J. Pundareekam Goud

Resonant spectrum method for characterizing Ba0.5Sr0.5TiO3 based high overtone bulk acoustic wave resonators

This letter reports the use of the resonant spectrum method to characterize a high overtone bulk acoustic wave resonator (HBAR) which has a thin film ferroelectric BaSrTiO3 (BSTO) active layer on a YAG substrate. The HBAR works on the principle of electric field induced piezoelectricity of the thin film ferroelectric BSTO and exhibits switching functionality. From the parallel and series resonant frequencies of each of the multiple peaks in the frequency spectrum of the HBAR, the distribution of spacing of parallel resonance frequency and the distribution of effective coupling coefficient are studied and parameters like acoustic wave velocity, electromechanical coupling coefficient, elastic constant, and density for the thin film are determined. The influence of dc bias voltages on the distribution of the effective coupling coefficient and the electromechanical coupling coefficient is also reported. This letter also establishes the relationship between the relative tunability of the device capacitance and...

Switchable high overtone resonances in BST film with MIM structure on sapphire substrate

DC bias field dependent high overtone resonances are observed in a metal insulator metal (MIM) structure based on Ba0.5Sr0.5TiO3 (BST) thin films on a sapphire substrate. The microwave measurement shows the bias dependent nature of the device, wherein without any bias it acts like a MIM capacitor but upon biasing resonant peaks start appearing in its frequency spectra, which is typical of a response given by a high overtone bulk acoustic wave resonator (HBAR). Acoustic velocity of the sapphire substrate is calculated to be 11440 m/s and the HBAR exhibits a high quality factor of 4370 around 1.39 GHz.

Microwave dielectric and optical properties of amorphous and crystalline Ba0.5Sr0.5TiO3 thin films

The thin films of composition Ba0.5Sr0.5TiO3 (BST5) were deposited by Pulsed Laser Deposition technique on amorphous fused silica substrates at room temperature (RT) and at 700°C. The film deposited at RT is amorphous while the other crystallized in cubic structure. The refractive index (n) and optical band gap (Eg) extracted from transmission spectra in the 190 -2500 nm range. Microwave dielectric properties were investigated using the Split Post Dielectric Resonators (SPDR) technique at spot frequencies of 10GHz and 20GHz. The experimental results show that thin films deposited at high temperature (700°C) shows very high dielectric constant for both 10GHz and 20 GHz. These high dielectric constant films can be used in a wide range of applications such as capacitors, non-volatile high speed random access memories, and electro-optic devices.

Optical and microwave dielectric properties of pulsed laser deposited Na0.5Bi0.5TiO3 thin film

Optical properties of pulsed laser deposited (PLD) sodium bismuth titanate thin films (NBT), are investigated at wavelengths of 190-2500 nm. Microwave dielectric properties were investigated using the Split Post Dielectric Resonator (SPDR) technique. At 10 GHz, the NBT films have a dielectric constant of 205 and loss tangent of 0.0373 at room temperature. The optical spectra analysis reveals that NBT thin films have an optical band gap Eg=3.55eV and it has a dielectric constant of 3.37 at 1000 nm with dielectric loss of 0.299. Hence, NBT is a promising candidate for photonic device applications.

Study of amorphous and crystalline phases of sodium bismuth titanate thin films by optical and Raman spectroscopy

Amorphous and crystalline Na0.5Bi0.5TiO3 (NBT) thin films were deposited at different substrate temperatures on fused silica by plused laser deposition method. The phase and microstructure of the deposited films were investigated by XRD and FE-SEM respectively. The noticeable difference is observed in the Raman and optical spectra of amorphous and crystalline films. To grasp further insight, the dispersion data of the refractive index is fitted with the single oscillator model. The oscillator strength and oscillator energy are computed. The refractive index of NBT thin films decrease with increase in wavelength and approach a constant value in long wavelength limit while extinction coefficient increase with increase in wavelength. In Raman spectra of amorphous materials, many Raman peaks coalesce and form very broad spectral bands, whereas the polycrystalline material shows distinct band.

Zr-substituted Ba0.6Sr0.4TiO3 ferroelectric thin films grown by pulsed laser deposition (PLD) at different laser fluence

ABSTRACT Zr-substituted Ba0.6Sr0.4TiO3 ((Ba0.6Sr0.4)(Ti0.8 Zr0.2)O3) - BSZT) thin films are deposited by using Pulsed Laser Deposition method with different fluence at optimized conditions on amorphous fused silica substrates. The X-ray diffraction (XRD) pattern of the films confirms the formation of cubic phase. Raman studies are performed to understand vibrational modes present in the films. The optical band gap of deposited BSZT thin films were calculated from the transmittance measurements. Microwave dielectric properties of the thin films deposited at 2 J/cm2 were measured. These results show BSZT thin films are useful in tunable microwave devices.

Effect of sintering temperature on structural and dielectric properties of Bi and Li co-substituted SrTiO3

Sintering is an important factor that affects the microstructure development in ceramics. In this work, Bi and Li co-substituted Strontium Titanate (ST) ceramics samples sintered at different temperatures are prepared and analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD was used to detect phase structure of the sintered samples and SEM was used for microstructure analysis. Dielectric properties of Bi and Li co-substituted SrTiO3 samples were measured using Agilent 4294A Impedance analyzer in the frequency range 40 Hz to 5 MHz at room temperature. The result reveals that the dielectric constant of Bi and Li co-substituted SrTiO3 ceramics increases with increasing sintering temperature up to 1250°C and then decreases beyond that. The highest value of dielectric constant obtained is 860 at 1KHz frequency and lowest dielectric loss observed is 0.04 at the same frequency for samples sintered at 1250°C. Also the grain size increases with increase of sintering temperature.

Microwave absorption properties of LiNb3O8 in X-band prepared by combustion synthesis

Single phase LiNb3O8 powders were prepared using combustion synthesis technique. The powders were prepared by heat treating Li2CO3+Nb2O5/urea mixture in 1:3 ratio. Structural and morphological details have been done to confirm the presence of LiNb3O8. The S-parameters were measured using rectangular waveguide method in the X-band frequency (8.2GHz to 12.4GHz) by Vector Network Analyzer. The dielectric characteristics like dielectric constant (e′) and dielectric loss (e″) were calculated using Nicolson-Ross-Weir algorithm. Complex permittivity of 28-0.2j and 26-1.0j at 8.2GHz and 12.4GHz respectively are observed. Reflection loss was derived with permittivity and permeability as input parameters. Microwave absorber thickness is optimized and the RL< -20dB is obtained in the X-band frequency.