Teknologian Tutkimuskeskus Vtt Oy

Teknologian Tutkimuskeskus Vtt

Johanna Meltaus

Tuomas Pensala

Markku Antero Ylilammi

Aarne Oja

Tomi Juha Mattila

Tommi Riekkinen

The invention relates to an acoustically coupled thin-film BAW filter, comprising a piezoelectric layer, an input-port on the piezoelectric layer changing electrical signal into an acoustic wave (SAW, BAW), and an output-port on the piezoelectric layer changing acoustic signal into electrical signal. In accordance with the invention the ports include electrodes positioned close to each other, and the filter is designed to operate in first order thickness-extensional TE1 mode.

Wide-band acoustically coupled thin-film BAW filter

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) TEand the second harmonic thickness shear (TS) 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.

The invention relates to a laterally coupled bulk acoustic wave (LBAW) filter comprising a vibration layer for carrying bulk acoustic waves, electrode means comprising a first electrode coupled to the vibration layer for exciting to the vibration layer at least one longitudinal wave mode having a first frequency band and one shear wave mode having a second frequency band, and a second electrode coupled to the vibration layer for sensing the filter pass signal, the first and second electrodes being laterally arranged with respect to each other, and an acoustic reflector structure in acoustic connection with the vibration layer. According to the invention, the reflector structure is adapted to acoustically isolate the vibration layer from its surroundings at the first frequency band more efficiently than at the second frequency band for suppressing the effect of the shear wave mode at the second frequency band from the filter pass signal. The invention helps to improve the quality of LBAW filter passbands.

Laterally coupled bulk acoustic wave filter with improved passband characteristics

The invention describes a manufacturing method for an acoustic balanced-unbalanced (balun) or balanced-balanced thin-film BAW filter based on lateral acoustic coupling. In laterally acoustically coupled thin-film BAW filters (LBAW) one can realize transformation from unbalanced to balanced electric signal if the electrodes of the balanced port are placed on the opposite sides of the piezoelectric film. The manufacturing process is simpler than in the corresponding component based on vertical acoustical coupling. The device can also realize impedance transformation.

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Espoo, Finland

Johanna Meltaus