In some embodiments, the present disclosure provides a MEMS package. The MEMS package includes a MEMS IC comprising a MEMS substrate, a dielectric layer disposed over the MEMS substrate, and a piezoelectric layer disposed over the dielectric layer. The dielectric layer includes a flexible diaphragm made of dielectric material, and the piezoelectric layer includes a piezoelectric opening over the flexible diaphragm. A CMOS IC includes a CMOS substrate and an electrical interconnect structure. The CMOS IC is bonded to the MEMS IC so the electrical interconnect structure is proximate to the piezoelectric layer and so the CMOS IC encloses a back cavity over the flexible diaphragm. A support layer is disposed between the electrical interconnect structure and the piezoelectric layer. The support layer has a support layer opening which is disposed at a position vertically aligned with the flexible diaphragm and which is a part of the back cavity.