Properties Of BiFeO3 Thin Films Research Articles

Effects of ion-doping at different sites on multiferroic properties of BiFeO3 thin films

A-site Ce and B-site Zr codoped Bi1−x Ce x Fe1−y Zr y O3 (BCFZ) thin films with different compositions were successfully prepared on the Pt/Ti/SiO2/Si substrates by chemical solution deposition. The influence of the A-site Ce and B-site Zr codoping on the structure, surface morphology, electrical and magnetic properties of BFO films were investigated, respectively. The comparative study suggested that the A-site Ce doping with various contents have notable influences on the electrical properties of the BFO films, while the B-site Zr doping with different contents affect mainly the magnetic properties of the BFO films. Compared with the other BCFZ films studied here, the Bi0.97Ce0.03Fe0.97Zr0.03O3 film showed the lowest dielectric loss and leakage current density, a well-squared P–E loop and fatigue-free characteristics as well as the strong magnetization.

Influence of Zr doping on the structure and ferroelectric properties of BiFeO3 thin films

We have prepared thin films of BiFe1−xZrxO3 (x=0.0–0.15) by chemical solution deposition on Pt/Si substrates. Structural characterization of the films using x-ray diffraction and Raman spectroscopy suggests lattice distortion upon doping for x<0.15. This also appears to be the limit for pure phase formation. Ferroelectric measurements reveal that Zr doping leads to reduction in the remnant polarization and an increase in the coercive field, attributed to lattice distortion. Dielectric measurements indicate that the doped compositions exhibit absence of low frequency relaxation, usually associated with defects and grain boundaries. Absence of Fe2+ in our films was verified using x-ray photoelectron spectroscopy. Role of Zr in controlling the film’s properties has been explained in terms of changes in the bond strength.

Effect of annealing temperature on the ferroelectric properties of BiFeO3 thin films prepared by sol-gel process

Sol-gel process was adopted to prepare BiFeO3 films. BiFeO3 films were deposited on LaNiO3 coated Si(100) substrates annealed at 500 and 550 °C, respectively. The X-ray diffraction results reveal that BiFeO3 film has a rhombohedrally distorted perovskite structure with space group R3c. The film annealed at 500 °C has larger remnant polarization (Pr) of 35.3 µC/cm2. For the film annealed at 550 °C, smaller remnant polarization of Pr=4.8 µC/cm2 is observed for its low breakdown electric field. Lower leakage conduction is observed in the film annealed at 500 °C at low applied field.

Tuning the atomic and domain structure of epitaxial films of multiferroicBiFeO3

Recent works have shown that the domain walls of room-temperature multiferroic BiFeO3 (BFO) thin films can display distinct and promising functionalities. It is thus important to understand the mechanisms underlying domain formation in these films. High-resolution x-ray diffraction and piezo-force microscopy, combined with first-principles simulations, have allowed us to characterize both the atomic and domain structure of BFO films grown under compressive strain on (001)-SrTiO3, as a function of thickness. We derive a twining model that describes the experimental observations and explains why the 71o domain walls are the ones commonly observed in these films. This understanding provides us with a new degree of freedom to control the structure and, thus, the properties of BiFeO3 thin films.

Influences of Pr and Mn co-substitution on crystallinity and electric properties of BiFeO3 thin films

Pr and Mn co-substituted BiFeO3 (BFO) thin films were fabricated on a Pt-coated (100) SrTiO3 substrates by pulsed laser deposition (PLD) method. X-ray diffraction patterns indicated that the formation of impurity phases was suppressed by Pr substitution in the BFO thin films. Furthermore, by combining with small amount of Mn substitution, Pr substitution was effective for reducing the leakage current density. The polarization vs electric field curves showed well-saturated hysteresis loops with measurement frequency of 20 kHz at room temperature. The remnant polarization at a maximum electric field of 1500 kV/cm was approximately 50–70 µC/cm2.

Effect of Mn doping on electric and magnetic properties of BiFeO3 thin films by chemical solution deposition

The effect of Mn doping on crystal structure, electric and magnetic properties of BiFeO3 thin films prepared via a chemical deposition method on (111) Pt/Ti/SiO2/Si substrates was studied. The substitution of Fe ions by a small amount (5%) of Mn ions could facilitate the stabilization of Fe3+ in BiFeO3 thin films, while larger substitution (e.g., 10% and 15% Mn substitution) could lead to the increase in Fe2+ concentration. Well saturated polarization hysteresis loops were observed in the Mn-doped BiFeO3 films, with remanent polarization value of 32 μC/cm2 and 53 μC/cm2 for the 5% and 10% Mn-doped BiFeO3 films, respectively. Mn substitution also affect ferroelectric domain structures and microstructures of the films. It was observed that Mn substitution does not affect the intrinsic weak magnetism of BiFeO3. The enhanced ferroelectric and weak magnetic behaviors by Mn substitution were further studied through the analysis of the bonding state of Fe and Mn ions.

Enhanced multiferroic properties of BiFeO3 thin films by Nd and high-valence Mo co-doping

Pure BiFeO3 (BFO), Nd-doped BFO (BNF) and Nd and Mo co-doped BFO (BNFM) multiferroic thin films were prepared by pulsed laser deposition on Pt/Ti/SiO2/Si substrates. Among these films, the BNFM film exhibited the lowest dielectric loss and leakage current density, a well-saturated P–E loop, excellent charge-retaining ability and fatigue-free behaviour. Furthermore, improved ferromagnetism was observed in this film with a saturation magnetization of ∼15 emu cm−3. These significant improvements in ferroelectric and ferromagnetic properties could be preliminarily attributed to the elimination of oxygen vacancies and the increase in the Fe2+ ions in the film by Nd and high-valence Mo co-doping, respectively.

Effect of Ce doping on the microstructure and electrical properties of BiFeO3 thin films prepared by chemical solution deposition

Ce-doped Bi1−xCexFeO3 (BCFOx) thin films with x = 0–0.12 were successfully prepared on SnO2 : F(FTO)/glass substrates by chemical solution deposition. The BCFOx films showed a gradual phase transition from a rhombohedral to a pseudotetragonal structure with increase in the Ce content. The substitution of Bi with Ce greatly reduced the leakage current and the dielectric loss of the BCFOx films, which showed an Ohmic conduction mechanism. The BCFOx films with x = 0.06 exhibited a well squared-shaped P–E hysteresis loop with a remanent polarization (2Pr) of 92.3 µC cm−2 and an improved anti-fatigue characteristic after 1010 read/write polarization cycles.

Improvement of ferroelectric properties of BiFeO3 thin films by postmetallization annealing and electric field application

We have investigated effects of the postmetallization annealing and the electric field application on ferroelectric properties of BiFeO3 thin films prepared by chemical solution deposition. The leakage current is reduced after the postmetallization annealing although the crystallinity of the polycrystalline BiFeO3 is unchanged. In addition, double coercive field is reduced at about 90 kV/cm after the postmetallization annealing, while remanent polarization of 90 μC/cm2 is almost the same at 80 K. The postmetallization annealing is considered to lead the improvement of contact between the BiFeO3 film and the Pt electrode or the reduction in defects near the interface between the BiFeO3 film and the Pt electrode. Moreover, once a high electric field of 2.8 MV/cm is applied, the ferroelectric property of BiFeO3 thin films is dramatically improved. This effect may be due to the relaxation of pinned domains or locked polarizations in the BiFeO3 film. The postmetallization annealing and the electric field application are effective to improve ferroelectric properties of BiFeO3 thin films.

Effects of rare earth manganites on structural, ferroelectric, and magnetic properties of BiFeO3 thin films

The results of structural studies of pure-phase perovskite thin films of BiFeO3–10% RMnO3 (R=La, Eu, Gd, Tb, and Dy) are presented. Raman scattering studies show line broadening similar to what is reported for RMnO3; they were attributed to Jahn–Teller distortion and orthorhombic structural change. Evidence of an anomaly of the orthorhombic distortion at GdMnO3 could be obtained. Interestingly the addition of GdMnO3 leads to a substantial increase in magnetization, combined with moderate ferroelectric polarization. All other compositions are characterized by higher ferroelectric polarization but almost no magnetization.

Microwave dielectric properties of BiFeO3 thin film prepared by aqueous chemical solution deposition method

We report high frequency dielectric properties of multiferroic BiFeO3 (BFO) thin film deposited by means of aqueous chemical solution deposition on platinized silicon substrate. The structure analysis of the BFO performed by X-ray diffraction and energy dispersive analysis showed pure, single-phase quality of the thin films. The impedance measurements were performed by vector network analyzer in frequency range 100 MHz to 10 GHz at ambient temperature. The film leakage currents dominate dielectric losses at low frequencies. The dielectric constant of the film is around 40. An internal charged defects acting as energy traps for electrons dominate dielectric losses in the frequency region above 4 GHz. .

Correlation between structure, dielectric, and ferroelectric properties in BiFeO3–LaMnO3 solid solution thin films

Chemical solution processed BiFeO3 thin films usually show high leakage currents and poor ferroelectric properties. The optimizations of processing conditions and doping with appropriate elements have been among the most promising strategies to enhance the overall properties of BiFeO3 thin films. However, detailed studies on the effects of doping elements on the structure and through it on the properties are still lacking. In this work we investigate the interplay between structure and dielectric-electric-ferroelectric properties of BiFeO3–LaMnO3 [Bi1−xLaxFe1−xMnxO3 (0≤x≤0.1)] solid solution thin films grown on Pt-terminated silicon substrates. The BiFeO3–LaMnO3 system is shown to undergo a structural transition from monoclinic to orthorhombic-tetragonal with various degrees of orthorhombic distortion. All LMO-containing films show a Debye-like dielectric relaxation with the activation energy of 0.90 eV. Both dielectric relaxation and leakage current mechanisms were interpreted in terms of ionized oxygen vacancy hopping. On the basis of comparative studies on individual doping with La and Mn it is shown that Mn is responsible for the dielectric anomaly and structural transition whereas La alone seems to stabilize the perovskite structure. A correlation between the degree of orthorhombic distortion, leakage current, and polarization properties was also found, with a minimum of leakage current and fairly high polarization at the highest distortion.

Influences of Surface Texture and Bi/Fe Ratio on Electric Properties of BiFeO3 Thin Films Prepared by Chemical Solution Deposition

We have investigated the influences of surface texture and Bi/Fe ratio on the electric property of BiFeO3 thin films prepared by chemical solution deposition. All the BiFeO3 films have a rosette structure, which consists of circular regions with BiFeO3 crystals and outer regions with amorphous phase. Circular regions tend to increase with an increase in Bi/Fe ratio. Leakage current increases with an increase in the area of circular regions and in surface roughness as well as with an increase in Bi/Fe ratio. On the other hand, remanent polarization increases with an increase in the area of circular regions as well as with an increase in Bi/Fe ratio, but decreases in a BiFeO3 film prepared using a 20 mol % Bi-excess solution owing to the mixed phase. Consequently, a 10 mol % Bi-excess solution gives the best ferroelectric property for a BiFeO3 thin film with more circular regions and its remanent polarization is 85 µC/cm2.

STRESS DEPENDENCE OF FERROELECTRIC AND MAGNETOELECTRIC PROPERTIES OF BiFeO3 THIN FILMS ON MEMBRANE STRUCTURE

ABSTRACT Multiferroic 350-nm-thick BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/ Si(54 μm) membrane substrates by pulsed laser deposition. To confirm the influence of stress from substrate, ferroelectric and magnetoelectric properties of BiFeO3 thin films have been evaluated with applying stress. For applying stress, we tried to pump out backside of the membrane structure at various pressures. From ferroelectric hysteresis loops, the remanent polarization at the pumping pressure of 0.01 atm increase from 105 to 110 μC/cm2, comparing to that without pumping. Under magnetic field of 0.4 T, polarization at zero electric field at pumping pressure of 0.01 atm with maximum applied voltage of 15 V increased from 100 μC/cm2 to 103 μC/cm2.

Effects of Gd substitution on structure and ferroelectric properties of BiFeO3 thin films prepared using metal organic decomposition

Bi Fe O 3 and Bi1−xGdxFeO3 (BGFO) (x=0.03, 0.05, 0.07, 0.10, and 0.15) thin films were deposited on Pt∕Ti∕SiO2∕Si substrates using a metal organic decomposition process. X-ray diffraction results show that a gradual phase transition from rhombohedral to pseudotetragonal structure may occur in BGFO films with the increase of Gd content. Due to the lower leakage currents resulting from the smaller grain sizes and smoother surfaces, well saturated P-E hysteresis loops, which show weak dependence of frequency in the range of 3–50kHz, can be observed in all BGFO films at room temperature. The remanent polarization for BGFOx=0.03 film is about 79μC∕cm2. In addition, no evident fatigue can be observed after 109 switching cycles.

La 0.8 Sr 0.2 MnO 3 buffer layer effects on microstructure, leakage current, polarization, and magnetic properties of BiFeO3 thin films

BiFeO 3 thin films were processed on La0.8Sr0.2MnO3 (LSMO) buffered silicon substrate via chemical solution deposition. Short-wave ultraviolet assisted pyrolysis was conducted in oxygen atmosphere in order to improve microstructure. A fine, homogeneous, and phase-pure grain structure with smooth topography was obtained. X-ray photoelectron spectroscopy analysis indicates diffusion of lanthanum and manganese from LSMO into the BiFeO3 film leading to a diffuse interface. Nevertheless, improved polarization and leakage resistance properties were obtained. For the first time polarization switching was obtained in sol-gel BiFeO3 films using capacitance-voltage (C−V) curves. This has been imputed to homogeneous local electrical properties of the film, corroborated by surface scanning potential microscopy investigations. The leakage current mechanisms were investigated as function of temperature, and could be interpreted in terms of the Frenkel-Poole mechanism with a trap depth of 1.6 eV. Finally, the magnetic properties of the LSMO∕BiFeO3 heterostructure are presented in comparison to those of BiFeO3 on platinized silicon. An exchange coupling between BiFeO3 and LSMO layers is suggested.

Effects of Excess Bismuth Content in Precursor Solutions on Ferroelectric Properties of BiFeO3 Thin Films Prepared by a Chemical Solution Deposition

Cr-substituted BiFeO3 (BFCr) thin films prepared from precursor solutions with stoichiometric composition and various excess Bi contents ranged from 5 to 20 mol% were fabricated on Pt/TiO2/SiO2/Si(100) substrates by a chemical solution deposition method, and the effects of excess Bi content in precursor solutions on the ferroelectric properties of the as-deposited BFCr thin films were studied. It was found that the BFCr thin film prepared from precursor solution with excess Bi content of 5 mol% exhibited the best dielectric constant–frequency and polarization–electric field characteristics. In detail, its dielectric constant is 158 at frequency of 100 kHz and remnant polarization (P r ) value is 49 μ C/cm2 at electric field of 600 kV/cm.

Growth and Properties of BiFeO3 Thin Films by Molecular-Beam Epitaxy

This is a copy of the slides presented at the meeting but not formally written up for the volume. Description: Epitaxial thin films of the multiferroic BiFeO3 have been grown by molecular beam epitaxy in an adsorption-controlled growth regime where substrate temperature and bismuth oxide over pressure establish phase and stoichiometry control. 30 nm thick BiFeO3 films have been deposited directly on (001) SrTiO3 and SrRuO3/(110) DyScO3, and on (0001) GaN containing a 1 nm thick TiO2 overlayer to enable the epitaxial transition between (0001) GaN and (0001) BiFeO3. Films grown on (001) SrTiO3 possess rocking curves identical to that of the underlying substrate, e.g., a full width at half maximum (FWHM) in u of 25 arc sec in the best case. This is over 40 times narrower than the best published result for epitaxial BiFeO3 films deposited by any technique. On all of the above substrates, the BiFeO3 films exhibit rhombohedral symmetry. The in-plane epitaxial alignment observed for BiFeO3/TiO2/(0001) GaN differs by a 30° in-plane rotation from that observed in previous work for BiFeO3/SrTiO3/TiO2/(0001) GaN. Specifically, our (0001) BiFeO3/TiO2/(0001) GaN is oriented in-plane with [10-10]BiFeO3 [11-20]GaN, accompanied by a 180° in-plane rotational twin variant. The results of this work will be discussed in the context of the interfacial and crystallographic orientation dependence on the ferroelectric, antiferromagnetic, and dielectric properties of this multiferroic.

Effect of Oxygen Annealing on Ferroelectricity of BiFeO3 Thin Films Formed by Pulsed Laser Deposition

In this study, BiFeO3 (BFO) epitaxial film was deposited on SrRuO3(100)/SrTiO3(100) substrates by pulsed laser deposition (PLD). Phase-pure BFO thin film was obtained by introducing a mask between the target and the substrate in the deposition chamber. The use of the mask brought about an improvement in the morphology. The surface roughness was changed from 47.8 to 7.7 nm rms roughness under conditions without and with the mask, respectively. The composition and the electrical properties of BFO thin films were examined before and after annealing the samples for 1 h in atmospheric pressure O2 gas at 600 °C. An improvement of the polarization–electric field (P–E) hysteresis curve was obtained when BFO film was annealed in an O2 atmosphere. O2 gas annealing resulted in a remanent polarization (Pr) value increase from 17 to 25 µC/cm2 at room temperature. At a low temperature (80 K), the BFO thin film annealed in an O2 atmosphere showed the highest Pr of 142 µC/cm2. We also investigated the optimum measurement conditions of the P–E hysteresis curve for BiFeO3.

Infrared optical properties of BiFeO3 thin films prepared by chemical solution deposition

BiFeO3 thin films have been grown on Pt(111)/Ti/SiO2/Si substrates by chemical solution deposition. It is shown that the films are polycrystalline by the measurement of X-ray diffraction. The infrared optical properties of BiFeO3 thin films have been investigated using the infrared spectroscopic ellipsometry in the wavelength range of 2.5 to 12.6 μm. The infrared optical constants of the BiFeO3 thin films are obtained by fitting the measured ellipsometric spectra data using a three-medium model and a classical dielectric function model. The absorption coefficient of BiFeO3 thin films is greater than 100 cm-1 in total measured wavelength region and greater than 1000 cm-1 at the wavelength region above 7.5 μm. It is bigger than that of PbTiO3, Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3 thin films. It indicates that the BiFeO3 thin films are excellent candidates for infrared detectors.