KR20060131508A - Pixel array with mirror symmetry - Google Patents

Abstract

A pixel array is provided to reduce remarkably an allocated area per each unit pixel by using a symmetrical mirror structure. A pixel array includes a plurality of unit pixels, wherein the plurality of unit pixels are arranged like a two-dimensional structure. The plurality of unit pixels of the pixel array are symmetrically arranged by using a virtual horizontal line(H/L) as a first reference. The plurality of unit pixels of the pixel array are symmetrically arranged by using a virtual vertical line(V/L) as a second reference. The virtual horizontal line penetrates a geometrical center position of the pixel array. The virtual vertical line penetrates the geometrical center position of the pixel array.

Description

Pixel Array with mirror symmetry

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the drawings cited in the detailed description of the invention, a brief description of each drawing is provided.

1 shows an angle of incidence of principal rays incident on a CMOS image sensor.

2 shows the photosensitivity of the CMOS image sensor according to the incident angle of the main light beam.

3 is an optical schematic diagram of the principal ray with respect to the pixel.

4 illustrates a pixel array of a mirror symmetric structure according to an embodiment of the present invention.

5 is an example of a mirror symmetric structure according to an embodiment of the present invention.

6 is another example of a mirror symmetric structure according to an embodiment of the present invention.

7A illustrates a portion in which pixels are arranged in the CMOS image sensor.

FIG. 7B is a measure of photosensitivity for three colors of pixels arranged in 640 columns.

FIG. 7C normalizes the photosensitivity for the three colors shown in FIG. 7B.

FIG. 7D is a measure of photosensitivity for three colors of pixels arranged in 512 rows.

FIG. 7E normalizes the photosensitivity for the three colors shown in FIG. 7D.

The present invention relates to a CMOS image sensor, and more particularly, to a CMOS image sensor having a pixel array of mirror symmetry.

The CMOS image sensor is a photosensitive device used in a digital camera and includes a plurality of pixels (hereinafter, referred to as pixels). Each pixel includes a light receiving unit for receiving light applied from the outside and converting the light into a predetermined electric signal, and a data processor for storing and processing the electric signal transmitted from the light receiving unit. do. Above the pixel area, a metal layer having a constant width used as transmission / reception lines of signals used in the data processing device and power voltage lines supplied to the data processing device is located. Color filters are positioned on the metal thin films, respectively. In addition, a micro lens is positioned above the color filter to collect color information output from the color filter.

The light receiver includes a photo diode to receive light applied from the outside. The data processing apparatus processes a data transmitted from a light receiving unit and includes a readout circuit including a plurality of thin film transistors.

The larger the number of pixels, the more precise the digital information corresponding to the input image signal. However, in order to meet the demands of consumers who want to improve the quality even though the size of the digital camera is reduced, the area of the image sensor must be smaller and the number of pixels must be increased. In order to increase the number of pixels included in the limited area of the image sensor, the area occupied by the unit pixel is inevitably reduced. In addition, since there is a limit in reducing the size of the thin film transistors and the width of the metal thin film, which occupy a certain portion of the pixel region, in order to reduce the area of the pixel, the size of the photosensitive region that receives light, that is, the photodiode You can only reduce it.

Thus, if the area allocated to a pixel is reduced,

First, the ratio (open factor, fill factor) of the optical sensitive area to the area of the entire pixel is reduced, thereby reducing the quantum efficiency generated by the input optical particles, and thus the reception capability of the input signal. Reduces the

Second, there is a disadvantage that the photosensitivity of the sensor is largely dependent on the chief ray angel.

These drawbacks have already been found in small camera modules such as camera phones, PDAs.

To overcome this situation, a method of shifting the position of the microlenses (Masaharu Deguchi, Takesuke Maruyama, et al. "Microlens Design Using Simulation Program for CCD Image Sensor", IEEE Transactions on Consumer Electronics, vol. 38, No. 3 , August 1992) or how to optimize the shape of microlenses (Mao-Kuo Wei, Ming-Chang Jung, et al. "Real-time Observations for the Formation of Microlens Arrays Fabricated Using Thermal Reflow Process", Tamkang Journal of Science and Engineering, vol. 7, No. 2, pp. 81-86 (2004)).

The above proposals have all attempted to overcome various disadvantages resulting from the decreasing area of pixels using the microlenses of CMOS image sensors. The method of precisely shifting the position of the microlenses or optimizing the shape of the microlenses has a disadvantage of high cost.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a pixel array having a mirror symmetric structure in which a plurality of pixels have an arrangement structure such that the plurality of pixels are mirrored to each other with a virtual central horizontal line and a virtual central vertical line interposed therebetween.

According to an aspect of the present invention, there is provided a pixel array having a mirror symmetric structure including a pixel array in which a plurality of unit pixels form a two-dimensional array, and the plurality of pixels included in the pixel array includes the pixel array. It is arranged to achieve the same symmetry as reflected on the mirror with respect to the imaginary horizontal line located at, and to achieve the same symmetry as seen on the mirror with respect to the imaginary vertical line located in the pixel array.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings that illustrate preferred embodiments of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

As described above, the pixel readout circuit occupies a certain area of the pixel region, and a photodiode is formed in the remaining portions except for the portion occupied by the pixel readout circuit. The electrical characteristics of the pixel readout circuit should be a value within a certain deviation range through the entire pixels, and the layout of the thin film transistors should be considered very important. Since the layout of the pixel lead-out circuit is made with or without considering other patterns around it, the shape of a square or circle is symmetrical in the form of a photodiode, especially an open window that receives light. It causes the disadvantage of not having.

1 shows an angle of incidence of principal rays incident on a CMOS image sensor.

Referring to FIG. 1, the incident angle of the chief ray is a counterclockwise incident angle θ and a clockwise incident angle with respect to a vertical line with respect to a surface of a CMOS image sensor (CIS). (-θ).

2 shows the photosensitivity of the CMOS image sensor according to the incident angle of the main light beam.

Referring to FIG. 2, the sensitivity of the main ray according to the incident angle is indicated by a solid line. Photosensitive curve according to the change in the incident angle of the main beam incident in the clockwise direction (-θ) indicated on the left (-) of the coordinates and the incident angle of the main beam incident in the counterclockwise direction indicated on the right (+) of the coordinates The photosensitive capacity curve with the change of (θ) has no symmetry. That is, compared with the case where the incident angle (-θ) of the main beam incident in the clockwise direction is increased, the photosensitivity of the case where the incident angle θ of the main beam incident in the counterclockwise direction is increased is relatively bad. In order to compare the symmetry of the photosensitive ability with respect to the incident angle (theta) in the counterclockwise direction and the incident angle (-theta) in the clockwise direction, the curve in symmetry is shown with the thick dotted line.

This shading unbalance effect occurs because the shape of a photodiode, especially an open window that receives light, does not have the shape of a square or circle with symmetry. In particular, in the case of a portable camera module having a unit pixel of less than 3 μm × 3 μm, the above-described asymmetry is not necessary when the absolute value of the incident angle of the principal ray exceeds 20 °. The effect on function is relatively large.

3 is an optical schematic diagram of the principal ray with respect to the pixel.

Referring to FIG. 3, the incident angles of the principal rays at the central pixel, the left edge of the pixel, and the right pixel of the pixel may be known.

Normally, the clockwise incidence angle (-θ) with respect to the left edge portion of the main beam incident through any one point A of the upper center of the pixel and the counterclockwise incidence angle θ with respect to the right edge portion are Only the sign is reversed and the size is the same. Likewise, it can be easily inferred that the angle of incidence to the left edge of the main ray and the angle of incidence to the right edge of the main beam, incident through the two points B, C of the top edge of the pixel, are opposite in sign and of the same magnitude. have.

Referring to the description of FIG. 3 for the normal case, an example of the asymmetry of the photosensitive ability according to the change of the incident angle of the main beam shown in FIG. 2 is that the photosensitive ability of the main beam when the incident angle of the main beam increases counterclockwise is mainly used. This is a bad case compared to the photosensitive ability when the incident angle of the light beam increases in the clockwise direction, and there is a 50% probability that the opposite situation occurs.

In the present invention, it is practically impossible to form a symmetrical form of an open window for receiving light and a change in the photosensitive ability according to the change in the incident angle of the main beam, which is understood through the description of FIGS. 1 to 3. On the premise, a mirror symmetry is proposed for the arrangement method of the pixels in order to relatively alleviate the various adverse effects that may occur in the process of manufacturing the plurality of pixels.

4 illustrates a pixel array of a mirror symmetric structure according to an embodiment of the present invention.

Referring to FIG. 4, the mirror symmetry structure may be divided into four regions A, B, C, and D. FIG. The two regions A and B located at the top and the two regions C and D located at the bottom have the same symmetry as mirrors are projected with an imaginary horizontal line H / L interposed therebetween. The two regions B and C located on the left side and the two regions A and D located on the right side also have the same symmetry as reflected in the mirror with an imaginary vertical line V / L interposed therebetween. The virtual horizontal line (H / L) and the virtual vertical line (V / L) is preferably passed through the geometric intermediate point of the mirror symmetry structure.

In summary, the plurality of pixels included in the area A and the plurality of pixels included in the area B have a mirror symmetrical structure as seen in the mirror based on the boundary line (V / L) of the area A and the area B. . The plurality of pixels included in the area B and the plurality of pixels included in the area C also have a mirror symmetrical structure as reflected in the mirror based on the boundary line H / L of the area B and the area C. The plurality of pixels included in the region C and the plurality of pixels included in the region D also have a mirror symmetrical structure as reflected in the mirror based on the boundary lines V / L of the regions C and D.

Referring to FIG. 4, it will be apparent to those skilled in the art that a method of forming a pixel array having a mirror symmetric structure according to an embodiment of the present invention can also be inferred.

5 is an example of a mirror symmetric structure according to an embodiment of the present invention.

6 is another example of a mirror symmetric structure according to an embodiment of the present invention.

5 and 6, it can be seen that various types of mirror symmetric structures are possible according to the structure of the unit pixel. However, the two examples are identical in that they are arranged to have the same symmetry as mirrored with each other with respect to the virtual horizontal line H / L and the virtual vertical line V / L.

7A illustrates a portion in which pixels are arranged in the CMOS image sensor.

Referring to FIG. 7A, horizontal lines and vertical lines indicate where pixels for which photosensitive capability is to be arranged are arranged.

FIG. 7B is a measure of photosensitivity for three colors of pixels arranged in 640 columns.

Referring to FIG. 7B, the number of pixels arranged in column 640 is 1000, and three colors are RGB (red, green, and blue).

FIG. 7C normalizes the photosensitivity for the three colors shown in FIG. 7B.

Referring to FIG. 7C, it can be seen that the normalized photosensitive capacity curve has a symmetry around an intermediate point.

FIG. 7D is a measure of photosensitivity for three colors of pixels arranged in 512 rows.

Referring to Fig. 7D, the number of pixels arranged in 512 rows is 1200, and the three colors are RGB.

FIG. 7E normalizes the photosensitivity for the three colors shown in FIG. 7D.

7A to 7E, the photosensitive capability of a CMOS image sensor having a pixel array of mirror symmetry according to the present invention is, as originally intended, a plurality of pixels arranged in two dimensions in rows and columns. Have a constant symmetry with respect to the

As described above, optimal embodiments have been disclosed in the drawings and the specification. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not intended to limit the scope of the invention as defined in the claims or the claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, the pixel array of the mirror symmetric structure according to the present invention solves the disadvantage that the aperture ratio decreases and the photosensitivity to the change of the incident angle of the main beam decreases as the area allocated to the pixel decreases. Since it optimizes the layout of the pixels in consideration of the situation, there is an advantage of not having to spend any additional cost of controlling the microlens.

Claims (3)

A pixel array in which a plurality of unit pixels form a two-dimensional array; A plurality of pixels included in the pixel array, Mirror symmetry, characterized in that arranged to achieve the same symmetry as seen in the mirror with respect to the imaginary horizontal line located in the pixel array, and mirror symmetry, characterized in that arranged to achieve the same symmetry as seen in the mirror Pixel array of the structure. The method of claim 1, wherein the imaginary horizontal line, A pixel array having a mirror symmetry structure, characterized in that it penetrates the geometric midpoint of the pixel array. The method of claim 1, wherein the virtual vertical line, A pixel array having a mirror symmetry structure, characterized in that it penetrates the geometric midpoint of the pixel array.

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