Potentiometric pCO2 Sensor and the Fabrication Method thereof

Abstract

This invention provides a pCO2 sensor, and more particularly, a potentiometric pCO2 sensor. The potentiometric pCO2 sensor has a substrate, a solid ion-sensing layer on the substrate, a solid electrolyte layer on the solid ion-sensing layer, and a gas-permeable layer on the solid electrolyte layer. In addition, the gas-permeable layer allows air molecules to diffuse through, the solid electrolyte layer change the pH value thereof according to the CO2 concentration in the diffusing air molecules, and the solid ion-sensing layer senses the pH change of the solid electrolyte layer to generate a sensing signal. By doing so, the quantity of the CO2 dissolved in the liquid can be measured.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram illustrating part of fabrication steps and sectional structure of the potentiometric pCO₂ sensor in a preferred embodiment of the present invention;

FIG. 1B is a schematic diagram illustrating part of fabrication steps and sectional structure of the potentiometric pCO₂ sensor in a preferred embodiment of the present invention, based on FIG. 1A;

FIG. 1C is a schematic diagram illustrating part of fabrication steps and sectional structure of the potentiometric pCO₂ sensor in a preferred embodiment of the present invention, based on FIG. 1B;

FIG. 2 is a schematic system block diagram illustrating the measurement by the potentiometric pCO₂ sensor in a preferred embodiment of the present invention;

FIG. 3 is a characteristic curve of the potentiometric pCO₂ sensor of the present invention;

FIG. 4 is another characteristic curve of the potentiometric pCO₂ sensor of the present invention; and,

FIG. 5 is another characteristic curve of the potentiometric pCO₂ sensor of the present invention.

Claims

1. A potentiometric pCO2 sensor, comprising: a substrate;a solid ion-sensing layer on said substrate;a solid electrolyte layer on said solid ion-sensing layer; anda gas-permeable layer on said solid electrolyte layer;wherein said gas-permeable layer allows air molecules to diffuse through, the pH value of said solid electrolyte layer changes in response to the CO2 concentration in the diffusing air molecules, and said solid ion-sensing layer senses the pH change of said solid electrolyte layer to generate a sensing signal.

2. The potentiometric pCO2 sensor according to claim 1, wherein said solid ion-sensing layer includes tin dioxide.

3. The potentiometric pCO2 sensor according to claim 1, wherein the thickness of said solid ion-sensing layer is about 2000 Å.

4. The potentiometric pCO2 sensor according to claim 1, wherein said solid electrolyte layer includes sodium bicarbonate, sodium chloride, and polyvinyl alcohol.

5. The potentiometric pCO2 sensor according to claim 1, wherein said gas-permeable layer includes bis(2-ethylhexyl)sebacate, valinomycin, silicon rubber, and tetrahydrofuran.

6. The potentiometric pCO2 sensor according to claim 1, further comprising a sealing layer provided to enclose the peripheral of said substrate and said solid ion-sensing layer and cover the top thereof wherein said sealing layer has a window to expose part of said solid ion-sensing layer.

7. The potentiometric pCO2 sensor according to claim 6, wherein said sealing layer includes epoxy resin.

8. The potentiometric pCO2 sensor according to claim 6, wherein the area of said window is about 2*2 mm2.

9. The potentiometric pCO2 sensor according to claim 1, further comprising a conducting wire for connecting with said solid ion-sensing layer to output the sensing signal.

10. A method for fabricating a potentiometric pCO2 sensor, comprising: depositing a solid ion-sensing layer on a substrate;connecting a conducting wire to said solid ion-sensing layer;performing a sealing process to form a sealing layer provided to enclose the peripheral of said substrate and said solid ion-sensing layer and cover the top of said substrate and said solid ion-sensing layer wherein said sealing layer has a window to expose part of said solid ion-sensing layer;forming a solid electrolyte layer on said solid ion-sensing layer; andforming a gas-permeable layer on said solid electrolyte layer;wherein said gas-permeable layer allows air molecules to diffuse through, the pH value of said solid electrolyte layer changes in response to the CO2 concentration in the diffusing air molecules, said solid ion-sensing layer senses the pH change of said solid electrolyte layer to generate a sensing signal, and the sensing signal is outputted by said conducting wire.

11. The method for fabricating a potentiometric pCO2 sensor according to claim 10, wherein said solid ion-sensing layer is formed by using tin dioxide as the sputtering target and depositing on said substrate under the conditions that the temperature of said substrate is maintained at 150° C., the deposition pressure is 20 mtorr, and RF power is 50W.

12. The method for fabricating a potentiometric pCO2 sensor according to claim 10, wherein the thickness of said solid ion-sensing layer is about 2000 Å.

13. The method for fabricating a potentiometric pCO2 sensor according to claim 10, wherein said conducting wire is adhered to said solid ion-sensing layer by silver adhesive.

14. The method for fabricating a potentiometric pCO2 sensor according to claim 10, wherein said sealing layer includes epoxy resin.

15. The method for fabricating a potentiometric pCO2 sensor according to claim 10, wherein the area of said window is about 2*2 mm2.

16. The method for fabricating a potentiometric pCO2 sensor according to claim 10, wherein the method for forming said solid electrolyte layer includes the following steps: providing 5 mM sodium bicarbonate and 0.5 mM sodium chloride in deionized water to form a first solution;adding 4 wt % of polyvinyl alcohol into said first solution to form a second solution; andtaking out 2 μl of said second solution and then dripping on said solid ion-sensing layer in said window to stay still under room temperature for ca. 30˜60 minutes.

17. The method for fabricating a potentiometric pCO2 sensor according to claim 10, wherein the method for forming said gas-permeable layer includes the following steps: dissolving 21.5 wt % bis(2-ethylhexyl)sebacate, 0.8 wt % valinomycin, and 77.7 wt % silicon rubber in tetrahydrofuran to form a third solution wherein every 100 mg of silicon rubber require 200 μl of tetrahydrofuran; andtaking out 5 μl of said third solution and then dripping on said solid electrolyte layer to stay still under room temperature for ca. 8 hours.

18. A pCO2 measurement method, comprising: using a potentiometric pCO2 sensor to detect the CO2 dissolution amount in a liquid specimen wherein said potentiometric pCO2 sensor uses a gas-permeable layer for allowing air molecules to diffuse through, a solid electrolyte layer changing the pH value thereof in response to the CO2 concentration in the diffusing air molecules, a solid ion-sensing layer for sensing the pH change of said solid electrolyte layer to generate a sensing signal; andproviding one end of an electrode in said liquid specimen and grounding the other end of said electrode to have reference potential.

19. The pCO2 measurement method according to claim 18, further comprising: inputting the sensing signal and the reference potential into an instrumentation amplifier; andinputting the output of said instrumentation amplifier into a processing and display module to process and display the CO2 dissolution amount in the liquid specimen.