Shunt capacitive radio-frequency microelectromechanical (RF MEMS) switches were modelled, fabricated and characterized in the K-band domain. Design allowed to predict the RF behaviour of the switches as a function of the bridge geometric parameters. The modelled switches were fabricated on silicon substrate, using a surface micromachining approach. In addition to the geometric parameters, the material structure in the bridge-actuator area was modified for switches fabricated on the same wafer, thanks to the removal/addition of two technological steps of crucial importance for RF MEMS switches performance, which are the use of the sacrificial layer and the deposition of a floating metal layer on the actuator. Surface profilometry analysis was used to check the material layer structure in the different regions of the bridge area as well as to investigate the mechanical behaviour of the moveable bridge under the application of a loaded force. The RF behaviour of all the fabricated switches was measured, observing the impact on the isolation of the manipulation of the bridge size and of the variations in the fabrication process.
The modification of the surface reception properties of nanocrystalline structures is of great interest in environmental, catalysis and energy related applications. For instance, an oxide surface covered with a layer of another oxide opens the possibility of creating the nanosized counterparts of bulk catalytic systems. A relevant example is the TiO2-WO3, which is an active catalysts in a broad range of reactions. The chemical synthesis of the colloidal, nanocrystalline version of such system will first be exposed, by coupling suitable sol-gel chemistry with solvothermal processing. Then, the range of obtained structures will be discussed, ranging from WOx-surface modified TiO2 to TiO2-WO3 heterojunctions. The complex structural evolution of the materials will be discussed, depending on the W concentration. A summary of the acetone sensing properties of these systems will be shown. In particular, the surface activation of the otherwise almost inactive pure TiO2 by surface deposition of WO3-like layers will be highlighted. Addition of the smallest W concentration boosted the sensor response to values comparable to those of pure WO3, ranging over 2-3 orders of magnitude of conductance variation in presence of ethanol or acetone gases. Simple analysis of the sensing data will evidence that the combination of such nanocrystalline oxides results in catalytic activation effects, with exactly opposite trend, with respect to pure TiO2, of the activation energies and best responses.
Digital holography (DH) is a well-established interferometric tool in optical metrology allowing the investigation of engineered surface shapes with microscale lateral resolution and nanoscale axial precision. With the advent of charged coupled devices (CCDs) with smaller pixel sizes, high speed computers and greater pixel numbers, DH became a very feasible technology which offers new possibilities for a large variety of applications. DH presents numerous advantages such as the direct access to the phase information, numerical correction of optical aberrations and the ability of a numerical refocusing from a single hologram. Furthermore, as an interferometric method, DH offers both a nodestructive and no-contact approach to very fragile objects combined with flexibility and a high sensitivity to geometric quantities such as thicknesses and displacements. These features recommend it for the solution of many imaging and measurements problems, such as microelectro-optomechanical systems (MEMS/MEOMS) inspection and characterization. In this work, we propose to improve the performance of a DH measurement on MEMS devices, through digital filters. We have developed an automatic procedure, inserted in the hologram reconstruction process, to selectively filter the hologram spectrum. The purpose is to provide very few noisy reconstructed images, thus increasing the accuracy of the conveyed information and measures performed on images. Furthermore, improving the image quality, we aim to make this technique application as simple and as accurate as possible.
Present work shows recent progresses in thin film-based flexible and wearable thermoelectric generator (TEG), finalized
to support energy scavenging and local storage for low consumption electronics in Ambient Assisted Living (AAL)
applications and buildings integration. The proposed TEG is able to recover energy from heat dispersed into the
environment converting a thermal gradient to an effective electrical energy available to power ultra-low consumption
devices. A low cost fabrication process based on planar thin-film technology was optimized to scale down the TEG
dimensions to micrometer range. The prototype integrates 2778 thermocouples of sputtered Sb2Te3 and Bi2Te3 thin films
(1 μm thick) on an area of 25 cm2. The electrical properties of thermoelectric materials were investigated by Van der
Pauw measurements. Transfer Length Method (TLM) analysis was performed on three different multi-layer contact
schemes in order to select the best solution to use for the definition of the contact pads realized on each section of the
thermoelectric array configuration to allow electrical testing of single production areas. Kapton polyimide film was used
as flexible substrate in order to add comfortable lightweight and better wearability to the device. The realized TEG is
able to autonomously recover the thermal gradient useful to thermoelectric generation thanks to an appropriate package
designed and optimized by a thermal analysis based on finite element method (FEM). The proposed package solution
consists in coupling the module realized onto Kapton foil to a PDMS layer opportunely molded to thermally insulate
TEG cold junctions and enhance the thermal gradient useful for the energy scavenging. Simulations results were
compared to experimental tests performed by a thermal infrared camera, in order to evaluate the real performance of the
designed package. First tests conducted on the realized TEG indicate that the prototype is able to recover about 5°C
between hot and cold thermocouples junctions with a thermal difference of 17°C initially available between body skin
and environment, generating about 2 V of open circuit output voltage.
Present work proposed design, finite element tools simulation and prototype fabrication of a low cost energy
autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG), finalized to power very
low consumption electronics Ambient Assisted Living (AAL) applications. The prototype, integrating an array of 100
thin films thermocouples of Sb2Te3 and Bi2Te3, generates, at 40 °C, an open circuit output voltage of 430 mV and an
electrical output power up to 32 nW with matched load. In real operation conditions of prototype, which are believed to
be very close to a thermal gradient of 15°C, the device generates an open circuit output voltage of about 160 mV, with
an electrical output power up to 4.18 nW. In this work we proposed design, thermal simulation and fabrication of a
preliminary flexible and wearable micro thermoelectric generator (μTEG), finalized to power very low consumption
electronics for Ambient Assisted Living (AAL) applications. Presented simulations show the performances of different
fabrication solution for the PDMS/Kapton packages, considering flat and sloped walls approach for thermal gradient
enhancement.
We develop shunt capacitive RF MEMS switches in III-V technology making use of materials which can be alternative
to the ones commonly used, in order to overcome some technological constraints concerning the RF MEMS reliability.
Specifically, we evaluate the potential of tantalum nitride (TaN) and tantalum pentoxide (Ta2O5) to be used for the
switches actuation pads and dielectric layers, respectively. To this scope, a compositional, structural and electrical
characterization of TaN and Ta2O5 films as a function of the deposition parameters, such as the substrate temperature and
the sputtering mixture composition, is performed. The realized switches show good actuation voltages, in the range 15-
20 V, an insertion loss better than -0.8 dB up to 30 GHz, and an isolation of ~ -40 dB at the resonant frequency. A
comparison between the measured S-parameter values and the results of a circuit simulation is also presented and
discussed, providing useful information on the operation of the fabricated switches.
We report on the potentiality of the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique for the deposition of
thin films of colloidal nanoparticles to be used for gas sensors based on electrical transduction mechanisms. The MAPLE
technique seems very promising, since it permits a good thickness control even on rough substrates, generally used to
enhance the active surface for gas adsorption.
TiO2 (with a capping layer of benzyl alcohol) and SnO2 (with a capping layer of trioctylphosphine) colloidal
nanoparticles were diluted in suitable solvents (0.2% concentration), frozen at liquid nitrogen temperature and ablated
with a ArF (λ=193 nm) or KrF (248 nm) excimer laser. The nanoparticle thin films were deposited on silica,
interdigitated alumina and <100> Si substrates and submitted to morphological (SEM-FEG), structural (XRD, FTIR),
optical (UV-Vis transmission) and electrical (sensing tests) characterizations.
A uniform distribution of TiO2 nanoparticles, with an average size of ~10 nm, was obtained on flat and rough substrates.
The deposited TiO2 nanoparticles preserved the anatase crystalline structure, as evidenced by the XRD spectra. FTIR
analysis showed that the SnO2 nanoparticles maintained the capping layer after the laser-assisted transfer process. This
protective layer was removed after annealing at 400 °C. The starting nanoparticle dimensions were preserved also in this
case. Electrical tests, performed on TiO2 nanoparticle films, in controlled atmosphere in presence of ethanol and acetone
vapors, evidenced a high value of the sensor response even at very low concentrations (20-200 ppm in dry air). In
contrast, in the case of SnO2 nanoparticle films, electrical tests to ethanol vapor presence showed poor gas sensing
properties probably due to the small nanoparticle sizes and interconnections.
A cheap nanofabrication process for Titania (TiO2) polycristalline nanowire array for gas sensing applications with lateral size ranging from 90 to 180 nm, and gas sensing characterizations are presented. Alternatively to typical pattern transfer techniques for submicron fabrication, authors focused on a standard 365 nm UV photolithographic process able to fabricate sol-gel nanostructured titania nanowires from a solid thin film. Main aim of present work is the experimental validation of enhanced gas sensing response of nanopatterned metal oxide thin film sensors. Two different kind of gas sensor with nanopatterned sensitive area have been realized onto silicon substrates and tested towards different EtOH concentrations; experimental tests have been carried out with a contemporary output signals collection from a nanowires-based gas sensor and a second device with solid sensitive film without patterning, in order to validate effects of nano-machining on sensitive material response.
We developed a novel method to detect the presence of unburned diesel fuel in used diesel fuel engine oil. The method is
based on the use of an array of different gas microsensors based on metal oxide thin films deposited by sol-gel technique
on Si substrates. The sensor array, exposed to the volatile chemical species of different diesel fuel engine oil samples
contaminated in different percentages by diesel fuel, resulted to be appreciable sensitive to them. Principal Component
Analysis (PCA) and Self-Organizing Map (SOM) applied to the sensor response data-set gave a first proof of the sensor
array ability to discriminate among the different diesel fuel diluted lubricating oils. Moreover, in order to get information
about the headspace composition of the diesel fuel-contaminated engine oils used for gas-sensing tests, we analyzed the
engine oil samples by Static Headspace Solid Phase Micro Extraction/Gas Chromatograph/Mass Spectrometer (SHS-SPME/
GC/MS).
Pulse voltammetry was employed to discriminate among different concentrations of defects in wine. The microelectrodes were fabricated as patterned platinum thin films on silicon wafers by means of silicon fabrication technology. The film pattern was as interdigitated fingers having a 2 μm fingers gap and active area of 100x100 μm2; a silicon nitride passivation permits a selective exposure of microelectrodes to electrolyte. Principal Component Analysis (PCA) of the current responses indicated that concentrations of acetaldehyde and L-ascorbic acid could be discriminated in a white wine electrolyte. Finally the capability of defects concentrations detection in two-defects solutions (acetaldehyde + L-ascorbic acid) has been investigated.
Electronic Tongue systems have been widely used during last decades, reaching an high level of
performances in the detection and quantification of several matrices, such as for example waters, soft
and alcoholic drinks. Next step in research is represented by the miniaturization of these systems: it
is made possible by the integration of the knowledge on materials suitable for sensorial purpose and
the silicon technology, which allows the development of micro-dimensioned sensors. In this work
we report the development of a sensor array composed of 8 electro-polymerized porphyrin based
membranes, with an active area exposed to liquid of 0.5 mm2. The miniaturized system, integrated
on a single silicon wafer and completed by read-out electronics, was firstly tested towards standard
analytes and then applied on real white wine samples for the detection of some analytes mimicking
wine defects, namely H2S, SO2 and CH3CO2H.
In this work, we describe the design implementation, validated by experimental results, of an innovative gas sensor array
for wine quality monitoring. The main innovation of this integrated array deals with the simultaneous outputs, from a
single chip on TO-12 socket, of 8 different signals coming from a WO3 thin film structure heated in a linear temperature
gradient mode, allowing an overall evaluation of gas sensing properties of the material in a 100°C-wide window,
typically from 300 to 400°C. The implemented sensitive layer is a WO3 film deposed by RF-sputtering. Preliminary tests
of gas sensing showed good responses to the target analytes for the specific application (1-heptanol, 3-methyl butanol,
benzaldehyde and ethyl-hexanoate).
The aim of this work is the fabrication of a cheap sol-gel Pt-doped TiO2 thin film sensor on silicon substrate, evaluate electrical performances of electrical interconnections and responses of sensitive film in severe environment like exhaust of combustion process. The sensor will be implemented as microsensors for NOx or oxygen detection, while a preliminary investigation on real operative conditions shows that the transducers perform a response time (t90) in real condition smaller than 1 second at 600 °C. Application field of this type of transducer will be evaluated in a real spark ignition engine, to monitor air/fuel ratio and also monitoring the combustion quality in other industrial combustion processes like domestic heating systems. The production process of this devices, and particularly thin film deposition, can be carried out on a 3" silicon wafer and obtaining with a single batch process more than 300 sensors for wafer, 2x2 mm2. The sensors are provided with an integrated heater and a thermometer to perform temperature compensation. Actually this work try to develop an affordable process to integrate cheap sol-gel deposition process with silicon technology; a particular study is devoted to a complete photolithographic patterning of titania sensitive film, that is very difficult to etch after complete annealing, in order to have sensitive film only onto well defined areas of wafer. Same process, with little modification, can be applied to different kind of sensitive film, pure and doped ones. Different strategies on protective coating were evaluated to reduce electrical contacts degradation at high temperatures, obtaining long time stability of overall microsensor.
Spin-coated layers of ZnPc and CuP have been used as chemically interacting materials for the detection of alcohols, amines, ketones, alkanes and pyridine for applications in food quality control. The UV-VIS variations obtained by the exposure of the sensing layers to the mentioned analytes in controlled atmosphere have been analyzed and compared with those deriving by a single thin film obtained by mixing the two metal complexes in an appropriate ratio. A multichannel monitoring of the main bands of the sensing layer due to the interaction with the analyte vapors became the basis to construct a set of independent sensors located on a single sensing element. The effects in the variation of the absorption bands of the blend system are compared with the variations in absorbance observed with the two sensing layers fabricated separately with each single compound. The interaction between the VOCs species and the heterogeneous sensing layer shows a different behavior in the responses respect to the results obtained with each single compound.
MoO3-WO3 thin films have been fabricated via the sol-gel method. FESEM, TEM, RBS and SIMS analysis techniques have been employed to analyse the films and material properties for use as gas sensors to detect CO and NO2. FESEM shows the film made up of segregated molybdenum crystals. TEM highlights the nano-sized grains sructure and crystallinity. RBS analysis confirmed the films are stoichimetric and that the Mo component of the system decreases as the annealing temperature is increased. SIMS illustrates the interesting elemental depth profiles of the films. The films were exposed to CO and NO2. MoO3-WO3 shows better NO2 sensitivity and selectivity compared to its single metal oxide constituents.
Sol-gel organic synthesis of SnO2 thin films from tin ethoxide precursor is reported here as a promising and cheap alternative of the 'classical' chemical and physical preparation methods of the SnO2 thin films, for gas sensing applications. A simple, integrated circuit compatible test structure, for rapid evaluation of the sensing properties of the SnO2 sol-gel derived thin films is described. The main features of our microstructure consists of a a heating resistor integrated on chip, made of highly boron doped silicon and a metallization system from Au/W deposited on a planarized chemically vapor deposited SiO2 layer. The SnO2 films have shown the well-known increase-maximum-decrease dependence of chemoresistance as a function of temperature, with a maximum at about 380 degrees C, when they are measured in clean, dry air. The sensitivity of SnO2 films to high concentration of H2 in air was studied within a quartz furnace, externally heated in the temperature range from 200 to 450 degrees C. The relative sensitivity is equal to 100 percent at temperatures as low as 200 degrees C, while its maximum value is anticipated to be above 450 degrees C. The CO sensing properties of SnO2 layers were evaluated as a function of input power applied on the integrated heating resistor. We have obtained relative sensitivities of 30 percent for 500 ppm CO concentration in dry air and an input power of 209 mW.
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