Active matrix substrate and display device
An active matrix substrate has pixel regions, and includes a substrate, pixel TFTs disposed to respectively correspond to the pixel regions, and pixel electrodes electrically connected to the pixel TFTs. The pixel TFTs are each a top gate structure TFT that has an oxide semiconductor layer, a gate insulating layer on the oxide semiconductor layer, and a gate electrode opposing the oxide semiconductor layer with the gate insulating layer therebetween. The gate insulating layer is formed of silicon oxide and includes a lower layer contacting the oxide semiconductor layer, and an upper layer on the lower layer. The lower layer H/N ratio of hydrogen atoms to nitrogen atoms in the lower layer is 1.5 to 5.0. The upper layer H/N ratio of hydrogen atoms to nitrogen atoms in the upper layer is 0.9 to 2.0. The lower layer H/N ratio is larger than the upper layer H/N ratio.
1. An active matrix substrate that has a plurality of pixel regions arranged in a matrix, the active matrix substrate comprising:
a substrate;
pixel TFTs supported by the substrate and disposed to respectively correspond to the plurality of pixel regions; and
pixel electrodes respectively disposed in the plurality of pixel regions and electrically connected to the pixel TFTs,
wherein each of the pixel TFTs is a top gate structure TFT that has an oxide semiconductor layer, a gate insulating layer disposed on the oxide semiconductor layer, and a gate electrode disposed to oppose the oxide semiconductor layer with the gate insulating layer therebetween,
the gate insulating layer is formed of silicon oxide,
the gate insulating layer includes a lower layer in contact with the oxide semiconductor layer and an upper layer placed on the lower layer, and
when a ratio of the number of hydrogen atoms to the number of nitrogen atoms contained in the lower layer is referred to as a lower layer H/N ratio and a ratio of the number of hydrogen atoms to the number of nitrogen atoms contained in the upper layer is referred to as an upper layer H/N ratio,
the lower layer H/N ratio is 1.5 or more and 5.0 or less,
the upper layer H/N ratio is 0.9 or more and 2.0 or less, and
the lower layer H/N ratio is larger than the upper layer H/N ratio.
2. The active matrix substrate according to claim 1 , wherein the lower layer H/N ratio is 1.5 or more and 2.5 or less.
3. The active matrix substrate according to claim 1 , wherein the upper layer H/N ratio is 0.9 or more and 1.3 or less.
4. The active matrix substrate according to claim 1 , wherein the oxide semiconductor layer contains an In—Ga—Zn—O-based semiconductor.
5. The active matrix substrate according to claim 4 , wherein the In—Ga—Zn—O-based semiconductor contains a crystalline portion.
6. A display device comprising the active matrix substrate according to claim 1 .
7. The display device according to claim 6 , wherein the display device is a liquid crystal display device comprising:
a counter substrate disposed to oppose the active matrix substrate;
a liquid crystal layer disposed between the active matrix substrate and the counter substrate.
8. The display device according claim 6 , wherein the display device is an organic EL display device comprising an organic EL layer disposed on the pixel electrodes.