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Setup of the in-operando HAXPES measurements. The wire-bonded 0.7 × 0.7 mm2 MIM device (a), mounted on a printed circuit board (b) and (c) and connected via SMA connectors and vacuum feedthroughs to a semiconductor characterization system, can be in-situ studied inside the HAXPES vacuum chamber (d).
DC sweep I-V characteristics of the RS obtained in-situ. Seven cycles were performed with a ROFF/RON ratio of ∼7. The inset shows the current levels for both ON- and OFF-states before and after the HAXPES experiments (a). A double logarithmic plot of the I-V characteristics during the Set process (on the left) and the Reset process (on the right) (b).
Ti 2p HAXPES spectra of the RRAM cell in the virgin- (a), OFF- (b), and ON- (c) states, recorded at an excitation energy of 8 keV. A Shirley background and five spectral components corresponding to the titanium oxidation states between 0 and 4+ are shown.
Normalized and smoothed HAXPES spectra of (a) the Hf 4f doublet and the O 2s line and (b) the O 1s and Hf 4s lines recorded at an excitation energy of 8 keV from the sample in the virgin-, OFF-, and ON-states. A Shirley background was subtracted. The shifts of the Hf 4f 7/2 and O 1s main peaks are highlighted in the insets.
Sketch of the proposed electronic and chemical modifications between the virgin- (a), OFF- (b), and ON- (c) states of the RS in the Ti/HfO2/TiN-based system. The different concentrations of oxygen vacancies (VO ··) at the Ti/HfO2 interface in the OFF- and ON-states give rise to the band bending. The used symbols are defined as: Φ b—the conduction band offset, Φ m—the metal work function, BE—the binding energy, E g—the gap energy, E F—the Fermi level, CB—the conduction band, VB—the valence band, and χ—the electron affinity.
Differences in the concentration Φ of the different oxidation states of the titanium 2p core level between the virgin-, OFF-, and ON-states. The bold values show the main differences between the OFF- and ON-states.
Experimental peak shifts (ΔBEOFF/ON = BEOFF/ON − BEvirgin) between the OFF- or ON-states and the virgin-state, for metallic Ti 2p 3/2 (Ti0), Hf 4f 7/2, and O 1s lines.
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