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 [3]. 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.
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 (SiO2) placed between substrate and metal was necessary to
avoid the use of large electrical currents to generate the incandescence in the light source. A SiO2 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.
In this work we describe the fabrication and characterization of MOEMS-based integrated optical switches with
improved ON/OFF performance. These structures consist of silicon oxynitride-based optical waveguides, through which
a light beam of 633-nm can be conducted, and mobile thermo-electro actuated cantilevers, which form part of the
waveguide and can work as ON-OFF switches for the laser. These switches allow the laser light to pass or block the laser
light when activated electrically. The cantilevers are fabricated by freeing regions of the waveguide, which is done by
front side micromachining the silicon wafer used as substrate. Also, they are actuated electrically through the heating of
a metallic resistance positioned in the device, where the applied current heats the cantilevers and, due to the difference in
thermal expansion coefficients of the constituent materials, it is possible to produce a controlled motion proportional to
the heating current. Therefore, the switches can be electrically polarized in on/off cycles allowing or blocking the light
through the waveguide, similar to logic "1's" and "0's".
(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 (SiOxNy) film with a SiOxNy 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.
In this work we describe the fabrication and characterization of micro-opto-electro-mechanical AND, OR and XOR logic
gates based in a combination of optical and micro-electro-mechanical devices. These structures consist of silicon
oxynitride-based optical waveguides, through which a light beam of 633-nm can be conducted, and mobile thermo-electro
actuated cantilevers, which form part of the waveguide and can work as ON-OFF switches for the laser. These
switches are combined to form AND, OR and XOR gates, allowing the laser light to pass or blocking the laser light
when activated electrically. The cantilevers are fabricated by freeing regions of the waveguide, which is done by front
side micromachining the silicon wafer used as substrate. Also, they are actuated electrically through the heating of a
metallic resistance positioned in the device, where the applied current heats the cantilevers and, due to the difference in
thermal expansion coefficients of the constituent materials, it is possible to produce a controlled motion proportional to
the heating current. Therefore, the switches can be electrically polarized in on/off cycles allowing or blocking the light
through the waveguide, similar to logic "1's" and "0's". These switches are adequately arranged to produce an output
that is similar to the conventional digital logic gates through electric control (input) of cantilever-based ON-OFF
switches.
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