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The effective electromechanical coupling coefficient ( ${K}_{eff}^{2}{)}$ of resonators is crucial for application in radio communication such as fabricating bandpass filters. In this letter, we present a $0^{\text {th}}$ symmetry ( ${S}_{0}{)}$ mode Lame mode resonator (LMR) operating at 2.563 GHz with a high ${K}_{\vphantom {D_{j}}{eff}}^{2}$ of 7.83%. A 20% Scandium-doped Aluminum Nitride (Sc0.2Al0.8N)/AlN composite piezoelectric film is used as the piezoelectric layer. The ratio of piezoelectric layer thickness ( ${t}_{\vphantom {D_{j}}{pie}}{)}$ and electrode pitch ( ${P}_{ele}{)}$ is optimized by finite element analysis (FEA) method and the highest experimental ${K}_{eff}^{2}$ is obtained at ${t}_{pie}/{P}_{ele} =0.65$ . The proposed LMR with Sc doping and structural optimization shows fascinating prospects for constructing broadband filters. [2021-0113]