Pixel structure, image sensor, and terminal

Abstract

The present invention discloses a pixel structure, an image sensor and a terminal, belonging to the technical field of image sensor processes. The pixel structure includes a substrate; a floating diffusion region of a first conductivity type, formed in the substrate; at least two photosensitive regions of a second conductivity type with different areas, formed in the substrate, and all the photosensitive regions are distributed around the floating diffusion region and share the floating diffusion region; an isolation region, disposed in the substrate between adjacent photosensitive regions on the same side of the floating diffusion region; and transfer gates, corresponding to each of the photosensitive regions one by one and disposed on the substrates of each of the photosensitive regions. By providing photosensitive regions with different areas in the pixel structure, images with different sensitivities can be obtained through each photosensitive region, and then these images with different sensitivities are synthesized and processed, so that a high-HDR image can be obtained, improving the problem of overexposure or underexposure of images in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of image sensor processes, and particularly relates to a pixel structure, an image sensor, and a terminal. Background Art

[0002] High Dynamic Range Imaging (HDRI or HDR for short) is a technology used to achieve a larger exposure dynamic range (i.e., a larger difference between light and dark) than ordinary digital image technologies. The purpose of high dynamic range imaging is to correctly represent the range of brightness from direct sunlight to the darkest shadows in the real world, providing more dynamic range and image details. For an image sensor, the luminance dynamic range refers to the relative ratio of the highest and lowest values of the electrical signal, which is reflected in a photo as the details that can be shown in the highlight area and the dark area. Therefore, the larger the dynamic range, the richer the levels.

[0003] As Figure 1 A schematic structural diagram of a pixel arrangement in the traditional technology shown. This pixel structure includes: four photosensitive regions 10 arranged in a 2*2 pattern, four relatively arranged transfer gates 11 correspondingly arranged with the photosensitive regions 10, a floating diffusion region 12 located on the side of the four transfer gates 11 facing away from the photosensitive regions 10, and the four photosensitive regions 10 have the same area and share a floating diffusion region 12. Based on the above traditional pixel structure, if you want to improve HDR, you need to take multiple photos with different exposure values and then synthesize them into a high dynamic range photo through software. The usage scenario of this operation method is limited. When the light ratio of the usage scenario (referring to the ratio of the light received by the dark side and the bright side of the object to be photographed in the lighting environment) is too large and the electronic shutter speed of devices such as mobile phones is limited, it is particularly difficult to capture photos with appropriate exposure values for extremely bright and extremely dark areas. And for scenes where the subject moves quickly, taking multiple photos requires a certain interval time, which is also likely to cause subject ghosting and result in failed shooting. Summary of the Invention

[0004] The purpose of the present invention is to provide a pixel structure, an image sensor, and a terminal to solve the problem of limited usage scenarios of HDR.

[0005] To solve the above technical problems, the present invention provides a pixel structure, including:

[0006] A substrate;

[0007] A floating diffusion region of a first conductivity type, formed in the substrate;

[0008] At least two photosensitive regions of a second conductivity type with different areas, formed in the substrate, and all the photosensitive regions are distributed around the floating diffusion region and share the floating diffusion region;

[0009] An isolation region is disposed in the substrate between adjacent photosensitive regions on the same side as the floating diffusion region.

[0010] Transfer gates, corresponding to each of the photosensitive regions one by one and disposed on the substrate of each of the photosensitive regions.

[0011] Preferably, the areas of all the photosensitive regions are in a gradient relationship of decreasing or increasing.

[0012] Preferably, the shape of each of the photosensitive regions is circular, and the photosensitive region with the largest area is located on one side of the floating diffusion region, and the remaining photosensitive regions are located on the other side of the floating diffusion region.

[0013] Preferably, the shape of the floating diffusion region is an arc, and the arc is centered on the center of the photosensitive region with the largest area, and the radius is greater than the radius of the photosensitive region with the largest area.

[0014] Preferably, the diameters of each of the photosensitive regions are 0.5 μm to 10 μm; and / or, the line width of the isolation region is at least 0.2 μm.

[0015] Preferably, the isolation region is an ion doping region of the first conductivity type.

[0016] Preferably, each of the transfer gates is located on the side of the corresponding photosensitive region close to the floating diffusion region.

[0017] The present invention also provides an image sensor, including the pixel structure described in any one of the above.

[0018] Preferably, the image sensor further includes:

[0019] A readout logic circuit, corresponding to the floating diffusion region of the pixel structure one by one and electrically connected to the floating diffusion region, so that the photosensitive regions sharing the same floating diffusion region in the pixel structure share the same readout logic circuit, and further obtain the images of each photosensitive region sharing the same floating diffusion region.

[0020] An image processing circuit, electrically connected to the readout logic circuit, for synthesizing the images of each photosensitive region sharing the same floating diffusion region obtained by the readout logic circuit to obtain the required HDR image.

[0021] The present invention also provides a terminal, including the image sensor described in any one of the above.

[0022] In the pixel structure, image sensor, and terminal provided by the present invention, by providing photosensitive regions with different areas in the pixel structure, and the images of each photosensitive region can be separately formed into photos. Thus, multiple images with different sensitivities can be obtained in one exposure. Obviously, compared with the prior art solution that requires a series of different exposure values for multiple exposures to obtain multiple images with different sensitivities, the operation is simpler. Especially for the scene where the subject moves quickly, multiple images can be taken simultaneously in one shot. Therefore, the problem of ghosting caused by the need to intermittently take multiple images when photographing a moving subject can be avoided.

[0023] Moreover, since the areas of the respective photosensitive regions are different and are set in a gradient manner, and the images of each photosensitive region can be separately formed into photos. Therefore, under the condition that the overall imaging environment is relatively bright, the small photosensitive region can be used to improve the overexposure problem of traditional terminals (such as mobile phones and cameras). At the same time, under the condition that the overall imaging environment is relatively dark, the large photosensitive region can be used to improve the underexposure problem of traditional terminals (such as mobile phones and cameras).

[0024] Furthermore, in actual operation, the multiple images with different sensitivities obtained by using the photosensitive regions with different areas in one exposure can be synthesized and processed into a single high dynamic range (HDR) image, so as to obtain a high HDR image, which can improve the overexposure phenomenon of highlights and avoid local overbrightness or overdarkness of the image. Description of the Drawings

[0025] Figure 1 is a schematic diagram of the pixel structure under the current technology;

[0026] Figure 2 is a schematic diagram of an embodiment of the pixel structure provided by the present invention;

[0027] Figure 3 is a schematic diagram of another embodiment of the pixel structure provided by the present invention.

[0028] In the figure:

[0029] 10. Photosensitive region; 11. Transfer gate; 12. Floating diffusion region; 13. P-type isolation region.

[0030] 14. Photosensitive region; 141. First photosensitive region; 142. Second photosensitive region; 143. Third photosensitive region; 144. Fourth photosensitive region; 145. Fifth photosensitive region; 15. Transfer gate; 16. Floating diffusion region; 17. Isolation region. Detailed Embodiments

[0031] The following further describes in detail the pixel structure, image sensor, and terminal proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description and the claims, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, only for conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention.

[0032] The inventors have found through research that the luminance dynamic range refers to the relative ratio of the highest and lowest values of the electrical signal, and what is reflected in the photo is the details that can be shown in the highlight area and the dark area. The larger the dynamic range, the richer the levels. HDR requires taking a series of photos with different exposure values and synthesizing them into a high-dynamic-range photo through an algorithm. The limitation of traditional HDR is that it is difficult to process scenes with a large light ratio and fast-moving subjects, which easily leads to shooting failures.

[0033] Based on this, the core idea of the present invention is to obtain multiple images with different sensitivities through a single exposure by setting photosensitive areas with different areas, so as to synthesize a high-HDR image.

[0034] Specifically, please refer to Figures 2-3 , which is a schematic diagram of an embodiment of the present invention. As Figure 2 shown, a pixel structure includes:

[0035] A substrate (not shown);

[0036] A floating diffusion region 16 of the first conductivity type, formed in the substrate;

[0037] At least two photosensitive regions 14 of the second conductivity type with different areas, formed in the substrate, and all the photosensitive regions 14 are distributed around the floating diffusion region 16 and share the floating diffusion region 16;

[0038] An isolation region 17, provided in the substrate between adjacent photosensitive regions 14 on the same side of the floating diffusion region 16;

[0039] A transfer gate 15, corresponding to each photosensitive region 14 and provided on the substrate of each photosensitive region 14.

[0040] In this embodiment, at least two photosensitive regions 14 with different photosensitive areas are provided, and the photosensitive regions 14 are provided facing the light incident port (not shown). Further, a filter (not shown) is also provided at the incident port to form at least one specific wavelength of light signal after the light passes through the filter, so that the photosensitive regions 14 in the pixel structure absorb the light signal of the same wavelength.

[0041] As an example, please refer to Figure 2, five photosensitive regions 14 are provided, and the five photosensitive regions 14 are sequentially denoted as a first photosensitive region 141, a second photosensitive region 142, a third photosensitive region 143, a fourth photosensitive region 144, and a fifth photosensitive region 145. Among them, the areas of the first photosensitive region 141, the second photosensitive region 142, the third photosensitive region 143, the fourth photosensitive region 144, and the fifth photosensitive region 145 present a decreasing gradient relationship, and the area of the first photosensitive region 141 is the largest.

[0042] Optionally, the area of the first photosensitive region 141 is similar to or the same as the photosensitive region of a conventional photodiode (i.e., Figure 1 the photosensitive region 10 shown), and its area is, for example, 75 μm 2 ~85 μm 2 . The first photosensitive region 141 enables the pixel structure proposed by the present invention to obtain a sensitivity image under the current technology. At this time, since the areas of the other photosensitive regions 14 are all smaller than that of the first photosensitive region 141 and are all different, images under other sensitivities can be obtained in one exposure. In practical applications, by synthesizing the five images obtained by the first photosensitive region 141, the second photosensitive region 142, the third photosensitive region 143, the fourth photosensitive region 144, and the fifth photosensitive region 145, a high HDR image can be obtained.

[0043] In this embodiment, the number of the photosensitive regions 14 can also be more than or equal to 2 and less than 5, or can be more than 5, and the areas of these photosensitive regions 14 present a gradient decreasing or increasing relationship to obtain multiple images with different sensitivities accordingly. In addition, each of the photosensitive regions 14 can be arranged around the floating diffusion region 16 in a uniform or non-uniform distribution, and the present invention does not make specific limitations thereto. Preferably, the distribution density of the photosensitive regions 14 is greater in the region with a large light input amount to make the obtained image clearer.

[0044] Optionally, the shapes of each of the photosensitive regions 14 can all be circular, and the photosensitive region 14 with the largest area is located on one side of the floating diffusion region 16, and the remaining photosensitive regions 14 are located on the other side of the floating diffusion region 16. The floating diffusion region 16 is in the shape of an arc, and the arc has the center of the photosensitive region 14 with the largest area as the center, and the radius is greater than the radius of the photosensitive region 14 with the largest area.

[0045] In this embodiment, if the photosensitive regions 14 are all circular, then in order to enable each of the photosensitive regions 14 to share the same floating diffusion region 16, the floating diffusion region 16 is an arc structure concentric with the first photosensitive region 141. The floating diffusion region 16 partially surrounds the first photosensitive region 141, and the arc radius of the floating diffusion region 16 is greater than the radius of the first photosensitive region 141.

[0046] As Figure 2In an arrangement of the photosensitive region 14 shown, in a rectangular pixel region (not marked), five circular photosensitive regions 14 are provided. The areas of the first photosensitive region 141, the second photosensitive region 142, the third photosensitive region 143, the fourth photosensitive region 144, and the fifth photosensitive region 145 decrease in sequence. The centers of the first photosensitive region 141 and the second photosensitive region 142 are arranged along the diagonal of the rectangular pixel region, while the remaining third photosensitive region 143, fourth photosensitive region 144, and fifth photosensitive region 145 are respectively arranged on both sides of the diagonal of the rectangular pixel region. That is, the floating diffusion region 16 is arranged along the outer edge of the first photosensitive region 141 (i.e., the first photosensitive region 141 is arranged on one side of the floating diffusion region 16), and the second photosensitive region 142, the third photosensitive region 143, the fourth photosensitive region 144, and the fifth photosensitive region 145 are arranged on the other side of the floating diffusion region 16, and are arranged in an alternating size manner and unevenly distributed.

[0047] As Figure 3 In another arrangement of the photosensitive region 14 shown, in a rectangular pixel region (not marked), five circular photosensitive regions 14 are provided. The areas of the first photosensitive region 141, the second photosensitive region 142, the third photosensitive region 143, the fourth photosensitive region 144, and the fifth photosensitive region 145 decrease in sequence. The first photosensitive region 141 is arranged at or around the geometric center of the rectangular pixel region, and the second photosensitive region 142, the third photosensitive region 143, the fourth photosensitive region 144, and the fifth photosensitive region 145 are respectively arranged on both sides of the diameter parallel to one side of the rectangular pixel region along the first photosensitive region 141. That is, the floating diffusion region 16 is arranged along the outer edge of the first photosensitive region 141 (i.e., the first photosensitive region 141 is arranged on one side of the floating diffusion region 16), and the second photosensitive region 142, the third photosensitive region 143, the fourth photosensitive region 144, and the fifth photosensitive region 145 are arranged on the other side of the floating diffusion region 16. The fourth photosensitive region 144 and the fifth photosensitive region 145 with smaller areas are arranged between the second photosensitive region 142 and the third photosensitive region 143 with larger areas, and are equally spaced.

[0048] In another arrangement of the photosensitive region 14 (not shown), the first photosensitive region 141 is located at the geometric center of the rectangular pixel structure, and the floating diffusion region 16 is arranged around the first photosensitive region 141. The remaining photosensitive regions 14 are arranged radially and evenly or unevenly around the first photosensitive region 141, and isolation regions 17 are provided between the photosensitive regions 14 for isolation. Specifically, the diameters of the respective photosensitive regions 14 are 0.5 μm to 10 μm; and / or, the line width of the isolation region 17 is at least 0.2 μm.

[0049] Specifically, the isolation region 17 is an ion doping region of the first conductivity type.

[0050] In this embodiment, the first conduction type is P-type, the second conduction type is N-type, the conduction type of the isolation region 17 is P-type, and the photosensitive region 14 is N-type.

[0051] Specifically, each transfer gate 15 is located on the side of the corresponding photosensitive region 14 close to the floating diffusion region 16.

[0052] In this embodiment, since the floating diffusion region 16 is shared, the transfer gates 15 are all arranged in the direction of the photosensitive region 14 towards the floating diffusion region 16.

[0053] It should be understood that in this embodiment, to ensure a larger photosensitive area, the shapes of the photosensitive regions 14 are set to be circular. However, the technical solution of the present invention is not limited thereto. In other embodiments of the present invention, the shapes of the photosensitive regions 14 can also be oval, regular polygons or any other suitable irregular shapes.

[0054] An embodiment of the present invention also provides an image sensor, which includes any one of the above pixel structures. The image sensor includes one or more pixel structures given in the above embodiments. The multiple pixel structures form a pixel array according to a specific arrangement. The pixel array includes a plurality of pixels (not shown) arranged two-dimensionally in an array form. Each pixel converts light into charge according to the intensity of the light incident thereon.

[0055] For example, the image sensor can adopt a complementary metal oxide semiconductor (CMOS) photosensitive element or a charge-coupled device (CCD) photosensitive element.

[0056] Optionally, the image sensor of this embodiment further includes:

[0057] A readout logic circuit (not shown), which is arranged in one-to-one correspondence with the floating diffusion regions of the corresponding pixel structures and is electrically connected to the floating diffusion regions, so that the photosensitive regions sharing the same floating diffusion region in the pixel structure share the same readout logic circuit, and further obtain the images of the photosensitive regions sharing the same floating diffusion region;

[0058] An image processing circuit (not shown), which is electrically connected to the readout logic circuit and is used to synthesize the images of the photosensitive regions sharing the same floating diffusion region obtained by the readout logic circuit to obtain the required HDR image.

[0059] Among them, signals obtained from a number of photosensitive areas 14 with different photosensitive areas are output through a readout logic circuit, so as to obtain images of each photosensitive area 14. Further, each image is processed and synthesized through an image processing circuit to obtain a high HDR image, thereby improving high-light overexposure and avoiding local over-brightness or over-darkness of the image.

[0060] An embodiment of the present invention further provides a terminal, including the above-mentioned image sensor. The terminal can be a mobile phone, a tablet computer, a notebook computer, a smart wearable device (such as a smart watch, a smart bracelet, smart glasses, a smart helmet, etc.), a head-mounted display device, a virtual reality device, etc., which are not limited herein.

[0061] In summary, in the pixel structure, image sensor and terminal provided by the embodiments of the present invention, by setting photosensitive areas with different areas in the pixel structure, and images of each photosensitive area can be separately formed into photos. Thus, multiple images with different sensitivities can be obtained in one exposure. Obviously, compared with the prior art solution that requires a series of different exposure values for multiple exposures to obtain multiple images with different sensitivities, the operation is simpler. Especially for the scene where the main body moves quickly, multiple images can be taken at the same time in one shot. Therefore, the problem of ghosting caused by the need to intermittently take multiple images when shooting a moving main body can be avoided. Moreover, since the areas of the respective photosensitive areas are different and are set in a gradient manner, and images of each photosensitive area can be separately formed into photos. Therefore, under the condition that the overall shooting environment is relatively bright, the small photosensitive area can be used to improve the overexposure problem of traditional terminals (such as mobile phones, cameras). At the same time, under the condition that the overall shooting environment is relatively dark, the large photosensitive area can be used to improve the underexposure problem of traditional terminals (such as mobile phones, cameras).

[0062] The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention in any way. Any changes and modifications made by those of ordinary skill in the art of the present invention according to the above disclosure shall fall within the protection scope of the claims.

Claims

1. A pixel structure, characterized in that, it includes: a substrate; a floating diffusion region of a first conductivity type, formed in the substrate; at least two photosensitive regions of a second conductivity type with different areas, formed in the substrate, all the photosensitive regions are distributed around the floating diffusion region and share the floating diffusion region; an isolation region, arranged in the substrate between adjacent photosensitive regions on the same side of the floating diffusion region; transfer gates, corresponding to each of the photosensitive regions one by one and arranged on the substrate of each of the photosensitive regions; the shapes of all the photosensitive regions are circular, and the photosensitive region with the largest area is located on one side of the floating diffusion region, and the remaining photosensitive regions are located on the other side of the floating diffusion region. The shape of the floating diffusion region is an arc, and the arc takes the center of the photosensitive region with the largest area as the center, and the radius is greater than the radius of the photosensitive region with the largest area.

2. The pixel structure according to claim 1, characterized in that, the areas of all the photosensitive regions have a gradient relationship of decreasing or increasing.

3. The pixel structure according to claim 1, characterized in that, the diameters of each of the photosensitive regions are 0.5 μm to 10 μm respectively; and / or, the line width of the isolation region is at least 0.2 μm.

4. The pixel structure according to claim 3, characterized in that, the isolation region is an ion doping region of a first conductivity type.

5. The pixel structure according to claim 1, characterized in that, each of the transfer gates is located on the side of the corresponding photosensitive region close to the floating diffusion region.

6. An image sensor, characterized in that, it includes the pixel structure according to any one of claims 1-5.

7. The image sensor according to claim 6, characterized in that, it further includes: a readout logic circuit, arranged corresponding to the floating diffusion region of the pixel structure one by one and electrically connected to the floating diffusion region, so that the photosensitive regions sharing the same floating diffusion region in the pixel structure share the same readout logic circuit, and further obtain the images of each photosensitive region sharing the same floating diffusion region; an image processing circuit, electrically connected to the readout logic circuit, for synthesizing the images of each photosensitive region sharing the same floating diffusion region obtained by the readout logic circuit to obtain the required HDR image.

8. A terminal, characterized in that, it includes the image sensor according to claim 6 or claim 7.

Images