Fig. 3: Performances of DMNUDT on HIP substrate.

a, b TEM images of the fabricated HIP substrates. Inset in (b) is the FFT image for the reciprocal lattice. c Admittance phase responses of resonators on different propagating directions. Typical vibrating profiles of the modes of interest are labelled. The vibrating profiles refer to the antisymmetric mode of SH SAW, symmetric mode of SH SAW, symmetric mode of LL SAW, and antisymmetric mode of LL SAW from i to iv. d Schematic of the SAW resonator, which composes of IDT and reflectors at each side. The resonator is measured by the SG connection as plotted. e Optical image of the fabricated SAW resonator. f, g Extracted effective electromechanical coupling coefficient (\({k}_{{eff}}^{2}\)) of vibrating modes from the admittance responses, by \({k}_{{eff}}^{2}=(\,{f}_{a}^{2}-{f}_{r}^{2})/{f}_{a}^{2}\). \({f}_{r}\) and \({f}_{a}\) are the resonant and anti-resonant frequencies of the mode, respectively. f Variation of SH SAW \({k}_{{eff}}^{2}\) with in-plane orientation. g Variation of LL SAW \({k}_{{eff}}^{2}\) with in-plane orientation. For both SH SAW and LL SAW, the symmetric mode and antisymmetric mode show a seesaw characteristic. Noted that \({k}_{{eff}}^{2}\) of mode ii may not be extracted accurately, because its \({k}_{{eff}}^{2}\) is small, and the frequency spectrum is close to the stop-band resonance of the gratings. Scale bars in a, b, e are 200 nm, 20 nm, and 20 μm, respectively.