AlN/IDT/AlN/Sapphire SAW Heterostructure for High-Temperature Applications

Ouarda Legrani (1, 2) , Thierry Aubert (2) , Omar Elmazria (1) , Ausrine Bartasyte (1) , Pascal Nicolay (3) , Abdelkrim Talbi (4, 5) , Pascal Boulet (1) , Jaafar Ghanbaja (1) , Denis Mangin (1)

1 IJL - Institut Jean Lamour
2 LMOPS - Laboratoire Matériaux Optiques, Photonique et Systèmes
3 CTR - Carinthian Tech Research
4 IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520
5 AIMAN-FILMS - IEMN - Acoustique Impulsionnelle & Magnéto-Acoustique Non linéaire - Fluides, Interfaces Liquides & Micro-Systèmes - IEMN

Recent studies have evidenced that Pt/AlN/Sapphire SAW devices are promising for high-temperature high-frequency applications. However, they cannot be used above 700°C in air atmosphere as the Pt interdigital transducers (IDTs) agglomerate and the AlN layer oxidizes in such conditions. In this paper, we explore the possibility to use an AlN protective overlayer to concurrently hinder these phenomena. To do so, AlN/IDT/AlN/Sapphire heterostructures undergo successive annealing steps from 800°C to 1000°C in air atmosphere. The impact of each step on the morphology, microstructure and phase composition of AlN and Pt films is evaluated by means of optical microscopy, scanning and transmission electron microscopy (SEM & TEM), X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS). Finally, acoustical performance at room temperature of both protected and unprotected SAW devices are compared, as well as the effects of annealing on these performance. These investigations show that the use of an overlayer is one possible solution to strongly hinder the Pt IDTs agglomeration up to 1000°C. Moreover, AlN/IDT/AlN/Sapphire SAW heterostructures show promising performances in terms of stability up to 800°C. At higher temperatures, the oxidation of AlN is more intense and makes it inappropriate to be used as a protective layer.

Mots clés: AlN; high-temperature; SAW; protective layer; platinum IDTs

Domaines: Matériaux

Ouarda Legrani, Thierry Aubert, Omar Elmazria, Ausrine Bartasyte, Pascal Nicolay, et al.. AlN/IDT/AlN/Sapphire SAW Heterostructure for High-Temperature Applications. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2016, 63 (6), pp.898 - 906. ⟨10.1109/TUFFC.2016.2547188⟩. ⟨hal-01525494⟩