This work presents a low temperature coefficient of frequency (TCF) and high-performance S4 mode acoustic resonator based on 128∘Y LiNbO3/SiO2/a-Si/Si (trap-rich layer assisted LiNbO3-on-insulator, TR-LNOI) substrate. The electromechanical coupling, quality factor, and TCF are optimized for S4 mode by adjusting the thickness ratio of stack layers and the geometry design of the inter-digital transducer. The optimized resonators exhibit a TCF of resonant frequency as low as 0.24 ppm/K, an electromechanical coupling ( k2 ) of 14.8%, a maximum quality factor ( Qmax ) of 1406 at 7.43 GHz, resulting a k2⋅Qmax of 208.

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