Abstract:
To provide a light emitting element having a top emission structure, which can be easily manufactured without considering an ionization potential of an electrode (particularly an electrode in contact with a substrate) and a manufacturing method therefor. A light emitting device having the top emission structure according to the present invention includes: a first electrode ( 101 ) formed of general-purpose metal (specifically, a wiring material such as Ti or Al) having a light-shielding property or reflectivity; a conductive polymer layer ( 102 ) formed by applying a conductive polymer material onto the first electrode ( 101 ); an electroluminescence film ( 103 ) formed in contact with the conductive polymer layer ( 102 ); and a light-transmissive second electrode ( 104 ) formed on the electroluminescence film  103 , in which the conductive polymer layer ( 102 ) is formed of materials including a redox polymer etc., while being free of problems regarding work function (as shown in FIG.  1 A).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a light emitting device with a light emitting element that emits fluorescent light or phosphorescent light upon application of electric field to a pair of electrodes of the element which sandwich a organic compound-containing layer (hereinafter, an electroluminescence film), and to a method of manufacturing the light emitting device. In the present invention, the term light emitting device includes an image display device using a light emitting element, a light emitting device and a light source (including illuminating device). Also, the following modules are included in the definition of the light emitting device: a module obtained by attaching to a light emitting device a connector such as an FPC (flexible printed circuit; terminal portion), a TAB (tape automated bonding) tape, or a TCP (tape carrier package); a module in which a printed wiring board is provided at an end of the TAB tape or the TCP; and a module in which an IC (integrated circuit) is directly mounted to a light emitting element by the COG (chip on glass) system. 
   2. Description of the Related Art 
   Light emitting elements, which employ materials as light emitting member and are characterized by their thinness and light-weight, fast response, and direct current low voltage driving, are expected to develop into next-generation flat panel displays. Among display devices, ones having light emitting elements arranged to form a matrix shape are considered to be particularly superior to the conventional liquid crystal display devices for their wide viewing angle and excellent visibility. 
   It is said that light emitting elements emit light through the following mechanism: a voltage is applied between a pair of electrodes that sandwich a light emitting layer comprising an organic material, electrons injected from the cathode and holes injected from the anode are re-combined at the luminescent center of the electroluminescence film to form molecular excitons, and the molecular excitons return to the base state while releasing energy to cause the light emitting element to emit light. Known as excitation states are singlet excitation and triplet excitation, and it is considered that luminescence can be conducted through either one of those excitation states. 
   Such light emitting devices having can be arranged to form a matrix can employ passive matrix driving (simple matrix light emitting devices), active matrix driving (active matrix light emitting devices), or other driving methods. However, if the pixel density is increased, active matrix light emitting devices in which each pixel (or each dot) has a switch are considered as advantageous because they can be driven with low voltage. 
   As an active matrix light emitting device, it is generally that a thin film transistor (hereinafter, TFT) is formed on an insulating film, then, a light emitting element that is connected electrically to TFT is formed via an interlayer insulating film that is formed on the TFT. In addition, the light emitting element is composed of an anode, a cathode, an electroluminescence film, and a cathode. 
   The mainstream structure of conventional active matrix light emitting device is a bottom emission structure that light generated in an electroluminescence film in a light emitting element composed of an anode connected electrically to TFT, an electroluminescence film, and a cathode in this order (the normally laminated form) is emitted through an anode to a TFT side (that is, a substrate side). Thus, the material for an anode in this case is a conductive material that transmits visible light and has a large ionization potential (which has the same value as that of a work function in case of metal) is used, typically, indium tin oxide, indium zinc oxide. 
   However, there is a problem in that an opening ratio is restricted depending on a position of a TFT, wirings, or the like when resolution is to be improved. In recent years, the top emission structure that emits light through a cathode side (an electrode side that is formed on an electroluminescence film and positioned opposite to a substrate) is brought to attention, for example, patent reference 1: Kokai 2001-43980. 
   However, in manufacturing a light emitting device of a top emission structure, in a case of using a transparent conductive film made of ITO or the like, which is appropriate as an anode material for a light emitting element when forming the normally laminated ones as described above, problems arise in that visible light is allowed to pass therethrough, which leads to light leak on a substrate side. Therefore, according to such a merit that an ionization potential is large and conductivity is achieved, when the transparent conductive film is used as an anode of the top emission element in the normally laminated form, there is a need to shield the light by forming a material into a film, through which the light cannot pass, below the transparent conductive film or the like, resulting in a complicated process. 
   Also, when using a metal film as the anode of the light emitting element in the normally laminated form, which is of the top emission structure, the light can be shielded. Considering materials having ionization potentials as high as ITO exhibits, however, noble metals such as gold and platinum only suffice for the above requirement, which causes problems in terms of costs. Also, there arises a problem in that the metal exhibits poor adhesion to materials for forming an electroluminescence film. 
   On the other hand, provided that an electrode electrically connected with a TFT serves as a cathode and the light emitting element (in the reversely laminated form) formed by sequentially laminating the electroluminescence film and the anode on the cathode is used to attain the top emission structure, the anode may be made of ITO. Thus, it becomes easy to take out the light from the top surface. In this case, however, the metal having the low ionization potential is used as the cathode, which causes a problem in that the adhesion to the materials for forming the electroluminescence film is insufficient to thereby make it difficult to inject electrons thereinto. 
   That is to say, regarding the light emitting element having the top emission structure in either normally or reversely laminated ones, the above-mentioned difficulty is involved due to the limitations of ionization potential of the electrode. 
   SUMMARY OF THE INVENTION 
   In view of the aforementioned problems, an object of the present invention is to provide a light emitting element having a top emission structure, which can be easily manufactured without taking into consideration an ionization potential of an electrode (in particular, an electrode in contact with a substrate) and a manufacturing method therefor. In addition, another object of the present invention is to provide a light emitting device that can be manufactured with high efficiency at low costs by using the light emitting element. 
   Accordingly, the inventors of the present invention have devised a light emitting device of a top emission structure as shown in  FIG. 1A , which includes: a first electrode  101  made of general-purpose metal having a light-shielding property or reflectivity (typically, a wiring material such as Ti or Al); a conductive polymer layer  102  formed by applying onto the first electrode  101  a conductive polymer material; an electroluminescence film  103  formed in contact with the conductive polymer layer  102 ; and a light-transmissive second electrode  104  formed on the electroluminescence film  103  while being free of problems regarding work function. 
   Note that the present invention is characterized by adopting as materials for forming the conductive polymer layer  102  a redox polymer (oxidation-reduction polymer) having a function of taking carriers out of the first electrode  101  brought into contact with the conductive polymer layer  102 ; or a polymer doped with a dopant (donor or acceptor) for increasing existence probability of the carriers. 
   Note that when using the redox polymer for the conductive polymer layer  102 , a reaction shown in  FIG. 1B  develops at an interface with the first electrode  101 . First, in the case where the first electrode  101  becomes the anode, the redox polymer functions as a reluctant and thus, serves to take holes out of the first electrode  101  (in other words, emit electrons) at the interface with the first electrode  101 . As a result, the redox polymer itself exists as the carrier (hole). On the other hand, in the case where the first electrode  101  becomes the cathode, the redox polymer functions as an oxidant and thus, serves to take the electrons out of the first electrode  101  at the interface with the first electrode  101 . As a result, the redox polymer itself exists as the carrier (electron). Consequently, when the first electrode  101  becomes either the anode or the cathode, the redox polymer serves to take the carriers out of the first electrode  101 , thereby enhancing a property of injecting the carriers from the first electrode  101 . 
   Also, in the case of using for the conductive polymer layer  102  the polymer doped with the dopant, when the first electrode  101  serves as the anode, the polymer doped with an acceptor molecule as the dopant is used, whereas when the first electrode  101  serves as the cathode, the polymer doped with a donor molecule as the dopant is used. 
     FIG. 1C  is a conceptual view for showing the case where the acceptor molecule is doped in the conductive polymer layer  102 . In this case, the first electrode (anode)  101  serves to take out the electrons from the acceptor level existing in the conductive polymer and at the same time, inject the holes in the conductive polymer layer to the acceptor level. Note that the holes thus injected move to an HOMO level in the conductive polymer layer and further to the HOMO level in the electroluminescence film  103 . Here, in this case, the movement from the first electrode  101  to the conductive polymer layer easily takes place since there is hardly involved energy difference. Furthermore, as to the movement of the injected holes from the acceptor level to the HOMO level in the electroluminescence film  103  as well, the energy difference is reduced as compared with the case of directly injecting the holes from the first electrode  101 . As a result, it is possible to increase the property of injecting the holes from the first electrode. 
     FIG. 1D  is a conceptual view for showing the case where the donor molecule is doped in the conductive polymer layer  102 . In this case, the electrons are injected from the first electrode (cathode)  101  to the donor level existing in the conductive polymer layer  102 . Note that the electrons thus injected move to an LUMO level in the conductive polymer layer  102  and further to the LUMO level in the electroluminescence film  103 . Here, in this case, the movement from the first electrode  101  to the conductive polymer layer easily takes place since there is hardly involved energy difference. Furthermore, as to the movement of the injected electrons from the LUMO level in the conductive polymer layer  102  to the LUMO level in the electroluminescence film  103  as well, the energy difference is reduced as compared with the case of directly injecting the electrons from the first electrode  101 . As a result, it is possible to increase the property of injecting the electrons from the first electrode. 
   Further, according to a structure of the present invention, there is provided a light emitting device including: 
   a first electrode; 
   a conductive polymer layer; 
   an electroluminescence film; and 
   a second electrode, characterized in that: 
   the conductive polymer layer is made of a redox polymer and formed between the first electrode and the electroluminescence film in contact therewith; and 
   the second electrode is formed of a transparent conductive film. 
   Also, in the above structure, the light emitting device is characterized in that: 
   when the first electrode is made to function as an anode, the hole transporting layer out of the hole transporting layer and the electron transporting layer, which both constitute the electroluminescence film, is formed in contact with the conductive polymer layer; and 
   the second electrode is formed of a material small in work function (specifically, the work function of 3.5 eV or less being preferably used). 
   Also, in the above structure, the light emitting device is characterized in that: 
   when the first electrode is made to function as a cathode, the electron transporting layer out of the hole transporting layer and the electron transporting layer, which both constitute the electroluminescence film, is formed in contact with the conductive polymer layer, and 
   the second electrode is formed of a material large in work function (specifically, the work function of 4.0 eV or more being preferably used). 
   Further, according to another structure of the present invention, there is provided a light emitting device including: 
   a first electrode; 
   a conductive polymer layer; 
   an electroluminescence film; and 
   a second electrode, characterized in that: 
   the first electrode functions as an anode; 
   the conductive polymer layer is made of a conductive polymer material doped with an acceptor material and formed between the first electrode and the electroluminescence film in contact therewith; and 
   the second electrode is formed of a transparent conductive film. 
   Also, in the above structure, the light emitting device is characterized in that: 
   when the first electrode is made to function as an anode, the first electrode is preferably formed of a material large in work function and the electron transporting layer out of the hole transporting layer and the electron transporting layer, which both constitute the electroluminescence film, is formed in contact with the conductive polymer layer, and 
   the second electrode is formed of a material small in work function. 
   Further, according to another structure of the present invention, there is provided a light emitting device including: 
   a first electrode; 
   a conductive polymer layer; 
   an electroluminescence film; and 
   a second electrode, characterized in that: 
   the first electrode functions as a cathode; 
   the conductive polymer layer is made of a conductive polymer material doped with a donor material and formed between the first electrode and the electroluminescence film in contact therewith; and 
   the second electrode is formed of a transparent conductive film. 
   Also, in the above structure, the light emitting device is characterized in that: 
   when the first electrode is made to function as a cathode, the first electrode is preferably formed of a material small in work function and the hole transporting layer out of the hole transporting layer and the electron transporting layer, which both constitute the electroluminescence film, is formed in contact with the conductive polymer layer, and 
   the second electrode is formed of a material large in work function. 
   In the above structures, the electroluminescence film can be made of known materials and formed by using low molecular weight organic or inorganic materials or polymeric organic or inorganic materials in the form of single layer or laminate in which the plural materials are used in combination. 
   With the above structure, the light emitting element can be formed without considering the work function of the electrode material formed in contact with the conductive polymer layer unlike the conventional cases. Thus, the selection range of the electrode materials can be widened. For example, when manufacturing the light emitting device having the light emitting element connected with the TFT, wirings for electrically connecting between the TFT and the light emitting element can double as the electrode of the light emitting element, so that the process can be simplified as compared with the case where the electrode and the wiring are manufactured in different steps. As a result, low costs can be realized along with improvement in yield. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIGS. 1A to 1D  are explanatory views of an element structure of a light emitting element according to the present invention; 
       FIGS. 2A and 2B  are explanatory views of an element structure of a light emitting element in which a first electrode serves as an anode; 
       FIGS. 3A and 3B  are explanatory views of an element structure of a light emitting element in which a first electrode serves as an anode; 
       FIGS. 4A and 4B  are explanatory views of an element structure of a light emitting element in which a first electrode serves as a cathode; 
       FIGS. 5A and 5B  are explanatory views of an element structure of a light emitting element in which a first electrode serves as a cathode; 
       FIG. 6  is a sectional view for illustrating a structure of a light emitting element connected with a TFT; 
       FIGS. 7A and 7B  are explanatory views of a light emitting device; and 
       FIGS. 8A to 8H  are explanatory views of electric appliances. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiment Mode 
   Hereinafter, Embodiment Mode of the present invention will be described. 
   Embodiment Mode 1 
   In Embodiment Mode 1, the case will be described with reference to  FIG. 2  in that a redox polymer layer  202  made from redox polymer is formed as a conductive polymer layer on a first electrode  201 , an electroluminescence film  203  on the redox polymer layer  202 , and a second electrode  204  is formed thereon. 
   The first electrode  201  is usually formed from an anode material having high work function since the first electrode  201  functions as an anode, however, since the first electrode  201  is formed in contact with the redox polymer layer  202  in this embodiment, materials having high work function are not necessary to be used. It is preferable that a metal material is used that give the first electrode  201  light blocking effects or light reflecting effects. Specifically, Al can be formed to have a thickness of approximately 120 nm as shown in  FIG. 2B . 
   The redox polymer layer  202  is formed on the first electrode  201 . In addition, emeraldine base polyaniline (hereinafter, EB-PAni) can be used for forming the redox polymer layer  202 . The redox polymer layer  202  is formed to have a thickness of 20 to 50 nm (preferably, 30 nm). In addition, another known redox polymer can be also used. 
   The electroluminescence film  203  is formed on the redox polymer layer  202 . The electric light emitting film  203  can be formed with one kind of material but also plural kinds of materials to have a lamination structure. 
   If the electroluminescence film  203  has a lamination structure, it may be formed with a hole injection layer, a hole transporting layer, a light emitting layer, a hole blocking layer, an electron transporting layer, an electron injection layer. At least one luminescent layer is necessary to be included thereinto. 
   In Embodiment Mode 1, the electroluminescence film  203  can be formed to compose a hole transporting layer  211  and an electron transporting layer  212  in a lamination structure. Specifically, the hole transporting layer  211  can be formed with 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereafter referred to as α-NPD) to have a thickness of 50 nm, which has hole transporting characteristics, the electron transporting layer  212  can be formed with tris(8-quinolinate) aluminum (hereafter referred to as Alq 3 ) to have a thickness of 50 nm, which has electron transporting characteristics. In this lamination structure, Alq 3  that forms the electron transporting layer  212  has a luminescent property. 
   Next, the second electrode  204  is formed on the electroluminescence film  203 . The second electrode  204  is formed with cathode materials having a low work function since it serves as a cathode. The cathode  204  may be a single layer structure formed with a one kind of material, but also lamination structure formed with plural kinds of materials. Embodiment Mode 1 shows that the cathode  204  is formed by laminating lithium fluoride (LiF) having 2 nm in thick and aluminum (Al) having 20 nm in thick with reference to  FIG. 2B . In addition, LiF can decrease the work function of the cathode  204 , and Al can increase the conductivity of the cathode  204 , so that the cathode has at the same time these plural functions. In addition, materials having a low work function can be freely combined for forming the cathode. 
   The second electrode  204  is necessary to have transmittance that is enough to pass visible light, since it should be transparent to the light generated in the electroluminescence film  203  and communicate the light output to the light emitting device. Specifically, it is preferable that second electrode  204  has a transmittance of more than 30% for visible light. 
   Embodiment Mode 2 
   In Embodiment Mode 2, the case in which a doping layer  302  that is polymer doped with dopant is formed as a conductive polymer molecular layer on a first electrode  301 , and a second electrode  304  is formed thereon as shown in  FIG. 3A  will be described. 
   The first electrode  301  serves as an anode in Embodiment Mode 2 as well as Embodiment Mode 1. Materials for forming the first electrode  301  are preferable to have a high work function (specifically, materials having at least 4.0 eV work function). 
   Next, a doping layer  302  is formed on the first electrode  301 . The doping layer  302  described in Embodiment Mode 2 is p-type, and made from polymer materials and dopant that is an acceptor molecule. Specifically, the doping layer  302  is made from polymer materials that polyethylenedioxythiophene (hereinafter, PEDOT) doped with polystyrene sulphonic acid (hereinafter, PSS) to have a thickness of 20 to 50 nm (preferably, 30 nm). Another known materials can also be used as polymer materials and dopant that is an acceptor molecule. 
   Next, an electroluminescence film  303  is formed on the doing layer  302 . The electroluminescence film  303  may be formed using one kind of material, and also plural kinds of materials to have a lamination structure. 
   If the electroluminescence film  303  has a lamination structure, it may be formed with a hole injection layer, a hole transporting layer, a light emitting layer, a hole blocking layer, an electron transporting layer, an electron injection layer. At least one luminescent layer is necessary to be included thereinto. 
   In Embodiment Mode 2, the electroluminescence film  303  is formed to compose a hole transporting layer  311  and an electron transporting layer  312  in a lamination structure as shown in  FIG. 3B . Specifically, a hole transporting layer  311  is made from α-NPD to have a thickness of 50 nm, and an electron transporting layer  312  is made from Alq 3  to have a thickness of 50 nm. In this lamination structure, Alq 3  that forms the electron transporting layer  312  is luminescent. 
   Then, a second electrode  304  is formed on an electroluminescence film  303 . Serving as a cathode, the second electrode  304  is made from cathode materials with a low work function. In addition, the cathode  304  can be formed with one kind of material but also plural kinds of materials to have a lamination structure. In Embodiment Mode 2, the case in which the cathode  304  is formed by stacking LiF 2 nm in thick, and Al in 20 nm in thick will be described as shown in  FIG. 3B . Thereby, the electrode has plural functions at the same time that can reduce work function of the cathode  304  by using LiF, and increase conductivity thereof by using Al. The cathode is made from known materials having a low work function that are freely combined. 
   The second electrode  304  is necessary to have transmittance that is enough to pass visible light, since it should be transparent to the light generated in the electroluminescence film  303  and communicate the light output to the light emitting device. Specifically, it is preferable that second electrode  304  has a transmittance of more than 30% for visible light. 
   Embodiment Mode 3 
   In Embodiment Mode 3, the case in which a redox polymer layer  402  made from redox polymer is formed as a conductive polymer layer on a first electrode  401 , an electroluminescence film  403  is formed thereon, and a second electrode  404  is formed thereon as shown in  FIG. 4A  will be described. 
   Serving as a cathode, the first electrode  401  is generally made from cathode materials with a low work function. However, since the first electrode  401  is formed in contact with the redox polymer layer  402 , it is not necessary to use materials with a low work function. In the present invention, it is preferable: that a metal material is used that give the first electrode  401  light blocking effect or light reflective effects. Specifically, Al can be formed as the first electrode  401  to have approximately a 120 nm thickness as shown in  FIG. 4B . 
   The redox polymer layer  402  is formed on the first electrode  401 . Further, the redox polymer layer  402  is made from EB-PAni to have a thickness of 25 to 50 nm (preferably, 30 nm). In addition, known redox polymer can be used. 
   Then, the electroluminescence film  403  is formed on the redox polymer  402 . The electroluminescence film  403  may be formed using one kind of material, and also plural kinds of materials to have a lamination structure. 
   Further, if the electroluminescence film  403  has a lamination structure, it may be formed with a hole injection layer, a hole transporting layer, a light emitting layer, a hole blocking layer, an electron transporting layer, an electron injection layer. At least one luminescent layer is necessary to be included thereinto. 
   In Embodiment Mode 3, as shown in  FIG. 4B , an electron transporting layer  411 , a hole transporting layer  412 , and a hole injecting layer  413  are laminated to form an electroluminescence film  403 . Specifically, the electron transporting layer  411  is formed of Alq 3  as a material having an electron transporting property with a thickness of 50 nm. The hole transporting layer  412  is formed of α-NPD as a material having a hole transporting property with a thickness of 30 nm. The hole injecting layer  413  is formed of Cu-Pc as a material having a hole injecting property with a thickness of 20 nm. Those layers constitute the laminate structure. Note that in the case of the laminate structure, Alq 3  used for forming the electron transporting layer  411  exhibits the light emitting property. 
   Following this, a second electrode  404  is formed on the electroluminescence film  403 . Note that the second electrode  404  functions as the anode and thus, is formed of an anode material having the large work function. Here, the second electrode  404  may have either a single-layer structure composed or a single material or a laminate structure composed of plural materials. In Embodiment Mode 3, as shown in  FIG. 4B , Au is deposited into a film having a thickness of 20 nm to obtain the second electrode. As an anode material for the second electrode  404 , known materials having high work function can be freely combined. 
   The second electrode  404  is necessary to have transmittance that is enough to pass visible light, since it should be transparent to the light generated in the electroluminescence film  403  and communicate the light output to the light emitting device. Specifically, it is preferable that second electrode  304  has a transmittance of more than 30% for visible light. 
   Embodiment Mode 4 
   In Embodiment Mode 4, as shown in  FIG. 5A , a description will be given of a case where a doping layer  502  obtained by doping a dopant into a polymer as a conductive polymer layer is formed on a first electrode  501  and a second electrode  504  is formed thereon. 
   Similarly to Embodiment Mode 3, in Embodiment Mode 4, the first electrode  501  functions as a cathode. Here, the first electrode  501  is preferably formed of materials having a small work function (specifically, materials having the work function of 3.5 eV or less). 
   Next, the doping layer  502  is formed on the first electrode  501 . Note that the doping layer  502  of Embodiment Mode 4 is of n-type conductivity. The doping layer is formed of a polymer material and a dopant as a donor molecule. To be specific, EB-PAni serving as a redox polymer as well as the polymer material, which is doped with tetrathiafluvalene (hereinafter, referred to as TTF) can be used therefor. It is formed with a thickness of 20 to 50 nm (preferably, 30 nm). Note that, as the polymer material and the dopant as the donor molecule, other known materials can be adopted. 
   Next, the electroluminescence film  503  is formed on the doping layer  502 . The electroluminescence film  503  may be formed of a single material but may have a laminate structure composed of plural materials. 
   Further, in the case of adopting the laminate structure, layers having various functions, such as a hole injecting layer, a hole transporting layer, a light emitting layer, a hole blocking layer (blocking layer), an electron transporting layer, and an electron injecting layer, are combined. The laminate structure may include at least the layer having the light emitting property. 
   In Embodiment Mode 4, as shown in  FIG. 5B , an electron transporting layer  511 , a hole transporting layer  512 , and a hole injecting layer  513  are laminated to form an electroluminescence film  503 . Specifically, the electron transporting layer  511  is formed of Alq 3  as a material having an electron transporting property with a thickness of 50 nm. The hole transporting layer  512  is formed of α-NPD as a material having a hole transporting property with a thickness of 30 nm. The hole injecting layer  513  is formed of Cu-Pc as a material having a hole injecting property with a thickness of 20 nm. Those layers constitute the laminate structure. Note that in the case of the laminate structure, Alq 3  used for forming the electron transporting layer  511  exhibits, the light emitting property. 
   Following this, a second electrode  504  is formed on the electroluminescence film  503 . Note that the second electrode  504  functions as the anode and thus, is formed of an anode material having the large work function. Here, the second electrode  504  may have either a single-layer structure composed of a single material or a laminate structure composed of plural materials. In Embodiment Mode 4, as shown in  FIG. 5B , Au is deposited into a film having a thickness of 20 nm to obtain the second electrode. 
   Also, the second electrode  504  to be formed in this case is needed to allow the light emitted from the electroluminescence film  503  to pass therethrough to the outside and thus, it should ensure transmissivity high enough for visible light to pass therethrough. To be specific, it is preferable that the transmissivity of the visible light be equal to or more than 30%. 
   Embodiments 
   Hereinafter, embodiments of the present invention will be described. 
   Embodiment 1 
   In this embodiment, an example of forming a light emitting panel in which TFT on a substrate having an insulating surface is connected to a light emitting element is shown in  FIG. 6 . A cross-sectional view of one TFT that is connected to a light emitting element in a pixel portion is shown in this embodiment. 
   A semiconductor layer is formed on a substrate  601  having an insulating surface. In addition, although not shown here, a base insulating film made from lamination layer including an oxide silicon layer, a nitride silicon layer, or an oxynitride silicon layer can be formed on the substrate  601 . 
   Subsequently, a semiconductor layer is formed as follows: an amorphous semiconductor film is formed by known means (a sputtering, an LPCVD, a plasma CVD, or the like), then, the film is crystallized by a known crystallization method (a laser crystallization method, a thermal crystallization method or a thermal crystallization method using a catalyst such as nickel), and then, the crystalline semiconductor film is patterned into a desired form. This semiconductor layer is formed in a thickness of 25 to 80 nm (preferably 30 to 60 nm). The material of the crystalline semiconductor film, although not limited in material, is preferably formed of silicon or a silicon-germanium alloy. 
   In the case of forming a crystalline semiconductor film by a laser crystallizing process, it is possible to use an excimer laser of a pulse-oscillation or continuous-oscillation type, a YAG laser, or an YVO 4  laser. In the case of using such laser, preferably used is a method that the laser light emitted from a laser oscillator is condensed by an optical system into a linear form to be irradiated onto the semiconductor film. The condition of crystallization is to be appropriately selected by those who implement the invention. In the case of using an excimer laser, pulse oscillation frequency is 30 Hz and laser energy density is 100 to 400 mJ/cm 2  (typically 200 to 300 mJ/cm 2 ). Meanwhile, in the case of using a YAG laser, preferably its second harmonic is used and pulse oscillation frequency is 1 to 10 kHz and laser energy density is 300 to 600 mJ/cm 2  (typically 350 to 500 mJ/cm 2 ). The laser light focused linear to a width of 100 to 1000 μm, e.g. 400 μm, is irradiated throughout the substrate entirety, whereupon the overlap ratio of linear laser beam may be taken 80 to 98%. 
   Then, the surface of the semiconductor layer is cleaned by an etchant containing a hydrogen fluoride, to form a gate insulating film  605  covering the semiconductor layer. The gate insulating film  605  is formed by an insulating film containing silicon having a thickness of 40 to 150 nm by the use of plasma CVD or sputtering. In this embodiment, a silicon oxide nitride film is formed (composition ratio: Si=32%, O=59%, N=7% and H=2%) to have a thickness of 115 nm by plasma CVD. Of course, the gate insulating film  605  is not limited to a silicon oxide nitride film but may be made another insulating films in a single layer or a laminated layer. 
   After cleaning the surface of the gate insulating film  605 , a gate electrode  606  is formed. Then, a p-type providing impurity element (such as B), herein, adequate amounts of boron is added to the semiconductor to form a source region  603  and a drain region  604 . After the addition of the impurity element, heating process, intense light radiation or laser irradiation is made in order to activate the impurity element. Simultaneously with activation, restoration is possible from the plasma damage to the gate insulating film or from the plasma damage at the interface between the gate insulating film and the semiconductor layer. Particularly, it is extremely effective to irradiate the second harmonic of a YAG laser at a main or back surface thereby activating the impurity element in an atmosphere at room temperature to 300° C. YAG laser is preferable activating means since it requires a few maintenances. 
   An insulating film  608  made form an organic material or an inorganic material is formed. Here, a case where a protection film  609  made from a silicon nitride film is formed after the interlayer insulating film  608  is formed using nonphotosensitive organic resin film will be described. 
   Then, contact holes that reach a source region  603  and a drain region  604  are formed. And then, a wiring  607  that is connected to the source region  603  and the drain region  604  are formed to complete a TFT  622  (a p-channel TFT). The TFT  622  will serve as a TFT which controls current which is supplied to a light emitting element  616 . In this embodiment, the wiring that is connected to the drain region  604  also serves as a first electrode  611  of a light emitting element  616  that will be formed in the next. 
   The first electrode  611  serves as an anode or a cathode of the light emitting element  616 . Next, an insulating layer (referred to as a bank, a barrier, or the like)  612  is formed to cover both side edges of the first electrode  611 . The insulating layer  612  is made from photosensitive organic resin. Then, a conductive polymer layer  613  is formed on the first electrode  611 , an electroluminescence film  614  is formed thereon, further, a second electrode  615  is formed thereon to complete the light emitting element  616 . The second electrode  615  will serve as a cathode or an anode of the light emitting element, and polarized different from the first electrode  611 . 
   In the present invention, materials for forming the first electrode  611  are conductive, since the first electrode is formed in contact with the conductive polymer layer  613 . Further, the materials are required to have a light blocking effect or a reflectiveness for increasing light emitting efficiency. It is preferable in case that the first electrode serves as an anode that the materials have high work function (specifically, at least 4.0 eV work function), and in case that the first electrode serves as a cathode that the materials have low work function (specifically, at most 3.5 eV work function). 
   Specifically, materials having above-mentioned properties as the first electrode  611  include an element selected from aluminum (Al), tantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), nickel (Ni), copper (Cu), titanium (Ti), chrome (Cr), silver (Ag), or alloy which includes these elements. Materials having high work function include nitride or carbide of elements belonging to the fourth group, the fifth group, or sixth group in the periodic table of the elements such as titanium nitride (TiN), tantalum nitride (TaN), zirconium nitride (ZrN), molybdenum nitride (MoN), chrome nitride (CrN), tungsten nitride (WN), titanium carbide (TiC), tantalum carbide (TaC), zirconium carbide (ZrC), molybdenum carbide (MoC), or the like. Materials having low work function include alkali metals or metal materials a part of which include alkali metals. For example, aluminum-lithium alloy (Al:Li), magnesium-silver alloy (Mg:Ag) and a lamination of Al and LiF can be used. 
   In addition, in case where a redox polymer layer is formed as the conductive polymer layer  613  as shown in Embodiment Mode 1 and Embodiment Mode 3, EB-PAni or another known redox polymer (oxidation-reduction polymeric materials) are used as the conductive polymer layer  613 . In case where a doping layer is formed as the conductive polymer layer  613  as shown in Embodiment Mode 2 and Embodiment Mode 4, PEDOT doped with PSS (p-doped polymer) or TFT doped with EB-PAni (n-doped polymer) are used as the conductive polymer layer  613 . A solution for forming the conductive polymer layer  613  in which various kinds of materials are dissolved in a solvent such as water, n-methylpyrrolidone (NMP), dimethylsulfoxide (DMSO), or the like is deposited by coating or spin coating. 
   Known low molecular electroluminescence materials or high molecular electroluminescence materials are used as an electroluminescence film  614 . In this embodiment, a case where the electroluminescence film  614  is deposited using low molecular electroluminescence material by evaporation will be described. The electroluminescence film  614  is formed to have a single structure made from one kind of material, and also a lamination structure made from plural materials. The lamination structure may include, but an organic compound layer in the present invention is not limited to, a hole transporting layer made from hole transporting materials, a light emitting layer made from luminous materials, and an electron transporting layer made from electron transporting materials. The lamination structure that includes hole injecting layer made from hole injecting materials and a hole blocking layer made from hole blocking material can be formed as an organic compound layer. Hereinafter, preferable materials are described, but materials for forming the electroluminescence film  614  of the present invention is not limited thereto. 
   As the hole transporting material used for forming the hole transporting layer, an aromatic amine-based (that is, the one having a benzene ring-nitrogen bond therein) compound is preferred. Widely used materials include, for example, in addition to the above-mentioned TPD, derivatives thereof such as 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereafter, referred to as “α-NPD”). Also used are star burst aromatic amine compounds, including: 4,4′,4″-tris(N,N-biphenyl-amino)-triphenyl amine (hereafter, referred to as “TDATA”); and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenyl amine (hereafter, referred to as “MTDATA”). 
   Specific examples of the light emitting material used for forming the light emitting layer include metal complexes such as Alq 3 , tris(8-quinolinolate) aluminum (hereafter, referred to as Alq 3 ), tris(4-methyl-8-qiuinolinolate) aluminium (hereafter, referred to as Almq 3 ), and bis (10-hydroxybenzo[h]-quinolinate) beryllium (hereafter, referred to as BeBq 2 ), and bis (2-methyl-8-quinolinolate)-(4-hydroxy-biphenylyl)-aluminum (hereafter, referred to as BAlq). The examples also include metal complexes including such as bis [2-(2-hydroxyphenyl)-benzooxazolate]zinc (hereafter, referred to as Zn(BOX) 2 ) and bis [2-(2-hydroxyphenyl)-benzothiazolate]zinc (hereafter, referred to as Zn(BTZ) 2 ). Also, fluorescent dyes thereof may be used. Triplet light emission materials may also be used and main examples thereof include complexes with platinum or iridium as central metal. Known triplet light emission materials include tris(2-phenylpyridine) iridium (hereafter, referred to as Ir(ppy) 3 ), 2,3,7,8,12,13,17,18-octaethyl-21H, and 23H-porphyrin-platinum (hereafter, referred to as PtOEP). 
   Metal complexes are often used as the electron transporting material. Preferred examples thereof include: metal complexes having a quinoline skeleton or benzoquinoline skeleton, such as the aforementioned Alq 3 , Almq 3 , BeBq 2 ; and mixed ligand complexes such as BAlq. Other examples include metal complexes having oxazole-based and thiazole-based ligands such as Zn(BOX) 2  and Zn(BTZ) z . Other materials that are capable of transporting electrons than the metal complexes are: oxadiazole derivatives such as 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereafter referred to as PBD), and 1,3-bis [5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene (hereafter, referred to as OXD-7); triazole derivatives such as 3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (hereafter, referred to as TAZ) and 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (hereafter, referred to as p-EtTAZ); and phenanthroline derivatives such as bathophenanthroline (hereafter, referred to as BPhen) and bathocuproin (hereafter, referred to as BCP). 
   Above-mentioned materials are stacked on the electrode that serves as an anode in such order that a hole injection layer, a hole transporting layer, a light emitting layer, a hole blocking layer, and an electron transporting layer. All these layers are not necessary to be deposited, a part of which can be combined appropriately. With respect to a light emitting layer, when another layer have a light emitting property, it is not necessary to be included in the lamination structure. 
   The second electrode  615  should be formed with translucent materials in order to output the light generated in the electroluminescence film  614  in the present invention. Specifically, the second electrode is preferable to have 30% and more transmittance for visible light by being formed with a transparent conductive film, or a thin conductive film. In addition, the second electrode  615  serves as an anode or cathode that is different from polarity of the first electrode  611 . 
   When the second electrode  615  serves as a cathode, low work function alkali metal or metal materials (specifically, at most 3.5 eV work function) a part of which includes alkali metal, which is described as materials for the first electrode  611 , can be used in a thin film of approximately 10 to 20 nm in thick for the second electrode  615 . For example, aluminum-lithium alloy (Al:Li), magnesium-silver (Mg:Ag) and a lamination of Al and LiF can be used. 
   On the other hand, when the second electrode  615  serves as an anode, high work function (specifically, at least 4.0 eV work function) transparent conductive film can be used for the second electrode  615 . For example, indium tin oxide (ITO) film, a transparent film which an indium oxide is mixed with 2 to 20% zinc oxide (ZnO), and IZO (indium zinc oxide) can be used. In addition, the second electrode  615  is formed by evaporation since it is formed on the electroluminescence film  614 . 
   Therefore, a light emitting panel having a light emitting element connected to a TFT on a substrate is formed. 
   Embodiment 2 
   Further, a whole appearance view of an active matrix type light-emitting device in which the light emitting panel is included described in Embodiment 1 will be described with reference to  FIG. 7 . Further,  FIG. 7A  is a top view showing the light emitting apparatus and  FIG. 7B  is a sectional view constituted by cutting  FIG. 7A  by a line A-A′. Reference numeral  701  indicated by a dotted line designates a source side driving circuit, reference numeral  702  designates a pixel portion, and reference numeral  703  designates a gate side driving circuit. Further, reference numeral  704  designates a seal substrate, reference numeral  705  designates a sealing material and an inner side surrounded by the sealing material  705  constitutes a space or resin (sealing materials)  707 . 
   Further, reference numeral  708  designates a connection wiring for transmitting signals inputted to the source side driving circuit  701  and the gate signal line driving circuit  703  for receiving a video signal or a clock signal from FPC (flexible printed circuit)  709  for constituting an external input terminal. Further, although only FPC is illustrated here, the FPC may be attached with a printed wiring board (PWB). The light emitting apparatus in the specification includes not only a main body of the light emitting apparatus but also a state in which FPC or PWB is attached thereto. 
   Next, a sectional structure will be explained in reference to  FIG. 7B . Driver circuits and the pixel portion are formed over a substrate  710  and here, the source side driving circuit  701  as the driver circuit and the pixel portion  702  are shown. 
   Further, the source signal line driving circuit  701  is formed with a CMOS circuit combined with an n-channel type TFT  723  and a p-channel type TFT  724 . Further, TFT for forming the driver circuit may be formed by a known CMOS circuit, PMOS circuit or NMOS circuit. Further, although according to this embodiment, a driver integrated type formed with the driver circuits over the substrate is shown, the driver integrated type is not necessarily be needed and the driver circuits can be formed not over the substrate but at outside thereof. 
   Further, the pixel portion  702  is formed by a plurality of pixels each including a switching TFT  711 , a current controlling TFT  712 , and a first electrode (anode)  713  electrically connected to a drain of the current controlling TFT  712 . An insulating layer  714  is formed to cover both side edges of the first electrode (anode)  713 . 
   A conductive polymer layer  715  of the present invention, an electroluminescence film  716 , and a second electrode (cathode)  717  are respectively formed on the first electrode  713 . In addition, concerning a specific structure may be referred to Embodiment 1. 
   The second electrode  717  functions also as a wiring common to all the pixels and electrically connected to FPC  709  via the connection wiring  708 . 
   Further, in order to seal the light emitting element  718  formed over the substrate  710 , the seal substrate  704  is pasted by the sealing material  705 . Further, a spacer comprising a resin film may be provided for ensuring an interval between the seal substrate  704  and the light emitting element  718 . Further, the space  707  on the inner side of the sealing material  705  is just a space. Further, it is preferable to use epoxy species resin for the sealing material  705 . Further, it is preferable that the sealing material  705  is a material for permeating moisture or oxygen as less as possible. 
   Further, according to this embodiment, as a material for constituting the seal substrate  704 , other than glass substrate or quartz substrate, a plastic substrate comprising FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), Mylar, polyester or acrylic resin can be used. Further, it is possible to adhere the seal substrate  704  by using the sealing material  705  and thereafter seal to cover a side face (exposed face) by a sealing material. 
   By sealing the light emitting element  718  in the space  707  as described above, the light emitting element can completely be blocked from outside and a substance for expediting to deteriorate the organic compound layer such as moisture or oxygen can be prevented from invading from outside. Therefore, the highly reliable light-emitting device can be provided. 
   Further, this embodiment can freely be combined with Embodiment Mode 1 to 4 and Embodiment 1. 
   Embodiment 3 
   The light emitting device fabricated in accordance with the present invention is of the self-emission type, and thus exhibits more excellent recognizability of the displayed image in a light place as compared to the liquid crystal display device. Furthermore, the light emitting device has a wider viewing angle. Accordingly, various electronic apparatuses can be completed by using the light emitting device of the present invention. 
   Such electronic apparatuses manufactured by the present invention include a video camera, a digital camera, a goggles-type display (head mount display), a navigation system, a sound reproduction device (a car audio equipment, an audio set and the like), a laptop personal computer, a game machine, a portable information terminal (a mobile computer, a cellular phone, a portable game machine, an electronic book, or the like), an image reproduction apparatus including a recording medium (more specifically, an apparatus which can reproduce a recording medium such as a digital versatile disc (DVD) and so forth, and includes a display for displaying the reproduced image), or the like. In particular, in the case of the portable information terminal, use of the light-emitting device with a light-emitting element is preferable, since the portable information terminal that is likely to be viewed from a tilted direction is often required to have a wide viewing angle.  FIGS. 8A to 8H  shows various specific examples of such electronic apparatus. 
     FIG. 8A  illustrates a display device which includes a frame  2001 , a support table  2002 , a display portion  2003 , a speaker portion  2004 , a video input terminal  2005  or the like. The light-emitting device manufactured by the present invention can be used for the display portion  2003 . The light emitting device is of the self-emission type and therefore requires no backlight. Thus, the display portion thereof can have a thickness thinner than that of the liquid crystal display device. The display device is including all of the display devices for displaying information, such as a personal computer, a receiver of TV broadcasting and an advertising display. 
     FIG. 8B  illustrates a digital still camera which includes a main body  2101 , a display portion  2102 , an image receiving portion  2103 , an operation key  2104 , an external connection port  2105 , a shutter  2106 , or the like. The light emitting device manufactured by the present invention can be used for the display portion  2102 . 
     FIG. 8C  illustrates a laptop type (notebook type) personal computer which includes a main body  2201 , a casing  2202 , a display portion  2203 , a keyboard  2204 , an external connection port  2205 , a pointing mouse  2206 , or the like. The light emitting device manufactured by the present invention can be used to the display portion  2203 . 
     FIG. 8D  illustrates a mobile computer which includes a main body  2301 , a display portion  2302 , a switch  2303 , an operation key  2304 , an infrared port  2305 , or the like. The light emitting device manufactured by the present invention can be used to the display portion  2302 . 
     FIG. 8E  illustrates an image reproduction apparatus including a recording medium (more specifically, a DVD reproduction apparatus), which includes a main body  2401 , a casing  2402 , a display portion A  2403 , another display portion B  2404 , a recording medium (DVD or the like) reading portion  2405 , an operation key  2406 , a speaker portion  2407  or the like. The display portion A  2403  is used mainly for displaying image information, while the display portion B  2404  is used mainly for displaying character information. The light emitting device manufactured by the present invention can be used to the display potion A  2403  and the display portion B  2404 . Note that the image reproduction apparatus including a recording medium further includes a domestic game machine or the like. 
     FIG. 8F  illustrates a goggle type display (head mounted display) which includes a main body  2501 , a display portion  2502 , an arm portion  2503 . The light emitting device manufactured by the present invention can be used to the display portion  2502 . 
     FIG. 8G  illustrates a video camera which includes a main body  2601 , a display portion  2602 , an casing  2603 , an external connecting port  2604 , a remote control receiving portion  2605 , an image receiving portion  2606 , a battery  2607 , a sound input portion  2608 , an operation key  2609 , an eyepiece potion  2610  or the like. The light emitting device manufactured by the present invention can be used to the display portion  2602 . 
     FIG. 8H  illustrates a cellular phone which includes a main body  2701 , a casing  2702 , a display portion  2703 , a sound input portion  2704 , a sound output portion  2705 , an operation key  2706 , an external connecting port  2707 , an antenna  2708 , or the like. The light-emitting device manufactured by the present invention can be used to the display portion  2703 . Note that the display portion  2703  can reduce power consumption of the cellular phone by displaying white-colored characters on a black-colored background. 
   When the brighter luminance of the organic material becomes available in the future, the light-emitting device manufactured by the present invention will be applicable to a front-type or rear-type projector in which light including output image information is enlarged by means of lenses or the like to be projected. 
   The aforementioned electronic apparatuses are more likely to be used for display information distributed through a telecommunication path such as Internet, a CATV (cable television system), and in particular likely to display moving image information. The light-emitting device is suitable for displaying moving images since the organic material can exhibit a high response speed. 
   A portion of the light-emitting device that is emitting light consumes power so it is desirable to display information in such a manner that the light-emitting portion therein becomes as small as possible. Accordingly, when the light-emitting device is applied to a display portion which mainly displays character information, e.g., a display portion of a portable information terminal, and more particular, a cellular phone or a sound reproduction device, it is desirable to drive the light-emitting device so that the character information is formed by a light-emitting portion while a non-emission portion corresponds to the background. 
   As set forth above, the light-emitting device formed by using the present invention can be applied variously to a wide range of electronic apparatuses in all fields. The electronic apparatuses in this embodiment can be completed by using a light-emitting device shown in Embodiment Mode 1 to 4 and Embodiments 1 and 2. 
   According as the present invention is embodied, the active matrix light emitting device can be manufactured with the top emission structure, which is free of problems concerning the opening ratio. Also, the conductive polymer layer is formed in contact with the first electrode of the light emitting element included in the light emitting device, which makes it possible to enhance the property of injecting the carrier from the first electrode. As a result, the device can be manufactured without particularly considering the ionization potential upon the selection of the materials for the first electrode. Consequently, the selection range of materials can be widened, whereby the highly efficient light emitting device can be manufactured at low costs.