Patent ID: 8830661

Claim:
A portable electronic device comprising: a display portion including a first transistor, a channel region of the first transistor comprising a first oxide semiconductor; a power source portion comprising a rechargeable battery capable of charge by contactless charge; and a signal processing portion comprising a semiconductor memory device, the semiconductor memory device comprising: a second transistor, a channel region of the second transistor comprising crystalline silicon; a third transistor, a channel region of the third transistor comprising a second oxide semiconductor; a capacitor; a source line; a bit line; a first signal line; a second signal line; and a word line, wherein a gate of the second transistor is electrically connected to one of a source and a drain of the third transistor, a source of the second transistor is electrically connected to the source line, and a drain of the second transistor is electrically connected to the bit line, wherein a gate of the third transistor is electrically connected to the second signal line, the one of the source and the drain of the third transistor is electrically connected to a first electrode of the capacitor, and the other of the source and the drain of the third transistor is electrically connected to the first signal line, and wherein the second oxide semiconductor in the channel region of the third transistor has an off-state current of lower than or equal to 1 aA/μm.