Application of photoimageable epoxy as an acoustic absorber for IF surface wave filter

It is a well recognized practice to apply some sort of acoustic absorber material at the ends of the piezoelectric surface and also on certain portions of the metal transducers as well as the multi-strip coupler of an IF SAW filter. By absorbing undesired modes of the surface acoustic wave, this technique significantly enhances both the frequency response of the filter as well as the sidelobes and the rejection of various time spurious responses such as edge reflections. In this paper a different type of material, Photo-Imageable-Epoxy (PIE), is used which belongs to a family of epoxies, which are commonly used in the semiconductor industry for IC and MEMS devices. Several PIE test patterns are examined for 3 SAW filters of differing IF frequencies. The performance of the SAW filters employing the PIE patters are compared with devices employing Screened Absorber (SA). Results of both types of acoustic absorbers when implemented on a high performance IF SAW filter centered at 144 MHz, are also presented.