Patent Publication Number: US-2010123209-A1

Title: Apparatus and Method of Manufacture for Movable Lens on Transparent Substrate

Description:
FIELD OF THE INVENTION 
     Embodiments described herein relate generally to imaging devices incorporating Micro-Electrical-Mechanical Systems (MEMS) technology. 
     BACKGROUND OF THE INVENTION 
     As wireless telephones and cameras decrease in size, there is an increased demand to use smaller lenses for the imaging modules included in these devices. In addition, it is desired that the small lenses retain mobility for operations such as automatic focus. To meet the increased need for smaller lenses with retained mobility, MEMS technology has been incorporated into lens stacks. 
     The process of manufacturing lens stacks incorporating MEMS technology is, however, expensive because the MEMS structures and lenses are created in separate processes, and then the two are combined in a subsequent process. In addition, the lens stacks use silicon or light inhibiting substrates between lenses that require the creation of an opening to allow for the full transfer of light through the lens stack. Such an opening, however, may be highly reflective and may cause undesirable stray light rays. 
     What is needed is an imaging module and method of manufacturing the module that directly replicates the lens onto a MEMS structure with a transparent substrate in the optical path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a lens stack according to an embodiment described herein. 
         FIG. 1B  shows a lens stack according to an embodiment described herein. 
         FIG. 1C  shows a top-down view of a lens stack according to an embodiment described herein. 
         FIG. 2A  shows a portion of a lens stack at an initial stage of processing according to an embodiment described herein. 
         FIG. 2B  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 2A . 
         FIG. 2C  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 2B . 
         FIG. 2D  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 2C . 
         FIG. 2E  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 2D . 
         FIG. 3A  shows a portion of a lens stack at an initial stage of processing according to an embodiment described herein. 
         FIG. 3B  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 3A . 
         FIG. 3C  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 3B . 
         FIG. 3D  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 3C . 
         FIG. 3E  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 3D . 
         FIG. 4A  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 3A . 
         FIG. 4B  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 4A . 
         FIG. 4C  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 4B . 
         FIG. 5A  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 3A . 
         FIG. 5B  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 5A . 
         FIG. 5C  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 5B . 
         FIG. 6A  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 3A . 
         FIG. 6B  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 6A . 
         FIG. 6C  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 6B . 
         FIG. 6D  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 6C . 
         FIG. 7A  shows a portion of a lens stack at an initial stage of processing according to an embodiment described herein. 
         FIG. 7B  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 7A . 
         FIG. 7C  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 7B . 
         FIG. 7D  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 7C . 
         FIG. 8A  shows a portion of a lens stack at an initial stage of processing according to an embodiment described herein. 
         FIG. 8B  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 8A . 
         FIG. 8C  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 8B . 
         FIG. 8D  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 8C . 
         FIG. 8E  shows a portion of a lens stack at a stage of processing subsequent to that shown in  FIG. 8D . 
         FIG. 9  shows a lens stack according to an embodiment described herein. 
         FIG. 10  shows an imaging module according to an embodiment described herein. 
         FIG. 11  shows digital camera according to an embodiment described herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, reference is made to various embodiments that are described with sufficient detail to enable those skilled in the art to practice them. It is to be understood that other embodiments may be employed, and that various structural or logical changes may be made. 
     Embodiments described herein related to lens stacks and methods of their manufacture. In desired embodiments, the lens stacks use only transparent substrates, therefore alleviating stray light issues found in the prior art that created openings in substrates. Embodiments described herein relate to lens stacks incorporating MEMS technology that contain only glass substrates, allowing for better coefficient of thermal expansion (CTE) matching than lens stacks with at least one silicon substrate. In addition, in desired embodiments, the lens stacks are manufactured by imprinting the movable lenses directly on the MEMS structures, avoiding additional manufacturing processes. Figures described herein show one structure of many that may be simultaneously formed at a wafer level. 
     Now referring to the figures, where like reference numbers designate like elements,  FIGS. 1A and 1B  show lens stacks  1  and  1 ′, respectively, according to embodiments described herein. Lens stack  1  has a movable lens structure  28  having two lenses  18 ,  21  and lens stack  1 ′ has a movable lens structure  28 ′ having one lens  18 . 
     Referring to  FIG. 1A , lens stack  1  contains movable lens structure  28  comprising two opposing lenses  18 ,  21 . MEMS structures  17  support lens structure  28 , and are attached to transparent substrate  10 . Transparent substrate  10  may have two opposing lenses  11 ,  12  formed therein, may only have one of the lenses  11 ,  12 , or may have no lenses at all. Cavity  16  separates lens  21  from lens  11  (or from the transparent substrate  10  if lens  11  is not present). 
     Referring to  FIG. 1B , lens stack  1 ′ contains movable lens structure  28 ′ comprising lens  18 . MEMS structures  17  support lens structure  28 ′, and are attached to transparent substrate  10 . Transparent substrate  10  may have two opposing lenses  11 ,  12  formed therein, may only have one of the lenses  11 ,  12 , or may have no lenses at all. Cavity  16  separates lens  21  from lens  11  (or from the transparent substrate  10  if lens  11  is not present). 
     The MEMS structures  17  shown in  FIGS. 1A and 1B  (and all subsequent figures) may be, e.g., piezoelectiric, electrostatic or magnetostatic, and may incorporate, e.g, hinges (not shown) or actuators (not shown). The MEMS structures  17  shown in  FIGS. 1A and 1B  (and all subsequent figures) are intended to be representative of any appropriate MEMS implementation and are, therefore, not intended to be limiting. In addition, the sizes and shapes of lenses  11 ,  12 ,  18  and  21  shown in  FIGS. 1A ,  1 B and all subsequent figures are only intended to be representative, and lens of any size and shape may be formed in any of the methods of manufacturing the lens structures shown in  FIGS. 1A and 1B . 
     While convex lenses are shown in  FIGS. 1A and 1B , concave or partially concave lenses may be used for any or all of the lenses  11 ,  12 ,  18 ,  21 . Each of the lenses may be comprised of a rigid material (e.g., an Ormocer® such as Ormocore® or Ormocomp®, manufactured by Microresist Technology GmbH, Berlin, Germany) or a flexible material (e.g., polydimethylsiloxane (PDMS)). When lenses  18  and  21  are comprised of a rigid material, they will be restricted to axial or lateral movement. When lenses  18  and  21  are comprised of a flexible material, other properties of the lenses may also change (e.g., shape, radius of curvature) by stretching or otherwise distorting the lenses. In addition, lens material can vary along the lens radius by, e.g., strong electromagnetic or particle radiation during fabrication, to influence the mechanical properties of the lens. The transparent substrate  10  may be comprised of a glass (e.g., Borofloat® 33 manufactured by Schott AG, Germany). 
       FIG. 1C  shows a top-down view of a lens stack  1 , V. Lens structure  28 ,  28 ′ may be centered in MEMS structures  17 . The top  27  of MEMS structures  17  may be solid, except for the opening that exposes lens  18 ,  18 ′. MEMS structures  17  may have small holes  19  through which is dissolved sacrificial material in embodiments described herein. 
       FIGS. 2A-2E  show a first example of a method of manufacturing lens stack  1  shown in  FIG. 1A . Referring to  FIG. 2A , the first step is to create lenses  11 ,  12  on opposite sides of transparent substrate  10 . Alternatively, only one lens  11  or  12  is formed on transparent substrate  10 , or no lenses are formed on transparent substrate  10 . The lenses  11 ,  12  may be formed by any suitable method, e.g., lens replication. A temporary carrier  15  is attached to one side of the transparent substrate  10 . The temporary carrier  15  may be comprised of, for example, silicon, polymer, glass or polymer-on-glass. In addition, the temporary carrier  15  need not support the entire surface of transparent substrate  10 . 
     Referring to  FIG. 2B , in a step separate from that described in  FIG. 2A , MEMS structures  17  are created on silicon carrier  14  by any suitable method, e.g., surface micromachining, such that a cavity  16  is formed. Lens  21  is imprinted on the MEMS structures  17  inside the cavity  16  by any suitable method, e.g., ultraviolet lens replication. The cavity  16  is then at least partially filled with sacrificial material  13 . The sacrificial material  13  may be, for example, SiO 2  or a polymer, and may be deposited in the cavity by any suitable method, e.g., vapor deposition, sputtering, dispensing or spin-coating. 
     Referring to  FIG. 2C , MEMS structures  17  are then attached to transparent substrate  10  by any suitable method. Referring to  FIG. 2D , the silicon carrier  14  is etched away to reveal lens  21 . Referring to  FIG. 2E , lens  18  is imprinted over lens  21  and MEMS structures  17  by any suitable method, e.g., lens replication, to produce movable lens structure  28 . 
     The sacrificial material  13  ( FIGS. 2B-2E ) is then removed by any available method, e.g., by being dissolved through small holes  19  ( FIG. 1C ) in the MEMS structures  17 , and the temporary carrier  15  ( FIGS. 2A ,  2 C- 2 E) is removed to produce the lens stack  1  illustrated in  FIG. 1A . 
       FIGS. 3A-3E  show a second example of a method of manufacturing a lens stack  1  shown in  FIG. 1A . Referring to  FIG. 3A , the first step is to create MEMS structures  17  over silicon carrier  14  by any suitable method, e.g., surface micromachining. A cavity  16  is formed in the process and is filled with a sacrificial material  13 , e.g., SiO 2 . 
     Referring to  FIG. 3B , the MEMS structures  17  and sacrificial material  13  are transferred from the silicon carrier  14  ( FIG. 3A ) to a transparent substrate  10  optionally having a lens  11  formed thereon. The transfer occurring in  FIG. 3B  is discussed below and shown in greater detail in  FIGS. 4A-6D . While the embodiment shown in  FIGS. 3A-3E  shows a transparent substrate  10  having a lens  11 , transparent substrate  10  need not have a lens  11 . If lens  11  is not present on transparent substrate  10 , the transfer shown in  FIG. 3B  can occur without the additional steps shown in  FIGS. 4A-6D . Referring to  FIG. 3C , a cavity  31  is formed in the sacrificial material  13  by any suitable method, e.g., etching or imprinting. 
     Referring to  FIG. 3D , lens structure  28  is replicated over the cavity  31 , creating lenses  18  and  21 . Prior to lens replication, cavity  31  may be coated with a thin polymer, e.g., an Ormocer® such as Ormocore® or Ormocomp®, manufactured by Microresist Technology GmbH, Berlin, Germany, as described in U.S. patent application Ser. No. ______, entitled Over-Molded Glass Lenses and Method of Forming the Same, filed Jul. 1, 2008 and assigned to Micron Technology, Inc, which is incorporated herein by reference. 
     In a first alternative embodiment, the sacrificial material  13  is a material that can be imprinted by hot embossing, e.g., polycarbonate. In a second alternative embodiment, the sacrificial layer  13  is removed and replaced with an ultraviolet-curing sacrificial layer, e.g., a polymer, that can be imprinted by a standard ultraviolet embossing process. 
     Referring to  FIG. 3E , the sacrificial material  13  is removed by any available technique such as, e.g., by being dissolved through small holes  19  ( FIG. 1C ) in the MEMS structures  17 . A lens  12  ( FIG. 1A ) may be imprinted on the bottom of transparent substrate  10  by any suitable method, e.g., lens replication, to produce the finished lens stack  1  shown in  FIG. 1A . 
       FIGS. 4A-4C  show a first example of a method for transferring MEMS structures  17  from a silicon carrier  14  to a transparent substrate  10  having a lens  11 , as discussed above for the example shown in  FIG. 3B . Referring to  FIG. 4A , a cavity  41  is created in the sacrificial material  13  by any suitable method, e.g., etching or imprinting. Referring to  FIG. 4B , the cavity  41  is filled with a lens replication material, e.g., a ultraviolet-curable polymer, to create lens  11 . The lens  11  is then planarized. Referring to  FIG. 4C , the transparent substrate  10  is attached to lens  11  and MEMS structures  17  and carrier  14  is removed. 
       FIGS. 5A-5C  show a second example of a method for transferring MEMS structures  17  from a silicon carrier  14  to a transparent substrate  10  having a lens  11 , as discussed for the example shown in  FIG. 3B . Referring to  FIG. 5A , a cavity  41  is created in the sacrificial material  13  by any suitable method, e.g., etching. Referring to  FIG. 5B , the cavity  41  is filled with a lens replication material  55 , e.g., a ultraviolet-curable polymer, and transparent substrate  10  is attached to MEMS structures  17  such that the lens replication material  55  is compressed into the cavity  41  to create lens  11  ( FIG. 5C ). Referring to  FIG. 5C , the silicon carrier  14  is then removed. 
       FIGS. 6A-6D  show a third example of a method for transferring MEMS structures  17  from a silicon carrier  14  to a transparent substrate  10  having a lens  11 , as discussed for the example shown in  FIG. 3B . Referring to  FIG. 6A , the MEMS structures  17  are attached to a transparent substrate  10  and removed from the silicon carrier  14  ( FIG. 3B ). Referring to  FIG. 6B , the sacrificial material  13  is removed by any available method, e.g., by being dissolved through small holes  19  ( FIG. 1C ) in the MEMS structures  17 . Referring to  FIG. 6C , the lens  11  is imprinted on the transparent substrate  10  by any suitable method, e.g., ultraviolet lens replication. Referring to  FIG. 6D , the cavity  16  is filled with sacrificial material  13  and planarized. 
       FIGS. 7A-7D  show a first example of a method of manufacturing a lens stack  1 ′ shown in  FIG. 1B . Referring to  FIG. 7A , the first step is to create lenses  11 ,  12  on opposite sides of the transparent substrate  10 . Alternatively, only one lens  11  or  12  is formed on transparent substrate  10 , or no lenses are formed on transparent substrate  10 . The lenses  11 ,  12  may be formed by any suitable method, e.g., ultraviolet lens replication. 
     Referring to  FIG. 7B , a temporary carrier  15  is attached to one side of the transparent substrate  10 . The temporary carrier  15  may be comprised of, for example, silicon, polymer, glass or polymer-on-glass. A silicon carrier  14  is attached to the other side of the transparent substrate  10 . The silicon carrier  14  has a cavity  16  at least partially filled with sacrificial material  13 . The cavity may be created by any suitable method, e.g., etching. The sacrificial material  13  may be, for example, SiO 2 , and may be deposited in the cavity by any suitable method, e.g., vapor deposition, sputtering, dispensing or spin-coating. 
     Referring to  FIG. 7C , silicon surface micromachining is performed on silicon carrier  14  ( FIG. 7B ) to form the MEMS structures  17 . Referring to  FIG. 7D , lens  18  is created over the MEMS structures  17  and sacrificial material  13 . In a preferred embodiment, the lens  18  is imprinted in an ultraviolet lens replication material. To create the finished lens stack  1 ′ shown in  FIG. 7B , the sacrificial material  13  is removed by any available method, e.g., by being dissolved through small holes  19  ( FIG. 1  C) in the MEMS structures  17 . In addition, the temporary carrier  15  ( FIGS. 7A-7D ) is removed. 
       FIGS. 8A-8E  show a second example of a method of manufacturing a lens stack  1 ′ shown in  FIG. 1B . Referring to  FIG. 8A , the first step is to create MEMS structures  17  over silicon carrier  14  by any suitable method, e.g., surface micromachining. Cavity  16  is formed therein and is filled with a sacrificial material  13 , e.g., SiO 2 . 
     Referring to  FIG. 8B , transparent substrate  10  is attached to the top of the MEMS structures  17  and the silicon carrier  14  is removed by, e.g., etching. While the embodiment shown in  FIG. 8B  does not have a lens  11  on the transparent substrate  10 , a lens  11  may be present as in the embodiment shown in  FIGS. 3A-3E . If lens  11  is present, additional steps, e.g., those shown in  FIGS. 4A-6D , must be taken to allow for transfer to the transparent substrate  10 . 
     Referring to  FIG. 8C , a lens  18  is replicated over the MEMS structures  17  and sacrificial material  13 . Referring to  FIG. 8D , the sacrificial material  13  is removed by any available method, e.g., by being dissolved through small holes  19  ( FIG. 1C ) in the MEMS structures  17 . Referring to  FIG. 8E , a lens  12  may be imprinted on the exposed side of transparent substrate  10  to produce the lens stack  1 ′ shown in  FIG. 1B  without optional lens  11 . It should be noted that lens  12  is also optional. 
     In the method embodiments described in  FIGS. 2A-8E , it is important that the lens replication material used to create lens  18  does not contact any of the movable parts of joints of the MEMS structures  17 , to avoid obstructing the movement of the MEMS structures  17 . This can be achieved by a relative replication as described in U.S. patent application Ser. No. ______, entitled Stamp with Mask Pattern for Discrete Lens Replication, filed on ______ and assigned to Micron Technology, Inc. 
       FIG. 9  shows an alternative embodiment where glass substrate  10  has MEMS structures affixed to both sides, thus creating a lens structure  1 ″ with two movable lens structures  28 ,  28 ″. MEMS structures  17  and lens structure  28  are similar to MEMS structures  17 ,  17 ′ and lens structures  28 ,  28 ′, respectively in  FIGS. 1A ,  1 B and can be constructed according to an appropriate embodiment described herein in  FIGS. 2A-8E . Likewise, MEMS structures  17 ″ and lens structures  28 ″ are similar to MEMS structures  17 ,  17 ′ and lens structures  28 ,  28 ′ in  FIGS. 1A ,  1 B and can be constructed according to an appropriate embodiment described herein in  FIGS. 2A-8E . As with 
       FIGS. 1A and 1B , lens structures  28 ,  28 ″ can have two lenses as shown in  FIG. 9 , or one or both of lens structures  28 ,  28 ″ can have only one lens. In addition, lenses  11  and  12  are optional such that transparent substrate  10  may have only one lens ( 11  or  12 ) attached or may have no lens attached. 
       FIG. 10  shows one example of how a lens stack  1 ,  1 ′ can be used in an imaging module  900 . Imaging module  900  contains a lens stack  1 ,  1 ′ according to an embodiment described herein, over an image sensor  901 . The lens stack lens stack  1 ,  1 ′ is used to focus an image on the image sensor  901 . 
       FIG. 11  shows a typical imaging system  950  modified to include an imager  900  constructed and operated in accordance with an embodiment described above. The system  950  is a system having digital circuits that could include imaging devices. Without being limiting, such a system could include a computer system, camera system, scanner, machine vision, vehicle navigation, video telephone, surveillance system, automatic focus system, star tracker system, motion detection system, image stabilization system, or other image acquisition system. 
     In the system  950 , for example a digital still or video camera system, a lens  920  is used to focus light onto an image sensor  901  ( FIG. 10 ) of the imaging device  900  when a shutter release button  922  is pressed.