Key Takeaways & Executive Findings
- •• • Achieved resistive switching on/off ratio of 8.4 × 10^4 in Lu-doped Hf0.4Zr0.6O2 (LHZO) thin films, two orders of magnitude higher than ZrO2 (1.2 × 10^3), enabling more reliable read operations in memory arrays. • • Bandgap widened to 4.95 eV via Lu doping, suppressing off-state leakage current by reducing p-type conductivity, critical for lowering power consumption in high-resistance state. • • Lu3+ doping enriches oxygen vacancies, stabilizing ohmic conductive filaments in low-resistance state, ensuring consistent on-state conductivity and device uniformity. • • Retention exceeds 10^4 s, demonstrating non-volatile memory stability suitable for long-term data storage applications.
Abstract
Fluorite-structured oxides (HfO2, ZrO2) are promising for resistive random-access memory (RRAM) due to their scalability and tunable properties. However, achieving high resistive switching on/off ratios remains challenging. Here, we report a collaborative strategy combining Hf/Zr ratio optimization and Lu3+ doping to regulate band structure and oxygen vacancy concentration in Hf0.4Zr0.6O2 (LHZO) thin films. The resulting LHZO devices exhibit a resistive switching ratio of 8.4 × 10^4, two orders of magnitude higher than that of ZrO2 (1.2 × 10^3). Electrical characterization and synchrotron radiation photoemission spectroscopy reveal that Lu doping widens the bandgap to 4.95 eV, downshifts the valence band, and introduces defect states, collectively suppressing p-type conductivity and reducing off-state leakage current. Simultaneously, Lu3+ doping enriches oxygen vacancies, stabilizing ohmic conductive filaments in the on-state. This co-optimization of band structure and oxygen vacancies effectively enhances insulating properties in the high-resistance state and ohmic conductivity in the low-resistance state, leading to superior resistive switching performance with robust retention (>10^4 s). Our findings establish a fundamental strategy for tailoring electronic properties of doped HfZrO2 thin films toward high-performance RRAM applications.
1. Introduction
Resistive random-access memory (RRAM) is a leading candidate for next-generation nonvolatile memory, but existing metal oxide systems face trade-offs. TaOx offers exceptional endurance (>10^12 cycles) yet suffers from low on/off ratio (~10), causing read errors. WO3-based nanocomposites achieve stable ratios but are not scalable due to their vertical dimensions. Fluorite-structured oxides like HfO2 and ZrO2 are attractive for their CMOS compatibility and wide bandgap, yet HfO2 suffers from limited oxygen vacancy mobility, while ZrO2 exhibits high leakage currents, restricting memory windows.
This work addresses these bottlenecks by co-optimizing the Hf/Zr ratio and Lu3+ doping in Hf0.4Zr0.6O2 thin films. The strategy simultaneously widens the bandgap to suppress leakage and increases oxygen vacancy concentration to stabilize conductive filaments, achieving a record on/off ratio of 8.4 × 10^4. This dual approach provides a pathway to high-performance RRAM with improved read accuracy and scalability.
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LI Jiaqi, LI Qiang, WANG Hongwei, YU Xiaoxia, TU Jie, LEI Yu, LI Zhiguo, WU Han, MIAO Jun, ZHANG Linxing, XING Xianran (2026). High Resistive Switching On/Off Ratio in Lu-Doped Hf0.4Zr0.6O2 Thin Films via Band Structure and Oxygen Vacancy Co-Strategy. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4235-6
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Frequently Asked Questions
What is the endurance of the LHZO devices under repeated switching cycles?
The paper does not specify endurance cycling data; it focuses on the on/off ratio and retention. However, the stable ohmic filament formation suggests potential for reliable cycling, but further testing is required to quantify endurance.
How does the on/off ratio of 8.4 × 10^4 compare to state-of-the-art HfO2-based RRAM devices?
The achieved ratio is two orders of magnitude higher than ZrO2 (1.2 × 10^3) and significantly exceeds typical HfO2 devices, which often exhibit ratios below 10^3. This improvement is attributed to the synergistic band structure and vacancy engineering.
What is the operating voltage range for the LHZO devices?
The paper does not explicitly report operating voltages. However, the enhanced insulating properties in the high-resistance state may allow for lower forming voltages, but specific values are not provided.
Are the LHZO films compatible with CMOS back-end-of-line (BEOL) processing?
HfZrO2 materials are known for CMOS compatibility. The deposition method is not detailed, but typical atomic layer deposition or sputtering can be integrated. The Lu doping may require additional precursor development, but no fundamental incompatibility is indicated.
What is the physical mechanism behind the improved on/off ratio?
Lu doping widens the bandgap (to 4.95 eV) and downshifts the valence band, reducing p-type leakage in the high-resistance state. Simultaneously, it increases oxygen vacancy concentration, which stabilizes conductive filaments in the low-resistance state, enhancing the contrast between states.
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