Abstract:
A miniature image capture lens is disclosed, comprising a wafer scale lens system, which comprises a first lens group including a first substrate, a first surface disposed on a first side of the first substrate, a second surface disposed on a second side of the first substrate, and a second lens group including a second substrate, a third surface disposed on a first side of the second substrate, and a fourth surface disposed on a second side of the second substrate, wherein the first surface, the second surface, the third surface and the fourth surface are aspherical, one of the first surface and the second surface, and one of the third surface and the fourth surface have a high refraction index Nd_h and a high abbe number Vd_h, another one of the first surface and the second surface, and another one of the third surface and the fourth surface have a low refraction index Nd_l and a low abbe number Vd_l, and the miniature image capture lens meets the following conditions:
 
 Nd   —   h =1.58˜1.62;
 
 Nd   —   l =1.48˜1.53;
 
 Nd   —   l/Nd   —   h =0.91˜0.97;
 
 Vd   —   h =35˜45; and
       Vd_l=25˜35, wherein one of the first and second surfaces is convex shaped and another one of the first and second surfaces is concave shaped, and one of the third and fourth surfaces is convex shaped and another one of the third and fourth surfaces is concave shaped.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a lens system, and more particularly relates to a wafer scale miniature image capture lens system. 
     2. Description of the Related Art 
     Mobile phones or personal computers employing imaging devices have become popular due to employment of solid-state image capture elements such as CCD (a charged coupled device) type image sensors, CMOS (a complementary metal oxide semiconductor) type image sensors and the like, allowing for higher performance and miniaturization of imaging devices. Additionally, there is demand for further miniaturization of image capture lenses loaded on the imaging devices. 
     However, despite demands, limits for further miniaturization of image capture lenses are being reached. As for the conventional image capture lenses, because they are true three dimensional structures and sensors therein need to also be miniaturized, it is difficult to control accuracy of lateral shift and tilt for each lens surface and fabrication thereof. Namely, fabrication tolerance is decreased. 
       FIG. 1  shows an imaging device using a published wafer scale lens module system. Light passes through the wafer scale lens modules  102  and  104  to the sensing element  106 . In this art, the wafer scale lens modules  102  and  104  and the sensing element  106  can be fabricated by VLSI process technologies. Therefore, the image device can have a smaller size suitable for portable electronic devices, such as cell phones or personal digital assistants (PDAs). The wafer scale lens allows for further miniaturization along with technological advances driven by semiconductor processes such as Moore&#39;s law, as accuracy control is better. Moreover, while conventional lenses are fabricated by a discrete process, which assembles the lenses one by one, in contrast, the wafer scale lens is fabricated by a batch process, which can stack thousands of lens on a lens plate into a lens module array. However, despite the smaller volume, it is difficult to design a wafer scale optical lens system with good performance and high enough tolerance. Therefore, a wafer scale lens system with good performance and high tolerance is required. 
     Wafer scale optics has a lot of design constraints due to glass substrate structure and replication process limitations, such as limitations with lens material, substrate thickness, lens sag height and size, optical center alignment accuracy etc. For wafer scale lenses to become as main stream and as popular as plastic and glass lenses, wafer scale lens modules must have comparable optical design performance in accordance with appropriate manufacturing tolerance for the above described design constraints. 
     BRIEF SUMMARY OF INVENTION 
     According to the issues described, the invention provides a miniature image capture lens, comprising an aperture diaphragm having an aperture through which an image is captured and a wafer scale lens system. The wafer scale lens system comprises a first lens group including a first substrate, a first surface disposed on a first side of the first substrate, a second surface disposed on a second side of the first substrate, and a second lens group including a second substrate, a third surface disposed on a first side of the second substrate, and a fourth surface disposed on a second side of the second substrate, wherein the first surface, the second surface, the third surface and the fourth surface are aspherical, one of the first surface and the second surface, and one of the third surface and the fourth surface have a high refraction index Nd_h and a high abbe number Vd_h, another one of the first surface and the second surface, and another one of the third surface and the fourth surface have a low refraction index Nd_l and a low abbe number Vd_l, the high refraction index Nd_h is greater than the low refraction index Nd_l, and the high abbe number Vd_h is greater than the low abbe number Vd_l, and the miniature image capture lens meets the following conditions:
 
 Nd   —   h= 1.58˜1.62;
 
 Nd   —   l= 1.48˜1.53;
 
 Nd   —   l/Nd   —   h= 0.91˜0.97;
 
 Vd   —   h= 35˜45; and
 
 Vd   —   l= 25˜35
         wherein one of the first and second surfaces is convex shaped and another one of the first and second surfaces is concave shaped, and one of the third and fourth surfaces is convex shaped and another one of the third and fourth surfaces is concave shaped.       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows an imaging device using a published wafer scale lens module system. 
         FIG. 2A  shows a lens design of a first embodiment of the invention. 
         FIG. 2B  shows a lens design of a second embodiment of the invention. 
         FIG. 2C  shows a lens design of a third embodiment of the invention. 
         FIG. 2D  shows a lens design of a fourth embodiment of the invention. 
         FIG. 2E  shows a lens design of a fifth embodiment of the invention. 
         FIG. 2F  shows a lens design of a sixth embodiment of the invention. 
         FIG. 2G  shows a lens design of a seventh embodiment of the invention. 
         FIG. 2H  shows a lens design of an eighth embodiment of the invention. 
         FIG. 3  shows a lens design of an example of the invention. 
         FIG. 4  shows an exploded view of an example of the invention. 
         FIG. 5  shows aberration curves of a miniature image capture lens of an example of the invention. 
         FIG. 6  shows lateral color of a miniature image capture lens of an example of the invention. 
         FIG. 7A  shows field curvature of a miniature image capture lens of an example of the invention. 
         FIG. 7B  shows distortion of a miniature image capture lens of an example of the invention. 
         FIG. 8  shows relative illumination of a miniature image capture lens of an example of the invention. 
         FIG. 9A  shows tangential lines of tolerance analysis of an example of the invention. 
         FIG. 9B  shows sagittal lines of tolerance analysis of an example of the invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The following descriptions are of the contemplated mode of carrying out the invention. This descriptions are made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense, not for limiting the invention. 
     The invention is related to a wafer scale lens system which includes two-side optical surfaces on opposite sides of a glass substrate. The two surfaces of the lens of the invention can be made of two different materials, where one has a high refractive index and the other has a low refractive index and the lens material can be a UV curable polymer compound. As well, the invention provides a two-side wafer scale lens, and the lens presents high and low refraction index for the surfaces at either sides and has convex and concave shapes at either sides to minimize optical dispersion. Note that the high and low refraction index for the surfaces at either sides of the substrate can be achieved by using different materials for the surfaces on opposite sides of the glass substrate. 
     According to the design rules above, the lens structure of the invention can be designed to have different materials having different refraction indices at two sides and also have convex and concave shapes at either sides. Therefore, there are eight possible lens designs of the lens module of the invention, including (+h, −l, +h, −l), (+l, −h, +l, −h), (+h, −l, −l, +h), (+l, −h, −h, +l), (−h, +l, +l, −h), (−l, +h, +h, −l), (−h, +l, −h, +l), and (−l, +h, −l, +h), wherein +h means positive curvature and high refraction index, −h means negative curvature and high refraction index, +l means positive curvature and low refraction index, and −l means negative curvature and low refraction index. 
     Referring to  FIG. 2A , which shows a lens design of a first embodiment of the invention, a first substrate  202  and a second substrate  210  are provided, and a first surface  204  is disposed on the first side of the first substrate  202 , a second surface  206  is disposed on a second side of the first substrate  202  to constitute a first lens group  208 , a third surface  212  is disposed on the first side of the second substrate  210 , and a fourth surface  214  is disposed on the second side of the second substrate  210  to constitute a second lens group  216 . In the embodiment, the first surface  204  has high refraction index Nd_h, high abbe number Vd_h and convex shaped (positive curvature), the second surface  206  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature), the third surface  212  has high refraction index Nd_h, high abbe number Vd_h and convex shaped (positive curvature), and the fourth surface  214  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature). 
     Referring to  FIG. 2B , which shows a lens design of a second embodiment of the invention, a first substrate  218  and a second substrate  226  are provided, and a first surface  220  is disposed on the first side of the first substrate  218 , a second surface  222  is disposed on a second side of the first substrate  218  to constitute a first lens group  224 , a third surface  228  is disposed on the first side of the second substrate  226 , and a fourth surface  230  is disposed on the second side of the second substrate  226  to constitute a second lens group  232 . In the embodiment, the first surface  220  has low refraction index Nd_l, low abbe number Vd_l and convex shaped (positive curvature), the second surface  222  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature), the third surface  228  has low refraction index Nd_l, low abbe number Vd_l and convex shaped (positive curvature), and the fourth surface  230  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature). 
     Referring to  FIG. 2C , which shows a lens design of a third embodiment of the invention, a first substrate  234  and a second substrate  242  are provided, and a first surface  236  is disposed on the first side of the first substrate  234 , a second surface  238  is disposed on a second side of the first substrate  234  to constitute a first lens group  240 , a third surface  244  is disposed on the first side of the second substrate  242 , and a fourth surface  246  is disposed on the second side of the second substrate  242  to constitute a second lens group  248 . In the embodiment, the first surface  236  has high refraction index Nd_h, high abbe number Vd_h and convex shaped (positive curvature), the second surface  238  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature), the third surface  244  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature), and the fourth surface  246  has high refraction index Nd_h, high abbe number Vd_h and convex shaped (positive curvature). 
     Referring to  FIG. 2D , which shows a lens design of a fourth embodiment of the invention, a first substrate  250  and a second substrate  258  are provided, and a first surface  252  is disposed on the first side of the first substrate  250 , a second surface  254  is disposed on a second side of the first substrate  250  to constitute a first lens group  256 , a third surface  260  is disposed on the first side of the second substrate  258 , and a fourth surface  262  is disposed on the second side of the second substrate  258  to constitute a second lens group  264 . In the embodiment, the first surface  252  has low refraction index Nd_l, low abbe number Vd_l, and convex shaped (positive curvature), the second surface  254  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature), the third surface  260  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature), and the fourth surface  262  has low refraction index Nd_l, low abbe number Vd_l and convex shaped (positive curvature). 
     Referring to  FIG. 2E , which shows a lens design of a fifth embodiment of the invention, a first substrate  266  and a second substrate  274  are provided, and a first surface  268  is disposed on the first side of the first substrate  266 , a second surface  270  is disposed on a second side of the first substrate  266  to constitute a first lens group  272 , a third surface  276  is disposed on the first side of the second substrate  274 , and a fourth surface  278  is disposed on the second side of the second substrate  274  to constitute a second lens group  280 . In the embodiment, the first surface  268  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature), the second surface  270  has low refraction index Nd_l, low abbe number Vd_l and convex shaped (positive curvature), the third surface  276  has low refraction index Nd_l, low abbe number Vd_l and convex shaped (positive curvature), and the fourth surface  278  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature). 
     Referring to  FIG. 2F , which shows a lens design of a sixth embodiment of the invention, a first substrate  282  and a second substrate  290  are provided, and a first surface  284  is disposed on the first side of the first substrate  282 , a second surface  286  is disposed on a second side of the first substrate  282  to constitute a first lens group  288 , a third surface  292  is disposed on the first side of the second substrate  290 , and a fourth surface  294  is disposed on the second side of the second substrate  290  to constitute a second lens group  296 . In the embodiment, the first surface  284  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature), the second surface  286  has high refraction index Nd_h, high abbe number Vd_h and convex shaped (positive curvature), the third surface  292  has high refraction index Nd_h, high abbe number Vd_h and convex shaped (positive curvature), and the fourth surface  294  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature). 
     Referring to  FIG. 2G , which shows a lens design of a seventh embodiment of the invention, a first substrate  298  and a second substrate  257  are provided, and a first surface  251  is disposed on the first side of the first substrate  298 , a second surface  253  is disposed on a second side of the first substrate  298  to constitute a first lens group  255 , a third surface  259  is disposed on the first side of the second substrate  257 , and a fourth surface  261  is disposed on the second side of the second substrate  257  to constitute a second lens group  263 . In the embodiment, the first surface  251  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature), the second surface  253  has low refraction index Nd_l, low abbe number Vd_l and convex shaped (positive curvature), the third surface  259  has high refraction index Nd_h, high abbe number Vd_h and concave shaped (negative curvature), and the fourth surface  261  has low refraction index Nd_l, low abbe number Vd_l and convex shaped (positive curvature). 
     Referring to  FIG. 2H , which shows a lens design of a eighth embodiment of the invention, a first substrate  265  and a second substrate  273  are provided, and a first surface  267  is disposed on the first side of the first substrate  265 , a second surface  269  is disposed on a second side of the first substrate  265  to constitute a first lens group  271 , a third surface  275  is disposed on the first side of the second substrate  273 , and a fourth surface  277  is disposed on the second side of the second substrate  273  to constitute a second lens group  279 . In the embodiment, the first surface  267  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature), the second surface  269  has high refraction index Nd_h, high abbe number Vd_h and convex shaped (positive curvature), the third surface  275  has low refraction index Nd_l, low abbe number Vd_l and concave shaped (negative curvature), and the fourth surface  277  has high refraction index Nd_h and convex shaped (positive curvature). 
     Specifically, the first surface, the second surface, the third surface and the fourth surface are aspherical and the miniature image capture lens meets the following conditions:
 
 Nd   —   h= 1.58˜1.62;
 
 Nd   —   l= 1.48˜1.53;
 
 Nd   —   l/Nd   —   h= 0.91˜0.97;
 
 Vd   —   h= 35˜45; and
 
 Vd   —   l= 25˜35
 
     Referring to  FIG. 3 , which shows a lens design of a example of the invention, the miniature image capture lens from the image to be captured (not shown) to an image plane  322  (or sensor) comprises a front cover glass  302 , a first lens group  310  including a first substrate  306 , a first surface  304  and a second surface  308  at opposite sides of the first substrate  306 , a second lens group  318  including a second substrate  312 , a third surface  314  and a fourth surface  316  at opposite sides of the second substrate  312 , and a back cover glass  320 . The first surface  304  and the third surface  314  have low refraction index, and the second surface  308  and the fourth surface  316  have high refraction index. In more detail, the first surface  304  has a center thickness d 1  of 100 μm, the third surface  314  has a center thickness d 2  of 169 μm, and the fourth surface  316  has an edge thickness d 3  of 125 μm. The third surface  314  has an aspect ratio of 0.14, and the fourth surface  316  has an aspect ratio of 0.07. Note that the first and second surfaces  304 ,  308  have aspect ratios that are less than that of the third and fourth surfaces  314 ,  316  in the example. Therefore, aspect ratios of the first and second surfaces  304 ,  308  are not a critical condition during fabrication and are not specifically described in the example. The distance from the fourth surface  316  to the image plane  322  is 0.55 mm and the miniature image capture lens has a total track length of 2.5 mm. The front cover glass  302  includes an aperture diaphragm having an aperture through which an image is captured and a IR cut filter can be coated on the front cover glass  302  or on the first surface  304  of the first lens group  310 . Also referring to  FIG. 4 , which shows an exploded view of the example, the miniature image capture lens comprises a front cover glass  302 , a spacer dam  305 , a first lens group  310  including a first surfaces  304 , a first substrate  306  and the second surfaces  308 , a first spacer  311 , a second lens group  318  including a third surfaces  312 , a second substrate  314  and the fourth surfaces  316 , a second spacer  319 , and a back cover glass  320  from the top side to the bottom side. It is noted that the invention does not specifically limit the arrangement of the IR cut filter. For example, the IR cut filter can be formed on the front cover glass  302  or on the first surface  304  of the miniature image capture lens. 
     Referring in  FIG. 5 , which shows aberration curves of a miniature image capture lens of the example of the invention, the miniature image capture lens of the invention can achieve a small enough aberration. Referring in  FIG. 6 , which shows lateral color of a miniature image capture lens of the example of the invention, the miniature image capture lens of the invention can achieve good color aberration aspect performance. Referring in  FIGS. 7A and 7B , wherein  FIG. 7A  shows field curvature of a miniature image capture lens of the example of the invention and  FIG. 7B  shows distortion of a miniature image capture lens of the example of the invention, the miniature image capture lens of the invention can achieve both good field curvature and distortion aspect performances. Referring in  FIG. 8 , which shows relative illumination of a miniature image capture lens of the example of the invention, the miniature image capture lens of the invention can achieve good illumination aspect performance. Referring in  FIGS. 9A and 9B , wherein  FIG. 9A  shows tangential lines of tolerance analysis, and  FIG. 9B  shows sagittal lines of tolerance analysis and the tolerance analysis is based on ±10 μm decenter error, the yield rate can be as high as nearly 100% according to the criteria MTF&gt;40 for a 0.8 field at ¼ Nyquist frequency. 
     According to the description above, the miniature image capture lens of the invention at least has the advantages as follows. First, the invention can form lens modules with different materials on different sides of the substrate to minimize optical dispersion. Specifically, the cost of fabricating the lens module is not substantially increased, because even for conventional wafer scale lens modules, the surfaces on the opposites of the substrate have to be formed in different process steps. Second, the IR cut filter can be coated on surfaces of the glass substrate. Third, the invention can achieve lens modules with shorter optical track length. 
     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. To 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.