Microelectromechanical systems (MEMS) filters have advantages in being able to reduce the size, weight, and power required when used as part of electronic systems such as radios; however, MEMS-type filters have limitations. For example, thickness MEMS-type filters (e.g., thickness-extensional mode piezoelectric resonators) are typically limited to a single operating frequency per substrate die. Also, lithographically determined operating frequency resonators cannot meet low-impedance specifications.
This invention is a piezoelectric resonator device that includes a top electrode layer with a patterned structure; a top piezoelectric layer adjacent to the top layer; a middle metal layer adjacent to the top piezoelectric layer, opposite the top layer; a bottom piezoelectric layer adjacent to the middle layer, opposite the top piezoelectric layer; and a bottom electrode layer with a patterned structure and adjacent to the bottom piezoelectric layer, opposite the middle layer.
The top layer includes electrodes inter-digitated with a second group of electrodes. One of the electrodes in the top layer and one of the electrodes in the bottom layer are coupled to a contact, and another one of the electrodes in the top layer and one of the electrodes in the bottom layer are coupled to a second contact.
A piezoelectric resonator device comprises a set of layers suspended using tethers. The set of layers comprises two piezoelectric layers separated by a middle metal layer and metal electrode layers adjacent to the outside of the piezoelectric layers. The metal electrode layers have patterns of electrodes that are correlated with each other. The metal electrodes on the top and bottom layers and middle metal layer are used to apply, sense, or apply and sense an electric potential across each of the two piezoelectric layers. The piezoelectric effect of the piezoelectric layers transduces the electric potential across each layer into mechanical stress in the layer. The inverse piezoelectric effect of the piezoelectric layers transduces the mechanical stress in each piezoelectric layer into an electric potential across the layer.
The resonator structure can be operated at mechanical resonance by varying the applied electric field in time at the natural frequency of the device. In various embodiments, the piezoelectric layer is comprised of one of the following: aluminum nitride, zinc oxide, lead zirconate titanate, quartz, gallium arsenide, lithium niobate, or any other appropriate material. In various embodiments, the two piezoelectric layers are comprised of different materials or are comprised of the same materials. The spacing of the electrodes and the connectivity of the electrodes and the middle metal layer determine a frequency response of the resonator structure.