Method of fabricating and structure of an active matrix light-emitting display device

Abstract

The invention concerns active matrix light-emitting display devices and a method of their fabrication wherein the problem of chemically unstable cathode electrode layers is solved, simultaneously offering a considerably higher aperture ratio and brightness with rather low driving voltages. These advantages are achieved by separate manufacture of a first substrate bearing TFT elements of which the source and drain regions are at first covered by a non-conductive passivation layer followed by a deposition of a chemically stable cathode material layer and deposition of an appropriately selected EL material layer. The anode side substrate is independently prepared by at first depositing an anode layer followed by application of an EL layer, then the two independently manufactured layered substrates are alligned face-to-face and are combined to a unified structure under application of heat and pressure, the temperature being selected to have the glass transition temperature of said EL layers in case of polymeric EL material or to have the phase transition temperature for solid to liquid crystalline state or isotropic state in case of crystalline EL material.

1 . A method for fabricating an active matrix display device formed of a plurality of pixels and comprising: 
 at least one thin film transistor element (TFT element) ( 2 ) is deposited on a first substrate ( 1 ) for each pixel,    at least the source region (S) and the channel region (C) of said at least one TFT element ( 2 ) for each pixel are covered by a non-conductive passivation layer ( 3 ) such as to leave parts or all of the drain region (D) uncovered,    a cathode material layer structured into a plurality of pixel electrode regions ( 5   a ,  5   b , . . . ) is deposited so as to cover at least a substantial part of each of said TFT elements,    a first active organic and/or polymeric electroluminescent material layer (EL layer) ( 6 ) is applied to cover at least said pixel electrode regions ( 5   a ,  5   b , . . . ),    a second substrate ( 8 ) is separately prepared by depositing an anode layer ( 7   a ,  7   b , . . . ) on one surface of said second substrate and subsequently coating said anode layer with a second active organic and/or polymeric EL material layer ( 6 ′),    said two substrates thus prepared and coated are laminated together, said first and second EL material layers ( 6 ,  6 ′) being face-to-face and appropriately alligned, under application of heat and/or pressure for a predetermined time, the temperature being selected to have a glass transition temperature of at least one of said EL layers ( 6 ,  6 ′) in case of a polymeric EL material or to have the phase transition temperature for solid to liquid crystalline state or isotropic state in case of crystalline EL material.    
     
     
         2 . The method of  claim 1 , characterized in that a flattening layer ( 4 ) is deposited before or after deposition of said cathod material layer ( 5 ).  
     
     
         3 . The method of  claim 1  or  2 , characterized in that after the process of lamination the display device is encapsulated.  
     
     
         4 . The method of  claim 1  or  2  wherein said first substrate ( 1 ) is non-transparent, characterized in that a stable metal which is resistant to photolithographic processing is selected for said cathode material layer ( 5 ).  
     
     
         5 . The method of  claim 4 , characterized in that Al or an Al alloy is selected as said stable metal.  
     
     
         6 . The method of  claim 1  or  2 , characterized in that at least one of said EL layers ( 6 ,  6 ′) is prepared as a laminated composite layer system of a plurality of EL materials.  
     
     
         7 . The method of  claim 1  or  2 , characterized in that before applying said EL material layer(s), said cathode material layer ( 5   a ,  5   b , . . . ) and/or said anode layer ( 7   a ,  7   b , . . . ) is/are modified by chemical treatment to adsorb functionalized dipoles.  
     
     
         8 . The method of  claim 7 , characterized in that for optimization of charge carrier injection from said cathode and/or said anode material layer(s), said chemical treatment is selected such that the molecules attached to said cathode and/or said anode layer(s) are of the same functional group for light emission and/or charge transport as the active organic or polymeric EL material which is adjacent to the such modified electrode layer(s).  
     
     
         9 . The method of  claim 1  or  2 , characterized in that said heat-supported lamination process of said two EL material coated substrates is performed under a pressure of more than 10 g/cm 2 .  
     
     
         10 . An active matrix display device formed of a plurality of pixels and comprising: 
 at least one thin film transistor (TFT) element adhered on a first substrate ( 1 ) for each pixel;    a structured non-conductive passivation layer ( 3 ) covering the source (S) and drain (D) regions of said TFT clement ( 2 ) and leaving at least part of the drain region (D) uncovered;    a low work function material layer structured into pixel electrode areas ( 5   a ,  5   b , . . . ) and electrically contacting said uncovered part of said drain regions;    a second substrate ( 2 ) bearing an electrically conducting high work function layer ( 7   a ,  7   b , . . . ); and    an active organic or polymeric electroluminescent EL material layer ( 6 ,  6 ′) placed between said low work function pixel structured layer and said high work function layer on said second substrate ( 8 ).    
     
     
         11 . The display device of  claim 10 , characterized in that said low work function material layer ( 5   a ,  5   b , . . . ) and/or said high work function layer ( 7   a ,  7   b , . . . ) on said second substrate ( 8 ) are modified by chemical treatment to comprise adsorbed functionalized dipoles.  
     
     
         12 . The display device according to  claim 11 , characterized in that the functional groups used to attach the dipoles are carboxylic acids, hydroxamine, thiols, phosphonates, sulfonates and/or amines.  
     
     
         13 . The display device according to  claim 11 , characterized in that molecules attached to said modified electrodes comprise the same functional group for light emission and/or charge transport as the active organic or polymeric layer in the device adjacent to said modified electrode.  
     
     
         14 . The display device according to  claim 11 , characterized in that molecules attached to said modified electrodes comprise structures of the following formula  
       R d —P—R a    
       where P is a π-conjugated system such as  
       
         
           
           
               
               
           
         
       
       where R d  is an electron donor group and R a  is an electron acceptor group, 
 wherein R d  may be chosen from the groups NR′R″, OR′ and SR′ where R′ and R″ represent independently of each other ═H or C n H(2 n+1 )R att  with R att =attachement group according to  claim 12  or H and n=0-20, wherein R′ and R″ may be the same or different, but one of R′ and R″ must be ≠H and  
 wherein R a  may be chosen from the groups R att —C n H o F p —SO 2 —NO 2  and COOR att , where o+p=2n+1 and n=0-20,  
 under the condition that one of R att ≠H.  
 
     
     
         15 . The display device according to  claim 14 , characterized in that the molecule attached to said modified electrode has the following structural formula:  
       
         
           
           
               
               
           
         
       
     
     
         16 . The display device according to  claim 11 , characterized in that molecules attached to said modified electrodes comprise structures of the following formula  
       
         
           
           
               
               
           
         
       
       where R′ and R″ independently of each other ═H or C n H( 2n+1 )R att , wherein R att =attachment group according to  claim 12  or H, n=0-20 and wherein R′ and R″ may be the same or different, under the condition that one of R′ and R″ must be ≠H.  
     
     
         17 . The display device according to  claim 16 , characterized in that the molecule attached to said modified electrode has the following structural formula: