Investigations on AlN/sapphire piezoelectric bilayer structure for high-temperature SAW applications

Abstract

This paper explores the possibility of using AlN/sapphire piezoelectric bilayer structures for high-temperature SAW applications. To determine the temperature stability of AlN, homemade AlN/sapphire samples are annealed in air atmosphere for 2 to 20 h at temperatures from 700 to 1000°C. Ex situ X-ray diffraction measurements reveal that the microstructure of the thin film is not affected by temperatures below 1000°C. Ellipsometry and secondary ion mass spectroscopy investigations attest that AlN/sapphire is reliable up to 700°C. Beyond this temperature, both methods indicate ongoing surface oxidation of AlN. Additionally, Pt/Ta and Al interdigital transducers are patterned on the surface of the AlN film. The resulting SAW devices are characterized up to 500°C and 300°C, respectively, showing reliable frequency response and a large, quasi-constant temperature sensitivity, with a first-order temperature coefficient of frequency around -75 ppm/°C. Between room temperature and 300°C, both electromechanical coupling coefficient K(2) and propagation losses increase, so the evolution of delay lines' insertion losses with temperature strongly depends on the length of the propagation path.

Effects of Coating Layers on Properties of LGS SAW Resonators

“…The prepared SAW resonators were characterized in terms of the SAW velocity (v s ), quality factor (Q factor) and K 2 to evaluate the performances of the SAW devices. The v s was calculated by The K 2 of a SAW device was deduced from the following equation [1],…”

“…Surface acoustic wave (SAW) sensors are wireless and very sensitive to the external environment, so SAW sensors such as temperature, strain and gas sensors are particularly utility and widely used in every environment [1]. However, because of sensitivity characteristics, SAW sensors must be protected from surface scratching, oxidation and chemical degradation, especially when SAW sensors are working in a complex environment.…”

First investigations on stoichiometric lithium niobate as piezoelectric substrate for high-temperature surface acoustic waves applications

“…Other notable performances have been obtained with AlN/Sapphire bilayer structure. AlN suffers from steady oxidation above 700°C in air [9], but can be operated up to at least 1000°C under low-O environments [10] or in air if protected by an overlayer [11].…”

Nanoparticles of wurtzite aluminum nitride from the nut shells

“…3 Another important application for AlN is its application as an RF filter for mobile phones, which is also called a thin film bulk acoustic resonator (FBAR). 4 AlN is synthesized in the bulk form by the carbothermal reduction of aluminum oxide in the presence of gaseous nitrogen or ammonia or by direct nitridation of aluminum. In order to get fully dense form, Y 2 O 3 or CaO are required as additives during the hot pressing.…”