Abstract:
An image sensor is disclosed, in which the image sensor changes the diameter of a lens from a center area of a chip to an edge of it to obtain uniform sensitivity as a whole. The image sensor comprises a plurality of light-receiving portions for converting a signal corresponding to the light of an object to an electric signal, and a pixel array area having a plurality of micro lenses formed above the light-receiving portions and respectively corresponding to the light-receiving portions to focus the light. In the image sensor, the respective micro lenses change their diameters from the center of the pixel array area to the edge of it.

Description:
[0001]    This application claims the benefit of the Korean Application No. 2001-44954 filed on Jul. 25, 2001, which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an image sensor, and more particularly, to an image sensor that increases the diameter of a lens from the center of a chip to its edge to obtain uniform sensitivity as a whole.  
           [0004]    2. Discussion of the Related Art  
           [0005]    Researches to increase the photo sensitivity in manufacturing an image sensor is on the way. As one example of them, there is light-condensing technology.  
           [0006]    For example, an effort for increasing the fill factor(the ratio of a light-receiving portion to the whole image sensor area) is being done to improve the photo sensitivity in a CMOS image sensor having a light-receiving portion for sensing the light and a CMOS logic circuit part where the sensed light is converted to an electric signal to be used as data.  
           [0007]    The problem awaiting solution other than a matter of the fill factor in the light-condensing technology is to overcome a sensitivity difference between areas according to the incident angle.  
           [0008]    This is a critical factor that determines the quality of the equipments required for an extreme near-by pick-up.  
           [0009]    A micro lens construction of a related art image sensor and the photo sensitivity between areas according to light incident angles will be described with reference to the accompanying drawings.  
           [0010]    [0010]FIG. 1 is a sectional block diagram of a related art image sensor, and FIGS. 2A and 2B are block diagrams illustrating light paths respectively in case of a long-distance pick-up and a near-by pick-up.  
           [0011]    In the related art, a micro lens used in a CCD or CMOS image sensor controls a light path and increases a total amount of the light received.  
           [0012]    In other words, in the related art, micro lenses formed on one chip have the same shape and size as one another.  
           [0013]    As shown in FIG. 1, a micro chip  13  has micro lenses  12  which are positioned above light-receiving portions  11  and respectively corresponding to them. Every micro lens  12  has the same diameter ‘III’ and the same height ‘I ’.  
           [0014]    That is, the micro lenses are formed with an identical size whether they are on the center part of the chip or on the edge of it.  
           [0015]    Also, the light-receiving portions  11  are designed in such a way that they have the same size ‘II’ as one another and the distance ‘IV’ between the respective light-receiving portions  11  is uniform whether they are on the center part of the chip or on the edge of it.  
           [0016]    The distance ‘V’ between the micro lenses  12  is designed to be uniform as well.  
           [0017]    In the related art image sensor, the incident angle of the light depends on the position of a chip. Also, the photo sensitivity deteriorates as the incident angle is maximized in case of an extreme near-by pick-up.  
           [0018]    [0018]FIG. 2A is a block diagram illustrating a long-distance pick-up. As shown in FIG. 2A, an incident angle of the light has different degrees as a chip is differently positioned.  
           [0019]    [0019]FIG. 2B is a block diagram illustrating an extreme near-by pick-up. As shown in FIG. 2B, an incident angle is maximized at the edge of a chip.  
           [0020]    A path of the light started from an object  15  is focused by passing through a lens  14  and it has different incident angles on the center part of the image sensor chip  13  from at the edge of it.  
           [0021]    That is, as shown in FIG. 2A, the incident angle θ1 at the edge of the image sensor chip is bigger than the incident angle θ2 on the center part of it. Also, as shown in FIG. 2B, the incident angle θ3 at the edge of the image sensor chip is bigger than the incident angle θ4 on the center part of it.  
           [0022]    The change of the incident angle is more noticeable in case of a near-by pick-up(FIG. 2). Thus, even on the same area of the chip, the light incident angle θ4 is bigger than θ2, and the light incident θ3 is bigger than θ1.  
           [0023]    At this instance, on the part that the incident θ3 is positioned and on its neighboring pixels, the incident angle becomes much more bigger such that the pick-up of the object is difficult as the incident angle goes out of a permissible range.  
           [0024]    That the incident angle differs as its location on the chip changes means that the sensitivity of the light differs on the respective light-receiving portions.  
           [0025]    The related art image sensor, however, has some limitations as follows.  
           [0026]    First, because the micro lenses are identically designed despite of the difference of a light incident angle according to different chip areas, the difference in the photo sensitivity occurs in the areas.  
           [0027]    Second, a pick-up or decoding of information may be impossible. Even though the unevenness caused by the photo sensitivity difference in case of a general pick-up is invisible to the naked eye, when equipments required for an extreme near-by pick-up(e.g., equipments required for a pick-up/detection of a dot code) are used, the characteristic differences caused by the photo sensitivity difference are very big such that a pick-up or decoding of information is impossible.  
         SUMMARY OF THE INVENTION  
         [0028]    Accordingly, the present invention is directed to an image sensor that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
           [0029]    An object of the present invention is to provide an image sensor that changes a diameter of a lens from the center part of a chip to the edge of it, thereby obtaining an even sensitivity as a whole.  
           [0030]    To achieve this object and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the image sensor of the present invention includes a plurality of light-receiving portions for converting a signal corresponding to the light of an object to an electric signal, and a pixel array area having a plurality of micro lenses respectively positioned above their corresponding light-receiving portions to focus the light. The respective micro lenses change their diameters from the center part of the pixel array area to the edge of it.  
           [0031]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0032]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0034]    [0034]FIG. 1 is a sectional block diagram illustrating a related art image sensor;  
         [0035]    [0035]FIGS. 2A and 2B are block diagrams illustrating light paths respectively in case of a long-distance pick-up and a nearby pick-up;  
         [0036]    [0036]FIG. 3 is a plane view illustrating the change of a micro lens diameter of an image sensor in accordance with the present invention;  
         [0037]    [0037]FIG. 4 is a sectional block diagram illustrating an image sensor in accordance with the present invention; and  
         [0038]    [0038]FIG. 5 is a graph illustrating a photo sensitivity difference according to a light incident angle of an image sensor in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0040]    [0040]FIG. 3 is a plane view illustrating the change of a micro lens diameter of an image sensor in accordance with the present invention and FIG. 4 is a sectional block diagram illustrating an image sensor in accordance with the present invention.  
         [0041]    [0041]FIG. 5 is a graph illustrating a photo sensitivity difference according to a light incident angle of an image sensor in accordance with the present invention.  
         [0042]    The construction of a micro lens of an image sensor according to the present invention can be applied to either a CCD image sensor or a CMOS image sensor.  
         [0043]    The micro lens of the present invention is devised to have a longer(or shorter) diameter from the center of the chip to the edge of it to minimize a light incident difference and ultimately to restrain the photo sensitivity difference even in case of an extreme near-by pick-up.  
         [0044]    A micro lens having a diameter which gradually becomes great will be described below.  
         [0045]    The following description is according to a plane view illustrating the micro lens in accordance with the present invention. On the basis of the center of a pixel array area  31 , “A” denotes a diameter of micro lenses positioned on a first micro lens diameter divisional section  32   a  having a first semidiameter from the center. “B” denotes a micro lens diameter positioned on a second micro lens diameter divisional section  32   b , which is started from the circumference of the first micro lens diameter divisional section  32   a , having a second semidiameter(a+b) from the center. The diameter “B” has a longer diameter than “A”. “C” denotes a micro lens diameter positioned on a third micro lens diameter divisional section  32   c , which is started from the circumference of the second micro lens divisional section  32   b , having a third semidiameter(a+b+c) from the center. “C” has a longer diameter than “B”. “D” denotes a micro lens diameter positioned on a fourth micro lens diameter divisional section  32   d , which is started from the circumference of the third micro lens section  32   c , having a fourth semidiameter(a+b+c+d) from the center. “D” has a longer diameter than “C”.  
         [0046]    In this instance, a,b,c, and d may be-defined as the same length, or a&lt;b&lt;c&lt;d, or a&gt;b&gt;c&gt;d.  
         [0047]    Also, each of the micro lens diameter sections can have either a quadrangular shape or a polygonal shape.  
         [0048]    Of course, considering a design margin, not only four micro lens divisional sections  32   a  to  32   d  but also more than four or less than four may be provided.  
         [0049]    Also, the micro lens diameters may be formed to have longer or shorter diameters toward the outer side even in one micro lens divisional section.  
         [0050]    Also, a concave lens can be applied in case that the diameters of the micro lens get shorter from the center to the outer side.  
         [0051]    A sectional construction of an image sensor in accordance with the present invention will be described below.  
         [0052]    As shown in FIG. 4, micro lenses  41  corresponding to respective light-receiving portions  43  are formed. The widths  43   a  to  43   d  of the respective light-receiving portions  43  are equally formed ( 43   a = 43   b = 43   c = 43   d ) regardless of their position on a chip(whether on the center part or an edge area of the chip), and the respective light-receiving portions  43  are spaced apart from each other ( 44   a = 44   b = 44   c ).  
         [0053]    At this time, uniform sensitivity is obtained on the center part and edge of the chip by making the width of the light-receiving portions and the distance between them different within a permissible range of a partial resolution difference on the same screen.  
         [0054]    This includes increasing or decreasing the width of the light-receiving portions and the distance between them from the center to the outer side.  
         [0055]    The diameters  41   a  to  41   d  of the micro lenses increase from the center to the edge of the chip( 41   a &lt; 41   b &lt; 41   c &lt; 41   d ).  
         [0056]    Because of the change of the diameters  41   a  to  41   d  of the micro lenses, the distances  45   a ,  45   b , and  45   c  between adjacent micro lenses increase toward the center of the chip ( 45   a &gt; 45   b &gt; 45   c ).  
         [0057]    The height  42  of the respective micro lenses  41  may be either equal in all the areas or different according to the design margin.  
         [0058]    A curvature change degree of the micro lenses  41  is controlled in such a way that the depth of focus of the light differs in a permissible range. That is, the diameter of the micro lenses  41  changes within the permissible error range of the depth of focus of the light.  
         [0059]    In other words, the micro lenses do not necessarily have the same diameter in all the directions. If a central axis of a micro lens is positioned on a line going towards all directions (e.g., radial type) from the center of the chip), the micro lens can have a shape in which a diameter gradually increases toward the outer side in a complete circle shape.  
         [0060]    That is, if a major axis of the micro lens is positioned on a line going from the edge to the center of the chip, the diameter of the major axis increases toward the edge and a minor axis perpendicular to the major axis is designed to be uniform.  
         [0061]    The features of the photo-sensitivity of the image sensor in accordance with present invention will be described below.  
         [0062]    As shown in FIG. 5, an area  51  in which the incident angle is 0° is a center part of a chip, and an area  52  in which the incident angle is maximized is an edge area of the chip. In this instance, a deviation  53  of sensitivity in accordance with the present invention is very small.  
         [0063]    This means that the photo-sensitivity of the chip is almost even either on the center or on the edge of the chip. Also, because the incident angle of all the directions has a size that belongs to a permissible range even in case of an extreme near-by pick-up, an effective pick-up can be done.  
         [0064]    On the other hand, the related art image sensor has a great sensitivity deviation  54  depending on the incident angle. That is, the sensitivity of the related art image sensor differs when the incident angle is 0° from when the incident angle is within a permissible range (based on 20°). For this reason, all areas except for a portion of the center of the chip have the incident angles out of the permissible range in case of the extreme near-by pick-up, which makes it impossible to pick up the whole object.  
         [0065]    Therefore, the image sensor in accordance with the present invention is devised to change its diameter from the center to the edge of the chip, thus to minimize the incident angle difference and ultimately to reduce the sensitivity difference in the whole area.  
         [0066]    Accordingly, thanks to the evenness of the photosensitivity in the present invention, even in case of the near-by pick-up in which most areas are out of the permissible range of the incident angle, the pick-up and decoding of the object can be done.  
         [0067]    It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.