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Advanced materials for integrated active optic

Updated on November 30, 2009
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Advanced materials for integrated active optic Students : S. Gueroudj, A. Khan, N. Macsporran, P. Marotel, N. Rousseau, F.E. Ruchon, R. Salhi Objectives Applications where the interaction between photon and matter plays the main role are very large. Achieving more efficient devices relies on the evolution of technologies and requires the development of new and advanced materials. Our activity in this field deal with thin films for optical telecommunications, transparent electronics, image sensors and photonic crystals. Main results 
  • Optical telecommunication component : With the continuing evolution of optical telecommunications, the introduction of the optical signal at the access networks requires the development of low cost components. As for microelectronics, a way to achieve cost reduction is miniaturization and collective manufacturing of components, although optical densities of integration are and will remain lower. This integration requires to use thin film materials and therefore to implement a propagation of light in layer plane, i.e. in waveguide integrated configuration. A first project deals with the fabrication of an optical isolator. We tried to create a hybrid structure composed of a magneto-optical ferrite garnet layer, chosen for its high Faraday effect, on a passive ion-exchanged glass waveguide. Because of thermal restraints, the growth of a crystallised garnet film is impossible on glass. The original idea was to split the elaboration of the component in two steps. The garnet layer is first grown by liquid phase epitaxy at high temperature and the garnet film is than integrated on the waveguide by ionic implantation and direct wafer bonding techniques based on molecular adhesion. A patent was taken out on this process. Concerning the optical part of this component, Er doped nanocomposite oxide thin films were developed. Layers formed by grains of a nanometric size (<50 nm), are crucial to minimize the losses by absorption in the light propagation. We developed two approaches for this purpose. The first approach was to use low deposition temperatures with an UV activated CVD process in order to minimize the grain size and the organic  contamination. The second approach consisted of co-depositing with the ceramic (Y2O3) another immiscible oxide, which would limit the growth of grains during deposition or crystallization and create a dilution effect. Immiscible tested oxides were alumina and phosphorus pentoxide. For the proportions of 10% to 25%, a decrease in grain size was observed by X-ray diffraction and a broadening of spectral lines of fluorescence in the visible.
    • Collaborations CEA LETI,
    • Fundings Région Rhônes-Alpes
  • Inorganic colour filter for Image sensors : CMOS imager, present in camera phones, webcams, security camera, etc, is one of the important and growing market with a main trend which is higher resolution while keeping small sensors. Emphasizing the problem of light collection inside the pixel, in CMOS image sensors, a solution would be to minimize the distance between the colour filters and the photodiode. That implies that colour filters need to support a thermal process above 450°C under reducing atmosphere. We investigated inorganic transmission colour filters based on thin films of several oxide matrices doped by various transition metals. These thin films were deposited by aerosol assisted MOCVD (Metal Organic Chemical Vapour Deposition) process. Filters stable under annealing "forming gas "(N2-H2 5% 450°C) were obtained from thin layers of a thickness of 1 micron of zinc oxide doped by cobalt for the green colour and of cobalt aluminate Al2CoO4 for blue colour. (Fig.1.17)
Figure 1.17 - Garnet film transferred on a glass substrate
  • Study of new P-type TCO thin films : Transparent conductive oxides (TCOs) are materials displaying a remarkable combination of high electrical conductivity and optical transparency. Most of the currently known TCOs exhibit only n-type electrical conductivity and due to the lack of controlled and reproducible -type conduction in these oxides there is a limited number of oxide-based p-n junctions. Since May 2005 within the frame of an European project NATCO, we tried to growth p-type films of Cu based TCOs. The SrCu2O2 (SCO) is considered to be a promising candidate for p-type TCOs due to its direct band gap. One innovative aspect of the project methodology is the strong correlation and interaction between theoretical first principle modelling and experimental studies in order to determine the best candidate as dopant. The first principle calculations and computer simulations show that Ba doped SCO could have the best electrical conductivity. By using Strontium, Barium and Copper tetramethylheptanedionate as precursors dissolved in meta Xylene, mixed Ba-doped strontium copper films have been grown by injection MOCVD in the 450°C- 550°C deposition temperature range. As deposited, FTIR and XRD analysis have shown that the films were composed of a mixture of copper oxide (CuO) and strontium carbonate. Post-deposition treatments were necessary in order to obtain SCO. In a first route, films were firstly annealed under O2 to eliminate carbonates and to be crystallized. This annealing under O2 develops a new phase, SrCu2O3. The SCO phase was obtained in the second step annealing under Ar. With another route the SCO phase was also obtained by one annealing under N2 with SrCuO2 and Cu2O as intermediate phases. SCO was obtained only when using Rapid Thermal Annealing (JL. Deschanvres, Physica Status Solidi (a) 205 (2008)2013). In fact, in-situ Raman characterization of the phase transformation during annealing established that a rapid cooling is necessary to retain the SCO phase.
    • Collaborations  THALES, Tyndall Institut - Cork,
    • Fundings : EU project NATCO

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Date of update November 30, 2009

Université Grenoble Alpes