Inhomogeneous chemical states in resistance-switching devices with a planar-type Pt/CuO/Pt structure

Yasuhara, Ryo; Fujiwara, K.; Horiba, Koji; Kumigashira, Hiroshi; Kotsugi, Masato; Oshima, Masaharu; Takagi, H.

doi:10.1063/1.3175720

Cited by 98 publications

(70 citation statements)

References 12 publications

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“…Filaments in some reports have been observed by means of scanning electron microscopy before and after voltage has been applied. 9,11,26 While a single bridge-like path has been confirmed, detailed investigations into what is inside the bridge are necessary. In addition, real-time observations on the formation of filaments would be very helpful in allowing the switching mechanism to be better understood.…”

Section: Introductionmentioning

confidence: 99%

Analysis of resistance switching and conductive filaments inside Cu-Ge-S using in situ transmission electron microscopy

et al. 2012

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In situ transmission electron microscopy (TEM) was carried out to investigate the dynamics of resistance switching in a solid electrolyte, Cu-Ge-S. By applying voltage to Pt-Ir/Cu-Ge-S/Pt-Ir, where Pt-Ir constituted the electrodes, a deposit containing conductive filaments composed mainly of Cu was formed around the cathode. As voltage continued to be applied, the deposit grew and finally narrow conductive filaments made contact with the anode. This corresponded to resistance switching from high-to low-resistance states (HRS and LRS). By alternating the voltage, the deposit contracted toward the cathode and detached from the anode. The resistance immediately changed from LRS to HRS. By applying voltage, the deposit containing Cu-based filaments grew and shrank, and resistance switching occurred at the electrolyte-anode interface. This conductive filament-formation model, which was recently reported, was experimentally confirmed with TEM through dynamic observations of the deposit-containing filaments.

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Section: Introductionmentioning

confidence: 99%

Analysis of resistance switching and conductive filaments inside Cu-Ge-S using in situ transmission electron microscopy

et al. 2012

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“…Recently, conductive filament, which is formed in not only cation-type but also in aniontype electrolytes, was observed by scanning electron microscopy ͑SEM͒. 5,15,16 However, no detailed experimental results to confirm the existence of the filament during the switching process have been reported. Therefore, in situ transmission electron microscopy ͑TEM͒ with simultaneous electrical measurements has attracted a great deal of attention.…”

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confidence: 99%

In situ transmission electron microscopy analysis of conductive filament during solid electrolyte resistance switching

Fujii¹,

Arita²,

Takahashi³

et al. 2011

Applied Physics Letters

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An in situ transmission electron microscopy ͑TEM͒ analysis of a solid electrolyte, Cu-GeS, during resistance switching is reported. Real-time observations of the filament formation and disappearance process were performed in the TEM instrument and the conductive-filament-formation model was confirmed experimentally. Narrow conductive filaments were formed corresponding to resistance switching from high-to low-resistance states. When the resistance changed to high-resistance state, the filament disappeared. It was also confirmed by use of selected area diffractometry and energy-dispersive x-ray spectroscopy that the conductive filament was made of nanocrystals composed mainly of Cu. Cu-SiO 2 , 12 and bilayer-types. 13,14 The mechanism of resistance switching is attributed to the formation and disappearance of the conductive filament in the solid electrolyte. When a bias voltage is applied, the ions generated at the anode are thought to migrate toward the cathode where they undergo reduction and become metal atoms. 8 Contrarily, an opposite bias voltage dissolves the metal composing filaments into the solid electrolyte.11 Therefore, an analysis of the conductive filament must provide important information for understanding this switching mechanism. Recently, conductive filament, which is formed in not only cation-type but also in aniontype electrolytes, was observed by scanning electron microscopy ͑SEM͒. 5,15,16 However, no detailed experimental results to confirm the existence of the filament during the switching process have been reported. Therefore, in situ transmission electron microscopy ͑TEM͒ with simultaneous electrical measurements has attracted a great deal of attention. 10,[17][18][19][20][21] In this letter, we use this in situ TEM method to reveal the switching mechanism of a solid electrolyte. Real-time observations of the filament formation and disappearance process were performed with the TEM instrument. We also clarified the structure and composition of the filament by the use of selected area diffractometry ͑SAD͒ and energydispersive x-ray spectroscopy ͑EDX͒.For the in situ TEM experiments, 21 commercially available Pt-Ir tips for scanning tunneling microscopy were further sharpened by ion milling. One Pt-Ir tip was used as the substrate and the other was used as a counter electrode. CuGeS thin films were deposited at room temperature by rf sputtering on Pt-Ir substrate. Since the substrate and the counter electrode of Pt-Ir were different in shape, the structure of Pt-Ir/Cu-GeS/Pt-Ir was asymmetric. The atomic composition of the sample layer was analyzed by means of EDX. The proportion of Cu:Ge:S was 4:4:2. The film thickness was between 8 and 60 nm, and no remarkable difference depending on thickness was recognized. The system was composed of a custom-made TEM holder with a PCcontrolled operating system. [21][22][23] The TEM instrument used mainly was a JEM-2010 microscope ͑200 kV, C s = 0.5 mm͒, having a vacuum of about 10 −5 Pa. The conduction properties were measured between the Pt-Ir counter...

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“…18 The oxygen in NiO might continually disperse into the vacuum as has been suggested by earlier work. 9,19 Based on this assumption, the filament is hardly ruptured by oxidation in TEM. This may be why the filament could not be reset in the present work.…”

Section: Resultsmentioning

confidence: 96%

I-V measurement of NiO nanoregion during observation by transmission electron microscopy

Fujii

Arita

Hamada

et al. 2011

Journal of Applied Physics

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Conduction measurements with simultaneous observations by transmission electron microscopy (TEM) were performed on a thin NiO film, which is a candidate material for resistance random access memories (ReRAMs). To conduct nanoscale experiments, a piezo-controlled TEM holder was used, where a fixed NiO sample and a movable Pt-Ir counter electrode were placed. After the counter electrode was moved to make contact with NiO, I-V measurements were carried out from any selected nanoregions. By applying a voltage of 2 V, the insulating NiO film was converted to a low resistance film. This phenomenon may be the "forming process" required to initialize ReRAMs. The corresponding TEM image indicated a structural change in the NiO layer generating a conductive bridge with a width of 30-40 nm. This finding supports the "breakdown" type forming in the so-called "filament model" of operation by ReRAMs. The inhomogeneity of resistance in the NiO film was also investigated.

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Inhomogeneous chemical states in resistance-switching devices with a planar-type Pt/CuO/Pt structure

Cited by 98 publications

References 12 publications

Analysis of resistance switching and conductive filaments inside Cu-Ge-S using in situ transmission electron microscopy

Analysis of resistance switching and conductive filaments inside Cu-Ge-S using in situ transmission electron microscopy

In situ transmission electron microscopy analysis of conductive filament during solid electrolyte resistance switching

I-V measurement of NiO nanoregion during observation by transmission electron microscopy

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