Abstract:
A new electronic imaging system is achieved. The system comprises a sensor having a first color region, a second color region, and a third color region. A prism system comprises a first prism having a first index of refraction and overlying the first color region. The first prism directs incident light of the first color to the first color region of the sensor. A second prism has a second index of refraction and overlies the second color region. The second prism directs incident light of the second color to the second color region of the sensor. A third prism has a third index of refraction and overlies the third color region. The third prism directs incident light of the third color to the third color region of the sensor.

Description:
[0001]    This application claims priority to U.S. Provisional Application serial No. 60/450,088 filed on Feb. 26, 2003, and herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    (1) Field of the Invention  
           [0003]    The invention relates to color imaging, and, more particularly, to a color-imaging sensor using color prisms.  
           [0004]    (2) Description of the Prior Art  
           [0005]    Several prior art inventions relate to imaging systems. U.S. Pat. No. 6,211,906 B1 to Sun describes an imaging spectrometer system for acquiring ground track images. A modified CCD video imager is provided having a detector array that is spectrally filtered by an attached linear variable interference filter. U.S. Pat. No. 5,333,076 to Wight describes a stabilized imaging system for aerial reconnaissance. Fixed and rotating prisms are used to improve image stability. A linear CCD array is used.  
         SUMMARY OF THE INVENTION  
         [0006]    A principal object of the present invention is to provide an effective and very manufacturable imaging system.  
           [0007]    A further object of the present invention is to provide a means to translate multiple color images into one dimension.  
           [0008]    A yet further object of the present invention is to provide a reduced cost imaging sensor.  
           [0009]    In accordance with the objects of this invention, an electronic imaging system is achieved. The system comprises a sensor having a first color region, a second color region, and a third color region. A prism system comprises a first prism having a first index of refraction and overlying the first color region. The first prism directs incident light of the first color to the first color region of the sensor. A second prism has a second index of refraction and overlies the second color region. The second prism directs incident light of the second color to the second color region of the sensor. A third prism has a third index of refraction and overlies the third color region. The third prism directs incident light of the third color to the third color region of the sensor.  
           [0010]    Also in accordance with the objects of this invention, a method to form an electronic imaging system is achieved. The method comprises forming a plurality of light sensors on a semiconductor wafer. A plurality of prisms is formed overlying the light sensors. Each prism overlies one of the light sensors. Each prism has an index of refraction. Each prism has a height. Each prism directs incident light of a color to the light sensor underlying the prism. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    In the accompanying drawings forming a material part of this description, there is shown:  
         [0012]    [0012]FIGS. 1 through 3 illustrates a preferred embodiment of the present invention showing the formation of the imaging sensor in cross-section.  
         [0013]    [0013]FIG. 4 illustrates the preferred embodiment of the present invention.  
         [0014]    [0014]FIG. 5 illustrates a tri-color sensor of the present invention.  
         [0015]    [0015]FIG. 6 illustrates a single color sensor of the present invention.  
         [0016]    [0016]FIG. 7 illustrates the tri-color sensor in top view.  
         [0017]    [0017]FIG. 8 illustrates a wafer level view of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The preferred embodiments of the present invention disclose an imaging sensor. It should be clear to those experienced in the art that the present invention can be applied and extended without deviating from the scope of the present invention.  
         [0019]    This invention provides a method of separating an incoming light signal into red, green, and blue images translated in one dimension. Solid state sensors can be designed to minimize their bordering dimensions such that three adjacent sensor color regions can be packaged to provide auto registered three color imaging. This reduces the cost of the system and simplifies any correction needed. To further reduce costs, each sensor region is designed to be identical to allow for any three contiguous sensor color regions yielded from a wafer. These “superdie” are cut from the wafer without cutting the regions between the color regions of the sensor.  
         [0020]    By using several optical glass elements with differing indices of refraction, the color components can be separated from each other in a linear fashion. This differs from a standard prism in that the color separation can be performed in a single plane. The optical elements can be fabricated into an assembly by attaching the three glass elements together. Rotational artifacts are not present, and this represents an improvement in traditional 3-CCD assemblies on prisms.  
         [0021]    [0021]FIGS. 1 through 3 illustrated a preferred embodiment of the present invention. Referring particularly to FIG. 1, a cross section of a substrate  10  is shown. Preferably, the substrate  10  comprises a semiconductor material, such as monocrystalline silicon. Referring now to FIG. 2, sensor regions  14 ,  18 , and  22  are formed in the substrate  10 . These sensor regions  14 ,  18 , and  22 , are also called color regions because each region will be used to detect light of a particular color. The sensor regions  14 ,  18 , and  22 , comprise light sensing structures as are known in the art. For example, each color region may comprise a doped region, n-type or p-type, as part of a diode structure. It is known in the art that such diode structures will generate an electrical response to incident light and that this response is proportional to the intensity of the incident light. In the cross section, three color regions  14 ,  18 , and  22 , are depicted. However, preferably, a large number of light sensing regions are formed on the substrate  10 .  
         [0022]    Referring now to FIG. 3, several important features of the present invention are illustrated. A plurality of prisms  26 ,  30 , and  34 , are formed overlying the light sensing regions  14 ,  18 , and  20 . Each prism  26 ,  30 , and  34 , comprises a material with a relative high index of refraction. Preferably, the prisms  26 ,  30 , and  34 , of three adjacent color regions  14 ,  18 , and  22 , are structured to transmit three, different colors. For example, a first prism  26  may be structured to transmit the blue component of incident light to the underlying color region  14 , while a second prism  30  is structured to transmit green light to the underlying color region  18 , and a third prism  34  is structured to transmit red light to the underlying color region  22 . In this scheme, the three adjacent color regions would be structured to especially detect blue, green, and red for a RGB detection scheme.  
         [0023]    Each prism  26 ,  30 , and  34 , for a multiple color sensing imager as shown has a prism length. In the example case, the first prism  26  has a length H1, the second prism  30  has a length H2, and the third prism  34  has a length H3. It is the combination of the length and the index of refraction that causes each prism  26 ,  30 , and  34 , to transmit certain colors of incident light while reflecting other colors. Each prism  26 ,  30 , and  34 , preferably has a topmost surface  38 ,  42 , and  46 , that is at an angle with respect to the topmost surface  39 ,  43 , and  47 , of each color region  14 ,  18 , and  22 . These angled topmost surfaces allow each prism  26 ,  30 , and  34 , to both transmit and reflect incident light as is described below.  
         [0024]    Referring now to FIG. 4, the preferred embodiment of a tri-color (RGB) imaging system is again shown in cross section. The illustration shows a system with a lens  64 , prisms  26 ,  30 , and  34 , and color regions  14 ,  18 , and  22  suitable for use with this invention. Referring to FIG. 7, a top view shows that the overall sensor  10 ′ comprises a blue color region  14 , a green color region  18 , and a red color region  22 . Referring again to FIG. 4, each of the prisms  26 ,  30 , and  34 , has a reflecting surface  38 ,  42 ,  46  corresponding to the topmost surface as described above. A first reflecting surface  38  is on the first prism  26 , a second reflecting surface  42  is on the second prism  30 , and a third reflecting surface  46  is on the third prism  34 . Fill regions  50 ,  54 , and  58  comprise a transparent material and are used to regulate the heights H1-H3 of the prisms.  
         [0025]    In the schematic, the lens  64  focuses polychromatic, external light into a beam  70  incident on the first prism  26 . Polychromatic light is light containing several colors of the visible spectrum as is typically useful in imaging applications. A particular type of polychromatic light is white light that comprises light frequencies across the visible spectrum. The first reflecting surface  38  is designed to reflect about two thirds of the polychromatic incident light beam  70  as the first reflected beam  78  while transmitting about one third of the incident light beam  70  as the first transmitted beam  74 . If the first color region  14  is a blue region, then the blue components of the polychromatic light source  70  are transmitted in the first transmitted beam to the blue color region  14 . The red and green components are reflected by the first reflecting surface  38  as the first reflected beam  78 .  
         [0026]    The second prism  30  is configured such that the first reflected beam  78  will intersect the second reflecting surface  42  of the second prism  30 . Further, the second reflecting surface  42  is designed to transmit about one half of the remaining incident light  70  (the first reflected beam  78 ) and to reflect about one half of the remaining incident light beam  70  (the first reflected beam  78 ) to the second color region  18 . As a result of the first reflected beam  78  intersecting the second reflecting surface  42 , a second reflected beam  82  is directed to the second color region  18  and a second transmitted beam  86  is directed toward the third prism  34 . If the second color region  18  is the green region, then the second reflected beam comprises the green color components of the polychromatic light  70 .  
         [0027]    The third reflecting surface  46  is designed to reflect about all of the remaining incident light beam (the second transmitted beam  86 ) to the third color region  22 . The second transmitted beam  86  intersects the third reflecting surface  46  at the third prism  34  and the reflected light is the third reflected beam  90  that is directed to the third color region  22 . Some light may be transmitted through the third reflecting surface  46  as the third transmitted beam  94 . If the third color region is red, then the third reflected beam  90  comprises the red component of the polychromatic light  70 .  
         [0028]    Referring again to FIG. 3, the prisms  26 ,  30 , and  34  comprise relative high indexes of refraction. The length H1 of the first prism  26  is preferably greater than the length H2 of the second prism  30 . The length H2 of the second prism  30  is preferably greater than the length H3 of the third prism  34 . The indexes of refraction and the lengths are chosen so that mostly blue light reaches the blue region  14  of the sensor  10 , mostly green light reaches the green region  18  of the sensor  10 , and mostly red light reaches the red region  22  of the sensor  10 .  
         [0029]    Referring now to FIG. 5, after the plurality of color regions  14 ,  18 , and  22 , and prisms  26 ,  30 , and  34 , are formed on the substrate  10 , then the substrate  10  can be sawed to form a tri-color sensor  10 ′ as shown. The design of the prisms  26 ,  30 , and  34  allows sensors for the individual component colors (RGB) to be made in-line in a single super die that can be cut from a substrate wafer. This feature removes the need to align the sensors in a packaging step since the color regions of the sensor are aligned when they are formed together on the wafer as was shown in FIG. 7.  
         [0030]    Referring now to FIG. 8, when all of the sensor color regions are the fabricated on a single wafer  310 , then additional economic advantages may be realized. The wafer  310  has 40 color region positions  312 ,  314 ,  316 ,  318 ,  320 ,  322 ,  324 ,  326 , and  328 . A tri-color sensor may be formed according to the present invention by forming a red sensor region  312 , a green sensor region  314 , and a blue sensor region  316  in a row. Further, it is preferred that the sensor regions be tested prior to sawing the wafer into die. In this way, groups of wafers such as the red, green, and blue group  324 ,  326 , and  328 , can be kept together as a single die. That is, the wafer is sawed such that the red, green, and blue sensor regions  324 ,  326 , and  328  are removed as a single, “super die” sensor. Alternatively, if one of the sensor regions of a group is defective then the remaining sensor regions can be sawed and removed to form single, monochromatic sensors  320 . Referring now to FIG. 6, a single color, or monochromatic sensor, is shown with a single color region  18  and prism  30 .  
         [0031]    The advantages of the present invention may now be summarized. An effective and very manufacturable imaging system is achieved. A means to translate multiple color images into one dimension is provided. The resulting sensor has reduced cost.  
         [0032]    As shown in the preferred embodiments, the novel device and method of the present invention provide an effective and manufacturable alternative to the prior art.  
         [0033]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.