Acoustic waveguide with diffraction grating

A package, comprising:

• a semiconductor die;
• and
• an acoustic waveguide including an array of capacitors in the semiconductor die, the array of capacitors including:
• a first portion comprising a two-dimensional array of first capacitors, the first capacitors having a first size;
• a second portion adjacent the first portion, the second portion comprising a two-dimensional array of second capacitors, the second capacitors having a second size, the second size smaller than the first size;
• and
• a third portion adjacent the second portion, the third portion comprising a first row of third capacitors and a second row of fourth capacitor, the third capacitors having a third size, fourth capacitors having a fourth size, the fourth size different than the third size.

A semiconductor package comprising:

• a semiconductor die having a first surface and a second surface opposing the first surface;
• an acoustic waveguide in the semiconductor die, the acoustic waveguide including an array of capacitors, the array of capacitors including a transducer portion and a diffraction grating portion, the transducer portion configured to produce first acoustic waves based on receiving first electrical signals and to produce second electrical signals based on receiving second acoustic waves, the diffraction grating portion configured to direct the first acoustic waves toward the second surface and to receive the second acoustic waves from the second surface;
• and
• a mold compound over the first surface of the semiconductor die and a portion of the second surface, a cavity in the mold compound exposing a portion of the second surface.