Analysis and optimization of acoustic wave micro-resonators integrating piezoelectric zinc oxide layers
Résumé
This paper reports on the design, simulation, fabrication and test results of ZnO-based contour-mode micro-resonators integrating piezoelectric zinc oxide (ZnO) layers. The inter-digitated (IDTs) type micro-resonators are fabricated on ZnO films and suspended top of 2µm thick silicon membranes using silicon-on insulator (SOI) technology. We analyze several possibilities of increasing the quality factor (Q) and the electromechanical coupling coefficient (k t 2) of the devices by varying the numbers and lengths of the IDTs electrodes and using different thicknesses of the ZnO layer. We designed and fabricated IDTs of different finger numbers (n=25, 40, 50 and 80) and lengths (L=100/ 130/ 170/ 200 µm) for three different thicknesses of ZnO films (200, 600 and 800 nm). The measured Q factor confirms that reducing the length and the number of IDTs fingers enables to reach better electrical performances at resonant frequencies around 700 MHz. The extracted results for an optimized micro-resonator device having a IDTs length of 100 μm and 40 finger electrodes, show a Q of 1180 and a k t 2 of 7.4%. We demonstrate also that the reduction of the ZnO thickness from 800 nm to 200 nm increases the quality factor from 430 to 1600 respectively, around 700 MHz. Experimental data are in very good agreement with theoretical simulations of the fabricated devices
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