Riadh Lakhmi

Force Sensors Based on Screen-Printed Cantilevers

In this paper, the design, the fabrication, and the characterization of glass ceramic screen-printed force sensors are described. They are based on the use of cantilevers with integrated piezoresistors. The choice of the materials constituting the cantilever and the strain gauge, so as the dimensions of the cantilever have been optimized in order to measure forces in mN range. The sensors have been fabricated using the screen-printing technique associated with the sacrificial layer technique to release the freestanding part of the cantilevers. Afterwards, they have been characterized: measurement of sensitivity, reproducibility, and materials properties (Youngs modulus and strain gauge factor). The performances of these sensors are compared to the existing silicon, polymer, and ceramic sensors.

Study of Free-Standing Electroded PZT Thick-Films: From Materials to Microsystems

Free-standing electroded piezoelectric PZT thick-lms are straightforward fabricatedthanks to the association of the low-cost screen-printing technology with the sacricial layermethod. Au/PZT/Au bridges are directly attached onto the alumina substrate on top of it theyare processed. In addition, completely released disks are also processed. A study of the behaviourof these components shows the inuence of both the releasing process and the densicationon the piezoelectric properties of the PZT layer. From the electromechanical measurements,electroded PZT cantilevers and disks are promising for actuator, sensor or SHM applications.

Feasibility of screen-printed PZT microceramics for Structural Health Monitoring piezocomposites applications

Using the association of the low-cost screen-printing technology with the sacrificial layer method, the feasibility of totally released piezoelectric thick-films microceramics of gold electroded PZT type is studied. After the deposition of the sacrificial layer on an alumina substrate and subsequent printing and drying of gold, PZT and gold layers, the final firing is performed at low temperature. This is followed by the releasing step of the Au/PZT/Au in diluted acidic solution. Impedance analysis shows that the electrical properties and electromechanical coefficients of poled PZT thick-films are still lower than those of PZT ceramics. This result is correlated to the high porosity rate of the PZT layer. However these piezoelectric microceramics present a good electromechanical behaviour and can be used as sensors when solicited by vibrations or as actuators to generate vibrations in a structure on which they are bonded. Moreover, the successful fabrication associated to a good electromechanical signatur...

P1.2.8 Screen-printed PZT cantilevers coated with PEUT for toluene detection. Comparison with silicon cantilevers

Self-actuated and self read-out PZT cantilevers made of Au/PZT/Au (8x2x0.08mm 3 ) beam layers on an alumina substrate are fabricated thanks to the association of screen-printing and sacrificial layer technique. Then, PZT cantilevers used as piezoelectric resonant type sensors are functionalized with an organic PEUT layer for toluene detection at room temperature. Due to their higher resonant frequency, cantilevers using the unusual 31 longitudinal vibration mode have higher sensitivities (0.047Hz/ppm) than those actuated with the classical flexural mode. These interesting results demonstrate the potentialities of printed PZT cantilevers for gas detection. Their performances are compared with those of silicon cantilevers.

P1.2.12 Uncoated PZT thick film cantilever for chemical species detection in gaseous phase

Coated silicon cantilevers functioning with flexural mode are classically used for chemical species detection. Recently, new types of entirely screen-printed piezoelectric PZT cantilevers operated with the unusual “in-plane” 31-longitudinal mode have been shown to be good candidates for actuation, sensing or energy harvesting applications. In order to prevent from ageing phenomena linked to the sensitive layer, the cantilever sensors may be used without any coating. Detection of water and ethanol is successfully performed using the 31-longitudinal mode of uncoated PZT cantilever sensors giving respectively negative and positive frequency shifts. As the viscosity and density of those gases don’t allow explanation of such high values of frequency shifts, responses have to be found in the competition between mass and stiffness effects. Differences between the cantilever’s response to water and ethanol can be explained by the higher wettability of gold towards ethanol. Indeed, whereas the main effect of water onto the gold surface seems to be linked to mass effects, only stiffness effects can justify the positive shifts observed in the case of ethanol vapour.

Study of self-actuated screen-printed PZT-cantilevers

Usually, resonating cantilevers come from silicon technology and are generally activated with pure bending mode. In this work, we suggest to combine high sensitive cantilever structure with full self-actuated piezoelectric thick-film for high electrical-mechanical coupling. This cantilever is realized through the screen-printing deposition associated with a sacrificial layer. The beam part of the cantilever is composed of a PZT layer between two gold electrodes. Optimum performances of ferroelectric ceramics strongly rely on their composition and microstructure which imply generally the use of mechanical pressure and very high sintering temperature. These conditions are not compatible with the screen-printing process. As already shown with ceramics, addition of eutectic composition Li2CO3-CuO-Bi2O3 or borosilicate glass-frit to PZT powder and application of isostatic pressure, the sintering temperature of cantilevers may be decreased. Screen-printed piezoelectric samples are thus fired at 850°C, 900°C and...

Benzene gas sensor based on screen-printed PZT cantilevers

Benzene gas detections at ppm level are performed at room temperature with a piezoelectric resonant type sensor. For this purpose, self-actuated PZT cantilevers made of multi-layered Au/PZT/Au beam (8×2×0.1 mm3) partially released from an alumina substrate, are fabricated thanks to the association of screen-printing and sacrificial layer technique. Then, PZT cantilevers are functionalized with different organic (polypyrrole and polyaniline) and inorganic (active carbon and tin dioxide) coatings. The high sensitivity (tens of hertz/ppm) is achieved by using the unusual 31s longitudinal vibration mode of the PZT cantilever, unlike classical modes like transversal bending resonating mode. With the second “in-plane” 31-longitudinal mode of the PZT beam, benzene detection at sub-ppm level is expected with the organic and inorganic sensitive coatings. These very interesting results already demonstrate the potentialities of coated PZT cantilevers for gas detection and can be extended to species detection in liq...