In this work we investigate the possibility to use Zinc Oxide (ZnO) thin films, deposited by RF magnetron sputtering, for
the realization of integrated optical structures working at 1550 nm. Structural properties of sputtered zinc oxide thin
films were studied by means of X-ray Diffraction (XRD) measurements, while optical properties were investigated by
spectrophotometry and Spectroscopic Ellipsometry (SE). In particular, ellipsometric measurements allowed to determine
the dispersion law of the ZnO complex refractive index (see manuscript) = n - jk through the multilayer modeling using Tauc-Lorentz
(TL) dispersion model. We have found a preferential c-axis growth of ZnO films, with slightly variable deposition rates
from 2.5 to 3.8 Å/s. Conversely, the refractive index exhibits, from UV to near IR, a considerable and almost linear
variation when the oxygen flux value in the deposition chamber varies from 0 to 10 sccm. In order to realize a waveguide
structure, a 3-&mgr;m-thick ZnO film was deposited onto silicon single crystal substrates, where a 0.5-&mgr;m-thick thermal SiO2
buffer layer was previously realized, acting as lower cladding. Dry and wet chemical etching processes have been
investigated to achieve controllable etching rate and step etching profile, with the aim to realize an optical rib waveguide.
The etched surfaces were inspected using scanning electron microscopy (SEM) and optical microscopy. Moreover, we
carried out the experimental measurements of the fringes pattern and Free Spectral Range (FSR) of an integrated Fabry-
Perot etalon, obtained by cleaving of a single mode rib waveguide.
In this paper is reported a method for measuring the thickness of a silicone nitride layers employed for fabricating silicon MEMS bi-morph structures. The method allows the precise evaluation of layer thickness by adopting Digital Holographic Microscope. The measurement is based on the fact that the silicon nitride layer is transparent to the visible light. The optical phase difference (OPD) between the light beam traveling through the layer and portion of the beam in air is measured exploiting an interferometric technique. The approach is very simple and can be utilized even for inspection of non-planar or stressed structures. Experimental values have been compared with ellipsometric measurements.
Infrared absorption photoinduced by visible light in a-SixC1-x:H is characterized by in guide pump and probe measurements in order to test its applicability to a low-cost micromodulator, fully integrable as a post-processing on-top of a standard microelectronic chip. The Photoinduced Absorption phenomenon in amorphous silicon arises from an alteration of the defect state population by decay of carriers photogenerated by visible light. These levels, deep in the gap, are strongly involved in interactions with IR radiation, and then the VIS illumination modifies their optical properties by increasing the IR absorption coefficient value. Test waveguiding devices are fabricated by Plasma Enhanced Chemical Vapour Deposition on silicon wafers, at temperatures lower than 180°C, and consist of a a-SiC:H/oxide stack. In particular, devices having a-SixC1-x:H cores with different doping and different carbon concentration are characterized. The 1.55 μm probe radiation generated by a DFB laser diode is efficiently transmitted through the a-SixC1-x core thanks to the step index waveguide structure. The pump system consists of low cost AlInGaP LEDs pulsed by a function generator, for an illumination intensity ranging from 0.15 up to 0.85 mW/mm2. Results show that the modulation effect increase for longer pump penetration depth and for higher doping concentration. The phenomenon strongly depends on the carbon introduction in a-Si:H. Digital transmissions tests at 300 kbit/s were performed.