Amorphous Oxide And Thin Film Transistor

Abstract

The present invention relates to an amorphous oxide and a thin film transistor using the amorphous oxide. In particular, the present invention provides an amorphous oxide having an electron carrier concentration less than 10 18 /cm 3 , and a thin film transistor using such an amorphous oxide. In a thin film transistor having a source electrode 6 , a drain electrode 5 , a gate electrode 4 , a gate insulating film 3 , and a channel layer 2 , an amorphous oxide having an electron carrier concentration less than 10 18 /cm 3 is used in the channel layer 2.

1 . An amorphous oxide having an electron carrier concentration less than 10 18 /cm 3 .  
     
     
         2 . An amorphous oxide having an electron carrier concentration less than 10 17 /cm 3 .  
     
     
         3 . An amorphous oxide having an electron carrier concentration less than 10 16 /cm 3 .  
     
     
         4 . An amorphous oxide wherein electron mobility thereof increases with the electron carrier concentration.  
     
     
         5 . The amorphous oxide according to  claim 4 , wherein the electron mobility is more than 0.1 cm 2 /(V·sec).  
     
     
         6 . The amorphous oxide according to  claim 5 , exhibiting degenerate conduction.  
     
     
         7 . The amorphous oxide according to  claim 1 , wherein the amorphous oxide is a compound that contains at least one element selected from Zn, In, and Sn as a constituent and is represented by [(Sn 1-x M4 x )O 2 ]a.[In 1-y M3 y ) 2 O 3 ]b.[(Zn 1-z M2 z )O]c (wherein 0≦x≦1,0≦y≦1, 0≦z≦1; x, y, and z are not simultaneously 1; 0≦a≦1, 0≦b≦1, 0≦c≦1, and a+b+c=1; M4 is a group IV element having an atomic number smaller than that of Sn; M3 is Lu or a group III element having an atomic number smaller than that of In; and M2 is a group II element having an atomic number smaller than that of Zn).  
     
     
         8 . The amorphous oxide according to  claim 7 , further comprising at least one element selected from group V elements M5 and W.  
     
     
         9 . The amorphous oxide according to  claim 7 , wherein the amorphous oxide is a single compound represented by [(In 1-y M3 y ) 2 O 3 (Zn 1-x M2 x )O] m  (wherein 0≦x≦1; 0≦y≦1; x and y are not simultaneously 1; m is zero or a natural number less than 6; M3 is Lu or a group III element having an atomic number smaller than that of In; and M2 is a group II element having an atomic number smaller than that of Zn) in a crystallized state or a mixture of the compounds with different values of m.  
     
     
         10 . The amorphous oxide according to  claim 9 , wherein M3 is Ga.  
     
     
         11 . The amorphous oxide according to  claim 9 , wherein M2 is Mg.  
     
     
         12 . The amorphous oxide according to  claim 1 , wherein the amorphous oxide is formed on a glass substrate, a metal substrate, a plastic substrate, or a plastic film.  
     
     
         13 . A field effect transistor wherein the amorphous oxide according to  claim 1  is used in a channel layer.  
     
     
         14 . The field effect transistor according to  claim 13 , wherein a gate insulating layer comprises one of Al 2 O 3 , Y 2 O 3 , and HfO 2  or a mixed crystal compound containing at least two of these compounds.  
     
     
         15 . A thin film transistor comprising a source electrode, a drain electrode, a gate electrode a gate insulating film and a channel layer, wherein the channel layer comprises an amorphous oxide having an electron carrier concentration of less than 10 18 /cm 3 .  
     
     
         16 . The thin film transistor according to  claim 15 , wherein the electron carrier concentration of the amorphous oxide is  10   17 /cm 3  or less.  
     
     
         17 . The thin film transistor according to  claim 15 , wherein the electron carrier concentration of the amorphous oxide is 10 16 /cm 3  or less.  
     
     
         18 . The thin film transistor according to  claim 15 , wherein the amorphous oxide is an oxide comprising In, Ga, and Zn, and the atomic ratio In:Ga:Zn is 1:1:m (m<6).  
     
     
         19 . The thin film transistor according to  claim 15 , wherein the amorphous oxide is an oxide comprising In, Ga, Zn, and Mg and the atomic ratio In:Ga:Z 1-x Mg x  is 1:1:m (m<6), wherein 0<x≦1.  
     
     
         20 . The thin film transistor according to  claim 15 , wherein the amorphous oxide is selected from In x Ga 1-x  oxides (0≦x≦1), In x Zn 1-x  oxides (0.2≦x≦1), In x Sn 1-x  oxides (0.8≦x≦1), and In x (ZnSn) 1-x  oxides (0.15≦x≦1).  
     
     
         21 . The thin film transistor according to  claim 15 , wherein the electron mobility of the amorphous oxide increases with the electron carrier concentration.