Active matrix substrate, and liquid crystal display device provided with active matrix substrate

3:

• The active matrix substrate of claim 1, wherein
• the plurality of oxide semiconductor TFTs include at least one single-gate structure TFT that does not have a back gate.

4:

• The active matrix substrate of claim 1, wherein
• the active matrix substrate has a plurality of pixel regions, each of the plurality of pixel regions has a pixel TFT formed on the substrate and a pixel electrode electrically connected to a drain electrode of the pixel TFT, a source electrode of the pixel TFT is coupled to one of the plurality of source bus lines, and a gate electrode of the pixel TFT is coupled to one of the plurality of gate bus lines.

5:

• active matrix substrate of claim 4, wherein
• the back-gate electrode of the first TFT and the pixel electrode are formed of a same transparent conductive film.

6:

• The active matrix substrate of claim 4, further comprising:
• a common electrode disposed on the substrate side of the pixel electrode or an opposite side from the substrate of the pixel electrode, with a dielectric layer interposed therebetween, and
• the back-gate electrode of the first TFT and the common electrode are formed of a same transparent conductive film.

8:

• The active matrix substrate of claim 1, wherein
• the back-gate electrode of the first TFT is coupled to the positive power supply voltage VDD or the ground potential GND through a resistor and a capacitor.

9:

• The active matrix substrate of claim 1, wherein
• the back-gate electrode of the first TFT is coupled to a circuit allowed to switch a potential of the back-gate electrode between a high potential and a low potential lower than the high potential, and the high potential is the positive power supply voltage VDD.

10:

• The active matrix substrate of claim 1, wherein
• the plurality of oxide semiconductor TFTs are each a channel-etch TFT.

11:

• The active matrix substrate of claim 1, wherein
• the plurality of oxide semiconductor TFTs are each an etch-stop TFT.

12:

• The active matrix substrate of claim 1, wherein
• the oxide semiconductor layer contains an In—Ga—Zn—O based semiconductor.

13:

• The active matrix substrate of claim 12, wherein
• the In—Ga—Zn—O based semiconductor contains a crystalline portion.

14:

• The active matrix substrate of claim 1, wherein
• the oxide semiconductor layer has a multilayer structure.

17:

• The active matrix substrate of claim 2, wherein
• the back-gate electrode of the first TFT is coupled to the positive power supply voltage VDD or the ground potential GND through a resistor and a capacitor.