Patent ID: 7719082

Claim:
A memory device comprising: a first electrode; a second electrode; a memory thin film sandwiched between said first and second electrodes; and a layer in contact with said memory thin film, said layer being formed on the first electrode, wherein said memory thin film includes an oxide material including at least a rare earth element, said layer in contact with said memory thin film includes any one of the elements selected from Cu, Ag and Zn, said layer in contact with said memory thin film further includes any one of the elements selected from Te, S and Se, a first state is recordable in the memory device by applying a first voltage or a first current pulse between the first electrode and the second electrode to form a conduction path containing at least one of said elements selected from Cu, Ag and Zn in the memory thin film and changing an impedance of said memory thin film, a second state is recordable in the memory device by applying a second voltage or a second current pulse opposite in polarity to the first voltage or the first current pulse between the first electrode and the second electrode to eliminate the conduction path formed in the memory thin film and changing the impedance of said memory thin film, and said memory thin film has a composition gradient such that the concentration of the rare earth element decreases in a direction proceeding toward the first electrode.