Transistor, semiconductor device, and electronic device
摘要
說明書
When the semiconductor layer 109b is an In-M-Zn oxide containing In, the element M, and Zn at an atomic ratio of x2:y2:z2 and each of the semiconductor layer 109a and the semiconductor layer 109c is an In-M-Zn oxide containing In, M, and Zn at an atomic ratio of x1:y1:z1, y1/x1 is preferably larger than y2/x2. Further preferably, the semiconductor layer 109a, the semiconductor layer 109c, and the semiconductor layer 109b in which y1/x1 is 1.5 or more times as large as y2/x2 are selected. Still further preferably, the semiconductor layer 109a, the semiconductor layer 109c, and the semiconductor layer 109b in which y1/x1 is 2 or more times as large as y2/x2 are selected. Still further preferably, the semiconductor layer 109a, the semiconductor layer 109c, and the semiconductor layer 109b in which y1/x1 is 3 or more times as large as y2/x2 are selected. In the semiconductor layer 109b of this case, y2 is preferably larger than or equal to x2 because the transistor can have stable electrical characteristics. However, when y2 is five or more times as large as x2, the field-effect mobility of the transistor is reduced; accordingly, y2 is preferably smaller than five times x2. When the semiconductor layers 109a and 109c each have the above structure, each of the semiconductor layers 109a and 109c can be a layer in which oxygen vacancy is less likely to occur than in the semiconductor layer 109b.
