Thin-film transistor formed on insulating substrate

Abstract

There is provided a thin-film transistor that is formed on an insulating substrate, is capable of a high-speed operation, has small non-uniformity among devices, is hardly susceptible to device destruction due to high voltage, and is free from the effect of a parasitic transistor that forms at an edge part of an Si island. The thin-film semiconductor device is formed using a thin-film semiconductor provided on the insulating substrate and includes a gate region for formation of a channel region through which a drain current flows. The gate region has a ring shape in plan on the insulating substrate. High concentration impurity-doped regions are dividedly provided on an inside and an outside of the ring-shaped gate region, and the channel region is formed of a plurality of fan-shaped semiconductor single-crystal portions.

1 . A thin-film semiconductor device comprising: 
 a thin-film semiconductor layer that is provided on an insulating substrate;    a ring-shaped channel region that is provided in the thin-film semiconductor layer;    one of a source region and a drain region that is provided on an inside of, and adjacent to, the ring-shaped channel region;    the other of the source region and the drain region that is provided on an outside of, and adjacent to, the ring-shaped channel region;    a gate insulating film that is provided on the ring-shaped channel region; and    a gate electrode that is provided on the gate insulating film,    wherein at least a semiconductor portion of the thin-film semiconductor layer, where the ring-shaped channel region is formed, is an semiconductor portion in which fan-shaped semiconductor single-crystal portions are provided in a ring shape.    
   
   
       2 . A thin-film semiconductor device comprising: 
 a thin-film semiconductor layer that is provided on an insulating substrate;    a ring-shaped channel region that is provided in the thin-film semiconductor layer;    one of a source region and a drain region that is provided on an inside of, and adjacent to, the ring-shaped channel region;    the other of the source region and the drain region that is provided on an outside of, and adjacent to, the ring-shaped channel region;    a gate insulating film that is provided on the ring-shaped channel region; and    a gate electrode that is provided on the gate insulating film,    wherein a ring-shaped offset region, which has a same impurity concentration as the ring-shaped channel region, is provided between the drain region and the ring-shaped channel region.    
   
   
       3 . A thin-film semiconductor device comprising: 
 an insulating layer that is provided on a semiconductor substrate;    a thin-film semiconductor layer that is provided on the insulating layer;    a ring-shaped channel region that is provided in the thin-film semiconductor layer;    one of a source region and a drain region that is provided on an inside of, and adjacent to, the ring-shaped channel region;    the other of the source region and the drain region that is provided on an outside of, and adjacent to, the ring-shaped channel region;    a gate insulating film that is provided on the ring-shaped channel region; and    a gate electrode that is provided on the gate insulating film,    wherein a ring-shaped offset region, which has a same impurity concentration as the ring-shaped channel region, is provided between the drain region and the ring-shaped channel region.    
   
   
       4 . A thin-film semiconductor device comprising: 
 a thin-film semiconductor layer that is provided on an insulating substrate;    a ring-shaped channel region that is provided in the thin-film semiconductor layer;    one of a source region and a drain region that is provided on an inside of, and adjacent to, the ring-shaped channel region;    the other of the source region and the drain region that is provided on an outside of, and adjacent to, the ring-shaped channel region;    a gate insulating film that is provided on the ring-shaped channel region; and    a gate electrode that is provided on the gate insulating film,    wherein a ring-shaped LDD region, which is doped with impurities with a concentration that is lower than a concentration in the drain region and is higher than a concentration in the ring-shaped channel region, is provided between the drain region and the ring-shaped channel region.    
   
   
       5 . A thin-film semiconductor device comprising: 
 an insulating layer that is provided on a semiconductor substrate;    a thin-film semiconductor layer that is provided on the insulating layer;    a ring-shaped channel region that is provided in the thin-film semiconductor layer;    one of a source region and a drain region that is provided on an inside of, and adjacent to, the ring-shaped channel region;    the other of the source region and the drain region that is provided on an outside of, and adjacent to, the ring-shaped channel region;    a gate insulating film that is provided on the ring-shaped channel region; and    a gate electrode that is provided on the gate insulating film,    wherein a ring-shaped LDD region, which is doped with impurities with a concentration that is lower than a concentration in the drain region and is higher than a concentration in the ring-shaped channel region, is provided between the drain region and the ring-shaped channel region.    
   
   
       6 . A thin-film semiconductor device of a MOSFET type, which is formed using a thin-film semiconductor layer provided on an insulating substrate,  
     comprising: 
 a source region;  
 a channel region; and  
 a drain region, the source region, the channel region and the drain region being adjacent to each other,  
 wherein the channel region has a ring shape in plan on the insulating substrate, and one of the source region and the drain region and the other thereof are provided on an inside and an outside of the channel region, respectively.  
 
   
   
       7 . A thin-film semiconductor device of a MOSFET type, which is formed using a thin-film semiconductor layer provided on an insulating substrate,  
     comprising: 
 a source region;  
 a channel region; and  
 a drain region, the source region, the channel region and the drain region being adjacent to each other,  
 wherein the channel region is formed in a polygonal strip shape, and one of the source region and the drain region and the other thereof are provided on an inside and an outside of the channel region, respectively.  
 
   
   
       8 . The thin-film semiconductor device according to  claim 6 , wherein the channel region is formed of a plurality of single-crystal regions that extend radially from a central part of the thin-film semiconductor layer and are defined by crystal grain boundaries.  
   
   
       9 . The thin-film semiconductor device according to  claim 7 , wherein the channel region is formed of a plurality of single-crystal regions that extend radially from a central part of the thin-film semiconductor layer and are defined by crystal grain boundaries.