Method for Modifying and Controlling the Threshold Voltage of Thin Film Transistors

Abstract

Doped semiconductor ink formulations, methods of making doped semiconductor ink formulations, methods of coating or printing thin films, methods of forming electronic devices and/or structures from the thin films, and methods for modifying and controlling the threshold voltage of a thin film transistor using the films are disclosed. A desired dopant may be added to an ink formulation comprising a Group IVA compound and a solvent, and then the ink may be printed on a substrate to form thin films and conductive structures/devices, such as thin film transistors. By adding a customized amount of the dopant to the ink prior to printing, the threshold voltage of a thin film transistor made from the doped semiconductor ink may be independently controlled upon activation of the dopant.

What is claimed is: 
     
         1 . A thin film transistor, capacitor, diode, resistor device, circuit, RFID tag, display backplane, sensor and/or photovoltaic device, comprising a semiconductor film having 0.1 to 50 ppm of dopant atoms therein. 
     
     
         2 . The device of  claim 1 , wherein the semiconductor film comprises a printed doped silicon film on a substrate. 
     
     
         3 . The device of  claim 2 , wherein the dopant atoms comprise B, P, As, or Sb. 
     
     
         4 . The device of  claim 1 , wherein the semiconductor film comprises 1-10 ppm of dopant atoms therein. 
     
     
         5 . The device of  claim 4 , wherein the device is a thin film transistor. 
     
     
         6 . The device of  claim 4 , wherein the dopant atoms are present in an amount sufficient to control a threshold voltage of the thin film transistor. 
     
     
         7 . The device of  claim 2 , further comprising a conductor on the printed doped silicon film. 
     
     
         8 . A method of controlling a threshold voltage of a thin film transistor comprising:
 a) making a semiconductor ink comprising a Group IVA compound containing at least five Si and/or Ge atoms, a dopant in an amount effective to provide a film with a dopant atom concentration of from 0.1 to 50 ppm, relative to the number of Group IVA atoms, and a solvent;   b) forming a film from the ink; and   c) activating the dopant in the film.   
     
     
         9 . The method of  claim 8 , wherein forming the film comprises:
 a) printing the semiconductor ink by inkjetting, gravure printing, off-set lithography, screen printing, flexographic printing, microspotting, pen-coating, syringe dispensing, spray jetting, and/or pump dispensing;   b) heating the printed ink to form a doped semiconductor; and   c) annealing and/or irradiating the doped semiconductor sufficiently to at least partially crystallize, reduce a hydrogen content of, and/or electrically activate the dopant in the doped semiconductor and form the doped semiconductor film.   
     
     
         10 . The method of  claim 9 , wherein said ink is printed in a pattern corresponding to the thin film transistor. 
     
     
         11 . The method of  claim 9 , further comprising irradiating the composition with UV radiation, simultaneously with or immediately subsequent to printing the composition onto the substrate. 
     
     
         12 . The method of  claim 8 , wherein forming the film comprises:
 a) blanket depositing the ink;   b) heating the blanket deposited ink to form a doped semiconductor;   c) annealing and/or irradiating the doped semiconductor sufficiently to at least partially crystallize, reduce a hydrogen content of, and/or electrically activate the dopant in the doped semiconductor and form the doped semiconductor film; and   d) patterning the doped semiconductor or the doped semiconductor film by photolithography and/or etching processes.   
     
     
         13 . The method of  claim 12 , further comprising irradiating the composition with UV radiation, simultaneously with or immediately subsequent to blanket-depositing the composition onto the substrate. 
     
     
         14 . The method of  claim 8 , wherein the Group IVA compound comprises a polysilane having at least 15 Si and/or Ge atoms, and the solvent is selected from the group consisting of linear alkanes, cycloalkanes, arenes, fluoroalkanes, and siloxanes. 
     
     
         15 . The method of  claim 8 , wherein the dopant comprises an organoborane, a hydroborane, a haloborane, or a borane complex. 
     
     
         16 . The method of  claim 15 , wherein the organoborane has the formula BR 3  or B 2 R 6 , where each R is independently selected from the group consisting of C 1 -C 10  alkyl, C 6 -C 10  aryl, C 6 -C 10  aryl substituted with 1 to 3 C 1 -C 4  alkyl groups, C 7 -C 12  aralkyl, halogen, hydrogen, GeR′ 3 , SiR′ 3  and Si x H 2x+1 , where R′ is independently hydrogen, halogen, C 1 -C 10  alkyl, C 6 -C 10  aryl, C 6 -C 10  aryl substituted with 1 to 3 C 1 -C 4  alkyl groups, C 7 -C 12  aralkyl, or Si x H 2x+1 , and x is an integer of from 1 to 4, such that the combined R and/or R′ groups include at least 6 carbon atoms per boron atom. 
     
     
         17 . The method of  claim 8 , wherein the dopant comprises elemental phosphorus, a phosphane, an arsane, a stibane, an organophosphine, an organophosphine oxide, an organophosphite, an organophosphoramide, organophosphate, an organoarsine and/or an organostibine. 
     
     
         18 . The method of  claim 17 , wherein the organophosphine has the formula PR 3 , where each R is independently selected from the group consisting of C 1 -C 10  alkyl, C 6 -C 10  aryl, C 6 -C 10  aryl substituted with 1 to 3 C 1 -C 4  alkyl groups, C 7 -C 12  aralkyl, halogen, hydrogen, GeR′ 3 , SiR′ 3  and Si x H 2x+1 , where R′ is independently hydrogen, halogen, C 1 -C 10  alkyl, C 6 -C 10  aryl, C 6 -C 10  aryl substituted with 1 to 3 C 1 -C 4  alkyl groups, C 7 -C 12  aralkyl, or Si x H 2x+1 , and x is an integer of from 1 to 4, such that the combined R and/or R′ groups include at least 6 carbon atoms per phosphorous atom. 
     
     
         19 . The method of  claim 8 , wherein the dopant has a boiling point greater than 150° C. 
     
     
         20 . The method of  claim 8 , wherein the dopant is present in an amount sufficient to provide a film with a dopant atom concentration of from 1 to 10 ppm, relative to Group IVA atoms.