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Tracking oxygen vacancy migration in memristor devices using operando hard X-ray photoelectron spectroscopy
F Capocasa1, A K Rumaiz2, C Weiland3
1Instrumentation Department, Brookhaven National Laboratory, Upton, NY, 11973, USA.
Scientific Reports
|December 2, 2025
Summary
Ultrathin oxide semiconductor memristors were precisely fabricated using atomic layer deposition. Operando Hard X-ray PhotoElectron Spectroscopy revealed oxygen vacancy redistribution during switching, crucial for memristor function.
Area of Science:
- Materials Science
- Solid State Physics
- Nanotechnology
Background:
- Fabricating ultrathin (sub-2 nm) oxide semiconductor memristors requires atomic precision in oxide growth, electronic structure, and defect control.
- Atomic layer deposition (ALD) enables precise fabrication of ultrathin memristors using bilayers of mixed HfO2 and MgO atomic layers.
- Oxygen vacancies are key to memristor functionality, and their control is achieved by strategically placing MgO layers within HfO2.
Purpose of the Study:
- To systematically investigate the switching behavior of ultrathin HfO2/MgO memristors using operando Hard X-ray PhotoElectron Spectroscopy (HAXPES).
- To correlate electronic structure changes with device performance using complementary current-voltage (I-V) and capacitance-voltage (C-V) measurements.
- To understand the role of oxygen vacancies in the switching dynamics and potential retention mechanisms.
Main Methods:
- Fabrication of ultrathin memristor stacks (HfO2/MgO) via in vacuo atomic layer deposition.
- Operando HAXPES to probe chemical states and oxygen vacancy distribution during device switching.
- Complementary I-V and C-V measurements to characterize electrical performance and frequency dependence.
Main Results:
- HAXPES revealed significant chemical shifts in aluminum oxide during switching, indicating oxygen vacancy redistribution within the active layer.
- Hysteresis observed during OFF-state switching suggests retention of oxygen vacancies in the top HfO2 layer.
- C-V measurements showed frequency-dependent responses in the OFF state, consistent with polarization and vacancy trapping at low frequencies.
Conclusions:
- The study demonstrates precise atomic control over oxygen vacancies in ultrathin HfO2/MgO memristors using ALD.
- Operando HAXPES provides direct evidence of oxygen vacancy redistribution driving memristor switching.
- Vacancy retention and stochastic switching behavior are linked, offering insights into memristor reliability and future design.
