Process for manufacturing an optical microelectromechanical device having a tiltable structure with an antireflective surface

A picoprojector apparatus for use in a portable electronic apparatus, comprising:

• a light source, configured to generate a light beam as a function of an image to be generated;
• an optical microelectromechanical device comprising:
• a sensor body of semiconductor material, having a first surface and a second surface and comprising a suspended mirror structure upon which the generated light beam impinges, a fixed structure surrounding the suspended mirror structure, elastic supporting elements extending between the fixed structure and the suspended mirror structure, and an actuation structure coupled to the suspended mirror structure;
• a protective cap comprised of semiconductor material and bonded to the first surface of the sensor body and comprising a chamber overlying the actuation structure, the chamber being delimited by a wall having a through opening and having an outer surface, the outer surface being absorbent or diffusive to light, and the through opening being aligned to the suspended mirror structure;
• wherein the through opening is devoid of a solid material extending between and in contact with sidewalls of the opening;
• and
• a supporting body bonded to the second surface of the sensor body;
• and
• a driving circuit configured to supply electrical driving signals for rotating the suspended mirror structure.

An optical microelectromechanical device, comprising:

• a first wafer of semiconductor material having a first surface and a second surface;
• a suspended mirror structure formed in the first wafer;
• a fixed structure surrounding the suspended mirror structure;
• elastic supporting elements extending between the fixed structure and the suspended mirror structure;
• an actuation structure coupled to the suspended mirror structure;
• a chamber formed in a second wafer and bonded to the first surface of the first wafer, the chamber overlying the actuation structure and having a through opening aligned with the suspended mirror structure, the second wafer comprising a protective cap comprised of semiconductor material;
• and
• a third wafer bonded to the second surface of the first wafer, wherein the second wafer has an outer surface that is absorbent or diffusive with respect to light.