Oxide semiconductor, thin film transistor, and display device

Abstract

An object is to control composition and a defect of an oxide semiconductor, another object is to increase a field effect mobility of a thin film transistor and to obtain a sufficient on-off ratio with a reduced off current. A solution is to employ an oxide semiconductor whose composition is represented by InMO3(ZnO)m, where M is one or a plurality of elements selected from Ga, Fe, Ni, Mn, Co, and Al, and m is preferably a non-integer number of greater than 0 and less than 1. The concentration of Zn is lower than the concentrations of In and M. The oxide semiconductor has an amorphous structure. Oxide and nitride layers can be provided to prevent pollution and degradation of the oxide semiconductor.

1 . (canceled) 
     
     
         2 . A display device comprising:
 a pixel comprising a transistor, a scan line, and a signal line;   a first input terminal comprising a first conductive layer and a second conductive layer over and overlapping with the first conductive layer; and   a second input terminal comprising a third conductive layer and a fourth conductive layer over and overlapping with the fourth conductive layer,   wherein the transistor comprises:
 a source electrode and a drain electrode; 
 an oxide semiconductor layer electrically connected to the source electrode and the drain electrode; 
 a gate electrode overlapping with the oxide semiconductor layer; and 
 a gate insulating layer between the oxide semiconductor layer and the gate electrode, 
   wherein the oxide semiconductor layer comprises In, Ga, and Zn,   wherein the first conductive layer is formed with the same layer as the scan line,   wherein the third conductive layer is formed with the same layer as the signal line, and   wherein each of the second conductive layer and the fourth conductive layer comprises a transparent conductive material.   
     
     
         3 . The display device according to  claim 2 , wherein a concentration of Zn is lower than a concentration of In in the oxide semiconductor layer. 
     
     
         4 . The display device according to  claim 2 , wherein a concentration of Zn is lower than a concentration of Ga in the oxide semiconductor layer. 
     
     
         5 . The display device according to  claim 2 , wherein the third conductive layer is in contact with the fourth conductive layer.