Preventing stray currents in sensors in conductive media

• US 9,140,662 B1
• Filed: 08/19/2014
• Issued: 09/22/2015
• Est. Priority Date: 08/19/2014
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Carlson, Robert Jon, Nohava, Thomas E.
• Primary Examiner(s): Roman, Angel
• Application Number:
  US14/463,087
• Time in Patent Office: 399 Days
• US Class Current: 1/1
• CPC Class Codes: G01N 27/414 Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS

Abstract

A sensor is provided. The sensor includes a conductive substrate having side-walls; a dielectric layer overlaying a first surface of the conductive substrate, the dielectric layer including a gate dielectric having a first thickness and a field dielectric having a second thickness; a sensing layer overlaying a first surface of the gate dielectric; a non-conductive carrier wherein a second surface of the conductive substrate overlays a portion of the non-conductive carrier; and an insulating layer conformally coating at least the side-walls of the conductive substrate, wherein a first surface of the sensing layer is uncoated by the insulating layer.

Claims

1. A sensor comprising:

a conductive substrate having side-walls;

a dielectric layer overlaying a first surface of the conductive substrate, the dielectric layer including a gate dielectric having a first thickness and a field dielectric having a second thickness;

a sensing layer overlaying a first surface of the gate dielectric;

a non-conductive carrier wherein a second surface of the conductive substrate overlays a portion of the non-conductive carrier; and

an insulating layer conformally coating at least the side-walls of the conductive substrate, wherein a first surface of the sensing layer is uncoated by the insulating layer.

2. The sensor of claim 1, wherein the insulating layer is an atomic layer having a thickness less than 1000 Angstroms.

3. The sensor of claim 1, wherein the insulating layer conformally coats the field dielectric.

4. The sensor of claim 1, wherein the insulating layer conformally coats the field dielectric, and an exposed surface of the non-conductive carrier.

5. The sensor of claim 1, further comprising:

circuit components, wherein the dielectric layer, the sensing layer, and the circuit components are operable to sense pH of a conductive fluid when the sensing layer is exposed to the conductive fluid.

6. The sensor of claim 1, further comprising:

a first electrode;

a second electrode;

a first via formed in the conductive substrate, the first via electrically connecting a source diffusion region to the first electrode; and

a second via formed in the conductive substrate, the second via electrically connecting a drain diffusion region to the second electrode, wherein, when the sensor is operable, the sensing layer functions as a gate, and the conductive substrate functions as a channel.

7. The sensor of claim 6, further comprising:

a layer of silicon dioxide formed between the non-conductive carrier and the second surface of the conductive substrate, the layer of silicon dioxide overlaying the first electrode and the second electrode.

8. The sensor of claim 1, wherein the conductive substrate is a silicon substrate.

9. The sensor of claim 1, wherein the conductive substrate is a p doped silicon substrate.

10. The sensor of claim 1, wherein the dielectric layer and sensing layer sense pH when exposed to a conductive fluid.

11. A method of forming a sensor that is immune to stray currents, comprising

coating a first surface of a conductive substrate with a dielectric layer;

coating a portion of the dielectric layer with a sensing layer;

segmenting the conductive substrate, wherein sidewalls are exposed; and

conformally forming an insulating layer over at least the sidewalls, wherein a first surface of the sensing layer is uncoated by the insulating layer.

12. The method of claim 11, further comprising:

positioning the conductive substrate on a non-conductive carrier.

13. The method of claim 11, further comprising:

positioning the conductive substrate on a non-conductive carrier prior to conformally forming the insulating layer over at least the sidewalls, wherein the insulating layer overlays a portion of a surface of the non-conductive carrier.

14. The method of claim 11, further comprising;

etching a portion of the dielectric layer, wherein coating the portion of the dielectric layer with the sensing layer includes;

coating the etched portion of the dielectric layer with the sensing layer.

15. The method of claim 11, further comprising:

forming a first electrode in a non-conductive carrier;

forming a second electrode in the non-conductive carrier;

forming a first via in the conductive substrate;

forming a second via in the conductive substrate; and

positioning the conductive substrate on a non-conductive carrier.

16. The method of claim 15, further comprising:

forming an insulating layer between the non-conductive carrier and a second surface of the conductive substrate, the insulating layer overlaying the first electrode and the second electrode;

forming a first conductive material in the insulating layer; and

forming a second conductive material in the insulating layer.

17. The method of claim 15, further comprising:

forming a layer of silicon dioxide between the non-conductive carrier and a second surface of the conductive substrate, the layer of silicon dioxide overlaying the first electrode and the second electrode;

forming a first conductive pad in the layer of silicon dioxide; and

forming a second conductive pad in the layer of silicon dioxide.

18. The method of claim 15, wherein forming the first via in the conductive substrate comprises:

etching a first cavity in the conductive substrate; and

coating an inner surface of the first cavity with a metal or a metal alloy, and wherein forming the second via in the conductive substrate comprises;

etching a second cavity in the conductive substrate; and

coating an inner surface of the second cavity with the metal or the metal alloy.

19. A pH sensor comprising:

a non-conductive carrier;

a first electrode inlaid in the non-conductive carrier;

a second electrode inlaid in the non-conductive carrier;

a conductive substrate having a first surface, a second surface, and side-walls, the conductive substrate overlaying at least a portion of the non-conductive carrier;

a dielectric layer overlaying the first surface of the conductive substrate, the dielectric layer including a gate dielectric having a first thickness and a field dielectric having a second thickness;

a sensing layer overlaying a first surface of the gate dielectric;

an insulating layer conformally coating at least the side-walls of the conductive substrate, wherein a first surface of the sensing layer is uncoated by the insulating layer;

a first via formed in the conductive substrate, the first via electrically connecting a source diffusion to the first electrode; and

a second via formed in the conductive substrate, the second via electrically connecting a drain diffusion to the second electrode, wherein, when the pH sensor is operable, the sensing layer functions as a gate, and the conductive substrate functions a channel.

20. The pH sensor of claim 19, further comprising:

a layer of oxide formed between the non-conductive carrier and the second surface of the conductive substrate overlaying the first electrode and the second electrode;

a first conductive pad extending through the layer of oxide; and

a second conductive pad extending through the layer of oxide.