CN110112156B - A pixel structure, CMOS image sensor and terminal - Google Patents

Abstract

The embodiment of the application discloses a pixel structure, wherein the pixel structure comprises an optical filter, a photodiode and a reading circuit, wherein the optical filter is used for filtering received incident light to obtain light with a specific wavelength, the photodiode is arranged on one side of the surface, back to the incident light, in the optical filter, the light receiving surface of the photodiode is arranged opposite to the surface, back to the incident light, in the optical filter, the photodiode is used for absorbing the received specific wavelength according to the resonance wavelength of the light receiving surface of the photodiode when the side length of the square light receiving surface in the pixel structure is smaller than the specific wavelength and converting the absorbed light into an electric signal, and the reading circuit is connected with the negative electrode of the photodiode and used for reading the electric signal. The embodiment of the application also provides a CMOS image sensor and a terminal.

Description

A pixel structure, CMOS image sensor and terminal

technical field

The present application relates to a technology for absorbing light by a pixel structure of a Complementary Metal Oxide Semiconductor (CMOS, Complementary Metal Oxide Semiconductor) image sensor in a terminal, and in particular, to a pixel structure, a CMOS image sensor and a terminal.

Background technique

CMOS image sensors are widely used in photography and videography products because of their low manufacturing cost and low power consumption. For CMOS image sensors, higher sensitivity, shorter exposure time and increasingly smaller pixel size have become the development of CMOS image sensors. trend.

At present, the pixel size of the conventional pixel structure is about 800nm, however, when the pixel size is reduced to a wavelength lower than that of natural light, for example, the pixel size is lower than 200nm, the light absorption rate of the photodiode in the pixel structure drops sharply, resulting in absorption The rate is very low, which is not conducive to the imaging of the CMOS image sensor; it can be seen that the existing small-sized pixel structure has the technical problem of low light absorption rate.

SUMMARY OF THE INVENTION

The embodiments of the present application are expected to provide a pixel structure, a CMOS image sensor and a terminal, aiming at improving the light absorption rate of a small-sized pixel structure.

The technical solution of the present application is realized as follows:

An embodiment of the present application provides a pixel structure, the pixel structure includes a filter, a photodiode, and a readout circuit; wherein,

The optical filter is used to filter the received incident light to obtain light of a specific wavelength;

The photodiode is placed on the side of the filter facing away from the surface of the incident light, and the light-receiving surface of the photodiode is placed opposite to the surface of the filter facing away from the incident light, The photodiode is used for absorbing the specific wavelength according to the resonance wavelength of the light receiving surface of the photodiode when the side length of the square light-receiving surface in the pixel structure is smaller than the specific wavelength, and absorbing the specific wavelength. The absorbed light is converted into an electrical signal; wherein, the resonance wavelength is the wavelength at which resonance absorption occurs on the light receiving surface of the photodiode;

The readout circuit is connected to the cathode of the photodiode for reading out the electrical signal.

In the above pixel structure, the specific wavelength is within the range of the resonance wavelength.

In the above pixel structure, the specific wavelength includes any one of the following: red light wavelength, yellow light wavelength, and blue light wavelength.

In the above pixel structure, the area of the light receiving surface of the photodiode is smaller than the area of the square light receiving surface in the pixel structure.

In the above pixel structure, the shape of the light receiving surface of the photodiode includes any one of the following: circle, square, triangle, pentagon and hexagon.

In the above pixel structure, the shape of the photodiode is a cylinder; wherein, the light receiving surface of the photodiode is one of the circular bottom surfaces of the cylinder.

In the above pixel structure, when the light receiving surface of the photodiode is circular, the resonance wavelength of the light receiving surface of the photodiode is positively correlated with the diameter of the circle.

In the above pixel structure, when the specific wavelength is blue light wavelength and the side length of the square light receiving surface in the pixel structure is 100 nm, the diameter of the circular light receiving surface of the photodiode is 70 nm.

Embodiments of the present application further provide a CMOS image sensor, where the CMOS image sensor includes the pixel structure described in one or more of the foregoing embodiments.

An embodiment of the present application further provides a terminal, where the terminal includes the CMOS image sensor described in the foregoing embodiments.

Embodiments of the present application provide a pixel structure, a CMOS image sensor, and a terminal. The pixel structure includes an optical filter, a photodiode, and a readout circuit, wherein the optical filter is used to filter received incident light to obtain a specific wavelength of light, the photodiode is placed on the side of the filter facing away from the surface of the incident light, the light-receiving surface of the photodiode is placed opposite the surface of the filter facing away from the incident light, and the photodiode is used when the pixel structure When the side length of the square light-receiving surface is less than a specific wavelength, the specific wavelength is absorbed according to the resonant wavelength of the light-receiving surface of the photodiode, and the absorbed light is converted into an electrical signal, where the resonant wavelength is the light of the photodiode The wavelength when resonance absorption occurs on the receiving surface, the readout circuit is connected to the negative electrode of the photodiode for reading out the electrical signal; that is, in the embodiment of the present application, after the monochromatic light is filtered by the filter, the When the size of the pixel structure is smaller than the wavelength of the monochromatic light, the resonant wavelength of the light-receiving surface of the photodiode is used to absorb the monochromatic light. In this way, only the resonant wavelength of the light-receiving surface of the photodiode needs to be adjusted, so that the monochromatic light can pass through. The resonant absorption method is absorbed by the photodiode, thereby avoiding the low absorption rate caused by the small pixel structure, and improving the light absorption rate of the small-sized pixel structure, thereby facilitating the imaging of light.

Description of drawings

1 is a schematic structural diagram of a pixel structure;

FIG. 2 is a schematic structural diagram of an optional pixel structure provided by an embodiment of the present application;

3 is a top view of an optional pixel structure provided by an embodiment of the present application;

4 is an absorption spectrum diagram of an optional cylindrical photodiode provided in an embodiment of the present application;

5 is a schematic structural diagram of an optional photodiode with a circular light-receiving surface provided by an embodiment of the present application;

FIG. 6 is a schematic diagram of the arrangement of the polarization directions of light of a specific wavelength corresponding to FIG. 5 according to an embodiment of the present application;

7 is a schematic structural diagram of an optional photodiode with a square light-receiving surface provided by an embodiment of the present application;

8 is a schematic structural diagram of another optional photodiode with a square light-receiving surface provided by an embodiment of the present application;

FIG. 9 is a schematic structural diagram of an optional CMOS image sensor provided by an embodiment of the present application;

FIG. 10 is a schematic structural diagram of an optional terminal provided by an embodiment of the present application.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application.

Example 1

The embodiments of the present application provide a pixel structure.

At present, in practical applications, the pixel structure, as an important part of the CMOS image sensor, can complete the photoelectric conversion of the received natural light to obtain electrical signals. However, when the pixel size of the pixel structure is about 800nm, the The absorption rate of natural light can meet the requirements, but when the pixel size of the pixel structure is about 200 nm, the absorption rate of natural light by the pixel structure is extremely low, which affects the imaging of the CMOS image sensor.

Specifically, FIG. 1 is a schematic structural diagram of a pixel structure. Referring to FIG. 1, a traditional pixel structure is generally composed of three parts, which are a filter, a photodiode and a metal cable. The photodiode is placed in the filter. The side of the film that faces away from the surface of the incident light, and generally, the photodiode made by CMOS technology is in the shape of a cuboid, and the light-receiving surface of the photodiode is placed opposite the surface of the filter that faces away from the incident light. The light receiving surface of the diode is basically the same shape as the filter, and the light receiving surface of the photodiode is the positive electrode of the photodiode, the negative electrode of the photodiode is located on the lower surface of the photodiode, and the negative electrode of the photodiode is connected with the metal cable. So that the metal cable can read out the electrical signal.

In Figure 1, the filter is used to filter natural light to filter out monochromatic light. Then, when the pixel structure is a square light-receiving surface, the side length (equivalent to the above pixel size) is greater than or equal to the wavelength of the monochromatic light. , the photodiode can absorb monochromatic light, convert the absorbed light into an electrical signal, and use the metal cable to read out, so as to realize the imaging of light.

However, when the side length of the square light-receiving surface in the pixel structure is smaller than the wavelength of the monochromatic light, the natural light enters the filter. After filtering, since the wavelength of the monochromatic light is greater than the side length of the pixel structure, it will be diffracted. As a result, light cannot be absorbed, so that the CMOS image sensor cannot image.

In order to improve the light absorption rate of a small-sized pixel structure, an embodiment of the present application provides a pixel structure. FIG. 2 is a schematic structural diagram of an optional pixel structure provided by an embodiment of the present application. Referring to FIG. 2 , the The pixel structure may include a filter 21, a photodiode 22 and a readout circuit 23; wherein,

The filter 21 is used to filter the received incident light to obtain light of a specific wavelength;

The photodiode 22 is placed on the side of the filter 21 facing away from the surface of the incident light. The light receiving surface of the photodiode 22 is placed opposite to the surface of the filter 21 facing away from the incident light. The photodiode 22 is used as a pixel structure. When the side length of the square light-receiving surface is smaller than the specific wavelength, the specific wavelength is absorbed according to the resonance wavelength of the light-receiving surface of the photodiode 22, and the absorbed light is converted into an electrical signal;

The readout circuit 23 is connected to the cathode of the photodiode 22 for reading out electrical signals.

Here, the resonance wavelength is the wavelength at which resonance absorption occurs on the light receiving surface of the photodiode 22 .

Specifically, after the natural light is filtered by the filter, light of a specific wavelength is obtained. When the side length of the square light-receiving surface in the pixel structure is smaller than the specific wavelength, in order to prevent the specific wavelength from being diffracted, a photodiode is used here. The resonant absorption characteristics of the light-receiving surface of the photodiode make the photodiode absorb specific wavelengths according to the resonant wavelength of its light-receiving surface.

The resonant wavelength of the light-receiving surface of the photodiode is related to the refractive index of the light-receiving surface of the photodiode and the size of the light-receiving surface of the photodiode. Therefore, by adjusting the refractive index of the light-receiving surface of the photodiode, and/or , and adjust the size of the light-receiving surface of the photodiode to adjust the resonant wavelength of the light-receiving surface of the photodiode.

Usually, the resonant wavelength of the light receiving surface of the photodiode is adjusted by adjusting the size of the light receiving surface of the photodiode, so that the specific wavelength is within the range of the resonance wavelength of the light receiving surface of the photodiode, so that the light receiving surface of the photodiode is Resonant absorption is achieved in the face of light of a specific wavelength.

That is to say, in the embodiments of the present application, the photodiode can be resonantly absorbed with light of a specific wavelength by utilizing the resonant absorption characteristics of the light receiving surface of the photodiode, thereby improving the light absorption rate of the small-sized pixel structure.

In order to improve the absorption rate of light of a specific wavelength, in an optional embodiment, the specific wavelength is within the range of the resonance wavelength.

Here, the specific wavelength can be a wavelength range, for example, the blue light wavelength. Since the resonant wavelength of the light-receiving surface of the photodiode is related to the shape of the light-receiving surface, the resonant wavelength of the light-receiving surface of different shapes can be a wavelength range, wherein, Part of the specific wavelength may be within the range of the resonance wavelength, or all of the specific wavelength may be within the range of the resonance wavelength. It should be noted that in the light of a specific wavelength, the more light that can achieve resonance absorption, the more light is absorbed. higher rate.

Regarding the above specific wavelength, in an optional embodiment, the light of the specific wavelength includes any one of the following: red light wavelength, yellow light wavelength, and blue light wavelength.

In practical applications, the specific wavelength can be any wavelength of visible light.

Wherein, the above-mentioned filter may be a red filter for filtering red light, a yellow filter for filtering yellow light, or a blue filter for filtering blue light. The application examples are not specifically limited.

In order to make the specific wavelength within the range of the resonance wavelength, in an optional embodiment, the area of the light receiving surface of the photodiode is smaller than the area of the square light receiving surface in the pixel structure.

Specifically, in the traditional pixel structure, the light-receiving surface of the photodiode is basically the same shape as the filter. However, for the small-sized pixel structure, the traditional photodiode structure is used, and the absorption rate of light is extremely low. , in order to improve the light absorption rate, the resonant wavelength of the light receiving surface of the photodiode can be adjusted. Here, the area of the light receiving surface of the photodiode is mainly reduced, and the area of the light receiving surface of the photodiode Light of a specific wavelength on the light-receiving surface of the photodiode is resonantly absorbed.

Wherein, the shape of the light receiving surface of the photodiode includes any one of the following: circle, square, triangle, pentagon and hexagon.

That is to say, the light receiving surface of the photodiode may have a regular shape, for example, a regular polygon, or may have an irregular shape, which is not specifically limited in the embodiments of the present application.

The light-receiving surface of the photodiode is a regular shape, which can be a circle or a square shape. FIG. 3 is a top view of an optional pixel structure provided by an embodiment of the present application. Referring to FIG. 3 , the outer square is For the light-receiving surface of the pixel structure, in order to adjust the resonant wavelength of the light-receiving surface of the photodiode, the light-receiving surface of the photodiode is made into a circle, and the resonant wavelength of the light-receiving surface of the photodiode is adjusted by adjusting the diameter of the circle.

In order to reduce the coupling between the photodiodes, in an optional embodiment, the photodiodes are cylinders;

Wherein, the light receiving surface of the photodiode is one of the circular bottom surfaces of the cylinder.

That is to say, when fabricating a CMOS image sensor, it is necessary to leave a space between the photodiodes in each pixel structure and the photodiodes of the adjacent pixel structures. Since the photodiodes undergo resonance absorption, the fringe field will be very strong, increasing the The spacing is to prevent mutual crosstalk of light between photodiodes of adjacent pixel structures. Therefore, in practical applications, the use of a cylindrical structure in the process can not only achieve resonance absorption of light, but also better control the interval between two adjacent photodiodes.

FIG. 4 is an absorption spectrum diagram of an optional cylindrical photodiode provided by the embodiment of the present application. As shown in FIG. 4 , the abscissa is the absorption wavelength, the ordinate is the absorption rate, and different radii of the bottom surface of the cylinder correspond to different , where, as shown in Figure 4, the radius r=30nm (the short dashed line in Figure 4), r=35nm (the alternate long and short dashed line in Figure 4), r=40nm (the solid line in Figure 4) and r=45nm (dotted line in Fig. 4), and also includes the absorption spectrum corresponding to the conventional photodiode structure (long dotted line in Fig. 4); the simulation in Fig. 4 is based on linearly polarized light.

In order to better adjust the resonant wavelength of the light-receiving surface of the photodiode, in an optional embodiment, when the light-receiving surface of the photodiode is circular, the resonant wavelength of the light-receiving surface of the photodiode is the same as that of the circular light-receiving surface. diameter is positively correlated.

Specifically, for a photodiode with a circular light-receiving surface, FIG. 5 is a schematic structural diagram of an optional photodiode with a circular light-receiving surface provided by an embodiment of the present application, as shown in FIG. 5 , The light-receiving surface of the photodiode is circular; FIG. 6 is a schematic diagram of the arrangement of the polarization directions of light of a specific wavelength corresponding to FIG. 5 provided by the embodiment of the application. As shown in FIG. 6 , since there is no polarization in natural view, In other words, there are polarizations in all directions, so for photodiodes with a circular light-receiving surface, all directions are the same. Therefore, a photodiode with a circular light-receiving surface absorbs the same light as ordinary light.

In addition, considering that the light receiving surface of the photodiode is a square, FIG. 7 is a schematic structural diagram of an optional photodiode with a square light receiving surface provided by an embodiment of the present application. As shown in FIG. The receiving surface is a square; assuming that the side length of the square light receiving surface in the pixel structure is determined to be 100 nm, and the side length of the square light receiving surface of the photodiode is 70 nm, for the polarized light parallel to the square side length (Figure 7 (shown by the straight line with double arrows in ), its resonance position should be similar to that of a circle with a diameter of 70 nm.

FIG. 8 is a schematic structural diagram of another optional photodiode with a square light-receiving surface provided by an embodiment of the present application. As shown in FIG. arrow), its diagonal length is about 100 nm, the corresponding resonance position is red-shifted, and the maximum absorption position moves to long wavelengths (similar to the red-shift of the absorption peak caused by changing the diameter of the bottom of the cylinder in Figure 4) , when the natural light is applied, the final absorption should be similar to the superposition state equivalent to the absorption from r=35nm to r=45nm. Compared with the original spectral line, the half-peak width of the original absorption peak may be broadened. At around 50nm, the absorption peak of squares for natural light may be broadened to 100nm. However, in the case of filters, this is not affected.

For a photodiode with a circular light-receiving surface, the resonance wavelength=refractive index of the light-receiving surface of the photodiode×circular diameter+constant, where the constant is a constant related to the structure of the photodiode.

In order to make the photodiode better achieve resonance absorption, in an optional embodiment, when the specific wavelength is blue light wavelength, and the side length of the square light receiving surface in the pixel structure is 100 nm, the circular light of the photodiode The diameter of the receiving surface is 70 nm.

In practical applications, if the side length of the square light-receiving surface in the pixel structure is determined to be 100 nm, in order to make the wavelength of blue light within the range of the resonance wavelength, the diameter of the circular light-receiving surface of the photodiode can be set to 70 nm. , so that the fabricated small-sized pixel structure can better absorb light and thus better image.

In an example, the side length of the square light-receiving surface in the pixel structure is determined to be 100 nm, and a cylindrical photodiode structure is used. The diameter of the bottom surface of the cylinder is 70 nm, which can absorb 95% of blue light, so that blue monochromatic light imaging can be realized.

The embodiment of the present application provides a pixel structure, the pixel structure includes a filter, a photodiode and a readout circuit, wherein the filter is used to filter the received incident light to obtain light of a specific wavelength, the said The photodiode is placed on the side of the filter facing away from the surface of the incident light, the light-receiving surface of the photodiode is placed opposite the surface of the filter facing away from the incident light, and the photodiode is used in the pixel structure When the side length of the square light-receiving surface is less than a specific wavelength, the specific wavelength is absorbed according to the resonant wavelength of the light-receiving surface of the photodiode, and the absorbed light is converted into an electrical signal, where the resonant wavelength is the light of the photodiode The wavelength when resonance absorption occurs on the receiving surface, the readout circuit is connected to the negative electrode of the photodiode for reading out the electrical signal; that is, in the embodiment of the present application, after the monochromatic light is filtered by the filter, the When the size of the pixel structure is smaller than the wavelength of the monochromatic light, the resonant wavelength of the light-receiving surface of the photodiode is used to absorb the monochromatic light. In this way, only the resonant wavelength of the light-receiving surface of the photodiode needs to be adjusted, so that the monochromatic light can pass through. The resonant absorption method is absorbed by the photodiode, thereby avoiding the low absorption rate caused by the small pixel structure, and improving the light absorption rate of the small-sized pixel structure, thereby facilitating the imaging of light.

Embodiment 2

FIG. 9 is a schematic structural diagram of an optional CMOS image sensor provided by an embodiment of the present application. As shown in FIG. 9 , an embodiment of the present application provides a CMOS image sensor 900 . The CMOS image sensor 900 includes one or more of the above The pixel structure described in the embodiment.

FIG. 10 is a schematic structural diagram of an optional terminal provided by an embodiment of the present application. As shown in FIG. 10 , an embodiment of the present application provides a terminal 1000 . The terminal 1000 includes the CMOS image sensor described in the above embodiment.

As will be appreciated by those skilled in the art, the embodiments of the present application may be provided as a method, a system, or a computer program product. Accordingly, the application may take the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media having computer-usable program code embodied therein, including but not limited to disk storage, optical storage, and the like.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It will be understood that each flow and/or block in the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce Means for implementing the functions specified in a flow or flow of a flowchart and/or a block or blocks of a block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture comprising instruction means, the instructions The apparatus implements the functions specified in the flow or flow of the flowcharts and/or the block or blocks of the block diagrams.

These computer program instructions can also be loaded on a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process such that The instructions provide steps for implementing the functions specified in the flow or blocks of the flowcharts and/or the block or blocks of the block diagrams.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the protection scope of the present application.

Claims (10)

1. A pixel structure, characterized in that the pixel structure comprises a filter, a photodiode and a readout circuit; wherein, The optical filter is used to filter the received incident light to obtain light of a specific wavelength; The photodiode is placed on the side of the filter facing away from the surface of the incident light, and the light-receiving surface of the photodiode is placed opposite to the surface of the filter facing away from the incident light, The photodiode is used for absorbing the specific wavelength according to the resonance wavelength of the light receiving surface of the photodiode when the side length of the square light-receiving surface in the pixel structure is smaller than the specific wavelength, and absorbing the specific wavelength. The absorbed light is converted into an electrical signal; wherein, the resonance wavelength is the wavelength at which resonance absorption occurs on the light receiving surface of the photodiode; The readout circuit is connected to the cathode of the photodiode for reading out the electrical signal. 2 . The pixel structure of claim 1 , wherein the specific wavelength is within the range of the resonance wavelength. 3 . 3 . The pixel structure according to claim 1 , wherein the specific wavelength comprises any one of the following: red light wavelength, yellow light wavelength, and blue light wavelength. 4 . 4 . The pixel structure according to claim 3 , wherein the area of the light receiving surface of the photodiode is smaller than the area of the square light receiving surface in the pixel structure. 5 . 5 . The pixel structure according to claim 4 , wherein the shape of the light receiving surface of the photodiode comprises any one of the following: circle, square, triangle, pentagon and hexagon. 6 . 6 . The pixel structure according to claim 5 , wherein the shape of the photodiode is a cylinder; wherein, the light receiving surface of the photodiode is one of the circular bottom surfaces of the cylinder. 7 . 7 . The pixel structure according to claim 5 , wherein when the light-receiving surface of the photodiode is circular, the resonant wavelength of the light-receiving surface of the photodiode is related to the diameter of the circle. 8 . positive correlation. 8. The pixel structure according to claim 5 or 6, wherein when the specific wavelength is a blue light wavelength, and the side length of the square light-receiving surface in the pixel structure is 100 nm, the photodiode has a The diameter of the circular light-receiving surface was 70 nm. 9 . A complementary metal-oxide-semiconductor CMOS image sensor, characterized in that, the CMOS image sensor comprises the pixel structure of any one of claims 1 to 8 . 10. A terminal, characterized in that the terminal comprises the CMOS image sensor of claim 9.

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