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Hybrid BAW/SAW Thin Film Piezoelectric Transducer

Vladimir Pashchenko / CTR

Abstract: A novel type of the transducer combining bulk and surface acoustic waves was investigated in theory and experiment. Such a transducer combines advantages of both SAW and BAW devices like the control of frequency behavior by periodic structures on the surface and the often higher electromechanical coupling and quality factors achieved with bulk acoustic waves. The investigated device was based on a piezoelectric AlN and AlScN (Sc doped AlN) thin film deposited onto a non-piezoelectric substrates. A periodical spacing of the FBAR elements with a period equal to λSAW/2 and a thickness of about λBAW/2 – both wavelength corresponding to the same frequency - leads to an efficient excitation of a surface wave on the substrate surface. FEM simulations confirmed the feasibility of proposed concept. Its advantages are a higher electromechanical coupling (up to k2=7%) as compared to a SAW device based on a homogeneous piezoelectric film on top of a non-piezoelectric substrate (k2 <1% with AlN), low acoustical losses (and as a result high Q factor), and no need for an acoustical isolation like a Bragg mirror or an air gap. The potentially large coupling coefficient makes the concept interesting for RF filters in telecommunication and wireless sensors in harsh environment exploiting.

About the presenter: Vladimir Pashchenko was born in 1985 (Merke, Kazakhstan) and received his PhD in Condensed Matter Physics in 2014 from the Saint-Petersburg State Polytechnical University in Saint-Petersburg, Russia. From 2010 to 2015 Vladimir have been worked as a SAW&BAW device design engineer in R&D company Avangard, Saint-Petersburg. Between 2015-2018 he worked in postdoc position at the Electroceramic Thin Films Group, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland. In EPFL Vladimir worked under development and investigation of the new type of piezoelectric device - hybrid BAW/SAW transducer. Also he was involved in the project of extracting the piezoelectric and elastic parameters of AlScN films from the resonance characteristics.

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