Abstract:
A method of fabricating a liquid lens which can prevent unstable movement of liquids while sealing a hole containing the liquids by applying voltage to a chamber containing the liquids to induce electrowetting, and a liquid lens fabricated thereby. The method includes providing a chamber with a hole formed therein for containing liquid and injecting two non-miscible liquids with different refractive indices. The method also includes placing a conductive transparent plate to be in contact with the liquid on the top and applying voltage to the conductive transparent plate and the chamber to induce electrowetting, thereby changing the shape of meniscus between the two liquids. The method further includes covering an upper surface of the chamber with the conductive transparent plate to seal the hole.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims the benefit of Korean Patent Application No. 2005-130642 filed on Dec. 27, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method of fabricating a liquid lens containing at least two liquids and a liquid lens fabricated thereby, and more particularly, to a method of fabricating a liquid lens which applies voltage to a chamber containing liquids to induce electrowetting, thereby preventing unstable movement of the liquids when sealing a hole containing the liquids, and a liquid lens fabricated thereby. 
         [0004]    2. Description of the Related Art 
         [0005]    A general lens module uses lenses manufactured with solid material such as glass at a fixed focal distance. In such a lens module, a plurality of solid lenses are provided and the distance of each lens is adjusted to control the focus. Thus, such a lens module is limited in miniaturization and requires a complicated operation to adjust focus. 
         [0006]    To overcome such problems, there has been proposed a liquid lens which is configured to adjust the focus by varying the curvature of meniscus between the different liquids. This liquid lens has a simple internal configuration to facilitate miniaturization and to more easily adjust the focus. 
         [0007]    Since the researches on the liquid lens utilizing electrowetting have gained attention in early 2000, various applications have been introduced, and efforts for its industrialization have been accelerated. In general, liquid lenses have advantages such as small size, low power consumption, prompt response rate and good reproducibility. Therefore, auto-focusing modules for cameras mounted to mobile phones, PDAs and the like have continued to be actively developed. 
         [0008]    A conventional method of fabricating a liquid lens will now be explained hereunder with reference to the accompanying drawings. 
         [0009]      FIG. 1  is a sectional view illustrating a conventional method of fabricating a liquid lens, in which liquid is filled in a hole inside a chamber,  FIG. 2  is a sectional view illustrating the conventional method of fabricating a liquid lens, in which an upper transparent plate is in contact with electrolyte, and  FIG. 3  is a sectional view illustrating the conventional method of fabricating a liquid lens in which the upper transparent plate is attached to an upper surface of the chamber to seal the hole. 
         [0010]    The conventional method of fabricating the liquid lens is as follows in detail. 
         [0011]    First, as shown in  FIG. 1 , a chamber  100  having an inner wall to form a hole  110  with a circular section is provided. The lower surface of the hole  110  is sealed by a lower transparent plate  120 , and thus the lower transparent plate  120  and the chamber  100  are bonded to each other by a bonding layer (not shown). In addition, a hydrophobic insulation film is coated on an inner wall of the hole  110  to allow the operation of the liquid lens. 
         [0012]    When the chamber  100  is provided, two non-miscible liquids  300  and  400  are filled in the hole  110 . At this time, these two liquids are provided in substantially the same proportions but have different refractive indices. One is conductive while the other one is non-conductive. In general, the liquid on the top is electrolyte  300  having conductivity whereas the liquid at the bottom is insulation liquid  400  having non-conductivity. 
         [0013]    When the liquids are filled in the hole  110 , the electrolyte  300  at the top tends to dewet to an inner wall of the hole  110  whereas the insulation liquid  400  tends to wet an inner wall of the hole  110 . At this time, due to affinity difference between the two liquids and an insulation film formed on an inner wall of the hole  110 , the insulation liquid  400  wetting the inner wall of the hole  110  tends to enclose the electrolyte  300  as shown in  FIG. 1 . That is, the meniscus between the electrolyte  300  and the insulation liquid  400  has a concave central portion. 
         [0014]    In addition, the upper surface of the electrolyte  300  filled in the hole  110  has an upwardly-convexed shape due to surface tension. And when the upper transparent plate  500  attached to an upper surface of the chamber  100  comes in contact with the electrolyte  300 , the electrolyte  300  adheres to an undersurface of the upper transparent plate  500  due to mutual attraction, as shown in  FIG. 2 . 
         [0015]    When the electrolyte  300  adheres to an undersurface of the upper transparent plate  500  as described above, the insulation liquid  400  is also pulled toward the upper transparent plate  500  and its peripheral portion is positioned near an upper opening of the hole  110 . In this state, when the upper transparent plate  500  is attached to an upper end of the chamber  100 , the electrolyte  300  leaks between an upper surface of the chamber  100  and an undersurface of the upper transparent plate  500 , and the insulation liquid  400  also is pulled along with the electrolyte  300  to leak between an upper surface of the chamber  100  and an undersurface of the upper transparent plate  500 . The leakage of the electrolyte  300  and the insulation liquid  400  as described above may cause optical and operational problems of the lens, degrade the sealing state of the liquids and cause bubbles to be formed inside the hole  110 . The bubble formation in the hole  110  hinders maintenance of a regulated level of refractive index of light, thus fatally impairing the normal function of the lens. 
         [0016]    Besides the problematic bubble formation in the hole  110 , when the upper transparent plate  500  is attached, if the insulation liquid  400  wraps around the entire inner surface of the hole  110  as shown in  FIG. 3 , current is not applied to the electrolyte  300  even with voltage application, impeding electrowetting. Without the electrowetting, the meniscus between the electrolyte  300  and the insulation liquid  400  is not changed, making it impossible to adjust focus. 
         [0017]    In addition, when desired to inject additional liquid before finally attaching the upper transparent plate  500 , additional injection of liquid into the hole in a state depicted in  FIG. 2  results in leakage of a peripheral portion of the insulation liquid to the outside, due to the pressure of the liquid being additionally injected. 
         [0018]    To overcome such a problem, the hole  110  should be formed deeper, which entails increased thickness of the chamber  100 , resulting in an increased overall size of the liquid lens. 
       SUMMARY OF THE INVENTION 
       [0019]    The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a method of fabricating a liquid lens which stably seals liquid without leakage of insulation liquid or change in meniscus, maintains a contact state of the electrolyte and the chamber to stably induce electrowetting and reduces an overall size of the liquid lens, and to a liquid lens fabricated thereby. 
         [0020]    According to an aspect of the invention, a method of fabricating a liquid lens includes: providing a chamber with a hole formed therein for containing liquid; injecting two liquids in a stacked structure, the two liquids being non-miscible and having different refractive indices; placing a conductive transparent plate to be in contact with the liquid on the top; applying voltage to the conductive transparent plate and the chamber to induce electrowetting, thereby changing the shape of meniscus between the two liquids; covering an upper surface of the chamber with the conductive transparent plate to seal the hole. 
         [0021]    Of the two liquids, the liquid disposed on the top is electrolyte and the liquid disposed at the bottom is insulation liquid 
         [0022]    The step of applying voltage causes the meniscus of the two liquids to be horizontally flat or upwardly convexed with a lower peripheral portion. 
         [0023]    In addition, the exemplary method further includes additionally injecting at least one of the liquids in the hole after inducing electrowetting to alter the shape of the meniscus. 
         [0024]    According to an aspect of the invention for realizing the object, there is provided a liquid lens including: a chamber having an inner wall to provide a hole for containing liquid; two liquids in a stacked structure, which are non-miscible and have different refractive indices; and a conductive transparent plate for covering the upper surface of the chamber to seal the hole. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0026]      FIG. 1  is a sectional view illustrating a conventional method of fabricating a liquid lens, in which liquids are filled in a hole of a chamber; 
           [0027]      FIG. 2  is a sectional view illustrating the conventional method of fabricating a liquid lens, in which an upper transparent plate is attached to contact electrolyte; 
           [0028]      FIG. 3  is a sectional view illustrating the conventional method of fabricating a liquid lens, in which the upper transparent plate is attached to an upper surface of the chamber to seal the hole of the chamber; 
           [0029]      FIG. 4  is a sectional view illustrating the exemplary method of fabricating a liquid, in which an upper transparent plate is attached to contact electrolyte; 
           [0030]      FIG. 5  is a sectional view illustrating the exemplary method of fabricating a liquid lens, in which voltage is applied to the upper transparent plate and a chamber to induce electrowetting; and 
           [0031]      FIG. 6  is a sectional view illustrating the exemplary method of fabricating a liquid lens, in which the upper transparent plate is attached to an upper surface of the chamber to seal the hole of the chamber. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0033]    A method of fabricating a liquid lens according to the present invention first starts with providing a chamber  100  including a hole  110  therein having a circular section, with a lower transparent plate  200  attached to a bottom thereof to seal a lower surface of the hole  110 , and filling non-miscible two liquids, i.e., electrolyte  300  and insulation liquid  400  inside the hole  110 . 
         [0034]    It is preferable that an insulation film (not shown), which is coated on the inner wall of the hole  110  for operation of the liquid lens, is coated with a dielectric material without pin-holes such as parylene, and that the insulation film has such a coating thickness that it does not break down when the voltage is applied to obtain an optically desirable range of results. In this embodiment, the thickness of the coating is set at 2.5 μm. 
         [0035]    The hole  110  has a circular horizontal section so that the meniscus between the electrolyte  300  and the insulation liquid  400  (hereinafter, referred to as ‘the meniscus’) has a uniform sag. In addition, according to the characteristics of the electrolyte  300  and the insulation liquid  400 , the meniscus maintains a predetermined contact angle with an inner wall of the hole  110 . Here, if the hole  110  has a cylindrical shape, the meniscus has a steeply upwardly inclined peripheral portion so that the total height of the meniscus, i.e., the distance from the peripheral portion to the central portion of the meniscus becomes too large. Thus, the hole  110  has an inclined inner wall to have a section decreasing toward a bottom thereof. With the inclined inner wall of the hole  110 , the meniscus has a decreased slope of the peripheral portion, resulting in the decreased total height of the meniscus, thereby achieving miniaturization of the chamber  100 . 
         [0036]    The procedures of providing the chamber  100  of such a structure and filling in the electrolyte  300  and the insulation liquid  400  are identical to those in the conventional method of fabricating a liquid lens, and thus additional explanation is omitted. 
         [0037]      FIG. 4  is a sectional view illustrating the exemplary method of fabricating a liquid lens, in which the conductive transparent plate is attached to contact the electrolyte, and  FIG. 5  is a sectional view illustrating the exemplary method of fabricating a liquid lens, in which voltage is applied to the conductive transparent plate and the chamber to induce electrowetting. 
         [0038]    When the conductive transparent plate  600  is placed to contact an upper surface of the electrolyte  300 , i.e., to be attached to an upper surface of the chamber  100 , the electrolyte  300  adheres to the conductive transparent plate  600  as shown in  FIG. 4 , and the insulation liquid  400  also is pulled toward the upper transparent plate  500  with its peripheral portion positioned near an upper opening of the hole  110 , as in the conventional method shown in  FIG. 2 . 
         [0039]    In this state, when the conductive transparent plate  500  is tightly attached to an upper surface of the chamber  100  to seal the hole  110 , the electrolyte  300  leaks out of the hole  110  and a portion of the insulation liquid  400  leaks along with the electrolyte  400 , out of the hole  110 . The leakage of the electrolyte  300  and the insulation liquid  400  may cause bubbles to be formed or the meniscus of the electrolyte  300  and the insulation liquid  400  to be moved toward the inner wall. Even if appropriate amounts of the electrolyte  300  and the insulation liquid  400  are injected by calculating the various conditions including the dimension of the inner space, the leakage of the electrolyte  300  and the insulation liquid  400  may occur in the subsequent fabrication processes. 
         [0040]    To prevent such a problem, the exemplary method of fabricating the liquid lens includes applying voltage to the chamber  100  and the conductive transparent plate  500  to vary the meniscus between the electrolyte  300  and the insulation liquid  300  by electrowetting, as shown in  FIG. 5 . 
         [0041]    When voltage is applied to the chamber  100  and conductive transparent plate  600 , the meniscus has a lower peripheral portion, i.e., a sag with an upwardly-convexed central portion thereof, due to electrowetting. 
         [0042]    At this time, the degree of the peripheral portion being lowered is determined by the magnitude of the voltage applied to the chamber  100  and the conductive transparent plate  600 . That is, before the voltage is applied to the chamber  100  and the conductive transparent plate  600 , the peripheral portion of the meniscus rises along the inner wall of the hole  110 , but as the voltage is increased, the peripheral portion of the meniscus comes down along the inner wall of the hole  110 . 
         [0043]    To make the peripheral portion of the meniscus come down, the magnitude of the voltage applied to the conductive transparent plate  600  and the chamber  100  is determined according to the thickness of the insulation film. For example, in a case where the insulation film has a thickness of about 5 μm, it is preferable that the voltage applied to the conductive transparent plate  600  and the chamber  100  is set at 60V or higher. With such voltage applied, the meniscus has a lower peripheral portion than a central portion, i.e., an upwardly-convexed central portion, as shown in  FIG. 5 . With an upwardly-convexed central portion of the meniscus, the electrolyte  300  and the insulation liquid  400  have more stable operation of adjusting the focal distance in response to variation of the voltage application. 
         [0044]    Here, the electrowetting is identical to the conventional one which causes change of the meniscus of the electrolyte  300  and the insulation liquid  400 , and thus additional explanation is omitted. 
         [0045]    In addition, the exemplary method of fabricating a liquid lens may further include additionally injecting the electrolyte  300  or the insulation liquid  400  into the hole  110  while the electrolyte  300  contacting an undersurface of the conductive transparent plate  600  and the meniscus forming a lower peripheral portion due to electrowetting, as shown in  FIG. 5 . 
         [0046]    In the conventional method of fabricating a liquid lens, when the electrolyte  300  or the insulation liquid  400  is injected into the hole  110  while the electrolyte  300  is contacting an undersurface of the upper transparent plate, the insulation liquid  400  may leak out of the hole  110  through a periphery of the hole  110 . However, according to the exemplary method of fabricating a liquid lens, as the meniscus has a sag with a lower peripheral portion, even if the electrolyte  300  or the insulation liquid  400  is additionally injected into the hole  110 , the insulation liquid  400  does not leak out of the hole  110 . 
         [0047]    As additional injection of the electrolyte  300  or the insulation liquid  400  is possible as described above, the amount of each liquid  300  or  400  can be modified in the middle of the fabrication process of a liquid lens. 
         [0048]      FIG. 6  is a sectional view illustrating the exemplary method of fabricating a liquid lens, in which the conductive transparent plate is attached to an upper surface of the chamber to seal the hole. 
         [0049]    In the state illustrated in  FIG. 5 , as the conductive transparent plate  600  is tightly attached to an upper surface of the chamber  100  to seal the hole  110 , regardless of the pressure or vibration transmitted to the liquids  300  and  400  in the hole  110 , the insulation liquid  400  maintains a sag with a lower peripheral portion in response to the voltage applied to the chamber  100  and the conductive transparent plate  600 , as shown in  FIG. 6 . This reduces the possibility of the liquids leaking out of the hole  110 . 
         [0050]    Therefore, according to the exemplary method of fabricating a liquid lens, the hole  110  does not have to be formed in a great depth to prevent the leakage of the insulation liquid  400  in the process of sealing the hole  110 , thus resulting in a liquid lens with a reduced overall thickness. 
         [0051]    In addition, according to the exemplary method of fabricating a liquid lens, the possibility of leakage of the electrolyte  300  and insulation liquid  400  can be decreased, allowing more stable fabrication of the liquid lens, thereby improving productivity. Moreover, according to the exemplary method of fabricating a liquid lens, the liquid lens can advantageously maintain a contact state of the electrolyte  300  and the chamber  100  even after the hole  110  is finally sealed by the conductive transparent plate  600 . 
         [0052]    According to the exemplary method of fabricating a liquid lens, a meniscus forms a sag with a lower peripheral portion due to electrowetting to stably seal liquids without leakage of insulation liquid or deformation of meniscus. Moreover, the exemplary method allows electrolyte and a chamber to maintain a contact state with each other, stably inducing electrowetting. Further, the exemplary method allows a decreased depth of a hole containing the electrolyte and the insulation liquid to reduce an overall size of the liquid lens. 
         [0053]    In addition, the exemplary method of fabricating a liquid lens reduces the possibility of leakage of liquids filled in the hole to more stably fabricate a liquid lens, thereby improving productivity. 
         [0054]    Furthermore, a liquid lens according to the present invention has a smaller thickness than the conventional liquid lens, realizing miniaturization of a final product adopting the liquid lens. 
         [0055]    While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.