Coating liquid for gate insulating film, gate insulating film and organic transistor

Abstract

To provide a coating fluid for a gate insulating film, which can be baked at a low temperature of at most 180° C.; a gate insulating film having excellent solvent resistance and further having good characteristics in e.g. specific resistance or semiconductor mobility; and an organic transistor employing the gate insulating film. A coating fluid for a gate insulating film, which comprises a polyimide obtainable by cyclodehydration of a polyamic acid having repeating units of a specific structure, a gate insulating film employing the coating fluid, and the organic transistor employing the gate insulating film.

1 . A coating fluid for a gate insulating film, which comprises a polyimide obtainable by cyclodehydration of a polyamic acid having repeating units represented by the following formula (1): 
     
       
         
         
             
             
         
       
     
     wherein A is a tetravalent organic group, B 1  is at least one bivalent organic group selected from the following formulae (2) to (9), and B 2  is a bivalent organic group other than the following formulae (2) to (9): 
     
       
         
         
             
             
         
       
     
     (wherein each R 5  independently is hydrogen, a methyl group or a trifluoromethyl group),
 each of b1 and b2 represents a compositional ratio, and b1 and b2 have a relationship of 0.5≦(b1/(b1+b2))≦1 in ratio (mol). 
 
   
   
       2 . A gate insulating film made of a polyimide film, wherein the polyimide film is a film obtained by applying and baking a solution containing an organic solvent-soluble polyimide, and further the organic solvent-soluble polyimide is a polyimide obtained by cyclodehydration of a polyamic acid having repeating units represented by the following formula (1), and the baking temperature for the polyimide film is at most 180° C., 
     
       
         
         
             
             
         
       
     
     wherein A is a tetravalent organic group, B 1  is at least one bivalent organic group selected from the following formulae (2) to (9), and B 2  is a bivalent organic group other than the following formulae (2) to (9): 
     
       
         
         
             
             
         
       
     
     (wherein each R 5  independently is a hydrogen, a methyl group or a trifluoromethyl group),
 each of b1 and b2 represents a compositional ratio, and b1 and b2 have a relationship of 0.5≦(b1/(b1+b2))≦1 in ratio (mol). 
 
   
   
       3 . The gate insulating film according to  claim 2 , wherein in the formula (1), A is a tetravalent organic group having an alicyclic structure. 
   
   
       4 . The gate insulating film according to  claim 3 , wherein the tetravalent organic group having an alicyclic structure is at least one member selected from the group consisting of the following formulae (10) to (14): 
     
       
         
         
             
             
         
       
     
     (in the formula (10), each of R 1 , R 2 , R 3  and R 4  which are independent of one another, is hydrogen, fluorine or a C 1-4  organic group.) 
   
   
       5 . The gate insulating film according to any one of  claims 2  to  4 , wherein in the formula (1), B 1  represents the above formula (2), (4), (6) or (8). 
   
   
       6 . The gate insulating film according to any one of  claims 2  to 5, wherein in the formula (1), R 5  in B 1  represents a methyl group or a trifluoromethyl group. 
   
   
       7 . The gate insulating film according to any one of  claims 2  to  6 , wherein the baking temperature for the polyimide film is at most 150° C. 
   
   
       8 . The gate insulating film according to any one of  claims 2  to  7 , wherein the organic solvent-soluble polyimide has an imidated ratio of at least 50%. 
   
   
       9 . The gate insulating film according to any one of  claims 2  to  8 , wherein the solvent in the solution containing an organic solvent-soluble polyimide has a boiling point of at most 200° C. 
   
   
       10 . An organic transistor employing the gate insulating film as defined in any one of  claims 2  to  9 .