Floating gate field effect transistors for chemical and/or biological sensing
Specific ionic interactions with a sensing material that is electrically coupled with the floating gate of a floating gate-based ion sensitive field effect transistor (FGISFET) may be used to sense a target material. For example, an FGISFET can use (e.g., previously demonstrated) ionic interaction-based sensing techniques with the floating gate of floating gate field effect transistors. The floating gate can serves as a probe and an interface to convert chemical and/or biological signals to electrical signals, which can be measured by monitoring the change in the device's threshold voltage, V T .
1. A method for fabricating a floating gate field effect transistor, the method comprising:
a) fabricating a floating gate field effect transistor using a 2-polysilicon and 2-metal layer 1.2 μm (or micron) process technology, wherein a floating gate is electrically coupled with a receptor on a second metal layer;
b) encapsulating the second metal layer in glass;
c) removing some of the glass to
i) expose bonding pads on the second metal layer to create bond wire connections for packaging, and
ii) expose at least a portion of the second metal layer; and
d) immobilizing a ligand to the exposed portion of the second metal layer, wherein the act of immobilizing includes spin coating the exposed portion of the second metal layer with ion-sensitive material.
2. The method of claim 1 wherein the ion-sensitive material has a charge that changes in the presence of the target substance.
3. The method of claim 2 wherein the target substance is one of (A) a specific chemical and (B) a specific class of chemicals.
4. The method of claim 2 wherein the target substance is one of (A) a specific biological material and (B) a specific class of biological materials.
5. The method of claim 1 further comprising:
e) electrically coupling the floating gate of the floating gate field effect transistor to a substrate of the floating gate field effect transistor, thereby providing a discharge path for any accumulated charges on the floating gate; and
f) making the electrical coupling non-conducting after fabrication steps involving plasma.
6. The method of claim 1 further comprising:
e) electrically coupling the floating gate of the floating gate field effect transistor to a substrate of the floating gate field effect transistor using a second metal layer interconnect; and
f) making the second metal layer interconnect non-functional after fabrication steps of the 2-polysilicon and 2metal layer 1.2 μm (or micron) process technology involving plasma.
7. The method of claim 6 wherein the act of making the second metal layer interconnect non-functional includes cutting the second metal layer interconnect with a focused laser beam.