Semiconductor device

A semiconductor device comprising:

• a first transistor and a second transistor,
• wherein a portion where one of a source and a drain of the second transistor is electrically connected to a gate of the second transistor is provided,
• wherein data is written in the portion through the first transistor,
• wherein the data is kept when the first transistor is an off-state,
• wherein a channel formation region of the first transistor includes a first oxide semiconductor layer,
• wherein a channel formation region of the second transistor includes a second oxide semiconductor layer,
• wherein the first oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the first oxide semiconductor layer, and
• wherein the second oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the second oxide semiconductor layer.

A semiconductor device comprising:

• a first transistor and a second transistor,
• wherein a floating gate portion is provided where one of a source and a drain of the second transistor is electrically connected to a gate of the second transistor,
• wherein a channel formation region of the first transistor includes a first oxide semiconductor layer,
• wherein a channel formation region of the second transistor includes a second oxide semiconductor layer,
• wherein the first oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the first oxide semiconductor layer, and
• wherein the second oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the second oxide semiconductor layer.

A semiconductor device comprising:

• a first transistor, a second transistor, and a capacitor element,
• wherein a portion where one of a source and a drain of the second transistor is electrically connected to a gate of the second transistor is provided,
• wherein data is written in the portion through the first transistor,
• wherein the data is kept when the first transistor is an off-state,
• wherein a channel formation region of the first transistor includes a first oxide semiconductor layer,
• wherein a channel formation region of the second transistor includes a second oxide semiconductor layer,
• wherein the first oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the first oxide semiconductor layer,
• wherein the second oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the second oxide semiconductor layer, and
• wherein the capacitor element is electrically connected to the gate of the second transistor.

A semiconductor device comprising:

• a first transistor, a second transistor, and a capacitor element,
• wherein a floating gate portion is provided where one of a source and a drain of the second transistor is electrically connected to a gate of the second transistor,
• wherein a channel formation region of the first transistor includes a first oxide semiconductor layer,
• wherein a channel formation region of the second transistor includes a second oxide semiconductor layer,
• wherein the first oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the first oxide semiconductor layer, wherein the second oxide semiconductor layer includes a crystal whose c-axis is arranged perpendicular to a surface of the second oxide semiconductor layer, and
• wherein the capacitor element is electrically connected to the gate of the second transistor.