Abstract
In this study, a novel mechanical soft-contact (MSC) scheme is proposed, for the first time, to enable selective mode suppression in aluminum nitride (AlN) S1 Lamb wave resonators (LWR). For MSC-LWRs, the degree of energy dissipation introduced at the contact point depends heavily on the vibrational modes. We have demonstrated that in MSC-LWR, the ratio of the quality factor (Q) for the S1 and S0 Lamb modes can be as high as 37.7 (944 for QS1 and 25 for QS0) to effectively eradicate the S0 mode. The proposed resonators are fabricated via surface micromachining and exploit residual stress-induced structural deformation to create a mechanically soft contact between the resonator plate and the substrate. As a result, a spectrum-clean MSC-LWR achieves QS1 of 1,381 and an effective electromechanical coupling coefficient ( k2) of 2.72% at 2.19 GHz. Furthermore, we show that QS1 can be further optimized by adjusting the tether width, which is presumably dominated by the normal force at the contact point induced by the supporting structure.