Floating gate field effect transistors for chemical and/or biological sensing

• US 20050230271A1
• Filed: 01/11/2005
• Published: 10/20/2005
• Est. Priority Date: 01/12/2004
• Status: Active Grant

• Current Assignee: Polytechnic Institute Of New York University (New York University)
• Original Assignee: Polytechnic Institute Of New York University (New York University)
• Inventors: Rahman, Arifur, Levon, Kalle, Zhao, Ben, Sai, Tsunehiro
• Granted Patent: US 7,462,512 B2
• Time in Patent Office: Days
• US Class Current: 205/789
• CPC Class Codes: G01N 27/4145 specially adapted for biomolecules, e.g. gate electrode with immobilised receptors
• CPC Class Codes: G01N 27/4148 Integrated circuits therefor, e.g. fabricated by CMOS processing CMOS processing per se H01L21/82

Abstract

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.

Claims

1. A method for determining the presence or concentration of a target material 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 having a charge that changes in the presence of the target substance; and

b) determining a presence or concentration of the target substance based on the determined current-voltage characteristic.

2. The method of claim 1 wherein the current-voltage characteristic is a threshold voltage of the floating gate field effect transistor.

3. The method of claim 1 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.

4. The method of claim 3 wherein the other current-voltage characteristic is one determined from the floating gate field effect transistor before it is applied to the medium.

5. The method of claim 3 wherein the other current-voltage characteristic is one determined from another floating gate field effect transistor having a floating gate that is not electrically coupled with a sensing material having a charge that changes in the presence of the target substance.

6. The method of claim 5 wherein the other floating gate field effect transistor has components that substantially match those of the floating gate field effect transistor.

7. The method of claim 5 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 differential amplifier.

8. The method of claim 1 further comprising

applying a predetermined voltage to the 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 optimum operating range.

9. A device for determining the presence or concentration of a target substance in a medium, the device comprising:

a) a floating gate field effect transistor; and

b) sensing material, the sensing material

i) being electrically coupled with a floating gate of the floating gate field effect transistor; and

ii) having a charge that changes in the presence of the target substance.

10. The device of claim 9 wherein the floating gate field effect transistor includes

i) a substrate;

ii) a source;

iii) a drain;

iv) a first insulator electrically isolating the floating gate from the substrate;

v) a control gate; and

vi) a second insulator electrically isolating the floating gate from the control gate.

11. The device of claim 9 wherein the sensing material is applied to the floating gate.

12. The device of claim 9 wherein the floating gate field effect transistor includes

i) a substrate;

ii) a source;

iii) a drain;

iv) a first insulator electrically isolating the floating gate from the substrate;

v) a control gate;

vi) a second insulator electrically isolating the floating gate from the control gate; and

vii) a metal layer electrically coupled with the floating gate, wherein the sensing material is applied to the metal layer.

13. The device of claim 12 wherein the floating gate field effect transistor further includes

viii) a second metal layer;

ix) a first conductor electrically coupling the floating gate with the second metal layer; and

x) a second conductor electrically coupling the second metal layer with the metal layer.

14. The device of claim 12 wherein the first conductor and the second conductor are metal wires.

15. The device of claim 9 wherein the sensing material is polyaniline and the target material is DNA.

16. The device of claim 9 wherein the sensing material is Pheochromocytoma cells and the target material is cellular activities.

17. 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 μ

m process technology, wherein the 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) spin coating the exposed portion of the second metal layer with ion-sensitive material.

18. The method of claim 17 wherein the ion-sensitive material has a charge that changes in the presence of the target substance.

19. The method of claim 18 wherein the target substance is one of (A) a specific chemical and (B) a specific class of chemicals.

20. The method of claim 18 wherein the target substance is one of (A) a specific biological material and (B) a specific class of biological materials.

21. The method of claim 17 further comprising:

e) electrically coupling 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.

22. A device for determining the presence or concentration of one or more target substances in a medium, the device comprising:

a) an array of elements, each element of the array including

i) a floating gate field effect transistor, and

ii) sensing material, the sensing material

A) being electrically coupled with a floating gate of the floating gate field effect transistor; and

B) having a charge that changes in the presence of a specific one of the one or more target substances; and

c) means for determining the presence or concentration of the one or more target substances using signals from a plurality of the elements of the array.