JPS60171443A - Capacity type thin film humidity sensor and its preparation - Google Patents

Abstract

PURPOSE:To make it possible to selectively control humidity-sensitive characteristics, by providing a humidity sensor, which is formed by layering a lower electrode, a thin film comprising a metal compound active to humidity and an upper electrode, on a non-conductive substrate of which the surface is roughened in a specific range. CONSTITUTION:The surface of a non-conductive substrate 10 such as a glass substrate is manually ground for about 5-10min by an abrasive such as alumina particles to form a roughened surface 13 having a roughness degree of about 0.7-1.3mum in a particle dimension and a pair of lower electrodes 12, 12, which are not contacted but meshed to each other, are formed to the surface of the substrate 10 in a comb shape. In the next step, an evaporation source 26 is heated in a vacuum chamber 20 to form an aluminum ion and a metal compound membrance 14 comprising an alumina film is formed onto the substrate 10 and the lower electrodes 12 under the reaction with a gaseous mixture and, thereafter, a humidity pervious metal upper electrode 18 such as a gold film is vapor deposited on the membrane 14. By this method, sensitivity can be enhanced in a range good in linearity.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to an acoustic thin-film humidity sensor, and more specifically, to a sensor in which a non-quadramid substrate, a lower electrode, a metal compound thin film, and an upper electrode are sequentially laminated. The present invention relates to a capacitive thin film humidity sensor and a manufacturing method thereof.

[Prior art and its problems]

With the recent development of electronics, various types of sensors are being actively developed. From the viewpoint of humidity control, it is being expanded not only to the industrial field but also to the medical field, home appliances, housing, and buildings.

Broadly speaking, they are classified into electrolyte-based, organic-based, and metal oxide-based based on the materials used, and many utilize the electrical changes caused by humidity in each material. Some electrolyte systems use lithium chloride, while organic systems utilize the hygroscopic properties of polymeric materials. Although metal oxide-based materials are considered to be physically and chemically relatively stable compared to the above-mentioned materials, they all have advantages and disadvantages, and there are many problems that must be solved.

In general, an electric hygrometer is understood as a type of transducer that displays changes in electrical characteristics due to changes in humidity conditions as relative humidity.The basic principle is that it uses changes in electrical resistance and changes in capacitance. There are two main types: Among these, the latter type of humidity sensor, which measures humidity by measuring changes in capacitance when the moisture sensing part absorbs moisture, traditionally uses specially processed ceramic plates, glass fibers, and thin alumite plates. Although these materials are used as dielectric materials, it is said that there are problems in practical use due to poor measurement sensitivity. In addition, humidity sensors that use an organic polymer film as a dielectric material that functions as a humidity sensing part have been proposed in recent years. and US Patent No. 33!0911/.

By the way, in general, when a dielectric material made of an organic polymer film is used as a moisture-sensitive layer, this dielectric material has excellent responsiveness to humidity, good repeatability, and the relative relationship between humidity and container lid. It has advantages such as improved measurement accuracy because it appears extremely sharply. However, on the other hand,
If the organic polymer film dielectric is left under excessively dry conditions or high humidity conditions for a long time, it may peel off from the substrate, etc.
There is a disadvantage that the moisture sensitivity characteristics deteriorate.

In addition, since organic polymer films are easily attacked by organic solvents (e.g. acetone), they are adversely affected in environments where organic solvent vapor is present in many needles, such as in printing factories and paint factories. Difficulties are pointed out, such as the lack of

Therefore, there is a strong demand in the industry for practical use of a container-type humidity sensor with excellent mechanical strength that can be used suitably even under adverse environments such as high temperature conditions and organic solvent atmospheres. To meet this kind of demand, for example, Japanese Patent Application Publication No. 2003-120011, 2-/,
No. 211-7 “Metal oxide film moisture-sensitive device” and JP-A-1987-
No. 9595 [Moisture content detection element 1 using an anodic oxide film of aluminum is proposed. In both of these methods, a conductive porous metal oxide film is formed on the substrate itself, such as an aluminum plate, by electrolysis or other means, but measurement errors tend to occur because the element surface is rough, and the metal oxide film itself However, the mechanical strength was not sufficient, and the above-mentioned requirements were still not met.

Therefore, as a result of various research and trial production in order to solve the above-mentioned drawbacks, the applicant has decided to use a metal compound on an insulating substrate that is not compatible with oxidation, such as glass, instead of forming a film on the substrate itself by oxidation or electrolysis. If a film of metal oxide, metal nitride, metal fluoride, etc. (for example, metal oxide, metal nitride, metal fluoride) is formed by ion blasting by introducing vapor of the corresponding metal and oxygen, nitrogen, ammonia gas, or fluorine gas into a high-frequency electric field, The resulting metal compound film has extremely high strength and can be made into a thin film, so it can withstand use in the harsh environments mentioned above.Moreover, the film surface is smooth and dense, so it has excellent responsiveness and repeatability. It was discovered that the measurement accuracy was also improved, and the patent application was made! , filed as f-/7tJ'0g <
*See Kaisho jt7-10 3/ri issue).

Furthermore, the applicant has found that a suitable method is to perform ion blating by sputtering in a high frequency electric field while introducing a mixed gas of oxygen and argon, ammonia gas, or a mixed gas of nitrogen and hydrogen under high vacuum. Moreover,
We discovered that if the surface of a metal compound film is roughened by mechanical processing, such as plasma etching, its responsiveness can be significantly improved. Special request for a capacitive humidity sensor and its manufacturing method that can provide extremely good response and accurate humidity measurement sound without exhibiting performance deterioration! rt-/
No. '14t2/ (the disclosure of which is hereby cited for reference).

Special request for the above! According to the manufacturing method of the invention of 6-/Hat11.2/+J, ion blating is preferably used in a high frequency electric field as a method for forming a metal compound film on a substrate, and the obtained metal compound film is The surface is roughened by plasma etching using the same equipment. Therefore, the method for manufacturing a humidity sensor according to the present invention is to support a non-2#, electrically conductive substrate on a high voltage electrode in a vacuum forming chamber, apply a high voltage, and bring the impurity gas in the vacuum forming chamber to a high vacuum. After removing the metal plate or metal compound placed in the vacuum forming chamber by introducing a predetermined gas from the outside and forming a high frequency electric field in the vacuum forming chamber, the metal plate or metal compound placed in the vacuum forming chamber is evaporated with an electron gun or sputtered to form metal ions or Metal compound ions are generated, the metal ions are converted into metal compound ions by the introduced gas, and a metal compound film is independently formed on the non-conductive substrate and the electrode, and then the application of the high voltage is increased to The metal compound film is roughened by plasma etching, and a moisture permeable metal film is formed on the rough surface.

Thereafter, the present applicant further discovered that, in manufacturing a capacitive thin film humidity sensor using the above-mentioned ion-blating method, if this ion-blating is performed in the coexistence of argon and oxygen at a specific ratio, the humidity-sensing characteristics of the humidity sensor can be improved. Patent application Sho 3g-4t, 2
No. 307 (the disclosure of which is incorporated herein by reference).

Although the capacitive thin film humidity sensor has been improved to a considerable level through the various improvements described above, there are still some points left to be improved. For example, improvements are required to arbitrarily control the moisture sensitivity characteristics in accordance with a specific humidity range, and to further improve the sensitivity and obtain good linearity in that humidity range.

Therefore, the present inventor developed a technique that can be commonly applied to the various humidity sensors mentioned above in this field, by roughening the surface of the non-conductive substrate to a predetermined roughness using an abrasive material before installing the lower electrode. We developed a technology to arbitrarily control the humidity sensitivity characteristics according to a specific humidity range, and succeeded in achieving even better sensitivity in a range with good linearity.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a non-conductive substrate, a lower electrode disposed opposite to each other on the substrate, a moisture-active metal compound thin film independently formed on the lower electrode, and a metal compound thin film. An upper electrode made of a moisture-permeable metal film formed on top of the film is successively laminated, allowing the moisture sensitivity characteristics to be controlled arbitrarily to suit a specific humidity range, and further increasing the sensitivity in a range with good linearity. It is an object of the present invention to provide a capacitive thin film humidity sensor and a method for manufacturing the same that can be improved.

[Key points of the invention]

According to the present invention, the above object is achieved by roughening the surface of the non-conductive substrate in the capacitive thin film humidity sensor having the above structure.

The degree of roughness of the substrate surface is measured with a frost roughness meter and is
S ~ /, 6 μm range, preferably 0.7 ~ /, 3 μm
is within the range of Ota. Preferably, the non-conductive substrate is made of alumina, glass or sapphire, and the thin metal compound film is made of metal oxides, nitrides and fluorides, especially alumina, sapphire, magnesium fluoride or chromium fluoride. In particular, it is preferable to use a metal fluoride because it shows little change over time.

In another aspect of the present invention, there is provided a method for manufacturing a thin film humidity sensor having the above structure, which method comprises roughening the surface of a non-conductive substrate by polishing it with abrasive particles before disposing the lower electrode. It is characterized by

As the abrasive particles, the particle size is f1000 to -3000.
．． Preferably, alumina particles, iron oxide particles, or diamond powder of firθ0 to 2jOθ can be used, and polishing of this pole is well known in the art of polishing glass such as lenses. If polishing is carried out manually for 5 to 70 minutes using a conventional method, the degree of surface roughening specified above can be obtained.

In the method of the present invention, the metal compound thin film can be deposited using any method known in the art, such as ion blasting, vacuum evaporation or sputtering, with ion blasting being particularly preferred.

The container-type thin film humidity sensor and its manufacturing method according to the present invention are disclosed in 5 conventional humidity sensors of this type and Japanese Patent Application No. 716011 filed by the present applicant. P4#2
It goes without saying that the present invention can also be applied to No. 1, TL-112307, and the same effect as the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail by way of embodiments with reference to the accompanying drawings.

[Embodiments of the invention]

1 and 2 show an embodiment of a capacitive humidity sensor according to the present invention, with reference numeral IO being approximately /
X/,,! The figure shows a glass substrate cut into dimensions of r The lower electrodes are formed to have a thickness of about 7 μm by means of vapor deposition, photoetching, etc., facing each other. The lower electrode is preferably made of chemically inert gold or palladium.The substrate 10 on which the lower electrode/2.
Then, as described below, an ion blating method using a high-frequency power source was carried out to form a moisture-active metal compound film lp(
For example, a film of metal oxide, nitride, fluoride, especially alumina, chromium fluoride) is formed independently on the substrate to a thickness of about .lambda..mu.. Furthermore, a moisture-permeable and chemically stable metal, such as a total film or a palladium film, is applied on the surface of the obtained metal compound film/hiro to a thickness of 2OO~2! O
The upper electrode is formed by vapor deposition on A.

As a result, a humidity sensor with extremely excellent mechanical strength and extremely good responsiveness can be obtained.

Next, roughening of the surface of the substrate 10, which is a feature of the present invention, will be explained. As described above, the non-conductive substrate 10 may be made of glass, aluminum, alumina, etc., and the surface of the substrate 10 is roughened by polishing with abrasive particles. As the abrasive particles, particles having a particle size of 1000 to 1000 are used, which are well-known in the technique of polishing glass such as lenses.
Alumina particles, iron oxide particles or diamond powder of 300 θ, preferably 600 to 600 θ are used, and it is preferable to use alumina particles for glass substrates and diamond powder for sapphire substrates. .

Polishing is carried out by polishing the surface of the substrate with the above abrasive material using a conventional method.
This can be done by manually polishing for 0 minutes. This results in
As shown in Figure 3, a sampling test chart of a white edge polished entire surface measured with a frost roughness meter (measured by Matsunami Glass Industries Co., Ltd., Kishiwada City, Osaka Prefecture), the degree of roughness of the substrate surface is ( 1), j-7,6μm5 preferably 0.7
A substrate of ˜7.3 μm is obtained. An SEM image of the substrate surface roughened in this manner is shown in the attached reference photograph. In the present invention, #ZOOO-f300 in the SEM image
A degree of roughening with a particle size of 0 (Japanese standard sieve size) is suitable.

On the surface of the substrate thus roughened (/J), a comb-shaped lower electrode 1 was then placed as shown in FIGS.
2. /λ are placed opposite each other.

Next, a metal compound film is formed on the substrate IO whose surface has been roughened (/3) and on which the lower electrode /2°/2 has been formed. This process is preferably carried out by an ion blating method using the technique disclosed in No. 2307, and this method will be explained below, but this step may be carried out by any method known in the art such as vacuum evaporation or sputtering. should be understood.

Further, an example using alumina as the metal compound will be explained, but in addition to alumina, metal oxides or fluorides such as sapphire, magnesium fluoride, chromium fluoride, etc., or fluorides can also be used, and in particular, metal fluorides can be used. It has also been found that it is particularly suitable when used because it shows little change over time.

Figure 5 shows an example of an apparatus for applying the method of forming a metal compound film/≠.

That is, a substrate holding electrode 2.2, an ionization electrode, 2≠, and an evaporation source 26 for evaporating a metal or a metal compound (particularly aluminum) are provided in a vacuum forming chamber (Pelger) that can be hermetically isolated from the outside world, in 2θ. It is arranged like this. The substrate holding electrode 2-2 is connected to a DC power source 2g, and is configured to apply a DC voltage of, for example, -0, θj~/kV, and the ionization electrode 2≠ is connected to a high frequency power source 30, For example/3. ! l Ml-1
A high frequency force of between 200 and 200 t is applied. The evaporation source 2t is preferably of a type in which the substance to be evaporated (aluminum) is directly bombarded with an electron beam to heat it, and is connected to a power source 32 for heating the electron beam. In this case, the evaporation source 2t is surrounded by a shield 36 having an opening 3μ at the top. Furthermore, the empty forming chamber 20 has an exhaust port 3 for maintaining the inside in a vacuum state.
are appropriately provided and connected to a predetermined exhaust system. Similarly, a gas introduction pipe Goo is connected to the vacuum forming tube -0 via the leak pulp≠θ.

During operation, the substrate /θ on which the lower electrode 2, 7.2 (see Figure 1) is formed is fixed horizontally on the lower surface of the substrate holding electrode 2.2, and aluminum is attached to the evaporation source 27. After that, the vacuum forming chamber-〇 is hermetically closed. Next, impurity gas in the vacuum forming chamber 2θ was removed under the action of the exhaust system, and when the degree of vacuum reached /O-5 to /0-6 Torr, the Terreckhalp 4tO was opened and the main gas was pumped from the specified gas source. A mixed gas of oxygen and argon in the ratio specified in the invention is introduced into the chamber 20, and the degree of vacuum is approximately J'x10 Torr.
Stabilize the substrate holding electrode 2.2 to -10~1o
Apply a DC voltage of oV. Furthermore, the ionization electrode 24
t / 3.1 t MHz, 200~♂o.

High frequency power of W is applied and the evaporation source 2t is heated to generate aluminum ions, and the aluminum ions are reacted with the mixed gas to the substrate 10 and the lower electrode/
, 2 to form an aluminum oxide (alumina) film. Then, by ion blating for 20 minutes at aO, the thickness of the aluminum compound film becomes / to λμ.

-No! - In this case, the film thickness can be controlled by adjusting the heating temperature of the evaporation source, the voltage applied to each electrode, etc.

After forming the so-called metal compound film /41- in this manner, by depositing, for example, a full film or a palladium film on the moisture-permeable metal upper electrode 7g1, approximately
200. ．． A film with a thickness of 2jOA is formed.

As mentioned above, the present invention differs from the prior art except for roughening the surface of the non-conductive substrate, in particular by Guzhao, fl-ILt, 23.
The technology disclosed in Specification No. 07 can be applied as is, and the latter technology is included here for reference.

The humidity characteristics of the humidity sensor produced as described above according to the present invention were measured using the humidity chamber shown in FIG.

Generally, humidity chambers using a constant temperature method, a constant pressure method, a split flow method, or a saturated salt aqueous solution are used. However, these humidity generation methods have problems such as assuming R, H, 2/00% and salt precipitation on the sensor surface. Therefore, to measure the humidity characteristics, we used a newly devised and prototype humidity chamber shown in Fig. 5.

However, this measuring device does not form part of the invention. This humidity chamber uses a stainless steel vacuum chamber.
It is designed to be able to exhaust air down to approximately 0 Torr. After evacuating the tank to about 1O-2 Torr, close the valve.
Distilled water is measured using a microsyringe and directly injected into the tank (~7). /μl of water is about 0.
It corresponds to the relative humidity (R, H) of the air, and by changing the amount of water injected, the desired R, H can be obtained in about seconds.

Temperature changes within the premises due to water evaporation cannot be detected by measurements using a thermistor thermometer.

Changes in the set humidity due to moisture absorption and desorption on the inner wall of the humidity chamber are caused by high humidity (
In the low humidity setting after ≠g time had passed, an error of the maximum R, H, J% occurred. However, within 2 hours after setting, no change in the set humidity was observed in any case.

Inside the humidity chamber are a calibrated humidity sensor, a sensor to be measured,
A crystal resonator film thickness gauge is attached.

An alumina thin film with the same thickness as the humidity sensor is attached to the surface of the crystal resonator, and the mass (m H2O) of water molecules incorporated into the thin film can be measured. Here m H
, 0 is converted to the average film thickness (d H2o ), and the minimum detection sensitivity is 2OA.

In the humidity chamber shown in Fig. 5, the reference symbol SO is the vacuum level, j, 2 is the micro weight, j4t is the sensor (i positive), etc.
tx is a sensor, j is a rubber sheet, to is a microsyringe, t2 is a stainless steel container, t≠ is a thermometer, JA is a zeolite composition, 2 is a valve body, 7θ is a reduced pressure source 17- is dry nitrogen .

FIG. 2 shows the humidity sensitivity characteristics of a capacitive thin film humidity sensor according to the present invention using the above humidity chamber and having a roughened substrate surface.

Figure 5 shows a humidity sensor fabricated using abrasive particles with particle sizes too, #-〇oo and fP300θ, and a humidity sensor fabricated in the same manner using a non-roughened (i.e. flat) substrate. The C% properties are shown respectively.

As can be seen from Figure 2, it should be noted that roughening with an abrasive having a particle size of 3000 is particularly suitable in terms of moisture sensitivity and linearity.

〔Effect of the invention〕

According to the present invention, in a capacitive thin film humidity sensor formed by sequentially laminating a non-conductive substrate, a lower electrode, a metal compound thin film, and an upper electrode, by roughening the surface of the non-conductive substrate, a specific A humidity sensor can be obtained in which the humidity sensitivity characteristics can be arbitrarily controlled according to the humidity range, and the sensitivity can be further improved in a range with good linearity.

[Brief explanation of drawings]

FIG. 1 is a plan view of a capacitive thin film humidity sensor according to the present invention;
FIG. 1 is a sectional view taken along line 1-1 of the humidity sensor shown in FIG. A schematic configuration diagram showing an example of an apparatus for carrying out the manufacturing method, FIG. 5 is a schematic diagram of a humidity tank for measuring humidity characteristics, and FIG. 6 shows the humidity sensitivity characteristics of the capacitive thin film humidity sensor according to the present invention. It is a characteristic curve diagram. 10...Substrate /, 2... Lower electrode /3... Roughening of the substrate surface /4',... Metal compound film/2...
Surface/do...upper electrode, 20...vacuum forming chamber
22...Substrate holding electrode, 22...Ionization electrode,
26... Evaporation source-g... DC power supply 30... High frequency power supply 3.2... Heating power supply 3≠... Opening 3z.
...Shield 3g...Exhaust port <10...Leak pulp 4'2...Gas inlet pipe 0...Vacuum level j
, 2... Micro weight, t4Z jJ... Sensor 3
g...Rubber sheet to...Micro syringe t, 2
...Stainless steel container...Thermometer AJ...
Zeolite t♂... Valve body 70... Decompression source 72... Dry nitrogen -, 23- FIG, 5 FIG, 6 0 kg00 x sweet 2000 A: It'] α loss C (PF), 81

Claims (1)

[Scope of Claims] (1) A non-conductive substrate, a lower electrode disposed opposite to each other on this substrate, a moisture-active metal compound thin film independently formed on this lower part 11t&, and this metal A capacitive thin film humidity sensor comprising a compound thin film and an upper electrode made of a moisture permeable metal film successively laminated, the capacitive thin film humidity sensor being characterized in that the surface of the non-conductive substrate is roughened. type thin film humidity sensor. (2) The humidity sensor according to claim 1, wherein the degree of roughening of the substrate surface is in the range of 0.2r-/.6 μm as measured by a frost roughness meter. (3) The humidity sensor according to claim 2, wherein the degree of roughening of the substrate surface is in the range of 0.7 to 7.3 μm as measured by a frost roughness meter. (4) The substrate is selected from the group consisting of alumina, glass, and sapphire, and the metal compound thin film is a metal oxide,
The humidity sensor according to claim 1, wherein the humidity sensor is selected from the group consisting of nitrides and fluorides. (5) The humidity sensor according to claim 1I, wherein the metal compound is alumina, sapphire, magnesium fluoride, or chromium fluoride. (6) Lower electrodes are arranged facing each other on a non-conductive substrate, a moisture-active metal compound thin film is independently formed on the lower electrode, and a moisture-permeable metal film is formed on the metal compound thin film. A method for manufacturing a capacitive thin film humidity sensor forming an upper electrode, wherein the surface of a non-conductive substrate is roughened by polishing with abrasive particles before disposing the lower electrode. Production method. (7) Particle size 41000 to #30 as abrasive particles
00 alumina particles, iron oxide particles, or diamond powder. (8) The particle size of the abrasive particles is 4f/600 to fj2!
8. The method according to claim 7, wherein the method is: 00. (9) A method according to claim 1, in which a metal compound thin film is deposited on the lower electrode by an ion blasting method or a vapor deposition method. (IOl Measure the surface of the substrate with a frost roughness meter.
3. The method according to claim 2, wherein the surface is polished with an ox to achieve a surface roughness of s-i, s μm. α1) The method according to claim io, in which polishing is performed until the degree of surface roughening is 0.7 to 7.3 μm. (12) The method according to claim 6, wherein the substrate is selected from the group consisting of alumina, glass and sapphire, and the metal compound thin film is selected from the group consisting of gold oxides, nitrides and fluorides. Claim 7.) The metal compound is alumina, sapphire, magnesium fluoride or chromium fluoride.
The method described in Section 2.