IMF2017

Thin film bulk acoustic resonators (TFBAR) offer significant potential in the area of modern microwave electronics. They are widely used in miniaturized filters for communication and navigation systems. Modern TFBARs are multilayer thin-film structures containing one piezoelectric layer. The operating frequency of these resonators is determined by the thickness of the structure and by the elastic properties of layers, and as a rule have no electrical tuning. Therefore, the development of TFBARs with the capability of electrically controlling their resonance frequency is a challenging problem whose solution could lead to a significant improvement of the modern filter devices and microwave systems. A possible solution of this problem is to replace the piezoelectric materials traditionally used for TFBAR fabrication, with ferroelectric materials in the paraelectric phase. A good candidate is strontium titanate (STO). STO is a relatively low loss dielectric material with a centro-symmetric crystal structure, in which an external electrical field induces the piezoelectric effect. The magnitude of the applied field determines the value of the piezoelectric coefficient. This work presents a TFBAR architecture that allows significant improvement of the device’s operational range by introducing multi-resonance frequency switching ability. In such a way it is possible to vary the magnitude and the sign of the induced piezoelectric coefficients together, hence to control the excitation efficiency of each normal acoustic mode in the structure.