JP3047137B2 - Manufacturing method of humidity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor, and more particularly to a method for forming a moisture permeable electrode of a polymer capacitance type humidity sensor.

[0002]

2. Description of the Related Art In general, for detecting humidity, a humidity sensor for detecting a change in electric resistance or capacitance due to adsorption of water molecules on a moisture-sensitive film made of a polymer film or ceramic is used.

As an example of a conventional humidity sensor, for example, as shown in a manufacturing process in FIG. 4, a lower electrode 102 made of a platinum thin film is formed on a quartz substrate 101 having high thermal insulation.
And a moisture sensitive film 103 made of a polyimide film and an upper electrode 104 made of gold are sequentially laminated, and a capacitance change due to humidity of the moisture sensitive film 103 sandwiched between the lower electrode 102 and the upper electrode 104 is measured. There is something.

This is conventionally formed as follows.

[0005] First, as shown in FIG.
01, a platinum thin film is deposited thereon by sputtering, and is patterned to form a lower electrode 10
2 is formed (FIG. 4B).

Next, as shown in FIG. 4C, a polyimide precursor 103p is applied by a spin coating method.

Thereafter, a heat treatment at 300 to 400 ° C. is performed to cause a condensation reaction on the polyimide precursor 103p, thereby forming a moisture-sensitive film 103 made of a polyimide thin film (FIG. 4 (d)).

Finally, as shown in FIG. 4E, an upper electrode 104 made of a gold thin film having a film thickness of 10 to 20 nm is formed as a moisture permeable electrode by a sputtering method.

In the humidity sensor thus formed, water molecules that have passed through the upper electrode 104 as a moisture-permeable electrode and reached the moisture-sensitive film are measured as a change in capacitance. Since it greatly contributes to the permeability of water molecules and the resistance value of the electrode itself, and greatly affects the sensor characteristics, it is necessary to control with high precision. That is, when the upper electrode is thicker from the viewpoint of moisture permeability, the moisture permeability decreases and the sensitivity is deteriorated. When the upper electrode is thinner, the resistance of the electrode itself increases, the power loss increases, and the sensitivity decreases.

As described above, in order to satisfy both the moisture permeability and the resistance, it is necessary to make the moisture permeable electrode thin and control the optimum value of the film thickness with extremely high precision so as not to increase the resistance value. However, when controlling the film thickness in such a thin region, the resistance value greatly changes with a slight variation, so that extremely high-precision film thickness control is required.
In reality, it could not be controlled.

[0011]

As described above, in the conventional method, when the upper electrode is thicker from the viewpoint of moisture permeability, if the thickness is higher, the moisture permeability is reduced and the sensitivity is poor. If the upper electrode is thinner, the resistance of the electrode itself is reduced. However, there is a problem that the power loss increases and the sensitivity decreases, and extremely high-precision film thickness control is required.On the other hand, control in a thin film thickness region is extremely difficult. There was a problem that the characteristics fluctuated greatly even with subtle changes.

The present invention has been made in view of the above circumstances, and has as its object to provide a humidity sensor with high measurement accuracy.

[0013]

Therefore, according to the present invention, after applying a precursor of a polymer film as a moisture-sensitive film, a metal film as an upper electrode is formed to a sufficient thickness prior to heat treatment for condensation. After that, heat treatment for precursor condensation is performed.

[0014]

According to the above construction, when the moisture generated by the condensation of the precursor of the polymer film comes out to the surface, the metal electrode becomes porous and becomes a moisture-permeable conductor film.

Accordingly, it is possible to obtain a humidity sensor which can greatly reduce the resistance of the electrode itself, has good moisture permeability, and has small variations in characteristics.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 (a) to 1 (e) are views showing the steps of manufacturing a humidity sensor according to an embodiment of the present invention. in this way,
Prior to heat treatment for causing a condensation reaction on the precursor of the polymer film as a moisture-sensitive film, a metal film as an upper electrode is formed to have a sufficient thickness, and then heat treatment for precursor condensation is performed. When the moisture generated by the condensation of the precursor of the polymer film comes to the surface, the metal electrode becomes porous and becomes a moisture-permeable conductor film, thereby reducing the resistance of the electrode itself and reducing the permeability. The present invention is characterized in that a humidity sensor having good wettability and small variation in characteristics is formed.

First, as shown in FIG.
Is prepared, and a platinum thin film is deposited thereon by a sputtering method, and is patterned to form a lower electrode 2 (FIG. 1B).

Next, as shown in FIG. 1C, a polyimide precursor 3p is applied by spin coating.

Up to this point, it is the same as the conventional method.

Thereafter, as shown in FIG. 1D, a film having a thickness of 30 to 1 is formed as a moisture-permeable electrode by vapor deposition or sputtering.
An upper electrode 4 made of a 00 nm gold thin film is formed.

Finally, a heat treatment at 300 to 400 ° C. is performed to cause a condensation reaction in the polyimide precursor 3p to form a moisture-sensitive film 3 made of a polyimide thin film. 4 is made porous (FIG. 1 (e)).

In the humidity sensor thus formed, the upper electrode can be made porous by water molecules generated by condensation, thereby increasing the moisture permeability and reducing the resistance of the electrode itself.

The operation of the humidity sensor thus obtained will be described with reference to the schematic diagram shown in FIG.

When a change in humidity occurs in the environment, the response time of the sensor is the time when water molecules diffuse into the moisture-sensitive film and the moisture-sensitive film reaches equilibrium.

Considering that the upper electrode does not exist,
This response time is determined by the thickness x (μm) of the moisture-sensitive film.

On the other hand, when a porous upper electrode is present, it is necessary to diffuse not only in the depth direction but also in the lateral direction, so that it depends on the relationship between the film thickness (x μm) and the average distance between holes (y μm). The factor that determines the response time t varies.

That is, i) In the case of x ≧ y / 2 t is limited by x.

Ii) In the case of x <y / 2 t is limited by y.

Therefore, if 2x ≧ y is satisfied, the hole interval y does not affect the response time.

For example, when x = 1 μm, it suffices that y ≦ 2 μm.

FIG. 3 shows an SEM photograph of the upper electrode surface.

From this photograph, it can be seen that the upper electrode is porous and the gap y between the holes satisfies y ≦ 2 μm.

The size or distribution of the pores can be controlled by controlling the film thickness condensation condition of the upper electrode.

Further, according to the above-mentioned method, it can be formed without increasing any man-hours, and it is not necessary to control the thickness of the upper electrode, so that the manufacturing becomes easy.

In the above embodiment, gold is used as the upper electrode. However, it is needless to say that the present invention is not limited to gold but can be applied to other metals such as platinum and chromium. In addition, the moisture-sensitive film and the lower electrode can be appropriately changed.

Further, in the above-described embodiment, a capacitance change type sensor is used as the humidity sensor, but the invention is also applicable to a resistance change type sensor.

In addition, in the above-described embodiment, the sandwich type sensor in which the moisture sensitive film is sandwiched between the lower electrode and the upper electrode has been described. However, the present invention is not limited to the sandwich type. Any sensor can be applied as long as it has a structure that forms

[0039]

As described above, according to the present invention, after applying a polymer film precursor as a moisture-sensitive film,
Prior to heat treatment for condensation, a metal film as an upper electrode is formed to have a sufficient thickness, and then heat treatment for precursor condensation is performed. The electrode becomes porous, becomes a moisture-permeable conductor film, and a humidity sensor having good moisture permeability and small variation in characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a humidity sensor according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of the humidity sensor.

FIG. 3 is a view showing an SEM photograph of a gold structure constituting an upper electrode.

FIG. 4 is a manufacturing process diagram of a conventional humidity sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower electrode 3 Moisture sensitive film 4 Upper electrode 101 Substrate 102 Lower electrode 103 Moisture sensitive film 104 Upper electrode

Claims (1)

(57) [Claims] 1. A precursor coating step of coating a precursor of a polymer film to be a moisture-sensitive film on a substrate surface; an electrode forming step of forming an electrode on an upper layer of the precursor; and a condensation reaction with the precursor. A heat treatment step of performing a heat treatment so as to cause the humidity.