Abstract:
Provided is an electronic circuit. The electronic circuit includes: a substrate including a device region and a wiring region; an electronic device disposed on the device region; and a conductive wire disposed on the wiring region and connected to the electronic device, wherein the substrate has a first side where the electronic device and the conductive wire contact and a second side facing the first side; the first side and the second side of the wiring region have a convex structure; the first side of the device region is flat; and the device region is thicker than the wiring region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2013-0013442, filed on Feb. 6, 2013, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention disclosed herein relates to an electronic circuit and a method of fabricating the same, and more particularly, to a stretchable electronic device and a method of fabricating the same. 
         [0003]    Recently, with the development of multimedia, the importance of a stretchable electronic circuit is increasing. The stretchable electronic device may be applied to various applications such as a sensor skin for robot, a wearable communication device, a human body built-in/attachable bio device, and/or a next generation display. Accordingly, an organic light emitting display (OLED), a liquid crystal display (LCD), an electrophoretic display (EPD), a plasma display panel (PDP), a thin-film transistor (TFT), a microprocessor, and random access memory (RAM) are required to be fabricated on a stretchable substrate. The stretchable substrate needs to maintain an electrical function even when it expands or contracts. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides a stretchable electronic circuit absorbing impact applied from outside and maintaining a circuit function. 
         [0005]    Embodiments of the present invention provide electronic circuits including: a substrate including a device region and a wiring region; an electronic device disposed on the device region; and a conductive wire disposed on the wiring region and connected to the electronic device, wherein the substrate has a first side where the electronic device and the conductive wire contact and a second side facing the first side; the first side and the second side of the wiring region have a convex structure; the first side of the device region is flat; and the device region is thicker than the wiring region. 
         [0006]    In some embodiments, an uppermost part of the wiring region may have a lower level than an uppermost part of the device region. 
         [0007]    In other embodiments, the wiring region may be more flexible than the device region. 
         [0008]    In still other embodiments, the convex structure may be rounded. 
         [0009]    In even other embodiments, the convex structure may have a waveform in which waves progress in one direction, a waveform in which waves progress in one direction and another direction perpendicular to the one direction, a waveform in which waves progress in a zigzag direction, or a waveform in which waves progress in an irregular direction. 
         [0010]    In yet other embodiments, the conductive wire may extend along the convex structure and may have a curve of a waveform. 
         [0011]    In further embodiments, the electronic circuits may further include a first capping layer disposed on the first side and configured to cover the electronic device and the conductive wire. 
         [0012]    In still further embodiments, the electronic circuit may further include a second capping layer spaced from the electronic device and the conductive wire on the second side. 
         [0013]    In even further embodiments, the device region may have a thickness of about 10 μm to about 100 μm, and the wiring region may have a thickness of about 1 μm to about 10 μm. 
         [0014]    In other embodiments of the present invention, provided are methods of fabricating an electronic circuit. The method include: providing a mold having a rounded pattern; forming a substrate covering the mold; forming a flat device region on the substrate by removing a portion of the substrate; forming a wiring region having a convex structure on the substrate; and forming a conductive wire on the wiring region and forming electronic devices on the device region, wherein the wiring region has a thinner thickness than the device region and has the convex structure extending along a pattern of the mold. 
         [0015]    In some embodiments, the forming of the wiring region may include spin-coating polymer to allow an uppermost surface of the wiring region to have a lower level than an uppermost surface of the device region. 
         [0016]    In other embodiments, the forming of the device region may include etching the substrate corresponding to the wiring region. 
         [0017]    In still other embodiments, the providing of the molding may include: 
         [0018]    providing a mother substrate having an angular recess; and forming a sacrificial layer having a rounded surface on the mother substrate. 
         [0019]    In even other embodiments, the providing of the mold may include: forming a photoresist layer on a mother substrate; forming an angular pattern on the photoresist layer; and forming the rounded pattern by reflowing the photoresist layer, wherein the rounded pattern may have a form corresponding to the convex structure. 
         [0020]    In yet other embodiments, the providing of the mold may include: providing a mother substrate coated with a photoresist layer; and forming a rounded pattern on the photoresist layer by using a grayscale photomask, wherein the rounded pattern may have a waveform corresponding to the convex structure. 
         [0021]    In further embodiments, the methods may further include a first capping layer covering the conductive wire and the electronic device on the substrate, wherein the first capping layer may include an elastomer. 
         [0022]    In still further embodiments, the methods may further include a second capping layer spaced from and facing the conductive wire and the electronic device, wherein the second capping layer may include an elastomer. 
         [0023]    In even further embodiments, the methods may further include separating the substrate from the mold. 
         [0024]    In yet further embodiments, the electronic devices may be spaced from each other, and the conductive wire may extend along the convex structure and electrically connect the electronic devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the drawings: 
           [0026]      FIG. 1  is a plan view illustrating an electronic circuit according to an embodiment of the present invention; 
           [0027]      FIG. 2  is a sectional view taken along a line A-B of  FIG. 1 ; 
           [0028]      FIGS. 3A to 3D  are perspective view illustrating a convex structure according to embodiments of the present invention; 
           [0029]      FIGS. 4 and 5  are sectional views illustrating a method of fabricating a mold according to an embodiment of the present invention; 
           [0030]      FIGS. 6 and 7  are sectional views illustrating a method of fabricating a mold according to another embodiment of the present invention; 
           [0031]      FIGS. 8 and 9  are sectional views illustrating a method of fabricating a mold according to another embodiment of the present invention; and 
           [0032]      FIGS. 10 to 16  are sectional views illustrating a method of fabricating an electronic circuit according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0033]    Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. 
         [0034]    The meaning of “include,” “comprise,” “including,” or “comprising,” specifies a property, a region, a fixed number, a step, a process, an element and/or a component but does not exclude other properties, regions, fixed numbers, steps, processes, elements and/or components. 
         [0035]    In the drawings, the dimensions of layers and regions are exaggerated for clarity of illustration. It will also be understood that when a layer (or film) is referred to as being ‘on’ another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being ‘under’ another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being ‘between’ two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
         [0036]    The meaning of “include,” “comprise,” “including,” or “comprising,” specifies a property, a region, a fixed number, a step, a process, an element and/or a component but does not exclude other properties, regions, fixed numbers, steps, processes, elements and/or components. Hereinafter, it will be described about an exemplary embodiment of the present invention in conjunction with the accompanying drawings. 
         [0037]    Unless otherwise defined therein, terms used in this specification are interpreted by those skilled in the art as typically known meanings. 
         [0038]    Hereinafter, an electronic circuit according to an embodiment of the present invention is described with reference to the accompanying drawings. 
         [0039]      FIG. 1  is a plan view illustrating an electronic circuit according to an embodiment of the present invention.  FIG. 2  is a sectional view taken along a line A-B of  FIG. 1 . 
         [0040]    Referring to  FIGS. 1 and 2 , the electronic circuit  1  includes a conductive wire  200 , an electronic device  300 , and a capping layer  400 , on a substrate  100 . 
         [0041]    The substrate  100  may include elastomeric material. For example, the substrate  100  may include polyimide. The substrate  100  includes a wiring region  100   a  and a device region  100   b . The device region  100   b  may be flat. The device region  100   b  has a thickness of about 10 μm to about 100 μm and may be more rigid than the wiring region  100   a . A convex structure  150  may be provided on the wiring region  100   a . The convex structure  150  may be rounded. For example, the convex structure  150  may have a waveform. The uppermost surface of the convex structure  150  may have a lower level than that of the device region  100   b . The wiring region  100   a  may have a thinner thickness than the device region  100   b , for example, a thickness of about 1 μm to about 10 μm. As the wiring region  100   a  has a thinner thickness than the device region  100   b  and the convex structure  150 , it may be more flexible than the device region  100   b.    
         [0042]      FIGS. 3A to 3D  are perspective view illustrating a convex structure according to embodiments of the present invention. Hereinafter, this will be described with reference to  FIGS. 1 and 2 . 
         [0043]    Referring to  FIG. 3A , the convex structure  150  may have a waveform in which waves progress in an x-axis direction. For example, an x-axis section of the convex structure  150  is curved and a y-axis section and plane of the convex structure  150  may have a straight line form. A z-axis of the convex structure  150  may have different heights. 
         [0044]    Referring to  FIG. 3B , the convex structure  150  may have a waveform in which waves progress in an x-axis and a y-axis. For example, x-axis and y-axis sections of the convex structure  150  may be curved. The convex structure  150  may have different heights in a z-axis. The z-axis of the convex structure  150  may have different heights. 
         [0045]    Referring to  FIG. 3C , the convex structure  150  may have a waveform in which waves progress in a zigzag direction. For example, an x-axis section, a y-axis section, and a plane (i.e., a z-axis section) of the convex structure  150  may be curved. The z-axis of the convex structure  150  may have different heights. 
         [0046]    Referring to  FIG. 3D , the convex structure  150  may have a waveform in which waves progress in an irregular direction. An x-axis section, a y-axis section, and/or a plane of the convex structure  150  may be curved in an irregular form. The z-axis of the convex structure  150  may have different heights. 
         [0047]    Referring to  FIGS. 1 and 2  again, the conductive wire  200  may be provided on the wiring region of the substrate  100 . The conductive wire  200  may have a pattern on the substrate  100 . The conductive wire  200  may have a plane including straight lines extending in one direction. The conductive wire  200  may further include straight lines extending in a different direction than the one direction. The conductive line  200  may extend on a portion of the device region  100   b . The conductive wire  200  may extend along the convex structure  150  of the substrate  100  and may be curved. For example, the conductive wire  200  may have the same waveform as that of  FIGS. 3A to 3D . The conductive wire  200  may contact the electronic device  300 . The conductive wire may be disposed between the electronic devices  300  to electrically connect the electronic devices  300 . The conductive wire  200  may include conductive material. For example, the conductive wire  200  may include at least one of aluminum, gold, copper, tungsten, polysilicon doped with an impurity and/or alloys thereof. 
         [0048]    The electronic device  300  may be provided on the device region  100   b  of the substrate  100 . The electronic device  300  may include at least one of an organic light emitting display (OLED), a liquid crystal display (LCD), an electrophoretic display (EPD), a plasma display panel (PDP), a thin-film transistor (TFT), a microprocessor, and/or random access memory (RAM). 
         [0049]    The capping layer  400  may include a first capping layer  410  and a second capping layer  420 . The first capping layer  410  may be provided on a first side  101  of the substrate  100 . The first capping layer  410  may cover the conductive wire  200  and/or the electronic device  300 . The capping layer  420  may be provided on a second side  102  of the substrate  100 . The second capping layer  420  may be spaced from the conductive wire  200  and the electronic device  300 . The capping layer  400  may include elastomeric material, for example, polydimethylsiloxane (PDMS). The capping layer  400  may protect the conductive wire  200  and/or the electronic device  300 . As another example, the first capping layer  410  and/or the second capping layer  420  may be omitted. 
         [0050]    The electronic circuit  1  may be a stretchable electronic circuit. External impact may be applied to the electronic circuit  1 . Since the convex structure  150  and/or the conductive wire  200  of the substrate  100  have/has a curvature of a waveform, the impact may be absorbed. The impact applied to the electronic circuit  1  may be distributed through the capping layer  400  in addition to the substrate  100 . In spite of the external impact, the conductive wire  200  may maintain an electrical connection between the electronic devices  300 . As the electronic device  300  is disposed on the flat device region  100   b , it may not be affected from external impact. Therefore, functions of the electronic circuit  1  may be maintained. 
         [0051]    A method of fabricating an electronic circuit according to embodiments of the present invention is described. Hereinafter, for conciseness of description, redundant content for the description of  FIGS. 1 to 3  is omitted. 
       EXAMPLE 1  
     Of Fabricating Mold 
       [0052]      FIGS. 4 and 5  are sectional views illustrating a method of fabricating a mold according to an embodiment of the present invention. 
         [0053]    Referring to  FIG. 4 , a mother substrate  510  having an angular recess  511  is provided. The mother substrate  510  may be hard. For example, the mother substrate  510  may be a silicon wafer. As another example, the mother substrate  510  may include at least one of glass, plastic, indium tin oxide (ITO), and/or fluoride containing tin oxide (FTO). The recess  511  may be formed by patterning the mother substrate  510 . The top surface of the recess  511  may have a lower level than that of the mother substrate  510 . 
         [0054]    Referring to  FIG. 5 , a sacrificial layer  520  may be formed on the mother substrate  510 . For example, the sacrificial layer  520  may be formed by spin-coating polymethylmethacrylate (PMMA) on the mother substrate  510 . The sacrificial layer  520  may cover the recess  511  of the mother substrate  510  to form a rounded pattern  500   a . The rounded pattern  500   a  may be formed to have a form corresponding to the convex structure  150  of the substrate  100  of  FIG. 1 . For example, the rounded pattern  500   a  may have a waveform such as that shown in  FIGS. 3A to 3D . Through the fabricating method according to the above-mentioned embodiment of the present invention, the mold  500  having the rounded pattern  500   a  may be completed. 
       EXAMPLE 2  
     Of Fabricating Mold  
       [0055]      FIGS. 6 and 7  are sectional views illustrating a method of fabricating a mold according to another embodiment of the present invention. As mentioned above, redundant description is omitted. 
         [0056]    Referring to  FIG. 6 , a mother substrate  510  including a photoresist layer  530  is provided. The mother substrate  510  may include silicon, glass, plastic, ITO, or FTO. The photoresist layer  530  may have an angular pattern  531 . The photoresist layer  530  may be formed on the mother substrate  510  through patterning including deposition and exposure processes of photoresist material. 
         [0057]    Referring to  FIG. 7 , a rounded pattern  500   a  may be formed on the photoresist layer  530 . Through a reflow process, the angular pattern  531  of  FIG. 5  may change into the angular pattern  500   a . The reflow process may be performed at more than a glass transition temperature of the photoresist layer  530 . The rounded pattern  500   a  may have a waveform such as that shown in  FIGS. 3A to 3D . Through the fabricating method according to the above-mentioned embodiment of the present invention, a mold  500  having the rounded pattern  500   a  may be completed. 
       EXAMPLE 3  
     Of Fabricating Mold  
       [0058]      FIGS. 8 and 9  are sectional views illustrating a method of fabricating a mold according to another embodiment of the present invention. As mentioned above, redundant description is omitted. 
         [0059]    Referring to  FIG. 8 , a mother substrate  510  including a photoresist layer  530  is provided. Each of the mother substrate  510  and the photoresist layer  530  may include the same or similar materials as described in  FIG. 6 . 
         [0060]    Referring to  FIG. 9 , a rounded pattern  500   a  may be formed on the photoresist layer  530 . The rounded pattern  500   a  may have a waveform such as that shown in  FIGS. 3A to 3D . Patterning is performed through a gray scale exposure process (lithography) using a grayscale photomask  600  capable of adjusting the amount of penetrating light. As light penetrates the grayscale photomask  600 , the degree of exposure of the photoresist layer  530  may vary according to the amount of penetrating light. The photoresist layer  530  may be exposed as periodically changing a progression direction of light, a transmittance of light, and/or the intensity of light. Accordingly, by adjusting the photoresist layer  530  removed during development, a form of the pattern  500   a  may be controlled. For example, a waveform may be formed by adjusting amplitude, period, and orientation. 
         [0061]    Through the fabricating method according to the above-mentioned embodiment of the present invention, a mold  500  having the rounded pattern  500   a  may be completed. 
       EXAMPLE OF FABRICATING ELECTRONIC CIRCUIT  
       [0062]      FIGS. 10 to 16  are sectional views illustrating a method of fabricating an electronic circuit according to an embodiment of the present invention. As mentioned above, redundant description is omitted. 
         [0063]    Referring to  FIG. 10 , a substrate  110  may be formed on a mold  500 . The mold  500  may be the one  500  having the rounded pattern  500   a  fabricated as an example of  FIGS. 6 and 7  or an example of  FIGS. 8 and 9 . For example, the substrate  110  may cover the mold  500  by spin-coating flexible polymer such as polyimide on the mold  500 . The substrate  110  may have a second side  102  contacting the mold  500  and a first side  101  facing the second side  102 . The substrate  110  may be formed to have the flat first side  101  by adjusting the thickness of the substrate  110 . 
         [0064]    Referring to  FIG. 11 , a portion of the substrate  110  may be removed thereby forming a device region  100   b . For example, the removal of the substrate  110  may be performed through wet etching. That is, the substrate  110  corresponding to the wiring region  100   a  may be removed. The substrate corresponding to the device region  100   b  may not be removed. The first side  101  of the device region  100   b  may be flat. 
         [0065]    Referring to  FIG. 12 , a substrate  120  corresponding to the wiring region  100   a  may be formed by spin-coating polymer such as polyimide on the mold  500 . The wiring region  100   a  may be formed to have a thickness of about 1 μm to about 10 μm. A convex structure  150  may be formed on a first side  101  in the wiring region  100   a . The convex structure  150  may extend along the pattern  500   a  of the mold  500  and may be rounded. The convex structure  150  may have a form corresponding to the pattern  500   a  of the mold  500 . The uppermost surface of the wiring region  100   a  may have a lower level than that of the device region  100   b.    
         [0066]    Referring to  FIG. 13 , the conductive wire  200  may be formed on the wiring region  100   a  of the substrate  100 . The conductive wire  200  may be formed on a portion of the device region  100   b . An electronic device  300  may be formed on the device region  100   b  of the substrate  100 . A formation process of the electronic device  300  may be performed before the conductive wire  200  is formed. 
         [0067]    Referring to  FIG. 14 , a first capping layer  410  is formed on the first side  101  of the substrate  100  so as to cover the conductive wire  200  and the electronic device  300 . The first capping layer  410  may be formed by coating and solidifying elastomeric material, for example, PDMS. 
         [0068]    Referring to  FIG. 15 , the mold  500  is removed so that the substrate  100  may be separated from the mold  500 . The removal of the mold  500  may be performed through a lift off process or mechanical separation. 
         [0069]    Referring to  FIG. 16 , a second capping layer  420  may be formed to cover a second side  102 . The second capping layer  420  may be formed by coating and solidifying elastomeric material, for example, PDMS. Therefore, the electronic device  1  may be fabricated completely. As another example, the formation of the second capping layer  420  may be omitted. 
         [0070]    Patterning by a pre-strain method may be difficult to adjust a position at which a pattern is formed, an area of the pattern, and a shape of the pattern. A method of fabricating the electronic circuit  1  according to an embodiment of the present invention may easily adjust the areas and positions of the wiring region  100   a  and the device region  100   b . The convex structure  150  may be fabricated to have a desired structure and/or form. For example, the convex structure  150  having a waveform may be fabricated by adjusting an amplitude, period, and/or orientation of a wave. Additionally, the stretchable electronic circuit  1  may be fabricated using polymer such as polyimide instead of elastomeric material. 
         [0071]    According to an embodiment of the present invention, an electronic device may include a substrate having a device region and a wiring region. The device region is flat and the wiring region has a rounded convex structure. The thickness of the wiring region is thinner than that of the device region. The wiring region may be more flexible than the device region. According to the concept of the present invention, an electronic device may be flexible and stretchable. An impact applied from the outside to the electronic device may be received by a wiring region and a conductive wire. That is, the electronic device may not be affected by external impact. Therefore, an electronic circuit may maintain its functions. 
         [0072]    The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.