation of discharging excess charge is very effective when the amount of light is large. The light receiving section 1 has a mechanism that provides a signal charge amount proportional to the amount of light and the light reception time, but when the signal charge amount reaches a saturation amount, the above proportional relationship is lost and the amount of saturation charge is constant. . Therefore, by sweeping out the excess charge and discharging it through the MOSFET 6, the proportional relationship can be restored again. Therefore,
If the time allocation of tn and ta is carried out appropriately, the detector can always be operated normally without being saturated. However, when the amount of light suddenly increases, the signal charge amount easily reaches the saturation charge amount. In addition, in the conventional device, the amount of signal charge can only be detected through the output section 4, so in order to avoid saturation of the detector, tn, t
It was not possible to quickly optimize the time allocation for a.

[0008]

[Problems to be Solved by the Invention] Since the conventional solid-state image sensor is configured as described above, even if the signal charge amount reaches the saturation charge amount, it cannot be detected until the output signal is examined via the CCD section 2. There was a problem in that it was not possible to detect that the container was saturated.

The present invention was made to solve the above-mentioned problems, and aims to provide a solid-state image sensor that can detect the amount of signal charge in the light receiving section in real time without going through a CCD section. shall be.

0010

[Means for Solving the Problems] A solid-state image sensor according to the present invention has a structure in which a transistor for detecting the amount of accumulated charge is formed on a substrate on which a light receiving section is formed, and the gate of the transistor and the light receiving section are connected. It is something.

Further, the transistor for detecting the amount of accumulated charge is connected to a peripheral circuit driven by the transistor, which detects a pixel with a maximum gate potential and reads out the amount of accumulated charge.

0012

[Operation] In the present invention, a voltage corresponding to the amount of charge of the detector can be detected in real time by the transistor formed on the substrate.

Furthermore, since the peripheral circuit can detect the pixel with the maximum gate potential, exposure can be optimally controlled by combining it with an electronic shutter.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a solid-state image sensor according to an embodiment of the present invention. In the figure, numerals 7 to 10 are parts similar to or equivalent to those of the conventional device shown in FIG. 22 is a MOSFET for detecting the amount of accumulated charge according to the present invention; 20 is a MOSFET for detecting the amount of accumulated charge according to the present invention;
The gate of SFET, 21 is the gate and the n-type layer 8 of the light receiving part 1.
This shows the metal wiring that connects the

Next, a circuit for detecting the amount of accumulated charge and transmitting it to the outside will be explained. In FIG. 2, numerals 1 to 6 indicate equivalent or equivalent parts in FIG. 22 is a MOSFET for detecting the amount of accumulated charge shown in FIG. 23 is a peripheral circuit for transmitting the state of the MOSFET 22 for detecting the amount of accumulated charge to the outside, and is formed on the P-type silicon substrate 7. 24 is a power supply voltage terminal for supplying power to the peripheral circuit 23, and a positive potential is applied thereto. 25 indicates an output terminal. Reference numeral 26 indicates a peripheral circuit resistor constituting the peripheral circuit 23, and 27 indicates a peripheral circuit MOSFET. One end of the resistor and the drain of the peripheral circuit MOSFET 27 are connected to the power supply voltage terminal 24, and the other end of the peripheral circuit resistor 26 and the gate of the peripheral circuit MOSFET 27 are connected to a MOSFET for detecting the amount of accumulated charge.
Connected to the drain of ET22. Note that the source of the peripheral circuit MOSFET 27 is connected to the output terminal 25,
The source of the MOSFET 22 for detecting the amount of accumulated charge is grounded to the P-type silicon substrate 7.

Next, the operation will be explained. In this embodiment, the gate of a MOSFET 22 for detecting the amount of accumulated charge is connected to the light receiving section 1, and the amount of accumulated charge in the light receiving section can be detected in real time by this MOSFET 22. Immediately after reading out the signal charges, the light receiving section 1 is reset to a constant positive potential. At this time, the MOSFE for detecting the amount of accumulated charge
The source and drain of T22 are in a low impedance state. As charges are accumulated in the light receiving section 1, the potential of the light receiving section 1 decreases, so the MOSFE for detecting the amount of accumulated charge is
The source and drain of T22 are in a high impedance state. Although the gate potential of the peripheral circuit MOSFET 27 becomes high, since the sources of all the peripheral circuit MOSFETs 27 are connected to the output terminal 25, all the peripheral circuit MOSFETs 27
Among the SFETs 27, only the FET with the highest gate potential is turned on, and other peripheral circuit MOSFETs are turned on.
27 is in an off state. Therefore, the potential of the output terminal 25 changes in an analog manner according to the gate potential of the peripheral circuit MOSFET 27 having the highest gate potential. That is, the peripheral circuit 23 can select the one with the largest amount of accumulated charge among all the light receiving sections 1 and output a corresponding potential from the output terminal 25.

As described above, according to this embodiment, the MOSFET 22 for detecting the amount of accumulated charge is formed so that its gate is connected to the light receiving section 1, and the MOSFET 22 for detecting the amount of accumulated charge is formed such that its gate is connected to the light receiving section 1.
The peripheral circuit consisting of a MOSFET driven by an ET and a resistor selects the one with the largest amount of accumulated charge among all the light receiving sections 1, so the largest amount of accumulated charge in the light receiving section is selected. It can be detected in real time, and the amount of accumulated charge just before saturation can be easily detected. Furthermore, by combining it with an electronic shutter, the exposure time can be optimized without reading out the amount of accumulated charge.

By the way, in the above explanation, the structure in which the light receiving sections 1 are arranged one-dimensionally has been explained, but the same applies to the case where they are arranged two-dimensionally. In addition, although an n-type MOSFET was used as the transistor for detecting the amount of accumulated charge, the light receiving section 1
A P-type MOSFET may be used as long as the transistor can supply a potential according to the potential, and any circuit configuration may be used for the peripheral circuit as long as the output changes depending on the accumulated charge. .

[0019]

As described above, according to the solid-state image sensor of the present invention, a transistor for detecting accumulated charge is formed on a semiconductor substrate on which a light receiving section is formed, and the gate thereof is connected to the light receiving section. Therefore, the charge accumulated in the light receiving section can be detected in real time, and the charge accumulation time can be optimized.

Furthermore, since the transistor for detecting the amount of accumulated charge is connected to a peripheral circuit that is driven by the transistor and detects the pixel with the maximum gate potential and reads out the amount of accumulated charge, the electronic shutter In combination with this, it is possible to optimally control exposure.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing an embodiment of the present invention.

FIG. 2 is a wiring diagram showing one embodiment of the present invention.

FIG. 3 is a sectional view of a main part of a conventional solid-state image sensor.

FIG. 4 is a plan view of a solid-state image sensor.

FIG. 5 is a timing chart diagram showing the operation of the solid-state image sensor.

FIG. 6 is a diagram showing changes in the amount of accumulated charge during one cycle.

[Explanation of symbols]

1 Light receiving section 2 CCD section 3 Readout MOSFET 4 Amplifier 5 Sweep drain 6 Sweep out MOSFET 7 P-type silicon substrate 8 N-type diffusion layer 9 Oxide film 10 Protective film 11 Operation of readout MOSFET 12 Timing and time when readout MOSFET turns on state 13 Operation of the sweep MOSFET 14 Timing and time when the sweep MOSFET turns on 15 Operation of the CCD section 16 Timing and time when the CCD section enters the transfer state 17 One cycle time 18 Time during which excess charges are accumulated 19 Signal charges are accumulated Time 20 Gate 21 of the MOSFET for detecting the amount of accumulated charge according to the present invention Metal arrangement 22 connecting the gate of the MOSFET for detecting the amount of accumulated charge and the light receiving part MOSFET 23 for detecting the amount of accumulated charge Peripheral circuit 24 Power supply voltage terminal 25 of the peripheral circuit Output terminal 26 Peripheral circuit resistance 27 Peripheral circuit MOSFET

Claims (2)

[Claims] 1. A solid-state imaging device having a structure in which a light receiving section that generates signal charges upon receiving light and a charge transfer section that transfers the signal charges are arranged on one principal surface of a semiconductor substrate, wherein each pixel 1. A solid-state image sensing device having a structure in which a transistor for detecting the amount of accumulated charge is formed on the same semiconductor substrate as a light receiving section, and a gate of the transistor for detecting the amount of accumulated charge is connected to each of the pixels. 2. The transistor for detecting the amount of accumulated charge includes:
2. The solid-state image sensing device according to claim 1, further comprising a peripheral circuit connected thereto that is driven by said transistor, detects a pixel having a maximum gate potential, and reads out the amount of charge accumulated therein.