JPH0464162B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a humidity sensing element that uses a humidity sensitive substance whose electrical resistance changes depending on humidity. [Prior Art and Disadvantages] Conventionally, moisture-sensitive elements using lithium chloride as a moisture-sensitive substance have been widely used, but in recent years, moisture-sensitive elements using metal oxides have been developed. This metal oxide-based humidity sensing element is superior to the lithium chloride-based humidity sensing element in terms of changes in characteristics over time and the size of the relative humidity range to which it can be applied. However, during humidity cycling, a stable metal hydroxide layer is formed on the surface of the humidity-sensitive resistor layer, resulting in a decrease in sensitivity, so it is necessary to perform periodic heating cleaning. Therefore, as a countermeasure, indirect heating type heaters are attached to such metal oxide-based moisture sensing elements, but this complicates the structure and poses a big problem in terms of mass production and manufacturing cost. is left behind. In addition, the adhesion between the substrate and the humidity-sensitive resistor layer may deteriorate during temperature and humidity cycles.
Cracks may occur in the moisture-sensitive resistor layer.
Many people have experienced this problem, and it is desired to improve the characteristics in this aspect. On the other hand, non-heated ceramic humidity sensors adsorb organic gases in the atmosphere and tend to change over time, so it is desired to improve the stability of the moisture-sensitive membrane surface. [Objective of the Invention] The present invention improves the above-mentioned drawbacks and has high sensitivity over a wide range of relative humidity and stable moisture sensing performance over a long period of time, as well as a good adhesive layer between the insulating substrate and the wet/dry resistor layer. An object of the present invention is to provide a moisture-sensitive element that does not require special cleaning means. In addition, in order to lower the resistance value for each relative humidity in the moisture sensitivity characteristics, spinel type and berovskite type oxides are added to control the resistance value, and in order to further improve stability, a second additive is added. The object of the present invention is to provide an element having moisture-sensitive characteristics, which is low in resistance, easy to mass produce, can be manufactured at a low price, and is easy to use. [Structure and Effects of the Invention] The element of the present invention is a humidity sensing element in which a pair of electrodes and a humidity sensing resistor layer extending between these two electrodes are formed on an insulating substrate such as ceramic. Composite oxides containing Li such as LiNbO ₃ , LiTaO ₃ ,
At least one kind of oxide powder selected from Li ₂ TiO ₃ , Li ₂ ZrO ₃ , Li ₂ MoO ₄ , Li ₂ WO ₄ and Al, Ba,
Pre-sintered fine powder of a composition in which vanadate compound powder is added to at least one kind of oxide powder selected from metal oxides consisting of the elements Bi, Ca, Pb, Cu, Fe, Mn, Sr, and Zn; In spinel type composite oxide (MeM ₂ O ₄ ) and berovskite type composite oxide (MeMO ₃ ), Me is Ni, Mn, Co, Fe,
The present invention is characterized in that it is a sintered body of a composition containing as additives at least one kind of oxide powder consisting of at least one kind of oxide powder and at least one kind of powder chosen from trivalent metal oxides. In the above composition, LiNbO ₃ , LiTaO ₃ , Li ₂ ZrO ₃ , Li ₂ TiO ₃ ,
At least one compound powder selected from Li ₂ MoO ₄ and Li ₂ WO ₄ is added as a Li ion source in the moisture sensitive membrane. In that case, if the blending ratio is 20 mol percent or less, the resistance value of the element increases significantly, and if the blending ratio is 70 mol percent or more, the effect of the addition is saturated. Oxides of the above elements are used as the metal oxide, but MnO, SrO, and PbO, which react with the Li ion source to lower the melting point of the ceramic, are preferable from the viewpoint of sinterability. In the case of PbO powder, if the blending ratio is less than 20 mol percent, the adhesive strength of the moisture-sensitive resistor layer to the insulating substrate will decrease, and if it is more than 70 mol percent, the purpose of addition as a compound powder as the ion source will be reduced. is inhibited. Furthermore, vanadine oxide was added for the purpose of sintering accelerator and surface stabilization,
V ₂ O ₅ , V ₂ O ₃ , VO ₂ , VN, VC, FeVO ₄ ,
MnV ₂ O ₆ or the like can be used, and in that case, it is desirable to select an appropriate amount within the range of 1 to 20 mol percent as an effective amount that does not inhibit the purpose of adding the two types of oxide powders mentioned above. In the spinel-type composite oxide (MeM ₂ O ₄ ) and berovskite-type composite oxide (MeMO ₃ ) to be added next, the oxide powder in which Me is Ni, Mn, Co, or Fe has a high resistance value for moisture-sensitive characteristics. When Li ions are dissolved in solid solution in these oxides, they form a ceramic semiconductor, increase the electron conduction component, and increase the blending ratio (20 to 80 mole percent). Therefore, a moisture sensitive film having a desired resistance value can be obtained. Furthermore, trivalent metal oxides Fe ₂ O ₃ , Cr ₂ O ₃ ,
Al ₂ O ₃ , Ga ₂ O ₃ , Sb ₂ O ₃ , In ₂ O ₃ , La ₂ O ₃ , Bi ₂ O ₃
By adding (3 to 40 mole percent), high-resistance particles are interposed in the moisture-sensitive film to improve the curvature and stability of the moisture-sensitive characteristics. Next, in order to form a moisture-sensitive resistor layer, a vehicle such as a vehicle consisting of ethyl cellulose, acrylic resin, butyl carbitol acetate, terpineol, etc. is added to the above mixed powder.
The composition may be baked into a paste-like composition having an appropriate viscosity by sufficiently mixing with a roller or ball mill or the like. The humidity sensing element according to the present invention has high sensitivity over a wide range of relative humidity, exhibits extremely stable characteristics especially when left in a high humidity atmosphere, and has little change over time due to organic gas adsorption. , almost no cleaning is required, so there is no need to provide extra cleaning means such as an indirect heater as in the past, and furthermore, this element can be produced by thick film technology. Therefore, it is suitable for mass production and cost reduction, and has the advantage of high industrial utility value. [Description of Examples] Next, the specific structure of the moisture sensitive element of the present invention will be described with reference to the drawings. FIG. 1 shows an example of the moisture-sensitive element of the present invention. In the figure, 11 is an insulating substrate made of ceramic or the like, and 12 and 13 are a pair of comb-shaped electrodes facing each other. , lead-out portions 12b and 1 in these electrodes 12 and 13, respectively.
A moisture-sensitive resistor layer 14 made of the sintered body described above is coated over the main parts 12a and 13a except for 3b. 15 and 16 are electrode 13 and electrode 1
3 to the respective external leads 17 and 18. Figure 2 shows 2- in Figure 1.
2' is shown. Such a moisture sensitive element is manufactured, for example, by the following method. First, using an insulating substrate 11 on which electrodes 15 and 16 have been provided in advance, comb-shaped electrodes 12 and 13 are formed on the surface thereof by screen printing, and the electrodes are fired at about 850 to 950°C in a firing furnace. Next, using the paste-like composition described above, screen printing is performed to a uniform thickness so as to completely cover the main parts 12a and 13b of the electrodes 12 and 13 to form a coating layer, and then the insulating substrate is coated. In order to increase the adhesion between the moisture-sensitive resistor layer 11 and the humidity-sensitive resistor layer 14, it is fired in a firing furnace at an appropriate temperature of, for example, 900 to 1200°C. During the cooling process of the firing furnace, the moisture-sensitive resistor layer 14 hardens and becomes a film that has good adhesion to the insulating substrate 11 and has an appropriate pore distribution. After this cooling, external leads 17 and 18 are attached, and then load aging is performed under high temperature and high humidity to stabilize the characteristics. In addition, in the structure of FIG. 1 and FIG. 2 mentioned above, the structure in which the humidity sensitive resistor layer 14 was formed in the state which covered the pair of electrodes 12 and 13 was demonstrated, but the humidity sensitive element of this invention This also includes a pair of electrodes formed on the humidity-sensitive resistor layer by reversing the formation order of the two, and a counter electrode in which the humidity-sensitive resistor layer is formed into a sandwich-like structure with electrodes. Next, the procedure for manufacturing the moisture sensitive element of the present invention will be explained. Li is mixed into a composite oxide at the compounding ratio shown in Table 1 below.
A vanadate compound V ₂ O ₅ was added as an additive to a type of fine powder of LiNbO ₃ and LiTaO ₃ and a fine powder of metal oxide PbO, and after mixing and pulverizing in a mortar,
Preliminary firing was performed at 1200° C. and humidity in the air for 3 to 5 hours. The above calcined product was finely pulverized to produce spinel-type composite oxides such as NiCr ₂ O ₄ , FeCr ₂ O ₄ , CoCr ₂ O ₄ ,
At least one kind of oxide powder selected from MnCr ₂ O ₄ and trivalent metal oxides Fe ₂ O ₃ , Cr ₂ O ₃ ,
At least one oxide powder selected from Bi ₂ O ₃ and Al ₂ O ₃ is mixed in a ball mill, a vehicle consisting of ethyl cellulose, butyl carbitol acetate, and terpineol is added, and a paste of uniform viscosity is made in an agate mortar. It was made into a composition. next,
In the configuration of this composition shown in FIGS. 1 and 2, electrodes 12 and 13 are RuO electrodes, electrode 1
5 and 16 are Ag-Pd electrodes on an alumina insulating substrate with a film thickness of 50 to 100 μm, and after heating in air at about 350°C to volatilize and remove vehicle components, 950 μm was applied. Sinter at °C.
After cooling, aging was performed by energizing at 60°C and 90% RH, and a moisture-sensitive element was obtained according to the conventional method. Table 2 below shows the values of the electrical resistance between the electrodes of the humidity sensing element obtained in the above example, measured at 25° C. while changing the relative humidity of the measurement atmosphere. FIG. 3 shows the relationship between relative humidity and resistance value for Sample 3 shown in Table 2 as a diagram. The solid line shows the initial characteristics, and the broken line shows the characteristics after the atmospheric test. In addition, in FIG. 3, for comparison, the characteristics of a conventional metal oxide moisture sensing element are also shown with a dashed line. As is clear from FIG. 3, the device of the above example has a lower resistance value and linearity (stability) than the conventional device over a wide range of relative humidity.
It exhibits excellent properties, especially when left in a high humidity atmosphere. Furthermore, as is clear from the above, this element can be easily produced using thick film technology.

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【table】 [Brief explanation of drawings]

Fig. 1 is a plan view showing an example of the humidity sensing element of the present invention, Fig. 2 is a sectional view taken along line 2-2' in Fig. 1, and Fig. 3 is a characteristic diagram showing the relationship between relative humidity and electrical resistance value. be. 11... Insulating substrate, 12, 13... A pair of opposing electrodes, 14... Moisture sensitive resistor layer.

Claims (1)

[Claims] 1. In a humidity sensing element in which a pair of electrodes and a humidity sensing resistor layer extending between these two electrodes are formed on an insulating substrate such as ceramic, the humidity sensing resistor layer is a composite oxide containing LiLbO ₃ , LiTaO ₃ Li ₂ TiO ₃ ,
At least one kind of oxide powder selected from Li ₂ ZrO ₃ , Li ₂ MoO ₄ , Li ₂ WO ₄ and Al, Ba, Bi, Ca,
A pre-calcined fine powder of a composition in which vanadate compound powder is added to at least one kind of oxide powder selected from metal oxides consisting of the elements Pb, Cu, Fe, Mn, Sr, and Zn, and a spinel-type composite oxide. (MeM ₂ O ₄ ) and berovskite-type composite oxide (MeMO ₃ ), Me is Ni, Mn, Co, Fe,
1. A moisture-sensitive element comprising a sintered body of a composition containing as additives at least one kind of oxide powder consisting of at least one kind of oxide powder and at least one kind of powder chosen from trivalent metal oxides.