Sannian Song

The effect of stress on the dielectric and tunable properties of barium stannate titanate thin films

Ba(Sn0.15Ti0.85)O3 thin films were grown on the LaNiO3 buffered LaAlO3, SrTiO3, MgO, and Al2O3 single crystal substrates, respectively. These substrates provide a systematic change in the stress while maintaining the same film microstructure. The stress in the thin film induces an obvious change in the dielectric behavior. The reduction in the ferroelectric transition temperature with increasing biaxial tensile stress is attributed to the suppression of in-plane polarization due to the small lateral grain size in the films. The in-plane tensile stress in this study reduces the unit cell along electric field in the parallel plate capacitor structure and decreases the tunability.

Thickness-dependent dielectric and tunable properties of barium stannate titanate thin films

Barium stannate titanate Ba(Sn0.15Ti0.85)O3 (BTS) thin films with different thicknesses were grown by sol-gel process on single crystal LaAlO3 (LAO) and Pt/Ti/SiO2/Si substrates, respectively. Coplanar capacitance and parallel plate capacitance structure configurations were formed by preparing interdigital electrodes and parallel plate electrodes on BTS thin films. Both of the films exhibited an enhanced dielectric constant and tunability as the film thickness increases but these two cases are actually based on different mechanisms. The thickness dependent dielectric properties of the films deposited on Pt/Ti/SiO2/Si substrates were mainly attributed to the “dead layer” effect while those of the films grown on LAO substrates were due to strain and grain size of the films.

Enhanced electric field tunable dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films

Highly (100)-oriented barium stannate titanate Ba(Sn0.15Ti0.85)O3 (BTS) thin films were deposited on SrTiO3 (STO) and Nb doped SrTiO3 (NSTO) single-crystal substrates through sol-gel process, respectively. Coplanar capacitance and parallel plate capacitance structure configurations were formed by preparing interdigital electrodes (IDEs) and parallel plate electrodes (PPEs) on BTS thin film. The tunability of films with IDE was 45.54%, while the tunability of films with PPE was only 11.54% at the frequency of 1 MHz with an applied electric field of 80 kV/cm. This result showed that the tunability in the a-b plane contributes markedly to the measurements obtained with the IDE.

Improvement of dielectric properties of graded Co-doped (Ba0.7Sr0.3) TiO3 thin films fabricated by sol-gel method

The undoped, homogeneous and graded Co-doped (Ba0.7Sr0.3) TiO3 (BST) thin films with compositionally gradient from 0 mol% to 5 mol% were prepared on Pt /Ti /SiO2/Si (100) substrates by sol–gel technique. All of the thin films crystallized into a pure perovskite structure after post-deposition annealing. Dielectric properties of undoped, homogeneous and graded Co-doped BST thin films were investigated as a function of frequency and direct current bias field. These results showed that the graded acceptor doping was a promising technique to reduce the loss tangent and leakage current while maintaining weak change in tunability of BST thin film.

Effect of (La0.5Sr0.5)MnO3 and (La0.5Sr0.5)CoO3 Buffer Layer on the Dielectric Properties of BaTiO3 Thin Films Prepared by a Sol-Gel Process

The dielectric properties of BaTiO3 thin films deposited on (La0.5Sr0.5)MnO3 (LSMO) and (La0.5Sr0.5)CoO3 (LSCO), respectively, as buffer layer, were studied. The influence of buffer layer on the phase of the thin films was examined. Dielectric properties of the thin films were investigated as a function of frequency and direct current electric field. These results showed that the buffer layer strongly influenced the structure and the dielectric properties of the films. The BaTiO3 thin films on LSMO buffered Pt/Ti/SiO2/Si substrates have enhanced tunability and lower leakage current.

Enhanced Dielectric Properties of Ba(Sn0.15Ti0.85)O3 Thin Films Grown on Pt/Ti/SiO2/Si Substrates

Ba(Sn0.15Ti0.85)O3 (BTS) thin films were deposited on Pt (111)/Ti/SiO2/Si substrates by sol-gel technique with a 30 nm thick BTS seed layer. The dielectric constant of the BTS films with and without seed layer was 720 and 395, respectively. The tunability of BTS thin films with seed layer was 52.1%, which was about two times larger than that of BTS thin films without seed layer at the frequency of 100 kHz with an applied electric field of 200 kV/cm. The results showed that the seed layer had an obviously effect on the orientation and dielectric properties of the BTS films.

The In-Plane Dielectric and Microwave Properties of Barium Stannate Titanate Thin Films

The microstructure and in-plane dielectric and microwave properties of barium stannate titanate Ba(Sn 0.15 Ti 0.85 )O 3 (BTS) thin films grown on c-plane Al 2 O 3 substrates through sol-gel process are investigated. X-ray diffraction and field emission scanning electron microscopy are used to characterize phase structure and microstructure of the thin films, respectively. Using interdigital capacitors (IDC) with Au electrodes on thin films, the dielectric constant and loss tangent as a function of applied voltage (0–40 V) are measured at low frequencies up to 1 MHz. Microwave properties of the films are measured at 10 GHz. This work clearly reveals the highly promising potential of BTS films for application in tunable microwave devices.

Investigation of Barium Stannate Titanate Thin Films for Tunable Microwave Applications

Barium stannate titanate Ba(Sn 0.15 Ti 0.85 )O 3 (BTS) thin films have been investigated as a prospective material for tunable microwave applications. The thin films were fabricated by sol-gel method on (100) MgAl 2 O 4 single-crystal substrates. The influence of post-annealing on the structure and tunable dielectric properties of the thin films was studied. Using interdigital capacitors with Au electrodes on thin films, the dielectric constant and loss tangent were measured as a function of electric filed and temperature at 1 MHz. A tunability of 28.86% at E max = 80 kV/cm and a loss tangent of 0.016 have been achieved for the sample annealed at 1000°C, measured at 1 MHz and room temperature. In addition, BTS films were also characterized at microwave frequencies up to 10 GHz. A capacitance change of 15.19% was observed at the frequency of 5 GHz with an applied electric field of 80 kV/cm.

THE MICROSTRUCTURE CHARACTERISTICS AND DIELECTRIC BEHAVIORS OF THE COMPOSITIONALLY GRADED Ba(Ti,Sn)O3 THIN FILMS

ABSTRACT The compositionally graded Ba(SnxTi1 - x)O3 (BTS) films with a compositional gradient from BaTiO3 to BaSn0.15Ti0.85O3 were fabricated on LNO-buffered Pt/Ti/SiO2/Si substrates by a sol-gel deposition method. The graded films crystallized into a pure perovskite structure after post-deposition annealing. The gradient of increasing Ti and decreasing Sn content from the surface of the film to the substrate was nicely demonstrated by the XPS data. Dielectric properties were investigated as a function of both temperature and frequency. It was observed that leakage currents increased asymmetrically for the negative and positive bias voltage with compositional gradient films. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range from −25°C to 150°C. Generally, ferroelectric material is tunable in only a narrow temperature range near a phase transition. Ba(SnxTi1 - x)O3 compositionally graded films with weak temperature dependence of tunability in the temperature range between −25°C and 30°C could make attractive materials for situations in which precise control of temperature would be either impossible or too expensive.