JP2004311666A - Solid-state imaging device - Google Patents

Abstract

A solid-state imaging device capable of reducing a shading amount with respect to a conventional solid-state imaging device and capable of following a change in an incident light angle to the solid-state imaging device due to a magnification change of an imaging optical system.
A plurality of pixels are two-dimensionally arranged, and a color filter, an opening of a light-shielding film, and a microlens formed of a shape-variable lens are sequentially arranged thereon. The curvature of the microlenses is configured to be variable independently or for each group on a concentric circle.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid-state imaging device, and more particularly, to a solid-state imaging device in which a microlens whose shape is variable is arranged on a light receiving surface of the solid-state imaging device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, video cameras, digital cameras, cameras with built-in mobile phones, and the like have rapidly become widespread. These cameras use a solid-state imaging device such as a CCD or C-MOS. In the solid-state imaging device, a large number of pixels are discretely arranged on the surface, and a light-shielding film is provided for each pixel. In addition, while an opening for receiving light is provided while cutting light from other directions, a microlens is arranged for each pixel in order to more efficiently receive light.
[0003]
FIG. 7 is an enlarged sectional view of a part of a conventional general solid-state imaging device. FIG. 8 is a graph showing the relationship between the light output and the pixel position of the solid-state imaging device in FIG.
[0004]
A light-shielding film 72 that forms an opening is provided on a photodiode 71 that is a pixel of the imaging unit, and a color filter 73 is disposed thereon. Further, a micro lens 74 corresponding to the photodiode 71 is joined to the upper surface. The maximum incident angle of the incident light 75 is limited by the opening formed by the light shielding film 72.
[0005]
In the above configuration, light is efficiently incident on each pixel. However, in actuality, the amount of light to the pixels in the peripheral portion is extremely increased as the distance from the center of the optical axis increases as shown in the graph of FIG. Decrease.
[0006]
That is, since there is a decrease in the amount of light around the imaging optical system due to the cosine fourth law, and vignetting occurs at the opening, shading increases.
[0007]
For this reason, at present, the imaging optical system is designed to have good telecentricity so that light is incident as parallel as possible, so that it can be used in digital cameras, mobile phones, and the like.
[0008]
In a camera module using these solid-state imaging devices, shading in the solid-state imaging device is greatly restricted, and the configuration of the imaging optical system is limited as described above. It was difficult to reduce the size of the module.
[0009]
Therefore, while miniaturization of digital video, digital camera, camera with built-in mobile phone, etc. is being promoted, it has been difficult to improve shading and design a high-resolution camera module.
[0010]
Therefore, various solid-state imaging devices that solve the above problem have been proposed.
[0011]
[Patent Document 1]
JP 2001-160973 A [Patent Document 2]
JP-A-1997-260624 [Patent Document 3]
Japanese Patent Application Laid-Open No. 1999-15024 [Patent Document 4]
In Japanese Patent Application Laid-Open No. 2001-189442, since the angle of the principal ray incident from the imaging optical system becomes larger as it approaches the periphery, shading can be performed as much as possible by shifting the microlens and the light receiving element by an appropriate amount. What reduces is disclosed.
[0012]
More specifically, the photodiode region near the light receiving end of the fixed solid-state imaging device that is distant from the center of the optical axis is displaced in the arrangement position corresponding to the inclination of the principal ray, and similarly, the light shielding layer is used. The opening and the microlens are also staggered.
[0013]
The configuration described in Patent Document 1 suppresses shading in a peripheral portion by such a configuration. However, although a certain degree of downsizing can be realized, further downsizing is difficult.
[0014]
In general, the incident angle of the imaging optical system must be set to a predetermined angle or less (for example, 20 degrees or less) in order to suppress shading for practical use to a required value or less. For this reason, in the optical system adopting the one described in Patent Document 1, the lens configuration of the imaging optical system must be complicated, such as an increase in the number of lenses, and this greatly imposes restrictions on the lens design.
[0015]
Patent Documents 2 and 3 disclose a technique in which the curvature of a microlens for each pixel on a solid-state imaging device is small near the center and is increased toward the periphery to increase the amount of light in the periphery.
[0016]
In Patent Documents 2 and 3, the diameter of the microlens is changed between the center and the end, but the opening at the center is limited with respect to the amount of light at the end, so that the entire amount of light is made uniform. Therefore, there is a problem that the overall light amount itself is reduced and the performance is reduced.
[0017]
In Patent Document 4, in order to improve the shading amount, the transmittance of the central portion of the microlens is made lower than that of the peripheral portion to average the light amount. Further, another proposed transmission light amount is reduced at the center and is matched with the periphery, so that the total light amount is reduced.
[0018]
These proposals merely improve the shading and do not address the miniaturization.
[0019]
[Problems to be solved by the invention]
There is a need for a solid-state imaging device that is not affected by the incident light angle, which is a problem of the conventional solid-state imaging device described above. In particular, when a solid-state imaging device is used together with a zoom lens, as shown in FIG. 9, when the focal length is short (WIDE) and when the focal length is long (TELE), the angle of incidence of the light beam on the solid-state imaging device is small. different. In such a case, in a normal microlens, the amount of light incident on a pixel of a solid-state imaging device, particularly, a pixel far from the optical axis differs. For this reason, if the microlens is designed to be optimal on the WIDE side, it cannot be optimal on the TELE side, and vice versa.
[0020]
Therefore, there is also a need for a solid-state imaging device that is not affected by the incident light angle when it changes with the zoom position.
[0021]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and a solid-state imaging device in which a light receiving element group including a plurality of light receiving elements and a micro lens group including a micro lens that forms an image of an object on each light receiving element is arranged. At least a part of the micro lens group is constituted by a shape-variable lens whose shape can be changed.
[0022]
Further, the solid-state imaging device according to the present invention is characterized in that the light amount incident on the light receiving element group is made uniform by the shape variable lens.
[0023]
Further, the solid-state imaging device according to the present invention is characterized in that the direction of incidence on the periphery of the light receiving surface of the solid-state imaging device is inclined in a direction perpendicular to the light receiving surface.
[0024]
Further, in the solid-state imaging device of the present invention, the microlens at the center and / or the periphery of the light receiving surface is a variable shape lens, and the curvature at the center is made larger than the curvature at the periphery by changing the lens shape. It is characterized by the following.
[0025]
Further, the solid-state imaging device according to the present invention is characterized in that the shape of the shape-variable lens can be changed by voltage or pressure.
[0026]
Further, the solid-state imaging device according to the present invention is characterized in that the shape of the variable shape lens is changed in accordance with an incident angle of light incident on the light receiving element.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0028]
FIG. 1 shows a configuration of an imaging optical system and a solid-state imaging device. In order to prevent shading, the image forming optical system has a telecentric configuration and is configured to make light incident on the light receiving element as parallel to the optical axis direction as possible.
[0029]
However, in the case of the solid-state imaging device shown in FIG. 1, the number of lenses increases and the configuration becomes complicated.
[0030]
FIG. 2 is a diagram in which a shape variable lens is provided in a micro lens portion of a solid-state imaging device.
[0031]
The configuration of the imaging optical system of the solid-state imaging device shown in FIG. 1 can simplify the imaging optical system or reduce the number of lenses as compared with the configuration of the imaging optical system of the solid-state imaging device shown in FIG. It is possible. This is because the incident angle of the peripheral light beam is sharp relative to the optical axis direction, but by using a deformable lens, the curvature of the micro lens around the solid-state imaging device is reduced and the power is increased. The amount of light is increasing.
[0032]
Hereinafter, description will be made step by step.
[0033]
FIG. 3 is a diagram illustrating a first embodiment of the solid-state imaging device.
[0034]
As shown in the drawing, the vicinity of the center is constituted by a normal microlens made of a conventional resin, and the periphery is constituted by a variable shape lens. Naturally, it is also possible to form the whole with a variable shape lens. Pixels (photodiodes) are arranged in a two-dimensional array on the light-receiving element of the solid-state imaging element unit, and a color filter, a light-shielding film, and an opening are formed thereon, and a microlens is further formed thereon. By changing the curvature between the center and the periphery of the microlens, shading can be corrected, and the angle of the incident light beam to the periphery can be set to, for example, more than the above-described 20 ° to form an imaging optical system.
[0035]
FIG. 4 shows an embodiment in which a liquid lens is used for the microlens portion. The shape of the upper liquid lens corresponding to each pixel is changed in accordance with the speed of light of the imaging optical system to increase the amount of light in the peripheral portion. In this case, even if the imaging optical system is configured to be able to change the magnification (zoom), the use of a variable focus lens enables fine and optimal response to changes in the incident light angle to the solid-state image sensor due to differences in zoom position. It becomes. In the case of a zoom lens, the angle of incidence of a light beam on the solid-state imaging device differs between a short focal length (WIDE) and a long focal length (TELE) (see FIG. 9). In such a case, in a normal microlens, the amount of light incident on a pixel of a solid-state imaging device, particularly, a pixel far from the optical axis differs. Here, if the microlens is formed of a variable focus lens, the curvature can be changed at each position on the focal plane by changing the lens shape according to the incident light angle that changes with the zoom position. It is possible to obtain the maximum light quantity without any.
[0036]
FIG. 5 shows an example of a liquid lens according to the sixth embodiment. The curvature of a liquid lens as disclosed in JP-A-2003-50303 is controlled by an applied voltage. This is a structure in which capacitive energy is stored between an electrode and a conductive liquid lens, and the area that becomes an electrode with respect to the insulating layer on the liquid lens side changes with applied voltage. At this time, the lens is formed in a state of being balanced with the surface tension of the liquid lens, and the curvature changes. With this function, it is possible to form a shape variable lens.
[0037]
FIG. 6 shows an embodiment in which a liquid lens is used as the variable shape lens. In this case, a voltage is applied to each liquid lens to change the shape. Shading is corrected by decreasing the curvature of the liquid lens toward the periphery and increasing the amount of light reaching the photodiode. In addition, even if concentric groups are controlled collectively instead of individually, the same effect can be obtained because the incident angle to the imaging optical system is the same.
[0038]
Note that, in the present embodiment, in the microlens group of the solid-state imaging device, a microlens whose shape is variable only at the peripheral portion may be arranged, or a microlens whose shape is variable only at the center portion may be arranged. Good. Further, all the micro lens groups may be formed of variable shape micro lenses.
[0039]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a solid-state imaging device that is not affected by the incident light angle.
[0040]
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a solid-state imaging device including an imaging optical system.
FIG. 2 is a cross-sectional view of a solid-state imaging device including a variable shape lens of the present invention including an imaging optical system.
FIG. 3 is a diagram showing an arrangement region of a microlens of a solid-state imaging device including the variable shape lens of the present invention.
FIG. 4 is a diagram illustrating an incident light angle on a variable-shape microlens of the present invention.
FIG. 5 is a view for explaining the principle of shape change in the shape variable micro lens of the present invention.
FIG. 6 is a diagram showing a control state of an incident light angle by the variable shape microlens of the present invention.
FIG. 7 is a cross-sectional view of a conventional solid-state imaging device.
FIG. 8 is a graph showing a relationship between a light output and a pixel position of a solid-state imaging device.
FIG. 9 is a diagram illustrating a difference in incident light angle to a solid-state imaging device due to a difference in focal length.
[Explanation of symbols]
71: photodiode 72: light blocking plate 73: color filter 74: micro lens 75: incident light

Claims (6)

In a solid-state imaging device in which a light receiving element group including a plurality of light receiving elements and a micro lens group including a micro lens that forms an image of an object on each light receiving element,
A solid-state imaging device, wherein at least a part of the microlens group is constituted by a shape-variable lens whose shape is variable. 2. The solid-state imaging device according to claim 1, wherein the light amount incident on the light receiving element group is made uniform by the shape variable lens. 2. The solid-state imaging device according to claim 1, wherein an incident direction to a peripheral portion of the light-receiving surface of the solid-state imaging device is inclined in a direction perpendicular to the light-receiving surface. 2. A micro lens at a central portion and / or a peripheral portion of the light receiving surface is a variable shape lens, and a curvature at the central portion is made larger than a curvature at the peripheral portion by changing the lens shape. Fixed solid-state imaging device. The solid-state imaging device according to claim 1, wherein the shape of the shape-variable lens can be changed by voltage or pressure. The solid-state imaging device according to claim 1, wherein a shape of the variable shape lens is changed according to an incident angle at which the light enters the light receiving element.

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