Bistable resistance switching in surface-oxidized C12A7:e− single-crystal

12CaO·7Al2O3 (C12A7) is a typical band insulator, but may be converted to a metallic conductor C12A7:e− by electron-doping via removal of free oxygen ions sitting in the subnanometer-sized cages as the counter ions. Also, C12A7 is known as a fast oxygen ion conductor. These unique features let us expect that it would be possible to dope electrons to C12A7 by removing the free oxygen ions by an external electric field. In this study, we fabricated C12A7/C12A7:e− stacking devices and examined their current–voltage characteristics. The thickness of the top C12A7 layer was controlled by low-temperature oxidation with an aid of an optical model analysis of spectroscopic ellipsometry. We found that the C12A7/C12A7:e− devices exhibited a bistable resistance switching effect with an on-to-off resistance ratio of ∼102 and operated as a resistive random access memory.