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Study of Self-Actuated Cantilevers Based on Screen-Printed PZT Layers
Keywords: Self-actuated PZT cantilever, Sintering optimization, Modeling and electro-mechanical characterizations
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 layer for high electrical-mechanical coupling. This cantilever is realized through the screen-printing deposition associated to a sacrificial layer. The beam part of the cantilever is composed of a PZT layer between two gold electrodes. The choice of PZT for the actuation was guided by its high ferroelectric properties. Optimum performances of ferroelectric ceramics strongly rely on the microstructure. This can be done by the use of uniaxial mechanical pressure and very high sintering temperature, conditions which are not compatible with the screen-printing process. In our case, eutectic or glass phases are added to decrease the sintering temperature of isostatically pressed layers. Samples fired at 850°C, 900°C and 950°C are prepared thanks to the addition of either Li2CO3,CuO,Bi2O3 composition or commercial glass-frit to PZT powder. SEM analyses performed on the cantilevers show a densification of the microstructure while increasing the sintering temperature. After poling, electrical and mechanical characterizations are achieved with an impedancemeter for different cantilever dimensions. In addition to the bending mode observed with a vibrometer, we pointed out other vibration modes related to the piezoelectric properties of the PZT cantilevers. Indeed, the three first orders of “in-plane” 31-longitudinal vibration mode and the first order “out-of-plane” 33-thickness resonance mode are revealed. Moreover, the resonance frequencies of the different modes deduced from analytical modeling are linked to the cantilever dimensions and thus confirm the experimental results. The piezoelectric parameters of PZT cantilevers are compared with those of ceramics. Quality factors of 300 to 400 associated to the first and second resonance frequencies of the unusual 31-longitudinal mode make self-actuated screen-printed PZT cantilevers good candidates for detection in liquid and gaseous media.
Riadh Lakhmi, PhD Student
Université de Bordeaux, Laboratoire IMS
Talence, Aquitaine 33405,
France


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