Amplified dual-gate bio field effect transistor

A method of fabricating a semiconductor device, the method comprising:

• forming a first gate structure on a front surface of a substrate, the first gate structure comprising a conductive layer and a dielectric layer;
• doping a region of the substrate to form a channel region beneath the first gate structure and to form a first source/drain region and a second source/drain region aligned relative to the first gate structure;
• removing material over a back side of the substrate to expose a back surface of the substrate, wherein the exposed back surface comprises the channel region, the first source/drain region, and the second source/drain region;
• depositing an isolation layer on the back surface of the substrate, the isolation layer being over at least the channel region, the first source/drain region, and the second source/drain region;
• forming an opening through the isolation layer to expose at least a portion of the channel region;
• and
• forming a second gate structure on the back surface of the substrate, wherein the second gate structure comprises an interface layer configured to bind to biomolecules, and wherein the interface layer is patterned such that at least a portion of the interface layer remains over the exposed portion of the channel region.

A method of using a BioFET sensor to detect target molecules, the method comprising:

• disposing a solution containing the target molecules over the BioFET sensor, wherein the BioFET sensor includes an interface layer on a backside of a substrate, the interface layer having receptors immobilized thereon that are exposed to the solution, and wherein the BioFET sensor further includes a gate structure pattered on a front side of the substrate, the interface layer being aligned with the gate structure, wherein the gate structure comprises a conductive layer and a dielectric layer, and wherein a thickness of the dielectric layer is less than a thickness of the interface layer;
• binding the target molecules to the receptors;
• changing a threshold voltage of the BioFET sensor based on the binding of the target molecules;
• and
• detecting a presence of the target molecules based on the change of the threshold voltage.