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M. Gillinger, K. Shaposhnikov, T. Knobloch, M. Stöger-Pollach, W. Artner, K. Hradil, M. Schneider, M. Kaltenbacher, U. Schmid:
"Enhanced c-axis orientation of aluminum nitride thin films by plasma-based pre-conditioning of sapphire substrates for SAW applications";
Applied Surface Science, 435 (2018), 432 - 437.

Aluminum nitride (AlN) on sapphire has been investigated with two different pretreatments prior to
sputter deposition of the AlN layer to improve the orientation and homogeneity of the thin film. An
inverse sputter etching of the substrate in argon atmosphere results in an improvement of the uniformity
of the alignment of the AlN grains and hence, in enhanced electro-mechanical AlN film properties. This
effect is demonstrated in the raw measurements of SAW test devices. Additionally, the impulse response
of several devices shows that a poor AlN thin film layer quality leads to a higher signal damping during
the transduction of energy in the inter-digital transducers. As a result, the triple-transit signal cannot be
detected at the receiver.

http://dx.doi.org/10.1016/j.apsusc.2017.11.113