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Deterministic conversion between memory and threshold resistive switching via tuning the strong electron correlation.

Peng HY, Li YF, Lin WN, Wang YZ, Gao XY, Wu T - Sci Rep (2012)

Bottom Line: Intensive investigations have been launched worldwide on the resistive switching (RS) phenomena in transition metal oxides due to both fascinating science and potential applications in next generation nonvolatile resistive random access memory (RRAM) devices.It is noteworthy that most of these oxides are strongly correlated electron systems, and their electronic properties are critically affected by the electron-electron interactions.Moreover, from first-principles calculations and x-ray absorption spectroscopy studies, we found that the strong electron correlations and the exchange interactions between Ni and O orbitals play deterministic roles in the RS operations.

View Article: PubMed Central - PubMed

Affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore.

ABSTRACT
Intensive investigations have been launched worldwide on the resistive switching (RS) phenomena in transition metal oxides due to both fascinating science and potential applications in next generation nonvolatile resistive random access memory (RRAM) devices. It is noteworthy that most of these oxides are strongly correlated electron systems, and their electronic properties are critically affected by the electron-electron interactions. Here, using NiO as an example, we show that rationally adjusting the stoichiometry and the associated defect characteristics enables controlled room temperature conversions between two distinct RS modes, i.e., nonvolatile memory switching and volatile threshold switching, within a single device. Moreover, from first-principles calculations and x-ray absorption spectroscopy studies, we found that the strong electron correlations and the exchange interactions between Ni and O orbitals play deterministic roles in the RS operations.

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X-ray absorption spectra of NiO.Oxygen K-edge (left) and Ni L-edge (right) XAS spectra for NiO prepared in different oxygen ambient, namely 0.01 Pa (black line) and 30 Pa (red line). The inset highlights the onset of peak A in the sample grown at the higher oxygen pressure.
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f5: X-ray absorption spectra of NiO.Oxygen K-edge (left) and Ni L-edge (right) XAS spectra for NiO prepared in different oxygen ambient, namely 0.01 Pa (black line) and 30 Pa (red line). The inset highlights the onset of peak A in the sample grown at the higher oxygen pressure.

Mentions: To confirm the theoretical result that the Ni-deficient NiO is a negative-charge-transfer insulator, we performed the x-ray absorption spectroscopy (XAS) measurements on NiO samples prepared at two different oxygen pressures. Our compositional analysis indicated that the growth pressure is effective in tuning the stoichiometry of the NiO films; an oxygen pressure of 0.01 Pa results in the stoichiometric composition, while various degrees of Ni deficiency was detected in samples grown at high oxygen pressures. As shown in Figure 5, for both samples, peak B at 530.5 eV in the O K-edge spectra corresponds to the transition from the O 1s level to the states with O 2p character in the upper Hubbard band43. The peaks C and D can be assigned to the Ni 4p bands44. Notably, for the Ni-deficient NiO film grown at the higher oxygen pressure, a new peak A centered at 527.3 eV was observed (inset of Fig. 5), which can be attributed to the transition from O 1s to the nickel vacancies induced O 2p states right above the Fermi level4445. This is consistent with the calculated result that this high-pressure NiO sample is a negative-charge-transfer insulator. At the Ni L-edge, the peaks E and F can be assigned to Ni 2p3/2 and Ni 2p1/2 to Ni 3d transitions, respectively46. In addition, the absence of any shift in peaks E and F at the Ni L-edge suggests that the nickel-deficiency-induced holes have more O 2p character than Ni 3d character4347, which is consistent with the result of our first-principles calculations (Fig. 4b).


Deterministic conversion between memory and threshold resistive switching via tuning the strong electron correlation.

Peng HY, Li YF, Lin WN, Wang YZ, Gao XY, Wu T - Sci Rep (2012)

X-ray absorption spectra of NiO.Oxygen K-edge (left) and Ni L-edge (right) XAS spectra for NiO prepared in different oxygen ambient, namely 0.01 Pa (black line) and 30 Pa (red line). The inset highlights the onset of peak A in the sample grown at the higher oxygen pressure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3369197&req=5

f5: X-ray absorption spectra of NiO.Oxygen K-edge (left) and Ni L-edge (right) XAS spectra for NiO prepared in different oxygen ambient, namely 0.01 Pa (black line) and 30 Pa (red line). The inset highlights the onset of peak A in the sample grown at the higher oxygen pressure.
Mentions: To confirm the theoretical result that the Ni-deficient NiO is a negative-charge-transfer insulator, we performed the x-ray absorption spectroscopy (XAS) measurements on NiO samples prepared at two different oxygen pressures. Our compositional analysis indicated that the growth pressure is effective in tuning the stoichiometry of the NiO films; an oxygen pressure of 0.01 Pa results in the stoichiometric composition, while various degrees of Ni deficiency was detected in samples grown at high oxygen pressures. As shown in Figure 5, for both samples, peak B at 530.5 eV in the O K-edge spectra corresponds to the transition from the O 1s level to the states with O 2p character in the upper Hubbard band43. The peaks C and D can be assigned to the Ni 4p bands44. Notably, for the Ni-deficient NiO film grown at the higher oxygen pressure, a new peak A centered at 527.3 eV was observed (inset of Fig. 5), which can be attributed to the transition from O 1s to the nickel vacancies induced O 2p states right above the Fermi level4445. This is consistent with the calculated result that this high-pressure NiO sample is a negative-charge-transfer insulator. At the Ni L-edge, the peaks E and F can be assigned to Ni 2p3/2 and Ni 2p1/2 to Ni 3d transitions, respectively46. In addition, the absence of any shift in peaks E and F at the Ni L-edge suggests that the nickel-deficiency-induced holes have more O 2p character than Ni 3d character4347, which is consistent with the result of our first-principles calculations (Fig. 4b).

Bottom Line: Intensive investigations have been launched worldwide on the resistive switching (RS) phenomena in transition metal oxides due to both fascinating science and potential applications in next generation nonvolatile resistive random access memory (RRAM) devices.It is noteworthy that most of these oxides are strongly correlated electron systems, and their electronic properties are critically affected by the electron-electron interactions.Moreover, from first-principles calculations and x-ray absorption spectroscopy studies, we found that the strong electron correlations and the exchange interactions between Ni and O orbitals play deterministic roles in the RS operations.

View Article: PubMed Central - PubMed

Affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore.

ABSTRACT
Intensive investigations have been launched worldwide on the resistive switching (RS) phenomena in transition metal oxides due to both fascinating science and potential applications in next generation nonvolatile resistive random access memory (RRAM) devices. It is noteworthy that most of these oxides are strongly correlated electron systems, and their electronic properties are critically affected by the electron-electron interactions. Here, using NiO as an example, we show that rationally adjusting the stoichiometry and the associated defect characteristics enables controlled room temperature conversions between two distinct RS modes, i.e., nonvolatile memory switching and volatile threshold switching, within a single device. Moreover, from first-principles calculations and x-ray absorption spectroscopy studies, we found that the strong electron correlations and the exchange interactions between Ni and O orbitals play deterministic roles in the RS operations.

Show MeSH