Near-Zero-TCF SAW Resonator Based on Z-Cut LiNbO₃/SiO₂/Si Substrate

In this work, surface acoustic wave (SAW) resonators based on Z-cut LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>/Si substrate have been designed and fabricated. By optimizing the thickness of the SiO2 layer and the geometries of the interdigitated electrodes (IDT), the temperature coefficients of frequency of series (TCF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf>) and parallel (TCF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf>) resonant frequencies are effectively reduced to approach zero. The SAW resonator with λ of 2.8 μm operating at 1.37 GHz exhibits k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 6.24% and high Bode-Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> of 3115. The SAW resonator with λ of 3.6 μm operating at 1.1 GHz exhibits k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 5.97% and Bode-Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> of 1793. The resonator with λ of 3.6 μm has the lowest TCF: TCF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> = 1.08 ppm/℃ and TCF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> = -3 ppm/℃. This demonstration verifies the effectiveness of designing IDT wavelength together with the SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> thickness to minimize the SAW resonator TCF for oscillator and timing applications.