We present a multisensor probe containing four ISFET (Ion Sensitive Field Effect Transistor) sensing elements aiming at the real time monitoring of nutrients in the soil. A miniature solid-state reference electrode is integrated with the probe, which renders the probe resistant against prolonged periods of drying. The sensing elements inside the probe are selective towards K+, NO3-, H2PO4- as well as pH. Our measurements show, that the probe can identify the specific ions at concentrations as low as 10-5M (for K+), with a sensitivity of 33mV/decade for NO3-, 48mV/decade for K+ and 55mV/decade for pH.

The development of organic electronic requires a non contact digital printing process. The European funded e-LIFT project investigated the possibility of using the Laser Induced Forward Transfer (LIFT) technique to address this field of applications. This process has been optimized for the deposition of functional organic and inorganic materials in liquid and solid phase, and a set of polymer dynamic release layer (DRL) has been developed to allow a safe transfer of a large range of thin films. Then, some specific applications related to the development of heterogeneous integration in organic electronics have been addressed. We demonstrated the ability of LIFT process to print thin film of organic semiconductor and to realize Organic Thin Film Transistors (OTFT) with mobilities as high as 4 10(-2) cm(2).V-1.s(-1) and I-on/I-off ratio of 2.8 10(5). Polymer Light Emitting Diodes (PLED) have been laser printed by transferring in a single step process a stack of thin films, leading to the fabrication of red, blue green PLEDs with luminance ranging from 145 cd.m(-2) to 540 cd.m(-2). Then, chemical sensors and biosensors have been fabricated by printing polymers and proteins on Surface Acoustic Wave (SAW) devices. The ability of LIFT to transfer several sensing elements on a same device with high resolution allows improving the selectivity of these sensors and biosensors. Gas sensors based on the deposition of semiconducting oxide (SnO2) and biosensors for the detection of herbicides relying on the printing of proteins have also been realized and their performances overcome those of commercial devices. At last, we successfully laser-printed thermoelectric materials and realized microgenerators for energy harvesting applications.

SnO2 gas sensors are known for their high sensitivity towards volatile organic compounds (VOC) but are often hampered by their low selectivity. In order to improve the performance of the MSGS SnO2 sensor it is combined with a polymer lined micro-fabricated capillary. When passing through the capillary, the components of a small sample of mixed gaseous VOCs separate and can be detected one after the other by the sensor. When combined with a suitable sample injection procedure, the detection module can be transformed into a miniature gas analysis system. In the following we will demonstrate the successful selective detection of VOC from mixed gaseous samples.

Front-side connected, N-channel, normally-off, chemical field effect transistor (ChemFET) microsensors including a SiO2/Si3N4 pH-sensitive gate have been fabricated using a standard P-well silicon technology. The fabrication and packaging processes are described and sensor properties and performances are demonstrated through pH measurements. Finally, the front-side connected ChemFETs microsensors have been adapted to the detection of ions thanks to polyHEMA/siloprene-based ionosensitive membranes. Application is performed through the NH4+ and NO3− ions detection in artificial solutions, evidencing quasi-Nernstian responses (s≈50 mV/pH) in the appropriate detection ranges. This microsensor will be used for the monitoring of environmental pollution and more precisely for ground water analysis.

An analysis of single gases using non-selective sensor elements is presented. It contains two steps: the identification of an unknown substance and the estimation of its concentration. To prepare the identification step, a calibration procedure is done to associate a class with each definite gas. In order to do this classification, the signals of the sensor array are transformed into quantities independent of the gas concentration but characteristic for its chemical compound. Then, the analysis parameters of an unknown substance allow to identify it with one of the calibration classes. After the identification of the gas, its concentration can be estimated with the model which is specific for each class of a single gas. The accuracy of this estimation is discussed.

Abstract Semiconducting oxides, like Nb2O5, can be used as sensitive materials in the manufacturing of gas sensors based on conductivity variation measurements. Since these materials are sensitive to many gases, precautions must be taken when they are operated. In the present paper, the sensitivity of Nb2O5 to NH3 is studied. NH3 behaves like an electron donor and induces an increase of the N-type semiconductor Nb2O5 conductivity. In presence of oxygen, the conductivity decreases and the sensitivity of the Nb2O5 oxide to the NH3 gas is much lower than in absence of oxygen. Humidity injects electronic carriers in the Nb2O5 material and acts like an electron donor. In presence of humidity, the conductivity of the Nb2O5 layer to NH3 is improved. Those results are interpreted by using a model where the sensor resistance is dominated by the grain boundary resistance.

Through a study of Nb2O5 sensors in the presence of CO and NH3 gases, the optimal operating conditions of these sensors are defined in order to make a model of their responses according to relations based on elementary physico-chemical interaction processes. The association of such sensors with other metallic oxide sensors within a sensor array, and processing of their response signals, can lead to selective devices towards the experimentally tested gas species.

The electrical properties of thin-film metal-oxide-metal Nb2O5 oxygen sensors have been investigated in the temperature range 400–600°C. They are shown to be strongly dependent on the electrode material. With Nb electrodes, the cathode is a good electron injector. At low bias, the oxygen pressure dependence of the conductivity follows P(O2)−1/n with n equal 1.0 ± 0.2 over a pressure range extending at least from 105 to 10 Pa. A model is proposed explaining this behaviour by the presence of surface electron traps associated with chemisorbed oxygen. The films present a very large concentration of chemisorption sites as atmospheric oxygen is able to diffuse into the bulk through channels running between the Nb2O5 chains of the crystal structure. Above a certain threshold voltage, a non-linear regime where the current density is proportional to the square of the applied voltage is observed. This regime is explained by the anodic oxidation of the Nb anode. Cr and Pt electrodes behave like valve contacts: they are blocking at low voltage and injecting at high applied voltage. Structures shorter than 50 μm are shown to be depleted of their oxygen vacancies for electric fields in the range 103–104 V cm−1. The electrical admittance presents a steep non-linear double-injection regime above a certain threshol voltage. In this bias range the current density varies like Vn with n ≥ 7. The threshold voltage is sensitive to the ambient and decreases when the sensor is exposed to an atmosphere with low oxygen concentration. It is shown that the migration of ionized oxygen vacancies induced by the electric field actually controls the electronic transport through the metal-oxide-metal structure. These results provide new insights into the capabilities and limitations of Nb2O5 sensors.

Microsens has developed miniaturized integrated semiconductor gas sensors using standard microelectronic technologies; these sensors include a semiconducting metal oxide layer (SnO2, Nb2O5) and an integrated heater on a silicon substrate. The selectivity and sensitivity of the devices to oxidizing or reducing gases depend on the metal oxide, on its doping and on the selection of an appropriate working temperature. Recently, in collaboration with LASMEA, the same microelectronic device has been used to develop gas sensors on which the metal oxide layer is replaced by a phthalocyanine thin film. Phthalocyanines are known to be sensitive to oxidizing gases at ppm concentrations, and the specificity of their responses makes them potential gas sensors or complementary elements of SnO2 in th realization of multi-array integrated gas sensors. This papers describes the successive steps of the manufacturing of miniaturized phthalocyanine gas sensors and shows that deposition of phthalocyanine thin films by evaporation is compatible with microelectronic technologies. Responses of CuPc and AlPcFn films to NO2, HCl and CO are reported. Each gas induces conductivity variations on both phthalocyanines; these variations are qualitatively and quantitatively different depending on the gas-phthalocyanine pair.

Free chlorine is generally monitored in drinking water in order to maintain and check the quality of the water. Low level detection of chlorine in a water distribution network is conferring a good water quality confidence. It is confirmed by recent field tests that a very low level of free chlorine present in the form of hypochlorous acid can be detected with a recently developed integrated electrochemical sensor [1]. The three-electrode planar amperometric microsensor is industrially manufactured on 4 inch silicon wafers using a microelectronic technology compatible with a CMOS process. Field tests over several months in «on-line» drinking water networks have already demonstrated the industrial importance of such a technology

Free chlorine is generally monitored in drinking water in order to maintain and check the quality of the water. Low level detection of chlorine in a water distribution network is conferring a good water quality confidence. It is confirmed by recent field tests that a very low level of free chlorine present in the form of hypochlorous acid can be detected with a recently developed integrated electrochemical sensor [1]. The three-electrode planar amperometric microsensor is industrially manufactured on 4 inch silicon wafers using a microelectronic technology compatible with a CMOS process. Field tests over several months in 'on-line' drinking water networks have already demonstrated the industrial importance of such a technology.

The use of SnO2 sensors in selective alarm systems and gas measurement devices is complicated by the presence of significant cross-sensitivity to various gases, mainly alcohol vapours. This paper presents a simple approach employing analog electronic circuitry which allows the detection of methane above a threshold concentration (2000–5000 ppm) in a domestic environment, while the interference of alcohol vapours is eliminated. The device uses two integrated semiconducting gas sensors and is based on a differential measurement of these two sensors.

Amorphous Nb2O5 thin films of three different thicknesses (10, 100, 400 nm) were deposited onto SiO2/Si substrates by reactive sputtering in an Ar–O2 plasma. Thermal treatments were performed at different temperatures between 500 and 1100 °C. The structural and morphological evolution with temperature is shown to be dependent on the film thickness. At 600 °C, the films essentially crystallize in the TT phase. On the thickest films, the T phase also appears. Annealing at higher temperature progressively increases the concentration of the T phase. The films show large flat grains extending over the whole film thickness. In addition, a large number of polyhedral bubbles is present in the 100 and 400 nm films due to Ar atoms trapped during sputtering. After annealing at 1100 °C the Ar bubbles are no longer present and partial diffusion of the films into the substrate is observed. The modification at high temperature, explained either by the M or the H phase, is favored on the thickest films and leads to plate shaped grains.

A new integrated catalytic gas sensor for detecting flammable gases or flammable vapours has been fabricated on silicon with thin film deposition and silicon micromachining techniques. This device is realized on the principle of the conventional catalytic gas sensor known under the name of ‘Pellistor’. The detection principle of this gas sensor is based on the measurement of heat emitted by the combustion of the gas with atmospheric oxygen on a small catalytic surface. The sensitive element and the reference element are integrated together on the same chip of size 2.84×2.46 mm2. This double structure requires a very low electrical power of typically 100 mW at an operating temperature of 400 °C. The excellent thermal insulation is realized by a 0.6 μm thin silicon nitride membrane. The sensitivity of the sensor is about 13 mV/% methane in air.

The deposition of diamond by different techniques on Si wafers of up to 8 in diameter has been reported by various groups. The uniformity of these blanket coatings is indicated to be of the order of ±10%. The commonly-used method of enhancing nucleation by scratching is not recommended for Si wafers, especially for selective-area diamond deposition. The selective area deposition of diamond on 4 in Si wafers has become possible by use of the standard lift-off technique as practised in ordinary microelectronic processing. The pretreatment is applied after masking on the free Si-substrate surface. A photoresist film is deposited either on Si wafers or on Si3N4 and/or SiO2 precoated (> 1000 Å) Si wafers by spin-coating, using a mask to obtain the desired pattern. Following a special pretreatment step of the selectively masked wafer surface, the photoresist is dissolved in acetone, then diamond is deposited. The diamond coating can be formed with or without boron doping. By this technique, thermistors and other sensor devices have been developed.

A new SnO2 low temperature deposition technique for integrated gas sensors is presented. Two different film thicknesses are investigated, as well as different catalysts. A correlation is established between the deposition parameters, the texture of the layers and the gas sensitivities. An explanation for the quite different behaviours of these layers is proposed. The best results are obtained with the thinner film gas sensors, for which Schottky barriers are formed between grains after thermal oxidation. A comparison between these integrated gas sensors and conventional sintered ones shows the major advantages of the integrated sensors.