Patent Publication Number: US-2023145723-A1

Title: Liquid crystal display device and manufacturing method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device and a method for manufacturing the same. 
     2. Description of the Related Art 
     In recent years, display devices have been used in a variety of places for a variety of applications and therefore have been required to have diverse characteristics and shapes. Accordingly, display devices serving their intended purposes have been actively developed. 
     For example, a liquid crystal panel using a plastic substrate has been produced to reduce the weight thereof (e.g., see Non-Patent Document 1). 
     REFERENCE 
     [Non-Patent Document 1] Akihiko ASANO and Tomoatsu KINOSHITA, SID DIGEST, 2002, pp. 1196-1199 
     SUMMARY OF THE INVENTION 
     Thus, an object of one embodiment of the present invention is to provide a more convenient liquid crystal display device which can be used for a variety of applications. Another object of one embodiment of the present invention is to manufacture, without complicating the process, a liquid crystal display device having a shape suitable for its intended purpose. 
     In the manufacturing process of the liquid crystal display device, the liquid crystal display device is shaped after the manufacture of an electrode layer and an element layer, thereby having a more useful function. 
     The shape of the liquid crystal display device can be freely determined by selecting the shape of a mold used for shaping the liquid crystal display device. Accordingly, it is possible to manufacture various kinds of liquid crystal display devices capable of being used in a variety of places for a variety of applications, which allows a convenient liquid crystal display device to be provided. 
     One embodiment of the invention disclosed in this specification includes: a supporting member that is at least partly curved; and a liquid crystal display panel that includes a liquid crystal material sealed between a pair of flexible substrates and is provided in contact with an inner surface of the supporting member. 
     Another embodiment of the invention disclosed in this specification includes: a supporting member that has a curved portion and has a first surface and a second surface with the curved portion therebetween; and a liquid crystal display panel that includes a liquid crystal material sealed between a pair of flexible substrates and is provided in contact with an inner surface of the supporting member. The liquid crystal display panel has a first display area, a second display area, and a third display area which are formed continuously, and the first display area is faces the first surface of the supporting member, the second display area faces the second surface of the supporting member, and the third display area faces the curved portion of the supporting member. 
     A still another embodiment of the invention disclosed in this specification includes: a first substrate that is at least partly curved; a second substrate fitting into the first substrate with a spacer interposed therebetween; and a liquid crystal material filling a space between the first substrate and the second substrate. 
     A further embodiment of the invention disclosed in this specification includes: a first substrate that is at least partly curved; a second substrate fitting into the first substrate with a spacer interposed therebetween; and a liquid crystal material filling a space between the first substrate and the second substrate. A first display area is formed on one of the surfaces holding the curved portion therebetween, and a second display area is formed on the other surface. A third display area is formed on the curved surface. The first display area and the second display area may be substantially flat, and a plane of the first display area may be perpendicular to a plane of the second display area. 
     A manufacturing method of a liquid crystal display having the above-mentioned structure is also included in an embodiment of the invention. 
     In the above structures, the liquid crystal display device may be provided with a protective film. The protective film may be formed to cover the outside of the liquid crystal display panel, or may be formed between a liquid crystal layer and each of the first substrate and the second substrate. The liquid crystal display device may include a sensor portion. For example, a touch sensor (a touch screen) can be provided in a supporting member on the viewer side. 
     In the case of a transmissive liquid crystal display device, a backlight may be provided to light a display area. The backlight is preferably curved in accordance with the shape of the liquid crystal display device. 
     Note that the ordinal numbers such as “first” and “second” are used for convenience and do not denote the order of steps and the stacking order of layers. In addition, the ordinal numbers in this specification do not denote particular names which specify the present invention. 
     Note that a semiconductor device in this specification refers to all the devices that can operate by using semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic appliance are all included in the semiconductor device. 
     The shape of the liquid crystal display device can be freely determined by selecting the shape of the mold used for shaping the liquid crystal display device. Accordingly, it is possible to manufacture various kinds of liquid crystal display devices capable of being used in a variety of places for a variety of applications, which allows a convenient liquid crystal display device to be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIGS.  1 A to  1 D  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  2 A to  2 C  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  3 A to  3 C  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  4 A to  4 D  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  5 A to  5 C  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  6 A to  6 C  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  7 A to  7 F  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  8 A and  8 B  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIGS.  9 A and  9 B  are diagrams each illustrating a liquid crystal display device; 
         FIGS.  10 A and  10 B  are diagrams each illustrating a liquid crystal display module; 
       FIGS.  11 A 1  to  11 C 2  are diagrams illustrating a method for manufacturing a liquid crystal display device; 
         FIG.  12    is a diagram illustrating a liquid crystal display module; 
         FIGS.  13 A to  13 D  are diagrams each illustrating a semiconductor element that can be used for a liquid crystal display device; 
         FIGS.  14 A to  14 D  are diagrams illustrating an example of a cellular phone using a liquid crystal display device; and 
         FIG.  15    is a diagram illustrating an example of a cellular phone using a liquid crystal display device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described in detail with reference to drawings. Note that the present invention is not limited to the description below, and it is apparent to those skilled in the art that modes and details can be modified in various ways without departing from the spirit and scope of the present invention. Accordingly, the present invention should not be construed as being limited to the description of the embodiments given below. Note that in the structures of the present invention described below, like portions or portions having a similar function are denoted by the same reference numerals, and the description thereof is omitted. 
     Embodiment 1 
     A liquid crystal display device will be described with reference to  FIGS.  1 A to  1 D ,  FIGS.  2 A to  2 C , and  FIGS.  3 A to  3 C . 
       FIGS.  1 A to  1 D ,  FIGS.  2 A to  2 C , and  FIGS.  3 A to  3 C  are cross-sectional views illustrating a method for manufacturing a liquid crystal display device. 
     The liquid crystal display device includes at least a liquid crystal layer, a pair of substrates holding the liquid crystal layer therebetween, and an electrode layer for applying voltage to the liquid crystal layer. The liquid crystal display device may also be provided with a semiconductor element, preferably a thin film transistor. In the case of an active matrix liquid crystal display device, a driving thin film transistor is provided in each pixel. 
     Although an active matrix liquid crystal display device is shown as an example in this embodiment, this embodiment can also be applied to a passive matrix liquid crystal display device. 
     In a manufacturing process of the liquid crystal display device in this embodiment, the liquid crystal display device is shaped after the manufacture of the electrode layer and an element layer, thereby having a more useful function. 
     An element layer  101  is formed over a manufacturing substrate  100  (see  FIG.  1 A ). The element layer  101  includes a thin film transistor. Next, the element layer  101  is transferred to a supporting substrate  102  (see  FIG.  1 B ). 
     A first substrate  110  is provided along a curved surface of a first support  111  serving as a mold for the liquid crystal display device (see  FIG.  1 C ). The first substrate  110  may be attached to the first support  111  with an adhesive layer or the like. By this step, the first substrate  110  is processed to a form having a curved region and a flat region. 
     The supporting substrate  102  and the first support  111  are arranged so that the element layer  101  faces the first substrate  110 , then, the element layer  101  is transferred to the first substrate  110  side in a direction indicated by arrows (see  FIG.  1 D ). That is, the element layer  101  is transferred from the supporting substrate  102  to a surface of the first substrate which is opposite to a surface contacting with the first support  111 . 
     The manufacturing substrate  100  may be selected as appropriate depending on the manufacturing process of the element layer  101 . For example, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, or a metal substrate having an insulating layer on its surface can be used as the manufacturing substrate  100 . It is also possible to use a plastic substrate which is heat resistant to a processing temperature. 
     Spacers  121  are formed on a second substrate  120  (see  FIG.  2 A ). The spacers  121  may be formed on another manufacturing substrate and then transferred to the second substrate  120 . 
     As the supporting substrate  102 , the first substrate  110 , and the second substrate  120 , a substrate having flexibility (a flexible substrate) is used. However, the first substrate  110  and the second substrate  120  that have been shaped and fixed do not need to have flexibility. The supporting substrate  102 , the first substrate  110 , and the second substrate  120  can be made of an aramid resin, a poly(ethylene naphthalate) (PEN) resin, a poly(ether sulfone) (PES) resin, a poly(phenylene sulfide) (PPS) resin, a polyimide (PI) resin, or the like. 
     Next, the second substrate  120  provided with the spacers  121  and a second support  123  which has a curved surface at least in a portion thereof are arranged so that a surface of the second substrate  120  on which the spacers  121  are not formed faces the inside of the second support  123  (see  FIG.  2 B ). The second support  123  may have a U-shape. 
     When the second substrate  120  is attached to the inside of the second support  123  in a direction indicated by arrows, the second substrate  120  provided with the spacers  121  is made into a shape similar to that of the second support  123  (see  FIG.  2 C ). By this step, the second substrate  120  is processed to a form having a curved region and a flat region. 
     The first support  111  provided with the element layer  101  and the first substrate  110  and the second support  123  provided with the spacers  121  and the second substrate  120  are arranged so that the element layer  101  faces the spacers  121  (see  FIG.  3 A ). 
     The first support  111  and the second support  123  fit into each other (are combined to each other) in a direction indicated by arrows. Then, with use of a sealant  124 , the first substrate  110  is bonded to the second substrate  120  with a liquid crystal layer  125  and the element layer  101  interposed therebetween (see  FIG.  3 B ). This attachment step may be performed under reduced pressure. 
     As the sealant  124 , it is typically preferable to use a visible light curable resin, an ultraviolet light curable resin, or a thermosetting resin. Typically, an acrylic resin, an epoxy resin, an amine resin, or the like can be used. The sealant  124  may include a photopolymerization initiator (typically, an ultraviolet light polymerization initiator), a thermosetting agent, a filler, or a coupling agent. 
     The liquid crystal layer  125  is formed by filling a space with a liquid crystal material. The liquid crystal layer  125  may be formed by a dispenser method (a dripping method) in which a liquid crystal is dripped before the attachment of the first substrate  110  to the second substrate  120 , or by an injection method in which a liquid crystal is injected by using a capillary phenomenon after the attachment of the first substrate  110  to the second substrate  120 . There is no particular limitation on the kind of liquid crystal material, and a variety of materials can be used. If a material exhibiting a blue phase is used as the liquid crystal material, an orientation film does not need to be provided. 
     The first support  111  and the second support  123  are removed, whereby a curved liquid crystal display panel  150  that reflects the shape of the first support  111  and the second support  123  can be manufactured (see  FIG.  3 C ). 
     Although not illustrated in this embodiment, a color filter (a coloring layer), a black matrix (a light-shielding layer), an optical member (an optical substrate) such as a polarizing member, a retardation member, or an anti-reflection member, and the like are provided as appropriate. For example, circular polarization may be obtained by using a polarizing substrate and a retardation substrate. In addition, a backlight, a sidelight, or the like may be used as a light source. 
     When the first substrate  110  and the second substrate  120  are shaped by the first support  111  and the second support  123 , they may be subjected to fixing treatment such as heat treatment or light irradiation treatment so that the obtained shape is fixed. Alternatively, the substrate may be shaped by heat treatment and cooled maintaining the obtained shape, so that the shape of the substrate can be fixed. 
     The element layer  101  may be directly formed on the supporting substrate  102  or the first substrate  110 . For example, an electrode layer may be directly formed on the supporting substrate  102  or the first substrate  110  by printing. 
     There is no particular limitation on the method for transferring the element layer  101  from the manufacturing substrate  100  to another substrate as shown in this embodiment, and a variety of methods can be used. For example, a separation layer may be formed between the manufacturing substrate  100  and the element layer  101 . 
     By sputtering, plasma CVD, coating, printing, or the like, the separation layer is formed with a single layer or staked layers made of an element selected from tungsten (W), molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium (Nb), nickel (Ni), cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and silicon (Si); or an alloy or a compound containing any of these elements as its main component. A layer containing silicon may have any crystalline structure: an amorphous structure, a microcrystalline structure, or a polycrystalline structure. Note that the coating method includes here a spin coating method, a droplet discharging method, and a dispensing method. 
     In the case where the separation layer has a single-layer structure, it is preferable to form a tungsten layer, a molybdenum layer, or a layer containing a mixture of tungsten and molybdenum. Alternatively, the separation layer may be a layer containing an oxide or oxynitride of tungsten, a layer containing an oxide or oxynitride of molybdenum, or a layer containing an oxide or oxynitride of a mixture of tungsten and molybdenum. Note that the mixture of tungsten and molybdenum corresponds to, for example, a tungsten-molybdenum alloy. 
     In the case where the separation layer has a multi-layer structure, it is preferable that a tungsten layer, a molybdenum layer, or a layer containing a mixture of tungsten and molybdenum be formed as a first layer, and a layer containing an oxide, nitride, oxynitride, or nitride oxide of tungsten, molybdenum, or a mixture of tungsten and molybdenum is formed as a second layer. 
     In the case where the separation layer has a multi-layer structure of a layer containing tungsten and a layer containing an oxide of tungsten, it may be formed in the following manner: a layer containing tungsten is formed and an insulating layer containing an oxide is formed thereover, so that a layer containing an oxide of tungsten can be formed at the interface between the tungsten layer and the insulating layer. Alternatively, a surface of the layer containing tungsten may be subjected to thermal oxidation treatment, oxygen plasma treatment, treatment with a highly oxidizing solution such as ozone-containing water, or the like, so that a layer containing an oxide of tungsten can be formed. The plasma treatment and the thermal treatment may be performed in an atmosphere of oxygen, nitrogen, or dinitrogen monoxide alone, or a mixed gas of any of these gasses and another gas. A layer containing a nitride, oxynitride, or nitride oxide of tungsten may be formed in a manner similar to that used for forming the layer containing an oxide of tungsten: after a layer containing tungsten is formed, a silicon nitride layer, a silicon oxynitride layer, or a silicon nitride oxide layer is formed thereover. 
     Note that the element layer can be transferred to another substrate by any of the following methods: a method in which a separation layer is formed between a substrate and the element layer and a metal oxide film is formed between the separation layer and the element layer and then weakened by crystallization so that the element layer can be separated; a method in which an amorphous silicon film containing hydrogen is formed between a high heat-resistant substrate and the element layer and then removed by laser light irradiation or etching so that the element layer can be separated; a method in which a separation layer is formed between a substrate and the element layer and a metal oxide film is formed between the separation layer and the element layer and then weakened by crystallization, and after part of the separation layer is etched away using a solution or a halogen-containing gas such as NF 3 , BrF 3 , or ClF 3 , the element layer is separated at the weakened metal oxide film; and a method in which a substrate over which the element layer is formed is mechanically removed or etched away using a solution or a halogen-containing gas such as NF 3 , BrF 3 , or ClF 3 . It is also possible to use a method in which a film containing nitrogen, oxygen, hydrogen, or the like (e.g., an amorphous silicon film containing hydrogen, an alloy film containing hydrogen, or an alloy film containing oxygen) is formed as a separation layer, and the separation layer is irradiated with laser light so that nitrogen, oxygen, hydrogen, or the like contained in the separation layer is released as gas to promote separation. 
     A combination of the above separation methods further facilitates the transferring step. That is, laser light irradiation, etching of a separation layer with a gas or a solution, and mechanical removal of a portion of the element layer with a sharp knife, scalpel, or the like may be performed so that the separation layer and the element layer can be easily separated from each other, then, the separation step can be achieved by physical force (with a machine or the like). 
     Alternatively, the interface between the separation layer and the element layer may be soaked with a liquid, whereby the element layer is separated from the substrate. 
     The shape of the liquid crystal display panel  150  can be freely determined by selecting the shape of the first support  111  and the second support  123 . Accordingly, it is possible to manufacture various kinds of liquid crystal display devices capable of being used in a variety of places for a variety of applications, which allows a convenient liquid crystal display device to be provided. 
     Embodiment 2 
     In this embodiment, an example of a method for manufacturing the liquid crystal display device shown in Embodiment 1, which is additionally provided with a protective film, will be described with reference to  FIGS.  4 A to  4 D ,  FIGS.  5 A to  5 C , and  FIGS.  6 A to  6 C . Therefore, the liquid crystal display device of this embodiment, except the protective film, can be manufactured in a manner similar to that shown in Embodiment 1; thus, description of the same components or components having the same functions as those in Embodiment 1, and the manufacturing process thereof will be omitted. 
       FIGS.  4 A to  4 D ,  FIGS.  5 A to  5 C , and  FIGS.  6 A to  6 C  are cross-sectional views illustrating a method for manufacturing the liquid crystal display device. 
     In a manufacturing process of the liquid crystal display device in this embodiment, the liquid crystal display device is shaped after the manufacture of an electrode layer and an element layer, thereby having a more useful function. Furthermore, the provision of a protective film increases the reliability of the liquid crystal display device. 
     The element layer  101  is formed over the manufacturing substrate  100  (see  FIG.  4 A ). In this embodiment, the element layer  101  includes spacers. Next, the element layer  101 , which includes a thin film transistor, is transferred to the supporting substrate  102  (see  FIG.  4 B ). 
     With use of the first support  111  serving as a mold for the liquid crystal display device, the first substrate  110  is provided along a curved surface of the first support  111 . The first substrate  110  may be attached to the first support  111  with an adhesive layer or the like. 
     A protective film  103  is formed on the first substrate  110  attached to the first support  111  (see  FIG.  4 C ). The protective film  103  is formed to cover the first substrate  110  that has been bent along the shape of the first support  111 . Since the first substrate  110  is not shaped after the formation of the protective film  103 , it is possible to prevent defects such as damage of the protective film  103  due to the shaping of the first substrate  110 . As a result, the protective film  103  which is a dense film blocks moisture or other impurities from the first substrate  110 , and the contamination of the element layer or the liquid crystal layer can be efficiently prevented. 
     The supporting substrate  102  and the first support  111  are arranged so that the protective film  103  and the first substrate  110  are interposed therebetween, then, the element layer  101  is transferred to the protective film  103  and first substrate  110  side in a direction indicated by arrows (see  FIG.  4 D ). 
     Next, the second substrate  120  and the second support  123  which has a curved surface at least in a portion thereof are arranged (see  FIG.  5 A ). 
     When the second substrate  120  is attached to the inside of the second support  123  in a direction indicated by arrows, the second substrate  120  is made into a shape similar to that of the second support  123  (see  FIG.  5 B ). 
     A protective film  122  is formed on the second substrate  120  attached to the second support  123  (see  FIG.  5 C ). The protective film  122  is formed to cover the second substrate  120  that has been bent along the shape of the second support  123 . Since the second substrate  120  is not shaped after the formation of the protective film  122 , it is possible to prevent defects such as damage of the protective film  122  due to the shaping of the second substrate  120 . As a result, the protective film  122  which is a dense film blocks moisture or other impurities from the second substrate  120 , and the contamination of the element layer or the liquid crystal layer can be efficiently prevented. 
     The protective film  103  and the protective film  122  can be formed by sputtering using an inorganic insulating material. Examples of the inorganic insulating material include silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, and aluminum oxynitride. 
     The first support  111  provided with the element layer  101 , the protective film  103 , and the first substrate  110 , and the second support  123  provided with the protective film  122  and the second substrate  120  are arranged so that the element layer  101  faces the protective film  122  (see  FIG.  6 A ). 
     The first support  111  and the second support  123  are combined to each other in a direction indicated by arrows. Then, with use of the sealant  124 , the element layer  101 , the protective film  103 , and the first substrate  110  are attached to the protective film  122  and the second substrate  120  with the liquid crystal layer  125  interposed therebetween (see  FIG.  6 B ). 
     Although the spacers formed on the element layer  101  are shown as an example in this embodiment, spherical spacers may be dispersed on the protective film  122 . 
     The liquid crystal layer  125  may be formed by a dispenser method (a dripping method) in which a liquid crystal is dropped before the attachment of the first substrate  110  to the second substrate  120 , or by an injection method in which a liquid crystal is injected by using a capillary phenomenon after the attachment of the first substrate  110  to the second substrate  120 . 
     The first support  111  and the second support  123  are removed, whereby the curved liquid crystal display panel  150  that reflects the shape of the first support  111  and the second support  123  can be manufactured (see  FIG.  6 C ). 
     The shape of the liquid crystal display panel  150  can be freely determined by selecting the shape of the first support  111  and the second support  123 . Accordingly, it is possible to manufacture various kinds of liquid crystal display devices capable of being used in a variety of places for a variety of applications, which allows a convenient liquid crystal display device to be provided. 
     In addition, the protective film protects the element layer and the liquid crystal layer from impurities and thus increases the reliability of the liquid crystal display device. 
     Embodiment 3 
     In this embodiment, a method for manufacturing a liquid crystal display device, which is different from that shown in Embodiments 1 and 2, will be described with reference to  FIGS.  7 A to  7 F  and  FIGS.  8 A and  8 B . Therefore, the liquid crystal display device of this embodiment, except a different part, can be manufactured in a manner similar to that shown in Embodiment 1; thus, description of the same components or components having the same functions as those in Embodiment 1, and the manufacturing process thereof will be omitted. 
       FIGS.  7 A to  7 F  and  FIGS.  8 A and  8 B  are cross-sectional views illustrating a method for manufacturing the liquid crystal display device. 
     In a manufacturing process of the liquid crystal display device in this embodiment, the liquid crystal display device is shaped after the attachment of a pair of substrates with a liquid crystal layer interposed therebetween, thereby having a more useful function. 
     The element layer  101  is formed over the manufacturing substrate  100  (see  FIG.  7 A ). The element layer  101  includes a thin film transistor. Next, the element layer  101  is transferred to the supporting substrate  102  (see  FIG.  7 B ). 
     The element layer  101  is transferred from the supporting substrate  102  to the first substrate  110  (see  FIG.  7 C ). 
     The spacers  121  and the sealant  124  are formed on the second substrate  120 . The spacers  121  may be formed on another manufacturing substrate and then transferred to the second substrate  120 . 
     Next, the second substrate  120  provided with the spacers  121  and the first substrate  110  are arranged so that a surface of the second substrate  120  on which the spacers  121  and the sealant  124  are formed faces the element layer  101  (see  FIG.  7 D ). 
     The first substrate  110  is attached to the second substrate  120  with the liquid crystal layer  125  interposed therebetween (see  FIG.  7 E ). Through the above steps, a flexible liquid crystal display panel  155  can be obtained. 
     The flexible liquid crystal display panel  155 , which is a structure body in which the first substrate  110  faces the second substrate  120  with the liquid crystal layer  125  interposed therebetween, is shaped to be bent, whereby the curved liquid crystal display panel  150  can be manufactured (see  FIG.  7 F ). The liquid crystal display panel may be shaped using the supports  111  and  123  shown in Embodiment 1. 
     The liquid crystal display panel  155  may be attached to a light-transmitting supporting member so that the liquid crystal display panel  155  can be shaped and fixed. 
       FIG.  8 A  illustrates an example in which the flexible liquid crystal display panel  155  manufactured in  FIG.  7 E  is attached to a light-transmitting supporting member  127  and then formed into a curved shape and fixed. The supporting member  127  has a curved portion on a side, and includes a first surface and a second surface with the curved portion therebetween. The liquid crystal display panel  155  is provided in contact with an inner side of the supporting member  127 , whereby a first display area and a second display area can be formed respectively on the first surface and the second surface of the supporting member  127 . A third display area is also formed in the curved surface of the supporting member  127  and is interposed between the first display area and the second display area. The liquid crystal display panel  155  may be attached to the supporting member  127  with a light-transmitting adhesive layer. 
     The liquid crystal display panel  150  illustrated in  FIG.  7 F  may be additionally provided with a protective film. 
     A protective film  126  is formed to surround the liquid crystal display panel  150  (see  FIG.  8 B ). 
     Since the protective film  126  is formed on the liquid crystal display panel  150  that has been formed into a curved shape, it is possible to prevent defects such as damage of the protective film  126  due to the shaping of the liquid crystal display panel  150 . As a result, the protective film  126  which is a dense film blocks moisture or other impurities from the outside, and the contamination of the liquid crystal display panel  150  can be efficiently prevented. 
     The protective film  126  can be formed by sputtering using an inorganic insulating material. Examples of the inorganic insulating material include silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, and aluminum oxynitride. 
     The shape of the liquid crystal display panel  150  can be freely determined by selecting the shape of the supporting member  127 . Accordingly, it is possible to manufacture various kinds of liquid crystal display devices capable of being used in a variety of places for a variety of applications, which allows a convenient liquid crystal display device to be provided. 
     In addition, the protective film protects the element layer and the liquid crystal layer from impurities and thus increases the reliability of the liquid crystal display device. 
     Embodiment 4 
     In this embodiment, an example of the liquid crystal display device shown in Embodiments 1 to 3, which is additionally provided with an optical member, will be described with reference to  FIGS.  9 A and  9 B . Therefore, the liquid crystal display device of this embodiment, except the optical member, can be manufactured in a manner similar to that shown in Embodiments 1 to 3; thus, description of the same components or components having the same functions as those in Embodiments 1 to 3, and the manufacturing process thereof will be omitted. 
     The liquid crystal display device shown in Embodiments 1 to 3 can be provided with an optical member. As the optical member, it is possible to use a light source such as a backlight or a sidelight, an optical film (such as a polarizing film, a retardation film, or an anti-reflection film), or the like. 
     The optical film may be provided on the outside of the first substrate and the second substrate (on the side opposite to the liquid crystal layer) or on the inside thereof (between the liquid crystal layer and each of the first substrate and the second substrate). 
     For the backlight, a light source such as a cold cathode fluorescent lamp or a light-emitting diode (LED) can be used. A planar light source may be formed using a plurality of LED light sources or a plurality of electroluminescent (EL) light sources. The planar light source may be formed using three or more kinds of LEDs or an LED emitting white light. 
       FIGS.  9 A and  9 B  each illustrate an example of the liquid crystal display device provided with a backlight. Note that the liquid crystal display panel  150  shown in Embodiments 1 to 3 is also referred to as a liquid crystal display device. The backlight is placed in a concave formed by the curved region and the flat region of the first substrate  110 . 
       FIG.  9 A  is the liquid crystal display panel  150  provided with a backlight  130 . The backlight  130  includes a cold cathode fluorescent lamp  131   a  as a light source. The cold cathode fluorescent lamp  131   a  is disposed in a housing  132  that is curved along the shape of the liquid crystal display panel. 
       FIG.  9 B  is also the liquid crystal display panel  150  provided with the backlight  130 . The backlight  130  includes an LED  131   b  as a light source. The LED  131   b  is disposed in the housing  132  that is curved along the shape of the liquid crystal display panel. 
     The backlight  130  illustrated in  FIGS.  9 A and  9 B  may include a light guide member (component) such as a light-diffusing member (film) or a light-reflecting member (film). The housing  132  includes a light-transmitting portion in a region through which light from the light source passes. 
     As shown in this embodiment, the optical member is also shaped and arranged so as to be curved in accordance with the shape of the curved liquid crystal display device. 
     The shape of the liquid crystal display device can be freely determined by selecting the shape of the mold used for shaping the liquid crystal display device. Accordingly, it is possible to manufacture various kinds of liquid crystal display devices capable of being used in a variety of places for a variety of applications, which allows a convenient liquid crystal display device to be provided. 
     Embodiment 5 
     In this embodiment, an example in which a plurality of element layers for the liquid crystal display devices shown in Embodiments 1 to 4 are manufactured over a large substrate (a so-called multi-panel technology) will be described with reference to FIGS.  11 A 1  to  11 C 2 . Therefore, the liquid crystal display device of this embodiment can be manufactured in a manner similar to that shown in Embodiments 1 to 4; thus, description of the same components or components having the same functions as those in Embodiments 1 to 4, and the manufacturing process thereof will be omitted. 
     As described in the above embodiments, the element layer  101  is formed over the manufacturing substrate  100  and then transferred from the manufacturing substrate  100  to the supporting substrate  102  that is a flexible substrate. 
     FIGS.  11 A 1  to  11 C 2  illustrate a method for transferring a plurality of element layers from a large manufacturing substrate to a supporting substrate. FIGS.  11 A 2 ,  11 B 2 , and  11 C 2  are plan views and FIGS.  11 A 1 ,  11 B 1 , and  11 C 1  are cross-sectional views along line X-Y of FIGS.  11 A 2 ,  11 B 2 , and  11 C 2 , respectively. 
     Element layers  101   a,    101   b,  and  101   c  are formed over a large manufacturing substrate  180  (see FIGS.  11 A 1  and  11 A 2 ). 
     A supporting substrate  182  is arranged so as to face the element layers  101   a ,  101   b,  and  101   c,  and the element layers  101   a,    101   b,  and  101   c  are transferred from the manufacturing substrate  180  to the supporting substrate  182  in a direction indicated by arrows (see FIGS.  11 B 1  and  11 B 2 ). 
     The supporting substrate  182  is divided into supporting substrates  102   a,    102   b , and  102   c  respectively for the element layers  101   a,    101   b,  and  101   c  (see FIGS.  11 C 1  and  11 C 2 ). There is no particular limitation on a dividing method as long as the supporting substrate can be cut off physically. For example, the supporting substrate  182  can be divided with a dicer or a scriber, or by laser light irradiation. 
     The element layers  101  ( 101   a,    101   b,  and  101   c ) formed over the supporting substrates  102  ( 102   a,    102   b,  and  102   c ) for panels are used for manufacturing liquid crystal display devices. The subsequent steps may be performed in a manner similar to those shown in Embodiments 1 to 4. 
     Such a step of simultaneously transferring a plurality of element layers with use of a large substrate allows a plurality of liquid crystal display devices to be provided at a higher productivity. 
     Embodiment 6 
     The invention disclosed in this specification can be applied to a passive matrix liquid crystal display device as well as an active matrix liquid crystal display device. 
     Thin film transistors are manufactured and used for a pixel portion and further a driver circuit, so that a liquid crystal display device having a display function can be manufactured. In addition, when part or whole of the driver circuit is formed over the same substrate as the pixel portion with use of the thin film transistors, a system-on-panel can be obtained. 
     The liquid crystal display device includes a liquid crystal element (also referred to as a liquid crystal display element) as a display element. 
     Furthermore, the liquid crystal display device includes a panel in which the display element is sealed, and a module in which an IC or the like including a controller is mounted on the panel. In this embodiment, liquid crystal display device modules will be illustrated in  FIGS.  10 A and  10 B  and  FIG.  12   . 
     Note that a liquid crystal display device in this specification refers to an image display device, a display device, or a light source (including a lighting device). Furthermore, the liquid crystal display device also includes the following modules in its category: a module to which a connector such as a flexible printed circuit (FPC), a tape automated bonding (TAB) tape, or a tape carrier package (TCP) is attached; a module having a TAB tape or a TCP at the tip of which a printed wiring board is provided; and a module in which an integrated circuit (IC) is directly mounted on a display element by the chip on glass (COG) technique. 
     The appearance and cross section of a liquid crystal display panel, which is one embodiment of the liquid crystal display device, will be described with reference to  FIGS.  10 A and  10 B  and  FIG.  12   .  FIGS.  10 A and  10 B  and  FIG.  12    are examples of liquid crystal display modules in which an FPC  4018  is attached to a liquid crystal display panel  4000 . Thin film transistors  4010  and  4011  and a liquid crystal element  4013  are sealed between a first substrate  4001  and a second substrate  4006  with a sealant  4005 .  FIGS.  10 A and  10 B  are perspective views of the liquid crystal display modules, and  FIG.  12    is a cross-sectional view along line M-N of  FIG.  10 A . 
     The liquid crystal display module of  FIG.  10 B  shows an example in which the liquid crystal display panel  4000  is attached to a light-transmitting supporting member  4040 . The liquid crystal display panel  4000  is provided in contact with an inner surface of the light-transmitting supporting member  4040 . 
     As illustrated in  FIGS.  10 A and  10 B , a pixel portion  4002  serving as a display area is continuously provided on the side surfaces and bottom surface of the liquid crystal display panel that is curved, so that a first display area can be provided on the bottom surface and a second display area can be provided on the side surfaces. 
     The sealant  4005  is provided to surround the pixel portion  4002  and a scan line driver circuit  4004  that are provided over the first substrate  4001 . The second substrate  4006  is provided over the pixel portion  4002  and the scan line driver circuit  4004 . Therefore, the pixel portion  4002  and the scan line driver circuit  4004  are sealed together with a liquid crystal layer  4008 , by the first substrate  4001 , the sealant  4005 , and the second substrate  4006 . 
     A signal line driver circuit  4003  is formed using a single crystal semiconductor film or a polycrystalline semiconductor film over a substrate separately prepared, and is mounted by TAB in a region different from the region surrounded by the sealant. 
     Further, a variety of signals and potentials are supplied from an FPC  4018  to the signal line driver circuit  4003  that is formed separately, and the scan line driver circuit  4004  or the pixel portion  4002 . 
     Note that there is no particular limitation on the connection method of the driver circuit separately formed, and the driver circuit may be connected by COG, wire bonding, TAB, or the like. 
     The pixel portion  4002  and the scan line driver circuit  4004  that are provided over the first substrate  4001  each include a plurality of thin film transistors.  FIG.  12    illustrates the thin film transistor  4010  included in the pixel portion  4002  and the thin film transistor  4011  included in the scan line driver circuit  4004 . Insulating layers  4020  and  4021  are provided over the thin film transistors  4010  and  4011 . Note that an insulating film  4023  is an insulating film serving as a base film. 
     Various kinds of thin film transistors can be applied to the thin film transistors  4010  and  4011  without particular limitation.  FIG.  12    illustrates an example in which inverted-staggered thin film transistors having a bottom-gate structure are used as the thin film transistors  4010  and  4011 . Although the thin film transistors  4010  and  4011  are channel-etched thin film transistors, they may be channel-protective inverted-staggered thin film transistors in which a channel protective film is provided over a semiconductor layer. 
     A pixel electrode layer  4030  is provided over the first substrate  4001  and electrically connected to the thin film transistor  4010 . The liquid crystal element  4013  includes the pixel electrode layer  4030 , a counter electrode layer  4031 , and the liquid crystal layer  4008 . Insulating films  4032  and  4033  serving as orientation films are provided so that the liquid crystal layer  4008  is interposed therebetween. The counter electrode layer  4031  is provided on the second substrate  4006  side and stacked over the pixel electrode layer  4030  with the liquid crystal layer  4008  interposed therebetween. 
     The first substrate  4001  and the second substrate  4006  can be made of plastic having light-transmitting properties. A plastic substrate may be a fiberglass-reinforced plastics (FRP) plate, a poly(vinyl fluoride) (PVF) film, a polyester film, or an acrylic resin film. Alternatively, a sheet with a structure in which an aluminum foil is sandwiched between PVF films or polyester films can be used. 
     Reference numeral  4035  denotes a columnar spacer obtained by selectively etching an insulating film and is provided to control the thickness of the liquid crystal layer  4008  (a cell gap). Alternatively, a spherical spacer may be used. 
     Although  FIG.  12    illustrates an example of a transmissive liquid crystal display device, an embodiment of the present invention can also be applied to a transflective liquid crystal display device. 
       FIG.  12    illustrates an example of the liquid crystal display device in which a polarizing films  4040   a  and  4040   b  are provided on the outside of the substrates; however, the polarizing films may be provided on the inside of the substrates. The polarizing films may be provided inside or outside the substrate as appropriate depending on materials of the polarizing film or conditions of manufacturing steps. Furthermore, a light-shielding layer serving as a black matrix may be provided. 
     The insulating layer  4020  serves as a protective film of the thin film transistors. 
     The protective film (insulating layer  4020 ) is provided to prevent entry of impurities floating in the air, such as organic substances, metal substances, or moisture, and is preferably a dense film. The protective film (insulating layer  4020 ) may be formed by sputtering with a single layer or stacked layers of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, and/or an aluminum nitride oxide film. 
     The insulating layer  4021  serving as a planarizing insulating film can be made of an organic material having heat resistance, such as polyimide, an acrylic resin, a benzocyclobutene-based resin, polyamide, or an epoxy resin. Other than such organic materials, it is also possible to use a low-dielectric constant material (a low-k material), a siloxane-based resin, PSG (phosphosilicate glass), BPSG (borophosphosilicate glass), or the like. Note that the insulating layer  4021  may be formed by stacking a plurality of insulating films made of these materials. 
     There is no particular limitation on the method for forming the insulating layer  4021 , and the insulating layer  4021  can be formed, depending on the material, by sputtering, spin coating, dipping, spray coating, droplet discharging (e.g., ink-jet, screen printing, or offset printing), roll coating, curtain coating, knife coating, or the like. In the case where the insulating layer  4021  is formed using a material solution, the semiconductor layer may be annealed (at 200° C. to 400° C.) at the same time as a baking step. The baking step of the insulating layer  4020  also serves as the annealing step of the semiconductor layer, whereby a liquid crystal display device can be manufactured efficiently. 
     In this specification, in the case where the liquid crystal display device is a transmissive liquid crystal display device (or a transflective liquid crystal display device) performing display by transmitting light from a light source, light needs to pass through at least a pixel region. Accordingly, the substrates and the thin films such as insulating films and conductive films existing in the pixel region through which light passes have light-transmitting properties in the visible wavelength range. 
     The electrode layer (such as a pixel electrode layer, a common electrode layer, or a counter electrode layer) for applying voltage to the liquid crystal layer may have light-transmitting properties or light-reflecting properties depending on the place where the electrode layer is provided or the pattern structure of the electrode layer. 
     The pixel electrode layer  4030  and the counter electrode layer  4031  can be made of a light-transmitting conductive material such as indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium tin oxide (hereinafter referred to as ITO), indium zinc oxide, or indium tin oxide to which silicon oxide is added. 
     The pixel electrode layer  4030  and the counter electrode layer  4031  can also be made of one or more kinds of materials selected from a metal such as tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), and silver (Ag); an alloy of these metals; and a nitride of these metals. 
     Alternatively, a conductive composition containing a conductive high molecule (also referred to as a conductive polymer) can be used for the pixel electrode layer  4030  and the counter electrode layer  4031 . As the conductive high molecule, a so-called π-electron conjugated conductive polymer can be used. For example, it is possible to use polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, or a copolymer of two or more kinds of them. 
     Since the thin film transistors are easily damaged by static electricity or the like, a protective circuit for protecting the driver circuits is preferably provided over the same substrate as a gate line or a source line. It is preferable to use a non-linear element for the protective circuit. 
     In  FIG.  12   , a connecting terminal electrode  4015  is formed using the same conductive film as that of the pixel electrode layer  4030 , and a terminal electrode  4016  is formed using the same conductive film as that of source and drain electrode layers of the thin film transistors  4010  and  4011 . 
     The connecting terminal electrode  4015  is electrically connected to a terminal included in the FPC  4018  through an anisotropic conductive film  4019 . 
       FIGS.  10 A and  10 B  illustrate an example in which the signal line driver circuit  4003  is formed separately and mounted on the FPC  4018 ; however, this embodiment is not limited to this structure. The scan line driver circuit may be separately formed and then mounted, or only part of the signal line driver circuit or part of the scan line driver circuit may be separately formed and then mounted. 
     This embodiment can be implemented in an appropriate combination with the structures described in the other embodiments. 
     Embodiment 7 
     There is no particular limitation on the kind of thin film transistor included in the liquid crystal display device disclosed in this specification. Therefore, a variety of structures and materials can be used for the thin film transistor. 
     Examples of the structure of the thin film transistor will be described with reference to  FIGS.  13 A to  13 D .  FIGS.  13 A to  13 D  illustrate examples of the thin film transistor that can be applied to the thin film transistor  4010  in Embodiment 6, and  FIGS.  13 A to  13 D  correspond to  FIG.  12   . 
     In  FIGS.  13 A to  13 D , the insulating film  4023  is formed over the first substrate  4001 , and thin film transistors  4010   a,    4010   b,    4010   c,  and  4010   d  are provided over the insulating film  4023 . The insulating layers  4020  and  4021  are formed over each of the thin film transistors  4010   a,    4010   b,    4010   c,  and  4010   d,  and the pixel electrode layer  4030  is provided thereover to be electrically connected to the thin film transistors  4010   a ,  4010   b,    4010   c,  and  4010   d.    
     The thin film transistor  4010   a  is an example of the thin film transistor  4010  illustrated in  FIG.  12   , in which wiring layers  405   a  and  405   b  serving as source and drain electrode layers are in contact with a semiconductor layer  403  without an n +  layer interposed therebetween. 
     The thin film transistor  4010   a  is an inverted-staggered thin film transistor in which a gate electrode layer  401 , a gate insulating layer  402 , the semiconductor layer  403 , and the wiring layers  405   a  and  405   b  serving as source and drain electrode layers are provided over the first substrate  4001  having an insulating surface, and over the insulating film  4023 . 
     The thin film transistor  4010   b  is a bottom-gate thin film transistor in which the gate electrode layer  401 , the gate insulating layer  402 , the wiring layers  405   a  and  405   b  serving as source and drain electrode layers, n +  layers  404   a  and  404   b  serving as source and drain regions, and the semiconductor layer  403  are provided over the first substrate  4001  having an insulating surface, and over the insulating film  4023 . In addition, an insulating film  4020  is provided in contact with the semiconductor layer  403  so as to cover the thin film transistor  4010   b.  The n +  layers  404   a  and  404   b  are semiconductor layers each having a lower resistance than the semiconductor layer  403 . 
     The n +  layers  404   a  and  404   b  may be provided between the gate insulating layer  402  and the wiring layers  405   a  and  405   b.  Alternatively, the n +  layers may be provided both between the gate insulating layer and the wiring layers and between the wiring layers and the semiconductor layer. 
     The gate insulating layer  402  exists in the entire region including the thin film transistor  4010   b,  and the gate electrode layer  401  is provided between the gate insulating layer  402  and the first substrate  4001  having an insulating surface. The wiring layers  405   a  and  405   b  and the n +  layers  404   a  and  404   b  are provided over the gate insulating layer  402 . Then, the semiconductor layer  403  is provided over the gate insulating layer  402 , the wiring layers  405   a  and  405   b,  and the n +  layers  404   a  and  404   b . Although not illustrated, a wiring layer is provided over the gate insulating layer  402  in addition to the wiring layers  405   a  and  405   b,  and the wiring layer extends beyond the perimeter of the semiconductor layer  403 . 
     The thin film transistor  4010   c  has another structure of the thin film transistor  4010   b,  in which source and drain electrode layers are in contact with a semiconductor layer without an n +  layer interposed therebetween. 
     The gate insulating layer  402  exists in the entire region including the thin film transistor  4010   c,  and the gate electrode layer  401  is provided between the gate insulating layer  402  and the first substrate  4001  having an insulating surface. The wiring layers  405   a  and  405   b  are provided over the gate insulating layer  402 . Then, the semiconductor layer  403  is provided over the gate insulating layer  402  and the wiring layers  405   a  and  405   b.  Although not illustrated, a wiring layer is provided over the gate insulating layer  402  in addition to the wiring layers  405   a  and  405   b,  and the wiring layer extends beyond the perimeter of the semiconductor layer  403 . 
     The thin film transistor  4010   d  is a top-gate thin film transistor and an example of a planar thin film transistor. The semiconductor layer  403  including the n +  layers  404   a  and  404   b  serving as source and drain regions is formed over the first substrate  4001  having an insulating surface, and over the insulating film  4023 . The gate insulating layer  402  is formed over the semiconductor layer  403 , and the gate electrode layer  401  is formed over the gate insulating layer  402 . In addition, the wiring layers  405   a  and  405   b  serving as source and drain electrode layers are formed in contact with the n +  layers  404   a  and  404   b.  The n +  layers  404   a  and  404   b  are semiconductor regions each having a lower resistance than the semiconductor layer  403 . 
     The thin film transistor may be a top-gate forward-staggered thin film transistor. 
     Although a single-gate transistor is described in this embodiment, a multi-gate transistor such as a double-gate transistor may also be used. In that case, a gate electrode layer may be provided above and below the semiconductor layer, or a plurality of gate electrode layers may be provided only on one side of (above or below) the semiconductor layer. 
     There is no particular limitation on the semiconductor material used for the semiconductor layer. Examples of the material used for the semiconductor layer of the thin film transistor will be described below. 
     As a material for the semiconductor layer included in the semiconductor element, it is possible to use an amorphous semiconductor (hereinafter, also referred to as an AS) that is formed by sputtering or vapor-phase growth using a semiconductor material gas typified by silane or germane, a polycrystalline semiconductor that is obtained by crystallizing the amorphous semiconductor by utilizing light energy or thermal energy, a microcrystalline semiconductor (also referred to as a semi-amorphous or microcrystal semiconductor, and hereinafter, also referred to as an SAS), or the like. The semiconductor layer can be deposited by sputtering, LPCVD, plasma CVD, or the like. 
     Considering Gibbs free energy, the microcrystalline semiconductor film is in a metastable state that is intermediate between an amorphous state and a single crystal state. That is, the microcrystalline semiconductor is in a third state that is thermodynamically stable, and has short-range order and lattice distortion. Columnar or needle-like crystals grow in the direction of the normal to the surface of the substrate. The Raman spectrum of microcrystalline silicon, which is a typical example of a microcrystalline semiconductor, is shifted to a lower wavenumber side than 520 cm −1  that represents single crystal silicon. In other words, the Raman spectrum of microcrystalline silicon has a peak between 520 cm −1  that represents single crystal silicon and 480 cm −1  that represents amorphous silicon. Furthermore, the microcrystalline semiconductor film contains 1 atomic % or more of hydrogen or halogen to terminate dangling bonds. The microcrystalline semiconductor film may further contain a rare gas element such as helium, argon, krypton, or neon to further promote lattice distortion, whereby a favorable microcrystalline semiconductor film with improved stability can be obtained. 
     This microcrystalline semiconductor film can be formed by a high-frequency plasma CVD method with a frequency of several tens of megahertz to several hundreds of megahertz, or a microwave plasma CVD apparatus with a frequency of 1 GHz or more. Typically, the microcrystalline semiconductor film can be formed using silicon hydride, such as SiH 4 , Si 2 H 6 , SiH 2 Cl 2 , or SiHCl 3 , or silicon halide such as SiCl 4  or SiF 4 , which is diluted with hydrogen. Furthermore, the microcrystalline semiconductor film can be formed with a gas containing silicon hydride and hydrogen which is diluted by one or more kinds of rare gas elements selected from helium, argon, krypton, and neon. In such a case, the flow rate ratio of hydrogen to silicon hydride is set to 5:1 to 200:1, preferably, 50:1 to 150:1, and more preferably, 100:1. 
     The amorphous semiconductor is typified by hydrogenated amorphous silicon, and the crystalline semiconductor is typified by polysilicon or the like. Polysilicon (polycrystalline silicon) includes so-called high-temperature polysilicon that contains polysilicon formed at a process temperature of 800° C. or higher as its main component, so-called low-temperature polysilicon that contains polysilicon formed at a process temperature of 600° C. or lower as its main component, and polysilicon formed by crystallizing amorphous silicon by using, for example, an element that promotes crystallization. It is needless to say that a microcrystalline semiconductor or a semiconductor partially including a crystalline phase can also be used as described above. 
     As a semiconductor material, a compound semiconductor such as GaAs, InP, SiC, ZnSe, GaN, or SiGe as well as silicon (Si) or germanium (Ge) alone can be used. 
     In the case of using a crystalline semiconductor film for the semiconductor layer, the crystalline semiconductor film may be manufactured by various methods (e.g., laser crystallization, thermal crystallization, or thermal crystallization using an element such as nickel that promotes crystallization). Alternatively, a microcrystalline semiconductor, which is an SAS, may be crystallized by laser irradiation to increase crystallinity. In the case where an element that promotes crystallization is not introduced, before being irradiated with laser light, an amorphous semiconductor film is heated at 500° C. for one hour in a nitrogen atmosphere, whereby hydrogen contained in the amorphous semiconductor film is eliminated to allow its concentration to be 1×10 20  atoms/cm 3  or less. This is because, if the amorphous semiconductor film contains much hydrogen, the amorphous semiconductor film is broken by laser irradiation. 
     In the case of the crystallization of the amorphous semiconductor film using the element that promotes crystallization, it is possible to use one or more kinds of metal elements selected from iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), copper (Cu), and gold (Au). There is no particular limitation on a method for introducing the metal element into the amorphous semiconductor film as long as the metal element can exist on the surface of or inside the amorphous semiconductor film. For example, sputtering, CVD, plasma processing (including plasma CVD), an adsorption method, or a method of applying a metal-salt solution can be employed. Among them, the method using a solution is simple and easy, and is useful in terms of easy concentration adjustment of the metal element. At this time, an oxide film may be deposited at the surface of the amorphous semiconductor film by UV light irradiation in an oxygen atmosphere, thermal oxidation, treatment with ozone-containing water or hydrogen peroxide including a hydroxyl radical, or the like in order to improve its wettability and to spread the solution containing the metal salt on the entire surface of the amorphous semiconductor film. 
     In the crystallization of the amorphous semiconductor film using the element that promotes crystallization, heat treatment (at 550° C. to 750° C. for 3 minutes to 24 hours) may be performed. 
     In order to remove or reduce the element that promotes crystallization of the crystalline semiconductor film, a semiconductor film containing an impurity element is formed in contact with the crystalline semiconductor film so as to function as a gettering sink. As the impurity element, an impurity element imparting n-type conductivity, an impurity element imparting p-type conductivity, a rare gas element, or the like can be used. For example, it is possible to use one or more kinds of elements selected from phosphorus (P), nitrogen (N), arsenic (As), antimony (Sb), bismuth (Bi), boron (B), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). A semiconductor film containing a rare gas element is formed in contact with the crystalline semiconductor film containing the element that promotes crystallization, and then heat treatment is performed (at 550° C. to 750° C. for 3 minutes to 24 hours). The element promoting crystallization that is contained in the crystalline semiconductor film moves into the semiconductor film containing a rare gas element, and thus the element promoting crystallization that is contained in the crystalline semiconductor film is removed or reduced. After that, the semiconductor film containing a rare gas element, which has functioned as a gettering sink, is removed. 
     The amorphous semiconductor film may be crystallized by a combination of thermal treatment and laser light irradiation. Alternatively, either thermal treatment or laser light irradiation may be performed plural times. 
     A crystalline semiconductor film can also be formed directly over the substrate by a plasma method. Alternatively, a crystalline semiconductor film may be selectively formed over the substrate by a plasma method. 
     It is also possible to use an oxide semiconductor such as zinc oxide (ZnO) or tin oxide (SnO 2 ) for the semiconductor layer. In the case of using ZnO for the semiconductor layer, a gate insulating layer is formed of Y 2 O 3 , Al 2 O 3 , TiO 2 , a stack thereof, or the like, and a gate electrode layer, a source electrode layer, and a drain electrode layer can be formed of ITO, Au, Ti, or the like. In addition, In, Ga, or the like may be added to ZnO. 
     As the oxide semiconductor, a thin film represented by InMO 3  (ZnO) m  (m&gt;0) can be used. Note that M denotes one or more of metal elements selected from gallium (Ga), iron (Fe), nickel (Ni), manganese (Mn), and cobalt (Co). For example, M is gallium (Ga) in some cases, and in other cases, M contains other metal elements in addition to Ga, such as Ga and Ni or Ga and Fe. Furthermore, the above oxide semiconductor may contain another transition metal or an oxide of the transition metal as an impurity element. For example, an In—Ga—Zn—O-based non-single-crystal film can be used as the oxide semiconductor layer. 
     An oxide semiconductor layer (InMO 3 (ZnO) m  film (m&gt;0)) in which M is another metal element may be used instead of the In—Ga—Zn—O-based non-single-crystal film. 
     This embodiment can be implemented in an appropriate combination with the structures described in the other embodiments. 
     Embodiment 8 
     A liquid crystal display device disclosed in this specification can be applied to a variety of electronic appliances (including an amusement machine). Examples of electronic appliances include a television set (also referred to as a television or a television receiver), a monitor of a computer or the like, a camera such as a digital camera or a digital video camera, a digital photo frame, a cellular phone (also referred to as a mobile phone or a mobile phone set), a portable game console, a portable information terminal, an audio reproducing device, and a large-sized game machine such as a pachinko machine. 
     In this embodiment, an example of a cellular phone using the liquid crystal display device disclosed in this specification will be described with reference to  FIGS.  14 A to  14 D  and  FIG.  15   . 
       FIG.  14 C  is a front view of the cellular phone;  FIG.  14 D , a side view; and  FIG.  14 B , a top view. The cellular phone includes a housing  1411   a  and a housing  1411   b , which include a light-transmitting supporting member at least in a region where display is performed.  FIG.  14 A  is a cross-sectional view of the inside of the housing  1411   a  and the housing  1411   b.  The front of the housing  1411   a  has a rectangular shape with a longer side and a shorter side, which may have a round corner. In this embodiment, the direction parallel to the longer side of the rectangle that is the front shape is referred to as a longitudinal direction, and the direction parallel to the shorter side is referred to as a lateral direction. 
     The sides of the housing  1411   a  and the housing  1411   b  also have a rectangular shape with a longer side and a shorter side, which may have a round corner. In this embodiment, the direction parallel to the longer side of the rectangle that is the side shape is referred to as a longitudinal direction, and the direction parallel to the shorter side is referred to as a depth direction. 
     The cellular phone illustrated in  FIGS.  14 A to  14 D  includes a display area  1413 , operating buttons  1404 , and a touch screen  1423 , and the housings  1411   a  and  1411   b  include a liquid crystal display panel  1421 , a backlight  1424 , and a wiring board  1425 . The touch screen  1423  may be provided as needed. 
     As the liquid crystal display panel  1421 , the liquid crystal display panel and the liquid crystal display module described in Embodiments 1 to 7 may be used. 
     As illustrated in  FIGS.  14 B and  14 C , the liquid crystal display panel  1421  is arranged along the shape of the housing  1411   a  so as to cover not only the front area on the viewer side but also parts of the top area and the bottom area. Accordingly, a display area  1427  can be formed on the top of the cellular phone in the lateral direction to be connected to the display area  1413 . That is, the display area  1427  is provided on the top surface of the cellular phone, which makes it possible to see the display area  1427  without taking out the cellular phone from, for example, the breast pocket. 
     On the display areas  1413  and  1427 , incoming mails or calls, dates, phone numbers, personal names, and the like may be displayed. Display may be performed only in the display area  1427  and not be performed in the other regions as needed, resulting in saving of energy. 
       FIG.  15    is a cross-sectional view of  FIG.  14 D . As illustrated in  FIG.  15   , the liquid crystal display panel  1421  is continuously provided on the top, front, and bottom of the inside of the housing  1411   a.  The backlight  1424 , the wiring board  1425  electrically connected to the liquid crystal display panel  1421 , and a battery  1426  are provided on the back side of the liquid crystal display panel  1421 . Furthermore, the touch screen  1423  is provided on the outside of the housing  1411   a  (on the viewer side). 
     Images and letters can be displayed on the cellular phone of this embodiment, whether it is placed horizontally or vertically for a landscape mode or a portrait mode. 
     The liquid crystal display panel  1421  is not manufactured separately in the front area and the top area, but manufactured to cover both the front display area  1413  and the top display area  1427 , resulting in a reduction in manufacturing cost and time. 
     The touch screen  1423  is provided on the housing  1411   a,  and buttons  1414  on the touch screen are displayed on the display area  1413 . By touching the buttons  1414  with a finger or the like, contents displayed on the display area  1413  can be changed. Furthermore, making calls or composing mails can also be performed by touching the buttons  1414  on the display area  1413  with a finger or the like. 
     The buttons  1414  on the touch screen  1423  may be displayed when needed, and when the buttons  1414  are not necessary, images or letters can be displayed on the entire display area  1413 . 
     A longer side of the top cross section of the cellular phone may have a radius of curvature. When the top cross section has a longer side with a radius of curvature, each of the liquid crystal display panel  1421  and the touch screen  1423  also has a top cross section having a longer side with a radius of curvature. Furthermore, the housing  1411   a  is also curved. That is, the display area  1413  is curved outwards when seen from the front. 
     This application is based on Japanese Patent Application serial No. 2009-093392 filed with Japan Patent Office on Apr. 7, 2009, the entire contents of which are hereby incorporated by reference.