Semiconductor device and method for manufacturing the same

A semiconductor device comprising:

• a gate electrode on an insulating surface;
• a gate insulating film over the gate electrode;
• a source electrode and a drain electrode over the gate insulating film;
• an oxide semiconductor film over the source electrode and the drain electrode;
• an insulating film over the oxide semiconductor film, the source electrode, and the drain electrode and in contact with the oxide semiconductor film;
• and
• a back gate electrode over the insulating film and overlapping with the gate electrode and the oxide semiconductor film,
• wherein the back gate electrode includes a hydrogen absorbing alloy.

A semiconductor device comprising:

• a gate electrode on all insulating surface;
• a gate insulating film over the gate electrode;
• an oxide semiconductor film over the gate insulating film;
• a channel protective film over the oxide semiconductor film;
• a source electrode and a drain electrode over the oxide semiconductor film;
• an insulating film over the channel protective film, the source electrode, and the drain electrode;
• and
• a back gate electrode over the insulating film and overlapping with the gate electrode and the oxide semiconductor film,
• wherein the back gate electrode includes a hydrogen absorbing alloy.

A method for manufacturing a semiconductor device, comprising the steps of:

• forming a gate insulating film over a gate electrode on an insulating surface;
• forming an oxide semiconductor film over the gate insulating film;
• forming a source electrode and a drain electrode over the oxide semiconductor film;
• forming an insulating film over the oxide semiconductor film, the source electrode, and the drain electrode and in contact with the oxide semiconductor film;
• forming a back gate electrode over the insulating film to overlap with the gate electrode and the oxide semiconductor film;
• and
• performing heat treatment in a state where the back gate electrode is exposed.

A method for manufacturing a semiconductor device, comprising the steps of:

• forming a gate insulating film over a gate electrode on an insulating surface;
• forming a source electrode and a drain electrode over the gate insulating film;
• forming an oxide semiconductor film over the source electrode and the drain electrode;
• forming an insulating film over the oxide semiconductor film, the source electrode, and the drain electrode and in contact with the oxide semiconductor film;
• forming a back gate electrode over the insulating film to overlap with the gate electrode and the oxide semiconductor film;
• and
• performing heat treatment in a state where the back gate electrode is exposed.

A method for manufacturing a semiconductor device, comprising the steps of:

• forming a gate insulating film over a gate electrode on an insulating surface;
• forming an oxide semiconductor film over the gate insulating film;
• forming a channel protective film over the oxide semiconductor film;
• forming a source electrode and a drain electrode over the oxide semiconductor film;
• forming an insulating film over the channel protective film, the source electrode, and the drain electrode;
• forming a back gate electrode over the insulating film to overlap with the gate electrode and the oxide semiconductor film;
• and
• performing heat treatment in a state where the back gate electrode is exposed.