Pressure type fingerprint sensor fabrication method

A fabrication method of a pressure type fingerprint sensor comprising:

• providing a CMOS process to form a plate sensor capacitor, which comprising:
• a first metal layer;
• a second metal layer;
• an interconnection layer;
• an inter metal dielectric layer arranged between the first metal layer and the second metal layer;
• and
• a passivation layer covering the first metal layer;
• wherein there are a plurality of first metal plugs connecting the first metal layer and the second metal layer and a plurality of second metal plugs connecting the second metal layer and the interconnection layer;
• and
• wherein the second metal layer comprises a floating electrode material, an alloy layer, and a fixed electrode material;
• removing a portion of the passivation layer, a portion of the inter metal dielectric layer, and a portion of the floating electrode material of the second metal layer to form an etching window exposing the alloy layer;
• and
• etching the plate sensor capacitor by an etching solution to remove the alloy layer via the etching window and leave the floating electrode material and the fixed electrode material to form an air gap between them.