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Benzene Gas Sensor Based on Screen-Printed PZT Cantilevers
Keywords: - gas sensing, - PZT screen-printed cantilever, - Inorganic and organic sensitive layers
Gas detection at a trace levels (ppm to ppb) is a great challenge in order to guarantee safe environments with low pollution and to prevent against toxic gases at low concentrations, such as methanol, toluene, nitric oxide, benzene, etc. Because of its high sensitivity and low power consumption, resonant piezoelectric cantilever sensor has been chosen. For this purpose, screen-printed PZT cantilevers made of multi-layered Au/PZT/Au beam (8x2x0.08 mm3) partially released from the alumina substrate, are fabricated thanks to the association of screen-printing and sacrificial layer technique. Electrical measurements of poled samples confirm the piezoelectric behavior of the cantilevers and the presence of “in-plane” and “out-of-plane” modes. The resonance frequency and the quality factor of the PZT beam which are respectively fR=65kHz and Q=300 for the first “in-plane” longitudinal mode, justify the choice of the latter for gas sensing. Then, PZT cantilevers have been functionalized with different organic (polypyrrole, polyaniline) and inorganic (carbon and SnO2) coatings which are good candidates for benzene detection. The deposition of polyaniline coatings onto the gold electrodes is carried out by electrochemical synthesis, while polypyrrole films are obtained by electrodeposition. Drop coating has been used for active carbon or SnO2 depositions. Coatings influence the resonant properties of both the first and the second 31's longitudinal modes. The observed positive shifts of the resonance frequency indicate that the sensitive layers correctly adhere to the gold electrode. Afterwards, gas sensors based on screen-printed PZT cantilevers covered with sensitive coatings have been tested under 1ppm benzene in air atmosphere. First, detections with SnO2 coating give promising results. Negative frequency shifts of 68Hz and 104Hz respectively for the first mode and the second mode, have been measured. Measurements are in progress with the other coatings. Limit of detection and selectivity will also be reported.
Hélène Debeda, Associate Professor
Université de Bordeaux, Laboratoire IMS
Talence, Aquitaine 33405,
France


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