Ladder type filter comprised of stacked tuning fork type resonators

A ladder type filter, comprising a plurality of tuning fork type piezoelectric resonators including at least two serial tuning fork type resonators and at least one parallel tuning fork type resonator, the serial resonators being connected in series between input and output electrodes and the parallel resonator being connected in parallel to a connection between the serial resonators,

• each tuning fork type piezoelectric resonator having at least two sides and comprising a piezoelectric substrate provided with first, second and third slits extending inward from a first edge thereof, said first slit being interposed in between said second and third slits thereby defining a tuning fork-shaped vibrating portion between said second and third slits, and electrodes operatively connected to said tuning fork-shaped vibrating portion for vibrating said tuning fork-shaped vibrating portion of said piezoelectric substrate;
• a plurality of layers each having a cavity provided therein, respective layers of said plurality being interposed between said plurality of tuning fork type piezoelectric resonators such that a cavity of said respective layers is provided at each of said two sides of said each tuning fork type piezoelectric resonator so as to allow vibration of the corresponding tuning fork-shaped vibrating portion,
• wherein said plurality of tuning fork type piezoelectric resonators are laminated with said plurality of layers interposed therebetween so as to comprise a laminated body, which further comprises spacers each disposed beside a corresponding one of said plurality of tuning fork type piezoelectric resonators so as to be spaced a predetermined distance away from said first edge of the corresponding piezoelectric substrate, and having a thickness, said thickness of each of said spacers being substantially equal to a corresponding thickness of the corresponding one of said plurality of tuning fork type piezoelectric resonators, said spacers being respectively fixed to said plurality of layers interposed therebetween.