Using 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 determining the presence or concentration of a target-substance in a medium, the method comprising:
a) determining a current-voltage characteristic of a floating gate field effect transistor having a floating gate electrically coupled with a sensing material via an electrical conductor, the sensing material having a charge that changes in the presence of the target substance and being selected from polyaniline, aniline, or pheochromocytoma cells; and
b) determining a presence or concentration of the target substance based on the determined current-voltage characteristic,
wherein the act of determining a presence or concentration of a target substance includes comparing the determined current-voltage characteristic with another current-voltage characteristic, and
wherein the another current-voltage characteristic includes one determined from another floating gate field effect transistor having a floating gate that is not electrically coupled with the sensing material,
wherein the floating gate field effect transistor has a control gate disposed at a location between a drain and a source, the floating gate being insulated from the drain and the source by a first insulation layer and the control gate being insulated from the floating gate by a second insulation layer, and
wherein the method further comprises:
coating the floating gate with the sensing material, the floating gate changing a threshold voltage of the floating gate field effect transistor due to the charge generated in the sensing material.
2. The method of claim 1 wherein the current-voltage characteristic indicates the threshold voltage of the floating gate field effect transistor.
3. The method of- claim 1 ,
wherein the another current-voltage characteristic-includes a current-voltage characteristic determined from the floating gate field effect transistor when it is not exposed to the medium.
4. The method of claim 1 wherein components of the another floating gate field effect transistor match those of the floating gate field effect transistor with an exception of the sensing material that is coated on the floating gate of the floating gate field effect transistor.
5. The method of claim 1 wherein the act of comparing the determined current-voltage characteristic with another current-voltage characteristic includes providing a first voltage and a second voltage to inputs of a differential amplifier.
6. The method of claim 1 further comprising applying a predetermined voltage to a control gate of the floating gate field effect transistor,
wherein the predetermined voltage is selected to place the floating gate field effect transistor into its operating range.
7. The method of claim 1 , wherein the floating gate field effect transistor coupled with the sensing material is fabricated by a 2-poly 2-metal process.