Abstract:
A lens assembly and method of adjusting a lens assembly using an electrically active polymer element. The assembly comprises a lens; a pixel array for receiving an image through said lens via an optical path; a moveable element for changing the optical properties of said optical path; and at least one electrically active polymer for changing volume in response to an applied voltage, said polymer being coupled to said moveable element such that changes in volume of said polymer causes movement of said moveable element.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to imaging devices, and specifically to imaging devices employing an adjustable focus or zoom assembly. 
         [0002]    Conventional lens adjustment assemblies move one or more lenses or an image sensor mechanically in a linear direction toward and away from one another to adjust zoom and focus. These conventional assemblies use known electromechanical or piezoelectric techniques which typically contain many moving parts making the lens adjustment assembly complex and expensive, particularly as image sensor sizes decrease. 
         [0003]    Accordingly, there is a desire and need for a lens adjustment assembly, to be used with an imaging device, that mitigates against these shortcomings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Advantages and features of the invention will become more apparent from the detailed description of embodiments provided below with reference to the accompanying drawings in which: 
           [0005]      FIG. 1A  is a cross-sectional view of an imager having a lens adjustment assembly according to an embodiment; 
           [0006]      FIG. 1B  is a cross-sectional view of the imager of  FIG. 1A  illustrating the activation of an electrically active polymer element within the assembly; 
           [0007]      FIG. 2A  is a cross-sectional view of an imager having a lens adjustment assembly according to another embodiment; 
           [0008]      FIG. 2B  is a cross-sectional view of the imager of  FIG. 2A  illustrating the activation of an electrically active polymer element within the assembly; 
           [0009]      FIG. 3A  is a cross-sectional view of an imager having a lens adjustment assembly according to another embodiment; 
           [0010]      FIG. 3B  is a cross-sectional view of the imager of  FIG. 3A  illustrating the activation of an electrically active polymer element within the assembly; 
           [0011]      FIG. 4A  is a cross-sectional view of an imager having a lens adjustment assembly according to another embodiment; 
           [0012]      FIG. 4B  is a cross-sectional view of the imager of  FIG. 4A  illustrating the activation of an electrically active polymer element within the assembly; 
           [0013]      FIG. 5  is a cross-sectional view of an imager having a lens adjustment assembly according to another embodiment; 
           [0014]      FIG. 6  is a cross-sectional view of an imager having a lens adjustment assembly according to another embodiment; 
           [0015]      FIG. 7  is a cross-sectional view of an imager having a lens adjustment assembly according to another embodiment; 
           [0016]      FIG. 8  is a cross-sectional view of an imager having a lens adjustment assembly according to another embodiment; 
           [0017]      FIG. 9  is a top-down illustration of portion of a CMOS imager employing a lens adjustment assembly according to an embodiment of the present invention; and 
           [0018]      FIG. 10  illustrates a computer system having an imager employing a lens adjustment assembly according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    In the following detailed description, reference is made to various specific embodiments in which the invention may be practiced. These embodiments are described with sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be employed, and that structural and electrical changes may be made without departing from the spirit or scope of the present invention. 
         [0020]    Embodiments of the invention employ an electrically active element, such as an electrically active polymer, which is enclosed within a chamber containing a non-compressible fluid and which is responsive to electrical signals to expand or contract which causes displacement of the fluid to move at least a portion of the wall of the chamber for zoom and/or focus adjustment of a lens. 
         [0021]      FIG. 1A  is a cross-sectional view of an imager  100  having a lens adjustment assembly according to a first embodiment. Imager  100  includes a substrate  101  supporting an imaging array  102 . In the illustrated embodiment, the imaging array  102  is shown as fabricated on top of substrate  101 , but for this and other embodiments, the array  102  may also be fabricated directly within semiconductor substrate  101  along with other images and/or camera circuitry, if desired. Imager  100  also includes one or more electrically active polymer (“EAP”) elements  108  and a lens adjustment assembly comprising a support structure  103 , a lens housing  104 , a sealing portion  105  and a lens  106 , enclosing the imaging array  102 , EAP element  108  and a volume of transparent fluid  107  having a known index of refraction. In the illustrated embodiment, the support structure  103 , housing  104  and sealing portion  105  are concentric rings which surround the lens  106 , but may be in any desired shape or configuration. In the illustrated embodiment, a single, ring-shaped EAP element  108  which encircles the array  102  is used. 
         [0022]    Suitable EAP elements  108  include electrostatically driven polymers such as ionomers. Suitable fluids  107  include perflourinated polyether (PFPE) fluids, a family of inert fluids having stable indexes of refraction. These EAP elements and fluids may be utilized in any of the described embodiments. 
         [0023]    The housing  104  and lens  106  move vertically toward and away from the array  102  in response to changes in volume of the enclosed EAP element  108 . The sealing portion  105  is interposed between the housing  104  and the support structure  103  to keep the array  102 , volume of liquid  107  and EAP element  108  in a fluid tight sealing relationship. In order to move the housing  104  and lens  106  vertically upward with respect to the array  102 , a voltage is applied to the EAP element  108  by control circuitry, for operating array  102  which, for example, may be fabricated in the substrate  101 , thereby causing the EAP element  108  to expand and move the fluid  107 . The fluid  107  presses on the lens  106  and housing  107 . 
         [0024]    As illustrated by  FIG. 1B , the activated EAP element  108  expands in response to the applied voltage. The pressure of the enclosed volume of liquid  107  increases and the liquid  107 , unable to compress to compensate for the expanded EAP element  108 , and unable to escape past the sealing portion  105 , forces the housing  104  and lens  106  vertically upward in proportion to the volumetric change of the activated EAP element  108  in order to bring the pressure of the volume of liquid  107  into equilibrium with the outside environment (typically air). 
         [0025]    The EAP element  108  is deactivated by removing the applied voltage, thereby returning the deactivated EAP element  108  to its original volume. The decrease in volume of the deactivated EAP element  108  decreases the pressure of the liquid  107  and moves the assembly in a downward vertical direction back towards the array  102 . Thus, by variably controlling the voltage applied to EAP element  108  a variably controlled movement of lens  106  can be obtained. 
         [0026]    The enclosed volume of fluid  107  has two uses. First, the fluid  107  in this embodiment is non-compressible, thereby maintaining the volume of the enclosed portion of the imager  100  at a constant level, allowing for more exact adjustment of the lens assembly. Second, the index of refraction of the liquid  107  is greater than that of air, allowing for designs that permit the lens  106  to be positioned closer to the array  102  than would be otherwise practical. 
         [0027]    Although an non-compressible liquid is used in the illustrated embodiment for the volume of liquid  107 , any liquid or gas having known compressibility properties may also be used. However, as the compressibility of the liquid or gas increases, more accurate control over the volumetric expansion of the EAP element  108  is required. 
         [0028]    Controlling the activation of the EAP element  108  may be achieved in a number of ways. In the embodiment illustrated in  FIGS. 1A-1B , a single EAP element  108  encircles the horizontal perimeter of the array  102  and is linearly responsive to an applied voltage. Thus, a desired increase in volume of the EAP element  108  is directly proportional to the applied voltage; the increase in volume of the EAP element  108  proportionally increases the pressure of the volume of liquid  107 , which in turn proportionally moves the assembly  104  and lens  106  up and away from the array  102 . Accordingly, the change in focal distance of the lens  106  from the array  102  is directly proportional to the voltage applied to the EAP element  108 . Other embodiments may include a plurality of EAP element  108 , each responsive to a fixed voltage, variable voltages, or a combination thereof in order to achieve the desired change in volume and movement of lens  106  relative to the array  102 . 
         [0029]    In the illustrated embodiment, for simplicity, the EAP element  108  is illustrated as increasing in volume in the vertical linear direction (see  FIG. 1B ), but an increase in volume in any direction, or more than one direction, will enable movement of the lens  106  relative to the array  102 . The EAP element  108  may be formed in other embodiments in a manner allowing for expansion in any or all directions. As long as the changes in volume of the EAP element  108  are measurable and as long as the expansion of the EAP element  108  does not obscure or obstruct the transmission of light to or from the imager array  102 , the direction of expansion of the EAP element  108  is generally not relevant to the operation of the imager  100 . 
         [0030]    Additionally, in the illustrated embodiment, the outside environment is air at atmospheric pressure, which is variable according to elevation and atmospheric conditions. In general, atmospheric pressure will not vary quickly enough to have a noticeable effect on the positioning of the housing  104  and lens  106 , but where exact positioning is required, for example, where a preset focal distance between the lens  106  and array  102  must be associated with a specific voltage or combination of voltages to be applied to the EAP element  108 , continuous monitoring of image focus may be performed by the imager or other associated circuitry (not shown) and corrective voltage may be applied to the EAP element  108 . 
         [0031]    It should be noted that the accompanying figures are not drawn to scale. Specifically, the upward movement of the assembly  104  and lens  106  shown in  FIG. 1B  will correspond with the volumetric change in EAP element  108 , and will not necessarily be proportional to the upward extension of the EAP element  108 . 
         [0032]      FIG. 2A  is a cross-sectional view of an imager  200  having a lens adjustment assembly according to another embodiment. In the illustrated embodiment, imager  200  includes a substrate  201  comprising an imaging array  202 . Imager  200  also includes one or more EAP elements  208  and a lens adjustment assembly comprising a support structure  203 , an elastic lens housing  204  and a lens  206 , enclosing the imaging array  202 , EAP element  208  and a volume of transparent fluid  207  having a known index of refraction. 
         [0033]    As shown in  FIG. 2B , and in a technique similar to the embodiment shown in  FIGS. 1A-1B , the EAP element  208  may be activated as discussed above, thereby increasing the pressure of the volume of fluid  207 . The elastic housing  204  stretches as the lens  206  is pushed upward and outward to compensate for and to equalize the increase in pressure. In this and other illustrated embodiments, the lens  206  is rigid, but in this or other embodiments, the lens  206  may be flexible if desired. In another embodiment, the elasticity of the lens housing  204  may also be taken into account when calculating the appropriate voltage or combination of voltages to be applied to the EAP element  208 . 
         [0034]      FIG. 3A  is a cross-sectional view of an imager  300  having a lens adjustment assembly according to another embodiment. In this embodiment, imager  300  includes a substrate  301  supporting an imaging array  302 . Imager  300  also includes one or more EAP elements  308 , and a fixed lens housing  303  and lens  306  enclosing the imaging array  302 , EAP element  308 , a first volume of transparent fluid  307  having a first index of refraction, and a transparent elastic membrane  309  enclosing the array  302  and a second volume of transparent fluid (either liquid or gas)  310  having a second index of refraction different from the first index of refraction. Suitable fluids for the second fluid  310  include PFPE fluids as described above, or nitrogen gas or dry air. 
         [0035]    As shown by  FIG. 3B , and in a technique similar to the embodiments shown in  FIGS. 1A ,  1 B,  2 A and  2 B, the EAP element  308  may be activated by applied voltage as discussed above, thereby increasing the pressure on the first volume of fluid  307 . The second fluid  310  is compressed accordingly as the pressure of the first fluid and second fluids  307 ,  310  reach equilibrium, altering the shape and positioning of the elastic membrane  309  accordingly. The membrane  309  may be formed of PDMS or PET material having a thickness between 10 and 50 microns. 
         [0036]    As the second fluid  310  is compressed, the focal distance between the lens  306  and the elastic membrane  309  increases, and the focal distance between the elastic membrane  309  and the array  302  decreases by the same amount. The change in focal distances between the lens  306  and membrane  309  and between the membrane  309  and array  302  changes the focus and/or zoom properties of the lens  306  due to the different indexes of refraction of the two fluids  307 ,  310 . Additionally, the membrane  309  may be formed so that its optical properties vary as the second fluid  310  compresses or expands. 
         [0037]    Therefore, the focus and zoom settings for the captured image can be controlled without physically moving the lens  306 . This embodiment has the additional advantage of sealing the first and second fluids  307 ,  310  within the rigid housing  303 , lens  306  and substrate  301  structure. This reduces the effect of atmospheric pressure on the operation of the imager  300 . 
         [0038]      FIG. 4A  is a cross-sectional view of an imager  400  having a lens adjustment assembly according to another embodiment. In the illustrated embodiment, imager  400  includes a substrate  401  supporting an imaging array  402 . Imager  400  also includes one or more EAP elements  408 , and a fixed lens housing  403  and lens  406  enclosing the imaging array  402 , EAP element  408 , a first volume of transparent fluid  407  having a first index of refraction, and a transparent elastic membrane  409  enclosing the lens  406  and a second volume of compressible fluid  410  having a second index of refraction different from the first index of refraction. 
         [0039]    As shown by  FIG. 4B , and in a technique similar to the  FIGS. 3A ,  3 B embodiment discussed above, the EAP element  408  may be activated by applied voltage, thereby increasing the pressure on the first volume of fluid  407 . The second volume of compressible liquid or gas  410  is compressed accordingly as the pressure equalizes between the elastic membrane  409 . 
         [0040]    Similar to  FIGS. 3A and 3B , as the second volume of matter  410  is compressed, the focal distance between the lens  406  and the elastic membrane  409  decreases, and the focal distance between the elastic membrane  409  and the array  402  increases by the same amount. The change in focal distances of these two materials having different indexes of refraction changes the focus and/or zoom properties of the lens  406 . 
         [0041]      FIG. 5  is a cross-sectional view of an imager  500  having a lens adjustment assembly according to another embodiment. In the illustrated embodiment, imager  500  includes a substrate  501  comprising an imaging array  502 . Imager  500  also includes one or more vertical EAP elements  508 , interposed between the substrate  501  and a fixed lens housing  503  for vertical adjustment of a lens  506 , and one or more horizontal EAP elements  508 ′ interposed between the fixed lens housing  503  and the lens  506  for horizontal adjustment of the lens  506 . The vertical and horizontal EAP elements  508 ,  508 ′, housing  503  and lens  506  may enclose the imaging array  502  and a first volume of transparent fluid or gas  507 , but as will become apparent this is not necessary. 
         [0042]    In this embodiment, one or more of the vertical EAP elements  508  are activated in order to move the housing  503  and lens  506  in a vertical direction with respect to the array  502 . The vertical EAP elements  508  can be activated individually and/or proportionally by applied voltage as discussed above in order to obtain varying degrees of focus or zoom. Additionally, one or more of the horizontal EAP elements  508 ′ may be selectively activated by applied voltage to adjust the horizontal placement of the lens  506  as desired. This horizontal adjustment feature adds additional optical control over the incoming light and may be combined with any of the other disclosed embodiments. 
         [0043]      FIG. 6  is a cross-sectional view of an imager  600  having a lens adjustment assembly according to another embodiment. In the illustrated embodiment, imager  600  includes a substrate  601  supporting an imaging array  602 . Imager  600  also includes one or more EAP elements  608  encircling an outer perimeter of a flexible lens housing  603  holding a lens  606 . Current may be applied by wires (not shown) formed within the lens housing  603  or by conventional leads. The housing  603  and lens  606  may enclose the imaging array  602  and a first volume of transparent fluid (e.g., liquid or gas)  607 . It should be appreciated, however, that the presence of fluid  607  is not necessary to practice the illustrated embodiment because all necessary movement of the housing  603  may be effected by EAP elements  608  alone. 
         [0044]    In the illustrated embodiment, one or more EAP elements  608  are activated by applied voltage in order to expand the flexible housing  603 , thereby causing the lens  606  to move vertically toward the array  602 . Deactivating or reducing the voltage applied to the EAP element  608  constricts the flexible housing, thereby causing the lens  606  to move vertically away from the array  602 . Each EAP element  608  can be activated individually and/or proportionally as discussed above in order to obtain varying degrees of focus or zoom. 
         [0045]      FIG. 7  is a cross-sectional view of an imager  700  having a lens adjustment assembly according to another embodiment. In the illustrated embodiment, imager  700  includes a substrate  701  supporting an imaging array  702 . Imager  700  also includes one or more EAP elements  708  encircling an inner perimeter of a flexible lens housing  703  holding a lens  706 . The housing  703  and lens  706  may enclose the imaging array  702 , the EAP element  708  and a first volume of transparent fluid (e.g., liquid or gas)  707 . It should be appreciated, however, that the presence of fluid  707  is not necessary to practice the illustrated embodiment because all necessary movement of the housing  703  may be effected by EAP elements  708  alone. 
         [0046]    In this embodiment, one or more of the EAP elements  708  are activated by applied voltage in order to expand the perimeter of the flexible housing  703 , thereby causing the lens  706  to move vertically toward the array  702 . Deactivating or reducing the voltage applied to the EAP element  708  allows the perimeter flexible housing to constrict, thereby causing the lens  706  to move vertically away from the array  702 . Each EAP element  708  can be activated individually and/or proportionally as discussed above in order to obtain varying degrees of focus and/or zoom. In another embodiment, EAP elements may be disposed around the inner and outer perimeters of the flexible housing  703  simultaneously. 
         [0047]      FIG. 8  is a cross-sectional view of an imager  800  having a lens adjustment assembly according to another embodiment. In the illustrated embodiment, imager  800  includes a substrate  801  supporting an imaging array  802 . Imager  800  also includes one or more EAP elements  808 , and a lens housing  803  and lens  806  enclosing the imaging array  802 , EAP element  808 , a first volume of transparent fluid  807  having a first index of refraction, and a transparent elastic membrane  809  enclosing the lens  806  and a second volume of compressible fluid  810  having a second index of refraction different from the first index of refraction. 
         [0048]    In a technique similar to the embodiments discussed above, the EAP element  808  may be activated by applied voltage, thereby raising the housing  803  in a manner similar to the embodiment shown in  FIG. 7 , and thus decreasing the pressure on the first volume of fluid  807  and increasing the pressure on the second volume of fluid in a manner similar to the embodiment shown in  FIGS. 4A and 4B . The second volume of compressible liquid or gas  810  is decompressed accordingly as the pressure equalizes between the elastic membrane  809 . 
         [0049]    As the second volume of matter  810  is decompressed, the focal distance between the lens  406  and the elastic membrane  809  increases, and the focal distance between the elastic membrane  809  and the array  802  decreases by the same amount minus the increase in focal distance caused by the expansion of the EAP elements  808 . The change in focal distances of these two materials having different indexes of refraction changes the focus and/or zoom properties of the lens  806 . 
         [0050]    In a modification of the  FIG. 8  embodiment, the transparent elastic membrane can enclose the pixel array  802  instead of lens  806 . 
         [0051]    The lens adjustment mechanism illustrated in the illustrated embodiments above may by used with any type of solid state imager providing an array of pixels for image capture. 
         [0052]      FIG. 9  illustrates a block diagram of an imager  900  constructed in accordance with one of or a combination of the embodiments described above. The imager  900  may be a CMOS imager, but, as noted, the imager can be any type of imager. The imager  900  contains a pixel array  902  and employs a lens adjustment assembly according to one of or a combination of the embodiments shown in  FIGS. 1A-7 . Attached to the pixel array  902  is signal processing circuitry for controlling the pixel array  902 . The pixel cells of each row in array  902  are all turned on at the same time by a row select line, and the pixel cells of each column are selectively output by respective column select lines. A plurality of row select and column select lines are provided for the entire array  902 . The row lines are selectively activated by a row driver  145  in response to row address decoder  155 . The column select lines are selectively activated by a column driver  160  in response to column address decoder  170 . Thus, a row and column address is provided for each pixel cell. 
         [0053]    The imager  900  is operated by a timing and control circuit  152 , which controls address decoders  155 ,  170  for selecting the appropriate row and column lines for pixel readout. The control circuit  152  also controls the row and column driver circuitry  145 ,  160  such that they apply driving voltages to the drive transistors of the selected row and column lines. The pixel column signals, which typically include a pixel reset signal V rst  and a pixel image signal V sig , are output to column driver  160 , on output lines, and are read by a sample and hold circuit  161 . V rst  is read from a pixel cell immediately after the pixel cell&#39;s floating diffusion region is reset. V sig  represents the amount of charges generated by the photosensitive element of the pixel cell in response to applied light during an integration period. A differential signal (V rst -V sig ) is produced by differential amplifier  162  for each readout pixel cell. The differential signal is digitized by an analog-to-digital converter  175  (ADC). The analog to digital converter  175  supplies the digitized pixel signals to an image processor  180 , which forms and outputs a digital image. The image processor, if it controls the image capture process, may be used to provide output signals to control the EAP elements in the embodiments discussed above. 
         [0054]      FIG. 10  illustrates a camera system  1100  that includes an imager  900  constructed in accordance with an embodiment. As discussed above, the imager  900  contains a pixel array  902  and employs a lens adjustment assembly according to any embodiment or a combination of the embodiments shown in  FIGS. 1A-7 . The system  1100  is an example of a system having digital circuits that could include image sensor devices. Without being limiting, such a system could include a computer system, camera system, scanner, machine vision, vehicle navigation, video phone, surveillance system, auto focus system, star tracker system, motion detection system, image stabilization system, and other image sensing and/or processing system. 
         [0055]    The system  1100 , for example a digital still or video camera system, generally comprises a central processing unit (CPU)  1102 , such as a microprocessor, that communicates with one or more input/output (I/O) devices  1106  over a bus  1104 . Imaging device  800  also communicates with the CPU  1102  over the bus  1104  and controls camera functions. In this regard, CPU  1102  may provide the control signals for EAP, if not provided by image processor  180 , via the I/O devices  1006  or directly. The processor system  1100  also includes random access memory (RAM)  1110 , and can include removable memory  1115 , such as flash memory, which also communicates with CPU  1102  over the bus  1104 . Imaging device  900  may be combined with a processor, such as a CPU, digital signal processor, or microprocessor, with or without memory storage on a single integrated circuit or on a different chip than the processor. Although  FIG. 10  shows one bus  1104  for communication among the separate components, it should be understood that one or more busses and/or bridges may be used as well. 
         [0056]    The above description and drawings are only to be considered illustrative of embodiments which achieve the features and advantages of the present invention. Modification and substitutions to specific structures can be made. Accordingly, the invention is not to be considered as being limited by the foregoing description and drawings, but is only limited by the appended claims.