Ali Boukabache

Methods for assessing biochemical oxygen demand (BOD): A review

The Biochemical Oxygen Demand (BOD) is one of the most widely used criteria for water quality assessment. It provides information about the ready biodegradable fraction of the organic load in water. However, this analytical method is time-consuming (generally 5 days, BOD5), and the results may vary according to the laboratory (20%), primarily due to fluctuations in the microbial diversity of the inoculum used. Work performed during the two last decades has resulted in several technologies that are less time-consuming and more reliable. This review is devoted to the analysis of the technical features of the principal methods described in the literature in order to compare their performances (measuring window, reliability, robustness) and to identify the pros and the cons of each method.

Development of a flexible microfluidic system integrating magnetic micro-actuators for trapping biological species

A flexible microfluidic system embedding microelectromagnets has been designed, modeled and fabricated by using a photosensitive resin as structural material. The fabrication process involves the integration of micro-coils in a multilayer SU-8 microfluidic system by combining standard electroplating and dry films lamination. This technique offers numerous advantages in terms of integration, biocompatibility and chemical resistance. Various designs of micro-coils, including spiral, square or serpentine wires, have been simulated and experimentally tested. It has been established that thermal dissipation in micro-coils depends strongly on the number of turns and current density but remains compatible with biological applications. Real-time experimentations show that these micro-actuators are efficient in trapping magnetic micro-beads without any external field source or a permanent magnet and highlight that the size of microfluidic channels has been adequately designed for optimal trapping. Moreover, we trap magnetic beads in less than 2 s and release them instantaneously into the micro-channel. The actuation solely relies on electric fields, which are easier to control than standard magneto-fluidic modules.

Fabrication and evaluation of an on-chip liquid micro-variable inductor

We propose a new type of on-chip micro-variable inductor fabricated by using microelectronic technology and lamination process. The proposed inductor is a dual circular coil and has an inductance of few nH. The fundamental idea is to place a liquid droplet between the metal turns of a coil in order to modify the capacitive/resistive coupling between metal tracks and hence to change the stored magnetic energy. In this study salt water has been used to fill partly or totally the channels constituting these three-dimensional coils. The numerical modeling allows us to obtain inductance values according to the liquid position, which can rise from zero to 100% of the total length of channels. The SU-8 resin was used to realize the microfluidic channels and Au as metallic tracks. The measured electrical characteristics show that these devices can be used up to 1.6 GHz frequency. The relationship between the inductance and the liquid position indicates that the tuning range of the inductance is approximately 107% (from 5.4 to 2.6 nH at a frequency of 1.6 GHz). Without liquid, the peak quality factor is 12, and the self-resonance frequency is 4 GHz; when the channels are completely full, these parameters become respectively 6 and 4.3 GHz.

Development of a microsystem based on a microfluidic network to tune and reconfigure RF circuits

This special issue presents devices and the results of a tunable microwave microsystem associating RF circuits and microfluidic components. A channel is buried inside the substrate of a microstrip waveguide. This channel is located beneath a resonant stub. With this configuration a microfluidic passive tunable filter can be fabricated. Dielectric fluids are used to disrupt the electric field in a microstrip structure and thus modify the effective permittivity of the substrate. In this work, a notch filter is realized with an open-ended quarter-wavelength stub placed on top of a hollow SU-8 structure. This structure offers two advantages: channels can easily be fabricated and a reduction of SU8 losses. The filter shows a good performance; the initial cut-off frequency of 25 GHz shifts more than 20% when deionized water is used in fluidic channels. And the shape of RF function is kept throughout the range.

Fabrication and characterization of a fully integrated biosensor associating microfluidic device and RF circuit

This paper presents the first results of the fabrication and characterization of a biological sensor based on two complementary parts. A microfluidic channel along with a micromachined stop-band filter are used to detect the type of fluid which flows beneath the electronic circuit. The tridimensional (3D) structure of the microstrip technology is integrated using SU8 material which thus supports the use of buried channels. Besides being a method without contact, this bio-sensor avoids evaporation, contamination, or label fixation. Changes to the cutoff frequency and attenuation allow us to differentiate three values of the salt in water concentration with a maximum variation of attenuation of 6.5%.

Experimental verification of temperature coefficients of resistance for uniformly doped P-type resistors in SOI

Many todays microsystems like strain-gauge-based piezoresistive pressure sensors contain doped resistors. If one wants to predict correctly the temperature impact on the performance of such devices, the accurate data about the temperature coefficients of resistance (TCR) are essential. Although such data may be calculated using one of the existing mobility models, our experiments showed that we can observe the huge mismatch between the calculated and measured values. Thus, in order to investigate the TCR values, a set of the test structures that contained doped P-type resistors was fabricated. As the TCR value also depends on the doping profile shape, we decided to use the very thin, 340 nm thick SOI wafers in order to fabricate the quasi-uniformly doped silicon layers ranging from 2 × 1017 at cm−3 to 1.6 × 1019 at cm−3. The results showed that the experimental data for the first-order TCR are quite far from the calculated ones especially over the doping range of 1018–1019 at cm−3 and quite close to the experimental ones obtained by Bullis about 50 years ago for bulk silicon. Moreover, for the first time, second-order coefficients that were not very consistent with the calculations were obtained.

Effect of the silicon membrane flatness defect on the piezoresistive pressure sensor response

In this paper, we present a new approach of the sensitivity loss of a silicon piezoresistive pressure sensor. This loss of sensitivity is due to the lack of parallelism of the two membrane sides. An experimental topographical result of bottom membrane realised in LAAS, is simulated to quantify the effects on the gauges electrical responses and on the sensor sensitivity. A bridge of four piezoresistors forms our sensor. A flatness defect less than 1% obtained experimentally on 30 /spl mu/m membrane has lead to an electrical response loss around 3% of each gauges while the full bridge give 1.5% loss of sensitivity as a result of the simulation. These values increase significantly as the membrane thickness decreases. The irregularity of the surface could be an important source of information about the voltage offset.

Study of the thermal drift of the offset voltage of silicon pressure sensor

Pressure sensors produced using microelectronic techniques, in particular those based on the piezoresistive effect of silicon, present a high gauge factor. However, the electrical behaviour of the sensor is highly dependent on the temperature gradient. Thus, they have also some limitations such as the offset voltage and its thermal drift. In this study, we present a theoretical approach and experiments to analyse the electrical response of a pressure sensor fabricated using monocrystalline silicon. This analysis is focused on the thermal behaviour of the offset voltage and its origins. It allows us to differentiate between the two kinds of the piezoresistors included in the Wheatstone bridge and to link their thermal coefficients to that of the thermal drift of the offset voltage.

RF MEMS fluidic variable inductor

This paper presents a continuously variable inductor for Radiofrequency applications. The inductor is built using lamination of photosensitive films process. The variation principle is based on the change area of the loop inductor. The fluid moves between inter-spires distance and shortening the path length of the current through the structure; leading to reduction of the stored magnetic energy, and hence the inductance. A detailed electrical analysis is conducted to predict the tuning range of the inductor using simulation tools such as HFSS. At 3 GHz, the simulated inductor is continuously varied from 7 nH to 2.98 nH, i.e., the variable range is above 100%. The fact that the device is fabricated on glass process enhances the potential for system integration. The proposed variable inductor is perspective key component for the multi-band RF circuits such as electrically controllable matching circuits and wide tuning range voltage controlled oscillator (VCO).

Effect of the membrane flatness defect on the offset voltage of a silicon piezoresistive pressure sensor

In this paper, we study the effect of the membrane sides parallelism defect on the offset voltage of a silicon piezoresistive pressure sensor. The study is based on an experimental profile plot of the membrane bottom of 30 /spl mu/m thickness realised in LAAS. By assuming dimensionless gauges implanted on the membrane, the value of the offset voltage was quantified as a function of average thickness of the membrane. In spite of the low values of the parallelism defect (typically about 1% of the membrane thickness), it is shown that there is an offset voltage which is relatively high and perfectly quantified.