S. B. Majumder

Investigations on solution derived aluminium doped zinc oxide thin films

Aluminium (Al) doped transparent zinc oxide thin films have been successfully grown on sapphire (0 0 0 1) substrates by an economical chemical solution deposition technique. These films were characterized in terms of their structural, optical, and electrical properties. Detailed XPS analysis of the O1s core level spectra has been carried out for the ZnO films annealed at different temperatures. Lower binding energy oxygen peak (O1) is related to ZnO bond, whereas higher binding energy peaks (O2 and O3) are related to the presence of OH and H2O species. Zn is bonded mainly to oxygen, however presence of metallic Zn was also detected by XPS. Decrease in O2 and O3 contents with the increase in annealing temperature has been correlated with the microstructure of the film. Higher annealing temperature was found to be effective to densify the film and thereby reduced the contents of the hydrated species. An optical transmittance 80/90% in the visible range and an optical band gap /3.25 eV was measured in case of undoped ZnO thin film. There is no significant change in band gap energy with Al doping. The resistivity of undoped ZnO was measured to be about 3.8 V cm. The resistivity of ZnO films decreased and remained in the range of 0.27/0.32 V cm for up to 4 at.% Al doping. Al doping content beyond 4 at.% was found to increase the resistivity of the films probably due to the segregation of aluminium as oxide resulting scattering of the electrons. # 2003 Elsevier B.V. All rights reserved.

Improvement in electrical characteristics of graded manganese doped barium strontium titanate thin films

Highly (100) textured graded manganese (Mn) doped Ba0.5Sr0.5TiO3 [BST (50/50)] thin films were deposited on lanthanum aluminate substrates using sol-gel technique. We have demonstrated that the graded acceptor doping is a promising technique to reduce the temperature coefficient of capacitance (TCC), loss tangent, and leakage current of BST thin films. In the temperature range between 175 and 260 K the reported TCC of Mn graded BST (50/50) films is less than 5.55×10−4/K, which is comparable to the best capacitors known so far. The lower temperature coefficient of the capacitance of the Mn graded films has been argued to be due to the induced compositional heterogeneity resulting into a distribution of the Curie temperature.

Improvement in mechanical properties of jute fibres through mild alkali treatment as demonstrated by utilisation of the Weibull distribution model

Chemically modified jute fibres are potentially useful as natural reinforcement in composite materials. Jute fibres were treated with 0.25%-1.0% sodium hydroxide (NaOH) solution for 0.5-48 h. The hydrophilicity, surface morphology, crystallinity index, thermal and mechanical characteristics of untreated and alkali treated fibres were studied.The two-parameter Weibull distribution model was applied to deal with the variation in mechanical properties of the natural fibres. Alkali treatment enhanced the tensile strength and elongation at break by 82% and 45%, respectively but decreased the hydrophilicity by 50.5% and the diameter of the fibres by 37%.

Phase transition studies of sol–gel deposited barium zirconate titanate thin films

The present work was focused to investigate the phase transition behavior of sol–gel derived Ba(ZrxTi1−x)O3 (BZT) (0≤x≤0.40) thin films on platinum substrates for their possible applications in piezoelectric sensors and actuators. The phase transition behavior of these films was studied using micro-Raman spectroscopy in conjunction with the temperature dependent dielectric measurements. The spectra clearly indicate that the room temperature BZT films with Zr ≤0.05 were crystallized into tetragonal structure and above 15 at.% Zr substitution BZT thin films transformed into a disordered cubic structure. This disorder behavior became more pronounced for films with Zr>20 at.% with a plateau-type feature developing approximately 700 cm−1 and on cooling such films to the liquid nitrogen temperature no appreciable spectral changes were noticed. The dielectric properties of such films for Zr ≥25 at.% clearly indicated relaxor behavior. These environmentally safe (non-lead based) BZT films may have significant impact for several micro-electromechanical systems (MEMs) devices.

Investigations on the sol-gel-derived barium zirconium titanate thin films

Abstract Barium zirconium titanate thin films are attractive candidates for dynamic random access memories and tunable microwave devices. In the present work, a wide range of Zr-doped BaTiO 3 thin films has been prepared by sol–gel technique. X-ray diffraction and micro-Raman scattering studies confirmed the structural phases in the powder and films of BZT and various structural transitions of BaTiO 3 , as a function of different Zr content, and compared well with the published result on ceramics and single crystalline BZT. The deposited films were smooth, crack-free and have homogeneous microstructure, and Zr content strongly influences the evolution of the microstructures of the films. Some selected compositions of these films are characterized in terms of their dielectric properties and phase transition behavior. BZT films with 20 at.% Zr have shown a ferroelectric to paraelectric transition in the vicinity of room temperature. Efforts are underway to optimize the annealing conditions and to grow epitaxial BZT films with various Zr contents on suitable single-crystalline substrates.

Relaxor behavior in sol–gel-derived BaZr(0.40)Ti(0.60)O3 thin films

In the present work, we have reported the phase transition behavior of sol–gel-derived BaZr0.4Ti0.6O3 (BZT40) thin films. The dielectric properties of these films were measured as a function of temperature in the frequency range of 1 kHz to 1 MHz. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behavior in the films. The index of relaxation (γ) and the broadening parameter (Δ) were estimated from a linear fit of the modified Curie–Weiss law. The value of γ≈1.79 and Δ≈76 K indicates the strong relaxor nature of these films. A remarkably good fit to the Vogel–Fulcher relation further supports such a relaxor nature. The films showed good polarization hysteresis at a low temperature, though that slims down yet persists even above the dielectric maximum temperature (Tm), which is about 170 K.

Dielectric and magnetic properties of sol-gel-derived lead iron niobate ceramics

In this work, we report the synthesis of sol-gel-derived lead iron niobate [Pb1.10(Fe0.5Nb0.5)O3] (PFN) powders and sintered ceramics. The PFN powders were calcined at (Ta), 973, 1073, 1173, 1273, and 1373 K for 3 h in air. As envisaged from x-ray-diffraction analyses, PFN powder calcined at 1173 K was crystallized into pure monoclinic perovskite phase whereas powders calcined at all other temperatures had varied amounts of retained pyrochlore (Pb3Nb4O13) phase coexisted with dominant monoclinic perovskite phase. The PFN pellet (prepared using the phase pure powder calcined at 1173 K) sintered at 1373 K for 4 h in air also had a minute quantity of retained pyrochlore phase coexisting with desired perovskite phase. From the temperature dependence of measured capacitance and loss tangent at different frequencies, the ferroelectric to paraelectric phase-transition temperature of PFN ceramics was observed at Tc≈370K. The diffused nature of this transition and high dielectric constant of PFN is related to the ...

Multiferroic properties of Pb(Zr,Ti)O3∕CoFe2O4 composite thin films

In the present work we report multiferroic behavior in lead zirconate titanate (PZT)–cobalt iron oxide (CFO) composite thin films. It is found that upon annealing, the multilayered structures are intermixed at least partially, and CFO is phase separated into PZT matrix to form a composite film. The phase separation behavior has been characterized by x-ray photoelectron spectroscopy depth profiling of the constituent elements in conjunction with dielectric spectroscopy measurements. The composite films exhibited ferroelectric as well as ferromagnetic characteristics at room temperature. The coupling between the ferroelectric and the ferromagnetic order parameters has been demonstrated through the reduction of ferroelectric polarization when measured under an applied magnetic field.

X-ray photoelectron spectroscopy and micro-Raman analysis of conductive RuO2 thin films

Ruthenium oxide (RuO2) was synthesized in thin film and powder forms using the solution chemistry technique. The oxide electrodes on Si substrates were characterized in terms of their structure, composition, stoichiometry, and conductivity. X-ray lattice parameter calculations and micro-Raman analysis revealed the rutile structure in the material. Both films and powders exhibited an unassigned Raman band at about 477 cm−1 in their Raman spectra. Performing peak frequency calculations for B2g and A1g modes of RuO2 using the rigid-ion model, which ruled out the possibility that this band originated from disorder induced symmetry, allowed silent mode. Based on the x-ray photoelectron spectroscopy (XPS) and temperature dependent Raman studies, this band was assigned to hydrated RuO2. XPS characterizations of our samples revealed minute surface contamination of oxygen and chlorine, probably due to the film preparation and high temperature deposition processes. Films with uniform microstructure, low surface rou...

Sol–gel derived grain oriented barium strontium titanate thin films for phase shifter applications

In the present work process methodology was optimized to synthesize oriented barium strontium titanate (BST) (50/50) and (60/40) thin films on strontium titanate (100) and lanthanum aluminate (LAO) (100) substrates by using the chemical solution deposition technique. These films were characterized in terms of their phase formation behavior and structural growth characteristics using x-ray diffraction and atomic force microscopy. A tentative mechanism of the epitaxial growth has been proposed. Films were also characterized in terms of their dielectric properties. The high tunability and low dielectric loss of these films make them attractive for fabricating tunable dielectric devices. Accordingly, we have fabricated eight element coupled microstrip phase shifters and tested them in terms of their degree of phase shift and insertion loss characteristics. An insertion loss of 8.435 dB, phase shift in the order of 320° (2.6–14.5 V/μm) and κ factor (phase shift/dB of loss) of about 38.0°/dB was achieved in BST (60/40) films deposited on LAO (100) substrate which is comparable to the films grown by other film deposition techniques reported in the literature. The microstructure of the sol–gel derived films show surface porosity which may be responsible for the low dielectric strength of these films. Presently, we are studying the sintering mechanism and kinetics of these films in order to improve the density which is believed to further improve the phase shift and lower insertion loss to result in an improved tunability.In the present work process methodology was optimized to synthesize oriented barium strontium titanate (BST) (50/50) and (60/40) thin films on strontium titanate (100) and lanthanum aluminate (LAO) (100) substrates by using the chemical solution deposition technique. These films were characterized in terms of their phase formation behavior and structural growth characteristics using x-ray diffraction and atomic force microscopy. A tentative mechanism of the epitaxial growth has been proposed. Films were also characterized in terms of their dielectric properties. The high tunability and low dielectric loss of these films make them attractive for fabricating tunable dielectric devices. Accordingly, we have fabricated eight element coupled microstrip phase shifters and tested them in terms of their degree of phase shift and insertion loss characteristics. An insertion loss of 8.435 dB, phase shift in the order of 320° (2.6–14.5 V/μm) and κ factor (phase shift/dB of loss) of about 38.0°/dB was achieved in BST...