Monolithic implementation of AlN-on-silicon bandpass filters with a high-Q notch within the passband

In this paper, we present acoustically coupled filters capable of inducing a high-Q notch within the filter passband. The origin of the notch is a result of charge cancellation across the output electrodes, which is a direct consequence of exciting higher order lateral modes with a displacement profile out-of-phase with the primary modes of the filter. We show multiple filters with a passband notch and demonstrate the viability of using top electrode layout to adjust the placement of the notch within the filter passband. A modified equivalent circuit is used to intuitively explain the response of a bandpass filter with an integrated notch. Such filters can have applications as pre-select bandpass filters capable of rejecting in-band interfering signals.