Ferroelectronics Lab

Understanding and utilizing non-volatile properties of materials

New Publication! “Conductive filament formation in the failure of Hf0.5Zr0.5O2 ferroelectric capacitors” 

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Abstract: Ferroelectric materials provide pathways to higher performance logic and memory technologies, with Hf0.5Zr0.5O2 being the most popular among them. However, critical challenges exist in understanding the material’s failure mechanisms to design long endurance lifetimes. In this work, dielectric failure due to repeated switching cycles, occurring through oxygen vacancy motion and leading to the formation of a conductive filament, is demonstrated. A field modified hopping barrier of ∼150–400 meV is observed, indicating a vacancy charge of 0.4–0.6e markedly different from the charge states predicted in the literature. After failure, the capacitor leakage current is high (∼25 mA) and constant with capacitor area, consistent with filament formation. Conductive atomic force microscopy measurements and field distribution simulations suggest a local failure mechanism consistent with filament formation along the boundary of the island capacitor due to an enhanced electric field.

Full text available at APL Materials

Matt defends his PhD dissertation! Congratulations Matt!

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On December 9th, Matt gave a great defense of his PhD dissertation, titled “Analysis of Phase Stability and Defect Mobility in Functional Oxides Exposed to Extreme Conditions“. In completing his work at the University of Michigan, he has accepted a position at Micron Technology. Excellent job! The Ferroelectronics Lab wishes you the very best luck in your future work!

New Publication! ” Local structure maturation in high entropy oxide (Mg,Co,Ni,Cu,Zn)1-x(Cr,Mn)xO thin films”

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Abstract: High entropy oxides (HEOs) have garnered much interest due to their available high degree of tunability. Here, we study the local structure of (MgNiCuCoZn)0.167(MnCr)0.083O, a composition based on the parent HEO (MgNiCuCoZn)0.2O. We synthesized a series of thin films via pulsed laser deposition at incremental oxygen partial pressures. X-ray diffraction shows lattice parameters to decrease with increased pO2 pressures until the onset of phase separation. X-ray absorption fine structure shows that specific atomic species in the composition dictate the global structure of the material as Cr, Co, and Mn shift to energetically favorable coordination with increasing pressure. Transmission electron microscopy analysis on a lower-pressure sample exhibits a rock salt structure, but the higher-pressure sample reveals reflections reminiscent of the spinel structure. In all, these findings give a more complete picture of how (MgNiCuCoZn)0.167(MnCr)0.083O forms with varying initial conditions and advances fundamental knowledge of cation behavior in high entropy oxides.

Full text available at The Journal of the American Ceramic Society

New Publication! “Thermodynamic Origins of Nonvolatility in Resistive Memory”

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Abstract: Electronic switches based on the migration of high-density point defects, or memristors, are poised to revolutionize post-digital electronics. Despite significant research, key mechanisms for filament formation and oxygen transport remain unresolved, hindering our ability to predict and design device properties. For example, experiments have achieved 10 orders of magnitude longer retention times than predicted by current models. Here, using electrical measurements, scanning probe microscopy, and first-principles calculations on tantalum oxide memristors, we reveal that the formation and stability of conductive filaments crucially depend on the thermodynamic stability of the amorphous oxygen-rich and oxygen-poor compounds, which undergo composition phase separation. Including the previously neglected effects of this amorphous phase separation reconciles unexplained discrepancies in retention and enables predictive design of key performance indicators such as retention stability. This result emphasizes non-ideal thermodynamic interactions as key design criteria in post-digital devices with defect densities substantially exceeding those of today’s covalent semiconductors.

Full text available from Matter

New Publication! “Perspective: Entropy-Stabilized Oxide Memristors”

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Abstract: A memristor array has emerged as a potential computing hardware for artificial intelligence (AI). It has an inherent memory effect that allows information storage in the form of easily programmable electrical conductance, making it suitable for efficient data processing without shuttling of data between the processor and memory. To realize its full potential for AI applications, fine-tuning of internal device dynamics is required to implement a network system that employs dynamic functions. Here, we provide a perspective on multicationic entropy-stabilized oxides as a widely tunable materials system for memristor applications. We highlight the potential for efficient data processing in machine learning tasks enabled by the implementation of “task specific” neural networks that derive from this material tunability.

Full text available from Applied Physics Letters

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Our research is at the intersection of multiple disciplines, drawing on principles and methodologies from materials science, chemistry, physics, and electrical engineering. Our mission is to pioneer … Read More

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Ferroelectronics Lab
Address: 2030 H.H. Dow

T: (734) 763-6914
E: jtheron@umich.edu