Mun Heum Park

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 550 °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 5.3×1011 cm−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...

Microstructure and electrical properties of cosubstituted BiFeO3 thin films prepared by a chemical solution deposition

5 mol % La 3 + , Nd 3 + or Y 3 + -cosubstituted BiFe 0.97 Cr 0.03 O 3 thin films (denoted by BLaFCr, BNdFCr, and BYFCr, respectively) have been successfully deposited on Pt (200)/TiO 2 /SiO 2 /Si substrates by a chemical solution deposition method. Well-saturated ferroelectric hysteresis loops and low leakage current densities have been observed in BLaFCr, BNdFCr, and BYFCr thin films with single-phase structure. The values of remanent polarization (P r ) and coercive field (E c ) were 64 μ C/cm 2 and 275 kV/cm, 61 μC/cm 2 and 290 kV/cm, and 31 μ C/cm 2 and 315 kV/cm for BLaFCr, BNdFCr and BYFCr thin films at the maximum electric field of 712 kV/cm, respectively. In the present study, the differences in values of P r seem to be related to the doped ionic radii.

Influences of Cr Doping on the Electrical Properties in BiFeO3 Thin Films

Cr-doped BiFeO3 (BFO) thin films were deposited on Pt(200)/TiO2/SiO2/Si(100) substrates by a chemical solution deposition method. The dielectric constant and dissipation factor of the BFO thin films decrease from 165 and 0.054 (undoped) to 100 and 0.02 (3 mol% Cr-doped) at a frequency of 10 kHz as the Cr content increases. The leakage current and ferroelectric properties were improved significantly by means of Cr doping. The leakage current density of 4.1×10−6 A/cm2 for the 3 mol% Cr-doped BFO thin film is about four orders of magnitude lower than that of undoped BFO thin film at an external electric field of 100 kV/cm. The 3 mol% Cr-doped BFO thin film exhibited a well-saturated hysteresis loop with a large remanent polarization (P r) of 61 μC/cm2 at room temperature. The reason for the improved leakage current and ferroelectric properties in Cr-doped BFO thin films can be attributed to the reduced oxygen vacancies in the films by Cr doping. Communicated by Dr. George W. Taylor

Effects of Annealing Temperature on the Electrical Properties of Cr-Substituted BiFeO3 Thin Films

Cr-substituted BiFeO 3 (BFCr-3 mol%) thin films were deposited on Pt(200)/TiO 2 /SiO 2 /Si substrates by a chemical solution deposition. The coated films were annealed in the temperature range of 500°C∼ 600°C for 30 min under nitrogen atmosphere. The electrical properties of BFCr thin films were found to be sensitive to the annealing temperature. It was found that BFCr thin films exhibited good ferroelectric properties, such as an improved leakage-current density and P−E hysteresis characteristics. The BFCr thin film annealed at 525°C exhibits a low leakage current density of 9.2 × 10− 7 A/cm 2 at an applied electric field of 100 kV/cm. The films exhibited a well-saturated hysteresis loop with a remanent polarization (P r ) of 47 μC/cm 2 at room temperature. The reason for the improved leakage current and ferroelectric properties in BFCr thin films can be attributed to the effects of increased grain size and oxygen vacancies reduced by Cr doping.

STRUCTURAL AND ELECTRICAL PROPERTIES OF FERROELECTRIC BI3.4PR0.6TI3O12 PREPARED BY A SOL-GEL METHOD

ABSTRACT The Bi3.4Pr0.6Ti3O12 (BPT) thin film and powder have been prepared by a sol-gel method with annealing at 700°C. Randomly oriented BPT thin film exhibits a large remanent polarization, 2P r = 62 μC/cm2. Structure of sol-gel derived BPT powder has been refined by a Rietveld method resulting a reasonable goodness of fit (wR p = 6.9%, and R p = 5.5%) using orthorhombic (B2cb, a = 5.4221 Å, b = 5.4032 Å, and c = 32.8361 Å). Two different TiO6 octahedra exhibit different polarization directions; (100) from Ti(1)O6, and close to (111) from Ti(2)O6, which explains large 2P r of the randomly oriented BPT thin film.