Low reflectivity surface acoustic wave transducers on GaAs

Experimental results are presented for fabrication and metallization techniques which achieve low reflectivity surface acoustic wave (SAW) interdigital transducer operation on GaAs. The transducer structures considered are single finger pair, quarter wavelength designs with chrome/aluminum/chrome (surface), aluminum (recessed) or gold-germanium/nickel/gold (surface) metallized electrodes which were fabricated directly onto a semi-insulating GaAs substrate. Triple transit signal suppression greater than 53 dB for the recessed aluminum metallization and greater than 62 dB for the Au-Ge/Ni/Au metallization has been achieved for test transducers operating at 159 MHz, compared to typically 30–35 dB for Cr/Al/Cr metallizations. These low reflectivity transducers provide the means for reducing spurious signal responses within monolithic programmable GaAs signal processors and for achieving higher Q performance of SAW resonator filters fabricated on GaAs substrates.