Semiconductor device and method for manufacturing semiconductor device

A semiconductor device comprising:

• a first oxide;
• a first conductor and a second conductor over the first oxide;
• a first insulator over the first conductor and the second conductor;
• a second insulator over and in direct contact with the first insulator;
• a third insulator over and in direct contact with the first oxide and between and in contact with the first conductor and the second conductor, the third insulator being in direct contact with a side surface of the first insulator, a side surface of the second insulator, a side surface of the first conductor, a side surface of the second conductor, and a top surface and a side surface of the first oxide;
• and
• a fourth insulator over and in direct contact with a top surface and a side surface of the third insulator,
• wherein the first oxide comprises a first n-type region, a second n-type region, and an i-type region between the first n-type region and the second n-type region,
• wherein the first n-type region overlaps with the first conductor, the first insulator, and the second insulator,
• wherein the second n-type region overlaps with the second conductor, the first insulator, and the second insulator,
• wherein the i-type region overlaps with the third insulator, and
• wherein each of the first insulator and the fourth insulator is configured to inhibit diffusion of oxygen.