Enhanced Infrared Sensing With 30% Scandium-Doped Aluminum Nitride Acoustic Delay Lines Integrated with Metamaterial Absorbers

This work introduces a novel type of infrared (IR) sensor that enhances sensitivity by pairing plasmonic absorbers with Lamb Wave Acoustic Delay Lines (ADLs). This technique allows for the expansion of the absorber’s area beyond the constraints of the device’s geometry, providing additional degrees of freedom to further optimize IR sensing performance. The device achieved an IR absorption of approximately 90% at a wavelength of 4.6 µm and exhibited a substantial frequency shift of 23.84 kHz, reflecting a large absorber area of 0.081 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> when exposed to 29.59 µW of incident IR power. Moreover, by replacing Aluminum Nitride (AlN) with highly doped Scandium Aluminum Nitride (ScAlN) in the resonant cavity of the delay line, we achieved a high temperature coefficient of frequency (TCF) of -53 ppm/°C and a large thermal resistance, leveraging ScAlN’s superior thermal properties. This design resulted in a high responsivity of 806 Hz/µW, outperforming our latest resonator-based IR sensor, which utilized a material stack featuring AlN as the dielectric in Metal-Insulator-Metal (MIM) plasmonic absorbers and 30%-doped ScAlN in the resonant cavity to enhance the TCF [1]. The results of this study demonstrate the potential of ScAlN ADLs to advance toward uncooled, miniaturized, and highly sensitive IR sensors.