arXiv subjects

Ruben Hamming-Green

Publications and source records attributed to Ruben Hamming-Green.

4 recordsLinked to original sources

arXiv2026

20 ps Non-Destructive Read and 1 ns Write Operations at <5 V in Ferroelectric HfO2/ZrO2 Non-Volatile Memories

Achieving low-voltage, nanosecond multi-level programming and non-destructive read-out of ferroelectric non-volatile memories (NVM) is critical for analog in-memory computing architectures relying on ferroelectric capacitive devices (FeCap). We integrate HfO2/ZrO2 ferroelectric nanolayers concurrently in the BEOL of CMOS and on SiO2/Si, achieving nanosecond multilevel switching with programming voltages below 5 V. Partial ferroelectric switching enhances FeCap endurance above 1011 cycles, leading to MemCapacitance (MC) states with non-destructive read-out and 10-year retention. However, experiments reveal the collapse of the MC window for read frequencies above 1 MHz. To overcome this speed limit, we introduce a novel, non-destructive readout methodology. Using electrical pulses with widths down to 20 ps, below the RC time constant of the FeCaps, we enable measurement of the polarization-dependent leakage current, providing ultrafast and non-destructive read operations at only 14 fJ.

physics.app-ph↗

arXiv2025

Epitaxial Sr(Sn, Ge)$_{x}$Ti$_{1-x}$O$_{3}$ buffer layers for continuous strain engineering on SrTiO$_{3}$ substrates

Epitaxial strain plays a key role in determining the structure and functionality of thin films, with the choice of substrate being traditionally used to control the magnitude of the applied strain. However, even in the large family of perovskite materials, this allows for only a limited, discrete set of strain states to be achieved. Here we report on an approach to controlling epitaxial strain for the growth of perovskite materials by involving a single SrTiO$_{3}$ substrate (the most available perovskite in single crystal form) and a buffer layer that consists of the solid solution Sr(Sn, Ge)$_{x}$Ti$_{1-x}$O$_{3}$, of which the lattice parameter can be tuned in a continuous fashion, from 3.880 \r{A} up to 4.007 \r{A}, while maintaining coherent epitaxial growth on SrTiO$_{3}$ with high quality interfaces. Using a BaTiO$_{3}$ overlayer as a model system, we show that changes to the buffer layer composition, i.e. increase of in-plane lattice parameter, change the strain state of BaTiO$_{3}$ from fully relaxed, through highly compressively strained, to an exotic state showing 'inverted' epitaxy in which the buffer layer is relaxed from the substrate but lattice matched to the overlayer.

cond-mat.mtrl-sci↗

arXiv2022

Investigating the Electromechanical Behavior of Unconventionally Ferroelectric $Hf_{0.5}Zr_{0.5}O_{2}$-based Capacitors Through Operando Nanobeam X-ray Diffraction

Understanding various aspects of ferroelectricity in hafnia-based nanomaterials is of vital importance for the development of future non-volatile memory and logic devices. Here, the unconventional and weak electromechanical response of epitaxial $La_{0.67}Sr_{0.33}MnO_{3}$/$Hf_{0.5}Zr_{0.5}O_{2}$/$La_{0.67}Sr_{0.33}MnO_{3}$ ferroelectric capacitors is investigated, via the sensitivity offered by nanobeam X-ray diffraction experiments during application of electrical bias. It is shown that the pristine rhombohedral phase exhibits a negative linear piezoelectric effect with piezoelectric coefficient ($d_{33}$) ~ -0.5 to -0.8 pm$V^{-1}$. First-principles calculations support an intrinsic negative piezoresponse. In addition, it is found that the piezoelectric response is suppressed above the coercive voltage. For higher voltages, and with the onset of DC conductivity throughout the capacitor, a second-order effect is observed. The electromechanical response observed in this work is clearly different from that of normal ferroelectrics, again underlining the unconventional nature of polarization switching in the samples.

cond-mat.mtrl-sci↗

arXiv2021

Structural modulation in potassium birnessite single crystals

We report on the growth of single-crystal potassium birnessite (K0.31MnO2*0.41H2O) and present both the average and local structural characterization of this frustrated magnetic system. Single crystals were obtained employing a flux growth method with a KNO3/B2O3 flux at 700 °C. Single-crystal X-ray diffraction revealed an average orthorhombic symmetry, with space group Cmcm. A combination of high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with atomic resolution energy dispersive X-ray spectroscopy (EDS) demonstrated the layered structure of potassium birnessite with manganese-containing planes well separated by layers of potassium atoms. MnO6 octahedra and the K/H2O planes were clearly imaged via integrated differential phase contrast (iDPC) STEM. Furthermore, iDPC-STEM also revealed the existence of local domains with alternating contrast of the manganese oxide planes, most likely originating from charge ordering of Mn3+ and Mn4+ along the c-axis. These charge-ordered domains are clearly correlated with a reduction in the c-lattice parameter compared to the rest of the matrix. The insight gained from this work allows for a better understanding of the correlation between structure and magnetic properties.

cond-mat.mtrl-sci↗