Determination of the d31 piezoelectric coefficient of PbZrxTi1−xO3 thin films using multilayer buckled micromembranes

International audienceThe aim of this paper consists in the determination of the piezoelectric transverse coefficient d31 of PbZrxTi1-xO3 (PZT) thin films integrated in dedicated multilayer silicon-based micromembranes exhibiting an initial buckled profile. An analytical model specific to this configuration was built and used for the calculation of d31 starting with the static profiles of the microfabricated devices determined by means of a double-beam interferometer. The influence of dc voltage and buckling effects on the d31 piezoelectric coefficient at the microscale were investigated, and high values were obtained, from 30to75pm/V, within a hysteresyslike cycle. These results demonstrated the good electrical behavior of PZT thin films at the microscale with a low influence of buckling effects and determined optimal operation conditions for high values of d31

Free-standing protein films for dynamic mode detection of cations binding

International audienceThis letter reports on the investigation of the mechano-chemical effect of cross-linked dried free-standing alpha-lactalbumin (α-lactalbumin) thin films induced by different cation, calcium, magnesium, and potassium binding. The protein membranes were fabricated by drying droplets of an α-lactalbumin solution on top of silicon through-wafer holes obtained by deep reactive ion etching. Then the membranes were consecutively exposed to solutions of the cations in HEPES buffer solution while their resonant frequencies were measured by full-field surface stroboscopic white light interferometry. Tests on more than 30 free-standing protein films showed more significant conformational changes of the α-lactalbumin after immersion in a calcium solution than those observed after immersion in magnesium and potassium solutions. These results demonstrate, the real potential of free-standing protein films to be used as resonant biosensors for multiple cation detection

SURFACE-TEMPERATURE CONTROL OF SILICON NANOWIRES IN DRY AND LIQUID CONDITIONS

In this paper we present the results of surface temperature control of silicon nanowires by using fluorescent thermometry at the nanometer scale. Rhodamine B is one of the stable fluorescent molecules, which rely on the characteristic of temperature-dependent change in fluorescent intensity, and it was used for nano-scale surface temperature sensing interface. The resistive heating on Si nanowires was carried out with applying voltage potential of 6 12 V. Surface-temperature measurement was performed by converting the changes in fluorescent intensity with calibration curve of Rhodamine B. The temperature at the central line along nanowires increasing from 30 degrees to 35-70 degrees was observed

On-chip self-sensing function of 4x4 matrix micromachined resonating piezoelectric membranes for mass detection applications [biosensor/chemical sensor applications]

In this paper, we studied the dynamic behavior of micromachined piezoelectric membranes as an alternative to the QCMs biosensors. Contrary to FPW sensors that use progressive waves at the resonance, we use standing waves on our mechanical structures which allow us to obtain higher integration density. 4×4 matrixes of piezoelectric membranes use PbZr xTi1-xO3 (PZT) as piezoelectric film which geometries have been drawn by lift-off techniques. Each membrane (circular shaped, with a radius equal to 150 microns) can be individually addressed for actuation and/or sensing. Here we show that the same kind of membranes exhibit excellent self-sensing capabilities by using the direct piezoelectric effect of the PZT layer. The open-loop resonant frequencies of several membranes were measured by examining the self-induced charge on the sense electrode using a proximity electronics circuit. We simultaneously performed resonant frequencies measures by means of a dynamic optical interferometer that completely matched the electrical self-sensed resonant spectra. In this case the piezoelectric membranes were actuated in two different ways, either by using an external transducer or by using the self-actuating (reverse piezoelectric effect) capability of each membrane

Silk and PEG as means to stiffen a parylene probe for insertion in the brain: toward a double time-scale tool for local drug delivery

International audienceThe use of soft materials as substrate for neural probes aims at achieving better compliance with the surrounding neurons while maintaining minimal rejection. Many strategies have emerged to enable such probes to penetrate the cortex, among which the use of resorbable polymers. We performed several tests involving two resorbable polymers considered most promising: polyethylene glycol (PEG) and silk fibroin (SF) from Bombyx Mori silkworms. Our coating method provides a repeatable, uniform structure optimized for a stress-reduced insertion of a parylene-C neural probe. Standard compression tests as well as in vitro and in vivo insertion assessments show that both SF and PEG-coated probes are stiff enough to avoid the buckling effect during insertion in the cortex. However, with a buckling force of 300 mN and a mechanical holding in vitro of tens of minutes, we assess silk fibroin to be more reliable for practical handling. In vivo first try-outs in mouse brain showed neither buckling issues of the probe nor undesired alteration of the signal recording. Moreover, we evidenced two distinct time scales in the bioresorption of our polymer coatings: silk fibroin degrades itself in a matter of weeks and PEG dissolves itself within seconds in the presence of water. We then present a hybrid PEG and SF coating that could be used as a drug delivery system with different time scales to reduce both the acute and the chronic body reaction

Geometry optimization of uncoated silicon microcantilever-based gas density sensors

International audienceIn the absence of coating, the only way to improve the sensitivity of silicon microcantilever-based density sensors is to optimize the device geometry. Based on this idea, several microcantilevers with different shapes (rectangular-, U-and T-shaped microstructures) and dimensions have been fabricated and tested in the presence of hydrogen/ nitrogen mixtures (H 2 /N 2) of various concentrations ranging from 0.2% to 2%. In fact, it is demonstrated that wide and short rectangular cantilevers are more sensitive to gas density changes than U-and T-shaped devices of the same overall dimensions, and that the thickness doesn't affect the sensitivity despite the fact that it affects the resonant frequency. Moreover, because of the phase linearization method used for the natural frequency estimation, detection of a gas mass density change of 2 mg/l has been achieved with all three microstructures. In addition, noise measurements have been used to estimate a limit of detection of 0.11 mg/l for the gas mass density variation (corresponding to a concentration of 100 ppm of H 2 in N 2), which is much smaller than the current state of the art for uncoated mechanical resonators