Abstract
Patterned piezoelectric films as inter-digital transducer (PP-IDT) structures on diamond substrates have been attracting extensive attention due to the increased working frequency, electromechanical coupling, and quality factor of piezoelectric devices. In this study, by conceiving every single patterned piezoelectric IDT bar as the longitudinal bulk acoustic wave (BAW) vibrating source, we study how the BAW excites and couples with the surface acoustic wave (SAW) on the surface of diamond substrates and resonates simultaneously. The classic delta-function model of the SAW and electric impedance theory of the film bulk acoustic resonator were innovatively combined to develop this conception. Resonating frequency and corresponding piezoelectric IDT thickness were calculated using MATLAB software based on the developed delta-function model. The resonance results coincided well with finite element method simulations, validating this conception and the developed delta-function model for PP-IDT structures.
Highlights
Surface acoustic wave (SAW) chips are of great importance in wireless communication, environmental/biological sensing, and micro-electromechanical systems (MEMS),1–6 where higher working frequency, electromechanical coupling, and quality factor are essential for the continuous improvement of device performance
The inter-digital transducers (IDTs) based on this patterned piezoelectric films, called the PPIDT or coupled SAW/bulk acoustic wave (BAW) structure, attracts intense interest, thanks to its characteristics, including reduced propagation loss, improved quality factor, and enhanced electromechanical coupling
Patterned piezoelectric IDTs are considered as longitudinal BAW vibrating sources, which can excite the SAW on the surface of diamond substrates
Summary
Surface acoustic wave (SAW) chips are of great importance in wireless communication, environmental/biological sensing, and micro-electromechanical systems (MEMS), where higher working frequency, electromechanical coupling, and quality factor are essential for the continuous improvement of device performance. The diamond-based chip structure of AlN multi-layers is a very promising candidate due to its high acoustic phase velocity, small velocity dispersion, chemical stability, and full compatibility with the semiconductor process. The c-axis oriented AlN layers can be completely etched to the top diamond surface as piezoelectric IDTs. The IDT based on this patterned piezoelectric films, called the PPIDT or coupled SAW/bulk acoustic wave (BAW) structure, attracts intense interest, thanks to its characteristics, including reduced propagation loss, improved quality factor, and enhanced electromechanical coupling.. The classic delta-function model for the metal IDT4 is employed and developed to investigate SAW characters of the PP-IDT by combining with the electric impedance theory of the film bulk acoustic resonator (FBAR), conceiving the patterned piezoelectric transducers as ideal BAW oscillating sources to excite and couple with the SAW. In the future, following this combination method, other conventional models for metal IDTs will be studied and developed to precisely design PP-IDT devices
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