Patent ID: 8891286

Claim:
A semiconductor device comprising: a substrate including a semiconductor material; a first flip-flop on the substrate, wherein the first flip-flop comprises a first transistor, and wherein a first channel formation region of the first transistor is formed in the substrate; and a second flip-flop over the first flip-flop, wherein the second flip-flop comprises a memory circuit, wherein the memory circuit comprises a second transistor, and wherein a second channel formation region of the second transistor comprises an oxide semiconductor, wherein in an operating state in which power is supplied to the first flip-flop and the second flip-flop, the first flip-flop retains data, wherein in a resting state in which supply of power to the first flip-flop and the second flip-flop is stopped, the second flip-flop retains data, wherein on transition from the operating state into the resting state, the data is transferred from the first flip-flop to the second flip-flop, and wherein on transition from the resting state into the operating state, the data is transferred from the second flip-flop to the first flip-flop.