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Solidly mounted resonators (SMRs) rely on high-quality Bragg reflectors, for which tungsten has been used as the high acoustic impedance layer. It is unclear about the effects of tungsten phases on the acoustic performance of SMRs. In this study, high-quality flat layers of different phase structures of W (α-W and β-W) are obtained by changing the post-growth annealing temperature and magnetron sputtering parameters. Our results show that the α-W has higher Young's modulus and acoustic impedance (205 GPa and 63 kg/m2s) than β-W (170 GPa and 57 kg/m2s). These small differences result in amplified difference in acoustic performance of Bragg reflectors using tungsten (W) as their high-impedance layer. Our tests show that the SMR of α-W Bragg reflector has a higher return loss (18.4 dB) at around 2.75 GHz and higher quality factor (687) than that of β-W Bragg reflector (9.2 dB and 228, respectively). • Different phase structures of W are obtained by changing the annealing temperature and magnetron sputtering parameters. • The acoustic impedance of α-W is 10% higher than that of β-W. • The influence of α- and β-W phases on performance of SMR devices is different. [ABSTRACT FROM AUTHOR]