Semiconductor structure

A semiconductor structure, disposed on a substrate, the semiconductor structure comprising:

• a top gate;
• an oxide semiconductor channel layer, disposed between the top gate and the substrate;
• a first dielectric layer, disposed between the top gate and the oxide semiconductor channel layer;
• a second dielectric layer, disposed between the first dielectric layer and the oxide semiconductor channel layer, wherein a dielectric constant of the first dielectric layer is different from a dielectric constant of the second dielectric layer;
• and
• a source and a drain, disposed at two corresponding sides of the oxide semiconductor channel layer, and extending from the two corresponding sides of the oxide semiconductor channel layer to a surface of the substrate, and located between the first dielectric layer and the substrate, wherein a portion of the oxide semiconductor channel layer is exposed between the source and the drain, and a portion of the first dielectric layer and a portion the second dielectric layer directly contact with and completely cover the portion of the oxide semiconductor channel layer, and the second dielectric layer directly covers a top surface of the source and a top surface of the drain.