Use of Periodic Pillar Array as Acoustic Coupler for AlN-Based Longitudinally-Coupled Resonator Filters

This paper discusses applicability of the periodic pillar array as the coupler for AlN-based longitudinally coupled resonator filters (LCRF). First, periodic pillar array composed of SiO2 and air is applied to the coupled layer of AlN-based LCRF, and its impact to the coupling strength is investigated. It is shown that the coupling strength increases with the duty ratio of SiO2 monotonically and changed parabolically with the thickness of the coupling layer. Besides, the critical coupling can be achieved for a wide range when the thickness of the coupler and duty ratio of SiO2 are set properly. Finally, 4.78% of -3 dB bandwidth of filter response can be obtained when the coupling strength is critically coupled.