Francisco J. Ramirez-Fernandez

Gas sensitive porous silicon devices: responses to organic vapors

Geometrically scaled PS-based structures were fabricated in order to develop gas sensing devices by exploring porous silicon (PS) electrical characteristics. The electrical behavior of PS devices respond to polar organic vapors (as acetone and ethanol) reversibly in a reproducible way. Devices were fabricated with three different perimeters, maintaining a constant area (5.76 mm 2 ) and constant PS porosity (60%) throughout samples, in order to evaluate their electrical impedance depending on the area/perimeter ratio. Electrical impedance was measured from 10 kHz to 10 MHz in acetone, ethanol and vacuum (as reference) environments. The results obtained show the general aspect for impedance variation as expected for disordered materials such as amorphous semiconductors or polymers. Measured impedance is fitted proportionally to (2pf) s , where f is the excitation frequency. The exponential factor ‘‘s’’ was found to be around � 0.55 for ethanol and � 0.45 for acetone, whereas in vacuum s equals � 0.97, thus providing a method for identifying polar molecules. The parameter ‘‘s’’ for the tested environments is independent of device geometry. # 2003 Elsevier Science B.V. All rights reserved.

Porous silicon optical cavity structure applied to high sensitivity organic solvent sensor

The present work reports the thermal annealing process, the number of layer and electrochemical process effect in the optical response quality of Bragg and microcavity devices that were applied as organic solvent sensors. These devices have been obtained by using porous silicon (PS) technology. The optical characterization of the Bragg reflector, before annealing, showed a broad photonic band-gap structure with blue shifted and narrowed after annealing process. The electrochemical process used to obtain the PS-based device imposes the limit in the number of layers because of the chemical dissolution effect. The interface roughness minimizations in the devices have been achieved by using the double electrochemical cell setup. The microcavity devices showed to have a good sensibility for organic solvent detection. The thermal annealed device showed better sensibility feature and this result was attributed to passivation of the surface devices.

Silicon Field-Emission Devices Fabricated Using the Hydrogen Implantation–Porous Silicon (HI–PS) Micromachining Technique

This paper presents a relatively simple method to fabricate field-emitter arrays from silicon substrates. These devices are obtained from silicon micromachining by means of the HI-PS technique - a combination of hydrogen ion implantation and porous silicon used as sacrificial layer. Also, a new process sequence is proposed and implemented to fabricate self-aligned integrated field-emission devices based on this technique. Electrical characteristics of the microtips obtained show good agreement with the Fowler-Nordheim theory, which are suitable for the proposed application.

Silicon micromechanical structures fabricated by electrochemical process

Silicon (Si) micromechanical structures were fabricated by means of sacrificial layers defined with porous silicon (PS) and masked by hydrogen ion implantation with adequate thermal annealing. The fabrication process to remove the PS layers with diluted KOH at room temperature does not cause damage in remaining Si microstructures which have less than 1 /spl mu/m thickness controlled by the anodization time.

Wavelet transform and cross-correlation as tools for seizure prediction

This paper describes the detection of preictal bursting using wavelet transform application and cross-correlation analysis. The wavelet transform is applied to data reduction and signal pre-processing. The extracted features provide simplified signals to process by means of the cross-correlation technique. The algorithm has been tested with a set of preictal data, interictal data and spontaneous crises, to determinate its sensitivity and its specificity (False Prediction Rate). The seizure occurrence period and the seizure prediction horizon are also calculated. The algorithms merits are: 1) high sensitivity and 2) easy implementation.

An RFID Bulk Cargo Supervising System

In this work, a system using active RFID tags to supervise truck bulk cargo is described. The tags are attached to the bodies of the trucks and readers are distributed in the cargo buildings and attached to weighs and the discharge platforms. PDAs with camera and support to a WiFi network are provided to the inspectors and access points are installed throughout the discharge area to allow effective confirmations of unload actions and the acquisition of pictures for future audit. Broadband radio equipments are used to establish efficient communication links between the weighs and cargo buildings which are usually located very far from each other in the field. A Web application software was especially developed to enable robust communication between the equipments for efficient device management, data processing and reports generation to the operating personal. The system was deployed in a cargo station of a Brazilian seashore port. The obtained results prove the effectiveness of the proposed system.

Electrogoniometer sensor with USB connectivity based on the IEEE1451 standard

The use of sensors and actuators has grown vertiginously in recent years. However, a diversity of communication standards to connect transducers to buses and networks has proliferated in different ways. The plurality of protocols required the creation of a standard to allow interoperability between transducers and networks. In this context, the IEEE1451 (Standards for Smart Transducer Interface for Sensors and Actuators) was proposed. Based on the IEEE1451.0 and the IEEE1451.2 protocols, an electrogoniometer was designed for rehabilitation engineering. The sensor measures the joint amplitude and transfers the data through an USB (Universal Serial Bus) interface. The system allows local and remote access through Web Services, contributing to the development of plug and play transducers.

Comparative analysis of classification algorithms on tactile sensors

A comparative analysis of classification algorithms of iCub platform humanoid hand tactile sensors is presented. The experimental data were analyzed with different learning supervised classification algorithms: Decision Trees Classifiers, k-Nearest Neighbors Classifiers (kNN), and Support Vector Machines (SVM). The best result was obtained with a Gaussian SVM kernel, which allowed 97.4% accuracy using 20% data for holdout validation. The results indicate the potential of categorization and learning of robotic hands for object grasping and manipulation.

P1.4.9 Improvement of Si Field Emission Sensors Fabrication Technology by Carbon Nanotubes

Field Emission (FE) devices were successfully improved by the association of silicon (Si) microtips and Multi-Walled Carbon Nanotubes (MWCNTs). MWCNTs were deposited over Si microtips by Electrophoretic Deposition (EPD), and improvements up to 80% in electron emission characteristics were reported, being suitable for the development of gas ionization sensors based on FE devices.

Optical properties modulation of porous silicon layers for optoelectronics applications

Refractive index of porous silicon (PS) were modulated throughout the chemical oxidation, thermal oxidation and controlling current density during PS formation. The oxidized PS layers showed a good gradient of refractive index to application in waveguide devices, with higher refractive index in sub layer near de surface and less refractive index close to PS/Substrate interface. In order to fabricate wave guide devices, Silicon wall were formed of 10 to 20 micrometer wide, 10 micrometer high and 1000 micrometer to 10000 micrometer length. Wall formation were achieved throughout anisotropic etching process in 7M KOH aqueous solution at 75 degrees Celsius. The properties of PS layer were analyzed by Raman spectroscopy, Infrared spectroscopy (FTIR), optical and scanning electron microscopy and reflectance spectroscopy. PS multilayers on the walls, as well as on the substrate, are formed by means of a chemical anodization process with various current densities. The structures are characterized using scanning electron microscopy, optical imaging, and Raman spectroscopy. Raman analysis shows a multilayer structure on the walls, suggesting different refractive indices for each layer. These results indicate the possibility of obtention of visible light waveguides formed by porous silicon multilayers made on silicon vertical walls.