Roberto Ambrosio

MICROBOLOMETERS FABRICATED WITH SURFACE MICROMACHINING WITH a-Si-Ge: H THERMO-SENSING FILMS

In this work we present the process flow for the fabrication of un-cooled IR detectors employing surface micro-machining techniques over silicon substrates. These detectors are based on thin films deposited by plasma at low temperatures. The thermo sensing film used is an intrinsic a-SixGe1-x:H film, which has demonstrated a very high temperature coefficient of resistance (TCR), and a moderated resistivity, these properties are better than those of the a-Si:H intrinsic film, which is commonly used in commercial IR devices. Two device configurations have been designed and fabricated, labeled planar and sandwich. The former is the configuration commonly used in commercial micro-bolometers, while the latter is proposed in order to reduce the high cell resistance observed in this kind of devices, without the necessity of doping the intrinsic film, which results in a decrement of the TCR and therefore in responsivity. Finally some performance characteristics of the devices studied are discussed in comparison with data reported in literature.

Un-Cooled Microbolometers with Amorphous Germanium-Silicon (a-GexSiy:H) Thermo-Sensing Films

Silicon integrated circuits (IC) in conjunction with the micro-machining technology for thin films, have opened new ways for the development of low cost and reliable night vision systems based on thermal detectors. Among the thermal detectors used as pixels on IR focal plane arrays, the microbolometer appears as one of them. A microbolometer is a device in which the IR transduction is performed through a change in the resistivity of its thermosensing material, due to the heating effect caused by the absorbed radiation. Among the requirements for the materials used as thermo-sensing layer in microbolometers it can be mentioned a high activation energy (Ea), high temperature coefficient of resistance (TCR), low noise, and compatibility with standard CMOS fabrication processes. A variety of materials have been used as thermo-sensing elements in microbolometers, as vanadium oxide (VOx) (B. E. Cole, 1998, 2000), metals (A. Tanaka, 1996), polycrystalline (S. Sedky, 1998) and amorphous semiconductors (A. J. Syllaios, 2000).

Study of Piezoelectric Energy Harvesting System Based on PZT

Harvesting energy from ambient vibrations to convert it into electrical energy is possible using piezoelectric elements; the energy can be stored and used to bias low power electronic devices. A lead zirconium titanate cantilever is studied as a power generator to an energy harvesting system. The optimal performance is determined in terms of power output; two different configurations of the piezoelectric element were studied: series and parallel. The maximum output power produced by the piezoelectric system was 120 mW at the operating frequency of 40 Hz across a resistive load of 70 kΩ. The useful power was capable to bias some electronic devices.

Designing and experimenting bio-inspired chromatic behaviours in surveillance robot

Numerous work has been done in biologically inspired robotics emulating models, systems and elements of nature for the purpose of solving traditional robotics problems. Chromatic behaviours are abundant in nature across a variety of living species to achieve camouflage, signaling, and temperature regulation. The ability of these creatures to successfully blend in with their environment by changing their colour is the fundamental inspiration for our research work. In this paper, we present a dwarf chameleon inspired chromatic behaviour in the context of an autonomous surveillance robot, Pachondhi. In our experiments, we successfully validated the ability of the robot to autonomously change its colour in relation to the terrain that it is traversing for both maximizing detectability to conspecifics as well as minimizing exposure to predators.

Microbolometers Based on Amorphous Silicon–Germanium Films With Embedded Nanocrystals

In this paper, we have fabricated and characterized uncooled microbolometers using as infrared element intrinsic amorphous silicon-germanium films with embedded nanocrystals with a dimension in the range of ~2-4 nm. The presence of nanocrystals in the amorphous films reduces the density of defects, improves the transport properties, and specially improves the films stability against radiation. On the other hand, the combination of silicon and germanium in one alloy allows to improve the film conductivity and the temperature coefficient of resistance (TCR), without the necessity of perform doping. Large values of TCR have been demonstrated in the microbolometers, as large as -6.6% K-1, which in fact is the largest value reported for this kind of devices, and consequently large detectivity values were obtained in the reported devices (2 × 109 cmHz1/2W-1).

Electrical characterization of textile electrodes for an ECG acquisition system

Electrocardiograph signals (ECG) are one of the most important parameters used for monitoring the human physiological state. Nowadays, the research works using fabric conductive textiles for ECG are focusing on reliable and wearable systems. However, a complete characterization of textile electrodes is required to integrate it in standard clothing. Therefore, this work is devoted to the electrical characterization of electrodes based on conductive textile for an ECG system that monitoring the different human positions and also a comparison using the traditional silver (Ag/AgCl) chloride electrodes is presented allowing to demonstrate that ECG measured signal with these devices is proper for applications in wearable health monitoring.

Optical fiber packaging for MEMS interfacing

An investigation study concerning positioning, alignment, bonding and packaging of optical fibers for interfacing with optical MEMS devices is being reviewed in this paper. The study includes a review of techniques and critical issues for optical fiber positioning, alignment, bonding, optical improvements, and coupling and interfacing through micro-lenses and waveguides. Also, we present a packaging design structure for hermetic sealing of optical MEMS devices requiring interfacing through optical fibers which considers aspects such as processes, assemble schemes and bonding techniques for Optical Fibers, which are briefly reviewed in this work. This packaging design considers the following conditions: hermeticity of the MEMS devices, optical fiber and MEMS die alignment and positioning, assembly process, and Simachined fixturing design for final assembly and positioning.

Un-cooled Micro-bolometer with Sandwiched Thermo-sensing Layer Based on Ge Films Deposited by Plasma

An un-cooled micro-bolometer with thermo-sensing layer sandwiched between two electrodes has been fabricated and characterized. The micro-bolometer has a “bridge” configuration for providing sufficient thermo-isolation of the thermo-sensing layer. Surface micro-machining techniques were used for its fabrication onto a silicon wafer. The support layer is of SiN and the thermo-sensing layer is a-Ge:H,F film, both have been deposited by low frequency PE CVD technique. The active area of the thermo-sensing layer is AB = 70x66 m 2 . The temperature dependence of conductivity (T), current-voltage characteristics I(U), spectral noise density and thermal response time have been measured in order to characterize its performance characteristics. The measured activation energy of the thermo-sensing layer is Ea = 0.34 eV providing a thermal coefficient of resistance = 0.043 K -1 . The pixel resistance is in the range of RB = (1-30)x10 5 Ohm. Measured current and voltage responsivities are in the range of ℜI = 0.314 AW -1 and ℜU = (1-2)10 5 VW -1 , respectively. The estimated value of the detectivity is in the range of D * = (1-40)x10 8 cmHz 1/2 W -1 and the obtained response time is = 1x10 -4 sec. The performance characteristics obtained in this micro-bolometer with sandwiched thermo-sensing layer make it promising for further development of IR imaging systems.

A comparative study of the emitter formation of a c-si solar cell using gas and spin on dopant sources

In this work, a comparative study for the n-type emitter formation in the fabrication of simple structures of crystalline silicon (c-Si) solar cells is reported. Gas and spin on dopant sources were employed in the pn junction formation of the solar cells in order to compare their performance. Phosphine (PH3) was used as n-type gas for phosphorus diffusion while the Filmtronics Spin-On Dopant SOD-P905 was used as n-type liquid source. From the results, we observed that there was a small discrepancy in the open circuit voltage, short circuit current and fill factor of the two processes, with similar efficiency. These results suggest that SOD-P905 can be used to produce low-cost silicon solar cells. Also in order to improve the efficiency of the SOD solar cells, a wet surface texturization stage was incorporated in the fabrication process.

Modeling and simulation of a photovoltaic array for a fixed-wing unmanned aerial vehicle

Nowadays the unmanned aerial vehicles (UAV) have received attention as a tool for the human and military applications, such as monitoring, surveillance and also in the development of sensors networks. Therefore, some of the critical tasks of UAVs are: planning, control and autonomy. Regarding the autonomy, it is limited for the durability and lifetime of battery. In this way, the solar energy plays and important role for the unmanned vehicles in order to provide the enough power. This work present the modeling and simulation of photovoltaic (PV) array for application in unmanned aerial vehicle to supply the energy of the UAV avionic. The model was developed in MATLAB/Simulink for 3 Watts of photovoltaic array. It is based on mathematical equations taking in account the equivalent circuit. The simulation allows determining the performance of PV array under different values of solar radiation and temperature. The model was validated and compared with experimental data and it presented an error of 11%.