Figure 4. The experimental and simulation spectra (a) and phase velocity (b) of the flexible ZnO/polyimide SAW devices with a 4 μm thick ZnO thin film as a function of wavelength.

The wavelength used for simulating the spectrum in (a) is 32 μm. The two well defined resonant peaks are in good agreement with the experimental result. As the wavelength increases, the phase velocity of the Rayleigh wave decreases and approaches the Rayleigh wave velocity in the polymer substrate, while the phase velocity of the Lamb wave increases and approaches that in the ZnO layer. The SAW devices have 20 pairs of IDT fingers.