Capacitive microphone sensor design and fabrication method for achieving higher signal to noise ratio

A method to fabricate a capacitive micro-electromechanical transducer, the method comprising:

• forming a mesa diaphragm in a layer of a first substrate, the mesa diaphragm spanning a first cavity in at least a second layer of the first substrate, the first cavity open at an exterior surface of the first substrate, the exterior surface opposed to an interior surface of the first substrate;
• providing a second substrate having an interior surface, an exterior surface, and a second cavity formed in the interior surface of the second substrate, the second cavity having a second opening and terminating in a cavity bottom surface, the cavity bottom surface being non-planar across at least one lateral or radial dimension thereof;
• attaching the interior surface of second substrate to the interior surface of the first substrate with the mesa diaphragm in registration with the second cavity and with the mesa diaphragm oscillatable along a longitudinal axis at least partially into the second cavity;
• and
• patterning the cavity bottom surface, which includes forming a plurality of stepped regions such that a depth of the second cavity as measured from the second opening to the cavity bottom surface increases as the cavity bottom surface is laterally or radially traversed from a perimeter thereof to a center thereof.

A method to fabricate a capacitive micro-electromechanical transducer, the method comprising:

• forming a mesa diaphragm in a layer of a first substrate, the mesa diaphragm spanning a first cavity in at least a second layer of the first substrate, the first cavity open at an exterior surface of the first substrate, the exterior surface opposed to an interior surface of the first substrate;
• providing a second substrate having an interior surface, an exterior surface, and a second cavity formed in the interior surface of the second substrate, the second cavity having a second opening and terminating in a cavity bottom surface, the cavity bottom surface being non-planar across at least one lateral or radial dimension thereof;
• attaching the interior surface of second substrate to the interior surface of the first substrate with the mesa diaphragm in registration with the second cavity and with the mesa diaphragm oscillatable along a longitudinal axis at least partially into the second cavity;
• and
• forming a plurality of holes in the second substrate that extend from the cavity bottom surface through the exterior surface of the second substrate, such that the plurality of holes are non-uniform in at least one of size or distribution, and such that a relative density of the holes or a relative size of the holes increases as the cavity bottom surface is laterally or radially traversed from a perimeter thereof to a center thereof.

A method to fabricate a capacitive micro-electromechanical transducer, the method comprising:

• forming a mesa diaphragm in a layer of a first substrate, the mesa diaphragm spanning a first cavity in at least a second layer of the first substrate, the first cavity open at an exterior surface of the first substrate, the exterior surface opposed to an interior surface of the first substrate;
• providing a second substrate having an interior surface, an exterior surface, and a second cavity formed in the interior surface of the second substrate, the second cavity having a second opening and terminating in a cavity bottom surface, the cavity bottom surface being non-planar across at least one lateral or radial dimension thereof;
• and
• attaching the interior surface of second substrate to the interior surface of the first substrate with the mesa diaphragm in registration with the second cavity and with the mesa diaphragm oscillatable along a longitudinal axis at least partially into the second cavity;
• forming a plurality of holes in the second substrate that extend from the cavity bottom surface through the exterior surface of the second substrate, such that the plurality of holes are uniform in size, and a density of the holes is higher at a center of the cavity bottom surface than at a perimeter of the cavity bottom surface.