Hybrid resonant structures for wireless sensor applications

In this work, we report on an original approach for increasing the coupling factor of Harmonic Bulk Acoustic Resonators (HBARs). It consists in adding a layer onto the top electrode to optimize the operation of the device. We avoid using metal layers and used an extra Aluminum Nitride (AlN) film to optimize the excitation energy localization in the stack and try and preserve the Q factor of the structure. We present simulation results demonstrating the efficiency of the optimization approach. Based on these simulations, test devices have been manufactured and tested, demonstrating the possibility to gain more than a factor of 2 on the coupling along the proposed approach. Finally, the possibility to wirelessly interrogate these resonators is demonstrated.