SiO2 Buffer Layer Research Articles

In-situ superconducting YBa2Cu3O7 thin films grown by ion beam co-deposition

We present superconducting YBa2C3O7 (YBCO) thin films grown in-situ by three-ion-beam sputtering. Y, Y2O3, Cu, Cu2O, BaF2 and BaCO3 sputter targets have been investigated. The highest quality films were prepared using a BaCO3 target. Auger analysis of films grown using a BaCO3 target show no carbon content. Y2O3 and Cu2O are more suitable than the native metals as sputter targets for YBCO growth as they are much less prone to sputter rate variations with oxygen partial pressure. They also supply oxygen to the growing film. As-deposited YBCO films are metallic (resistivity 240 μΩ cm at 100 K), reflective, and of highly homogeneous composition with TCO transition temperatures of 73 K and transition widths of 15 K. Post-annealing in flowing oxygen improves TCO's to 82 K. Critical currents are in excess of 105 A cm-2 at 77 K. Films are textured with c-axis orientation perpendicular to the (100) SrTiO3 substrate surface. As-deposited superconducting YBCO films have also been prepared on SiO2 and Y2O3 buffer layers on Si wafers.

Properties of ion beam deposited Pb1−xLax(ZryTiz)1−x/4O3

We have recently investigated ion beam sputtering and ion assisted deposition of Pb1−xLax(ZryTiz)1−x/4O3 (PLZT). Ion beam sputtered PLZT films display strong second-harmonic generation. Good quality material has been deposited on substrates of Si, Si with a buffer layer of SiO2 , and fused silica. The surface morphology of ion beam sputtered PLZT is of very high quality.

Analysis of interface states in CaS/Y2O3/SiO2/ITO multilayer thin films by AES.

Interface states between an insulating layer and a transparent electrode were investigated, being concerned with the stability and the luminescent properties of CaS thin film electroluminescent (EL) devices. It was found that Y2O3 and CaS thin films deposited on an ITO transparent electrode at 500°C were peeled off when these films were heat-treated at 500°C for one hour. The peeling-off is thoroughly prevented by inserting a SiO2 thin film as a buffer layer between the Y2O3 and ITO films. It was shown that the luminescent properties of the EL device was also improved by using the SiO2 buffer layer. The roles of the buffer layer are discussed from the results of the elemental depth profile measured by Auger electron spectroscopy.

Minimizing dc drift in LiNbO3 waveguide devices

Improved stability against electrical dc bias drift has been demonstrated in LiNbO3 electro-optic modulators by replacing the commonly used SiO2 buffer layer with indium tin oxide (ITO), a transparent conductor. The long term drift of the modulators having an ITO buffer layer with a sheet resistivity of ∼20 Ω/⧠ is less than 0.3% in 8 h. The mechanism of the dc drift phenomenon is discussed using an electrical equivalent circuit model of the modulator.

Optical losses in metal/SiO 2 -clad Ti:LiNbO 3 waveguides

We present measured excess loss resulting from electrode overlays for both TE and TM polarisations as a function of SiO2 buffer layer thickness for Ti:LiNbO3 strip waveguides at λ = 1.32 μm. We find there is negligible excess loss to the TE mode with no buffer layer and that the excess loss to the TM mode can be essentially eliminated with a SiO2 layer only 700 Å thick. A passive polariser with ̃ 1.5 dB fibre-waveguide-fibre insertion loss and > 13 dB extinction ratio is also demonstrated.

Laser crystallization of Si films on glass

By using glass substrates which approximate the thermal expansion of a deposited Si film, thermal stress cracking during laser crystallization is eliminated. Results on three types of transparent silicate glass are reported. Chemical vapor deposition is used to coat these substrates first with a buffer layer of SiO2 or Si3N4 and then with a Si film. When the Si films are melted with an argon ion laser beam, large crystal grains are produced. Secondary ion mass spectroscopy is used to determine the effectiveness of the buffer layer in isolating the Si from impurities in the glass.

Low-loss fibre-coupled waveguide directional coupler modulator

We report a fibre-coupled Ti: LiNbO3 directional coupler modulator with total fibre-device-fibre insertion loss as low as 1.5 dB for λ=1.32 μm. Low loss has been achieved by using diffusion parameters to give good mode match to the fibre and low propagation loss, an effective SiO2 buffer layer to eliminate electrode loading loss and a directional coupler geometry which minimises the effect of bend loss.

Silicon nitride films on silicon for optical waveguides

Silicon nitride (Si(3)N(4)) thin film optical waveguides with propagation losses of less than 0.1 dB/cm for the TE(0) mode at lambda(0) = 6328 A have been successfully grown by low-pressure chemical vapor deposition. Silicon wafers 5 cm in diameter were used as substrates, and the Si(3)N(4) was separated from the substrate by a steamoxide SiO(2) buffer layer. Propagation losses are examined for the various waveguide modes, and their dependence on waveguide parameters and wavelength are discussed and compared with exact calculations. Leakage into the silicon substrate is shown to be a major loss mechanism, especially at longer wavelengths and for higher mode numbers.