Agenda: Second International Workshop on Thin Films for Electronics, Electro-Optics, Energy and Sensors (TFE3S)

University of Dayton’s Center of Excellence for Thin Film Research and Surface Engineering (CETRASE) is delighted to organize its second international workshop at the University of Dayton’s Research Institute (UDRI) campus in Dayton, Ohio, USA. The purpose of the new workshop is to exchange technical knowledge and boost technical and educational collaboration activities within the thin film research community through our CETRASE and the UDRI

Epsilon-Near-Zero Transparent Conductive Oxides and the Application in Electro-Absorption Modulators

Transparent conductive oxides (TCOs), such as indium-tin oxide (ITO), have attracted increasing interests in integrated photonics and nanophotonics, owing to their large plasma dispersion and epsilon-near-zero (ENZ) effect. The refractive index modulation induced by free carriers in TCOs leads to a large electro-optic effect that can enable ultra-compact device footprint and unprecedented energy efficiency. However, the relatively low free carrier mobility of ITO and the interface between ITO/metal have constrained the high-speed performance of ITO modulators. In this thesis, we started with the optimization of sputtering deposition for ITO to achieve reliable optical and electrical properties. We also deposited high mobility titanium-doped indium oxide (ITiO), which can further improve the E-O modulator performance. On the device aspect, we designed and fabricated an 8-µm-long hybrid plasmonic-silicon modulator driven by an ENZ ITO capacitor, achieving a record of 100fJ/bit energy efficiency, 3.5 GHz modulation bandwidth and 4.5 Gb/s data rate. The electro-absorption modulator covers a broad optical bandwidth from 1515 to 1580 nm wavelength. For future development, we point out that by replacing ITO with high mobility ITiO, we can achieve a modulation bandwidth above 40 GHz and energy efficiency below 5 fJ/bit using a 3-µm-long device

Aerosol jet printing polymer dispersed liquid crystals on highly curved optical surfaces and edges

We demonstrate a new technique for producing Polymer Dispersed Liquid Crystal (PDLC) devices utilising aerosol jet printing (AJP). PDLCs require two substrates to act as scaffold for the Indium Tin Oxide electrodes, which restricts the device geometries. Our approach precludes the requirement for the second substrate by printing the electrode directly onto the surface of the PDLC, which is also printed. The process has the potential to be precursory to the implementation of non-contact printing techniques for a variety of liquid crystal-based devices on non-planar substrates. We report the demonstration of direct deposition of PDLC films onto non-planar optical surfaces, including a functional device printed over the 90° edge of a prism. Scanning Electron Microscopy is used to inspect surface features of the polymer electrodes and the liquid crystal domains in the host polymer. The minimum relaxation time of the PDLC was measured at 1.3 ms with an 800 Hz, 90 V, peak-to-peak (Vpp) applied AC field. Cross-polarised transmission is reduced by up to a factor of 3.9. A transparent/scattering contrast ratio of 1.4 is reported between 0 and 140 V at 100 Hz

Alkoxide Routes to Inorganic Materials

An all alkoxide solution chemistry utilizing metal 2-methoxyethoxide complexes in 2-methoxyethanol was used to deposit thin-films of metal oxides on single-crystal metal oxide substrates and on biaxially textured metal substrates. This same chemistry was used to synthesize complex metal oxide nanoparticles. Nuclear Magnetic Resonance spectroscopy was used to study precursor solutions of the alkaline niobates and tantalates. Film crystallization temperatures were determined from X-ray diffraction patterns of powders derived from the metal oxide precursor solutions. Film structure was determined via X-ray diffraction. Film morphology was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Epitaxial thin-films of strontium bismuth tantalate (SrBi2Ta2O9, SBT) and strontium bismuth niobate (SrBi2Nb2O9, SBN) were deposited on single crystal [1 0 0] magnesium oxide (MgO) buffered with lanthanum manganate (LaMnO3, LMO). Epitaxial thin films of LMO were deposited on single crystal [100] MgO via Rf-magnetron sputtering and on single crystal [100] lanthanum aluminate (LaAIO3) via the chemical solution deposition technique. Epitaxial thin-films of sodium potassium tantalate (Na0.5K0.5TaO3, NKT), sodium potassium niobate (Na0.5K0.5NbO3, NKN) and sodium potassium tantalum niobate (Na0.5K0.5Ta.05Nb0.5O3, NKTN) were deposited on single crystal [1 0 0] lanthanum aluminate and [1 0 0] MgO substrates (NKT and NKN) and biaxially textured metal substrates via the chemical solution deposition technique. Epitaxial growth of thin-films of NKT, NKN and NKTN was observed on LAO and Ni-5% W. Epitaxial growth of thin-films of NKN and the growth of c-axis aligned thin-films of NKT was observed on MgO. Nanoparticles of SBT, SBN, NKT and NKN were synthesized in reverse micelles from alkoxide precursor solutions. X-ray diffraction and transmission electron spectroscopy investigations reveal that amorphous nanoparticles (~5 nm) of SBT and SBN were synthesized. X-ray diffraction investigations reveal that nanoparticles (~3 nm) of NKT and NKN were also synthesized by this method

Hybrid Silicon Optoelectronic Technologies

The aim of this project was to realise integrated optical interferometers suitable for use in low-coherence optical sensor systems. The research focused on the development of waveguide fabrication techniques and the design of phase tuned interferometers. The flame hydrolysis deposition technique was employed to produce SiO2-GeO2-B2O3 glass films. The result was the production of high quality planar waveguide films with a controllable refractive index and thickness. A high degree of dopant homogeneity was observed between depositions, and across deposited glass films. Ridge waveguide fabrication was facilitated through the use of photolithography and reactive ion etching (RIE). Photolithography was used to define waveguide patterns in NiCr etch masks. A reproducible, high rate, high selectivity CHF3 reactive ion etch process was developed which reduced the typical RIE process time to approximately 1 hour for a 6 jam waveguide structure. The result of the processing was the fabrication of ridge waveguides with low sidewall roughness, and a sidewall angle >8