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RESEARCH GROUP


DR. BAEK, Seung-Hyub

Smart Electronic Materials Lab

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Epitaxial & Multifunctional oxide thin film

Complex oxide materials possess an enormous range of electrical, optical, and magnetic properties. For instance, insulators, high quality metals, dielectrics, ferroelectrics, semiconductors, ferromagnetics, colossal magnetoresistance materials, superconductors, and nonlinear optic materials have all been produced using oxide materials. A major challenge is the atomic layer controlled heteroepitaxial growth of various complex oxide materials so that these properties can be fully utilized in novel devices. We have grown various heterostructures by pulsed laser deposition with in situ high pressure RHEED on an atomic-layer level. This includes ferroelectric, ferromagnetic, 2-dimensional electron gas oxide heterointerfaces and multiferroic perovskite oxides whose structures are engineered using epitaxy.

Flexible 이미지

Schematic illustration of functionalizing 2DEG by epitaxial heterostructuring. This schematic displays that the physical properties of 2DEG can be modulated by various external signals which are selectively amplifi ed depending on the functionality of the overlayers. TEM image of epitaxial PZT and LAO thin film on SrTiO3.

"Non-Volatile Control of 2DEG Conductivity at Oxide Interfaces" S. I. Kim, D. H. Kim, Y. J. Kim, S. Y Moon, M. G. Kang, J. K. Choi, H. W. Jang, S. K. Kim, J. W. Choi, S. J. Yoon, H. Y. Chang, C. Y. Kang, S. Y. Lee, S. H. Hong, J. S. Kim and S. H. Baek accepted for publications in Advanced Materials (2013)

Mutiferroic Thin Films

Multiferroics, where (anti-) ferromagnetic, ferroelectric, and ferroelastic order parameters coexist, enables manipulation of magnetic ordering by electric field through switching of the electric polarization. It has been shown that realization of magnetoelectric coupling in single-phase multiferroic such as BiFeO3 requires ferroelastic (71˚, 109˚) rather than ferroelectric (180 ˚) domain switching. However, the control of such ferroleastic switching in a single-phase system has been a significant challenge as elastic interactions tend to destabilize small switched volumes, resulting in subsequent ferroelastic back-switching at zero electric field, thus disappearance of nonvolatile information storage. Guided by our phase-field simulations, we here report an approach to stabilize ferroelastic switching by eliminating the stress-induced instability responsible for back-switching using isolated monodomain BiFeO3 islands. This work demonstrates a critical step to control and utilize nonvolatile magnetoelectric coupling at the nanoscale. Beyond magnetoelectric coupling, it provides a framework for exploring a route to control multiple order parameters coupled to ferroelastic order in other low-symmetry materials.

Mutiferroic Thin Films 이미지
  • Schematic illustration of the ferro electric switching path of BiFeO3 thin films predicted by phase-field calculations.
  • Ferroelastic switching of isolated island studied by monodomain (001) BiFeO3 thin films.

"Ferroelastic Switching for Nanoscale Nonvolatile Magnetoelectric Devices" S. H. Baek, H. W. Jang, C. M. Folkman, Y. L. Li, B. Winchester, J. X. Zhang, Q. He, Y. H. Chu, C. T. Nelson, M. S. Rzchowski, X. Q. Pan, R. Ramesh, L. Q. Chen and C. B. Eom accepted for publications in Nature Materials (2010)

Giant Piezoelectric Nanosystems

Major challenges are emerging as electromechanical systems move to the nano-scale (nanoelectromechanical systems, or NEMS), with an integration density that demands faster and larger relative motion range. Our recently developed giant piezoelectric Pb(Mg,Nb)O3-PbTiO3 (PMN-PT) epitaxial thin-films directly on silicon can drastically increase the motion range and speed, with even potentially greater response by using engineered nanoscale strain distributions and domain structures. We have integrate epitaxial thin film heterostructures of giant piezoelectric materials directly on silicon to make hyper-active nano-electromechanical systems. These heterostructures are compatible with silicon nanofabrication processes, can be integrated with silicon-based electronics, and have large enough response to revolutionize active NEMS actuators. This research will develop a fundamental scientific understanding of nanoscale piezoelectric phenomena in active nanoscale electromechanical devices, with applications in high performance signal processing, communications, sensors, and nano-positioning actuators. The relationship between piezo-response and nanoscale strain and domain configurations developed here can be applied to multifunctional materials to develop new NEMS devices.

Giant Piezoelectric Nanosystems 이미지

Phase-pure, (001) oriented epitaxial PMN-PT thin film on a SrTiO3-buffered Si substrate. X-ray diffraction pattern measured with a 2D area detector of PMN-PT heterostructure on (001) Si substrates with 4° miscut along [110]. SEM image of piezoelectric cantilever and its giant piezo-response.

"Giant Piezoelectricity on Si for Hyperactive MEMS" S. H. Baek, J. Park, D. M. Kim, V. A. Aksyuk, R. R. Das, S. D. Bu, D. A. Felker, J. Lettieri, V. Vaithyanathan, S. S. N. Bharadwaja, N. Bassiri-Gharb, Y. B. Chen, H. P. Sun, C. M. Folkman, H. W. Jang, D. J. Kreft, S. K. Streiffer, R. Ramesh, X. Q. Pan, S. Trolier-McKinstry, D. G. Schlom, M. S. Rzchowski, R. H. Blick and C. B. Eom accepted for publications in Science (2011)

Anion-controlled semiconductors for transparent electronics

In the our group, we are working on the understanding and development of transparent conductivity oxides (TCOs) materials and its applications. TCOs are unusual materials that are both electrically conductive and visually transparent. They are widely used in high- and low- tech applications such as antistatic coatings, touch display panels, solar cells, flat panel displays, heaters, defroster and optical coatings. Our research is focused on studying high mobility material or develop process for looking forward to use similar TCO technologies for applications as transparent thin film transistors (TFTs). Also, exploitation of TCOs in devices will only become possible if suitable wide gap oxides, which can undergo p-type doping, will be able to developed.

Anion-controlled semiconductors for transparent electronics 이미지

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