Florence Razan

pH sensing from frequency response of SGFET

This paper presents suspended gate field effect transistors (SGFET) used as highly sensitive pH sensors. The devices are there characterized in dynamic mode. The gain, measured versus frequency, is studied for different pH values and shows a resonance frequency depending on the pH value. These results, obtained with different geometries of SGFET, give an opportunity to develop new microsystems, CMOS compatible, highly sensitive to pH.

The evolution of viscoelastic properties of silicone rubber during cross-linking investigated by thickness-shear mode quartz resonator

Characterizing the effects of cross-linking level and kinetics on the mechanical properties of rubber, especially viscoelasticity, provides information of importance to better understand and predict its final mechanical properties. Classically, the effects of cross-linking on the mechanical properties are investigated with a rheometer. Typical results give the evolution of elastic properties of rubber in the solid state with respect to time or to the cross-linking level. The frequency of the mechanical loading applied is generally a few hertz. In the case where the rubber is initially in the liquid state, such as some silicone rubbers, this type of characterization is not suitable anymore. In this study, a new characterization technique based on the Quartz Crystal Microbalance (QCM) principle has been developed in order to characterize the viscoelastic properties (elastic and viscous moduli) of a silicone rubber during cross-linking, i.e. from the liquid (uncross-linked) to the solid (final cross-linked) state. The device consists in a Thickness-Shear Mode (TSM) resonator generating ultrasonic waves, which provides viscoelastic properties of a material in contact with its surface from an electrical impedance analysis. In contrast to other characterization tools, it makes possible the continuous and non-destructive characterization of viscoelastic properties from a small material volume, under 1mL. Moreover, frequencies at which these properties are characterized are of the order of magnitude of the megahertz, which provides very complementary results to classical characterization, rather in the order of the hertz.

MADIX polymerization follow-up by viscosity sensing using Love-wave devices

Love wave sensors are highly sensitive microacoustic devices which are especially suited for sensing in liquids due to the shear polarized wave. In this contribution, a Love-wave device is used to follow the xanthate-mediated controlled free radical homopolymerization (MADIX technology) of butyl acrylate and acrylic acid. During the polymerization, using an automated synthesis workstation, a sample of the solution is taken into the reactors and deposited on the Love-wave sensor. Velocity changes of the Love-wave due to the liquid properties (e.g. viscosity) allowed to determine in real time the component fractions (e.g. monomer and polymer fractions) and give indications about the advance of the polymerization

Response of polymer-coated Love-wave device: a method to characterize thin film in the radio frequency domain

In this paper, we present Love-wave devices and their characteristics. Love-wave sensors present a high sensitivity for gas detection. High selectivity is achieved with a sensitive coating chosen for its affinities toward a target compound, this coating is often a polymer. Acoustic wave devices are sensitive to all types of propagation perturbations which include mass loading and mechanical properties changes (e.g. viscoelasticity) of the coating. Experimental results allow to determine the contribution of viscoelastic properties of the sensitive coating to Love wave devices responses. Furthermore, it can be a mean to characterize thin film materials in radio frequency domain. Experiments were done with a polymer as sensitive layer: PEUT (polyetherurethane).The first study of PEUT properties at high frequency allows to estimate the dynamic shear modulus of this polymer and to confirm the glassy-like state of the material at high frequency. Further experiments using PDMS (polydimethylsiloxane) with different viscosity and stiffnesses on Love-wave devices are then presented and analyzed.