Influence of annealing on the ferroelectric properties of Pt/Pb(Zr,Ti)O3/Pt thin film capacitors

The deformation in the hysteresis loop of Pt/Pb(Zr,Ti)O₃/Pt capacitors has been investigated by varying the annealing temperature after patterning the top sputter-deposited electrode using reactive ion etching (RIE) with Ar gas. It was observed that as-patterned capacitors were positively poled by the dc plasma potential during RIE of Pt. Voltage shift and slant in the hysteresis loop are found to be due to space charges trapped at domain boundaries during both sputtering and RIE rather than a nonferroelectric second phase. As Zr:Ti ratio decreases, internal bias field increases, and annealing temperature, at which maximum in polarization occurs, also increases due to lower permittivity and higher Curie temperature.     

Influence of a degraded SrTiO3 layer at the YBa2Cu3O7−δSrTiO3 interface on the dielectric behavior at cryogenic temperature

In an YBa₂Cu₃O_7−δ/SrTiO₃/YBa₂Cu₃O_7−δ parallel capacitor fabricated by a chemical mechanical planarization method, the dielectric constant and loss in the presence of electric fields at 2.2 K were more than 26,000 and less than 0.027, respectively. We propose a multilayer model that explains this behavior. The model assumes that the SrTiO₃ film is composed of single-crystal-like SrTiO₃ layers with a dielectric constant ε_r = 30,000 and degraded SrTiO₃ layers with dielectric constants that vary continuously from 25, the dielectric constant of YBa₂Cu₃O_7−δ, to 30,000. Results of a numerical calculation revealed that the thickness of the single-crystal-like SrTiO₃ layer was more than 92% of a 600-nm-thick SrTiO₃ film.     

Influence of the processing conditions on charge transfer and transport properties in poly(2-methoxy-5-(2′-ethylhexyloxy)1-4-phenylenevinylene):C60 composites for photovoltaics

Polymer-based photovoltaic devices have been elaborated by blending the conjugated polymer, poly(2-methoxy-5-(2′-ethylhexyloxy)1-4-phenylenevinylene) (MEH-PPV) with the buckminsterfullerene, C₆₀. The solvent used has a main influence on the optical and electrical properties of the photoactive layers. This could be attributed to different dispersion abilities of C₆₀ in the polymer layers shown by Atomic Force Microscopy and Scanning Electron Microscopy. Its effect on the transfer and transport properties has been studied. Thin film processing conditions have been modified by the preparation of blends of solutions of the polymer in Tetrahydrofuran and fullerene in Ortho-dichlorobenzene. The resulting spin casted layers show improved morphologies implying better dispersion of the fullerenes and increased short circuit currents. A decrease in the fullerene critical concentration to form percolation paths has been demonstrated. The improvement of the photovoltaic properties of the MEH-PPV/C₆₀ composites has been attributed to the nanosized fullerene domains formed upon phase separation. We used optical spectroscopy to study the charge transfer efficiency and electrical measurements to investigate charge transport properties in MEH-PPV:C₆₀.