Epitaxial Growth of Sc0.09Al0.91N and Sc0.18Al0.82N Thin Films on Sapphire Substrates by Magnetron Sputtering for Surface Acoustic Waves Applications.

Florian Bartoli,Jaafar Ghanbaja,Pascal Boulet,Sami Hage-Ali,Philippe Pigeat,Omar Elmazria,Natalya Naumenko,Jérémy Streque,A Redjaïmia,Thierry Aubert

doi:10.3390/s20164630

Abstract

Scandium aluminum nitride (ScxAl1−xN) films are currently intensively studied for surface acoustic waves (SAW) filters and sensors applications, because of the excellent trade-off they present between high SAW velocity, large piezoelectric properties and wide bandgap for the intermediate compositions with an Sc content between 10 and 20%. In this paper, the growth of Sc0.09Al0.91N and Sc0.18Al0.82N films on sapphire substrates by sputtering method is investigated. The plasma parameters were optimized, according to the film composition, in order to obtain highly-oriented films. X-ray diffraction rocking-curve measurements show a full width at half maximum below 1.5°. Moreover, high-resolution transmission electron microscopy investigations reveal the epitaxial nature of the growth. Electrical characterizations of the Sc0.09Al0.91N/sapphire-based SAW devices show three identified modes. Numerical investigations demonstrate that the intermediate compositions between 10 and 20% of scandium allow for the achievement of SAW devices with an electromechanical coupling coefficient up to 2%, provided the film is combined with electrodes constituted by a metal with a high density.

Highlights

In 2009, Akiyama et al experimentally demonstrated that scandium aluminum nitride (Scx Al1−x N)thin films show a large enhancement of the d33 piezoelectric constant as the scandium content increases up to 43%: the d33 coefficient of Sc0.43 Al0.57 N films is more than four times larger than that of aluminum nitride (AlN) [1,2]
The reciprocal achieved devices werethe electrically characterized at room temperature
fast Fourier transform (FFT) for both corresponding to three different surface acoustic waves (SAW) modes are visible on the obtained spectra, located at 720

Summary

Introduction

In 2009, Akiyama et al experimentally demonstrated that scandium aluminum nitride (Scx Al1−x N)thin films show a large enhancement of the d33 piezoelectric constant as the scandium content increases up to 43%: the d33 coefficient of Sc0.43 Al0.57 N films is more than four times larger than that of aluminum nitride (AlN) [1,2]. It has been shown that this phenomenon is related to the decrease of the C33 elastic constant [3] This result opened exciting new perspectives related to the enhancement of the electromechanical coupling coefficient k2 of high-frequency acoustic waves devices based on AlN material. As they are passive devices, SAW sensors offer attractive prospects for remote monitoring and control of moving parts, especially at high temperature, i.e., above 200 ◦ C and potentially up to 800 ◦ C and more [9] This technology requires the use of a piezoelectric material able to withstand these very harsh conditions. Langasite (La3 Ga5 SiO14 ; LGS) crystals have been demonstrated to be very serious candidates

Methods

Results

Conclusion