(182f) Characterization and Application of Aluminum Nitride-Based Flexible Surface Acoustic Wave Devices on Thermoplastic Polyethylene Naphthalate

Leonardo Lamanna^1,2,3, Francesco Rizzi¹, Pradipta Kr. Das³, Shuangming Li³, Venkat R. Bhethanabotla³, Massimo De Vittorio^1,2.

¹ Center for Biomolecular Nanotechnologies, Istituto Italiano di Tecnologia, Via Barsanti snc, Arnesano, Italy

² University of Salento, Department of Innovation Engineering, Campus Ecotekne, Via Monteroni, Lecce, Italy

³ Department of Chemical & Biomedical Engineering University of South Florida Tampa, USA

In the last decades, the development of wearable devices for biosensing increasingly requires flexible and biocompatible technology. These microsystems must integrate smart materials with transduction capability across multiple physical and biochemical domains. Surface Acoustic Wave (SAW) devices represent one of the most important MEMS building block, due to their low cost, light-weight, extremely low power needs and wireless control. Indeed, passive remotely controlled SAW RFID are currently applied into different fields such as structural monitoring or tire pressure wireless measurements and they can be potentially extended to biomedical applications. Nevertheless, there is still the lack of efficient biocompatible, flexible and compliant SAW devices, being usually fabricated on thick piezoelectric crystals such as LiNbO₃ and LiTaO₃ or on AlN and ZnO thin piezoelectric film grown on rigid substrate such as Silicon and Sapphire. In this work it is shown the fabrication of a transparent and flexible SAW delay line device based on piezoelectric Aluminum Nitride (AlN) on polymeric Polyethylene Naphthalate (PEN) substrate. The AlN depositions have been carried out successfully onto two different substrates: a 125µm thick PEN (Teonex®) and a silicon rigid substrate. Growths have been performed at low temperature using DC reactive magnetron sputtering in order to keep the material stress low. The fabricated PEN/AlN SAW devices show two resonant propagating modes, corresponding to Rayleigh and Lamb wave modes with a large transmission signals amplitude. The high AlN’s Lamb wave velocity (~10.000 m/s) combined with the flexibility of the PEN substrate resulted in an high resonance frequency (~500MHz) device using 5µm interdigitate electrodes. The technology was applied for the fabrication of a wearable flexible temperature sensor. The reported results demonstrate the potential of this flexible piezoelectric technology for wearable biosensing and wireless communication. Moreover, a characterization of the electroacoustic response of SAW device, has been carried out under light stimulation at different wavelength in order to examine the interaction of the light with the material property. The exploitation of the transparent property of PEN/AlN SAW device and a combination of different wave mode propagation Rayleigh and Lamb waves let us envision a high potential of this technology as multiple domain platform for wearable, implantable and edible biosensing.