High-frequency temperature-stable SAW filters based on a heterogeneous integrated multilayered structure

This study introduces the development of high-frequency surface acoustic wave (SAW) filters based on a novel, high-quality piezoelectric substrate. By utilizing a LiTaO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (LT)/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>/Poly-Si/Si substrate, we have successfully fabricated SAW devices that exhibit exceptional temperature stability and high operating frequencies. These devices demonstrate superior temperature performance over traditional LT and LN substrates, with the silicon dioxide interlayer and Poly-Si substrate contributing to temperature compensation and an enhanced quality factor, respectively. After optimizing the thickness of the temperature compensation layer, the SAW devices on the LT/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>/Poly-Si/Si substrate show a frequency temperature coefficient (TCF) that is nearly zero. The fabricated SAW filters on this substrate maintain a center frequency TCF of approximately -16 ppm/°C and achieve an electromechanical coupling coefficient (K<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) of the SAW resonator at 5.3%.