Abstract: A bulk acoustic wave resonator structure that isolates the core resonator from both environmental effects and aging effects. The structure has a piezoelectric layer at least partially disposed between two electrodes. The structure is protected against contamination, package leaks, and changes to the piezoelectric material due to external effects while still providing inertial resistance. The structure has one or more protective elements that limit aging effects to at or below a specified threshold. The resonator behavior is stabilized across the entire bandwidth of the resonance, not just at the series resonance. Examples of protective elements include a collar of material around the core resonator so that perimeter and edge-related environmental and aging phenomena are kept away from the core resonator, a Bragg reflector formed above or below the piezoelectric layer and a cap formed over the piezoelectric layer.