Thin-film lithium niobate-on-insulator (LNOI) shear horizontal surface acoustic wave resonators
Tzu-Hsuan Hsu, Kuan-Ju Tseng, Ming‐Huang Li
Abstract
Abstract This work investigates the design methodology to obtain large electromechanical coupling factor ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> ) and high quality factor ( Q ) of shear-horizontal surface acoustic wave (SH-SAW) resonators based on the thin-film lithium niobate-on-insulator (LNOI) technology. The guided SH wave can be excited through interdigital transducers and propagate at the very surface of the material stackings. Such a guided SH wave in LN/SiO 2 double layer structure is expected to offer high <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> by confining the elastic strain energy in the piezoelectric thin film. To capture the optimum design window for high-performance LNOI SH-SAW devices, the impact of electrode material and its thickness on the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> dispersive characteristics are intensively investigated by finite element method (FEM). In this study, various one-port resonators with wavelengths from 2.8 μ m to 8 μ m were fabricated on a LNOI wafer with LN and SiO 2 thickness of 0.7 and 2 μ m, respectively. The 100 nm thick gold film was chosen as the electrode of the devices, which demonstrate a similar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> dispersive behavior to the FEM simulation with small discrepancy. Among the measurement results over several tested samples, a high- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> of 25.5% and Q of 960 was recorded at a resonance frequency of 581 MHz (FOM = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> <mml:mo>⋅</mml:mo> <mml:mi>Q</mml:mi> </mml:math> = 245), revealing great potential for the application of wide-band frequency selection in telecommunications.