Semiconductor device

A semiconductor device comprising:

• a substrate;
• a first thin film transistor on the substrate and having polycrystalline silicon;
• and
• a second thin film transistor on the substrate and having an oxide semiconductor,
• wherein the oxide semiconductor has a channel region, a drain region, a source region, and low concentration regions which are lower in impurity concentration than the drain region and the source region, the low concentration regions being located between the channel region and the drain region, and between the channel region and the source region, and
• the second thin film transistor has:
• a gate insulating film on the channel region and the low concentration regions;
• an aluminum oxide film on a first part of the gate insulating film, the first part being located on the channel region;
• and
• a gate electrode on the aluminum oxide film and a second part of the gate insulating film, the second part being located on the low concentration regions,
• wherein the aluminum oxide film is located between the gate insulating film and the gate electrode,
• the gate insulating film is formed of a different material from the aluminum oxide film,
• the aluminum oxide film includes a lower surface, an upper surface, a first side surface and a second side surface,
• the lower surface of the aluminum oxide film is in direct contact with the gate insulating film,
• the upper surface of the aluminum oxide film is opposite the lower surface of the aluminum oxide film,
• the first side surface of the aluminum oxide film is closer to the source region compared to the second side surface of the aluminum oxide film, and
• the gate electrode covers the upper surface of the aluminum oxide film, the first side surface of the aluminum oxide film and the second side surface of the aluminum oxide film.