JPH10270673A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image pickup device requiring no image processing for expanding a dynamic range. SOLUTION: In the solid-state image pickup device, two n-layers 13, 15 are formed onto a p-type substrate 22, a photo-diode as a photoelectric conversion section and a vertical transfer section 16 are formed, and insulating films 26 and transfer gate electrodes 28 are shaped onto the substrate 22. In the solid- state image pickup device 10, a high molecular liquid crystal layer 30 and a transparent electrode 32 are formed onto the image sensing device. Accordingly, since the light transmissivity of the PDLC layer 30 is lowered with the intensified incident light and the quantity of light projected to a PD 12 is limited, a dynamic range is expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device provided in, for example, an electronic still camera, and more particularly to an expansion of a dynamic range of the image pickup device.

[0002]

2. Description of the Related Art With the practical use of high-definition television in recent years, the resolution of video systems has been greatly improved, but the resolution of luminance gradation, that is, the dynamic range has not been sufficiently improved. For example, when indoors and outdoors are present at the same time in the angle of view, or under the condition of retrograde, saturation or darkening occurs, and it is obvious that the dynamic range is insufficient as compared with the human visual system.

[0003]

Generally, a CCD (Charge Coupled Device) or the like is used as an image pickup device of a video camera. It is generally said that the dynamic range of a CCD type imaging device is narrow. As a method for improving the dynamic range, for example, a configuration that expands the dynamic range by obtaining two types of image data having different storage times during photoelectric conversion is considered. ing.

However, the image signal whose dynamic range has been expanded by the two types of image data as described above is a CC signal.
After reading from D, a process of synthesizing according to each signal level is required, so that image processing becomes complicated.

The present invention has been made in view of the above points, and an object thereof is to obtain an image pickup device which does not require image processing for expanding a dynamic range.

[0006]

According to the present invention, there is provided an image pickup device comprising: a charge accumulating portion for accumulating electric charges according to light incident on a light receiving surface corresponding to each pixel of an image to be formed; And a light amount control layer that changes the light transmittance of incident light to the light receiving surface in accordance with the light amount.

In the image pickup device, preferably, the light amount control layer has the maximum light transmittance in the initial state, and the light transmittance is restored to the initial state by removing charges from the charge storage portion. More preferably, the light quantity control layer comprises a polymer dispersed liquid crystal.

[0008] In the image pickup device, preferably, electric charges are accumulated in a state where a voltage is applied to the charge accumulating portion, and an electrode for applying a voltage to the charge accumulating portion is provided. More preferably, the electrode comprises a transparent electrode provided on the surface of the light quantity control layer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the image pickup device according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically showing a configuration of a signal transfer path of an image sensor according to an embodiment. FIG.
FIG. 3 is a partial cross-sectional view of one pixel of the image sensor.

As shown in FIG. 1, the image pickup device 10 includes a plurality of photodiodes (hereinafter referred to as PD) 12 arranged in a grid corresponding to pixels. Each PD 12 converts the optical image formed on the image sensor 10 into an electric signal and accumulates it as a signal charge. A vertical transfer CC to which the signal charge from the PD 12 is transferred is provided to the right of the PD 12 for each vertical line.
D16 is provided. Each PD 12 and vertical transfer CCD 16
A transfer gate 14 is provided between the transfer gate 1 and the transfer gate 1.
4, the signal charge from each PD 12 is transferred rightward in the figure.

A horizontal transfer CCD 18 is provided below the PD 12 and the vertical transfer CCD 16 in the figure, and each vertical transfer CC 18 is provided.
Connected to D16. The vertical transfer CCD 16 transfers the signal charges from the PD 12 to the horizontal transfer CCD 18 downward in the drawing for each horizontal line. Further, horizontal transfer C
The CD 18 transfers the signal charges from each of the vertical transfer CCDs 16 to the output terminal 20 toward the left in the figure. Thus, the signal charges sequentially transferred from each PD 12 are output from the output terminal 20 to the outside.

Next, referring to FIG. 2, a description will be given of a pixel unit configuration of the image sensor. The image sensor includes a p-type substrate (charge-carrier p-type semiconductor) 22 made of Si (silicon), and two n-layers (charge-carrier n-type semiconductor) 13 on the p-type substrate 22. , 15 are provided. The junction between the p-type substrate 22 and the n-layer 13 on the left side in the figure is a pn junction, and the PD 12 is formed by the pn junction. Similarly, a vertical transfer CCD 16 is formed by joining the p-type substrate 22 and the n-layer 15 on the right side in the figure. The region between the two n layers 13 and 15 of the p-type substrate 22 is the transfer gate 14.

The signal charges are transferred in the order of the n-layer 13, the transfer gate 14, and the n-layer 15 under predetermined conditions. Two n-layers 1
P ⁺ regions are formed on both sides of 3, 15 in order to prevent outflow of signal charges from the two n layers 13, 15 to the adjacent n layers. The p ⁺ region is called a channel stopper 24 and separates adjacent pixel portions.

On the surface of the substrate 22 excluding the n-layer 13 of the PD 12, an insulating film 26 made of SiO ₂ (silicon dioxide) is formed.
Is formed. A transfer gate electrode 28 is provided further on the insulating film 26. The transfer gate electrode 28 has a vertical transfer C
The transfer gate 14 is located above the CD 16 and the transfer gate 14, and is turned on / off. This transfer gate electrode 2
Reference numeral 8 has a role of blocking the incidence of external light on the vertical transfer CCD 16.

On the entire surface of the substrate 22, for example, ITO (in
A transparent electrode 32 made of dium-tin oxide; In ₂ O ₃ —SnO ₂ ) is provided, and is connected to an electrode 33 on the substrate 22 side via a control power supply 34. The direction in which the electrodes 32 and 33 are arranged is perpendicular to the transfer path of the charge carriers, and the electric fields generated by the two electrodes 32 and 33 generate the charge carriers and control the alignment of the liquid crystal described later. .

Between the substrate 22 and the transparent electrode 32, a polymer type liquid crystal (Polymer Dispersed Liquid) which is a light amount control layer is provided.
A layer 30 (crystal, hereinafter referred to as PDLC) is formed.
PDLC has a configuration in which liquid crystals are scattered in a polymer film of a polymer, and incident light is diffused by reflecting light at a boundary surface between the polymer and the liquid crystal. The molecular arrangement of the liquid crystal is oriented in various directions in an initial state, that is, in a state where no electric field is applied, and the molecular arrangement of the liquid crystal changes in a fixed direction by the application of the electric field. By the action of this liquid crystal, PDL
C has a property that the light transmittance increases as the electric field increases. In PDLC, while the electric field is applied, the molecular arrangement changes, but when the electric field disappears, the molecular arrangement of the liquid crystal returns to the initial state.

FIG. 3 is a graph showing the relationship between the electric field and the light transmittance of the PDLC. The light transmittance T is constant at the minimum value Tmin up to the electric field value E1, but starts to rise when the electric field value E1 is exceeded, and reaches the maximum value Tmax at the electric field value E2 (E1 <E2). Even when the electric field E becomes equal to or higher than E2, the light transmittance T remains constant at Tmax. Although the light transmittance T varies depending on the thickness of the PDLC, for example, Tmin is about 60 to 70%,
x is about 100%. The predetermined light transmittance change is determined by conditions such as the thickness.

Next, the operation of the image sensor will be described.
In FIG. 2, incident light B from above is transmitted by the transparent electrodes 32, P.
The light passes through the DLC layer 30 and irradiates the n-layer 13 of each PD 12. Electron-hole pairs are generated at the pn junction of the PD 12, and the holes flow into the p-type substrate 22 in the n-layer 13 to leave electrons. The amount of electric charge stored in each n layer 13 differs depending on the intensity of the incident light B, and the stored electric charge is a signal charge. When a subject image is formed on the surface of the image sensor 10 using a photographing optical system (not shown), the amount of signal charges accumulated in each pixel changes according to the optical image,
A charge pattern is created. By sequentially transferring the signal charges, an image signal of a subject image is obtained.

More specifically, first, the transfer gate electrode 28 is O
In the state of the FF, a predetermined voltage is applied to the transparent electrode 32. When a voltage is applied, the electrons in the n-layer 13 of the PD 12 and the holes in the p-layer 22 move away from the junction surface, so p
A depletion layer is formed at the n-junction, where charge carriers do not exist. The width of the depletion layer changes according to the magnitude of the applied voltage, and the n-layer 13 serves as a well having a low energy level with respect to the signal charge. At this time, the p ⁺ layer 24 has a higher potential level than the n layer 13 and serves as a charge stopper.

FIG. 4 is a potential diagram schematically showing the operation of transferring the signal charges from the PD 12 to the vertical transfer section 16. P
When light is incident on D12, an electron-hole pair is generated by photoexcitation at the pn junction, and as shown in FIG.
In 3, holes flow out to the p-type substrate 22 and electrons remain in the n-layer 13. In this way, the accumulated amount of electrons or signal charges is
It corresponds to the amount of incident light in the n-layer 13.

Next, the transfer gate electrode 28 is turned on by a transfer pulse from the outside, and as shown in FIG. 4B, the potential barriers of the transfer gate 14 and the vertical transfer CCD 15 located below the transfer gate electrode 28 are changed. Go down. And PD1
The signal charge of the second n-layer 13 is extracted and transferred to the n-layer 15 of the vertical transfer CCD 16 as shown in FIG.

As described above, the image signal photoelectrically converted by the PD 12 of each pixel is transferred to the vertical transfer unit 16 for each vertical column via the transfer gate 14 by a predetermined transfer pulse. Referring to FIG. 1 again, the image signals are transferred from the vertical transfer CCD 16 to the horizontal transfer CCD 18 by the transfer pulses having further different phases, and then output from the horizontal transfer CCD 18 via the output terminal 20 to the outside.

FIG. 5 is a PD taken along the line II of FIG.
It is a figure showing the potential distribution of. When light is not incident and electrons are not accumulated in the n layer 13 with the positive voltage Vo applied, the electric field value of the PDLC layer 30 is E2, and at that time, P
The light transmittance of the DLC layer 30 is high (see FIG. 3), and shows a potential distribution indicated by a solid line.

As described above, as light is incident and electrons are accumulated in the n-layer 13, the potential of the n-layer 13 decreases because the electrons are negative, and the electric field E of the PDLC layer 30 also decreases.
That is, the light transmittance of the PDLC layer 30 decreases as the incident light increases. Therefore, as described with reference to FIG. 3, the light transmittance of the PDLC layer 30 decreases, the amount of light incident on the n layer 13 decreases, and, for example, when the electric field value E3 (E3 <E2), the potential indicated by the broken line. Distribution.

As described above, the stronger the incident light, the more the PDL
Since it is diffused in the C layer 30, the amount of signal charges accumulated in the PD 12 is not saturated until high illuminance, as compared with the conventional PD 12 in which the PDLC layer 30 is not provided. Therefore, by using the image pickup device of the present invention, an image having a wide dynamic range can be easily obtained without requiring complicated image processing of combining two images having different accumulation times.

[0027]

According to the present invention, an image pickup device which does not require image processing for expanding a dynamic range can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a charge passage structure of an embodiment of an image sensor according to the present invention.

FIG. 2 is a partial cross-sectional view schematically showing the imaging device shown in FIG.

FIG. 3 is a diagram illustrating a relationship between an electric field and a light transmittance in a PDLC section of the imaging device illustrated in FIG. 2;

FIG. 4 is a potential diagram schematically showing a signal charge transfer operation of the image sensor shown in FIG.

5 is a diagram showing a potential distribution in a photodiode of the image pickup device shown in FIG.

[Explanation of symbols]

 Reference Signs List 10 imaging device 12 PD (photodiode) 13, 15 n layer 14 transfer gate 16 vertical transfer CCD 22 p-type substrate 26 insulating film 28 transfer gate electrode 30 PDLC (light quantity control layer) 32 transparent electrode

Claims (5)

[Claims] 1. A charge accumulating portion for accumulating electric charges according to light incident on a light receiving surface corresponding to each pixel of an image to be formed, and the incident light on the light receiving surface according to an amount of accumulated electric charges. And a light amount control layer for changing the light transmittance of the image pickup device. 2. The light transmittance is maximum in the initial state of the light amount control layer, and the light transmittance is restored to the initial state by removing charges from the charge storage portion. 1. The image sensor according to 1. 3. The imaging device according to claim 2, wherein the light amount control layer includes a polymer dispersed liquid crystal. 4. The imaging device according to claim 1, wherein the charge is stored while a voltage is applied to the charge storage unit, and an electrode for applying a voltage to the charge storage unit is provided. 5. The imaging device according to claim 4, wherein the electrode includes a transparent electrode provided on a surface of the light quantity control layer.