Abstract
“Forming” is a stage in resistive switching (RS) devices that occurs before switching and represents an important physical phenomenon in the universal operating mechanism of such devices. Forming in a resistance change material appears to be a kind of dielectric breakdown. In this study, we performed time-dependent forming (TDF) characterization of Pt/TiO2/Pt resistive switching cells with TiO2 layers of different crystallinities and oxygen compositions. We prepared two samples in which the grain boundary density and the density of oxygen vacancies differ, while both the TiO2 layers exhibited the similar crystal structures. Our results reveal that the Weibull slope and variation of time to forming are determined by the deposition method of the Pt bottom electrode (BE) films. Moreover, the initial cell resistance and distribution of the TDF characteristics depend not only on the crystallinity but also on the oxygen composition of the TiO2 layers. The variation of time to forming increases as the distribution of initial resistance is reduced in Pt/NiO/Pt resistive switching cells with different NiO crystallinities. Conversely, the variation of time to forming decreases as the distribution of the initial resistance is reduced in the case of the Pt/TiO2/Pt cells. These results reflect differences in both the grain boundary density (crystallinity) and the density of oxygen vacancies (oxygen composition) of resistance change materials used in the resistive switching cells. The clear difference of crystallinities and oxygen compositions might originate from differences in the oxide deposition mode during reactive sputtering.
Highlights
In recent years, resistive random access memories (ReRAMs)[1,2,3] have attracted attention as a candidate for next-generation nonvolatile memory devices
ReRAM can be integrated with current technologies owing to its simple structure featuring a transition metal oxide (TMO) as the resistance change material sandwiched between two metallic electrodes
The in-plane X-ray diffraction (XRD) measurements showed that the SP-Pt sample contained Pt top electrodes (TEs) layers and additional peaks derived from the polycrystalline Pt TE layers with an
Summary
Resistive random access memories (ReRAMs)[1,2,3] have attracted attention as a candidate for next-generation nonvolatile memory devices. ReRAM can be integrated with current technologies owing to its simple structure featuring a transition metal oxide (TMO) as the resistance change material sandwiched between two metallic electrodes. Various resistance change materials have been reported in binary-TMO devices, such as NiO,[4,5,6,7] TiO2,8–10 Ta2O5,11–13 and HfO2.14–16 ReRAM has attractive features, such as fast operation, low power consumption, and compatibility with complementary metal-oxide semiconductor devices. Resistive switching (RS) phenomenon in binary-TMO-based ReRAM has been intensively investigated, and a filament model is widely accepted to explain this phenomenon.[18] According to this model, forming is considered to be a stage during which a conductive filament forms by a kind of dielectric breakdown of a pristine cell under electric stress. Forming is a crucial process for elucidating the universal mechanism of RS phenomenon, the filament model is only qualitative and it remains unclear where the conductive filament is created
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