New surface acoustic wave interdigital transducers with narrow electrode gaps

A surface acoustic wave (SAW) interdigital transducer (IDT) and a unidirectional transducer (UDT) are described. A description is given of the lift-off etching method and lift-off anodic oxidation fabrication method techniques used to get controllable narrow gaps between electrodes with good insulation. Experimental results show a 7.2-dB insertion loss with ripple of 1.2 dB for a conventional IDT, and directivities of 6-dB/transducer at 438 MHz for a floating-electrode-type unidirectional transducer (FEUDT) and 17 dB/transducer for its second harmonic at 868.5 MHz. A minimum insertion loss of 3.6 dB for a low-loss group type unidirectional transducer (GUDT) filter at 477 MHz were obtained