Conduction band caused by oxygen vacancies in aluminum oxide for resistance random access memory

As a next-generation memory, we have developed a rare-metal-free memory using Al oxide with
a high-density of oxygen vacancies (Vos). The electronic structure has been simulated using
first-principles calculations. In this paper, we report the electronic structure of the band gap,
analyzed using thermally stimulated current measurements, to evaluate the simulated results. We
observed electronic states corresponding to resistance changes for the first time. These results show that Vo þ2 (electron empty Vo) changes to Vo
þ1 by electron injection; the overlapped Vo þ1 electron changes into a “Vo conduction band” (VoCB), and the changed structure is stabilized by structural relaxation of Al ions around Vo. VoCB is considered as a kind of mid-gap impurity band. The
origin of the on/off switching is considered to be generation/degeneration of the VoCB caused by
increasing/decreasing numbers of Vo electrons. Based on knowledge of the electronic mechanism,
we have changed metal/insulator/metal structure to a metal/insulator/semiconductor structure and
decreased the reset-current to 7 lA. The Vos of Al oxide are considered to be useful for electronic
memory storage.