Method for manufacturing oxide semiconductor layer and thin film transistor having oxide semiconductor layer

A method for manufacturing a thin film transistor, comprising following steps:

• providing a substrate;
• forming a channel layer on the substrate by sputtering a first kind of metallic ions from a first metallic oxide sputtering target, and sputtering at least two second kinds of metallic ions from a second metallic oxide sputtering target, the at least two second kind of metallic ions being different from the first kind of metallic ions, and a proportion of the first kind of metallic ions and the at least two second kind of metallic ions being adjustable by controlling a depositing speed of the channel layer and a period of using a baffle plate in sputtering;
• forming a gate electrode on the channel layer, the gate electrode being separated from the channel layer by a gate insulating layer;
• forming a source electrode electrically connected with a first portion of the channel layer;
• and
• forming a drain electrode electrically connected with a second portion of the channel layer.