Piezoelectrics & Acoustooptics, Volume. 47, Issue 3, 459(2025)
Acoustic Characterization of XBAR Resonators Based on PEN Flexible Substrates
WANG Dimao, XIE Pengfei, ZENG Long, MIU Jiayao, and WANG Yan
Author Affiliations
College of Electronic and Optical Engineering & College of Flexible Electronics（Future Technology），Nanjing University of Posts and Telecommunications，Nanjing 210009，Chinashow less
The acoustic characteristics of laterally excited bulk acoustic resonators（XBARs），based on a flexible polyethylene naphthalate（PEN）substrate，including the resonance frequency fr，electromechanical coupling coefficient K2eff，quality factor Qr，and temperature coefficient of frequency（TCF），are analyzed using finite-element method（FEM）. The results indicate that the XBAR performances improve upon introducing the flexible PEN substrate. For instance，for hPEN = 40 nm，an IDT/LiNbO3/PEN structure shows K2eff=35.68%，which is 35% higher than that of the IDT/LiNbO3 structure with the same parameters，while maintaining fr =4.4 GHz and Qr =112. At a special height of PEN，the PEN substrate and IDT/LiNbO3 show synchronized vibrations—coupled resonance，which increases the resonant frequency and quality factor of XBAR. At hPEN=105 nm，the frequency shift Δf and quality factor shift ΔQr of XBAR are 1.32 GHz and 75，respectively，owing to coupled resonance. In addition，the temperature stability of the XBAR with the IDT/LiNbO3/PEN structure is enhanced；TCF of the XBAR increases from −107×10−6/°C to −72.9×10−6/°C as hPEN increases from 0 nm to 120 nm. These results indicate that the XBAR with the IDT/LiNbO3/PEN structure shows outstanding acoustic properties，and the different performance parameters of the XBAR can be optimized by modulating the thickness of PEN flexible substrate. In addition，these results provide a theoretical basis for the design and development of XBARs with high frequencies，electromechanical coupling coefficients，and temperature stability.
