Capacitive humidity sensor

Abstract

A capacitive humidity sensor includes a detecting portion and a reference portion. The detecting portion includes a first sensor element, and a capacitance of the first sensor element varies in accordance with humidity. The reference portion includes a second sensor element and a capacitor. The second sensor element is connected to the first sensor element in series, and a capacitance of the second sensor element varies in accordance with the humidity. The capacitor has a constant capacitance relative to a humidity variation. The first sensor element has a gradient of a capacitance variation to the humidity variation, which is different from a gradient of the second sensor element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1A is a schematic plan view showing a capacitive humidity sensor according to a first embodiment, and FIG. 1B is a cross-sectional view taken along line IB-IB in FIG. 1A;

FIG. 2A is a cross-sectional view taken along line IIA-IIA in FIG. 1A, and FIG. 2B is a cross-sectional view taken along line IIB-IIB in FIG. 1A;

FIG. 3 is a graph showing a relationship between a relative humidity and capacitances in the sensor;

FIG. 4A is a plan view showing a modified electrodes pattern, and FIG. 4B is a plan view showing another modified electrodes pattern;

FIG. 5 is a cross-sectional view showing a modified capacitor in the sensor;

FIG. 6 is a schematic plan view showing a capacitive humidity sensor according to a second embodiment;

FIG. 7A is a schematic plan view showing a capacitive humidity sensor according to a third embodiment, and FIG. 7B is a cross-sectional view taken along line VIIB-VIIB in FIG. 7A; and

FIG. 8A is a plan view showing a conventional capacitive humidity sensor, and FIG. 8B is a graph showing a relationship between a relative humidity and capacitances in the conventional sensor.

Claims

1. A capacitive humidity sensor comprising: a detecting portion including a first sensor element having a first moisture-sensing film, wherein a relative permittivity of the first moisture-sensing film varies in accordance with humidity such that a first capacitance of the first sensor element varies in accordance with the humidity; anda reference portion including a second sensor element having a second moisture-sensing film, wherein the second sensor element is connected to the first sensor element in series, and a relative permittivity of the second moisture-sensing film varies in accordance with the humidity such that a second capacitance of the second sensor element varies in accordance with the humidity, anda capacitor connected to the second sensor element in parallel, wherein a third capacitance of the capacitor is constant relative to a humidity variation, whereinthe first sensor element has a first gradient of a first capacitance variation to the humidity variation, which is different from a second gradient of a second capacitance variation to the humidity variation in the second sensor element.

2. The capacitive humidity sensor according to claim 1, further comprising: a substrate, on which the first sensor element includes a first pair of electrodes facing each other through a first clearance, and on which the second sensor element includes a second pair of electrodes facing each other through a second clearance, whereinthe first moisture-sensing film on the substrate covers the first pair of electrodes and the first clearance, and the second moisture-sensing film on the substrate covers the second pair of electrodes and the second clearance.

3. The capacitive humidity sensor according to claim 2, wherein: each of the first pair of electrodes has a shape of comb-teeth engaging with each other; andeach of the second pair of electrodes has a shape of comb-teeth engaging with each other.

4. The capacitive humidity sensor according to claim 2, wherein: each of the first pair of electrodes has a plurality of comb-teeth, anda number of the comb-teeth of each of the first pair of electrodes is different from a number of comb-teeth of each of the second pair of electrodes.

5. The capacitive humidity sensor according to claim 4, wherein: the first and second moisture-sensing films are made of a same material.

6. The capacitive humidity sensor according to claim 2, wherein: the first clearance of the first pair of electrodes in the first sensor element is different from the second clearance of the second pair of electrodes in the second sensor element.

7. The capacitive humidity sensor according to claim 6, wherein: the first and second moisture-sensing films are made of a same material.

8. The capacitive humidity sensor according to claim 2, wherein: the first pair of electrodes have a first facing length in an electrode longitudinal direction, which is different from a second facing length of the second pair of electrodes.

9. The capacitive humidity sensor according to claim 8, wherein: the first and second moisture-sensing films are made of a same material.

10. The capacitive humidity sensor according to claim 2, wherein: the first and second moisture-sensing films are made of different materials.

11. The capacitive humidity sensor according to claim 10, wherein: the first pair of electrodes and the second pair of electrodes have approximately a same shape.

12. The capacitive humidity sensor according to claim 1, further comprising: a substrate, whereinthe first sensor element includes a first pair of electrodes facing each other in a thickness direction of the substrate, and the first moisture-sensing film is disposed between the first pair of electrodes, andthe second sensor element includes a second pair of electrodes facing each other in the thickness direction of the substrate, and the second moisture-sensing film is disposed between the second pair of electrodes.

13. The capacitive humidity sensor according to claim 12, wherein: the first pair of electrodes have a first facing area therebetween, which is different from a second facing area between the second pair of electrodes.

14. The capacitive humidity sensor according to claim 13, wherein: the first and second moisture-sensing films are made of a same material.

15. The capacitive humidity sensor according to claim 12, wherein: the first and second moisture-sensing films are made of different materials.

16. The capacitive humidity sensor according to claim 15, wherein: the first pair of electrodes have a first facing area therebetween, which is approximately equal to a second facing area between the second pair of electrodes.

17. The capacitive humidity sensor according to claim 1, further comprising: a substrate, on which the capacitor is disposed as an electrical component.

18. The capacitive humidity sensor according to claim 1, further comprising: a substrate, on which the capacitor is disposed, andthe capacitor is disposed under at least one of the first sensor element and the second sensor element.

19. The capacitive humidity sensor according to claim 1, further comprising: a substrate; anda circuit for processing a signal output from the detecting portion and the reference portion, whereinthe circuit is disposed on the substrate.

20. The capacitive humidity sensor according to claim 5, the first clearance of the first pair of electrodes is different from the second clearance of the second pair of electrodes; andthe first pair of electrodes have a first facing area therebetween, which is approximately equal to a second facing area between the second pair of electrodes.