Abstract:
An imaging sensor is provided. The imaging sensor includes: a filter array used for extracting a specified color component of an incident light; and photoelectric elements for receiving the incident light via the filter array. The filter array includes: a green filter for extracting a green component; a red filter for extracting a red component; a blue filter for extracting a blue component; and a first infrared filter for extracting a first infrared component for the green component. The first infrared filter is implemented by the green filter and an infrared high-pass filter of a specific wavelength.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an imaging sensor and, in particular, to an image device including red, green, and blue color filters and an infrared (IR) pass filter for better color balance. 
     2. Description of the Related Art 
     Traditional color imagers, image sensors, and pixelated imaging arrays use a Bayer pattern of pixels and pixel filters, which has a red-green-green-blue (R-G-G-B) pixel/filter configuration (shown in  FIG. 1 ). In such pixelated arrays, the sensor includes individual optical filters that transmit red, green or blue colors and that are disposed at or coated on the individual pixels. Thus, there is a “red pixel”  12   a , a “blue pixel”  12   b  and two “green pixels”  12   c  arranged to form a 2×2 sub-array  10  that is repeated over the pixelated array. 
     The three color filters (R, G, and B) not only pass ranges of wavelengths or spectral bands that are corresponding to red, green and blue colors, they also pass through a significant amount of wavelengths in the infrared (IR) or near infrared (NIR) region or band of the spectrum. Therefore, the color imager sensitivity or quantum efficiency spectrum typically has a rich IR or NIR response even with the R, G, and B color pixels. For example, a typical silicon CMOS color sensor&#39;s spectrum response is shown in  FIG. 2 . The spectrum response of the R, G and B pixels (e.g. curves  210 ,  220  and  230 ) is comparable or higher than the pixels&#39; response of visible spectrum. The IR light from the environment thus may wash-out the color response in the visible spectrum and may distort the image color reproduction. This is often referred to as IR contamination. 
     In a traditional color camera, in order to reproduce a true color image, an IR cut-off filter is usually used to cut off or reduce light or energy at or in the IR band or region of the spectrum so as to allow only (or substantially only) the visible light (e.g. light having wavelengths from 390 nm to 700 nm) to pass through the filter so as to be imaged by the RGGB pixels, in order to reduce, limit, or substantially eliminate the IR contamination. Such an IR cut-off filter is typically made of multilayer coatings on a glass or plastic element, such as a flat glass plate, that is added on to a lens assembly of the imager or onto a surface of a lens element of the lens assembly of the imager. The coating process and added material increase the cost of the lens, sometimes significantly 
     BRIEF SUMMARY OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     An imaging sensor is provided. The imaging sensor includes: a filter array used for extracting a specified color component of an incident light; and photoelectric elements for receiving the incident light via the filter array. The filter array comprises: a green filter for extracting a green component; a red filter for extracting a red component; a blue filter for extracting a blue component; and a first infrared filter for extracting a first infrared component for the green component. The first infrared filter is implemented by the green filter and an infrared high-pass filter of a specific wavelength. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a diagram of a typical Bayer pattern; 
         FIG. 2  is a diagram of a silicon CMOS RGB color sensor&#39;s spectrum response; 
         FIG. 3  is a spectrum diagram of the IRP4Gd filter in accordance with an embodiment of the invention; 
         FIG. 4A  is a diagram of the arrangement of the first color mosaic patterns in accordance with an embodiment of the invention; 
         FIG. 4B  is a diagram of the arrangement of the second color mosaic patterns in accordance with another embodiment of the invention; 
         FIG. 5  is a cross-sectional view of an imaging sensor according to a first embodiment of the invention; 
         FIG. 6  is a cross-sectional view of an imaging sensor according to another embodiment of the invention; and 
         FIG. 7  is a cross-sectional view of an imaging sensor according to yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 3  is a spectrum diagram of the IRP4Gd filter in accordance with an embodiment of the invention. The IRP4Gd filter of the present invention is designed to mix the spectrums of the green filter and an IR-pass filter (a high-pass filter) which allows light having a wavelength longer than 650 nm to pass through (hereinafter IR-pass@650 nm is used). For example, the spectrum of the green filter and the IR-pass filter are shown as curves  310  and  320  in  FIG. 3 . The spectrum of the IRP4Gd filter is shown as curve  330  in  FIG. 3 . The IRP4Gd filter can be implemented in 2 ways, such as stacking the green filter and the IR-pass@650 nm filter, or mixing the materials of the green filter and the IR-pass@650 nm filter as a single material. 
     For the color subtraction algorithm provided in the present invention, the spectrum of green, red, and blue color channels can be expressed as follows:
 
 S   G   −S   IRP4Gd   =S   G′V  
 
 S   R   −S   IRP4Rd   =S   R′V  
 
 S   B   −S   IRP4Bd   =S   B′V  
 
where S G , S R , and S B  denote the original signal for the green, red and blue color channels; S IRP4Gd  denotes the signal of the IR-pass filter for green deduction; S IRP4Rd  denotes the signal of the IR-pass filter for red deduction; S IRP4Bd  denotes the signal of the IR-pass filter for blue deduction; and S G′V , S R′V , S B′V  denote the modified (color-balanced) signal for the green, red, and blue color channels, respectively. Specifically, the infrared signal S IRP4Gd , S IRP4Rd , S IRP4Bd  are subtracted from the green, red, and blue color channels, respectively. Thus, no additional IR-cut filter is required in front of the image sensor in the invention, so that the cost of the whole imaging sensor can be reduced and the thickness of camera modules can be thinner.
 
     As described above, the IRP4Gd filter can be implemented by stacking the IR-pass@650 nm filter and the green filter or mixing the materials of the IR-pass@650 nm filter and the green filter. In addition, the IRP4Rd filter can be implemented by the IR-pass@650 nm filter, and the IRP4Bd filter can be implemented by the IR-pass filter which allows light having a wavelength longer than 800 nm to pass (hereinafter IR-pass@800 nm is used). However, the IR-pass@800 nm filter (a high pass filter) can be easily implemented by mixing the materials of the red and blue filters. 
     The imaging sensor of the present invention comprises a two-dimensional pixelated imaging array having a plurality of photo-sensing pixels or photoelectric elements arranged or disposed or established on a semiconductor substrate. For example, the imaging sensor may comprise a complementary-metal-oxide-semiconductor (CMOS) or a CCD imaging sensor or device or the like. The details can be referred to in the following embodiments. 
       FIG. 4A  is a diagram of the arrangement of the first color mosaic patterns in accordance with an embodiment of the invention. As shown in  FIG. 4A , since the IR subtraction algorithm is used, different IR pixels (e.g. IRP4Rd, IRP4Gd, IRP4Bd) can be placed in different locations in an array unit  400 . For example, the array unit  400 A comprises three horizontally adjacent color patterns  410 ,  420  and  430 . The color pattern  410  includes the R, G, B filters and the IRP4Bd filter. The color pattern  420  includes the R, G. B filters and the IRP4Rd filter. The color pattern  430  includes the R, G, B, filter and the IRP4Gd filter. Preferably, each of the color patterns  410 ,  420 , and  430  can also be used as a standalone in some implementations. 
       FIG. 4B  is a diagram of the arrangement of the second color mosaic patterns in accordance with another embodiment of the invention. Alternatively, the color patterns can be arranged in an array unit  400  having a 2×2 window. The array unit  400 B includes color patterns  440 ,  450 ,  460 , and  470 . The color patterns  440 ,  450 , and  460  are similar to the color patterns  410 ,  420  and  430  shown in  FIG. 4A . However, a transparent pixel  471  (i.e. a clear pixel) is included in the color pattern  470 . 
       FIG. 5  is a cross-sectional view of an imaging sensor according to a first embodiment of the invention. The imaging sensor  500  includes a semiconductor substrate  510 , a first layer  520 , and a second layer  530 . Photoelectric elements  511 ˜ 516  for different color channels (e.g. for green, red, blue, IRP4Rd, IRP4Gd, and IRP4Bd colors) are implemented on the semiconductor substrate  510 . The order of color filters from left to right on the first layer  520  is the green filter  521 , red filter  522 , blue filter  523 , IRP4Rd filter  524 , red filter  525 , and green filter  526 . The second layer  530  includes a transparent material  531 , a blue filter  532 , and an IRP4Rd filter  533 . The transparent material  531  covers on the filters  521 ˜ 524  in order to complete the flatness of the coating surface. The blue filter  532  covers on the red filter  525 , and the stacking of the blue filter  532  and the red filter  525  forms the IRP4Bd filter (i.e. B+R) which allows light having a wavelength longer than 800 nm to pass. The IRP4Rd filter  533  covers on the green filter  526 , and the stacking of the IRP4Rd filter  533  and the green filter  526  forms an IRP4Gd filter which allows incident light having a wavelength longer than 650 nm to pass. 
     Specifically, although there are 6 types of color filters, such as R, G, B, IRP4Gd, IRP4Rd, and IRP4Bd filters, the aforementioned six materials can be actually simplified into four materials during the manufacturing of the imaging sensor  500 . For example, since the blue filter  532  has to be disposed on the red filter  525  and the IRP4Rd filter has to be disposed on the green filter  526 , the manufacturing order of the color filters may be the green filters, the red filters, the blue filters and the IRP4Rd filters. After implementing the aforementioned color tilters, a “flatness of coating (FOC)” process is performed, so that the transparent material  531  can be placed on the filters  521 ˜ 524  for a flat surface. 
       FIG. 6  is a cross-sectional view of an imaging sensor according to another embodiment of the invention. The imaging sensor  600  includes a semiconductor substrate  610 , a first layer  620 , and a second layer  630 . Photoelectric elements  611 ˜ 616  for different color channels (e.g. for green, red, blue, IRP4Rd, IRP4Gd, and IRP4Bd colors) are implemented on the semiconductor substrate  610 . The order of color filters from left to right on the first layer  620  is the green filter  621 , red filter  622 , blue filter  623 , IRP4Rd filter  624 , blue filter  625 , and green filter  626 . The second layer  630  includes a transparent material  631 , a red filter  632 , and an IRP4Rd filter  633 . The transparent material  631  covers on the filters  621 ˜ 624  in order to complete the flatness of coating surface. The blue filter  632  covers on the red filter  625 , and the stacking of the red filter  632  and the blue filter  625  forms the IRP4Bd filter (i.e. B+R) which allows light having a wavelength longer than 800 nm to pass. The IRP4Rd filter  633  covers on the green filter  626 , and the stacking of the IRP4Rd filter  633  and the green filter  626  forms an IRP4Gd filter which allows incident light having a wavelength longer than 650 nm to pass. 
     The imaging sensor  600  is similar to the imaging sensor  500 . The difference between the imaging sensors  500  and  600  is that the stacking of the IRP4Bd filter is different. For example, the blue filter  532  is disposed on the red filter  525  in the imaging sensor  500  shown in  FIG. 5 , but the red filter  632  is disposed on the blue filter  625  in the imaging sensor  600  shown in  FIG. 6 . 
       FIG. 7  is a cross-sectional view of an imaging sensor according to yet another embodiment of the invention. Although the materials used in the manufacturing process can be simplified to 4 materials (e.g. R, G, B, and IRP4Rd) in the imaging sensors  500  and  600 , 6 materials can also be used in the imaging sensors  500  and  600 . For example, in addition to the 4 materials for R, G, B and IRP4Rd color channels, the materials for the IRP4Gd and IRP4Bd color channels can also be used in the imaging sensor  700 . In other words, the materials of the blue filter and the red filter can be mixed to generate the material of the IRP4Bd channel, and the materials of the green filter and the IRP4Rd filter can be mixed to generate the material of the IRP4Gd channel. The imaging sensor  700  includes a semiconductor substrate  710 , and a first layer  720 . Photoelectric elements  711 ˜ 716  for different color channels (e.g. for green, red, blue, IRP4Rd, IRP4Bd, and IRP4Gd colors) are implemented on the semiconductor substrate  710 . The order of color filters from left to right on the first layer  720  is the green filter  721 , red filter  722 , blue filter  723 , IRP4Rd filter  724 , IRP4Bd filter  725 , and IRP4Gd filter  726 . The IRP4Bd filter (i.e. B+R) allows light having a wavelength longer than 800 nm to pass, and the IRP4Gd filter allows incident light having a wavelength longer than 650 nm to pass. 
     In view of the above, an imaging sensor is provided. The imaging sensor comprises an infrared filter IRP4Gd for green color deduction, where the IRP4Gd filter is implemented by a mixture or stacking of the materials of the green filter and the 650 nm high pass infrared filter. With the material IRP4Gd filter, the infrared filters for the red and blue color deduction can be implemented using the existing red filter, blue filter, and the IRP4Gd filter, and thus each color channel (e.g. R, G. B) may have its own deduction channel. Accordingly, the imaging sensor of the present invention provides better color balance for the green, red, and blue color channels. Furthermore, no additional IR-cut filter is required in front of the image sensor in the invention, so that the cost of the whole imaging sensor can be reduced and the thickness of camera modules can be thinner. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.