Mid-infrared Transparent Thin Films And Integrated Photonic Devices

In recent years, on-chip integrated optical waveguides and resonators have attracted great interest. High-index-contrast optical materials and waveguides show advantages in device robustness, compact size and capability for high density integration. The key factors of materials used for integrated photonic devices are their wide transparency range, high index contrast to cladding materials and low propagation loss. Currently integrated optical waveguide materials include silicon, silicon nitride, silicon dioxide and chalcogenide glass, but the narrow transparent band or Non-CMOS compatible issues restrict the applications of these materials.To address the above challenges, this thesis studies high-K oxide materials as infrared optical waveguide materials, to take advantage of the characteristics of high refractive index, CMOS compatibility and wide-band transparency. This thesis focuses on amorphous high-K oxide thin film fabrication and optical properties characterization, and the fabrication and testing of high-K near and mid-infrared waveguides and resonators using nanofabrication processes.Firstly, optical waveguide theory and numerical modal simulation method are described, including the basic structure of the optical waveguide, the analytical modal solution of a slab waveguide, the effective refractive index approximate modal solution of a ridge waveguide and several commonly used numerical methods. Then the parameters of an optical resonator, the priciples of micro-ring resonator are discussed. The waveguide propagation loss is measured based on a micro-ring resonator and end-coupling waveguide transmission test method.Next, Zr1-x Tix O2(ZTO) films were deposited by composite target reactive sputtering method, and deposited Hf1-x Tix O2(HTO) films by DC-RF reactive co-sputtering method. The structure and optical properties of the thin films were systematically characterized by X-ray diffraction(XRD), UV/VIS spectrometer, Fourier transformed infrared spectroscopy(FTIR), X-ray photoluminescence spectroscopy(XPS), atomic force microscopy(AFM) and spectroscopic ellipsometry(SE). Amorphous, low roughness, highly transparent ZTO and HTO films with variable index depending on the element concentrations have been deposited, providing the materials basis for the fabrication of waveguides and resonators.Then the finite element method and COMSOL Multiphysics software were applied to study the mode of channel waveguide and ridge waveguide structures.The single-mode waveguide geometries were defined. Using photolithography, deposition and lift-off method, waveguides and resonators were fabricated. Propagation loss of the waveguide and resonator is characterized by end coupling method. Low-loss waveguides and resonators based on Hf O2 were achieved by adjusting the device process parameters.Lastly, the single-mode geometry of a Ge23Sb7S70/Zr0.6Ti0.4O2 mid-infrared waveguide was simulated. By photolithography and lift-off method, the waveguides and resonators were fabricated for mid infrared integrated photonic devices. Using an end coupling method, the transmittance spectrum of the Ge23Sb7S70/Zr0.6Ti0.4O2 resonators was characterized at around 5.2 ?m wavelength range. Using finite element simulation, the optical loss of ZTO films was estimated in the mid-infraed.The high-K oxide thin films developed in this thesis, including Hf O2, Ti O2 and Zr O2 and their solid solutions show high refractive indices, wide transparency window and low transmission loss. The optical waveguides and resonators fabricated using these materials show very low loss in the near infrared and mid infrared wavelength range. Therefore, high-K photonic materials and device are promsing candidates for infrared integrated photonics.