The researchers have developed a technique to study oxygen vacancy states in a resistive random access memory (ReRAM) without damaging the memory functions. They revealed the behavior of oxygen vacancies in a low resistance state (LRS) and a high resistance state (HRS) during conventional and ultra-low power operation modes.

Analyzed results of EBAC (electron beam absorbed current) images and the noise measurement data of ReRAM

An identical device can be used to investigate both conventional and low-power operation modes, making it possible to compare the oxygen vacancy states under different conditions. Only in HRS during the low-power operation, the frequency dependence of the current noise shows that a small number of oxygen vacancies are present. Even for LRS of the low-power operation, there remain a sufficient number of oxygen vacancies. Therefore, the researchers have concluded that the reduction of oxygen vacancies which contribute to electrical conduction is required to further reduce the power consumption of ReRAMs.

ReRAM is a promising memory device which shows fast switching with the low power consumption. Oxygen vacancies in an oxide layer are known to be involved in the operation of transition metal oxide-based ReRAMs. The widely used analysis method of oxygen vacancies is an electron microscope. However, due to the necessity of processing samples for the observation by the electron microscope, it has been difficult to investigate a small number of oxygen vacancies without damage to the memory functions. To achieve ultra-low power consumption in ReRAMs, as well as to improve their reliability and optimize the fabrication process, a technique that enables investigation of the effect of oxygen vacancies during different operations has been desired.

In AIST’s applied research on ReRAMs, it is necessary to precisely control the arrangement and diffusion of oxygen vacancies. AIST will apply the developed technique to achieve this.