Contour and flexure-actuated in-plane modes of AlN-based piezoelectric vibrating MEMS

In this work, we study the modes of vibration for two different families of aluminium nitride-actuated piezoelectric microstructures: contour modes and flexure-actuated modes. For the contour modes, the structure vibrates at frequencies determined by its edge dimensions whereas for the flexure-actuated modes a suspended structure is displaced by the lateral bending of the flexures. We combine electrical and optical techniques to fully characterize the vibrating modes of these types of in-plane MEMS structures. An electronic speckle pattern interferometry technique is used for a full 3D detection of the movement of the structures. Quality factors as high as 5000 and motional resistance as low as 4 KOhm were obtained for in-plane modes in air and a quality factor as high as 300 was obtained for an in-plane structure with water on the top surface. This work shows the great flexibility in the selection of resonant modes in piezoelectric resonators and actuators, implemented by a proper design of the electrode layout geometry.