Surface micromachined BAW resonators based on AlN

This contribution deals with surface micromachined BAW resonators based on AlN thin films. Process, design issues and first results are presented and discussed. Devices with two resonators in series having a resonance frequency between 7 and 8 GHz show promising results. Coupling coefficients of k(t)(2)=3.8% and quality factors of 100 to 150 have been obtained with resonators having a approximate size of 30x30 mum adapted for a 50Omega system. These results are clearly inferior to earlier 2 results obtained with SMR designs (k(t)(2)=5.5% and Q=580). Reasons are too high serial resistances caused by bad step coverage of the top electrode, possibly also incomplete etching of the sacrificial layer, and warping by too large film stresses.