Printed hygroscopic electrodes for low-cost capacitive relative humidity sensors

Patent metadata

Field	Value
Publication number	US-11143615-B2
Application number	US-201816176067-A
Country	US
Kind code	B2
Filing date	Oct 31, 2018
Priority date	Oct 31, 2018
Publication date	Oct 12, 2021
Grant date	Oct 12, 2021

Abstract

A capacitive relative humidity sensor includes a first electrode and a second electrode, where at least the one of the electrodes is a water-permeable electrode. The electrodes act in conjunction with a water-sensitive hygroscopic dielectric material. The design enables low-cost and simple fabrication of fast-responding and stable relative humidity sensors using digital fabrication techniques.

First claim

What is claimed is:

1. A method of forming a capacitive relative humidity sensor comprising:
optionally pre-treating a water absorptive dielectric layer;
depositing a first electrode on at least a portion of a surface of the water absorptive dielectric layer; and
depositing a second electrode on at least a portion of another surface of the water absorptive dielectric layer, wherein at least one of the first electrode and the second electrode is comprised of a water permeable material;
wherein a geometric dimension of the water absorptive dielectric layer changes with humidity, said changes of the geometric dimension causing changes in capacitance between the first electrode and the second electrode.

2. The method according to claim 1 further including treating the water absorptive dielectric layer prior to depositing the water permeable electrode, to at least one of (i) increase the wetting of the water absorptive dielectric layer and (ii) control at least one of an extent and rate of water uptake by the water absorptive dielectric layer.

3. The method according to claim 1 further including depositing a non-water absorptive dielectric between at least a portion of one of the surfaces of the water absorptive dielectric and one of the first electrode and the second electrode.

4. The method according to claim 1 further including
providing a carrier substrate;
the water absorptive dielectric layer being deposited on a surface of the carrier substrate; and
separating the water absorptive dielectric layer from the carrier substrate.

5. A method of forming a capacitive relative humidity sensor comprising:
depositing a first electrode on at least a portion of a substrate;
depositing a water absorptive dielectric layer on at least a portion of the first electrode;
optionally pre-treating the water absorptive dielectric layer; and
depositing a second electrode on at least a portion of the water absorptive dielectric layer, wherein the second electrode layer is made of a water permeable material;
wherein a geometric dimension of the water absorptive dielectric layer changes with humidity, said changes in the geometric dimension causing changes in capacitance between the first electrode and the second electrode.

6. The method according to claim 5 wherein one of the deposition methods is one of inkjet printing and aerosol printing.

7. The method according to claim 5 wherein the water permeable material is a PEDOT:PSS material.

8. The method according to claim 5 wherein a dielectric constant of the water absorptive dielectric layer changes with humidity, causing changes in capacitance between the first electrode and the second electrode.

9. A capacitive relative humidity sensor, comprising:
a water absorptive dielectric layer having a first surface and a second surface;
a first electrode positioned in contact with at least a portion of the first surface of the water absorptive dielectric layer; and
a second water-permeable electrode positioned in contact with at least a portion of the second surface of the of the water absorptive dielectric layer;
wherein a geometric dimension of the water absorptive dielectric layer changes in response to humidity, said changes in the geometric dimension causing changes in capacitance between the first electrode and the second electrode.

10. The capacitive relative humidity sensor according to claim 9 wherein the first electrode is a non-water permeable material.

11. The capacitive relative humidity sensor according to claim 9 wherein the first electrode is a water permeable material.

12. The capacitive relative humidity sensor according to claim 11 wherein the water permeable material is a PEDOT:PSS material.

13. The capacitive relative humidity sensor according to claim 9 wherein the second electrode is deposited across an entire surface of the water absorptive dielectric layer.

14. The capacitive relative humidity sensor according to claim 9 wherein the deposition of the first and/or second electrodes is by one of inkjet printing and aerosol printing.

15. The capacitive relative humidity sensor according to claim 9 wherein the water permeable material is a PEDOT:PSS material.

16. The capacitive relative humidity sensor according to claim 9 further including treating the water absorptive dielectric prior to depositing the water permeable electrode, to increase the wetting of the water absorptive dielectric and/or to control the extent and rate of water uptake by the water absorptive dielectric layer.

17. The capacitive relative humidity sensor according to claim 9 further including a non-water absorptive dielectric between at least a portion of one of the surfaces of the water absorptive dielectric and one of the first electrode and the second electrode.

18. A capacitive relative humidity sensor, comprising:
a water absorptive dielectric layer having a first surface and a second surface;
a first electrode positioned in contact with at least a portion of the first surface of the water absorptive dielectric layer;
a second electrode positioned in contact with at least a portion of the second surface of the of the water absorptive dielectric layer; and
a non-water absorptive dielectric positioned between at least a portion of one of the first and second surfaces of the water absorptive dielectric and one of the first and second electrodes;
wherein at least one of the first and second electrodes is water-permeable; and
wherein, in response to humidity, the water absorptive dielectric layer exhibits at least one of (i) changes in at least one of its geometric dimensions and (ii) changes in its relative permittivity, said changes causing changes in capacitance between the first electrode and the second electrode.

19. The sensor according to claim 18 , wherein the water absorptive dielectric layer has been treated by at least one of UV-ozone treatment and chemical etching to at least one of (i) increase the wetting of the water absorptive dielectric layer and (ii) control at least one of an extent and rate of water uptake by the water absorptive dielectric layer.

Assignees

• Palo Alto Res Ct Inc

Inventors

• Pierre Adrien
• Doris Sean Emerson
• Schwartz David Eric

Classifications

• G01N27/605

  for determining moisture content, e.g. humidity · CPC title

• G01N27/225 Primary

  by using hygroscopic materials · CPC title