Ferroelectronics Lab

Understanding and utilizing non-volatile properties of materials

New Publication! “Signatures of quantum spin liquid state and unconventional transport in thin film TbInO3”

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Abstract: Quantum spin liquids, where the frustrated magnetic ground state hosts highly entangled spins resisting long-range order to 0 K, are exotic quantum magnets proximate to unconventional superconductivity and candidate platforms for topological quantum computing. Although several quantum spin liquid material candidates have been identified, thin films crucial for device fabrication and further tuning of properties remain elusive. Recently, hexagonal TbInO3 has emerged as a quantum spin liquid candidate which also hosts improper ferroelectricity and exotic high-temperature carrier transport. Here, we synthesize thin films of TbInO3 and characterize their magnetic and electronic properties. Our films present a highly frustrated magnetic ground state without long-range order to 0.4 K, consistent with bulk crystals. We further reveal a rich ferroelectric domain structure and unconventional non-local transport near room temperature, suggesting hexagonal TbInO3 as a promising candidate for realizing exotic magnetic and transport phenomena in epitaxial heterostructures.

Read more at Nature Communications

Tony Chiang Defends His Thesis, Earning a PhD! Congratulations Tony!

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Tony gave his defence today, 8/19/25, on the ““Polarization Evolution Behavior in
Scaled Ferroelectric Capacitors.” Here, he discussed his research which involved the development of ferroelectric capacitors down to 100 nm in lateral dimention. Using these capacitors, he explored three ferroelectric materials to identify their switching kinetics and limits. Here, he identified a circuit limited and material limited behavior regime differentiated by lateral dimention, the latter which is useful for accurately isolating materials properties. He also establishes a criteria for identifying this regime.

Congratulations Tony, great work!

New Publication! Sub-100 Ω/□ sheet resistance of GaN HEMT with ScAlN barrier

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Abstract: A low sheet resistance of 95.5 Ω/□ at room temperature has been demonstrated in an MBE-grown Sc0.15Al0.85N/AlN/GaN epitaxial HEMT structure. Owing to the strong spontaneous and piezoelectric polarization of ScAlN, a large two-dimensional electron gas density of 7.8 × 1013 cm−2 and a relatively high mobility of 836 cm2/V·s were demonstrated with a 15 nm Sc0.15Al0.85N barrier. Further investigation under low temperature on this structure reveals a reduced sheet resistance to 33.3 Ω/□ and mobility increased to 4223 cm2/V·s at 10 K. The dependence of sheet carrier density, mobility, and the associated sheet resistance on ScAlN thickness was further studied. The compelling electron transport properties demonstrated in the structure position ScAlN as a strong contender as the barrier layer in future GaN HEMT devices.

Read more at Applied Physics Letters

Intel Awards John T. Heron and lab with Outstanding Researcher Award!

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Once a year, Intel presents an award acknowledging work that makes “a significant impact on future technology” and “celebrates exceptional achievements made through Intel sponcered research.” John T. Heron is among the 10 researchers who have recieved this distinguished award.

“The research team demonstrated ultrafast switching of La-doped BiFeO3 ferroelectric capacitors, developed novel metrologies to measure polarization dynamics at nanoscale, demonstrated modeling frameworks to understand the effect of key physical processes such as domain nucleation, growth, and circuit limits on the switching process, and determined a new regime of energy-delay scaling behavior relevant for computing technologies. Furthermore, the researchers developed novel materials critical for accelerating magneto-electric spin-orbit (MESO) device development to deliver target specifications, such as high entropy perovskite oxides with large spin Hall efficiency and resistivity as well as double perovskite ferromagnet layers epitaxially compatible with La-doped BiFeO3.”

Congratulations to both John and the remainder of the research team who supported this achievement! Read more on Intel’s website if you are interested about this achievement.

New Publication! “Investigating Vibrational Modes in High Entropy Oxides using Electron Energy Loss Spectroscopy”

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Abstract: The quest for novel materials with enhanced properties is ongoing. High entropy oxides (HEOs) have transformed material design by providing a vast compositional space and remarkable property tunability. These are multicomponent systems that consist of five or more cations randomly distributed within a solid solution. Since their discovery in 2015, HEOs have garnered significant attention for their potential applications such as ionic conductors, magnetic materials, ferroelectrics, thermoelectrics, and various other functional materials [1-3]. A notable property observed in HEOs is low thermal conductivity [3]. This is attributed to their enhanced phonon scattering because of the presence of local ionic charge disorder [4]. As the lattice vibrations, i.e. the phonon modes play a crucial in understanding the thermal conductivity of a material, it is necessary to investigate the phonons in HEOs.

The vibrational response of materials can be measured using Fourier Transform Infrared Spectroscopy (FTIR), neutron scattering, or Raman spectroscopy for bulk materials [5]. However, there is a need to probe the phonon modes at the nanoscale resolution to better understand the role of microstructural inhomogeneities or interfaces. With advancements in monochromators and spectrometers, Scanning/Transmission Electron Microscopy combined with Electron Energy Loss Spectroscopy (EELS) has now become an ideal tool for probing the phonon dynamics at the atomic scale. Recently, energy resolution in advanced electron microscopes have improved to 4.2meV, expanding the applications of STEM-EELS to probe phonons, excitons, band gaps, and more [6].

In this study, we utilize ultra-high energy resolution STEM-EELS combined with theoretical calculations to investigate the vibrational modes of the prototypical HEO called J14: (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O, as well as six component HEO thin films (J14+Mn and J14+Cr). These films are grown on MgO substrates using Pulsed Laser Deposition (PLD). Due to the presence of aliovalent cations, local structural variations are observed in J14Mn thin film [7]. Figure 1 shows the phonon spectra of J14Cr HEO in comparison to the MgO substrate, acquired in the dark-field EELS geometry (to probe impact phonon scattering and thus study the localized vibrational response of the system at the atomic scale [8]). The phonon spectrum of J14Cr exhibits a peak around 18 meV, which is not observed in the parent oxide (MgO). Between 40 meV and 70 meV, MgO shows a peak around 48 meV, while J14Cr has a peak around 60 meV, indicating a blue shift compared to the MgO peak. We use FTIR and theoretical analysis to investigate the origin of spectral changes and assign the corresponding phonon modes. This investigation focuses on understanding the influence of composition on the phonon resonances in HEOs. Additionally, the variation in vibrational properties resulting from local structural nuances will also be explored using STEM-EELS data [9].

Read more at Microscopy and Microanalysis

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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