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

Abstract

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 ABCD matrix and consequently the filter transmitted coefficient (S21). The filter bandwidth values extracted from the transmitted coefficient (S21) 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.