Patent Publication Number: US-11644702-B2

Title: Semiconductor substrate

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/151,924, filed on Jan. 19, 2021, which, in turn, is a continuation of U.S. patent application Ser. No. 16/812,461 (now U.S. Pat. No. 10,928,661), filed on Mar. 9, 2020, which, in turn, is a continuation of U.S. patent application Ser. No. 15/792,955 (now U.S. Pat. No. 10,620,464), filed on Oct. 25, 2017. Further, this application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2016-220419, filed on Nov. 11, 2016, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     One of embodiments of present invention relates to a display device such as an organic EL display device, a liquid crystal display device or the like, and a method for producing the same, for example, a flexible display device and a method for producing the same. 
     BACKGROUND 
     Representative display devices include a liquid crystal display device including a liquid crystal element in each of pixels, an organic EL (electroluminescence) display device including a light emitting element in each of pixels, and the like. These display devices each include a liquid crystal element or an organic light emitting element (hereinafter, referred to as a “light emitting element”) in each of a plurality of pixels provided on a substrate. The liquid crystal element or the light emitting element includes a layer containing a liquid crystal material or an organic compound between a pair of electrodes (hereinafter, the layer containing the organic compound will be referred to as an “organic layer” or an “EL layer), and is driven by a voltage applied between the pair of electrodes or by a current supplied to the pair of electrodes. 
     The substrate of such a display device may be flexible, so that a flexible display device is provided. For example, Japanese Laid-Open Patent Publication No. 2011-183916 discloses a display device including a flexible substrate and a plurality of display regions provided on the substrate. The substrate is folded at an optional angle at a position between the display regions, so that a plurality of display devices is provided on different curved surfaces. 
     SUMMARY 
     An embodiment of the present invention is directed to a display device. The display device includes a base film including a first region and a plurality of second regions having the first region therebetween. The display device further includes an inorganic insulating film on the base film, the inorganic insulating film being in contact with the plurality of second regions of the base film; a plurality of first pixels overlapping the first region; and a plurality of second pixels overlapping the plurality of second regions with the inorganic insulating film being between the plurality of second pixels and the plurality of second regions. The inorganic insulating film is divided by the first region and is discontinuous between the plurality of second regions. 
     An embodiment of the present invention is directed to a display device. The display device includes a base film including a first region and a second region; an underlying film on the base film, the underlying film being in contact with the first region and the second region of the base film; and a plurality of first pixels overlapping the first region and a plurality of second pixels overlapping the second region. The plurality of first pixels and the plurality of second pixels each include a semiconductor film and a gate electrode overlapping each other; and a gate insulating film between the semiconductor film and the gate electrode. The underlying film is thinner on the first region than on the second region. 
     An embodiment of the present invention is directed to a display device. The display device includes a base film including a first display region including a plurality of first pixels, a second display region including a plurality of second pixels, and a first region between the first display region and the second display region; and an inorganic insulating film overlapping the base film in the first display region and the second display region. The first region of the base film is exposed from the inorganic insulating film. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic perspective view of a display device in an embodiment according to the present invention; 
         FIG.  2    is a schematic exploded perspective view of the display device in an embodiment according to the present invention; 
         FIG.  3    is a schematic plan view of the display device in an embodiment according to the present invention; 
         FIG.  4    is a schematic cross-sectional view of the display device in an embodiment according to the present invention; 
         FIG.  5    is a schematic plan view of the display device in an embodiment according to the present invention; 
         FIG.  6 A  is a schematic cross-sectional view of a pixel of the display device in an embodiment according to the present invention; 
         FIG.  6 B  is a schematic cross-sectional view of a pixel of the display device in an embodiment according to the present invention; 
         FIG.  7    is a schematic perspective of the display device in an embodiment according to the present invention; 
         FIG.  8 A  is a schematic cross-sectional view of a pixel of a display device in an embodiment according to the present invention; 
         FIG.  8 B  is a schematic cross-sectional view of a pixel of the display device in an embodiment according to the present invention; 
         FIG.  9 A  is a schematic cross-sectional view showing a step of a method for producing a display device in an embodiment according to the present invention; 
         FIG.  9 B  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  10 A  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  10 B  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  11 A  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  11 B  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  12 A  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  12 B  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  13 A  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  13 B  is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  14    is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  15    is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  16    is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  17    is a schematic cross-sectional view showing a step of the method for producing the display device in an embodiment according to the present invention; 
         FIG.  18    is a schematic plan view of a display device in an embodiment according to the present invention; 
         FIG.  19    is a schematic cross-sectional view of the display device in an embodiment according to the present invention; 
         FIG.  20 A  is schematic plan view of a display device in an embodiment according to the present invention; 
         FIG.  20 B  is schematic plan view of a display device in an embodiment according to the present invention; 
         FIG.  21    is schematic plan view of a display device in an embodiment according to the present invention; 
         FIG.  22    is schematic cross-sectional view of the display device in an embodiment according to the present invention; 
         FIG.  23 A  is a plan view of wirings in the display device in an embodiment according to the present invention; 
         FIG.  23 B  is a plan view of wirings in the display device in an embodiment according to the present invention; 
         FIG.  23 C  is a plan view of wirings in the display device in an embodiment according to the present invention; 
         FIG.  24    is a plan view of wirings in the display device in an embodiment according to the present invention; 
         FIG.  25    is a schematic plan view of a display device in an embodiment according to the present invention; and 
         FIG.  26    is a schematic plan view of a display device in an embodiment according to the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The present invention may be carried out in various forms without departing from the gist thereof, and is not to be construed as being limited to any of the following embodiments. 
     In the drawings, components may be shown schematically regarding the width, thickness, shape and the like, instead of being shown in accordance with the actual sizes, for the sake of clearer illustration. The drawings are merely examples and do not limit the interpretations of the present invention in any way. In the specification and the drawings, components that have substantially the same functions as those described before with reference to a previous drawing(s) bear the identical reference signs thereto, and detailed descriptions thereof may be omitted. 
     In the present invention, in the case where one film is processed into a plurality of films, the plurality of films may have different functions or roles from each other. However, the plurality of films is derived from one, same film and are formed in the same step, and thus have the same layer structure and are formed of the same material as each other. Therefore, the plurality of films is defined as being in the same layer. 
     In the specification and the claims, an expression that a component is “on” another component encompasses a case where such a component is in contact with the another component and also a case where such a component is above or below the another component, namely, a case where still another component is provided between such a component and the another component, unless otherwise specified. 
     The embodiments of the present invention have an object of providing a highly reliable and flexible display device. The embodiments of the present invention have an object of providing a method for producing such a display device. 
     Embodiment 1 
     In this embodiment, a structure of a display device  100  in an embodiment according to the present invention will be described. 
     1. Overall Structure 
       FIG.  1    is a schematic perspective view of the display device  100 . As shown in  FIG.  1   , the display device  100  includes a substrate  102 , a counter substrate  104 , and a plurality of pixels  106  located in a row direction and a column direction between the substrate  102  and the counter substrate  104 . A region where the plurality of pixels  106  are located is a display region  108 . 
     The plurality of pixels  106  each include a display element such as a liquid crystal element, a light emitting element or the like. The display device  100  further includes scanning line driving circuits  110  and a data line driving circuit  112  provided on the substrate  102 . Various signals usable to drive the pixels  106  are input from an external circuit (not shown) to the scanning line driving circuits  110  and the data line driving circuit  112  via a connector such as a flexible printed circuit (FPC) or the like connected to terminals  114  provided on the substrate  102 . Based on these signals, the display element in each pixel  106  is controlled, so that an image is reproduced in the display region  108 . 
     The scanning line driving circuits  110  or the data line driving circuit  112  does not need to be provided directly on the substrate  102 . Alternatively, neither the scanning line driving circuits  110  nor the data line driving circuit  112  needs to be provided directly on the substrate  102 . The scanning line driving circuits  110  or the data line driving circuit  112  may be provided on a substrate different from the substrate  102  (a semiconductor substrate or the like) or a connector and drive the pixels  106 . In the example of  FIG.  1   , the display region  108  and the scanning line driving circuits  110  provided on the substrate  102  are covered with the counter substrate  104 , whereas the data signal driving circuit  112  provided on a different substrate is mounted on the substrate  102 . 
     The substrate  102  and the counter substrate  104  may each be a flexible substrate. In this case, the substrate  102  may be called a “base film” or a “base plate”, and the counter substrate  102  may be called a “cap film” or a “base plate”. In the case where the substrate  102  and the counter substrate  104  are each a flexible substrate, the display device  100  is flexible. The counter substrate  104  may be a resin film or a circularly polarizing plate. 
       FIG.  2    is a schematic exploded perspective view of the display device  100 . As shown in  FIG.  2   , the display device  100  includes an underlying film  116  provided on, and in contact with, the substrate  102 . The underlying film  116  does not need to cover the whole of a top surface of the substrate  102 , and may partially cover the top surface of the substrate  102 . Specifically, a part of the substrate  102  may be exposed from the underlying film  116  with no contact with the underlying film  116 . The underlying film  116  may contain an inorganic insulating material as described below. Therefore, the underlying film  116  may be called an “inorganic insulating film”. In the display device  100 , the plurality of pixels  106  are located in both of a region where the underlying film  116  is provided and a region where the underlying film  116  is not in contact with the substrate  102 . 
     Various types of patterned insulating films and conductive films are provided between the underlying film  116  and the counter substrate  104 . A stack structure of these films forms the pixels  106 , the scanning line driving circuits  110 , the data line driving circuit  112 , and the like. 
       FIG.  3    is a schematic plan view of the display device  100 .  FIG.  3    shows the substrate  102  and the underlying film  116  provided on the substrate  102 . In  FIG.  3   , the regions where the display region  108  and the scanning line driving circuits  110  are provided are represented by dashed lines. As described above, the underlying film  116  does not need to cover the whole of the substrate  102 . Specifically, the underlying film  116  is not provided on a partial region (first region)  120  of the substrate  102 , and the top surface of the substrate  102  is exposed in the first region  120  from the underlying film  116 . In the example of  FIG.  3   , the first region  102  of the substrate  102  is strip-like. The substrate  102  also includes two regions (second regions)  122 , which have the first region  120  therebetween and are covered with the underlying film  116 . The underlying film  116  is divided by the first region  120  and is discontinuous between the two second regions  122 . In other words, the underlying film  116  has an opening or a slit, and the region of the substrate  102  in positional correspondence with the opening or the slit is the first region  120 . 
     The first region  120  is provided to cross the display region  108 , and a part of the plurality of pixels  106  (first pixels) overlap the first region  120 . In this state, the pixels  106  overlapping the first region  120  are arrayed in a matrix. By contrast, the two second regions  122  overlap the display region  108  and a plurality of pixels  106  (second pixels) included in the display region  108 . Namely, the plurality of pixels  106  overlapping each of the two second regions  122  are arrayed in a matrix. As shown in  FIG.  3   , the first region  120  may overlap the scanning line driving circuits  110 . 
       FIG.  4    is a cross-sectional view of the display device  100  taken along chain line A−A′ in  FIG.  3   . As shown in  FIG.  4   , the first region  120  of the substrate  102  is exposed from the underlying film  116 . By contrast, the second regions  122  of the substrate  102  are in contact with the underlying film  116 . The first region  120  and the second regions  122  both overlap the plurality of pixels  106 . The plurality of pixels  106  each include a display element such as a light emitting element  170  or the like. Therefore, in the display device  100 , the whole of the display region  108  overlapping the first region  120  and the second regions  122  reproduces an image. 
     2. Cross-Sectional Structure 
       FIG.  5    is a schematic plan view of two adjacent pixels  106  each including the light emitting element  170 . In  FIG.  5   , the components are shown as not overlapping each other for visibility. A part of the components may overlap each other. A part of the components is omitted in  FIG.  5   . 
     As shown in  FIG.  5   , the display device  100  includes wirings, such as a plurality of gate lines  132 , a plurality of data lines  130 , a plurality of current supply lines  134  and the like. The gate lines  132  are each electrically connected with a plurality of pixels  106 , and two of the pixels  106  are shown in  FIG.  5   . The data lines  130  and the current supply lines  134  are each connected with a plurality of pixels located along the lines  130  and  134  respectively. 
     The pixels  106  each include transistors  140  and  150 . The transistor  140  includes a semiconductor film  142 , a gate  144  (gate electrode), a drain  146  (drain electrode), a source  148  (source electrode), and the like. The gate  144  is a part of the corresponding gate line  132 , and drain  146  is a part of the corresponding data line  130 . 
     The transistor  150  includes a part of a semiconductor film  164 , a gate  152  (gate electrode), a drain  154  (drain electrode), a source  156  (source electrode) and the like. The drain  154  is a part of the corresponding current supply line  134 . The source  148  of the transistor  140  is connected with a first capacitor electrode  160  located in the same layer as the gate line  132 , and a part of the first capacitor electrode  160  acts as the gate  152  of the transistor  150 . Therefore, a signal generated by the data line driving circuit  112  and input from the data line  130  is input to the gate  152  of the transistor  150  via the transistor  140 . 
     The semiconductor film  164  and a second capacitor electrode  162  are provided to overlap the first capacitor electrode  160 . Although not shown in  FIG.  5   , an insulating film acting as a gate insulating film  118  of the transistor  140  and the transistor  150  is provided between the first capacitor electrode  160  and the semiconductor film  164  as described below. An insulating film acting as an interlayer insulating layer (represented by reference numeral  124  in  FIG.  6 A  and the like) covering the gate  144  of the transistor  140  and the gate  152  of the transistor  150  is provided between the semiconductor film  164  and the second capacitor electrode  162 . The first capacitor electrode  160 , the gate insulating film  118 , the semiconductor film  164 , the interlayer insulating film  124 , and the second capacitor electrode  162  form a capacitor  158  ( FIG.  6 A  and  FIG.  6 B ). The capacitor  158  contributes to maintaining the potential of the gate  152  of the transistor  150 . 
     The pixel  106  further includes a storage capacitor electrode  166 . The storage capacitor electrode  166  may be electrically connected with the corresponding current supply line  134 . The pixel  106  includes a first electrode  172  acting as a pixel electrode. In  FIG.  5   , the first electrode  172  is not shown in the left pixel  106  for visibility. The first electrode  172  is electrically connected with the source  156  of the transistor  150 . Although not shown in  FIG.  5   , the storage capacitor electrode  166 , the first electrode  172  and an insulating film provided between the storage capacitor electrode  166  and the first electrode  172  form a storage capacitance. The storage capacitor contributes to maintaining the potential of the gate  152  of the transistor  150 . 
     Although not shown in  FIG.  5   , a second electrode  178  of the light emitting element  170  is provided on the first electrode  172 . The second electrode  178  is provided commonly for the plurality of pixels  106  and thus are shared by the plurality of pixels  106 . An EL layer (not shown in  FIG.  5   ; represented in  FIG.  6 A  by reference numeral  188 ) is provided between the first electrode  172  and the second electrode  178 . The light emitting element  170  includes the first electrode  172 , the second electrode  178  and the EL layer. Although not shown, the pixel  106  is not limited to having the above-described structure. The pixel  106  may further include another wiring, transistor, capacitor or the like. Alternatively, the pixel  106  does not need to include the storage capacitor. 
       FIG.  6 A  and  FIG.  6 B  are each a cross-sectional view of the display device  100  taken along a chain line B-B′ in  FIG.  5   .  FIG.  6 A  is a schematic cross-sectional view of the pixel  106  provided on the second region  122 .  FIG.  6 B  is a schematic cross-sectional view of the pixel  106  provided on the first region  120 . 
     As shown in  FIG.  6 A , the pixel  106  includes the underlying film  116  provided on the second region  122  of the substrate  102 . The underlying film  116  may contain an inorganic insulating material. Examples of the inorganic insulating material usable for the underlying film  116  include silicon-containing inorganic materials such as silicon oxide, silicon nitride, silicon nitride oxide, silicon oxide nitride, and the like. The underlying film  116  may have a single-layer structure or a stack structure of a plurality of layers. In the example of  FIG.  6 A , the underlying film  116  includes three layers (a first layer  116 _ 1 , a second layer  116 _ 2  and a third layer  116 _ 3 ). In this case, for example, the second layer  116 _ 2  may contain silicon nitride, whereas the first layer  116 _ 1  and the third layer  116 _ 3  may contain silicon oxide. The first layer  116 _ 1 , the second layer  116 _ 2  and the third layer  116 _ 3  may respectively have thicknesses of 20 nm to 50 nm, 20 nm to 50 nm, and 100 nm to 500 nm. 
     On the second region  122 , the transistor  150  is provided on the underlying film  116 . A part of the gate insulating film  118  of the transistor  150 , and the semiconductor film  164 , may be in contact with the underlying film  116 . 
     A part of the semiconductor film  164  also acts as one electrode of the capacitor  158 . On the semiconductor film  164 , the gate insulating film  118  and the first capacitor electrode  160  are provided. The interlayer insulating film  124  is provided to cover the first capacitor electrode  160  and the gate  152 . On the interlayer insulating film  124 , the second capacitor electrode  162  overlapping the first capacitor electrode  160  is provided. The second capacitor electrode  162  also acts as the source  156 . 
     Optionally, the pixel  106  may further include a first passivation film  126  covering the transistor  150  and the capacitor  158 . 
     On the transistor  150  and the capacitor  158 , a flattening film  168  is provided to absorb the ruggedness caused by these components and provide a flat surface. The flattening film  168  has an opening, and the first electrode  172  of the light emitting element  170  is electrically connected with the source  156  of the transistor  150  via a connection electrode  180  in the opening. 
     On the flattening film  168 , a partitioning wall  186  is provided to absorb the ruggedness caused by the opening of the flattening layer  168  and an end of the first electrode  172 . The EL layer  188  and the second electrode  178  are provided on the first electrode  172  and the partitioning wall  186 . The light emitting element  170  includes the first electrode  172 , the EL layer  188 , and the second electrode  178 . 
     Optionally, the pixel  106  may further include a second passivation film  190  on the light emitting element  170 . The second passivation film  190  prevents entrance of impurities such as water, oxygen and the like from outside. 
     The counter substrate  104  is provided on the light emitting element  170  or the second passivation film  190 . Although not shown, an adhesive layer or the like may be provided between the light emitting element  170  or the second passivation film  190  and the counter substrate  104 . 
     As shown in  FIG.  6 B , on the first region  120 , the underlying film  116  is not provided in the pixel  106 . Therefore, for example, a part of the gate insulating film  118  may be in contact with the substrate  102 . The semiconductor film  164  may also be in contact with the substrate  102 . The structure of the pixel  106  on the first region  120  is the same as that of the pixel  106  on the second region  122  except that the underlying film  116  is not provided on the first region  120 . Since the underlying film  116  is not provided on the first region  120 , the flattening layer  168  is thicker on the first region  120  than on the second region  122 . 
     As described above, the underlying film  116  contains an inorganic insulating material, and thus is more rigid than a film containing an organic material. Therefore, when the display device  100  is bent or folded to be deformed, the underlying film  116  is easily cracked. Generation of cracks causes wirings provided on the underlying film  116  to be broken or disconnected. For example, the wirings such as the gate line  132 , the data line  130 , the current supply line  134  and the like, or the electrodes such as the first capacitor electrode  160 , the second capacitor electrode  162 , the storage capacitor electrode  166 , the first electrode  172  and the like are broken or disconnected. As a result, light is not emitted from a part of or all of the pixels  106  in the display device  100 . In this case, the display device  100  does not function as a display device. 
     However, as shown in  FIG.  3    and  FIG.  4   , the display device  100  includes the first region  120 , on which the underlying film  116  is provided. The display device  100  is bent in the first region  120  easily or selectively. In the case where, for example, the substrate  102 , and thus the display device  100 , has a three-dimensional structure shown in  FIG.  7   , the substrate  102  is bent in the first region  120  so that the display device  100  is deformed such that the two second regions  122  overlap each other. On the first region  120 , the wiring or the electrodes are not broken or disconnected due to the breakage of the underlying film  116 . In this manner, the breakage or the disconnection of the wiring is effectively suppressed. Thus, the breakage of the display device  100  is prevented. Therefore, the display device  100  in this embodiment is highly reliable and flexible. 
     Embodiment 2 
     In this embodiment, a display device  200  having a different structure from that of the display device  100  will be described. Components the same as or similar to those in embodiment 1 may not be described. 
     Unlike in the display device  100 , in display device  200 , the underlying film  116  is provided both on the first region  120  and the second regions  122 , and the underlying film  116  is thinner on the first region  120  than on the second regions  122 . 
       FIG.  8 A  and  FIG.  8 B  are each a cross-sectional view of the display device  200  corresponding to cross section taken along a chain line B-B′ in  FIG.  5   .  FIG.  8 A  is a schematic cross-sectional view of the pixel  106  provided on the second region  122 .  FIG.  8 B  is a schematic cross-sectional view of the pixel  106  provided on the first region  120 . As shown in  FIG.  8 A , on the second region  122 , the pixel  106  is substantially the same as that in the display device  100 . The underlying film  116  is provided between the substrate  102  and the transistor  150 , and the underlying film  116  is in contact with the substrate  102 . 
     In the display device  200 , a part of the underlying film  116  extends from the second region  122  to the first region  120 , and is sandwiched by the transistor  150  in the pixel  106  and the first region  120  of the substrate  102 . In the example of  FIG.  8 B , the first layer  116 _ 1  extends from the second region  122  to the first region  120 . Therefore, the number of the layer(s) of the underlying film  116  or the thickness of the underlying film  116  is smaller on the first region  120  than on the first region  120 . Although not shown, the second layer  116 _ 2  or the third layer  116 _ 3  may extend to the first region  120  instead of the first layer  116 _ 1 . 
     With such a structure, in embodiment 2, like in embodiment 1, the first region  120  is more flexible than the second regions  122 , and the display device  200  is deformed more easily in the first region  120  than in the second regions  122 . Even though the first region  120  is bent to deform the display device  200 , the underlying film  116  is not easily cracked on the first region  120  because the underlying film  116  is thinner on the first region  120 . In this manner, the breakage or the disconnection of the wirings and the electrodes is suppressed. Thus, the breakage of the display device  100  is prevented. Therefore, the display device  200  in this embodiment is highly reliable and flexible. 
     Since the underlying film  116  is provided also on the first region  120 , entrance of impurities such as alkaline ions or the like from the first substrate  102  to the transistors  140  and  150  is prevented. This provides high reliability for the semiconductor element used to drive the display device  200 . 
     Embodiment 3 
     In this embodiment, a method for manufacturing the display device  100  in embodiment 1 will be described with reference to  FIG.  6 A ,  FIG.  6 B  and  FIG.  9 A  through  FIG.  17   . Components the same as or similar to those in embodiment 1 may not be described.  FIG.  9 A  through  FIG.  17    each correspond to  FIG.  6 A  and  FIG.  6 B .  FIG.  9 A  through  FIG.  17    each provide cross-sectional views of the pixels  106  on the second region  122  and the first region  120 . The cross-sectional views in  FIG.  9 A  through  FIG.  17    correspond to cross section taken along a chain line B-B′ in  FIG.  5   . 
     1. Underlying Film 
     As shown in  FIG.  9 A , the substrate  102  is formed on a support substrate  128 . The support substrate  128  has a function of supporting the substrate  102  and various other components formed on the substrate  102 , for example, the transistors  140  and  150 , the capacitor  158 , the light emitting element  170  and the like. Therefore, the support substrate  128  may be formed of a material that is resistant against the temperature of processes performed on the components to be formed thereon and is chemically stable against chemicals used in the steps. Specifically, the support substrate  128  may contain glass, quartz, plastics, a metal, ceramics or the like. 
     The substrate  102  is formed of a flexible insulating film, and may contain, for example, a polymer material. Examples of the polymer material usable for the substrate  102  include a polyimide, a polyamide, a polyester, a polycarbonate and the like. These polymer materials may be chain-like or may form a three-dimensional network by intermolecular crosslinking. The substrate  102  may be formed by, for example, a wet film formation method such as printing, ink-jetting, spin-coating, dip-coating or the like, or by lamination. Alternatively, the substrate  102  may be formed by forming precursors of any of the above-described polymer materials on the support substrate  128  and causing a polymer reaction of the precursors. 
     Next, as shown in  FIG.  9 A , the underlying film  116  is formed on the second region  122  of the substrate  102 . As described above in embodiment 1, the underlying film  116  may contain an inorganic insulating material such as silicon nitride, silicon oxide, silicon nitride oxide, silicon oxide nitride or the like. The underlying film  116  may be formed by chemical vapor deposition (CVD), sputtering or the like to have a single-layer structure or a stack structure. For example, the underlying film  116  may be formed on substantially the whole of the top surface of the substrate  102 , and then a part of the underlying film  116  that is on the first region  120  may be selectively removed by etching. In the case of having a stack structure, the underlying film  116  may include, for example, a silicon nitride layer sandwiched between silicon oxide layers. In the example of  FIG.  9 A , the underlying film  116  has a three-layer structure including the first layer  116 _ 1 , the second layer  116 -_ 2  and the third layer  116 _ 3 . 
     2. Transistors 
     Next, the semiconductor film  164  is formed in each of the pixels  106  ( FIG.  9 B ). The semiconductor film  164  may contain a Group 14 element such as silicon or the like. Alternatively, the semiconductor film  164  may contain an oxide semiconductor. Examples of the oxide semiconductor usable for the semiconductor film  164  include a Group 13 element such as indium, gallium or the like, for example, a mixed oxide of indium and gallium (IGO). In the case of containing an oxide semiconductor, the semiconductor film  164  may further contain a Group 12 element. Examples of the Group 12 element that may be contained in the semiconductor film  164  include a mixed oxide containing indium, gallium and zinc (IGZO). There is no specific limitation to the crystallinity of the semiconductor film  164 . The semiconductor film  164  may be single crystalline, polycrystalline, microcrystalline or amorphous. Alternatively, these crystalline states may be mixed in the semiconductor film  164 . 
     In the case of containing silicon, the semiconductor film  164  may be formed by CVD using silane gas or the like as a raw material. The obtained amorphous silicon may be heated or exposed to light such as laser light or the like to be crystallized. In the case of containing an oxide semiconductor, the semiconductor film  164  may be formed by sputtering or the like. 
     Next, the semiconductor film  164  is subjected to first doping. Specifically, the first doping is performed as follows. A resist mask  198  is formed on the semiconductor film  164  to cover a region where a channel of the transistor  150  is to be formed ( FIG.  9 B ). In this state, the semiconductor film  164  is doped with ion. Examples of the usable ion include ion of phosphorus or nitrogen that provides n-type conductivity and ion of boron that provides p-type conductivity. After that, the resist mask  198  is removed. As a result, as shown in  FIG.  10 A , doped regions  164 _ 1  and an undoped region  164 _ 2  are formed in the semiconductor film  164 . 
     Next, the gate insulating film  118  is formed to cover the semiconductor film  164  ( FIG.  10 A ). The gate insulating film  118  may have a single-layer structure or a stack structure. The gate insulating film  118  may contain a material usable for the underlying film  116 . The gate insulating film  118  may be formed by CVD, sputtering or the like. 
     Next, the gate  152  and the first capacitor electrode  160  are formed on the gate insulating film  118  by sputtering or CVD ( FIG.  10 B ). The gate  152  and the first capacitor electrode  160  are formed in the same layer. The gate  152  is formed to overlap the undoped region  164 _ 2 . The first capacitor electrode  160  is formed to overlap the doped region  164 _ 1 . The gate  152  and the first capacitor electrode  160  may be formed of a metal such as titanium, aluminum, copper, molybdenum, tungsten, tantalum or the like or an alloy thereof, and may be formed to have a single-layer structure or a stack structure. For example, the gate  152  and the first capacitor electrode  160  may have a stack structure including a layer of a highly conductive metal material such as aluminum, copper or the like and a layer of a high melting point such as titanium, tungsten, molybdenum or the like formed on a layer of a metal with a highly conductive metal. Alternatively, the gate  152  and the first capacitor electrode  160  may have a structure in which a layer of a highly conductive metal is sandwiched between layers of a metal with a high melting point. 
     Next, the semiconductor film  164  is subjected to second doping with the gate  152  being used as a mask. The conditions for the second doping are adjusted such that the semiconductor film  164  is doped with a dopant at a lower concentration than in the first doping. As a result, low concentration impurity regions  164 _ 3  are formed in a region of the undoped region  164 _ 2  that does not overlapping the gate  152  ( FIG.  11 A ). The low concentration impurity regions  164 _ 3  have a lower concentration of impurities than that of the doped regions  164 _ 1 . The undoped region  164 _ 2  is a region not doped with impurities or not substantially doped with impurities, and acts as a channel region. 
     Next, the interlayer insulating layer  124  is formed on the gate  152  and the first capacitor electrode  160  ( FIG.  11 B ). The interlayer insulating layer  124  may have a single-layer structure or a stack structure, and may contain a material usable for the underlying film  116 . The interlayer insulating layer  124  may be formed by CVD, sputtering or the like. 
     Next, the interlayer insulating layer  124  and the gate insulating film  118  are etched to form openings reaching the doped regions  164 _ 1  ( FIG.  11 B ). The openings may be formed, for example, by plasma etching in gas containing a fluorine-containing hydrocarbon. 
     Next, a metal film is formed to cover the openings and is etched. As a result, the source  156  and the drain  154  are formed ( FIG.  12 A ). The source  156  also acts as the second capacitor electrode  162 , and partially overlaps the first capacitor electrode  160 . A part of the doped region  164 _ 1  that overlaps the first capacitor electrode  160 , a part of the gate insulating film  118  that overlaps the first capacitor electrode  160 , the first capacitor electrode  160 , and a part of the interlayer insulating film  124  that is sandwiched between the first capacitor electrode  160  and the second capacitor electrode  162 , and the second capacitor electrode  162  form the capacitor  158 . The capacitor  158  contributes to maintaining the potential of the gate  152 . 
     The metal film may contain a metal usable for the gate  152 , and may have a single structure or a stack structure. The metal film may be formed by sputtering or CVD. 
     As a result of performing the above-described steps, the transistor  150  is formed. The transistor  140  may be formed by substantially the same process. 
     3. Intermediate Layers 
     Optionally, the first passivation film  126  may be formed on the transistor  150  ( FIG.  12 A ). The first passivation film  126  may have a single-layer structure or a stack structure and may contain an inorganic insulating material. Examples of the inorganic insulating material usable for the first passivation film  126  include silicon-containing inorganic insulating materials such as silicon oxide, silicon nitride, silicon nitride oxide, silicon oxide nitride, and the like. The first passivation film  126  may be formed by sputtering or CVD. 
     Next, the flattening film  168  is formed ( FIG.  12 B ). The flattening film  168  absorbs the ruggedness caused by the transistor  150 , the capacitor  158  and the like and provides a flat surface. The flattening film  168  may be formed of an organic insulating material. Examples of the organic insulating material usable for the flattening film  168  include polymers such as an epoxy resin, an acrylic resin, a polyimide, a polyamide, a polyester, a polycarbonate, a polysiloxane, and the like. The flattening film  168  may be formed by a wet film formation method described above. 
     Next, the flattening film  168  and the first passivation film  126  are etched to form an opening reaching the source  156  ( FIG.  12 B ). Then, the connection electrode  180  is formed to cover the opening ( FIG.  13 A ). The connection electrode  180  may be formed of a light-transmissive conductive oxide such as, for example, indium tin oxide (ITO), indium zinc oxide (IZO) or the like, and may be formed by sputtering or the like. It is not absolutely necessary to form the connection electrode  180 , but the connection electrode  180  protects exposed surfaces such as a surface of the source  156  and the like in subsequent steps and thus prevents increase in the contact resistance. 
     Although not shown, the storage capacitor electrode  166  ( FIG.  5   ) may be formed after the formation of the connection electrode  180 . The storage capacitor electrode  166  may be formed of, for example, a metal such as aluminum, copper, titanium, molybdenum, tungsten, tantalum or the like or an alloy thereof. The storage capacitor electrode  166  may have a single-layer structure or a stack structure. For example, the storage capacitor electrode  166  may have a structure of molybdenum/aluminum/molybdenum. The storage capacitor electrode  166  forms a storage capacitor together with the first electrode  172  of the light emitting element  170  to be formed in a later process. 
     Then, an insulating film  182  is formed ( FIG.  13 A ). The insulating film  182  also acts as a dielectric for the storage capacitance. The insulating film  182  may contain a material usable for the underlying film  116  or the gate insulating film  118 , exemplified by silicon nitride. The insulating film  182  may be formed by the same method as that of the underlying film  116  or the gate insulating film  118 . The insulating film  182  has an opening that exposes a part of a contact portion electrically connecting the transistor  150  and the light emitting element  170  to each other (namely, that exposes a bottom surface of the connection electrode  180  formed in the opening of the flattening film  168 ). 
     4. Light Emitting Element 
     Next, the first electrode  172  of the light emitting element  170  is formed ( FIG.  13 B ). In the case where light from the light emitting element  170  is output via the first electrode  172 , the first electrode  172  may be formed of a light-transmitting material, for example, a conductive oxide such as ITO, IZO or the like. By contrast, in the case where light from the light emitting element  170  is output from the side opposite to the first electrode  172  (namely, via the second electrode  178 ), the first electrode  172  may be formed of a metal such as aluminum, silver or the like or an alloy thereof. Alternatively, the first electrode  172  may have a stack structure of any of the above-listed metal or an alloy thereof and a conductive oxide. For example, the first electrode  172  may have a stack structure in which a layer of a metal is sandwiched between layers of a conductive oxide (e.g., ITO/silver/ITO, etc.). 
     After the first electrode  172  is formed, the partitioning wall  186  is formed ( FIG.  14   ). The partitioning wall  186  has a function of absorbing the steps caused by the end of the first electrode  172  and the opening formed in the flattening film  168 , and also a function of electrically insulating the first electrodes  172  of the adjacent pixels  106  from each other. The partitioning wall  186  is also referred to as a “bank” or a “rib”. The partitioning wall  186  may be formed of a material usable for the flattening film  168 . The partitioning wall  186  has an opening that exposes a part of the first electrode  172 , and an edge of the opening is preferably moderately tapered. Such a shape prevents coverage failure for the EL layer  188  or the second electrode  178  to be formed in a later step. 
     As shown in  FIG.  13 A ,  FIG.  13 B  and  FIG.  14   , an opening  184  may be formed in the insulating film  182  in order to allow the flattening film  168  and the partitioning wall  186  to be in direct contact with each other. Such a structure allows impurities such as water, desorbed from the flattening film  168 , and the like to be released via the partitioning wall  186  in a heat treatment or the like performed after the formation of the partitioning wall  186 . 
     After the formation of the partitioning wall  186 , the EL layer  188  of the light emitting element  170  is formed, and the second electrode  178  is formed on the EL layer  188  ( FIG.  15   ). In the example of  FIG.  15   , the EL layer  188  has a three-layer structure including a first layer  174 , a second layer  175  and a third layer  176 . The EL layer  188  is not limited to having such a structure, and may have a single-layer structure or a stack structure including four or more layers. For example, the EL layer  188  may optionally include a charge injection layer, a charge transfer layer, a light emitting layer, a charge blocking layer, an exciton blocking layer or the like. Alternatively, one layer may have functions of a plurality of layers. The EL layer  188  may be formed by vapor deposition, ink-jetting, printing, spin-coating or the like. 
     In the example of  FIG.  15   , the first layer  174  and the third layer  176  of the EL layer  188  are respectively a charge injection layer and a charge transfer layer, or each have a stack structure of a charge injection layer and a charge transfer layer. The first layer  174  and the third layer  176  may be formed commonly for the pixels  106  adjacent to each other. Namely, the first layer  174  and the third layer  176  may be shared by the pixels  106 . By contrast, the second layer  175  is a light emitting layer, and although not shown, may be formed of a different material or may have a different structure among the pixels  106  adjacent to each other. Thus, the adjacent pixels  106  emit light of different colors. Alternatively, the second layer  175  may have a structure for emitting white light and may be formed to be shared by all the pixels  106 . In this case, color filters or the like may be used so that a wavelength of light output from each pixel  106  is selected to provide full-color display. 
     After the formation of the EL layer  188 , the second electrode  178  is formed ( FIG.  15   ). The first electrode  172 , the EL layer  188  and the second electrode  178  form the light emitting element  170 . Carriers (electrons and holes) are injected from the first electrode  172  and the second electrode  178  into the EL layer  188 , and the carriers are recombined to provide an excited state. The excited state is relaxed to a ground state. As a result, light is emitted. Therefore, in the light emitting element  170 , a region where the EL layer  188  and the first electrode  172  are in direct contact with each other is a light emitting region. 
     In the case where light from the light emitting element  170  is output via the first electrode  172 , the second electrode  178  may be formed of a metal such as aluminum, silver or the like or an alloy thereof. By contrast, in the case where light from the light emitting element  170  is output via the second electrode  178 , the second electrode  178  is formed of any of the above-listed metal or an alloy thereof and may be formed to have such a thickness so as to transmit visible light. Alternatively, the second electrode  178  may be formed of a light-transmitting material, for example, a conductive oxide such as ITO, IZO or the like. Still alternatively, the second electrode  178  may have a stack structure of any of the above-listed metal or an alloy thereof and a conductive oxide (e.g., Mg—Ag/ITO, etc.). The first electrode  172  and the second electrode  178  may be both formed by sputtering, CVD or the like. 
     As a result of performing the above-described steps, the light emitting element  170  is formed. 
     5. Second Passivation Film 
     After the formation of the second electrode  178 , the second passivation film  190  may be optionally formed. ( FIG.  16   ). One of functions of the second passivation film  190  is to prevent entrance of moisture to the light emitting element  170  from outside. It is preferable that the second passivation film  190  has a high level of gas barrier property. The second passivation film  190  may have any structure, and may have a three-layer structure (a first layer  192 , a second layer  194 , and a third layer  196 ) as shown in  FIG.  16   . 
     The first layer  192  may contain an inorganic material such as, for example, silicon nitride, silicon oxide, silicon nitride oxide, silicon oxide nitride or the like, and may be formed by CVD, sputtering or the like. 
     Next, the second layer  194  is formed. The second layer  194  may contain an organic material such as an acrylic resin, a polysiloxane, a polyimide, a polyester or the like. As shown in  FIG.  16   , the second layer  194  may be formed to have a thickness so as to absorb the ruggedness caused by the partitioning wall  186  and thus provide a flat surface. The second layer  194  may be formed by a wet film formation method such as ink-jetting or the like. Alternatively, the second layer  194  may be formed by gasiform or atomizing oligomers, which are a material of the above-described polymers, under a reduced pressure, spraying the oligomers to the first layer  192 , and then polymerizing the oligomers. 
     Then, the third layer  196  is formed. The third layer  196  may contain a material usable for the first layer  192 , and may be formed by the same method as that of the first layer  192 . 
     6. Peeling Step 
     Then, as shown in  FIG.  17   , the counter substrate  104  is formed on the light emitting element  170  or the second passivation film  190 . Although not shown, the counter substrate  104  may be bonded to the light emitting element  170  or the second passivation film  190  with an adhesive layer. The counter substrate  104  may contain a polymer material like the substrate  102 . 
     Then, light such as laser light or the like is applied to decrease the adhesive force between the support substrate  128  and the substrate  102 . Next, a physical force is used to peel the support substrate  128  at the interface between the support substrate  128  and the substrate  102  (represented by the arrow in  FIG.  17   ). 
     As a result of performing the above-described steps, the display device  100  is produced. 
     Embodiment 4 
     In this embodiment, a display device  300  having a different structure from those in embodiment 1 and embodiment 2 will be described. Components the same as or similar to those in embodiments 1 and 2 may not be described. 
     Similar to the display device  100  in embodiment 1, the substrate  102  of the display device  300  includes the first region  120  and the second regions  122 , and the underlying film  116  is provided on the second regions  122 . The second regions  122  overlap a plurality of pixels  106 . The plurality of pixels  106  overlapping the second regions  122  are arrayed in a matrix. Unlike in the display device  100 , in the display device  300 , the underlying film  116  is provided on a part of the first region  120 . On the first region  120 , a plurality of the underlying film  116  are arrayed in stripes, and the underlying films  116  each have a width smaller than the width or the length of each pixel  106 . Therefore, in the display device  300 , the underlying films  116  provided on the first region  120  overlap a plurality of pixels  106 , but the plurality of pixels  106  are not arrayed in a matrix. 
       FIG.  18    shows a specific structure of the display device  300 .  FIG.  18    shows the substrate  102  and the underlying films  116  provided on the substrate  102 . The regions where the display region  108  and the scanning line driving circuits  110  are provided are represented by dashed lines. As shown in  FIG.  18   , the substrate  102  includes the first region  120  and the second regions  122  having the first region  120  therebetween. On a part of the first region  120 , the underlying films  116  are provided. For example, as shown in the enlarged view in  FIG.  18   , the striped underlying films  116  are provided on the first region  120 . On the first region  120 , the striped underlying films  116  are located parallel to the column direction of the pixels  106 . On the first region  120 , the pixels  106  overlapping each underlying film  116  are not arrayed in a matrix but are arrayed in a straight line. 
       FIG.  19    shows an example of a cross-sectional structure of one pixel  106 .  FIG.  19    is a schematic cross-sectional view corresponding to a cross-section taken along a chain line C-C′ in  FIG.  5   .  FIG.  19    shows a cross-section of the pixel  106  on the first region  120 . As shown in  FIG.  19   , the underlying films  116  are selectively provided in a region overlapping the gate line  132  and the gate  144  of the transistor  140 . By contrast, for example, in a region overlapping the second capacitor  162 , no underlying film  116  is provided, and the semiconductor film  164  is in contact with the substrate  102 . As shown in  FIG.  19   , the underlying films  116  may be provided between the substrate  102  and a region of the semiconductor film  142  or  164  that acts as a channel region of the transistor  140  or  150 . 
     Flexibility of substrate  102  is low in the region where the underlying films  116  are provided. By contrast, the substrate  102  is highly flexible and easily deformable in the region where no underlying film  116  is provided. Therefore, when being deformed, the display device  300  is preferentially deformed in the region where no underlying film  116  is provided. Therefore, even though the display device  300  is bent in the first region  120 , no significant load is applied to the underlying films  116 . Thus, the underlying films  116  are suppressed from being cracked. As a result, breakage and disconnection of the underlying films  116  and also of the gate line  132  formed on the underlying films  116  are prevented. Therefore, the display device  300  in this embodiment is highly reliable and flexible. 
     Embodiment 5 
     In this embodiment, display devices  400  and  410  having different structures from those in embodiments 1, 2 and 4 will be described. Components the same as or similar to those in embodiments 1, 2 and 4 may not be described. 
       FIG.  20 A  is a plan view of the display device  400 .  FIG.  20 A  shows the substrate  102  and the underlying film  116  provided on the substrate  102 . The regions where the display region  108  and the scanning line driving circuits  110  are provided are represented by dashed lines. As shown in  FIG.  20 A , the substrate  102  of the display device  400  includes a plurality of first regions  120  unlike the display devices  100 ,  200  and  300 . The number of the second regions  122  may be larger than the number of the first regions  120 . The first regions  120  are each sandwiched between the second regions  122 . In the example of  FIG.  20 A , there are two first regions  120 . Alternatively, three or more first regions  120  may be provided. Since the plurality of first regions  120  are provided, the display device  400  may be bent or folded at a plurality of positions. 
       FIG.  20 B  is a schematic plan view of the display device  410 . Similar to  FIG.  20 A ,  FIG.  20 B  shows the substrate  102  and the underlying film  116  provided on the substrate  102 . The regions where the display region  108  and the scanning line driving circuits  110  are provided are represented by dashed lines. Unlike in the display device  100 ,  200  and  300 , in the display device  410 , the first region  120  is provided in strips parallel to the longer side of the display region  108 . In this case, the first region  120  may overlap the data line driving circuit  112  or the terminals  114 . With such a structure, the display device  410  may be bent and deformed in a direction parallel to the shorter side so that ends of the display device  410  in the shorter side face each other. 
     Embodiment 6 
     In this embodiment, display devices  500 ,  510  and  520  having structures different from those in embodiments 1, 2, 4 and 5 will be described. Components the same as or similar to those in embodiments 1, 2, 4 and 5 may not be described. 
     Unlike in the display devices  100 ,  200 ,  300 ,  400  and  410 , in the display device  500 , a plurality of the display regions  108  are provided on the substrate  102 , the plurality of display regions  108  are selectively provided on the second regions  122 , and the first region  120  is provided between the plurality of display regions  108 . 
       FIG.  21    is a schematic plan view of the substrate  102  and the underlying film  116  provided on the substrate  102  in the display device  500 . In  FIG.  21   , the regions where the display region  108 , the scanning line driving circuits  110  and the like are provided are represented by dashed lines. As shown in  FIG.  21   , the substrate  102  of the display device  500  includes the plurality of (two in  FIG.  21   ) second regions  122 , on which the underlying film  166  is provided. The substrate  102  further includes the first region  120  between the two second regions  122 . On the two second regions  122 , display regions  108 _ 1  and  108 _ 2  are provided respectively. The display regions  108 _ 1  and  108 _ 2  each include a plurality of pixels  106 . The pixels  106  do not overlap the first region  120 . The display regions  108 _ 1  and  108 _ 2  may be independently driven by the scanning line driving circuits  110  or the like, and may reproduce different images from each other. The display regions  108 _ 1  and  108 _ 2  may have similar shapes to each other, or may have different shapes or area sizes from each other. 
     Wirings  136  extend from the terminals  144  to the pixels  106  via the data line driving circuit  112 . By contrast, wirings  138  extend from terminals  115  to the scanning line driving circuits  110 . The wirings  136  act as, for example, the data lines  130  or the current supply lines  134 . The wirings  136  are electrically connected with the pixels  106  in the display region  108 _ 1  closer to the terminals  114 , and further cross the first region  120  and are electrically connected with the pixels  106  in the display region  108 _ 2  farther from the terminals  114 . Similarly, the wirings  138  are electrically connected with the scanning line driving circuits  110  closer to the terminal  115 , and further cross the first region  120  and are electrically connected with the scanning line driving circuits  110  farther from the terminal  115 . Therefore, a connecter merely needs to be connected with one side of the display device  500  to drive both of two display regions  108 _ 1  and  108 _ 2 . 
     The wirings  136  and  138  are not limited to being arranged in the layout shown in  FIG.  21   . For example, as in a display device  510  shown in  FIG.  25   , the wirings  136  may be located such that a part of or all of the wirings  136  extend from the terminals  114 , cross the display region  180 _ 1  and a region overlapping the first region  120 , extend between the display region  180 _ 2  and the scanning line driving circuits  110  farther from the display region  180 _ 1 , and are connected with the display region  180 _ 2 . In this case, in the display region  108 _ 1 , the pixels  106  are sequentially connected with the wirings  136  from the pixel closest to the terminals  114 . By contrast, in the display region  108 _ 2 , the pixels  106  are sequentially connected with the wirings  136  from the pixel farthest from the terminals  114 . 
     Alternatively, as shown in  FIG.  26   , the terminals  114  and  115  connectable with the connector may be located along two sides of the substrate  102 , so that neither the wirings  136  nor the wirings  138  are located on the first region  120 . In a display device  520  having such a layout, the terminals  114  and  115  are located along two sides of the substrate  102  facing each other. The wirings  136  and  138  supplying signals to the display region  108 _ 1  and the scanning line driving circuits  110  driving the display region  108 _ 1  extend from the terminals  114  and  115  located in the vicinity of the side of the display region  108 _ 1  that is opposite to the first region  120 . By contrast, the wirings  136  and  138  supplying signals to the display region  108 _ 2  and the scanning line driving circuits  110  driving the display region  108 _ 2  extend from the terminals  114  and  115  located in the vicinity of the side of the display region  108 _ 2  that is opposite to the first region  120 . With such a structure, the first region  120  is more easily deformable. 
       FIG.  22    shows a cross-sectional structure of the display device  500 .  FIG.  22    is a cross-sectional view taken along a chain line D-D′ in  FIG.  21   . As shown in  FIG.  22   , for example, the data line  130  extends from the display region  108 _ 1  to the display region  108 _ 2 . Although not shown, the current supply line  134  also extends from the display region  108 _ 1  to the display region  108 _ 2  on the interlayer information film  124 . 
     The first region  120  of the substrate  102  is in contact with the gate insulating film  118 . By contrast, the second regions  122  of the substrate  102  are in contact with the underlying film  116 . Although not shown, on the first region  120 , the underlying film  116  having a smaller thickness than on the second regions  122  may be provided, similar to in the display device  200  in embodiment 2. In this case, on the first region  120 , the gate insulating film  118  is in contact with the underlying film  116  having such a smaller thickness. 
     The first region  120  with no underlying film  116  is more flexible than the second regions  122 . Therefore, the first region  120  is more easily bendable than the second regions  122 . The display device  500  may be structured such that the wirings  136  and  138  are wider on the first region  120  than on the second region  122 . For example, as shown in  FIG.  23 A , the wirings  136  and the wirings  138  may be wider on the first region  120  than on the second region  122 . 
     In this case, on the first region  120 , the wirings  136  and the wirings  138  (the wirings  136  in  FIG.  23 A ) may have a symmetrical configuration with respect to a straight line that is parallel to a direction in which the wirings  136  and  138  extend and passes the center of each of the wirings  136  and the wirings  138 . 
     Alternatively, as shown in  FIG.  23 B , the wirings  136  and the wirings  138  (only one wiring  138  is shown in  FIG.  23 B ) may be shaped such that a straight line that is parallel to the direction in which the wirings  136  and  138  extend and passes the center of the wider portion of each of the wirings  136  and the wirings  138  does not pass the thinner portion thereof. In this case, as shown in  FIG.  23 C , the wirings  136  and the wirings  138  (only one wiring  138  is shown in  FIG.  23 C ) may each include straight portions (in the circles in  FIG.  23 C ) having a vector perpendicular to the direction in which the wirings  136  and  138  extend, the straight portion being between the wider portion and the thinner portion. 
     Still alternatively, as shown in  FIG.  24   , the wirings  136  and the wirings  138  may be structured to be partially wider as described above and also to include straight portions (in the circles in  FIG.  24   ) having a vector oblique to the direction in which the wirings  136  and  138  extend. Such a structure improves the durability against bending or folding, and prevents the wirings  136  and  138  from being broken or disconnected. 
     In each of the display devices  500 ,  510  and  520 , the underlying film  116  is not provided on the first region  120 , which is bent when the display device  500 ,  510  or  520  is deformed. Alternatively, the underlying film  116  is provided with a smaller thickness on the first region  120 . Therefore, even though the display devices  500 ,  510  and  520  are each deformed in the first region  120 , breakage or disconnection of the wirings or the electrodes is prevented from being caused by the cracks in the underlying line  116 , and thus the breakage of the display device is prevented. Therefore, the display devices  500 ,  510  and  520  in this embodiment are highly reliable and flexible. 
     The above-described embodiments and modifications according to the present invention may be appropriately combined as long as no contradiction occurs. Devices described above in embodiments according to the present invention may have an element added thereto, or deleted therefrom, or may be changed in design optionally by a person of ordinary skill in the art. Methods described above in embodiments according to the present invention may have a step added thereto, or deleted therefrom, or may be changed in a condition optionally by a person of ordinary skill in the art. Such devices and methods are encompassed in the scope of the present invention as long as including the gist of the present invention. 
     In this specification, an EL display device is disclosed as an example. The embodiments of the present invention are also applicable to, for example, a self-light emitting display device other than the EL display device, a liquid crystal display device, an electronic paper-type display device including an electrophoretic element or the like, or any other flat panel display device. The embodiments of the present invention are applicable to small-, medium, large-size display devices with no specific limitation. 
     Even functions and effects that are different from those provided by the above-described embodiments but are obvious from the description of this specification or are easily expectable by a person of ordinary skill in the art are naturally construed as being provided by the present invention.