Optimization of interdigital transducers for the generation of surface acoustic waves over a large bandwidth (20-125 MHz)

In this paper, wideband interdigital transducers (IDT) to excite surface acoustic waves (SAW) have been developed and optimized. Three spatial chirp configurations were studied in order to cover a large bandwidth ranging from 20 to 125 MHz with sufficiently large displacement amplitudes to enable the characterization of surfaces (structures, thin layers, coatings, etc.). It is shown that by optimizing the configuration of the spatial distribution (width and spacing) of the electrodes, it is possible to adapt the spectral distribution of the SAW generated and to obtain a desired spectrum over the entire range of over 100 MHz. Finally, it is shown that high frequency attenuation of SAW can be overcome thanks to an additional optimization of the IDT by emitting more energy at high frequencies. It is thus possible with these transducers to measure displacements of the surface acoustic waves propagating along distances greater than 20 mm.