Enhanced electromechanical coupling in SAW resonators based on sputtered non-polar Al0.77Sc0.23N 112¯ thin films

Abstract

Non-polar a-plane Al0.77Sc0.23N 112¯0 thin films were prepared by magnetron sputter epitaxy on r-plane Al2O3(11¯02) substrates. Different substrate off-cut angles were compared, and the off-cut angle of 3° resulted in the best structural quality of the AlScN layer. Structural characterization by x-ray diffraction confirmed that single phase, wurtzite-type, a-plane AlScN 112¯0, surface acoustic wave resonators were fabricated with wavelengths λ = 2–10 μm (central frequency up to 1.7 GHz) with two orthogonal in-plane propagation directions. A strong dependence of electromechanical coupling on the in-plane orientation was observed. Compared to conventional c-plane AlScN based resonators, an increase of 185–1000% in the effective electromechanical coupling was achieved with only a fractional decrease of <10.5% in series resonance frequency.

Influence of Structural Parameters on Performance of SAW Resonators Based on 128° YX LiNbO3 Single Crystal

“…The resonator presents the advantage of having a high Q value 1364.5, which is essential for fabricating a SAW load sensor with higher sensitivity and a larger sensing range. [23] 1910 659 LiNbO 3 [24] 150 1150 Quartz [25] 433.05-434.79 8000 ZnO/6H-SiC [26] 688 1080 128 • YX LiNbO 3 (this work) 224.85 1364.5…”

SAW Resonators and Filters Based on Sc0.43Al0.57N on Single Crystal and Polycrystalline Diamond

“…On the other hand, the structure with embedded electrodes (ScAlN/IDT/diamond) has been reported to considerably increase the coefficient [ 31 ]. Additionally, in order to boost the SAW propagation, a-plane (instead of c-plane) ScAlN thin films have been recently employed [ 32 ].…”

Laser Ultrasound Investigations of AlScN(0001) and AlScN(11-20) Thin Films Prepared by Magnetron Sputter Epitaxy on Sapphire Substrates

“…AlScN(0001)/Al 2 O 3 (0001) and AlScN(11-20)/Al 2 O 3 (1-102) thin films were grown by the magnetron sputter epitaxy method [ 18 , 20 , 22 ]. In the case of non-polar AlScN, 3° substrate off-cut was found to be the best for high crystalline quality [ 20 ], a detailed growth optimization study including a proposed growth model for non-polar III-nitrides and different off-cut angles is published elsewhere [ 22 ]. All films were grown on ⌀ = 100 mm substrates in an Evatec sputter cluster tool (base pressure ~5 × 10 −6 Pa), using reactive pulsed-DC magnetron co-sputtering.…”

“…Prior to deposition, the sapphire substrates were cleaned in-situ using Ar inductively coupled plasma (ICP) etching and the targets were pre-sputtered in Ar behind a closed shutter. More details about the growth conditions can be found in [ 18 , 20 , 22 ], all parameters except for the N 2 gas flow were kept the same, as summarized in Table 1 .…”

“…The motivation was two-fold: sapphire substrate enables higher phase velocity and higher frequency of SAW and at the same time the higher material quality leads to improved electromechanical coupling and quality factor Q [ 19 ]. In order to further increase electromechanical coupling k eff 2 , epitaxial a-plane (non-polar) AlScN(11-20) SAW structures were successfully achieved on r-plane Al 2 O 3 (1-102) [ 20 , 21 ]. By aligning the SAW propagation direction with the piezoelectric constant d 33 , an additional 85% improvement in k eff 2 was demonstrated.…”