Magnetic sensor of very high sensitivity

A process for fabricating a magnetic sensor comprising:

• forming an epitaxial layer comprising at least one of Ge and SiGe alloy on a semiconductor substrate;
• forming a conductive layer on the epitaxial layer;
• etching two lateral trenches through the conductive layer, the epitaxial layer and into the semiconductor substrate to form a central stack defined by a portion of the conductive layer, a portion of the epitaxial layer, and a portion of the semiconductor substrate, with the portion of the epitaxial layer being exposed on two opposed lateral sides of the central stack;
• selectively removing part of the portion of the epitaxial layer to form a cavity bounded by the semiconductor substrate and the conductive layer, with the conductive layer forming a membrane;
• forming lateral spacers on the semiconductor substrate to close the cavity;
• doping the semiconductor substrate under the membrane with a dopant of a first type of conductivity to form a lower electrode of a capacitor;
• doping the membrane with a dopant of the first type of conductivity to form an upper electrode of the capacitor;
• and
• doping the semiconductor substrate exposed by the two lateral trenches with a dopant of a second type of conductivity to isolate the lower electrode of the capacitor.