Oxide semiconductor transistor structure in 3-d device and methods for forming the same

A method of forming an oxide semiconductor transistor, comprising:

• depositing a gate electrode;
• depositing a dielectric layer;
• depositing a channel layer, comprising:
• depositing a first oxide semiconductor layer;
• depositing a second oxide semiconductor layer;
• depositing a third oxide semiconductor layer,
• wherein an oxygen concentration of the second oxide semiconductor layer is lower than an oxygen concentration of the first oxide semiconductor layer, and
• an oxygen concentration of the third oxide semiconductor layer, and
• a thickness of the second oxide semiconductor layer is greater than a combined thickness of the first oxide semiconductor layer and third oxide semiconductor layer;
• and
• forming a source electrode and a drain electrode in contact with the channel layer.

A method of forming an oxide semiconductor transistor, comprising:

• depositing a gate electrode;
• depositing a dielectric layer;
• depositing a channel layer, comprising:
• depositing a first oxide semiconductor layer having a first oxygen concentration;
• depositing a second oxide semiconductor layer having a second oxygen concentration;
• subjecting the second oxide semiconductor layer to a thermal treatment at an elevated temperature in an environment that is essentially free of oxygen gas (O2);
• depositing a third oxide semiconductor layer having a third oxygen concentration;
• wherein the second oxygen concentration is lower than the first oxygen concentration and the third oxygen concentration;
• and
• forming a source electrode and a drain electrode in contact with the channel layer.