Chemically sensitive JFET transducer devices utilizing a blocking interface

• US 4,322,680 A
• Filed: 03/03/1980
• Issued: 03/30/1982
• Est. Priority Date: 03/03/1980
• Status: Expired due to Term

• Current Assignee: University of Utah Research Foundation (State of Utah)
• Original Assignee: University of Utah Research Foundation (State of Utah)
• Inventors: Janata, Jiri, Ure, Roland W. Jr.
• Primary Examiner(s): Tokar, Michael J.
• Application Number:
  US06/126,746
• Time in Patent Office: 757 Days
• Field of Search: 324/71 R, 324/71 SN
• US Class Current: 324/71.2
• CPC Class Codes: G01N 27/414 Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS

Abstract

A chemically sensitive junction field effect transistor transducer capable of selectively detecting and measuring chemical properties of substances to which the transducer is exposed. The transducer includes a substrate material, a semiconductor layer having a doping polarity laid over the surface of the substrate, a "source" contact connected to one part of the semiconductor layer, a "drain" contact connected to another part, and a chemically sensitive blocking interface gate structure overlying the upper surface of that portion of the semiconductor layer between the source and drain contacts. The gate structure is adapted to interact with selected chemical substances in the substance being tested and to produce an electric field in relation to the presence, concentration, or activity thereof. This electric field, in turn, causes a modulation of the depletion region in the semiconductor layer that affects the conductivity thereof, and hence the amount of source-drain current that can flow through the transducer. The gate structure also serves as a blocking interface and prevents current from flowing through the gate structure. The chemically sensitive blocking interface gate structure may include numerous configurations and materials adapted for sensing various chemical or biochemical properties.

Claims

1. A chemical sensitive junction field-effect transistor transducer for detecting chemical properties of substances to which said transducer is exposed comprising:

(a) a substrate material;

(b) a semiconductor layer having a doping polarity located at an upper surface of said substrate material, said doping polarity enabling an electrical current to flow through said layer;

(c) means for electrically connecting spaced apart regions of said semiconductor layer to an external voltage source, thereby allowing an electrical current to flow from said voltage source to a first of said spaced apart regions through a first of said electrical connecting means, through said semiconductor layer to a second of said spaced apart regions, and from said second spaced apart region through a second of said electrical connecting means back to said external voltage source;

(d) a blocking interface overlying that portion of said semiconductor layer that lies between said spaced apart regions and through which said electrical current flows, said blocking interface being adapted to interact with said substance so as to generate an electrical potential at said interface whose strength is a measure of selected chemical properties of said substance, said blocking interface having no insulating layer as a part thereof;

(e) a reference electrode connected in circuit relationship with said semiconductor layer through a second external voltage source such that a potential is created and added to the electric potential generated at said blocking interface, thus creating a resultant electric field that affects the conductivity of said semiconductor layer as a measure of the chemical properties of said substances by modulating the thickness of a depletion layer in the upper surface of said semiconductor layer which is void of free charge carriers, said depletion layer having a thickness related to said resultant electric field.

2. A transducer as defined in claim 1 wherein said blocking interface comprises a metal-semiconductor blocking interface comprising a conductive metal in combination with said semiconductor layer, said conductive metal being selectively chosen to react with desired ions, enzymes, antibodies, antigens, and the like so as to generate an electrical potential within said gate structure that varies as a measure of the presence, concentration, and activity of said ions, enzymes, antibodies, antigens, and the like within the substance to which said transducer is exposed.

3. A transducer as defined in claim 2 wherein said conductive metal is gold and said semiconductor layer is selected from a group of semiconductor materials consisting of silicon, gallium arsenide, germanium, and cadmium selenide.

4. A transducer as defined in claim 2 wherein said conductive metal is platinum and said semiconductor is selected from a group consisting of gallium arsenide, cadmium selenide, and cadmium sulfide.

5. A transducer as defined in claim 2 wherein said conductive metal is silver and said semiconductor is selected from a group consisting of gallium arsenide and cadmium sulfide.

6. A transducer as defined in claim 2 wherein said conductive metal is platinum silicide and said semiconductor is silicon.

7. A transducer as defined in claim 2 further comprising a chemical selective membrane overlying said conductive metal, said membrane adapted to selectively interact with ions, enzymes, antibodies, antigens, and the like, so as to change the electrical potential at the surface of said membrane, said potential change thereby contributing to the resultant electric field that affects the conductivity of said semiconductor layer.

8. A transducer as defined in claim 7 wherein said chemical selective membrane is selected from the group consisting of polyvinylchloride-valiomycin-plasticer and silver/silver choride.

9. A transducer as defined in claim 1 wherein said blocking interface comprises a solution-semiconductor blocking interface comprising the combination of said semiconductor layer being selectively chosen to react with desired ions, enzymes, antibodies, antigens, and the like so as to generate a potential at said gate structure that varies as a measure of the presence, concentration, and activity of said ions, enzymes, antibodies, antigens, and the like within said substance.

10. A transducer as defined in claim 9 wherein said semiconductor layer is selected from a group of semiconductor materials consisting of cadmium sulfide, silver sulfide, gallium arsenide, and indium phosphide.

11. A transducer as defined in claim 9 further comprising a chemical selective membrane overlying said semiconductor layer, said membrane adapted to selectively react with ions, enzymes, antibodies, antigens, and the like, so as to change the electrical potential at the surface of said membrane, said potential change thereby contributing to the resultant electric field that affects the conductivity of said semiconductor layer.

12. A transducer as defined in claim 1 wherein said blocking interface comprises a reverse biased p-n junction blocking interface comprising a p-doped semiconductor interfaced with an n-doped semiconductor, said semiconductor types being selectively chosen so as to be sensitive to specific chemical properties of said substance.

13. A transducer as defined in claim 12 wherein said p-doped semiconductor and n-doped semiconductor are selected from a group of semiconductor materials consisting of silicon, germanium, gallium arsenide, and indium phosphide.

14. A transducer as defined in claim 12 further comprising a chemical selective membrane adapted to selectively react with ions, enzymes, antibodies, antigens, and the like, so as to change the electrical potential at the surface of said chemical selective membrane, said potential change thereby contributing to the resultant electric field that affects the conductivity of said semiconductor layer.

15. A transducer as defined in claim 1 wherein said semiconductor layer is only slightly thicker than said depletion layer.

16. A transducer as defined in claim 15 wherein said semiconductor layer is on the order of one micrometer thick, being at least 0.1 micrometer thick and not greater than 10 micrometers thick.

17. A transducer as defined in claim 1 further including means for channeling the electrical current that passes through said semiconductor layer to flow under said blocking interface.

18. A transducer as defined in claim 17 wherein said channeling means comprises a physical configuration wherein said semiconductor layer only exists immediately underneath said blocking interface.

19. A transducer as defined in claim 18 wherein said physical configuration comprises a rectangular shaped strip of semiconductor layer immediately underneath a rectangular-shaped blocking interface of approximately the same dimensions, said means for electrically connecting the spaced apart regions of said semiconductor layer being attached to opposite ends of said rectangular semiconductor layer strip.

20. A transducer as defined in claim 18 wherein said physical configuration comprises a semiconductor layer of a closed geometrical shape to which said first electrical connecting means is attached at the center thereof and said second electrical connecting means is attached around the perimeter thereof, thereby allowing electrical current to flow in a radial pattern between said center and perimeter, such as a circular shaped semiconductor layer with electrical connecting means attached at the center and circumference thereof so as to allow electrical current to flow in a radial pattern between the center and the circumference, and further including similar closed geometrically shaped gate structure placed over those regions of said closed geometrically shaped semiconductor layer through which the radial electrical currents flow.

21. A transducer as defined in claim 1 wherein said substrate material comprises a semiconductor substrate material and further comprising means for preventing the electrical current flowing through said semiconductor layer from flowing in said semiconductor substrate.

22. A transducer as defined in claim 21 wherein the semiconductor substrate material has a doping polarity opposite that of said semiconductor layer and further wherein said prevention means comprises reverse biasing the semiconductor junction formed by said semiconductor substrate and semiconductor layer.

23. A transducer as defined in claim 21 wherein said prevention means comprises an insulator that electrically insulates said substrate from said semiconductor layer.

24. A transducer as defined in claim 1 wherein said substrate material comprises an electrically insulating material that precludes significant electric currents from flowing therein.

25. A transducer as defined in claim 24 wherein said semiconductor layer is silicon and said insulating substrate is chosen from the group consisting of spinel and sapphire.

26. A transducer as defined in claim 24 wherein said semiconductor layer is gallium arsenide and said insulating substrate is semi-insulating gallium arsenide.

27. A transducer as defined in claim 1 further comprising a substance impervious material disposed over said substrate material, semiconductor layer, and gate structure, with an opening therein for exposing a portion of said gate structure to the substances to which said transducer is exposed.

28. A multi-sensor chemically sensitive junction field effect transistor (JFET) for detecting chemical properties of substances to which said transducer is exposed comprising

(a) a substrate material;

(b) a plurality of independent semiconductor layers having a doping polarity located at an upper surface of said substrate material;

(c) means for electrically connecting spaced apart regions of each of said independent semiconductor layers to an external voltage source, thereby allowing electrical current to flow to, through, and from each of said semiconductor layers;

(d) a plurality of chemical sensitive blocking interfaces, one of which overlies that portion of each of said plurality of semiconductor layers that lies between said spaced apart regions and through which said electrical current flows, each of said blocking interfaces being adapted to interact with said substances so as to generate an electric potential at said interfaces whose strength is a measure of selected chemical properties of said substances, each of said blocking interfaces having no insulating layer as a part thereof;

(e) a reference electrode connected in circuit relationship with each of said semiconductor layers through a second external voltage source such that a potential is created and added to the electric potential generated at each of said blocking interfaces, a resultant electric field that affects the conductivity of each of said semiconductor layers as a measure of the chemical properties of said substances by inducing a depletion layer in the upper surface of each of said semiconductor layers which is void of free charge carriers, said depletion layer having a thickness proportional to said resultant electric field.

29. A multi-sensor transducer as defined in claim 28 wherein at least one of said plurality of blocking interfaces comprises a metal-semiconductor blocking interface comprising a conductive metal, in combination with said semiconductor layer.

30. A multisensor transducer as defined in claim 29 wherein the semiconductor layer associated with said metal-semiconductor blocking interface is selected from the group consisting of silicon, gallium arsenide, germanium, and cadmium selenide.

31. A multi-sensor transducer as defined in claim 28 wherein at least one of said plurality of blocking interfaces comprises a solution-semiconductor blocking interface comprising the combination of said semiconductor layer and said substance to which the transducer is exposed.

32. A multi-sensor transducer as defined in claim 31 wherein the semiconductor layer associated with said solution-semiconductor blocking interface is selected from the group consisting of cadmium sulfide, silver sulfide, gallium arsenide, and indium phosphide.

33. A multi-sensor transducer as defined in claim 28 wherein at least one of said plurality of blocking interfaces comprises a reverse biased p-n junction blocking interface, comprising a p-doped semiconductor interfaced with an n-doped semiconductor.

34. A multi-sensor transducer as defined in claim 33 wherein said p-doped semiconductor and n-doped semiconductor are selected from the group consisting of gallium arsenide and indium phosphide.

35. A multi-sensor transducer as defined in claim 28 further including at least one chemical selective membrane overlying one of said blocking interfaces, said chemical selective membrane adapted to selectively interact with ions, enzymes, antibodies, antigens, and the like, found in the substance to which said multi-sensor transducer is exposed so as to change the electrical potential at the surface of said chemical selective membrane, said potential change thereby contributing to the resultant electric field that affects the conductivity of the semiconductor layer over which said chemical selective membrane is laid.

36. A multi-sensor transducer as defined in claim 28 further including a substance impervious material disposed over said substrate material, semiconductor layers, and blocking interfaces, with a plurality of openings therein for exposing a portion of each of said gate structures to said substances to which said multi-sensor transducer is exposed.

37. A method of configuring a chemical sensitive junction field effect transistor (JFET) transducer comprising a substrate, a doped semiconductor layer on the surface of said substrate, conductive material electrically connected to a pair of spaced apart areas on said semiconductor layer, one of said areas being designated the drain and the other being designated the source, a blocking interface overlying that portion of said semiconductor layer lying between said spaced apart means, and a reference electrode connected in circuit relationship with said semiconductor layer, said chemical sensitive JFET configuration method being adapted to force electrical current flowing between the source and drain to flow under said blocking interface, said method comprising the steps of:

(a) configuring a shaped semiconductor layer, such as a circle, on the upper surface of said substrate;

(b) connecting a conductive material, such as a wire, to the center of said shaped semiconductor layer, said center serving as the source of said transducer;

(c) connecting other conductive material around the perimeter of said shaped semiconductor layer, said perimeter serving as the drain of said transducer; and

(d) configuring said blocking interface in a symmetrical fashion above the area of said semiconductor layer that lies between said source and drain.