Wide-band acoustically coupled thin-film BAW filter
First Claim
1. An acoustic filter comprising;
- a stack of materials suitable for an acoustic filter, the stack comprising at least one piezoelectric layer,at least two resonators having a width and a gap between them and comprising electrodes on different sides of the piezoelectric layer, where the electrodes on at least one side of the piezoelectric layer are separated to form at least two resonator regions,wherein the stack of materials, width and gap between the separated electrodes being adapted to produce at least two distinct acoustic plate wave modes each contributing at least one lateral standing wave resonance in the acoustic filter,wherein a structure is adapted to trap the at least two distinct plate wave modes having a total of at least three lateral standing wave resonances in the acoustic filterwherein the piezoelectric layer is selected from symmetry group 6 mm, with their c-axis in a tilted orientation.
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Abstract
In a bulk acoustic wave (BAW) filter based on laterally acoustically coupled resonators on piezoelectric thin films, one can utilize two distinct acoustic plate wave modes of different nature, for example the thickness extensional (longitudinal) TE1 and the second harmonic thickness shear (TS2) mode to form a bandpass response. The invention is based on the excitation of at least two lateral standing wave resonances belonging to different plate wave modes that facilitate the transmission of signal. The passband is designed by tailoring the wave propagation characteristics in the device such that the resonances are excited at suitable frequencies to form a passband of a desired shape. The bandwidth of the filter described herein may therefore be more than twice that of the existing state-of-the-art microacoustic filters. Consequently, it has significant commercial and technological value.
13 Citations
14 Claims
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1. An acoustic filter comprising;
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a stack of materials suitable for an acoustic filter, the stack comprising at least one piezoelectric layer, at least two resonators having a width and a gap between them and comprising electrodes on different sides of the piezoelectric layer, where the electrodes on at least one side of the piezoelectric layer are separated to form at least two resonator regions, wherein the stack of materials, width and gap between the separated electrodes being adapted to produce at least two distinct acoustic plate wave modes each contributing at least one lateral standing wave resonance in the acoustic filter, wherein a structure is adapted to trap the at least two distinct plate wave modes having a total of at least three lateral standing wave resonances in the acoustic filter wherein the piezoelectric layer is selected from symmetry group 6 mm, with their c-axis in a tilted orientation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of manufacturing an acoustic wide-band filter comprising the steps of;
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selecting a structure design and materials for the filter, designating a desired center frequency and bandwidth, whereby designing a stack using the selected structure design and materials along with a set of resonators having a width and gap between them so that coupling to at least two distinct laterally propagating thickness vibration plate wave modes is achieved having a total of at least two resonances, and fabricating the designed filter stack so that it couples the at least two distinct laterally propagating thickness vibration plate wave modes having the total of at least two resonances, wherein designing the stack so that the designated center frequency is between the onset frequencies of the at least two distinct plate wave modes, and the frequency difference between the onset frequencies two distinct plate modes is approximately one third the desired bandwidth. - View Dependent Claims (13, 14)
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Specification