Enhanced c-axis orientation of aluminum nitride thin films by plasma-based pre-conditioning of sapphire substrates for SAW applications

摘要

Highlights•Substrate surface pre-treatment for enhanced properties of piezoelectric AlN.•Improved SAW performance due to AlN deposition on sputter etched substrate.•Significantly reduced transduction losses for devices with sputter etch treatment.AbstractAluminum 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.