Integrated acoustic filter on complementary metal oxide semiconductor (CMOS) die

A radio frequency (RF) front-end (RFFE) device, comprising:

• a die including a front-side dielectric layer on an active device, the active device on a first semiconductor substrate located at a back-side of the die, and a plurality of back-end-of-line layers between the active device and the front-side dielectric layer;
• and
• a microelectromechanical system (MEMS) device integrated on the die at a different layer than the active device, the MEMS device having a cap layer comprised of a cavity in the front-side dielectric layer of the die, between the first semiconductor substrate and a second semiconductor substrate coupled to the front-side dielectric layer in which the MEMS device comprises an acoustic filter, comprising:
• a piezoelectric layer on the second semiconductor substrate, the piezoelectric layer bonded to the front-side dielectric layer;
• and
• a first electrode between the piezoelectric layer and the front-side dielectric layer and also between the piezoelectric layer and the cavity, the first electrode coupled to the active device through a first back-end-of-line (BEOL) interconnect.

A radio frequency (RF) front-end (RFFE) device, comprising:

• an RFFE die including a front-side dielectric layer on an active device, the active device on a first semiconductor substrate located at a back side of the RFFE die, and a plurality of back-end-of-line layers between the active device and the front-side dielectric layer;
• and an acoustic filter integrated on the die at a different layer than the active device, the acoustic filter having a cap layer comprised of a cavity in the front-side dielectric layer of the die, between the first semiconductor substrate and a second semiconductor substrate coupled to the front-side dielectric layer, the acoustic filter comprising a second dielectric layer between the second semiconductor substrate and bonded to the front-side dielectric layer of the die and arranged opposite the cap layer;
• and a piezoelectric layer between a first electrode and a second electrode, the first electrode coupled to the second dielectric layer and an inert layer of the acoustic filter, the first electrode coupled to the active device through a first back-end-of-line (BEOL) interconnect, and the second electrode coupled to the dielectric layer and the inert layer of the acoustic filter, the second electrode coupled to a second BEOL interconnect;
• and
• an antenna coupled to an output of the acoustic filter.

A radio frequency (RF) front-end (RFFE) device, comprising:

• an RFFE die including a front-side dielectric layer on an active device, the active device on a first semiconductor substrate located at a back side of the RFFE die, and a plurality of back-end-of-line layers between the active device and the front-side dielectric layer;
• and an acoustic filter integrated on the die at a different layer than the active device, the acoustic filter having a cap layer comprised of a cavity in the front-side dielectric layer of the die, between the first semiconductor substrate and a second semiconductor substrate coupled to the front-side dielectric layer, the acoustic filter comprising a filter layer on the second semiconductor substrate, the filter layer bonded to the front-side dielectric layer;
• and a first electrode between the filter layer and the front-side dielectric layer and also between the piezoelectric layer and the cavity, the first electrode coupled to the active device through a first back-end-of-line (BEOL) interconnect, in which the acoustic filter comprises a surface acoustic wave (SAW) filter;
• and
• an antenna coupled to an output of the acoustic filter.