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

Abstract

Recent studies have evidenced that Pt/AlN/Sapphire surface acoustic wave (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 using optical microscopy, scanning and transmission electron microscopy (SEM and 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.

The Limits of the Post‐Growth Optimization of AlN Thin Films Grown on Si(111) via Magnetron Sputtering

“…Due to the wurtzite structure and specific polar bonding, aluminium nitride exhibits considerable piezoelectric performance, enabling its application in modern micro‐electro‐mechanical systems (MEMS) . Other physical properties of AlN, such as the wide bandgap (6.2 eV) and high thermal conductivity, make it a promising candidate for optoelectronic devices operating in the deep ultraviolet region and at high temperatures . Combining its unique characteristics, it can surely become an important material in the field of optical MEMS …”

“…[1][2][3][4] Other physical properties of AlN, such as the wide bandgap (6.2 eV) and high thermal conductivity, make it a promising candidate for optoelectronic devices operating in the deep ultraviolet region and at high temperatures. [4,5] Combining its unique characteristics, it can surely become an important material in the field of optical MEMS. [6,7] The synthesis of high-quality AlN films in a cost-efficient manner remains a difficult task due to the binary nature of the material as well as the technological demands, such as fast growth rates, technology-compatible substrates, and wafer-scale deposition.…”

AlN/GaN/Sapphire heterostructure for high-temperature packageless acoustic wave devices

“…In practice, at least one of the layers has to be a piezoelectric material in order to generate the acoustic waves. One additional advantage of packageless WLAW sensors is that the electrodes are buried and thus protected from physical and chemical alterations [16]. The extreme miniaturization of the device, achieved by removing the package, is also interesting for industrial perspectives.…”

Modeling and Electrical Characterization of a Bilayer Pt/AlN/Sapphire One Port Resonator for Sensor Applications

“…The ZnO film structure is used to improve the sensitivity of bio-sensors [9] and AlN thin film is used for the high temperature sensor [10]. Further studies have shown that it is possible to produce SAW temperature sensors [11,12] and SAW magnetic sensors [2,13]. Besides being used in SAW devices associated with good piezoelectric coupling, AlN has high acoustic velocity and good thermal and chemical stability.…”