Study of High-Q Laterally Excited Bulk Wave Resonator With Smaller Gap-Width Reflectors
Xiyu Gu, Yan Liu, Ying Xie, Zhiwei Wen, Yuanhang Qu, Wenjuan Liu, Yao Cai, Shishang Guo, Chengliang Sun
Abstract
How to improve the quality factor (Q) of transversely excited bulk wave resonators (XBARs) has become a key technical problem in the RF field. In this study, a XBAR with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 ~\mu \text{m}$ </tex-math></inline-formula> gap-width reflector based on LiNbO3 was fabricated to attain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{p}$ </tex-math></inline-formula> value of 1211, exceeding the measurement in typical XABR ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{p}$ </tex-math></inline-formula> = 372). Simulation results indicate that the capacity of reflector gap width to inhibit the propagation of longitudinal wave energy increases first and then decreases as gap width increases from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5 ~\mu \text{m}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 ~\mu \text{m}$ </tex-math></inline-formula> . The measurement results obtained from XBAR with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 ~\mu \text{m}$ </tex-math></inline-formula> gap-width reflectors and XBAR with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 ~\mu \text{m}$ </tex-math></inline-formula> gap-width reflectors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{p}$ </tex-math></inline-formula> = 802) demonstrate excellent consistency with the simulation results. This study presents the XBAR with largest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{p} \times {K}_{\text {eff}}^{{2}}$ </tex-math></inline-formula> (237.4) currently, which highlights the significant potential of utilizing smaller gap-width reflectors in XBARs to construct filters with large bandwidth and high frequency.