Sushma Kotru

Improved ferroelectric property of LaNiO3/Pb(Zr0.2Ti0.8)O3/LaNiO3 capacitors prepared by chemical solution deposition on platinized silicon

We report a technique to prepare top and bottom oxide electrodes of LaNiO3 (LNO) for lead zirconate titanate (PZT) films using a chemical solution deposition. LNO/PZT/LNO sandwich structures were prepared on platinized silicon by spin coating combined with rapid thermal annealing. Pt dots were sputtered on top of LaNiO3 film to serve as protective masks during etching of the uncovered LaNiO3 layer using dilute hydrochloric acid. For comparison, Pt/PZT/Pt capacitors were also prepared using the same processing conditions. Electrical measurements were carried out on both Pt/LNO/PZT/LNO/Pt and Pt/PZT/Pt structures. The remnant polarizations and coercive fields for these two capacitors are 17.4 and 21.4μC∕cm2, 71 and 81.5kV∕cm respectively at 5V. The leakage current density for the Pt/LNO/PZT/LNO/Pt structure is about 1.38×10−6A∕cm2 at 5V, which is lower than that of PZT deposited on Pt electrode. After 109 bipolar switching cycles, no significant change in remnant polarization was observed in the Pt/LNO/PZT/...

Pulsed laser-deposited ilmenite-hematite films for application in high- temperature electronics

Abstract Members of the family of ilmenite–hematite (1−x)FeTiO3·xFe2O3 have been found to exhibit interesting semiconducting behavior over a wide range of temperatures. Low-voltage varistors were recently produced using ceramic specimens. The objective of this work was to grow and characterize epitaxial films of some members of the family that can be used for fabricating p–n junction devices. Epitaxial films of the (1−x)FeTiO3·xFe2O3 series (x=0, 0.10, 0.20, 0.27, 0.35, 0.45) were grown on (0001) sapphire substrates using pulsed laser deposition. The films are c-axis-oriented and exhibit good epitaxy.

Highly a-axis-oriented Nb-doped Pb(TixZr1−x)O3 thin films grown by sol–gel technique for uncooled infrared dectors

Pb(Nb0.02Zr0.2Ti0.8)O3 thin films with thickness of 900nm were spincoated on platinized silicon substrate using the sol–gel method. X-ray diffraction and field emission scanning electron microscopy show that the films are highly a-axis-oriented with columnar structure. A large remnant polarization (Pr+) ∼92.2μC∕cm−2 was observed for as-grown films. The coercive field (Ec+) for these films was 159.3kV∕cm. Good pyroelectric properties are obtained as a result of large remnant and spontaneous polarization and their strong temperature dependence. The pyroelectric coefficient and figure of merit at room temperature (22°C) are 10.8×10−4Cm−2K−1 and 2.34×10−5Pa−1∕2, respectively.

Chemical bonding, optical constants, and electrical resistivity of sputter-deposited gallium oxide thin films

Gallium oxide (Ga2O3) thin films were made by sputter deposition employing a Ga2O3 ceramic target for sputtering. The depositions were made over a wide range of substrate temperatures (Ts), from 25 to 600 °C. The effect of Ts on the chemical bonding, surface morphological characteristics, optical constants, and electrical properties of the grown films was evaluated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and four-point probe measurements. XPS analyses indicate the binding energies (BE) of the Ga 2p doublet, i.e., the Ga 2p3/2 and Ga 2p1/2 peaks, are located at 1118.0 and 1145.0 eV, respectively, characterizing gallium in its highest chemical oxidation state (Ga3+) in the grown films. The core level XPS spectra of O 1s indicate that the peak is centered at a BE ∼ 531 eV, which is also characteristic of Ga-O bonds in the Ga2O3 phase. The granular morphology of the nanocrystalline Ga2O3 films was evident from AFM measurements, which also indicate that the surface roughness of the films increases from 0.5 nm to 3.0 nm with increasing Ts. The SE analyses indicate that the index of refraction (n) of Ga2O3 films increases with increasing Ts due to improved structural quality and packing density of the films. The n(λ) of all the Ga2O3 films follows the Cauchys dispersion relation. The room temperature electrical resistivity was high (∼200 Ω-cm) for amorphous Ga2O3 films grown at Ts = RT-300 °C and decreased to ∼1 Ω-cm for nanocrystalline Ga2O3 films grown at Ts ≥ 500–600 °C. A correlation between growth conditions, microstructure, optical constants, and electrical properties of Ga2O3 films is derived.

Effect of kinetic growth parameters on leakage current and ferroelectric behavior of BiFeO3 thin films

Epitaxial BiFeO3 thin films have been grown on (100)-oriented SrTiO3 and Nb-doped SrTiO3 substrates using the pulsed laser deposition technique under identical thermodynamic and variable kinetic conditions. The variation of growth kinetics through laser fluence and pulse repetition rate had minimal effect on the structure and magnetic properties of films. However, large changes were observed in the microstructure, with initial island growth mode approaching toward step-flow type growth and roughness reducing from 12.5 to 1.8 nm for 50 nm thick film. Correspondingly, the leakage current density at room temperature dropped consistently by almost four orders of magnitude. The dominant mechanism in low leakage current films was space-charge-limited conduction. These findings suggest that the issue of leakage current can be dealt favorably by controlling kinetic growth parameters. The application of high electric field and observation of maximum polarization value up to 103 μC/cm2 could be possible in these sa...

Nonlinear current–voltage characteristics of ilmenite–hematite ceramic

Abstract Current–voltage ( I – V ) characteristics of solid solutions of ilmenite–hematite (IH) (1− x )FeTiO 3 · x Fe 2 O 3 , with x varying from 0 to 0.45, were studied. All compositions except x =0 exhibit a low-voltage varistor behavior. The switching voltage for these devices was found to be well below 10 V, with the lowest value being about 2 V. The nonlinear coefficient, α , of the devices varied between 1.75 and 3.7. These results indicate that varistors based on some members in the family of IH are suitable for protecting the Si-based microelectronic circuits from surge of transient currents.

Influence of work-function of top electrodes on the photovoltaic characteristics of Pb0.95La0.05Zr0.54Ti0.46O3 thin film capacitors

Photovoltaic properties of Pb0.95La0.05Zr0.54Ti0.46O3 thin film capacitors prepared using solution based method with metal top electrodes having different work functions are investigated in this work. It is shown that by using aluminum, a low work-function metal, as top electrode, the magnitude of photo voltage as well as photo current can be enhanced. More than one magnitude enhancement in the photovoltaic efficiency is observed with Al as top electrode compared to Pt electrodes. This work clearly highlights that an appropriate choice of low work function metal electrode can enhance the photovoltaic response of the ferroelectric thin film capacitors.

Design and Fabrication of a Meso-Scale Gyroscope

The purpose of this work was to develop a low-cost gyroscope for general aviation. The work was supported by FAA to fulfill their goal of replacing all or part of ground based navigation for general aviation which could help to overcome the difficulties related to GPS failures. To achieve this goal researchers are focusing on MEMS technology. We propose a new design for the gyroscope which should increase the accuracy by increasing the mass of the gyro, that is, produce a meso-scale gyro using MEMS technology and increase signal amplitude by using piezoelectric actuators and sensors (instead of conventional electrostatics). Nb-doped Pb(Zr20,Ti80)O3 films were grown on both sides of a 4 inch Pt/TiO2/SiO2/Si/SiO2/TiO2/Pt wafer by chemical solution deposition. The effective transverse piezoelectric coefficients (-e3t,f) of these films were measured for the pulse and DC poled films and found to be in the range of 3.21 ~6.36 C/m2. These films were then used to fabricate a meso-scale gyroscope using standard photo lithography, wet etching, ion milling and deep reactive ion etching techniques. One side of the film was used for actuation and the other side for sensing of the gyroscope. The resonance frequency of the gyroscope was obtained at 12.60 kHz which matches very well with the simulated results.

SbSI Films for Ferroelectric Memory Applications

Films of ferroelectric antimony sulphoiodide (SbSI) were grown on platinized silicon substrates by pulsed laser deposition (PLD). The films were grown at room temperature and later annealed at 200-250 C in air for crystallinity. The Curie temperature (T C ) of these films was 17-21 C, whereas the peak dielectric constant was up to 5000. These films showed nonzero remnant polarization above T C up to a temperature of 40 C and a low leakage current density of around 10 m 6 A/cm 2 at 2V. SbSI films were integrated with colossal magnetoresistive La 0.67 Ca 0.33 MnO 3 (LCMO) thin film, which acts as a p-type semiconductor. The LCMO-SbSI heterostructures, with SbSI as a ferroelectric gate, showed a channel modulation of about 10%.

Low-voltage varistors based on La–Ca–Mn–O ceramics

Varistor-like highly nonlinear current–voltage (I–V) characteristics were observed in the ceramics of colossal magnetoresistive La–Ca–Mn–O at room temperature, which is above its magnetic transition temperature. The switching voltage of all devices studied was less than 5 V with a nonlinearity coefficient a in the range of 2.6–32. The microstructure of the grains and the grain boundary region changes as the pelletization pressure and sintering temperature are varied. The contribution of grain boundary region to the electronic properties increases as the grains become smaller, which resulted in higher values of a and higher resistivity of the ceramic. This effect was observed at lower pelletization force and sintering temperature. It was also observed that higher values of a were associated with a higher switching voltage. D 2002 Elsevier Science B.V. All rights reserved.