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

Area of Science:

• Materials Science
• Nanotechnology
• Surface Acoustic Wave (SAW) Devices

Background:

• Platinum (Pt)/Aluminum Nitride (AlN)/Sapphire surface acoustic wave (SAW) devices show potential for high-temperature, high-frequency applications.
• Current limitations include degradation of Pt interdigital transducers (IDTs) and AlN layer oxidation above 700°C in air, restricting their operational environment.

Purpose of the Study:

• To investigate the efficacy of an AlN protective overlayer in mitigating Pt IDT agglomeration and AlN oxidation in SAW devices at elevated temperatures.
• To evaluate the thermal stability and acoustic performance of AlN-protected AlN/IDT/AlN/Sapphire heterostructures annealed in air.

Main Methods:

• Fabrication of AlN/IDT/AlN/Sapphire heterostructures.
• Successive annealing of heterostructures from 800°C to 1000°C in air atmosphere.
• Characterization using optical microscopy, SEM, TEM, XRD, and SIMS to analyze film morphology, microstructure, and phase composition.
• Comparison of acoustic performance of protected and unprotected SAW devices before and after annealing.

Main Results:

• The AlN overlayer effectively suppressed Pt IDT agglomeration up to 1000°C.
• AlN/IDT/AlN/Sapphire SAW heterostructures demonstrated stable performance up to 800°C.
• At temperatures above 800°C, increased AlN oxidation compromised its protective function.

Conclusions:

• An AlN overlayer is a viable strategy to enhance the high-temperature stability of Pt IDTs in SAW devices.
• AlN-protected SAW devices exhibit promising thermal stability up to 800°C in air, expanding their application range.
• The effectiveness of AlN as a protective layer diminishes at temperatures exceeding 800°C due to intensified oxidation.