Patent Publication Number: US-2016248044-A1

Title: Display Device and Method for Fabricating the Same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device having an element in which a light-emitting material is interposed between electrodes (hereinafter, such a device is referred to as the light-emitting device and such an element is referred to as the light-emitting element). In particular, the present invention relates to a device including on one and the same insulating surface, a pixel section and a driver circuit for transmitting a signal to the pixel section. In addition, the present invention can be used for a device having an element in which liquid crystal is interposed between electrodes (hereinafter, such a device is referred to as the liquid crystal display device and such an element is referred to as the liquid crystal element). It should be noted that in the present specification, the light-emitting device and the liquid crystal display device are collectively referred to as the display device. 
     Light-emitting materials that can be used in the present invention include all of light-emitting materials that emit light (phosphorescent light and/or fluorescent light) via singlet excitation or triplet excitation, or both of these excitations. 
     2. Description of the Related Art 
     Recently, developments for a light-emitting device including a light-emitting element which utilizes a light-emitting material capable of providing EL (Electro Luminescence) has been progressed (hereinafter, such a light-emitting device is simply referred to as the light-emitting device; such a light-emitting element is referred to as the EL element; and such a light-emitting material is referred to as the EL material). The light-emitting device has a structure having an EL element in which a thin film made of the EL material is interposed between an anode and a cathode. 
     Although in the developments for the light-emitting devices the passive-matrix type devices have been mainly focused. it has been considered that there will exist disadvantages with the passive-matrix type light-emitting devices in that a sufficient reliability (a long lifetime of the EL element) cannot be ensured with a higher precision pixel section which requires the luminance of the EL element to be increased. From the above circumstances, the active-matrix type light-emitting devices are recently drawing much attention for the purpose of realizing a higher precision display. The active-matrix type light-emitting device is characterized in that an active element is provided within each pixel so that the EL element is allowed to emit light in accordance with an input signal. As the active element, a TFT (Thin Film Transistor) is commonly employed. 
     Reference is now made to  FIG. 4 , which illustrates a pixel structure of the active-matrix type light-emitting device. In  FIG. 4 , reference numeral  401  denotes a source wiring,  402  denotes a gate wiring,  403  denotes a TFT functioning as a switching element (hereinafter referred to as the switching TFT), and  404  denotes a capacitor electrically connected to a drain of the switching TFT  403 . 
     The drain of the switching TFT  403  is also electrically connected to a gate electrode of a current-controlling TFT  405 . A source of the current-controlling TFT  405  is electrically connected to a current supply line  406 , while a drain thereof is electrically connected to an EL element  407 . In other word, the current-controlling TFT  405  can function as an element for controlling current flowing through the EL element  407 . 
     The luminance of the EL element can be controlled by thus providing the two TFTs having different functions, respectively, in each of the pixels. As a result, a light-emitting period can substantially correspond to one-frame period, and an image can be displayed while suppressing the luminance even with a higher precision pixel section. Furthermore, advantages of the active-matrix type device include the capability of forming, as a driver circuit for transmitting a signal to the pixel section, a shift register or a sampling circuit with TFTs on the same substrate. This enables fabrication of a very compact light-emitting device. 
     However, it is difficult to ensure a sufficient production yield of the active-matrix type light-emitting device, as compared to the passive-matrix type device that has a simpler structure, since a plurality of TFTs have to be formed on the same substrate in the active-matrix type device. Particularly in the case where the driver circuit is to he provided on the same substrate, a line defect may arise in which one line of the pixels does not operate because of a defect of operation. In addition, since fabrication steps for the TFTs are relatively complicated, there is the higher possibility of increasing a fabrication cost of the active-matrix type device, as compared to that of the passive-matrix type device. In such a case, a disadvantage of increasing a price of an electrical apparatus employing the active-matrix type light-emitting device in its display section may arise. 
     Thus, the present invention is intended to reduce a fabrication cost of the active-matrix type display device so as to provide an inexpensive display device. In addition, the present invention is also intended to provide an inexpensive electrical apparatus that employs in its display section, the display device in accordance with the present invention. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, in order to reduce a fabrication cost of an active-matrix type display device, all of the TFIs to be used in a pixel section are provided as a TFT of one conductivity type (indicating herein either a p-channel TFT or an n-channel TFT), and furthermore, a driver circuit is also formed entirely with TFTs of the same conductivity type as in the pixel section. Thus, a fabrication process can be significantly reduced, and therefore, the fabrication cost can be reduced. 
     For the above purpose, in accordance with one aspect of the present invention, all of a source wiring, a gate electrode, a gate wiring (which is a line that transmits a signal to the gate electrode), and a current supply line are simultaneously formed. In other word, an identical electrically conductive (hereinafter simply referred to as “conductive”) film is formed on the same surface. In addition, in accordance with another aspect of the present invention, a line (referred to as the connecting wiring in the present specification) that connects the TFT to a line for connecting a plurality of independently formed gate wirings to each other, or the source wiring, or the current supply line, is formed on the same surface with the identical conductive film as the drain wiring of the current-controlling TFT. 
     Furthermore, in accordance with a further important aspect of the present invention, a driver circuit is formed of TFTs of one and the same conductivity type. In other word, in contrast to the conventional driver circuit that is in general designed based on a CMOS circuit in which an n-channel TFT and a p-channel TFT are complimentarily combined to each other, the driver circuit in accordance with the present invention is formed by combining only the p-channel TFTs or the n-channel TFTs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  shows a structure of a gate-side driver circuit; 
         FIG. 2  shows a timing chart of decoder input signals; 
         FIG. 3  shows a structure of a source-side driver circuit; 
         FIG. 4  shows a circuit structure of a pixel section of a light-emitting device; 
         FIG. 5  shows a cross-sectional structure of the pixel section of the light-emitting device; 
         FIG. 6  shows a top-view structure of the pixel section of the light-emitting device; 
         FIGS. 7(A) and 7(B)  each show another cross-sectional structure of the pixel section of the light-emitting device; 
         FIGS. 8(A) through 8(D)  show various fabrication steps of the light-emitting device; 
         FIGS. 9(A) through 9(C)  show various fabrication steps of the light-emitting device; 
         FIG. 10  shows another circuit structure of a pixel section of a light-emitting device; 
         FIG. 11  shows yet another circuit structure of a pixel section of a light-emitting device; 
         FIGS. 12(A) through 12(C)  show various fabrication steps of the light-emitting device; 
         FIG. 13  shows another top-view structure of the pixel section of the light-emitting device; 
         FIGS. 14(A) through 14(C)  show various fabrication steps of the light-emitting device; 
         FIG. 15(A)  shows yet another top-view structure of the pixel section of the light-emitting device; 
         FIG. 15(B)  shows yet another cross-sectional structure of the pixel section of the light-emitting device; 
         FIGS. 16(A) and 16(B)  show yet other circuit structures of a pixel section of a light-emitting device; 
         FIGS. 17(A) and 17(B)  show yet other circuit structures of a pixel section of a light-emitting device; 
         FIG. 18  shows a thin film forming apparatus for forming an EL layer; 
         FIGS. 19(A) and 19(B)  show external appearances of a liquid crystal display device; 
         FIGS. 20(A) through 20(F)  show specific examples of an electrical apparatus, respectively; and 
         FIGS. 21(A) through 21(D)  show specific examples of an electrical apparatus, respectively; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With now reference to  FIGS. 1 and 2 , a driver circuit to be used in the present invention will be described. In accordance with the present invention, instead of a typical shift register, a decoder employing p-channel TFTs as shown in  FIG. 1  is used.  FIG. 1  illustrates an example of a gate-side driver circuit. 
     In  FIG. 1 , reference numeral  100  denotes a decoder in the gate-side driver circuit, and  101  denotes a buffer section of the gate-side driver circuit. Here, the buffer section refers to a section in which a plurality of buffers (buffer amplifiers) are integrated. Furthermore, the buffer refers to a circuit capable of exhibiting the driving capability without providing any adverse effects of a subsequent stage on a previous stage. 
     The gate-side decoder  100  will be now described. Reference numeral  102  denotes input signal lines (hereinafter referred to as the selection lines) of the decoder  100 , and more specifically indicates A 1 , A 1  bar (a signal having an inverted polarity with respect to A 1 ), A 2 , A 2  bar (a signal having an inverted polarity with respect to A 2 ), . . . , An, and An bar (a signal having an inverted polarity with respect to An). In other word, it can be considered that the  2   n  selection lines are arranged. 
     The number of the selection lines is determined based on the number of gate wirings to be output from the gate-side driver circuit. For example, in the case where a pixel section for VGA display is provided, 480 gate wirings are required, which in turn requires a total of 18 selection lines to be provided for 9 bits (corresponding to the case where n=9). The selection lines  102  transmit signals shown in the timing chart in  FIG. 2 . As shown in  FIG. 2 , assuming that a frequency of A 1  is normalized to be 1, a frequency of A 2  can be expressed as 2 −1 , a frequency of A 3  can be expressed as 2 −2 , and a frequency of An can be expressed as 2 −(n−1 ). 
     Reference numeral  103   a  denotes a first-stage NAND circuit (also referred to as the NAND cell), while  103   b  and  103   c  denote a second-stage and an n-th stage NAND circuits, respectively. The required number of the NAND circuits is equal to the number of the gate wirings, and specifically, n NAND circuits are required here. In other word, the decoder  100  in accordance with the present invention is composed of a plurality of the NAND circuits. 
     In each of the NAND circuits  103   a  to  103   c , p-channel TFTs  104  to  109  are combined to form a NAND circuit. Actually,  2   n  TFTs are employed in each of the NAND circuits  103 . Furthermore, a gate of each of the p-channel TFTs  104  to  109  is connected to either one of the selection lines  102  (A 1 , A 1  bar, A 2 , A 2  bar, . . . , An, An bar). 
     In this case, in the NAND circuit  103   a , the p-channel TFTs  104  to  106  that respectively have the gates connected to any of A 1 , A 2 , . . . , An (which are referred to as the positive selection lines) are connected to each other in parallel, and further connected to a positive power source wiring (V DH )  110  as a common source, as well as to an output line  111  as a common drain. On the other hand, the remaining p-channel TFTs  107  to  109  that respectively have the gates connected to any of A 1  bar, A 2  bar, . . . , An bar (which are referred to as the negative selection lines) are connected to each other in series, and a source of the p-channel TFT  109  positioned at one end of the circuit is connected to a negative power source wiring (V DL )  112  while a drain of the p-channel TFT  107  positioned at the other end of the circuit is connected to the output line  111 . 
     As described in the above, the NAND circuit in accordance with the present invention includes the n TFTs of one conductivity type (the p-channel TFTs in this case) connected in series and the other n TFTs of the one conductivity type (the p-channel TFTs in this case) connected in parallel. It should be noted that in the n NAND circuits  103   a  to  103   c , all of combinations among the p-channel TFTs and the selection lines are different from each other. In other word, the output lines  111  are configured so that only one of them is selected, and signals are input to the selection lines such that the output lines  111  are sequentially selected from one side thereof. 
     Then, the buffer  101  is composed of a plurality of buffers  113   a  to  113   c  so as to respectively correspond to the NAND circuits  103   a  to  103   c . It should be noted that the buffers  113   a  to  113   c  may have the same structure. 
     Furthermore, the buffers  113   a  to  113   c  are formed with p-channel TFTs  114  to  116  as TFTs of one conductivity type. The output line  111  from the decoder is input as a gate of the corresponding p-channel TFT  114  (a first TFT of the one conductivity type). The p-channel TFT  114  utilizes a ground power source wiring (GND)  117  as its source, and a gate wiring  118  as its drain. Moreover, the p-channel TFT  115  (a second TFT of the one conductivity type) utilizes the ground power source line  117  as its gate, a positive power source line (V DH )  119  as its source, and the gate wiring  118  as its drain. The p-channel TFT  115  is always in the ON state. 
     In other words, each of the buffers  113   a  to  113   c  in accordance with the present invention includes the first TFT of the one conductivity type (the p-channel TFT  114 ), and further includes the second TFT of the one conductivity type (the p-channel TFT  115 ) that is connected to the first TFT of the one conductivity type in series and utilizes the gate of the first TFT of the one conductivity type as the drain. 
     Furthermore, the p-channel TFT  116  (a third TFT of the one conductivity type) employs a reset signal line (Reset) as its gate, the positive power source line  119  as its source, and the gate wiring  118  as its drain. It should be noted that the ground power source line  117  may be replaced with a negative power source line (which is a power source line for providing a voltage that causes a p-channel TFT, to be used as a switching element of a pixel, to be in the ON state). 
     In this case, a channel width (indicated as W 1 ) of the p-channel TFT  115  and a channel width (indicated as W 2 ) of the p-channel TFT  114  satisfy the relationship of W 1 &lt;W 2 . The channel width refers to a length of a channel formation region measured in the direction perpendicular to a channel length. 
     The buffer  113   a  operates as follows. During a time period in which a positive voltage is being applied to the output line  111 , the p-channel TFT  114  is in the OFF state (i.e., its channel is not formed). On the other hand, since the p-channel TFT  115  is always in the ON state (i.e., its channel is formed), a voltage of the positive power source line  119  is applied to the gate wiring  118 . 
     On the other hand, in the case where a negative voltage is applied to the output line  111 , the p-channel TFT  114  comes into the ON state. In this case, since the channel width of the p-channel TFT  114  is wider than that of the p-channel TFT  115 , the electrical potential of the gate wiring  118  is pulled by an output on the side of the p-channel TFT  114 , thereby resulting in the electrical potential of the ground power source line  117  being applied to the gate wiring  118 . 
     Accordingly, the gate wiring  118  outputs a negative voltage (that causes the p-channel TFT, to be used as the switching element of the pixel, to be in the ON state) when a negative voltage is being applied onto the output line  111 , while always outputting a positive voltage (that causes the p-channel TFT, to be used as the switching element of the pixel, to be in the OFF state) when a positive voltage is being applied onto the output line  111 . 
     The p-channel TFT  116  is used as a reset switch for forcing the gate wiring  118 , to which the negative voltage is being applied, to be pulled up to a positive voltage. Namely, after a selection period of the gate wiring  118  is completed, a reset signal is input so that a positive voltage is applied to the gate wiring  118 . It should be noted that the p-channel TFT  116  maybe omitted. 
     With the gate-side driver circuit that operates in the above-described manner, the gate wirings are sequentially selected. Then, the structure of a source-side driver circuit is shown in  FIG. 3 . The source-side driver circuit as shown in  FIG. 3  includes a decoder  301 , a latch  302 , and a buffer  303 . Since the decoder  301  and the buffer  303  have the identical structures with those of the gate-side driver circuit, respectively, descriptions therefor are omitted here. 
     In the case of the source-side driver circuit shown in  FIG. 3 , the latch  302  is composed of a first-stage latch  304  and a second-stage latch  305 . Each of the first-stage latch  304  and the second-stage latch  305  includes a plurality of basic units  307  each composed of m p-channel TFTs  306   a  to  306   c . An output line  308  from the decoder  301  is input to gates of the respective m p-channel TFTs  306   a  to  306   c  that form the basic unit  307 . It should be noted that the number m is any integer. 
     For example, in the case of the VGA display, the number of the source wirings is  640 . In the case where m=1, the number of the NAND circuits required to be provided is also  640 , while 20 selection lines (corresponding to 10 bits) are required to be provided. On the other hand, however, when m=8, the number of the necessary NAND circuits is 80 and the number of the necessary selection lines is 14 (corresponding to 7 bits). Namely, assuming that the number of the source wirings is M, the number of necessary NAND circuits can be expressed as M/m. 
     Sources of the p-channel TFTs  306   a  to  306   c  are connected to video signal lines (V 1 , V 2 , . . . , Vk)  309 , respectively. Namely, when a negative voltage is applied to an output line  308 , all of the p-channel TFTs  306   a  to  306   c  are simultaneously put into the ON state, so that video signals are taken into the corresponding p-channel TFTs  306   a  to  306   c , respectively. The video signals thus taken in are retained in capacitors  310   a  to  310   c , respectively, connected thereto. 
     Furthermore, the second-stage latch  305  also includes a plurality of basic units  307   b  each composed of m p-channel TFTs  311   a  to  311   c . All of gates of the p-channel TFTs  311   a  to  311   c  are connected to a latch signal line  312 , so that when a negative voltage is applied to the latch signal line  312 , all of the p-channel TFTs  311   a  to  311   c  are simultaneously turned on. 
     As a result, the signals retained in the capacitors  310   a  to  310   c  are then retained respectively in capacitors  313   a  to  313   c  connected to the p-channel TFTs  311   a  to  311   c  and simultaneously output to the buffer  303 . Then, as described with reference to  FIG. 1 , those signals are output to the source wirings  314  via the buffer. With the source-side driver circuit that operates in the above-described manner, the source wirings are sequentially selected. 
     As described in the above, by composing the gate-side driver circuit and the source-side driver circuit only of the p-channel TFTs, all of the pixel sections and the driver circuits can be entirely formed of the p-channel TFTs. Accordingly, upon fabrication of an active-matrix type display device, a fabrication yield and a throughput of the TFT steps can be significantly improved, thereby resulting in a reduced fabrication cost. 
     It should be noted that the present invention can be embodied even in the case where either of the source-side driver circuit or the gate-side driver circuit, or both of them, are provided in an IC chip to be externally attached. 
     Embodiment 1 
     In the present invention, the pixel section, in addition to the driver circuit, is entirely composed of the p-channel TFTs. Thus, in the present embodiment, the structure of the pixel section for displaying an image in accordance with the signals transmitted by the driver circuit as shown in  FIGS. 1 and 3  will be described. 
     The structure of a pixel of an active-matrix type light-emitting device in accordance with the present invention is shown in  FIGS. 5 and 6 .  FIG. 5  illustrates a cross-sectional view of one pixel, while  FIG. 6  illustrates a top view of adjacent two pixels.  FIG. 5  shows a cross-sectional view cut along A-A′ in  FIG. 6 , and the same component is designated with the same reference numeral in both of these figures. In addition, the two pixels illustrated in  FIG. 6  are symmetric to each other with respect to the current supply line  525 , and therefore, have the same structure as each other. 
     In  FIG. 5 , reference numeral  501  denotes a substrate transparent to visible light, and  502  denotes an insulating film containing silicon. As the substrate  501  that is transparent to visible light, a glass substrate, a quartz substrate, a crystalline glass substrate, or a plastic substrate (including a plastic film) can be used. As the insulating film  502  containing silicon, a silicon oxide film, a silicon oxynitride film, or a silicon nitride film can be used. 
     In the present specification, TFTs are formed on an insulating surface. As the insulating surface, an insulating film (typically an insulating film containing silicon) or a substrate made of an insulating body (typically a quartz substrate) may be used. Accordingly, the expression “on the insulating surface” means “on the insulating film” or “on the substrate made of the insulating material”. 
     On the insulating film  502  containing silicon, a switching TFT  601  and a current-controlling TFT  602  are formed with p-channel TFTs. 
     The switching TFT  601  employs, as an active layer, a semiconductor region that includes regions  503  to  505  made of p-type semiconductor (hereinafter referred to as the p-type semiconductor regions) and regions  506  and  507  made of intrinsic or substantially intrinsic semiconductor (hereinafter referred to as the channel formation regions). On the other hand, the current-controlling TFT  602  employs, as an active layer, a semiconductor region including p-type semiconductor regions  508  and  509  and a channel formation region  510 . 
     The p-type semiconductor region  503  or  505  serves as a source region or a drain region of the switching TFT  601 . Furthermore, the p-type semiconductor region  508  serves as a source region of the current-controlling TFT  602 , while the p-type semiconductor region  509  serves as a drain region of the current-controlling TFT  602 . 
     The active layers of the switching TFT  601  and the current-controlling TFT  602  are covered with a gate insulating film  511 , and further thereon, a source wiring  512 , a gate electrode  513   a , a gate electrode  513   b , a drain wiring  514 , and a gate electrode  515  are formed. These components are simultaneously formed with the identical material. As the constituent material for these lines or electrodes, tantalum, tungsten, molybdenum, niobium, titanium, or a nitride of these metals may be used. Alternatively, an alloy in which these metals are combined, or a silicide of these metals, may be used. 
     Furthermore, as shown in  FIG. 6 , the drain wiring  514  is integrated with the gate electrode  515 . In addition, the gate electrodes  513   a  and  513   b  are integrated with the shared gate wiring  516 , so that the same voltage is always being applied to these gate electrodes  513   a  and  513   b.    
     Moreover, in  FIG. 5 , reference numeral  517  denotes a passivation film made of a silicon oxynitride film or a silicon nitride film, and an interlayer insulating film  518  is formed thereon. As the interlayer insulating film  518 , an insulating film containing silicon or an organic resin film is used. As the organic resin film, a polyimide film, a polyamide film, an acrylic resin film, or a BCB (benzocyclobutene) film can be used. 
     Further on the interlayer insulating film  518 , connecting wirings  519  to  522  and an electrode  523  made of a transparent conductive film are formed. At the same time, line  524  as shown in  FIG. 6  are also simultaneously formed. As the transparent conductive film, a thin film made of indium oxide, tin oxide, zinc oxide, a compound of indium oxide and tin oxide, a compound of indium oxide and zinc oxide, or a compound obtainable by adding gallium to these materials can be used. 
     In this case, the connecting wiring  520  is a line that provides electrical connection between the source wiring  512  and the p-type semiconductor region  503 , while the connecting wiring  521  is a line that provides electrical connection between the p-type semiconductor region  505  and the drain region  514 . Moreover, the connecting wiring  522  is a line that provides electrical connection between the source region  508  and the current supply line (see  FIG. 6 )  525 . 
     The connecting wiring  519  is a line that realizes connections among the gate wirings  516  divided and formed into a plurality of patterns, and is provided to overpass the source wiring  512  and the current supply line  525 . It is also possible to connect the source wiring or the current supply line, divided into a plurality of portions, with the connecting wiring formed so as to overpass the gate wiring. 
     An electrode  523  is an anode of the EL element, and is referred to as the pixel electrode or the anode in the present specification. The pixel electrode  523  is electrically connected to a drain region  509  of the current-controlling TFT  602 . In  FIG. 6 , the pixel electrode  523  can be considered as a drain wiring of the current-controlling TFT  602 . 
       FIG. 7(A)  shows a cross-sectional view obtainable by cutting  FIG. 6  along B-B′. As shown in  FIG. 7(A) , the connecting wiring  524  overpasses the current supply line  525  and provides connection among the gate wirings  516 . In addition,  FIG. 7(B)  shows a cross-sectional view obtainable by cutting  FIG. 6  along C-C′. As shown in  FIG. 7(B) , the connecting wiring  522  electrically connects the p-type semiconductor region  508  of the current-controlling TFT  602  with the current supply line  525 . 
     In the actual device, an EL layer (not shown) and a cathode (not shown) are formed thereafter on the pixel electrode  523  to complete an active-matrix type light-emitting device. The EL layer and the cathode may be formed with any known technique. 
     Furthermore, although a TFT having a top-gate structure (specifically, a planar-type TFT) has been described as an example in the above, the present invention is not limited to such a kind of TFT structure. Alternatively, the present invention can be applied to a TFT having a bottom-gate structure. Typically, it is possible to embody the present invention in a reverse-staggered type TFT. 
     With the pixel structure as described in the above, the fabrication process for the active-matrix type light-emitting device can be significantly simplified, and an inexpensive active-matrix type light-emitting device can be produced. In addition, an electrical apparatus that employs the same as a display section can be realized. 
     Embodiment 2 
     In the present embodiment, the fabrication process of an active-matrix type light-emitting device in which a pixel section and a driver circuit for transmitting a signal to the pixel section are formed on the identical insulating surface will be described with reference to  FIGS. 8(A) to 8(D)  and  FIGS. 9(A) to 9(C) . 
     First, as shown in  FIG. 8(A) , an underlying film (insulating body)  802  is formed on a glass substrate  801 . In the present embodiment, the underlying film  802  is formed by sequentially depositing a first silicon oxynitride film having a thickness of 50 nm and a second silicon oxynitride film having a thickness of 200 nm in this order from the side closer to the glass substrate  801 . The nitrogen content of the first silicon oxynitride film is larger than that of the second silicon oxynitride film so as to suppress diffusion of alkali metal from the glass substrate  801 . 
     Then, an amorphous silicon film (not shown) is formed on the underlying film  802  by a plasma CVD method to have a thickness of 40 nm. Thereafter, the amorphous silicon film is irradiated with laser light for crystallization to form a polycrystalline silicon film (polysilicon film)  803 . It should be noted that a microcrystalline silicon film or an amorphous silicon germanium film may be formed instead of the amorphous silicon film. Moreover, a method for crystallization is not limited to the laser crystallization method, but any other known crystallization method can be used. 
     Then, as shown in  FIG. 8(B) , the polycrystalline silicon film  803  is patterned to form respective independently isolated semiconductor layers  804  to  806 . Upon completion, the semiconductor layer denoted with reference numeral  804  becomes an active layer of a TFT that forms a driver circuit (this TFT is referred to as driver TFT). On the other hand, the semiconductor layer denoted with reference numeral  805  becomes an active layer of the switching TFT, while that denoted with reference numeral  806  denotes an active layer of the current-controlling TFT. 
     Thereafter, a gate insulating film  807  with a thickness of 80 nm, made of a silicon oxide film, is formed by a plasma CVD method so as to cover the isolated semiconductor layers  804  to  806 . Furthermore, a tungsten film (not shown) is formed by a sputtering method on the gate insulating film  807  to have a thickness of 350 nm, and is then patterned to form gate electrodes  808 ,  809 ,  810   a , and  810   b . Simultaneously, a source wiring  812  and a drain wiring  813  of the switching TFT are formed. Of course, the drain wiring  813  and the gate electrode  811  are formed integrally. 
     Then, elements belonging to Group 13 in the periodic table are added with the gate electrodes  808 ,  809 ,  810   a ,  810   b , the source wiring  812  and the drain wiring  813  being used as a mask. Any known methods may be used for the above purpose. In the present embodiment, boron is added by a plasma doping method at the concentration in the range of 5×10 19  to 1×10 21  atoms/cm 3 . Thus, the semiconductor regions with the p-type conductivity (hereinafter referred to as the p-type semiconductor regions)  814  to  821  are formed. Furthermore, channel formation regions  822  to  826  are formed immediately below the gate electrodes  808 ,  809 ,  810   a , and  810   b.    
     It should be noted that in the present embodiment, the p-type semiconductor regions  814  and  816  serve as source regions of the p-channel TFTs forming the driver circuit, while the p-type semiconductor region  815  serves as a drain region of the p-channel TFT forming the driver circuit. 
     Thereafter, a heat treatment is performed to activate the elements in the Group 13 of the periodic table contained in the p-type semiconductor regions. This activation process may be performed by either one of a furnace annealing method, a laser annealing method, and a lamp annealing method, or any combination thereof. In the present embodiment, a heat treatment is performed at 500° C. for four (4) hours in nitrogen atmosphere. In this case, it is preferable to reduce the concentration of oxygen in the nitrogen atmosphere to as low a level as possible. The active layers of the TFTs are formed by the above activation process. 
     After the activation process is completed, a silicon oxynitride film with a thickness of 200 nm is formed as a passivation film  827 , and a hydrogenation process for the semiconductor layers is then performed. Any known hydrogen annealing technique or a plasma hydrogenation technique may be used for the hydrogenation process. Thus, the structure as shown in  FIG. 8(C)  can be obtained. 
     Thereafter, as shown in  FIG. 8(D) , an interlayer insulating film  828  made of a resin is formed to have a thickness of 800 nm. As the resin for this purpose, polyimide, polyamide, acrylic resin, epoxy resin, or BCB (benzocyclobutene) may be used. Alternatively, an inorganic insulating film may be also used. 
     Contact holes are then formed in the interlayer insulating film  828 , and connecting wirings  829  to  835  and a pixel electrode  836  are formed. In the present embodiment, a conductive film made of a compound of indium oxide and tin oxide (Indium Tin Oxide; ITO) is used for forming the connecting wirings  829  to  835  and the pixel electrode  836 . It should be noted that of course, any conductive films made of other materials that are transparent to visible light can be used for this purpose. 
     The connecting wirings  829  and  831  serve as source wirings of the p-channel TFTs forming the driver circuit, while the connecting wiring  830  serves as a drain wiring of the p-channel TFT forming the driver circuit. Thus, in the present embodiment, the driver circuit is formed based on a PMOS circuit which is formed of p-channel TFTs. 
     In the above-described state, the p-channel TFTs forming the driver circuit as well as the switching TFT and the current-controlling TFT in the pixel section are completed. In the present embodiment, all of the TFTs are of the p-channel type. It should be noted that the switching TFT is formed such that the gate electrode thereof overpasses the active layer at two different positions so that the two channel formation regions are connected to each other in series. Such a structure can effectively suppress an OFF current value (i.e., a current that flows when a TFT is in the OFF state). 
     Then, as shown in  FIG. 9(A) , insulating bodies  837  and  838  made of a resin are formed so as to cover edge portions and concave portions (recesses formed due to the contact holes) of the pixel electrode  836 . These insulating bodies  837  and  838  may be formed by forming an insulating film made of a resin and then patterning the film. In this case, it is desirable to set a height (d) from the surface of the pixel electrode  836  to the top of the insulating body  838  to be at 300 nm or less (preferably 200 nm or less). It should be noted that the insulating bodies  837  and  838  may be omitted. 
     The insulating body  837  is formed for the purpose of covering the edge portions of the pixel electrode  836  and thereby avoiding an adverse effect of electric field concentration at the edge portions. Thus, deterioration of the EL layer can be prevented. On the other hand, the insulating body  838  is formed for the purpose of burying the concave portions of the pixel electrode which are formed due to the contact holes. Thus, any coverage defect of the EL layer to be later formed can be prevented, and any short-circuit between the pixel electrode and a cathode to be later formed can be prevented. 
     Thereafter, an EL layer  839  with a thickness of 70 nm and a cathode  840  with a thickness of 300 nm are formed by a vapor deposition method. In the structure of the present embodiment, a copper phthalocyanine layer (hole injection layer) with a thickness of 20 nm and an Alg 3  layer (light-emitting layer) with a thickness of 50 nm are formed as the EL layer  839 . It should be noted that any other known structure in which a hole injection layer, a hole transport layer, an electron transport layer or an electron injection layer are combined may be used for the light-emitting layer. 
     In the present embodiment, the copper phthalocyanine layer is first formed to cover all of the pixel electrodes, and thereafter, a red-color light-emitting layer, a green-color light-emitting layer, or a blue-color light-emitting layer are formed for each of the pixels corresponding to red, green and blue colors, respectively. The regions to which the layer is to be formed may be selected upon vapor deposition by means of a shadow mask. Thus, a color display can be realized. 
     When the green-color light-emitting layer is to be formed, Alq 3  (tris-8-quinolinolato aluminum complex) is used as a mother material of the light-emitting layer, and quinacridon or coumarine 6 is used as a dopant. When the red-color light-emitting layer is to be formed, Alq 3  is used as a mother material of the light-emitting layer, and DCJT, DCM 1 , or DCM 2  is used as a dopant. When the blue-color light-emitting layer is to be formed, BAlq 3  (a complex with five coordinations having a mixed ligand of 2-methyl-8-quinolinol and phenol derivative) is used as a mother material of the light-emitting layer, and perylene is used as a dopant. 
     It should be noted that the present invention is not limited to use of the above-mentioned organic materials, but rather, any known low-molecule type organic EL material, high-molecule type organic EL material, or inorganic EL material can be used. Alternatively, any combination of these materials can be also used. Furthermore, in the case where a high-molecule type organic EL material is used, a coating method can be used. 
     In the manner as mentioned in the above, the EL element composed of pixel electrode (anode)  836 , EL layer  839  and cathode  840  is formed (see  FIG. 9(B) ). 
     Thereafter, a cover member  842  is bonded by means of an adhesive  841 . In the present embodiment, a glass substrate is used as the cover member  842 . Alternatively, a flexible plastic film, a quartz substrate, a plastic substrate, a metal substrate, a silicon substrate, or a ceramic substrate may be used. It is advantageous to provide an insulating film containing silicon or a carbon film on a surface exposed to the surrounding air so as to prevent oxygen or water from entering or to provide protection against scratches caused by friction. 
     As the adhesive  841 , a UV curable resin or a thermosetting resin is typically used. For example, PVC (polyvinyl chloride), acrylic resin, polyimide, epoxy resin, silicone resin, PVB (polyvinyl butyral), or EVA (ethylene vinyl acetate) can be used. In the case where the adhesive  841  is positioned in the side closer to an observer when viewed from the EL element, the adhesive is required to be made of a material that allows light to pass therethrough. In addition, it is advantageous to provide a water-absorbing material (preferably barium oxide) and/or an anti-oxidization material (i.e., a substance that adsorbs oxygen) within the adhesive  841  for preventing deterioration of the EL element. 
     With the above-described structure, the EL element can be completely shut out from the ambient air. Thus, deterioration of the EL material due to oxidation can be substantially completely suppressed, so that reliability of the resultant EL element can be significantly improved. 
     The active-matrix type light-emitting device thus fabricated in the above-described manner has the pixel section that includes the circuit structure as shown in  FIG. 10 . Specifically, in  FIG. 10 , reference numeral  1001  denotes a source wiring,  1002  denotes a gate wiring,  1003  denotes a switching TFT,  1004  denotes a current-controlling TFT,  1005  denotes a current supply line, and  1006  denotes an EL element. In the present embodiment, each of the switching TFT  1003  and the current-controlling TFT  1004  is formed as the p-channel TFT. 
     It should be noted that a gate capacitance of the current-controlling TFT  1004  exhibits the same function as the capacitor employed in the conventional art (i.e., the capacitor  404  in  FIG. 4 ). This can be realized because in the case where a time-divisional grayscale display is performed by means of a digital driving scheme, necessary charges can be retained only by the gate capacitance of the current-controlling TFT since one-frame period (or one-field period) is short. 
     The active-matrix type light-emitting device of the present invention as described in the above requires only five masks in total for performing the patterning steps (this number can be further reduced to four when the insulating bodies  837  and  838  are omitted), which can in turn realize a high fabrication yield and a low fabrication cost. 
     Embodiment 3 
     In Embodiment 2 mentioned in the above, the circuit structure of the pixel section shown in  FIG. 10  can be modified as shown in  FIG. 11 . Specifically, in  FIG. 11 , reference numeral  1101  denotes a source wiring,  1102  denotes a gate wiring,  1103  denotes a switching TFT,  1104  denotes a current-controlling TFT,  1105  denotes a current supply line, and  1106  denotes an EL element. In the present embodiment, each of the switching TFT  1103  and the current-controlling TFT  1104  is formed as the p-channel TFT. 
     In this case, since the gate wiring  1102  and the current supply line  1105  are disposed in different layers, it is advantageous to provide these components so as to overlap each other with an interlayer insulating film interposed therebetween. Thus, an occupied area of these lines can be substantially made common, and therefore, the effective light-emission area of the pixel can be increased. 
     Embodiment 4 
     In the present embodiment, the active-matrix type light-emitting device is fabricated in the manner different from that described in Embodiment 1. The fabrication process will be described below with reference to  FIGS. 12(A) to 12(C) . 
     First, the fabrication steps up to the one as shown in  FIG. 8(D)  are performed as described previously in connection with Embodiment 2 to form connecting wirings  1201  to  1207  and a drain wiring  1208 . In the present embodiment, these connecting wirings are formed of a metal film. Although any material can be used as the metal film, a layered film having a three-layer structure in which an aluminum film is sandwiched between titanium films is employed in the present embodiment. 
     Then, as shown in  FIG. 12(B) , a pixel electrode  1209  made of a transparent conductive film is formed. In this case, the pixel electrode  1209  is formed such that a portion thereof comes into contact with the drain wiring  1208 . The current-controlling TFT and the pixel electrode can be thus electrically connected to each other.  FIG. 13  shows a top view in the above-described structure. It should be noted that the cross-sectional view shown in  FIG. 12(B)  is obtainable by cutting  FIG. 13  along A-A′. 
     In the present embodiment, the connecting wirings  1201  to  1207  can be made of a metal film. Accordingly, as compared to the transparent conducting film such as an ITO film or the like described in the previous embodiment modes, a reduction in a wiring resistance as well as a reduction in a contact resistance can be realized. Moreover, all of the lines for connecting various circuit portions in the driver circuit can be made of a low-resistance metal film, and therefore, a driver circuit capable of exhibiting a higher operating speed can be realized. 
     Although the pixel electrode  1209  is formed after the connecting wirings  1201  to  1207  and the drain wiring  1208  are completed, this fabrication order may be reversed. In other word, the connecting wirings and the drain wiring made of a metal film may be formed after the pixel electrode made of a transparent conductive film is formed. 
     Thereafter, as in Embodiment 2, an insulating body  1210  made of a resin is formed, and an EL layer  1211  and a cathode  1212  are sequentially formed. Furthermore, a cover member  1214  is formed with an adhesive  1213 . Thus, the active-matrix type light-emitting device as shown in  FIG. 12(C)  is completed. 
     Embodiment 5 
     In the present embodiment, an example of fabricating the active-matrix type light-emitting device in accordance with the present invention with a plastic substrate or a plastic film will be explained. Plastics that can be used in the present embodiment include PES (polyethylene sulfile), PC (polycarbonate), PET (polyethylene terephthalate), or PEN (polyethylene naphthalate). 
     First, the TFTs and the EL element are formed on the glass substrate  801  in accordance with the fabrication steps as described in Embodiment 2. In the present embodiment, however, a peeling layer  1401  is formed between the glass substrate  801  and the underlying film  802 . A semiconductor film can be used as the peeling layer  1401 . Typically, an amorphous silicon film may be used for the above purpose. 
     Moreover, in the present embodiment, a cover member  1403  is adhered by means of a first adhesive  1402 . An insulating film made of a resin (typically, polyimide, acrylic resin, polyamide, or epoxy resin) is used as the first adhesive  1402 . It should be noted that the material for the first adhesive  1402  is required to realize a sufficient selection ratio upon etching of the peeling layer  1401  by means of a gas containing halogen fluoride. As the cover member  1403  to be adhered with the first adhesive  1402 , a PET film is used in the present embodiment. 
     Then, the entire substrate on which the element has been formed is exposed to the gas containing halogen fluoride. This treatment allows the peeling layer  1401  to be selectively removed. Halogen fluoride refers to a substance that can be expressed as the chemical formula of XFn (where X indicates a halogen other than fluorine, and n is an integer). For example, as the halogen fluoride, chlorine monofluoride (ClF), chlorine trifluoride (ClF 3 ), bromine monofluoride (BrF), bromine trifluoride (BrF 3 ), iodine monofluoride (IF), iodine trifluoride (IF 3 ) can be used. 
     Halogen fluoride exhibits a large selection ratio between a silicon film and a silicon oxide film, thereby resulting in a selective etching of the silicon film being realized. Furthermore, this etching reaction can easily proceed at room temperature, and therefore, the process can be performed even after the EL element with low heat-resistance capability is formed. 
     Although the silicon film can be etched only by being exposed to the above-mentioned halogen fluoride, other fluorides (carbon tetrafluoride (CF 4 ) or nitrogen trifluoride) may be used in the present invention so long as they are put into a plasma condition. 
     In the present embodiment, chlorine trifluoride (ClF 3 ) is used as halogen fluoride and nitrogen is used for a dilution gas. Argon, helium, or neon may be used as the dilution gas. Flow rates of both of the gases may be set at 500 sccm (8.35×10 −6  m 3 /s), and a reaction pressure may be set in the range from 1 to 10 Torr (1.3×10 2  to 1.3×10 3  Pa). Moreover, a treatment temperature may be set at room temperature (typically in the range from 20 to 27° C.). 
     Thereafter, as shown in  FIG. 14(C) , a substrate (bonding substrate)  1405  made of a plastic substrate or a plastic resin is adhered by means of a second adhesive  1404 . In the present embodiment, a PET film is used as the bonding substrate  1405 . It is desirable for the cover member  1403  and the bonding substrate  1405  to be made of the same material as each other in order to satisfy a stress balance condition. 
     Thus, the active-matrix type light-emitting device in which the TFTs and the EL element are sandwiched by the plastic film can be obtained. Since the plastic film is bonded after the TFTs are formed in the present embodiment, no limitation is applied onto the fabrication process. For example, the TFTs can be formed without taking the heat-resistance capability of the plastic to be employed into consideration. 
     Furthermore, since a flexible, light-weighted light-emitting device can be obtained, the device in the present embodiment is suitable to a display section of portable information equipment such as a mobile phone, an electronic databook or the like. 
     The structure as described in the present embodiment can be freely combined with any structures in Embodiments 1 through 4. 
     Embodiment 6 
     In the present invention, it is advantageous to provide a DLC (diamond-like carbon) film on one side or both sides of the substrate or the cover member on which the TFTs and the EL element are to be formed. It should be noted that a thickness of such a DLC film is desirably not greater than 50 nm (more preferably in the range of 10 to 20 nm) since too large a thickness thereof causes transmittance of the film to be reduced. In addition, the DLC film may be formed by a sputtering method or an ECR plasma CVD method. 
     The DLC film is characterized by the Raman spectrum distribution including an asymmetric peak at around 1550 cm −1 , and a shoulder at around 1300 cm − . Moreover, the DLC film is also characterized by the hardness in the range of 15 to 25 Pa when measured by means of a micro-hardness tester. Furthermore, it is advantageous to provide the DLC film as a protection film for surface protection and/or heat dissipation since the DLC film has a larger hardness and a larger heat conductivity as compared to the substrate or the cover member. 
     The structure as described in the present embodiment can be freely combined with any structures in Embodiments 1 through 5. 
     Embodiment 7 
     In the present embodiment, external appearance views of the light-emitting device of the present invention as described in Embodiment 2 will be described.  FIG. 15(A)  shows a top view of the light-emitting device of the present invention, while FIG.  15 (B) shows a cross-sectional view thereof. 
     In  FIG. 15(A) , reference numeral  1501  denotes a substrate,  1502  denotes a pixel section,  1503  denotes a source-side driver circuit, and  1504  denotes a gate-side driver circuit. Each of these driver circuits is connected via a wiring  1505  to an FPC (flexible printed circuit)  1506 , which in turn is connected to an external apparatus. The gate-side driver circuit shown in  FIG. 1  is used in the gate-side driver circuit  1504  in  FIG. 15(A) , while the source-side driver circuit shown in  FIG. 3  is used in the source-side driver circuit  1503  in  FIG. 15(A) . Furthermore, the pixel section shown in  FIG. 5  is used in the pixel section  1502  in  FIG. 15(A) . In this case, a first sealing member  1511 , a cover member  1512 , an adhesive  1513  (see  FIG. 15(B) ), and a second sealing member  1514  are formed so as to surround the pixel section  1502 , the source-side driver circuit  1503 , and the gate-side driver circuit  1504 . 
       FIG. 15(B)  corresponds to the cross-sectional view obtainable by cutting  FIG. 15(A)  along A-A′. In this case, a region surrounded with a dashed line  1500  corresponds to the cross-sectional view shown in  FIG. 9(C) , and accordingly, any detailed descriptions thereof will be omitted here. 
     A cathode of the EL element is electrically connected to the wiring  1505  in the region denoted by reference numeral  1514 . The wiring  1505  is provided to supply a predetermined voltage to the cathode, and is electrically connected to the FPC  1506  via an anisotropic conductive film  1515 . Furthermore, the EL element is surrounded with the first sealing member  1511  and the cover member  1512  which is bonded to the substrate  1501  by the first sealing member  1511 . The EL element is encapsulated with an adhesive  1513 . 
     Furthermore, a spacer may be contained in the adhesive  1513 . In this case, if the spacer is formed of barium oxide, it is possible to allow the spacer itself to have water-absorbing capability. In the case where the spacer is provided, it is advantageous to provide on a cathode, a resin film as a buffer layer for mitigating a pressure from the spacer. 
     The wiring  1505  is electrically connected to the FPC  1506  via the anisotropic conductive film  1515 . The wiring  1505  transmits to the FPC  1506  the signal to be sent to the pixel section  1502 , the source-side driver circuit  1503 , and the gate-side driver circuit  1504 . The wiring  1505  is electrically connected to the external apparatus by the FPC  1506 . 
     Furthermore, in the present embodiment, the second sealing member  1514  is provided to cover an exposed portion of the first sealing member  1511  and a portion of the FPC  1506 , so that the EL element can be completely shut out from the ambient air. The light-emitting device having the cross-sectional structure shown in  FIG. 15(B)  is thus obtained. The light-emitting device in the present embodiment can be freely combined with any structures in Embodiments 1 through 6. 
     Embodiment 8 
     In the present embodiment, the pixel structure of the light-emitting device in accordance with the present invention will be described with reference to  FIGS. 16(A) and 16(B) . In the present embodiment, reference numeral  1601  denotes a source wiring of a switching TFT  1602 ,  1603  denotes a gate wiring of the switching TFT  1602 .  1604  denotes a current-controlling TFT,  1605  denotes a capacitor (that can be omitted),  1606  denotes a current supply line,  1607  denotes a power source controlling TFT.  1608  denotes an EL element, and  1609  denotes a power source controlling line. In this case, the source wiring  1601 , the gate wiring  1603 , the current supply line  1606 , and the power source controlling line  1608  are formed of the identical conductive film in the same layer. 
     With respect to operations of the power source controlling TFT  1607 , reference can be made to Japanese Patent Application No. 11-341272. It should be noted that in the present embodiment, the power source controlling TFT is formed as the p-channel type that has the structure identical to that of the current-controlling TFT. 
     Although the power source controlling TFT  1607  is provided between the current-controlling TFT  1604  and the EL element  1608  in the present embodiment, it is also possible to provide the current-controlling TFT  1604  between the power source controlling TFT  1607  and the EL element  1608 . Furthermore, the power source controlling TFT  1607  is preferably formed to have the identical structure with the current-controlling TFT  1604 , or to be connected in series with the current-controlling TFT  1604  while utilizing the identical active layer thereto. 
       FIG. 16(A)  illustrates an example in which the current supply line  1606  is shared with the two pixels. More specifically, the two pixels are formed to be symmetric to each other with respect to the current supply line  1606 . In this case, the number of the necessary current supply lines can be reduced, and thus the pixel section can be formed with higher precision. On the other hand,  FIG. 16(B)  illustrates an example in which the current supply line  1610  is arranged in parallel to the gate wiring  1603 , while the current controlling line  1611  is arranged in parallel to the source wiring  1601 . 
     The structure as described in the present embodiment can be freely combined with any structures in Embodiments 1 through 7. 
     Embodiment 9 
     In the present embodiment, the pixel structure of the light-emitting device in accordance with the present invention will be described with reference to  FIGS. 17(A) and 17(B) . In the present embodiment, reference numeral  1701  denotes a source wiring of a switching TFT  1702 ,  1703  denotes a gate wiring of the switching TFT  1702 ,  1704  denotes a current-controlling TFT,  1705  denotes a capacitor (that can be omitted),  1706  denotes a current supply line,  1707  denotes an erasing TFT,  1708  denotes an erasing gate wiring, and  1709  denotes an EL element. In this case, the source wiring  1701 , the gate wiring  1703 , the current supply line  1706 , and the erasing gate wiring  1708  are formed of the identical conductive film in the same layer. 
     With respect to operations of the erasing TFT  1707 , reference can be made to Japanese Patent Application No. 11-338786. It should be noted that in the present embodiment, the power source controlling TFT is formed as the p-channel type that has the structure identical to that of the current-controlling TFT. In the above-mentioned Japanese Patent Application. No. 11-338786, the erasing gate wiring is referred to as the erasing gate signal line. 
     A drain of the erasing TFT  1707  is connected to a gate of the current-controlling TFT  1704 , so that a gate voltage of the current-controlling TFT  1704  can be forceably changed. It is preferable to form the erasing TFT  1707  as a p-channel TFT that has the same structure as the switching TFT  1702  so that an OFF current can be reduced. 
       FIG. 17(A)  illustrates an example in which the current supply line  1706  is shared between the two pixels. Namely, the two pixels are formed to be symmetric to each other with respect to the current supply line  1706 . In this case, the number of the necessary current supply lines can be reduced, and thus the pixel section can be formed with higher precision. On the other hand,  FIG. 17(B)  illustrates an example in which the current supply line  1710  is arranged in parallel to the gate wiring  1703 , while the erasing gate wiring  1711  is arranged in parallel to the source wiring  1701 . 
     The structure as described in the present embodiment can be freely combined with any structures in Embodiments 1 through 7. 
     Embodiment 10 
     The light-emitting device in accordance with the present invention may have a structure in which several TFTs are provided in one pixel. Although Embodiments 8 and 9 have described examples in which the three TFTs are provided in one pixel, four through six TFTs may be provided. The present invention is not limited to the pixel structure of the light-emitting device, but can be embodied in other structures. 
     The structure as described in the present embodiment can be freely combined with any structures in Embodiments 1 through 7. 
     Embodiment 11 
     In the present embodiment, a film formation apparatus to be used for forming the EL layer and the cathode will be described with reference to  FIG. 18 . Specifically, in  FIG. 18 , reference numeral  1801  denotes a transportation chamber (A) in which a transportation chamber (A)  1802  is provided for realizing transportation of a substrate  1803 . The transportation chamber (A)  1801  includes a reduced-pressure atmosphere, and is blocked from other treatment chambers by means of gates. The substrate is passed from the transportation chamber (A)  1801  to the other treatment chambers by means of a transportation mechanism (A) when the corresponding gate is opened. 
     A cryopump is used to reduce the pressure in the transportation chamber (A)  1801 . An exhaust port  1804  is provided on a side surface of the transportation chamber (A)  1801 , and the exhaust pump is disposed below the exhaust port  1804 . Such a structure realizes an advantage in that a maintenance operation of the exhaust pump can be easily performed. 
     The respective treatment chambers will be described below. Since the transportation chamber (A)  1801  is provided with the reduced-pressure atmosphere, all of the treatment chambers that are directly coupled thereto are provided with an exhaust pump (not illustrated). As the exhaust pump, an oil rotary pump, a mechanical booster pump, a turbo molecular pump, or a cryopump can be used. 
     Reference numeral  1805  denotes a stock chamber in which a substrate is set (mounted). This chamber is also referred to as a load-lock chamber. The stock chamber  1805  is shielded from the transportation chamber (A)  1801  by a gate  1800   a , and a carrier (not illustrated) to which the substrate  1803  is set is disposed in this chamber  1805 . Furthermore, the stock chamber  1805  is provided with the above-mentioned exhaust pump as well as a purge line for introducing a nitrogen gas or an inert gas with high purity to the stock chamber  1805 . 
     In the present embodiment, the substrate  1803  is set onto the carrier with an element formation surface being faced-down. This is intended to facilitate the face-down orientation when films are formed by a vapor deposition method later. In the face-down orientation, films are formed on the substrate with the element formation surface of the substrate being facing downward. This orientation can suppress attachment of dust on the element formation surface of the substrate. 
     Reference numeral  1806  denotes a transportation chamber (B), that is coupled to the stock chamber  1805  via a gate  1800   b . The transportation chamber (B)  1806  is provided with a transportation mechanism (B)  1807 . Reference numeral  1808  denotes a baking chamber (bake chamber), that is coupled to the transportation chamber (B)  1806  via a gate  1800   c.    
     The baking chamber  1808  is provided with a mechanism for inverting the substrate orientation in the upside-down manner. Namely, the substrate that has been transported in the face-down orientation is once changed into a face-up orientation in the baking chamber  1808 . This is intended to allow a treatment in the subsequent spin coater chamber  1809  to be performed in the face-up orientation. After the treatment in the spin coater chamber  1809  is completed, the substrate is returned to the baking chamber  1808  to be again inverted upside-down into the face-down orientation, and then further returned to the stock chamber  1805 . 
     The spin coater chamber  1809  is coupled to the transportation chamber (B)  1806  via a gate  1800   d . The spin coater chamber  1809  is a film formation chamber for forming a film containing an EL material by applying a solution containing the EL material onto the substrate. In the spin coater chamber  1809 , a high-molecule type (polymer type) organic EL material is mainly formed. In this case, the film formation chamber is always filled with an inert gas such as nitrogen or argon. In particular, when a film is formed in the increased-pressure atmosphere at 1 to 5 atoms (preferably 1.5 to 3 atoms), it is possible to effectively prevent oxygen or water from entering the film formation chamber. 
     The EL material to be formed includes, not only that to be used as a light-emitting layer, but also that to be used as an electron injection layer or an electron transport layer. Any known high-molecule type organic EL material can be also used. Typical organic EL materials for serving as the light-emitting layer include PPV (polyparaphenylene vinylene) derivative, PVK (polyvinyl carbazole) derivative or polyfluorene derivative. These materials are also referred to as π-conjugated polymer. Furthermore, as the electron injection layer, PEDOT (polythiophene) or PAni (polyaniline) can be used. 
     Reference numeral  1810  denotes a treatment chamber for performing a surface treatment to an anode or a cathode to serve as the pixel electrode of the EL element (hereinafter, this chamber is referred to as the pre-treatment chamber). The pre-treatment chamber  1810  is shielded from the transportation chamber (A)  1801  by a gate  1800   e . The pre-treatment chamber can be modified in various manners based on the fabrication process of the EL element to be conducted. In the present embodiment, the pre-treatment chamber  1810  is configured to heat the pixel electrode at 100 to 120 C while irradiating the surface thereof with UV-light. Such a pre-treatment is effective when the anode surface of the EL element is to be processed. 
     Reference numeral  1811  denotes a vapor deposition chamber for forming the conductive film or the EL material by a vapor deposition method. The vapor deposition chamber  1811  is coupled to the transportation chamber (A)  1801  via a gate  1800   f . The vapor deposition chamber  1811  can be provided therein with a plurality of vapor deposition sources. In addition, it is also possible to cause the vapor deposition sources to be evaporated by resistive-heating or electron beams to form the intended film. 
     The conductive film to be formed in the vapor deposition chamber  1811  is provided as an electrode on the cathode side of the EL element. For this purpose, a metal having a relatively small work function, typically an element belonging to Group 1 or Group 2 in the periodic table (typically, lithium, magnesium, cesium, calcium, potassium, barium, sodium, or beryllium), or a metal having a work function which is close to those thereof can be deposited. Alternatively, aluminum, copper, or silver can be deposited to form a low-resistance conductive film. Furthermore, a conductive film made of a compound of indium oxide and tin oxide, or a conductive film made of a compound of indium oxide and zinc oxide, can be formed by the vapor deposition method as a transparent conductive film. 
     In the vapor deposition chamber  1811 , any known EL materials (in particular, low-molecule type organic EL materials) can be formed. Typical examples for the light-emitting layer include Alg 3  (tris-8-quinolinolato aluminum complex) or DSA (distyl allylene derivative), while typical examples for the charge injection layer include CuPc (copper phthalocyanine), LiF (lithium fluoride), or acacK (potassium acetylacetonate). Furthermore, typical examples for the charge transport layer include TPD (triphenylamine derivative) or NPD (anthracene derivative). 
     In addition, it is also possible to perform co-vapor deposition of the above-mentioned EL material and a fluorescent material (typically, coumarine 6, rubrene, Nile red, DCM, quinacridon, or the like). As the fluorescent material, any known materials may be used. Moreover, it is also possible to perform co-vapor deposition of the EL material and an element belonging to Group 1 or Group 2 in the periodic table, so that a portion of the light-emitting layer can exhibit a function as the charge transport layer or the charge injection layer. The term co-vapor deposition refers to a vapor deposition method in which a plurality of vapor deposition sources are simultaneously heated to mix different materials with each other during the film formation stage. 
     In either case, the vapor deposition chamber  1811  is shielded from the transportation chamber (A)  1801  by means of the gate  1800   f , and the film formation of the EL material or the conductive film can be performed in vacuum. The film formation is performed with the face-down orientation. 
     Reference numeral  1812  denotes an encapsulation chamber (also referred to as the sealing chamber or the grove box), that is coupled to the transportation chamber (A)  1801  via a gate  1800   g . In the encapsulation chamber  1812 , a process for finally sealing the EL element into a closed space is performed. This process is intended to provide the formed EL element with protection against oxygen or water. For this purpose, the EL element is mechanically sealed by means of the cover member. Alternatively, it is also possible to seal the EL element by means of a thermosetting resin or a UV-curable resin. 
     The cover member is adhered to the substrate with the EL element formed thereon by means of the thermosetting resin or the UV-curable resin. The resin is cured through a heat treatment or a UV irradiation process to form a closed space. 
     In the film formation apparatus shown in  FIG. 18 , a mechanism  1813  for UV irradiation is provided within the encapsulation chamber  1812  (such a mechanism is referred to as the UV irradiation mechanism  1813  hereinafter). Thus, the UV curable resin is allowed to be cured by UV light emitted from this UV irradiation mechanism  1813 . The inner pressure of the encapsulation chamber  1812  may be reduced by providing an exhaust pump, or increased while purging the inner space with a nitrogen gas or an inert gas having high purity. 
     A receiving chamber (path box)  1814  is coupled to the encapsulation chamber  1812 . The receiving chamber  1814  is provided with a transportation mechanism (C)  1815  for transporting to the receiving chamber  1814  the substrate for which the encapsulation of the EL element is completed in the encapsulation chamber  1812 . The inner pressure of the receiving chamber  1814  can be also reduced by providing an exhaust pump. The receiving chamber  1814  is intended to prevent the encapsulation chamber  1812  from being directly exposed to the ambient air, and the substrate is taken out from the receiving chamber  1814 . 
     As described in the above, the film formation apparatus shown in  FIG. 18  allows the EL element to be completely sealed into a closed space without being exposed to the ambient air, and accordingly, realizes fabrication of a light-emitting device having a high reliability. 
     Embodiment 12 
     The gate-side driving circuit as shown in  FIG. 1  and the source-side driving circuit as shown in  FIG. 3  can be applied, not only to the light-emitting device, but also to the liquid crystal display device. An external appearance of the liquid crystal display device in accordance with the present invention is illustrated in  FIG. 19(A) , while  FIG. 19(B)  illustrates the cross-sectional structure of its pixel section. 
     In  FIG. 19(A) , a pixel section  1901 , a gate-side driver circuit  1902  and a source-side driver circuit  1903  are formed on a substrate  1900 . In this case, the pixel section as shown in  FIG. 5  is used as the pixel section  1901 . Moreover, the gate-side driving circuit shown in  FIG. 1  is used as the gate-side driver circuit  1902 , while the source-side driving circuit shown in  FIG. 3  is used as the source-side driver circuit  1903 . 
     A gate wiring  1904  and a source wiring  1905  extend from the gate-side driver circuit  1902  and the source-side driver circuit  1903 , respectively, and a pixel TFT  1906  is formed at the crossing point of the gate wiring  1904  and the source wiring  1905 . To the pixel TFT  1906 , a retaining capacitance  1907  and a liquid crystal element  1908  are connected in parallel. Furthermore, connecting wirings  1910  and  1911  are formed to extend from an FPC  1909  to input terminals of the driver circuits. Reference numeral  1912  denotes a counter substrate. 
     In the pixel structure as shown in  FIG. 19(B) , the p-channel TFT  1913  forming the driver circuit and the p-channel TFT  1914  serving as the switching element may be fabricated in accordance with Embodiment 2 described previously. It should be noted that reference numeral  1915  denotes an orientation film,  1916  denotes a counter substrate,  1917  denotes a light shielding film,  1918  denotes a counter electrode,  1919  denotes an orientation film,  1920  denotes a sealing member,  1921  denotes a spacer made of a resin, and  1922  denotes liquid crystal. These components may be formed by any known method. Furthermore, the structure of the liquid crystal element is not limited to that described in the present embodiment. 
     Embodiment 13 
     Although the examples in which the pixel section and the driver circuit are formed of p-channel TFTs have been described in Embodiments 1 through 10 and 12, it is also possible to form the pixel section and the driver, only of n-channel TFTs. In this case, the driver circuits are required to be slightly modified such that, for example, the polarities of the power source lines are inverted in the driver circuits. 
     In such a case, the anode and the cathode are replaced with each other, so that the structure of the EL element is reversed. In other words, it is preferable to realize a structure in which the cathode is connected to a drain of the current-controlling TFT. It should be noted that in Embodiments 8 to 10, all TFTs other than the switching TFT and the current-controlling TFT, if they exist in the pixel, are formed as the n-channel TFT. 
     Embodiment 14 
     In the light-emitting device as described in Embodiment 1, it is preferable to provide a silicon nitride film or a silicon oxynitride film as the underlying film  502 , and to cover the switching TFT  601  and the current-controlling  602  with the passivation film  517  including a silicon nitride film or a silicon oxynitride film. 
     In such a structure, the switching TFT  601  and the current-controlling TFT  602  are sandwiched between the silicon nitride film or the silicon oxynitride film. Thus, water or movable ions can be effectively prevented from entering into the device from the external atmosphere. 
     Moreover, it is preferable to provide a silicon nitride film or a DLC (diamond-like carbon) film between the pixel electrode  523  and a planarization film  518  made of an organic resin formed on the passivation film  517 , and further provide the aforementioned silicon nitride film or DLC film on the cathode. 
     In such a structure, the EL element is sandwiched between the silicon nitride films or the DLC films. Thus, not only water or movable ions from the external atmosphere but also oxygen can be effectively prevented from entering into the device. Although the organic materials to be used in the light-emitting layer or the like in the EL element are otherwise likely to be easily oxidized thereby resulting in deterioration, the structure in the present embodiment can allow the reliability of the device to be significantly improved. 
     As described in the above, reliability of the entire light-emitting device can be improved by providing a measure for protecting the TFTs as well as a measure for protecting the EL element. 
     The structure as described in the present embodiment can be freely combined with any structures in Embodiments 1 through 10. 
     Embodiment 15 
     The display device formed by implementing the present invention can be used as a display portion of various kinds of electric equipments. For instance, when appreciating a television broadcast or the like, a display incorporating a 20 to 60 inch diagonal display device of the present invention in a casing may be used. Note that a personal computer display, a television broadcast receiving display, and a display for exhibiting all information such as a display for displaying announcements are included in the displays having the display device incorporated in a casing. 
     The following can be given as other electronic equipments of the present invention: a video camera; a digital camera; a goggle type display (head mounted display); a navigation system; an audio playback device (such as a car audio stereo or an audio component stereo); a notebook type personal computer; a game apparatus; a portable information terminal (such as a mobile computer, a portable telephone, a portable game machine, or an electronic book); and an image playback device equipped with a recording medium (specifically, device provided with a display portion which plays back images in a recording medium and displays the images). Specific examples of these electronic equipments are shown in  FIGS. 20 and 21 . 
       FIG. 20A  shows a display having a display device incorporated in a casing, and the display contains a casing  2001 , a support stand  2002 , a display portion  2003  and the like. The display device of the present invention can be used as the display portion  2003 . 
       FIG. 20B  shows a video camera, and contains a main body  2101 , a display portion  2102 , a sound input portion  2103 , operation switches  2104 , a battery  2105 , an image receiving portion  2106  and the like. The display device of the present invention can be used as the display portion  2102 . 
       FIG. 20C  is a portion (right side) of a head mounted EL display, and contains a main body  2201 , a signal cable  2202 , a head fixing band  2203 , a display portion  2204 , an optical system  2205 , a light-emitting device  2206  and the like. The present invention can be applied to the self-emitting device  2206 . 
       FIG. 20D  is an image playback device equipped with a recording medium (specifically, a DVD playback device), and contains a main body  2301 , a recording medium (such as a DVD)  2302 , operation switches  2303 , a display portion (a)  2304 , a display portion (b)  2305  and the like. The display portion (a)  2304  is mainly used for displaying image information. The display portion (b)  2305  is mainly used for displaying character information. The display device of the present invention can be used as the display portion (a)  2304  and as the display portion (b)  2305 . Note that the image playback device equipped with the recording medium includes devices such as household game machines. 
       FIG. 20E  shows a portable (mobile) computer, and contains a main body  2401 , a camera portion  2402 , an image receiving portion  2403 , operation switches  2404 , a display portion  2405  and the like. The display device of the present invention can be used as the display portion  2405 . 
       FIG. 20F  is a personal computer, and contains a main body  2501 , a casing  2502 , a display portion  2503 , a keyboard  2504  and the like. The display device of the present invention can be used as the display portion  2503 . 
       FIG. 21A  shows a rear type projector (projection TV) comprising a main body  2601 , an optical source  2602 , a liquid crystal display device  2603 , a polarization beam splitter  2604 , reflectors  2605  and  2606  and a screen  2607 . The present invention is applicable to the liquid crystal display device  2603 . 
       FIG. 21B  shows a front type projector comprising a main body  2701 , an optical source  2702 , a liquid crystal display device  2703 , an optical system  2704  and a screen  2705 . The present invention is applicable to the liquid crystal display device  2703 . 
     Note that, if the luminance further increases in the future, although not shown, then it will become possible to use the light-emitting device of the present invention in a front type or a rear type projector by expanding and projecting light containing output image information with a lens, an optical fiber or the like. 
     In addition, since the light-emitting device conserves power in the light-emitting portion, it is preferable to display information so as to make the light-emitting portion as small as possible. Consequently, when using the light-emitting device in a display portion mainly for character information, such as in a portable information terminal, in particular a portable telephone or an audio playback device, it is preferable to drive the light-emitting device so as to form character information by the light-emitting portions while non-light-emitting portions are set as background. 
       FIG. 21C  shows a portable telephone, and contains a main body  2801 , a sound output portion  2802 , a sound input portion  2803 , a display portion  2804 , operation switches  2805 , and an antenna  2806 . The light-emitting device of the present invention can be used as the display portion  2804 . Note that by displaying white color characters in a black color background, the display portion  2804  can suppress the power consumption of the portable telephone. Of course, it is possible to also use the liquid crystal display device of the present invention for the display portion  2804 . 
       FIG. 21D  shows an audio playback device, specifically a car audio stereo, and contains a main body  2901 , a display portion  2902 , and operation switches  2903  and  2904 . The light-emitting device of the present invention can be used as the display portion  2902 . Further, a car audio stereo is shown in this embodiment, but a portable type or a household audio playback device may also be used. Note that by displaying white color characters in a black color background, the display portion  2904  can suppress the power consumption. This is especially effective in a portable type audio playback device. Of course, it is possible to also use the liquid crystal display device of the present invention for the display portion  2804 . 
     Thus, the application range of the present invention is extremely wide, whereby it may be employed in electric equipments of all fields. Further, the electric equipments of this embodiment may employ the light-emitting device having any of the constitutions of Embodiments 1 through 14. 
     Thus, in accordance with the present invention, the display device can be fabricated with very small number of fabrication steps. Accordingly. a fabrication yield can be increased, while a fabrication cost can be reduced, thereby resulting in an inexpensive display device being fabricated. 
     Furthermore, since an inexpensive display device can be provided, various electrical apparatuses which employ the display device in their display section can be provided at a low price.