Thin film transistor, method for manufacturing same, display device, and method for manufacturing same

Abstract

A thin film transistor includes: an insulating layer; a gate electrode provided on the insulating layer; a gate insulating film provided on the gate electrode; a semiconductor layer provided on the gate insulating film, the semiconductor layer being formed of oxide; a source electrode and a drain electrode provided on the semiconductor layer; and a channel protecting layer provided between the source and drain electrodes and the semiconductor layer. The source electrode is opposed to one end of the gate electrode. The drain electrode is opposed to another end of the gate electrode. The another end is opposite to the one end. The drain electrode is apart from the source electrode. The channel protecting layer covers at least a part of a side face of a part of the semiconductor layer. The part of the semiconductor layer is not covered with the source electrode and the drain electrode above the gate electrode.

1 . A thin film transistor comprising:
 an insulating layer;   a gate electrode provided on the insulating layer;   a gate insulating film provided on the gate electrode;   a semiconductor layer provided on the gate insulating film, the semiconductor layer being formed of oxide;   a source electrode and a drain electrode provided on the semiconductor layer, the source electrode being opposed to one end of the gate electrode, the drain electrode being opposed to another end of the gate electrode, the another end being opposite to the one end, the drain electrode being apart from the source electrode; and   a channel protecting layer provided between the source and drain electrodes and the semiconductor layer, the channel protecting layer covering at least a part of a side face of a part of the semiconductor layer, the part of the semiconductor layer being not covered with the source electrode and the drain electrode above the gate electrode.   
   
   
       2 . The transistor according to  claim 1 , wherein the channel protecting layer covers at least the part of the side face of the semiconductor layer between an extension line of a side of the source electrode opposed to the drain electrode and an extension line of a side of the drain electrode opposed to the source electrode. 
   
   
       3 . The transistor according to  claim 2 , wherein the channel protecting layer further covers an upper face of the semiconductor layer between the extension line of the side of the source electrode opposed to the drain electrode and the extension line of the side of the drain electrode opposed to the source electrode. 
   
   
       4 . The transistor according to  claim 1 , wherein the channel protecting layer contains oxygen. 
   
   
       5 . The transistor according to  claim 1 , wherein the semiconductor layer includes an amorphous oxide which contains Zn. 
   
   
       6 . The transistor according to  claim 5 , wherein the amorphous oxide further contains at least one of In and Ga. 
   
   
       7 . A method for manufacturing a thin film transistor, the thin film transistor including:
 a substrate;
 a gate electrode provided on the substrate; 
 a gate insulating film provided on the gate electrode; 
 a semiconductor layer provided on the gate insulating film, the semiconductor layer being formed of oxide; 
 a source electrode and a drain electrode provided on the semiconductor layer, the source electrode being opposed to one end of the gate electrode, the drain electrode being opposed to another end of the gate electrode, the another end being opposite to the one end, the drain electrode being apart from the source electrode; and 
 a channel protecting layer provided between the source and drain electrodes and the semiconductor layer, 
   the method comprising:   forming the gate electrode on the substrate;   forming the gate insulating film on the gate electrode;   forming the semiconductor layer on the gate insulating film;   forming the channel protecting layer covering at least a part of a side face of the semiconductor layer above the gate electrode;   performing a heat treatment on the semiconductor layer and the channel protecting layer at a temperature not less than 160° C.; and   forming the source electrode and the drain electrode on the semiconductor layer and the channel protecting layer after the performing the heat treatment.   
   
   
       8 . The method according to  claim 7 , wherein the channel protecting layer is formed covering at least the part of the side face of the semiconductor layer between a first extension line of a first side of a first region and a second extension line of a second side of a second region, the source electrode being to be formed in the first region, the drain electrode being to be formed in the second region, the first side being opposed to the second region, the second region being opposed to the first region. 
   
   
       9 . A display device comprising:
 a thin film transistor including:
 an insulating layer; 
 a gate electrode provided on the insulating layer; 
 a gate insulating film provided on the gate electrode; 
 a semiconductor layer provided on the gate electrode, the semiconductor layer being formed of oxide; 
 a source electrode and a drain electrode provided on the semiconductor layer, the source electrode being opposed to one end of the gate electrode, the drain electrode being opposed to another end of the gate electrode, the another end being opposite to the one end, the drain electrode being apart from the source electrode; and 
 a channel protecting layer provided between the source and drain electrodes and the semiconductor layer, the channel protecting layer covering at least a part of a side face of a part of the semiconductor layer, the part of the semiconductor layer being not covered with the source electrode and the drain electrode above the gate electrode; 
   a pixel electrode connected to one of the source electrode and the drain electrode, the pixel electrode being formed of the oxide and having a lower electric resistance than the semiconductor layer; and   an optical element producing at least one of a change in optical characteristics and light emitting by an electric signal provided to the pixel electrode.   
   
   
       10 . The device according to  claim 9 , wherein the pixel electrode is not covered with the channel protecting layer. 
   
   
       11 . The device according to  claim 9 , wherein a concentration of oxygen contained in the pixel electrode is lower than a concentration of oxygen contained in the semiconductor layer. 
   
   
       12 . The device according to  claim 9 , wherein the oxide in the pixel electrode has a columnar structure. 
   
   
       13 . The device according to  claim 9 , further comprising
 a film provided under the pixel electrode and formed of the same material as the gate insulating film,   a surface of the gate insulating film on a side of the semiconductor layer being smoother than a surface of the film on a side of the pixel electrode.   
   
   
       14 . The device according to  claim 13 , wherein surface roughness of the surface of the film on the side of the pixel electrode is not less than five nanometers and not greater than ten nanometers. 
   
   
       15 . The device according to  claim 14 , wherein the surface roughness of the surface of the gate insulating film on a side of the semiconductor layer is not less than 10.1 nanometers and not greater than one nanometer. 
   
   
       16 . The device according to  claim 9 , further comprising:
 a plurality of the thin film transistors and a plurality of the pixel electrodes, each of the plurality of the pixel electrodes being connected to one of the source electrode and the drain electrode of each of the plurality of the thin film transistors, the plurality of the thin film transistors and the plurality of the pixel electrodes being arranged in a matrix form;   a plurality of scanning lines, each of the plurality of the scanning lines being connected to each of the gate electrodes of each of the plurality of the thin film transistors; and   a plurality of signal lines, each of the plurality of the signal lines being connected to another of the source electrode and the drain electrode of each of the plurality of the thin film transistors.   
   
   
       17 . A method for manufacturing a display device,
 the display device including:
 a thin film transistor including:
 a substrate; 
 a gate electrode provide on the substrate; 
 a gate insulating film provide on the gate electrode; 
 a semiconductor layer provided on the gate insulating film, the semiconductor layer being formed of oxide; 
 a source electrode and a drain electrode provided on the semiconductor layer, the source electrode being opposed to one end of the gate electrode, the drain electrode being opposed to another end of the gate electrode, the another end being opposite to the one end, the drain electrode being apart from the source electrode ; and 
 a channel protecting layer provided between the source and drain electrodes and the semiconductor layer; 
 
 a pixel electrode connected to one of the source electrode and the drain electrode; and 
 an optical element producing at least one of a change in optical characteristics and light emitting by an electric signal provided to the pixel electrode, 
   the method comprising:   forming the gate electrode on the substrate;   forming the gate insulating film on the gate electrode;   forming a layer of the oxide on the gate insulating film;   forming the channel protecting layer covering at least a part of a side face of the layer of the oxide above the gate electrode and exposing the layer of the oxide in a third region, the pixel electrode being to be formed in the third region;   performing a heat treatment on the layer of the oxide and the channel protecting layer at a temperature not less than 160° C. to decrease an electric resistance of the layer of the oxide not covered with the channel protecting layer to form the pixel electrode; and   forming the source electrode and the drain electrode on the semiconductor layer and the channel protecting layer after the performing the heat treatment.   
   
   
       18 . The method according to  claim 17 , further comprising:
 performing a surface processing selectively changing smoothness of a surface of the gate insulating film before the forming the layer of the oxide.   
   
   
       19 . The method according to  claim 18 , wherein the performing the surface processing includes making the surface of the gate insulating film in the third region rougher than a surface of the gate insulating film in a region except the third region. 
   
   
       20 . A method for manufacturing a display device,
 the display device including:
 a thin film transistor including:
 a substrate; 
 a gate electrode provided on the substrate; 
 a gate insulating film provided on the gate electrode; 
 a semiconductor layer provided on the gate insulating film, the semiconductor layer being formed of oxide; 
 a source electrode and a drain electrode provided on the semiconductor layer, the source electrode being opposed to one end of the gate electrode, the drain electrode being opposed to another end of the gate electrode, the another end being opposite to the one end, the drain electrode being apart from the source electrode; and 
 a channel protecting layer provided between the source and drain electrodes and the semiconductor layer; 
 
 a pixel electrode connected to one of the source electrode and the drain electrode; and 
 an optical element producing at least one of a change in optical characteristics and light emitting by an electric signal provided to the pixel electrode, 
   the method comprising:   forming the gate electrode on the substrate;   forming the gate insulating film on the gate electrode;   performing surface processing selectively changing smoothness of a surface of the gate insulating film; and   forming a layer of the oxide on the gate insulating film.