Semiconductor device

A semiconductor device comprising:

• a memory cell comprising:
• a first transistor comprising:
• a first conductive layer;
• a second conductive layer;
• an oxide semiconductor layer electrically connected to the first conductive layer and the second conductive layer;
• a first insulating layer over the first conductive layer, the second conductive layer, and the oxide semiconductor layer;
• and
• a third conductive layer over the first insulating layer, wherein the third conductive layer and the oxide semiconductor layer are overlapped with each other;
• and
• a fourth conductive layer over the first insulating layer, wherein the fourth conductive layer and the first conductive layer are overlapped with each other,
• wherein the oxide semiconductor layer comprises indium and zinc.

A semiconductor device comprising:

• a memory cell comprising:
• a first transistor comprising:
• a first conductive layer;
• a second conductive layer;
• an oxide semiconductor layer electrically connected to the first conductive layer and the second conductive layer;
• a first insulating layer over the first conductive layer, the second conductive layer, and the oxide semiconductor layer;
• and
• a third conductive layer over the first insulating layer, wherein the third conductive layer and the oxide semiconductor layer are overlapped with each other;
• and
• a fourth conductive layer over the first insulating layer, wherein the fourth conductive layer and the first conductive layer are overlapped with each other,
• wherein the oxide semiconductor layer comprises indium and zinc, and
• wherein the oxide semiconductor layer has a carrier density of less than 1×1012/cm3.

A semiconductor device comprising:

• a memory cell comprising:
• a second transistor;
• a second insulating layer over the second transistor and comprising an opening;
• a first transistor comprising:
• a first conductive layer over the second insulating layer and in the opening;
• a second conductive layer over the second insulating layer;
• an oxide semiconductor layer electrically connected to the first conductive layer and the second conductive layer;
• a first insulating layer over the first conductive layer, the second conductive layer, and the oxide semiconductor layer;
• and
• a third conductive layer over the first insulating layer, wherein the third conductive layer and the oxide semiconductor layer are overlapped with each other;
• and
• a fourth conductive layer over the first insulating layer, wherein the fourth conductive layer and the first conductive layer are overlapped with each other,
• wherein the first conductive layer is electrically connected to the second transistor, and
• wherein the oxide semiconductor layer comprises indium and zinc.