Jin Won Kim

Electrical properties of Cr-doped BiFeO3 thin films fabricated on the p-type Si (100) substrate by chemical solution deposition

Ferroelectric Cr-doped BiFeO3 (BFCr) thin films having a rhombohedrally distorted simple perovskite structure were fabricated on the p-type Si (100) substrate by the chemical solution deposition technique. The microstructures and the surface morphologies of BFCr thin films on the p-type Si (100) annealed at 550u2009°C for 30 min in nitrogen atmosphere were examined by an x-ray diffractometer and a scanning electron microscope, respectively. The capacitance-voltage (C−V) curves for BFCr thin film as the clockwise ferroelectric hysteresis loop were observed. Furthermore, the C−V characteristics for the metal-ferroelectrics-semiconductor structured BFCr thin films were measured as functions of the voltage and the frequency. From these results, the fixed charge density Nfc was calculated as 5.3×1011u2002cm−2. The leakage current characteristics of BFCr thin films were also measured by a thermally stimulated current measurement. Using the current-voltage curves, the current conduction mechanism of BFCr thin films on t...

Effect of the annealing temperature on the structural and multiferroic properties of mullite Bi2Fe4O9 thin films

Mullite Bi2Fe4O9 thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. The deposited Bi2Fe4O9 thin films were annealed at a series of temperatures in the range 700–850xa0°C in an oxygen atmosphere using a rapid thermal annealing process. The effect of the annealing temperature on the structural, electrical and multiferroic properties of the Bi2Fe4O9 thin films was investigated. The results showed that the Bi2Fe4O9 thin film that was annealed at 800xa0°C exhibits a well-crystallized orthorhombic phase with the complete absence of secondary phases, in marked contrast to the thin films that were annealed at 700, 750, and 850xa0°C for which the formation of secondary phases was observed. Moreover, the Bi2Fe4O9 thin film that was annealed at 800xa0°C was found to exhibit a low leakage current density and enhanced multiferroic properties, both of which are indicative of the formation of a pure mullite phase with a stable structure.

Effects of La-doping on structural, electrical and multiferroic properties of Bi6Fe2Ti3O18 thin films

Bi6Fe2Ti3O18 (BFTO) and La-doped Bi6−xLaxFe2Ti3O18 (BLFT) (xxa0=xa00.03; BLFT3, xxa0=xa00.06; BLFT6 and 0.09; BLFT9) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. All thin films were crystallized in a polycrystalline orthorhombic structures confirmed by X-ray diffraction and Raman spectroscopy. A low order of leakage current density 2.05xa0×xa010−4 A/cm2 and improved ferroelectric properties, such as large remnant polarization (2Pr) of 19.5 μC/cm2 with low coercive filed of 300xa0kV/cm at an applied electric field of 410xa0kV/cm, were observed for the BLFT6 thin film. The improved properties for the BLFT thin films were correlated to the reduction of oxygen vacancies, the structural distortion and the stabilization of perovskite structures by the La-ion doping into the Bi-site of the BFTO. At room temperature, the BLFT6 and the BLFT9 thin films showed ferromagnetism, while the BFTO and the BLFT3 thin films showed anti-ferromagnetism.

Structural and Multiferroic Properties of Chemical-Solution-Deposited (Bi0.95La0.05)(Fe0.97Cr0.03)O3/NiFe2O4 Double-Layered Thin Film

The structural, electrical, and multiferroic properties of the double-layered (Bi0.95La0.05)(Fe0.97Cr0.03)O3/NiFe2O4 thin film deposited on a Pt(111)/Ti/SiO2/Si(100) substrate by a chemical solution deposition method are reported. The formation of the perovskite-based distorted rhombohedral and spinel phases was confirmed by X-ray diffraction analysis and Raman spectroscopy. The surface morphology and film thickness were analyzed by field emission scanning electron microscopy. The low leakage current density (5.83×10-7 A/cm2 at 100 kV/cm) was measured from the double-layered thin film. Potential multiferroic properties, such as a well-saturated ferroelectric hysteresis loop with large 2 Pr (61 µC/cm2) and 2 Ec (652 kV/cm) (at an applied electric field of 952 kV/cm), and a ferromagnetic hysteresis loop having 2 Mr (18.6 emu/cm3) with 2 Hc (0.943 kOe) (at an applied magnetic field of 20 kOe), were observed from the double-layered thin film.

Effects of La-Doping on Electrical Properties of K0.5Bi4.5Ti4O15 Thin Films

The K0.5Bi4.5Ti4O15 (KBTi) and the La-doped K0.5Bi4.5Ti4O15 (KBLT) thin films were prepared on a Pt(111)/Ti/SiO2/Si(100) substrates by a chemical solution deposition method. The KBLT thin film shows better ferroelectric properties than the KBTi thin film. The values of remnant polarization (2P r) and coercive field (2E c) of the KBLT thin film were 56 μC/cm2 and 343 kV/cm at an electric field of 500 kV/cm, respectively. The leakage current density of the KBLT thin film was approximately one order of magnitude lower than that of the undoped K0.5Bi4.5Ti4O15 thin film. The KBLT thin film shows little change of switchable polarization up to 1.4 × 1010 switching cycles. Therefore, the La-doping is the effective method for improving the ferroelectric properties of the KBTi thin film.