Dominique Averty

Preparation of multi-coating PZT thick films by sol–gel method onto stainless steel substrates

PbZr0.45Ti0.55O3 ferroelectric films have been prepared by sol–gel method, using alkoxide precursor compounds and multi-layer technique. The gel films were deposited by spin-coating onto stainless steel substrates. In order to obtain crystallization in the perovskite phase, the samples were annealed at 600–700°C for 1 min. The dependence of the electric properties on the heat-treatment temperature is studied, and the coercive electric field as a function of the material thickness is determined. By SEM photography, the microstructure of the films could be shown to be homogeneous.

Electron emission from ferroelectric crystals of different thickness

Abstract Electron emission from the surface of ferroelectrics TGS crystals and PZT ceramics is investigated for thickness from 6 μm to 1 mm. Study of electron emission distribution in time from Triglycine Sulfate (TGS) crystals of different thickness have been investigated. The correlation in time between emitted and switching currents and applied electric voltage is experimentally studied. It was shown that the electron emission occurs when the negative polarization charges appear at the emitting surface. An emitted current density up to 20 A/cm2 have been measured without inducing discharge. Interpretation of the results by considering the evolution of the domain switching, thickness of the samples and geometry of the electrodes have been realized. Electron emission from PZT ferroelectric thin films of 6.3 μm thickness is presented.

Optical characterization of PZT thin films for waveguide applications

In order to develop an electro-optic waveguide, Pb(Zr, Ti)O3 ceramic ferroelectric thin films were elaborated by a modified sol-gel process on glass substrate. In the aim to study the optical properties of the PZT films, an accurate refractive index and thickness measurement apparatus was set up, which is called M-lines device. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on PZT layers. Two different processes of PZT elaboration were made and studied with this apparatus. The reproducibility of one fabrication process was tested and results are presented in this paper.

Study of lithium niobate with periodically reversed domains

Abstract Periodical domain structure on various surfaces of LiNbO3 crystals doped with Mg and Y or Dy was studied by scanning electron microscopy (SEM) and optical microscopy. A bright contrast of domain boundaries on both surfaces with P, lying in the plane (X-face) and on surfaces nearly normal to Ps was observed by SEM in the secondary electron emission mode. The domain structure periodicity of 5.5 μm was found on the X-face, whereas the domain periodicity of about 2.8 μm is visible on the surface nearly perpendicular to P. The second and third harmonic generation conditions were discussed.

INFLUENCE OF THE MORPHOLOGY OF BARIUM STRONTIUM TITANATE THIN FILMS ON THE FERROELECTRIC AND DIELECTRIC PROPERTIES

ABSTRACT In the present study, Ba0.8Sr0.2TiO3 thin films were realized by chemical solution deposition and spin-coating on stainless steel substrates using the classical multi-layer technique. In order to influence the morphology of the films, three solutions with a different concentration, 0.1 M (BST0.1M), 0.3 M (BST0.3M) and 0.6 M (BST0.6M), were prepared. The dilution is shown to influence the grain size of the films and as consequence also its ferroelectric and dielectric properties.

Pulse polarization inversion and phase transition in ferroelectric and antiferroelectric thick films

Fast switching in thin ferroelectrics has been investigated from the respective switching current and voltage wave form signals. The polarization inversion process, established for PZT (45/55) thin films in a nanosecond time scale, takes place at the “dynamic coercive electric field” and is mainly limited by the electric circuit components. Due to the low impedance of the ferroelectric during switching, the voltage across the ferroelectric rises only when polarization inversion is getting accomplished. Hence a voltage dependence of the switching has not be found. Pulse phase transition experiments in antiferroelectric PZT (95/5) have been performed, which show that the dynamic behavior of the transition between the ferroelectric and the antiferroelectric state follows the same principle. Thus, fast phase transitions can be realized, too. Derived from the voltage and current wave form data, “pulse hysteresis loops” have been established.

Nanosecond switching of ferroelectric thin films for application to a short-pulse micro electron emitter

Abstract We have analysed the electron emission characteristics from thin bulk ferroelectrics, and examined the contribution of the electrode pattern to the electric field distribution inside the ferroelectric and in the vacuum. It is shown that emission experiments performed with ferroelectric thin films up to now suffer from a not adapted electrode structure and are not optimized with respect to detection. Re-examination of the switching kinetics of ferroelectric thin films reveal that polarization can be inversed up to a certain distance from the electrode edge. Thus a first indication of the area that might participate in the emission process is found. In conclusion we discuss possibilities to improve the emission data, which may lead to the development of a micro electron-beam source based on emission from ferroelectric thin films.

Influence of temperature variations on the visualisation of the ferroelectric domains of TGS and TAAP crystals by scanning electron microscopy

Abstract Temperature variations of aged Triglycine Sulphate (TGS) and Telluric Acid Ammonium Phosphate (TAAP) samples increase the contrast between positive and negative ends of domains observed with a scanning electron microscope. For freshly cleaved surface of TGS, an increase of temperature of 2°C inverts the contrast between these domains. When the temperature of the TGS samples increases continuously, we observe a deformation of the picture on the screen, but it is not observed for TAAP samples. Thermally stimulated electron emission is also observed and measured. These phenomena are due to the surface charges produced by the modification of the spontaneous electric polarization of the samples when the temperature varies.

Preparation and Characterization of Barium Strontium Titanate Thin Films by Chemical Solution Deposition

In the present study, Ba 0.70 Sr 0.30 TiO 3 thin films were realized by chemical solution deposition based on the use of an alkoxide precursor. The solution is spin-coated onto stainless steel substrates and a classical multi-layer technique was used in order to obtain thicker films. The elaboration route is described and a study of the temperature dependence of the crystallization process is presented. The ferroelectric and the dielectric (permittivity and tanδ) properties were determined at different temperatures in order to determine the evolution of the tunability and the figure of merit of the films.

Ferroelectric domain structure of [N(CH3)4]2 ZnC14 single crystals

Abstract Ferroelectric domain structure of tetramethylammonium zinc chloride was revealed in the temperature range 275. 8R-279. OK by means of scanning electron microscopy. The domain patterns of lamellar type were observed. The mean width of the domains at 276.1 K amounted to 10 μm.