Optical and electrical properties of multiferroic bismuth ferrite thin films fabricated by sol-gel technique

Single-phase multiferroic BiFeO₃ thin films have been prepared on LaNiO₃/Si(100) and Si(100) wafer via sol-gel technique. The films are polycrystalline with preferring orientation of (101). The film has a conspicuous absorption in the blue and green light region, and band gap of 2.74 eV. The refractive index and the extinction coefficient of the film is about 2.36 and 0.06 at 600 nm, 2.26 and close to zero in the range of 800-1200 nm, respectively. The films also exhibit favorable ferroelectric and dielectric properties. A large photo induced open-circuit voltage was observed, indicating that the film exhibits photovoltaic behaviours.     

Magnetic and electrical properties of metal/ferrite composite thin films

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of annealing atmosphere on phase formation and electrical characteristics of bismuth ferrite thin films

Bismuth ferrite thin films were deposited on Pt/Ti/SiO₂/Si substrates by a soft chemical method and spin-coating technique. The effect of annealing atmosphere (air, N₂ and O₂) on the structure and electrical properties of the films are reported. X-ray diffraction analysis reveals that the film annealed in air atmosphere is a single-phase perovskite structure. The films annealed in air showed better crystallinity and the presence of a single BFO phase leading to lower leakage current density and superior ferroelectric hysteresis loops at room temperature. In this way, we reveal that BFO film crystallized in air atmosphere by the soft chemical method can be useful for practical applications, including nonvolatile digital memories, spintronics and data-storage media.     

Size effect in the electrical properties of thin epitaxial bismuth films

The thickness dependence of the electrical properties of thin epitaxial bismuth films (of thickness 0.2–3 μm) was studied at 4.2 and 77 K. The size effect theory developed by Mayadas and Shatzkes was modified so that it could be applied to a system with two carriers (electrons and holes). The thickness dependence of the carrier densities was also taken into account.The specularity parameter P at the surface and the reflection coefficient R at the grain boundaries were determined to be 0.7 and 0.2–0.3 respectively. It should be noted that the effect of scattering of the carriers at the grain boundary planes parallel to the electric field could not be neglected.     

Structure and electrical properties of bismuth thin films prepared by flash evaporation method

Polycrystalline Bi thin films with thickness in the range 40-160 nm have been successfully deposited on glass substrates at 453 K by flash evaporation method for the first time. XRD and FE-SEM were performed to characterize their structure and surface morphology respectively. Electrical resistivity measurement was carried out in the temperature range 300-350 K. Hall coefficient, electron concentration and mobility were measured at 300 K. A distinctly oscillatory behavior has been observed for the electrical properties of the Bi thin films.     

Ferroelectric behavior in bismuth ferrite thin films of different thickness

The ferroelectric behavior of BiFeO(3) thin films is modified by changing the film thicknesses, where the BiFeO(3) thin films with different thicknesses were grown on SrRuO(3)/Pt/TiO(2)/SiO(2)/Si(100) substrates by radio frequency sputtering. The mixture of (110) and (111) orientations is induced for all BiFeO(3) thin films regardless of their thicknesses, together with the columnar structure and the dense microstructure. Their dielectric behavior is almost independent of the film thickness where all thin films have a low dielectric loss. A giant remanent polarization of 2P(r) ≈ 156.6-188.8 μC/cm(2) is induced for the BiFeO(3) thin films in the thickness range of 190-600 nm. As a result, it is an effective way to improve the ferroelectric behavior of the BiFeO(3) thin film by tailoring the film thickness.     

Investigation of dark and light conductivities in calcium doped bismuth ferrite thin films

Electrical conductivities in dark and light were investigated in Calcium doped Bismuth Ferrite thin films. Higher dark conductivity, in the order of 10 times higher than conductivity of bismuth ferrite, was observed for Bi_0.85Ca_0.15FeO_3 ? δ. Structural analyses using Rietveld refinement showed a deviation from volume reduction for Bi_0.85Ca_0.15FeO_3 ? δ which could be the reason of abnormally high conductivity for this compound. Although higher calcium doping reduced conductivity, photoconductivity was observed again. Atomic Force Microscopy investigations showed that surface roughness and grain size decreased with increasing calcium concentration. Enhanced photoconductivity is reported for Bi_0.7Ca_0.3FeO_3 ? δ with ~ 2.8 eV direct optical band gap at 300 K with surface roughness of ~ 2 nm.     

Studies of the electrical properties of bismuth oxide films

A detailed study has been made of the resistivity , activation energy ΔE, Hall coefficient R_H, mobility μ, thermoelectric power and TCR of vacuum-deposited films of bismuth oxide evaporated from silica and molybdenum boats in the temperature range 78°–525°K. The electrical parameters of these films differed considerably from those of oxidized films and this difference has been attributed to the dissociation of the bismuth oxide and the formation of intermediate products.     

Optical and electric properties of strontium bismuth tantalate thin films

High quality SrBi₂Ta₂O₉ ferroelectric thin films were fabricated on platinized silicon using pulsed laser deposition. The optical properties of the thin films were studied by spectroscopic ellipsometry from the ultraviolet to the infrared region. Optical constants, n ∼ 0.25 in the infrared region and n ∼ 2.18 in the visible spectral region, were determined through multilayer analyses on their respective pseudodielectric functions. The band-gap energy is estimated to be 4.14 eV. It was found that the leakage current mechanism of the film was from bulk limited Poole-Frenkle emission to interface-controlled Schottky emission with applied field increasing, and that the breakdown field of the film had a negative linear variation with the logarithm of the electrode area.     

Microstructure and ferroelectric properties of dysprosium-doped bismuth titanate thin films

Bi₄Ti₃O₁₂ (BIT) ferroelectric thin films with Dy³⁺ substitution (Bi_4−xDy_xTi₃O₁₂, x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively) were grown on Pt(111)/Ti/SiO₂/Si(100) substrates using sol–gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that after annealing at 710 °C for 10 min, all Bi_4−xDy_xTi₃O₁₂ films became polycrystallites. Among all the deposited thin films, the Bi_3.4Dy_0.6Ti₃O₁₂ specimen exhibits improved ferroelectric properties with the largest average remanent polarization (2Pr) of 53.06 μC/cm² under applied field of 400 kV/cm and fatigue free characteristics (16% loss of 2Pr after 1.5 × 10¹⁰ switching cycles), indicating that it is suitable for non-volatile ferroelectric random access memories applications.     

Structural and electrical properties of Ti-Al thin films

We have studied thin films of Ti-Al for use as resistance elements. It was found that Ti-40 wt.% Al thin films with a resistivity of 10 ω/□ possess stable characteristics. We have also studied the structure of Ti-Al thin films. Analysis of electron and X-ray diffraction patterns showed that Ti-40 wt.% Al films contained a fine-grained disordered intermetallic face-centred cubic TiAl phase whereas bulk TiAl had a tetragonal CuAu-type structure.     

Microstructure and electrical properties of YBCO thin films

Microstructures of c-axis oriented YBCO thin films made by high-pressure d.c. sputtering on LaAlO₃ and MgO substrates were examined by TEM. The a-axis oriented grains, second phases and micro-twins were frequently observed in the film. The a-axis oriented grains expanded along their c-axis directions during film growth. The a- and b-axis misorientations were observed in the film on MgO due to serious lattice mis-match between YBCO and MgO. The second phases were often accompanied with a-axis oriented grains suggesting they act as nuclei. These observed results were correlated with the measured T _c and J _c of the films.     

Effects of substrate temperature on the magnetic and electrical properties of cobalt ferrite/metal composite thin films

The magnetic and electrical properties of the cobalt ferrite/metal composite thin films, prepared by reactive sputtering, were studied as a function of substrate temperature. With increasing substrate temperature, the saturation magnetization of the thin films increased owing to precipitation of the Co_0.67Fe_0.33 phase. Also, the electrical resistivity of the thin films decreased. From Hall experiments, the decrease of electrical resistivity of the composite thin films was mainly attributed to the increase of electron concentration. The Seebeck coefficient measurement shows that the electrical conduction mechanism of the thin films containing 37.8 and 33.7 at % Co changes from p-type to n-type and that of the thin films containing 28.5 at % Co remains n-type with increasing substrate temperature. This might be attributed to the change in composition of the cobalt ferrite matrix to Fe-excess with precipitation of Co-rich Fe alloy. ©1999 Kluwer Academic Publishers     

Superparamagnetic properties of thin films and small particles of magnesium ferrite

The magnetic properties of superparamagnetic thin films and small particles of magnesium ferrite obtained by thermal treatment of the iron films evaporated in vacuum on the     

Structure and dielectric properties of sputtered bismuth magnesium niobate thin films

The Bi_1.5MgNb_1.5O₇ (BMN) thin films were prepared on platinum coated sapphire by rf magnetron sputter deposition. Effects of substrate temperature, sputter pressure and O₂/(O₂ + Ar) mixing ratio on phase structures and dielectric properties of thin films were investigated. The results indicated that sufficiently high substrate temperature and low sputter pressure would facilitate the formation of cubic pyrochlore in BMN thin films. Meanwhile, the appropriate O₂/(O₂ + Ar) mixing ratio of sputter atmosphere was required. The deposited Bi_1.5MgNb_1.5O₇ cubic pyrochlore thin films with (222) oriented texture exhibited large tunability of ~ 50% at a maximum applied bias field of 1.5 MV/cm, with low dielectric loss of ~ 0.007. The temperature and frequency dependent dielectric measurements indicated that no noticeable dielectric dispersion was detected in BMN cubic pyrochlore thin films.     

Electric control of magnon frequencies and magnetic moment of bismuth ferrite thin films at room temperature

Here, we report the tuning of room-temperature magnon frequencies from 473 GHz to 402 GHz (14%) and magnetic moment from 4 to 18 emu∕cm(3) at 100 Oe under the application of external electric fields (E) across interdigital electrodes in BiFeO(3) (BFO) thin films. A decrease in magnon frequencies and increase in phonon frequencies were observed with Magnon and phonon Raman intensities are asymmetric with polarity, decreasing with positive E (+E) and increasing with negative E (-E) where polarity is with respect to in-plane polarization P. The magnetoelectric coupling (α) is proved to be linear and a rather isotropic α?=?8.5?×?10(-12) sm(-1).     

TiN薄膜的循环制备和电学性质

用金属有机物化学气相淀积（Metal Organic Chemical Vapor Deposition,MOCVD）制备了TiN薄膜,通过不同循环制备的、厚度相同的平面薄膜电阻率的比较研究了TiN薄膜的电学性质．结果表明,多次循环会引入界面而增大电阻率,与薄膜成分和微结构分析的结果一致．得到了单循环的最优厚度以使样品电阻率最低．通过相同循环、不同厚度样品在真实器件中电学性能的比较,发现介窗（Via）直径越小,TiN薄膜对介窗电阻的影响越大．