Micromachined thermal infrared emitters using heavily boron doped silicon as active material have been developed. The
proposed fabrication process allows the integration of infrared emitters with arrays of thermopile infrared detectors to
achieve integrated non dispersive infrared (NDIR) microspectrometers. A set of emitters with a common radiating silicon
slab size (1100x300x8μm3) has been successfully fabricated and characterized. The working temperature of Joule heated
radiating elements has been controlled by means of DC or pulsed electric signals, up to temperatures exceeding 800°C.
Measured thermal time constants, in the order of 50 ms, enable direct electrical modulation of emitted radiation up to a
frequency of 5Hz with full modulation depth. The temperature distribution in the radiating element has been analyzed
with infrared thermal imaging.
The present study is devoted to analyze the compatibility of yttria-stabilized zirconia thin films prepared by pulsed laser
deposition technique for developing new silicon-based micro devices for micro solid oxide fuel cells applications. Yttriastabilized
zirconia free-standing membranes with thicknesses from 60 to 240 nm and surface areas between 50x50 μm2
and 820x820 μm2 were fabricated on micromachined Si/SiO2/Si3N4 substrates. Deposition process was optimized for
deposition temperatures from 200ºC to 800ºC. A complete mechanical study comprising thermomechanical stability,
residual stress of the membranes and annealing treatment as well as a preliminary electrical characterization of ionic
conductivity was performed in order to evaluate the best processing parameters for the yttria-stabilized zirconia
In this paper, a preconcentrator-based sensor &mgr;-system for low level benzene detection is presented. It consists of a
spiral-shaped &mgr;-reconcentrator with dimensions of 10cm × 300&mgr;m × 300&mgr;m, followed by a &mgr;-hotplate sensor matrix. The
&mgr;-preconcentrator was fabricated on a silicon wafer by means of DRIE and anodic bonding techniques. To obtain the
concentration factor of the fabricated devices, a GC/MS: Shimadzu-QP5000 equipment was used. The results obtained
showed excellent repeatability and preconcentration factors up to 286. A considerable improvement (1500%) in the
sensor responses was achieved with Pd doped SnO2 sensors. The small size of the manufactured devices enables their
incorporation in an integrated GC/MS gas sensor system.
The development of an integrated gas chromatographic system using micro and nanotechnologies is presented in this
paper. For this purpose, the different components of the chromatographic system, namely the preconcentrator, the
chromatographic column and the gas sensors are being investigated and developed, and the actual state of this
investigation is presented. The proposed target application comes from the agrofood industry, in particular the
determination of the fish freshness. The structure of the preconcentrator has been fabricated using deep reactive ion
etching (DRIE). The same fabrication technique has been employed for the patterning of the silicon microcolumns,
which have been sealed with Pyrex glass. Inlet and outlets have been connected and initial experiments of
functionalization have been performed. Gas sensors have been obtained by microdeposition of doped WO3 or SnO2
nanomaterials on microhotplates and their responses to the gases of interest have been measured, proving that the target
gas concentrations can be detected.
Fabrication and characterization of a passive silicon microfabricated direct methanol fuel cell (&mgr;DMFC) are reported.
The main characteristics of the device are its capability to work without complex pumping systems, only by capillary
pressure, and the fact that its performance is not affected by the device orientation. A simple fabrication process, based in
DRIE (Deep Reactive Ion Etching), allows obtaining a reliable and low-cost final device. The device consists of two
silicon microfabricated plates mounted together with a commercial membrane electrode assembly (MEA). Current-voltage
(I-V) and current-power (I-P) curves of the device at different methanol concentration, orientation and geometric
variation of silicon plates are presented. Optimal performance was obtained with a methanol concentration of 3M, that
yielded a maximum power density of 10.5 mW/cm2. The results obtained in this work demonstrate the feasibility of the
device and give a guideline for design and conditions optimization.
Precise and continuous ethylene detection is needed in various fruit storage applications. The aim of this work is the development of a miniaturised mid-infrared filter spectrometer for ethylene detection at 10.6 μm wavelength. For this reason optical components and signal processing electronics need to be developed, tested and integrated in a compact measurement system. The present article describes the proposed system set-up, the status of the development of component prototypes and results of gas measurements performed using a first system set-up. Next to a microstructured IR-emitter, a miniaturised multi-reflection cell and a thermopile-array with integrated optical filters and microstructured Fresnel lenses for the measurement of ethylene, two interfering gases and one reference channel are proposed. Recently a miniaturised White cell as absorption path is tested with various commercial and a self-developed thermal emitter. First ethylene measurements have been performed with commercial twofold thermopile detectors and a Lock-in-amplifier. These showed significant absorption at an ethylene concentration of 100ppm. For the detection module different types of thermopiles were tested, first prototypes of Fresnel lenses have been fabricated and characterised and the parameters of the optical filters were specified. Furthermore a compact system electronics for signal processing containing a preamplification stage and Lock-in-technique is in development.
Micromachined microsensors for gas or flow detection based on physical behaviour of a special layer of a membrane have to fulfil high quality and reliability requirements especially in safety or security applications. For the reliability assessment a combination of simulative and experimental methods is usually carried out for the fully understanding of the thermo-mechanical behaviour. Due to the micromachining involved in the production of the sensor components the thermo-mechanical response of the layers are strongly dependent on process parameters. Therefore experimental methods for the 3D deformation detection are essential. In this paper experimental methods such as profilometry and scanning probe microscopy are tested for the evaluation of residual stresses and thermomechanical induced stress/strain fields.
This paper describes the development of a technological process that allows the integration of gas sensors and thin film CMOS circuitry. The main technological points for the integration of gas sensors in a standard CMOS process and the effects on the full process will be described. A set of preliminary tests have been done prior to the definition of a CMOS compatible process for µ-structures and a complete test of sensitive materials are presented in order to determine the materials with most appropriate annealing temperatures for CMOS compatibility. Results show that gas sensors can be integrated with their circuitry, although require of special materials and non-CMOS standard processing as post-processing sequences.
The requirements of flow measurement and control in the home-appliances field lead to the need of a measurement system able to monitor the flow and the quality of gas. The integration of a set of sensors with different functionalities on a single chip arises as an advantageous solution. In this paper, the description of the structures and technologies required for the gas, flow and temperature sensor devices is presented prior to the complete description of the process flow for the full on-chip compatibilization. In this sense, semiconductor gas sensors and thermal flow sensors have arisen as the best candidates to address the compatibilization.
A gas flow sensor has been developed for home-appliances applications. The main requirements were to obtain a low cost single device able to work in the range 0-1slm with high linearity, low power, reliability and robustness. A thermal flow sensor has been designed with the help of thermal and flow FEM simulation for the design of the sensor chip as well as its packaging. The process flow is based on a simple silicon micromachined technology. Chip-on-board solution has been selected to simplify the packaging. Electronics for driving the sensor and for compensation offsets and temperature dependence and for linearising the output signal has been implemented. Final device shows good sensitivity and linearity in different zones of the range of interest.
A laboratory model of a gas sensor substrate produced in microelectronic technology has been experimentally analyzed and simulated by means of a 3D FEM model. This paper discusses its thermal and mechanical behavior under different working temperatures. The thermal expansion mismatch between different materials induces thermal stresses and structure deflection. Simulated and experimental results are proved to be in good agreement. Moreover, the proposed design offers low-power consumption, good thermal uniformity, low thermal inertia and mechanical stability up to 650 degrees Celsius.
Current research on microstructures for semiconductor gas sensors is on development on low power and robust substrates. In this paper a microstructure based on the combination of micromachined silicon substrates and glass wafers is presented. This device shows high robustness and can reach high temperatures up to 700$DEGC with good power consumption. The optimisation of the design and the process fabrication is described.
Our researches were devoted to the micromechanical elements fabricated by the surface micromachining technology, in order to reduce or to eliminate the internal stress or the stress gradients. We used an analysis based on secondary ion mass spectroscopy and the spreading resistance profiling determinations, correlated with cross-section electron transmission spectroscopy. The stress induced in the polysilicon layers by the technological processes depends on: (i) the conditions of the low pressure chemical vapor deposition process; (ii) the phosphorus doping technique; (iii) the subsequent multi-step annealing processes. In our experiments the LP-CVD conditions were maintained the same, but the condition specified previously as items (ii) was varied by using two different doping techniques: thermal- chemical doping consisting in prediffusion from a POCl3 source in an open furnace tube; ionic implantation with an energy E equals 65KeV and a dose N equals 4.5 X 1015 cm-2. The implantation process was followed by an annealing at 900 degrees C in an oxygen ambient for 30 minutes. The thermal budget was varied after the doping in order to reduce the stress gradient in the polysilicon layers. The results of our analysis allow us to show that: (1) the doping gradients are correlated with the slower phosphorus grains forme by an excess of the oxygen atoms; a concurrent process induced by the silicon self-interstitial injection during the diffusion and oxidation, determines the enhancement of the grain growth and therefore the enhancement of the electrical activation especially near the internal polysilicon interface; (2) the post-doping annealing conditions could be varied in a convenient manner, so that the doping induced stress gradients into the polysilicon layers to be reduced or completely eliminated for suitable micromechanical induced stress gradients into the polysilicon layers to be reduced or completely eliminated for suitable micromechanical applications. The results were used for the process optimization of micromechanical elements. The internal stress was determined by using anew, pull-in voltage method, allowing the comparison of the theory with the experimental data. It was deduced a new form of the equations set useful to extract the mechanical parameters like the internal stress and the Young's module. It was also deduced a simplified approximate formula useful to apply the least square fitting method for the extraction of the mechanical parameters. The results confirms the conclusions of the doping and the structural analysis.
Technological modules that are needed to fabricate sensors on CMOS wafers are discussed. None of the process steps of the CMOS technology are modified in order to guarantee that the electronics are not affected by the additional sensor process steps. The definition of standardized `add-on' sensor modules to the CMOS process of a foundry is intended to limit the development cost of smart sensors. The application of these modules to the fabrication of a CMOS multisensor chip is described.