Micromachined cellular filters

Bulk wave acoustic resonators using thin piezoelectric films have the potential to become useful filters for telecommunication markets. These devices has been variously referred to as a thin film resonator (TFR) or a film bulk acoustic wave resonator (FBAR). Typically, the piezoelectric material is a sputter-deposited film of aluminum nitride or zinc oxide. Processing techniques such as the use of KOH or ethylene diamine pyrocatechol (EDP) to etch silicon or the use of sacrificial materials to form "air gap" structures (3) are needed to isolate the acoustic cavity from the underlying substrate. These same techniques are also part of the micromachinists "tools-of-the-trade" and are becoming better understood as well as becoming a part of an accepted processing infrastructure.