Thin film transistor and display device using the same

1. A thin film transistor comprising:

an insulating substrate;

a gate electrode provided on an upper surface of the insulating substrate;

a gate insulating film formed so as to cover the gate electrode;

an oxide semiconductor layer provided on the gate insulating film;

a channel protective layer provided at least on an upper surface of the oxide semiconductor layer; and

a source electrode and a drain electrode provided so as to come into contact with the oxide semiconductor layer,

wherein the channel protective layer is formed such that the film density of a portion provided so as to come into contact with the oxide semiconductor layer is higher than the film density of a portion distant from the oxide semiconductor layer,

wherein the channel protective layer is formed of a single thin film layer, and

wherein in the channel protective layer, the film density of a region provided so as to come into contact with the oxide semiconductor layer is higher than the film density of other regions, and the film density of the channel protective layer continuously and gradually decreases in a film thickness direction of the region provided so as to come into contact with the oxide semiconductor layer.

2. The thin film transistor according to claim 1 , wherein the film thickness of the channel protective layer is 600 nm or less.

3. A display device comprising:

a first substrate formed of an insulating substrate,

wherein the first substrate includes

video signal lines extending in a Y direction and disposed in parallel in an X direction;

scanning signal lines extending in the X direction and disposed in parallel in the Y direction;

pixel electrodes supplied with video signals from the video signal lines via thin film transistors; and

a common electrode supplied with a common signal which are used as a reference of the video signals,

wherein pixel regions surrounded by the video signal lines and the scanning signal lines are formed in a matrix, and

wherein each of the thin film transistors is formed of the thin film transistor according to claim 1 .

4. The display device according to claim 3 , further comprising:

a liquid crystal display panel including a second substrate disposed opposite to the first substrate with a liquid crystal layer interposed therebetween; and

a backlight unit disposed on a rear side of the liquid crystal display panel and applying backlight which is a light source of the liquid crystal display panel.

5. A method of manufacturing a display device, comprising:

forming a gate electrode on an upper surface of an insulating substrate;

forming a gate insulating film so as to cover the gate electrode;

forming an oxide semiconductor layer on the gate insulating film;

forming a channel protective layer at least on an upper surface of the oxide semiconductor layer by a method being selected from the group consisting of an increase in output density of Radio Frequency (RF), and an increase in dinitrogen oxide, such that the film density of a portion provided so as to come into contact with the oxide semiconductor layer is higher than the film density of a portion distant from the oxide semiconductor layer; and

forming a source electrode and a drain electrode so as to come into contact with the oxide semiconductor layer.

6. The thin film transistor according to claim 1 , wherein the channel protective layer is formed so as to also cover the upper surface of the insulating substrate along with the source electrode, the drain electrode, and the oxide semiconductor layer, and

wherein the channel protective layer covers the upper surface of the insulating substrate, and is also used as a passivation layer for protecting the thin film transistor.

7. The thin film transistor according to claim 1 , wherein the channel protective layer is formed so as to cover the upper surface of the insulating substrate along with the oxide semiconductor layer,

wherein the source electrode and the drain electrode are formed on an upper surface of the channel protective layer, and are electrically connected to the oxide semiconductor layer via a through-hole formed in the channel protective layer, and

wherein a passivation layer which is a protection film is formed so as to cover the source electrode, the drain electrode, and the channel protective layer.