Research

From Fundamental Science to Practical Applications

Research interests in our group include understanding the fundamental relationships among structure, property, and processing in functional materials such as dielectrics, ferroelectrics, antiferroelectrics, and piezoelectrics, and developing the properties of these materials. In particular, our group primarily focuses on insulating materials in metal-oxide-semiconductor field-effect transistor (MOSFET) and metal-insulator-metal (MIM) capacitors, such as HfO2 or ZrO2. We aim to enhance the performance of MOSFET and MIM capacitors by transforming the monoclinic and dielectric phases of HfO2 or ZrO2 to polar orthorhombic and ferroelectric phases. Additionally, our group uses advanced characterization tools such as X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, transmission electron microscopy, in situ X-ray diffraction, and synchrotron-based X-ray scattering to study the physical, chemical, structural, and electrical properties of the materials in depth.

1. Advanced structural characterization

Various functional properties of electroceramic materials originate from specific crystallographic phases. The ferroelectric property is known to appear in materials that exhibit non-centrosymmetric phases. The differences in crystallographic phases can be identified by measuring the diffraction patterns of the materials. Our research group particularly focuses on measuring diffraction patterns of materials while they are subjected to various conditions such as electric field cycling or heating/cooling. Furthermore, since diffraction patterns of thin films show low resolution, X-rays with smaller wavelengths (i.e., higher photon energy) are required, which can be generated at particle accelerators such as synchrotron light sources. Our group frequently utilizes synchrotron-based X-rays to conduct high-resolution experiments.

Lee, Y.†, Kim, S. H.†, Jeong, H. W., Park, G. H., Lee, J., Kim, Y. Y., & Park, M. H. (2024). Mitigation of field-driven dynamic phase evolution in ferroelectric Hf0.5Zr0.5O2 films by adopting oxygen-supplying electrode. Applied Surface Science, 648, 158948. (†co-1st author)

Kim, S. H.†, Lee, Y. †, Lee, D. H. †, Park, G. H., Jeong, H. W., Yang, K., ... & Park, M. H. (2024). Depolarization mitigated in ferroelectric Hf0.5Zr0.5O2 ultrathin films (< 5 nm) on Si substrate by interface engineering. Journal of Advanced Ceramics. (†co-1st author)

Schroeder, U., Mittmann, T., Materano, M., Lomenzo, P. D., Edgington, P., Lee, Y. H., ... & Jones, J. L.* (2022). “Temperature‐Dependent Phase Transitions in HfxZr1‐xO2 Mixed Oxides: Indications of a Proper Ferroelectric Material.” Advanced Electronic Materials, 2200265.

Hsain, H. A., Lee, Y., Parsons, G., & Jones, J. L.* (2020). “Compositional dependence of crystallization temperatures and phase evolution in hafnia-zirconia (HfxZr1-x)O2 thin films.” Applied Physics Letters, 116(19), 192901.

2. Processing engineering in atomic layer deposition

Thin films can be made by several deposition methods. Atomic layer deposition (ALD), a process in which an organic-based precursor and a reactant precursor are introduced alternately in sequence to fabricate thin films, is considered one of the most important deposition methods in the semiconductor industry due to its superiority in controlling thickness, homogeneity, step coverage, and conformality. Since the thickness of the thin films made by ALD is typically on an atomic scale, the structure and properties of the thin films can vary significantly by simply changing conditions in the ALD process. Often, introducing a single sequence of a different precursor during the ALD process can result in the emergence of an unconventional crystallographic phase. For example, the polar orthorhombic and ferroelectric phase of HfO2 can be induced by introducing dopant precursor such as Si, Al, and La, whereas without these dopant precursors, the phase would be the monoclinic and dielectric phase. Our research group studies fundamental science of ALD process and the impact on the films when various conditions are changed during the ALD process.

Yang, K.†, Kim, S. H.†, Jeong, H. W., Lee, D. H., Park, G. H., Lee, Y.*, & Park, M. H.* (2023). Perspective on Ferroelectric Devices: Lessons from Interfacial Chemistry. Chemistry of Materials, 35(6), 2219-2237 (*co-corresponding author)

Lee, Y., Broughton, R. A., Hsain, H. A., Song, S. K., Edgington, P. G., Horgan, M. D., ... & Jones, J. L. (2022). “The influence of crystallographic texture on structural and electrical properties in ferroelectric Hf0.5Zr0.5O2.” Journal of Applied Physics, 132(24), 244103.

Lee, Y., Alex Hsain, H., Fields, S. S., Jaszewski, S. T., Horgan, M. D., Edgington, P. G., ... & Jones, J. L.* (2021). “Unexpectedly large remanent polarization of Hf0.5Zr0.5O2 metal–ferroelectric–metal capacitor fabricated without breaking vacuum.” Applied Physics Letters, 118(1), 012903.

3. Interface engineering during thin film deposition

The structure and properties of thin films can also vary through interface engineering in atomic layer deposition (ALD) processing. By precisely manipulating interfaces during ALD, we can achieve new and enhanced properties in thin films. For example, the preferred orientation of the material deposited on the surface can be influenced by the preferred orientation of the material on the bottom surface. This control over crystallographic texture allows for the fine-tuning of material characteristics, leading to significant improvements in performance and functionality. Thus, the properties of thin films can be precisely controlled using interface engineering. Our research group studies the impact of varying interface property of thin films and push the boundaries of material science and technology through innovative interface manipulation.

4. Emerging memory devices for the next DRAM and NAND flash

As the Internet of Things (IoT) and information and communication technology (ICT) grow exponentially, the importance of memory devices has increased significantly. More than 98% of standalone memory devices are composed of two main types: dynamic random access memory (DRAM) and NAND flash memory. As the scale of technology nodes shrinks below 10 nm, the performance and miniaturization of memory devices reach their limits. Our research group focuses on methods to overcome these limitations and enhance device performance. For example, HfO2-based ferroelectric field-effect transistors (FeFETs) are expected to replace conventional 3D NAND flash memory devices. Similarly, HfO2-based ferroelectric random access memory (FRAM) is expected to replace conventional capacitors in DRAM.

5. Emerging devices for the neuromorphic computing

In the traditional von Neumann architecture, data is transferred sequentially between the main memory and the central processing unit, creating a bottleneck for parallel data processing. Neuromorphic computing, inspired by the human brain, allows for massive parallel data processing, making it a promising candidate for next-generation computing systems. To realize neuromorphic computing, neural and synaptic devices are required. The synaptic devices need the ability to modify the weight level to carry out massive parallel data processing. Ferroelectric tunnel junction (FTJ) and ferroelectric field-effect transistor (FeFET) are expected to fulfill this role by adjusting the conductance level of each cell via partial polarization switching. Our research group aims to advance the development of neuromorphic computing systems by studying HfO2-based FTJ and FeFET devices.

Lee, D. H.†, Lee, Y.†, Cho, Y. H., Choi, H., Kim, S. H., & Park, M. H. (2023). Unveiled Ferroelectricity in Well‐Known Non‐Ferroelectric Materials and Their Semiconductor Applications. Advanced Functional Materials, 2303956. (†co-1st author)

Lee, D. H.†, Lee, Y.†, Yang, K., Park, J. Y., Kim, S. H., Reddy, P. R. S., ... & Park, M. H.* (2021). “Domains and domain dynamics in fluorite-structured ferroelectrics.” Applied Physics Reviews, 8(2), 021312. (†co-1st author)