In previous works it was demonstrated that the electrical resistivity of Polypyrrole (PPY) changes when
exposed to different organic solvents which allowed the development of applications in gas sensors [1,2].
Also, is well known that optical gas sensors have several advantages over conventional electronic ones like
high sensitivity, reduced signal-to-noise ratio, and compatibility with combustible gases.
The optical properties of polymer materials have became of great importance in modern optical design of
polymer based optical sensors and devices. Thin polymer films appear in an ample spectrum of applications
such as photonics, data storage, communications and sensor devices . In this work an optical sensor for the
detection of water vapor using Polypyrrole (PPY) as active material is proposed. As a first step in studying
polypyrrole for this application, the refractive index of this material was measured after the films were
exposed to water vapor, and the results showed a variation of the refractive indices of the polymer in the
wavelength of 632.8 nm.
Finally, an optical device was fabricated using integrated optics technology over silicon, which uses
polypyrrole as active layer for sensing. The results of the characterization of this optical device showed that
for relative humidity concentrations above a specific value (~70%) the optical power at the output of the
device decays to insignificant values, which allows for the device to be used as an optical switch.
The applicability of anti-resonant reflecting optical waveguides fabricated on silicon substrates has been demonstrated
for different optical devices and sensors. In particular, it has been shown that in order to have virtual single-mode
operation in ARROWs, smaller constraints are imposed in the thickness and refractive index of the constituent layers
than in the case of Total Internal Reflection waveguides. On the other hand, if rib ARROWs are fabricated through
Reactive Ion Etching (RIE), high sidewall roughness is observed if metallic mask is used, which leads to undesirable
losses. This can be improved if the RIE step is done in the lower layers, leading to rounder but smoother core sidewalls.
In this work we present an alternative method for achieving the lateral confinement in ARROW waveguides fabricated
with silicon technology. This method consists in doing the RIE step before the core definition so as to have the lower
cladding layer and part of the silicon substrate etched away. Pedestal hollow core ARROWs have been proposed and
fabricated but in the case of conventional ARROW waveguides this has not been done, to our best knowledge.
Simulations results regarding propagation losses are presented for different rib heights and widths and compared to
Aluminum Nitride (AlN) is a wide band gap III-V semiconductor material often used for optical applications due to its
transparency and high refractive index. We have produced and characterized AlN thin films by reactive r.f. magnetron
sputtering in different Ar-N<sub>2</sub> atmospheres in order to verify the best gaseous concentration to be utilized as anti-resonant
layer in ARROW waveguides. The corresponding films were characterized by Fourier transform infrared spectroscopy
(FTIR), Rutherford backscattering spectroscopy (RBS), Ellipsometry and visible optical absorption. The AlN properties
did not varied significantly between the films deposited with 20 and 70 sccm of N<sub>2</sub>, most of the variations occurred for
films deposited with 18 sccm of N<sub>2</sub> or below. The film deposited with 20 sccm was selected to be used as the first
ARROW layer in the fabricated waveguides. Two routines were used to design the waveguides parameters, the transfer
matrix method (TMM) and the semi-vectorial non-uniform finite difference method (NU-FDM). Attenuation as low as
3.5dB/cm was obtained for a 7 μm wide waveguide.
In this work we report one simple fabrication process to build incandescent microlamps over silicon microtips. By taking
advantage of the underetch observed when the Si substrate is anisotropically etched in KOH solutions, specific silicon
microtips are created which serve as mechanical supports for the incandescent light sources. A thin film of chrome is
deposited by sputtering technique above the microtip and defined by photolitography in order to create an electrical
resistance. Consequently, the electrical energy transformed in heat is concentrated in a small spot achieving temperatures
high enough to produce incandescent light similar to a blackbody spectrum. To reduce the heat loss caused by the high
thermal conductivity of silicon, a layer of silicon dioxide (SiO<sub>2</sub>) placed between substrate and metal was necessary to
avoid the use of large electrical currents to generate the incandescence in the light source. A SiO<sub>2</sub> film is also used as a
protection layer against moisture and specially oxygen, since at high temperatures chrome can easily oxidize losing its
electrical conductivity. As the microtips are very tall compared to photoresist thickness, the lift-off process was needed in
order to guarantee that the top of the microtip would be covered by chrome. The results showed that it is possible to
produce light in all visible spectrum by applying electrical power higher than 4 W.
(This paper was presented in Session 4, Waveguide Devices, during the MEMS and Miniaturized Systems VIII conference.)
This work shows improvements on previous results related to the integration of optical waveguides and simple light
sources. These previous results showed the possibility of coupling the light emitted from an incandescent chromium
filament embedded in a self-supported region of silicon oxynitride (SiO<sub>x</sub>N<sub>y</sub>) film with a SiO<sub>x</sub>N<sub>y</sub> waveguide. This specific
work aims to increase optical power coupled to the waveguide through the investigation of the geometry of the
microlamp. Here, the length of the incandescent light is analyzed. The waveguide are fabricated on a (100) silicon
substrate using silicon oxynitride deposited by PECVD as the core and cladding layers. Bulk micromachining of the
silicon substrate in KOH solution is used to free from the substrate the embedded filament, reducing the thermal
dissipation of that region, allowing the filament to heat up to incandescent temperatures. A microannealing process of a
PECVD-obtained amorphous hydrogenated silicon carbide (a-SiC:H) deposited over the microlamp allows the correct
coupling of the light.