Manufacturing method of surface acoustic wave filter with back electrode of piezoelectric layer

A fabrication method of a surface acoustic wave (SAW) filter, comprising:

• obtaining a piezoelectric substrate;
• forming an interdigital transducer (IDT) on a first portion of the piezoelectric substrate;
• forming a sacrificial layer on the first portion of the piezoelectric substrate, the sacrificial layer covering an interdigital portion of the IDT;
• forming a first dielectric layer on the first portion of the piezoelectric substrate, covering the sacrificial layer and the IDT;
• forming a non-conductive layer on a bottom substrate;
• forming a buffer layer on the non-conductive layer formed on the bottom substrate;
• bonding the bottom substrate formed with the non-conductive layer and the buffer layer, to the first dielectric layer, wherein the buffer layer directly contacts the first dielectric layer;
• removing a second portion of the piezoelectric substrate to expose the first portion of the piezoelectric substrate, the first portion of the piezoelectric substrate constituting a piezoelectric layer having a first surface on which the IDT is formed and a second surface opposite to the first surface;
• forming a back electrode on the second surface of the piezoelectric layer;
• forming a release hole through the piezoelectric layer;
• and
• etching and releasing the sacrificial layer to form a lower cavity below the interdigital portion of the IDT.