Capacitive Sensors and Methods for Forming the Same

A device comprising:

• a first silicon substrate;
• a dielectric layer on the first silicon substrate;
• a first polysilicon via and a polysilicon membrane, wherein the polysilicon membrane is anchored on the dielectric layer through the first polysilicon via, and wherein the polysilicon membrane is configured to move in directions toward and away from the first silicon substrate;
• a second silicon substrate comprising a through-opening overlapping a portion of the polysilicon membrane, wherein the first and the second silicon substrates are on opposite sides of the polysilicon membrane;
• and
• a eutectic alloy bonding to the polysilicon membrane, wherein the eutectic alloy is disposed between the polysilicon membrane and the second silicon substrate.

A device comprising:

• a first semiconductor substrate;
• and
• a capacitive sensor comprising:
• a back-plate, wherein the back-plate forms a first capacitor plate of the capacitive sensor, and wherein the back-plate comprises a portion of the first semiconductor substrate;
• a conductive plate, wherein the conductive plate is spaced apart from the back-plate by an air-gap, and wherein the conductive plate acts as a second capacitor plate of the capacitive sensor;
• and
• a membrane underlying the first semiconductor substrate, wherein the membrane is configured to move in a direction perpendicular to a top surface of the conductive plate, and wherein the conductive plate is attached to the membrane, and is configured to move in response to a movement of the membrane.