US Patent 11302717 Transistor and method for manufacturing the same

An object is to provide a highly reliable transistor. In a bottom-gate transistor including an oxide semiconductor layer as a semiconductor layer where a channel is formed, an insulating layer containing excess oxygen is formed over the oxide semiconductor layer, and then an insulating layer through which impurities do not easily pass is formed without exposure to the air. As the insulating layer through which impurities do not easily pass, an aluminum oxide layer or the like can be used. When a conductive layer with a function of absorbing hydrogen is used for a source electrode and a drain electrode, the amount of hydrogen in the oxide semiconductor layer can be reduced.