Hyun Wook Shin

Ferroelectric BiFeO 3 nanodots formed in non-crystallized BiFeO 3 thin-films via a local heating process using a heated atomic force microscope tip

AbstractA BiFeO3 thin-film was prepared from a solution by deposition on a Pt/TiO2/SiO2/Si substrate via a spin coating process and was subsequently annealed at 300 °C for 1 h to afford a non-crystallized BiFeO3 thin-film. Locally crystallized BiFeO3 nanodots were formed in the non-crystallized BiFeO3 thin-film via a local crystallization process using an atomic force microscope tip heated to 550 °C. By controlling the local heating time, ferroelectric BiFeO3 nanodots with different diameters ranging from 65 to 120 nm were obtained. The ferroelectric properties of the BiFeO3 nanodots were further investigated by studying the local ferroelectric switching behaviors and local piezoelectric d33 hysteresis loops using a piezoresponse force microscope.

Ferroelectric properties and piezoresponse force micoroscopy study of Bi3TaTiO9 thin films

We investigate the ferroelectric properties and crystal structures of Bi3TaTiO9 (BTTO) thin films deposited on single-crystal Nb-doped (100) SrTiO3 substrates via pulsed laser deposition. The BTTO films exhibited either a (001)-epitaxial crystalline structure or a mixed a- and c-oriented polycrystalline structure depending on the substrate temperature. The ferroelectric polarization and piezoelectric coefficient of the mixed a- and c-oriented film were larger than those of the (001)-epitaxial film because its polar axis was perpendicular to the c-axis. Vertical and lateral piezoresponse force microscopy studies indicate that the ferroelectric domains of the (001)-epitaxial film were all parallel to the in-plane orientation, whereas the mixed a- and c-oriented film comprised both square grains with in-plane-oriented ferroelectric domains and longish grains with ferroelectric domains out of orientation with the plane.

Cu-Doped ZnO Thin Films Grown by Co-deposition Using Pulsed Laser Deposition for ZnO and Radio Frequency Sputtering for Cu

Cu-doped ZnO (CZO) thin films were fabricated on single-crystalline (0001) Al2O3 substrates by co-deposition using pulsed laser deposition for ZnO and radio frequency sputtering for Cu. CZO thin films with 0–20% molar concentrations are obtained by adjusting the deposition rates of ZnO and Cu. The CZO thin films exhibit room temperature ferromagnetism, and CZO with 5% Cu molar concentration has maximum remanent magnetization, which is consistent with theoretical results.

Nonvolatile ferroelectric memory based on PbTiO 3 gated single-layer MoS 2 field-effect transistor

We fabricated ferroelectric non-volatile random access memory (FeRAM) based on a field effect transistor (FET) consisting of a monolayer MoS2 channel and a ferroelectric PbTiO3 (PTO) thin film of gate insulator. An epitaxial PTO thin film was deposited on a Nb-doped SrTiO3 (Nb:STO) substrate via pulsed laser deposition. A monolayer MoS2 sheet was exfoliated from a bulk crystal and transferred to the surface of the PTO/Nb:STO. Structural and surface properties of the PTO thin film were characterized by X-ray diffraction and atomic force microscopy, respectively. Raman spectroscopy analysis was performed to identify the single-layer MoS2 sheet on the PTO/Nb:STO. We obtained mobility value (327 cm2/V·s) of the MoS2 channel at room temperature. The MoS2-PTO FeRAM FET showed a wide memory window with 17 kΩ of resistance variation which was attributed to high remnant polarization of the epitaxially grown PTO thin film. According to the fatigue resistance test for the FeRAM FET, however, the resistance states gradually varied during the switching cycles of 109.