Temperature Compensation of the AlN Lamb Wave Resonators Utilizing the S1 Mode

The temperature compensation techniques for the first-order symmetric (S-1) Lamb wave mode in the AlN Lamb wave resonators are firstly investigated in this paper. The S-1 mode simultaneously offers very high phase velocity (v(p)) and large coupling coefficient (k(2)) when h(AlN)/lambda is smaller than 0.4, but its thermal stability needs further improvement. The AlN/SiO2 bilayer and SiO2/AlN/SiO2 sandwiched temperature compensation structures are investigated and compared in this study. The SiO2/AlN/SiO2 symmetric structure shows higher v(p) and larger k(2) than the lowest-order quasi-symmetric (QS(1)) mode traveling in the AlN/SiO2 bilayer structure because the symmetric structure trapes more acoustic energy inside the AlN piezoelectric layer. Despite the trade-off between first-order temperature coefficient of frequency (TCF) and k(2), the SiO2/AlN/SiO2 structure can provide large k(2) and near-zero TCF at the same time with proper thickness selection of AlN and SiO2. The temperature-compensated resonator utilizing the S-1 mode in the symmetrical SiO2/AlN/SiO2 sandwiched membrane can simultaneously offer excellent thermal compensation, and large k(2) at super-high frequency.