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Functional oxides on Silicon and Sapphire substrates for photonic applications

Abstract : Silicon photonics is expected to allow the implementation of a wide range of applications including sensing, datacom and security with the potential to leverage the already existing CMOS fabrication facilities for cost-effective and large production. Among the building blocks to develop, optical modulator is considered as a key device for integrated circuits. The main physical effect to perform optical modulation in silicon is based on plasma dispersion effect. However the maximum modulation speed achievable with this approach is limited by the mobility and recombination time of the carriers. Furthermore, these types of modulators face some limitations in terms of power consumption, chirp and loss that may compromise their future integration in circuits. Our work focuses on the integration of Yttria-Stabilized Zirconia (YSZ) functional oxide on sapphire substrates and on silicon. The common aim for both integrations is to induce nonlinear optical effects at the wavelength around 1550nm, thanks to strain tuning in full oxide-or in hybrid oxide/Si-photonic structures. Indeed, we explore an alternative approach, based on the use of the Pockels effect for optical modulation [1]. Such an effect, commonly used in Lithium-Niobate, allows high speed and low power consumption optical modulation [2]. Unfortunately silicon is a centro-symmetric crystal leading to a vanishing of the second order nonlinear coefficient, i.e. no Pockels effect. To overcome this limitation, it is possible to break the crystal symmetry by straining the silicon lattice [3]. The new approach developed here is to generate strain by the epitaxial growth of crystalline functional oxides, which exhibit more appropriate strain-induced characteristics than the use of silicon nitride with lower defect concentration at the Si/oxide interface. Indeed, these functional oxides are deposited by epitaxial growth at high temperature with pulsed-laser deposition [4], [5]. The induced strain due to lattice parameter mismatch and the difference in the thermal expansion coefficients between oxides and silicon are strong. Furthermore, functional oxides exhibit very interesting multiferroicity and piezoelectricity properties that pave the way to a new route to implement silicon photonic circuits with unprecedented functionalities. Our study includes:-Epitaxial growth of YSZ functional oxide by pulsed-laser deposition and material characterizations with several complementary techniques such as X-ray diffraction, atomic-force (AFM) and electronic microscopies (SEM and TEM).-Fabrication processes with electronic lithography and different etching technics which allow us to fabricate photonic structures such as gratings coupler, strip or sub-wavelength waveguides on full oxide-and hybrid oxide/Si chips and their optical characterisation around 1550 nm.-Micro-Raman spectroscopy used to provide information about strain in silicon or YSZ structures throughout the processes [6]. Last results about full oxide-and hybrid oxide/Si-photonic structures will be presented and discussed.
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Submitted on : Wednesday, May 31, 2017 - 2:08:39 PM
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Guillaume Marcaud, Sylvia Matzen, Carlos Alonso-Ramos, Xavier Le Roux, Mathias Berciano, et al.. Functional oxides on Silicon and Sapphire substrates for photonic applications. Photonics North, 2017, Ottawa, Canada. ⟨hal-01527620⟩

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