MEMS filter’s design and modeling based on width-extensional mode plate resonator for wireless applications

This paper proposes a new filter’s design process and modeling that can be employed in RF wireless communication systems. The filter is constructed by two similar rectangular piezoelectric plates vibrating in the width-extensional mode. Each plate is formed by a piezoelectric film and is sandwiched between two metallic electrodes. The vibrating plates are mechanically coupled by a beam linkage. The resonance frequencies of the vibrating structure are defined by the plate’s lateral dimension which allows the integration of the multi-frequency filter banks on the same chip. The coupled resonators exhibit two mechanical resonance modes: in-phase and out-of-phase vibrating modes. These modes define the filter bandwidth. In the first part of this paper, we proposed a theoretical model allowing to define the desired filter bandwidth varying the coupling beams location. In the second part, we used the microwave circuit theory to calculate the generalized A B C D matrix and consequently the filter transmitted coefficient (S ₂₁ ). The filter bandwidth values extracted from the transmitted coefficient (S ₂₁ ) show a consistent agreement with the desired filter bandwidths determined by the theoretical model developed in the first part. As application, a filter with a center frequency of 217 MHz is able to operate with fractional bandwidth varying from very low value (close to 0 %) to 5.5 %. This modeling approach is very important for filter bandwidth control.