C.H. Yang

Low leakage current and enhanced ferroelectric properties of Ti and Zn codoped BiFeO3 thin film

BiFeO3 (BFO), Ti(2%)-doped BFO (BFTO), Zn(2%)-doped BFO (BFZO), as well as Ti (1%) and Zn (1%) codoped BFO (BFTZO) films were deposited on Pt∕Ti∕SiO2∕Si substrates by using a metal organic decomposition process. Well saturated P-E hysteresis loops can be obtained in BFZO and BFTZO films due to their lower leakage currents compared to those of BFO and BFTO films. In comparison with BFZO film, BFTZO film exhibits a much larger remanent polarization (Pr∼84μC∕cm2), a lower coercive field (2Ec∼570kV∕cm), as well as stronger charge-retaining ability and fatigue resistance. These phenomena can be explained based on the formation of the defect complexes between the acceptors and oxygen vacancies in the films.BiFeO3 (BFO), Ti(2%)-doped BFO (BFTO), Zn(2%)-doped BFO (BFZO), as well as Ti (1%) and Zn (1%) codoped BFO (BFTZO) films were deposited on Pt∕Ti∕SiO2∕Si substrates by using a metal organic decomposition process. Well saturated P-E hysteresis loops can be obtained in BFZO and BFTZO films due to their lower leakage currents compared to those of BFO and BFTO films. In comparison with BFZO film, BFTZO film exhibits a much larger remanent polarization (Pr∼84μC∕cm2), a lower coercive field (2Ec∼570kV∕cm), as well as stronger charge-retaining ability and fatigue resistance. These phenomena can be explained based on the formation of the defect complexes between the acceptors and oxygen vacancies in the films.

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

BiFeO3 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.

Reduced leakage current, enhanced ferroelectric and dielectric properties in (Ce,Fe)-codoped Na0.5Bi0.5TiO3 film

Na0.5Bi0.5TiO3 (NBT), Ce-doped NBT (NBTCe), Fe-doped NBT (NBTFe), and (Ce,Fe)-codoped NBT (NBTCeFe) thin films were fabricated on LaNiO3(100)/Si substrates by metal organic decomposition. The leakage current density of NBTCeFe at 500 kV/cm is reduced by approximately two orders of magnitude by reducing the density of oxygen vacancies and forming the defect complexes, compared with NBT film. Enhanced ferroelectricity is achieved in NBTCeFe with a large remanent polarization of 24 μC/cm2 due to the reduced leakage current, extra A-site vacancies, and lattice distortion. The NBTCeFe also exhibits a dielectric constant of 585 and dielectric loss of 0.05 at 10 kHz.

Ferroelectric properties, morphologies, and leakage currents of Bi0.97La0.03FeO3 thin films deposited on indium tin oxide/glass substrates

Bi0.97La0.03FeO3 (BLFO) films were prepared using the metal organic decomposition method on indium tin oxide (ITO)/glass substrates. Ferroelectric properties, morphologies and leakage currents of BLFO thin fims are very sensitive to the annealing temperature. The content of grain boundaries in the films is considered to be the dominant factor affecting the leakage currents in BLFO films. Well saturated P-E hysteresis loops can be obtained from all BLFO films due to their low leakage currents. The BLFO thin film annealed at 525 °C exhibits the highest remanent polarization (Pr≈72.9 μC/cm2), which can be explained by the high relative intensity of (110) peak.

Enhanced Piezoelectric Properties of Epitaxial W-Doped BiFeO3 Thin Films

BiFeO3 and BiFe1-xWxO3 (x = 0.005, 0.01, 0.02) films were epitaxially deposited on LaNiO3(100)/Si substrates using a metal organic decomposition process. Well-saturated polarization–electric field hysteresis loops can be observed in all BiFe1-xWxO3 films owing to their leakage currents being lower than that of the BiFeO3 film. Additionally, the domains in BiFe0.995W0.005O3 and BiFe0.99W0.01O3 films can be uniformly switched using a piezoelectric-mode atomic force microscope (AFM) due to the efficient deaging effect of W6+. More importantly, the BiFe0.99W0.01O3 film exhibits the highest piezoelectric coefficient (~132 pm/V) among all the films, making it promising for applications in high-temperature piezoelectric devices and AFM-tip-based data storage.

Enhanced ferroelectric properties of predominantly (100)-oriented CaBi4Ti4O15 thin films on Pt∕Ti∕SiO2∕Si substrates

Predominantly (100)-oriented CaBi4Ti4O15 (CBTi) films were fabricated on Pt (111)∕Ti∕SiO2∕Si substrates using a metal organic decomposition method at annealing temperatures ranging from 600to800°C. The growth mode of the predominantly (100)-oriented CBTi films fabricated by the sequential layer annealing method was discussed based on the structure evolution with the annealing temperature. The remanent polarization and coercive field of the CBTi film annealed at 750°C are 38.1μC∕cm2 and 216kV∕cm, respectively. No fatigue can be observed after 109 switching cycles. The remanent polarization of the purely a-axis-oriented CBTi film should be higher than 50μC∕cm2.

Effects of Bi2Ti2O7 buffer layer on memory properties of BiFe0.95Mn0.05O3 thin film

BiFe0.95Mn0.05O3 (BFMO) thin films with and without Bi2Ti2O7 (BTO) buffer layer were fabricated on p-type Si (111) substrates by metal organic decomposition. The maximum memory window of BFMO/Si is only 0.3 V due to the severe charge injection. In contrast, the larger memory windows are 0.8 and 2.4 V, respectively, for BFMO deposited on as-deposited BTO/Si and annealed BTO/Si. More importantly, the memory window of BFMO/annealed BTO/Si is not affected by changing voltage ramp rate and frequency at ±6 V. The BFMO also shows much reduced leakage current by using an annealed BTO buffer layer.

Enhanced multiferroic properties of (1 1 0)-oriented BiFeO3 film deposited on Bi3.5Nd0.5Ti3O12-buffered indium tin oxide/Si substrate

BiFeO3 (BFO) films with and without a Bi3.5Nd0.5Ti3O12 (BNT) buffer layer were fabricated on indium tin oxide (ITO)/Si substrates using a metal organic decomposition process. X-ray diffraction measurements reveal that a BNT buffer layer can favour the growth of (1 1 0)-oriented grains in the BFO film. BFO film with a BNT buffer layer exhibits well saturated P–E hysteresis loops with good rectangularity as well as large remanent polarization (~70.2 µC cm−2) owing to its higher volume fraction of (1 1 0)-oriented grains, lower leakage current and lower coercive field in comparison with those of the BFO film deposited directly on the ITO/Si substrate. In addition, the magnetization of the (1 1 0)-oriented BFO film is more easily saturated compared with that of the polycrystalline BFO film without a BNT buffer layer.

Na0.5Bi0.5)0.87Pb0.13TiO3 thin films on different substrates for ferroelectric memory applications

(Na0.5Bi0.5)0.87Pb0.13TiO3 thin films have been prepared on Pt∕Ti∕SiO2∕Si and Bi2Ti2O7∕Si substrates using a metal organic decomposition method. The electrical measurements were conducted on metal-ferroelectric-metal or metal-ferroelectric-insulator-semiconductor capacitors. As Bi2Ti2O7 is an effective diffusion barrier, the leakage current and memory properties of (Na0.5Bi0.5)0.87Pb0.13TiO3∕Bi2Ti2O7∕Si are relatively improved. The polarization-electric field and capacitance-voltage measurements of (Na0.5Bi0.5)0.87Pb0.13TiO3 on Pt show good ferroelectric properties. The three phase transitions in (Na0.5Bi0.5)0.87Pb0.13TiO3 can be recognized by the change of capacitance with temperature.

Enhanced electrical properties in Bi(Fe0·95Mn0·05)O3 modified Na0·5Bi0·5TiO3 thin film

Abstract 0·7Na0·5Bi0·5TiO3–0·3Bi(Fe0·95Mn0·05)O3 (NBT–BFOMn) and (Na0·5Bi0·5)TiO3 (NBT) thin films were fabricated on LaNiO3(l 00)/Si substrate by metal organic decomposition. Both films crystallise into the single perovskite structures with strong (l 00) diffraction peaks. The leakage current of NBT–BFOMn can be suppressed due to the decrease in the content for oxygen vacancies and the formation of defect complexes. Compared with the round shaped polarisation–electric field loop for pure NBT, much improved ferroelectric property with a remnent polarisation Pr of 28 μC cm−2 and coercive field Ec of 152 kV cm−1 at 630 kV cm−1 has been obtained for NBT–BFOMn thin film. In addition, the higher change of relative dielectric content ϵr variation versus voltage indicates the enhancement in the ferroelectric nature of NBT–BFOMn thin film. The ϵr and dissipation factor tanδ on frequency for NBT–BFOMn show small dispersion tendency with ϵr of 370 and tanδ of 0·167 at 100 kHz.