JPS60152946A - Humidity sensor and preparation thereof - Google Patents

Abstract

PURPOSE:To enhance the sensitivity of a humidity sensor and to attain the miniaturization thereof, by using a sintered body obtained from a mixture comprising two or more of selected aluminum oxides in a detection part to provide the humidity sensor and detecting humidity on the basis of the change in electrostatic capacity corresponding to the humidity of the atmosphere. CONSTITUTION:Anmonium a lum is perfectely dissolved in distilled water and a mixture comprising two or more of aluminum hydroxide, aluminum chloride and aluminum sulfate is selected and precipitated by using an aqueous urea solution as a reagnet while the precipitate is dried and formed into a powder. This powder is pressed into a disc shape to form a gamma-alumina disc and, further, a sintered body of a compound during transfer to alpha-alumina is molded while both end surfaces 1a, 1b of the molded body are used as electrodes to respectively extend a pair of lead wires 2a, 2b and the detection part 1 of a humidity sensor S1 is formed. By this method, the change with the elapse of time can be reduced and sensitivity can be improved over an almost all humidity range.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a humidity sensor using semiconductor ceramics and a method of manufacturing the same, and more particularly to a humidity sensor made of a sintered body of alumina and a method of manufacturing the same.

Conventional technology Conventional humidity sensors are zn○, zn 02, Al20
3. Thermistor type, which mainly consists of Fe2O3 and Fe3O4, etc., was the mainstream, but this utilizes changes in resistance value due to humidity, and the sensitivity changes significantly over time in the high humidity range of 80 to 100%. It has the following drawbacks. Therefore, as a sensor that eliminates such drawbacks, 7-A (1203 series or Mn 2
03. Humidity sensors have been proposed in which a TiO2-based anodic oxide film or an oxide film formed by other methods is formed. In this case, humidity is detected by changes in the resistance or capacitance of the oxide film in response to changes in humidity, but the amount of change in these changes over the humidity range of 11 to 98% is about one to two orders of magnitude, and the sensitivity is insufficient. It is. Furthermore, these thin films have the drawbacks of large hysteresis and large changes in sensitivity over time.

Purpose The present invention has been made in view of the above points, and it is an object of the present invention to provide a humidity sensor that has sufficient sensitivity to atmospheric humidity over almost the entire humidity range and has a small change over time, and a method for manufacturing the same. shall be.

Configuration Hereinafter, the configuration of the present invention will be explained in detail based on specific examples. FIG. 1 is a perspective view showing a temperature sensor S1 as one embodiment of the present invention, preferably γ-8 to 2.
03 (γ-alumina) to α-Al203 (α-alumina) is formed into a disk shape, for example, and a pair of electrodes are connected to each end surface 1a, 1b of the disk. Lead wires 2'a and 2b are extended.

Here, as an embodiment of the method of the present invention, a method for manufacturing the detection section 1 of the humidity sensor S1 configured as described above will be described.
explain. First, add Al2NH4・(SO4)2 to distilled water.
- Completely dissolve 12H20 (ammonium alum). In addition, the starting materials for the detection part 1 include Al(○H)3 (aluminum hydroxide), Al1Cρ3
・6H20 (aluminum chloride) and Al2 (SO
4) 1 of 3 ・14-18H20 (aluminum sulfate)
Species or mixtures of two or more of these compounds can be used. Next, aqueous ammonia is added as a precipitation reagent to the aqueous solution of ammonium alum to adjust the Pl (hydrogen ion concentration) to fall within the range of 7.5 to 9.0, thereby precipitating the dissolved ammonium alum.

In this case, Co (NH2) is also used as the precipitation reagent.
2 (urea water) etc. can also be used. The obtained precipitate is preferably filtered and washed twice or more, then dried at a temperature of 95° C. for 24 to 48 hours, and the dried product is ground with an alumina milk needle to form a powder.

Next, the obtained powdered product is subjected to, for example, 1,000 k
A high pressure of about cI/cm' is applied to press-form the material into a disk shape with a diameter of about iQn+m. Then, this press-formed product is fired (-second firing) at a temperature of 200 to 500°C to dehydrate it and obtain γ-alumina. Then, the obtained γ
- Alumina is subjected to a firing treatment (secondary firing) at a high temperature of 800 to 1,100°C to obtain a sintered body of a mixture in which γ-alumina transitions to α-alumina. By molding this sintered body into a desired shape, for example, a disk shape in this example, the detection section 1 of the humidity sensor is completed.

The transformation of the crystal structure of alumina with respect to the change in firing temperature in the above-mentioned secondary firing step is shown in spectrograms obtained by X-ray diffraction analysis as shown in Figures 2(a) to 2(d). The vertical axis is the X-ray intensity, and the horizontal axis is the rotation angle of the counter 2.
θ respectively. Figure 2(a) shows that the firing temperature is 80°C.
γ-alumina at 0°C, Fig. 2(d) shows calcination temperature of 1,
Each spectrum diagram of α-alumina at 100°C is shown, and the firing temperature was set to 900°C (Figure 2(b)) and 1.
It can be seen that the crystal structure of γ-alumina gradually shifts to the crystal structure of α-alumina as the temperature increases to OOO'C (Fig. 2(C)). FIG. 2(C) is a spectrum diagram of a hybrid of γ-alumina and α-alumina.

The results of an experiment conducted by the inventor of the present invention to confirm the useful effects of the humidity sensor manufactured as described above will be described. Figure 3 shows the response curves of the capacitance of the detection part 1 of the humidity sensor to the relative humidity of the atmosphere (horizontal axis) obtained at different sintering temperatures (secondary firing temperature to obtain a sintered body). The graph shows sintered body samples with different crystal structures. From Figure 3, it can be seen that for sintered bodies I and II with sintering temperatures of 800°C and 900°C, the change in capacitance with respect to relative humidity, that is, the sensitivity as a sensor, becomes especially large in a high humidity atmosphere, and eventually reaches a saturated state. You can see that it is. In addition, the sintering temperature is as high as 1,100°C and 1,200°C, which is essentially α
- On the contrary, the sintered bodies (1) and (2), which are aluminized, have extremely low humidity sensor sensitivity, and in particular, the sintered body (V) hardly responds. Thus, the sintered body (2) whose sintering temperature is i, ooo°C has a substantially linear response curve and exhibits a stable and substantially constant sensitivity over substantially the entire range of relative humidity. From the above results, at least the sintered body V is unsuitable for the detection part of the humidity sensor, and the suitable sintered bodies I, II,
Among H, the amount of change in capacitance as a sensitivity to relative humidity in the range of 11% to 98% is 10° to 10°.
It can be seen that the optimal sintered body is the sintered body (2) which is sufficiently thick and has a substantially constant sensitivity over a three-digit range of 11F.The detection section 1 of the humidity sensor in this embodiment is The sintering temperature was set in the range of 800 to 1,100°C, and the obtained sintered bodies therefore correspond to types 7 to 1 in Fig. 3.This result shows that the frequency of the current passing through the humidity sensor is In the case of 1 kHz, for example, the sensitivity of a sintered body sample at a sintering temperature of 1,000° C., using frequency as a parameter, is shown in FIG.

In this case, the temperature of the atmosphere is set to room temperature (about 21° C.). From FIG. 7, it can be seen that the sensitivity is highest when the frequency is 1 kHz.

Furthermore, the results of confirming changes in the sensitivity of the humidity sensor over time are shown in FIG. Figure 4 shows samples 11 to 98 of the five sintered samples mentioned above.
An appropriate number of points were selected in the range of % relative humidity, and changes in the capacitance value (vertical axis) of sintered body sample (1) responding at each point with respect to the number of days elapsed (horizontal axis) are shown. In this case as well, the frequency is set to 1 kHz and the ambient temperature is set to room temperature. From this, it can be seen that the capacitance value that responds at each relative humidity is approximately constant and stable for about 140 days, and therefore the sensitivity of the humidity sensor of this example changes over time extremely in the relative humidity range of 11 to 98%. It can be seen that it is a small and stable sensor. From the above results, it was confirmed that the humidity sensor of this example had sufficient performance in terms of sensitivity and sensitivity stability. The humidity sensor of this example not only has excellent sensitivity and stability, but also has high mechanical strength and high heat resistance due to the characteristics of the ceramic material, so there is no deterioration due to surface heat treatment of the sensor. It also has the advantage of

Next, some other embodiments of the humidity sensor of the present invention will be described. The perspective view of FIG. 5 shows a heating element 4 to which a pair of heaters 15 are connected, for example, a detection part 3 formed in the shape of a rectangular parallelepiped.
A humidity sensor S2 is shown fixedly attached thereto. The heating element 4 may be made of ruthenium oxide, molybdenum oxide, tungsten oxide, or the like. The detection unit 3 includes a pair of electrodes 3
a, 3b are provided, and a pair of lead wires 6a, 6b are provided thereto.
are combined respectively. Further, the perspective view of FIG. 6 shows a humidity sensor s3 in which a similarly formed heating element heater 8 is embedded inside a rectangular parallelepiped-shaped detection section 7. Similarly, a pair of electrodes 7a and 7b are provided on the detection section 7, and a pair of lead wires 9a are connected thereto.

9b are connected to each other. In this way, each heating element is 4.8
are provided, and each detection unit 3.
By pulse heating 7 to 400 to 600'C, impurities adhering to the surfaces of each detection section 3 and 7 can be removed, and accurate humidity detection function can be maintained at all times.

Effects As detailed above, according to the present invention, a humidity sensor is formed using a sintered body obtained using a selected aluminum oxide or a mixture of two or more thereof as a starting material as a detection part, and the humidity sensor is used to detect atmospheric humidity. By detecting humidity from the change in the capacitance of the detection unit that changes in response, the response change in capacitance, that is, the sensitivity is large, and the change in sensitivity over time is small over the entire humidity range. humidity sensor can be obtained. Further, due to the characteristics of the material of the sintered body of inorganic material at high temperatures, a humidity sensor with excellent mechanical strength and heat resistance can be obtained. It should be noted that the present invention should not be limited to the specific embodiments described above, and it goes without saying that occasional modifications can be made within the technical scope of the present invention.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing one embodiment of the present invention, Fig. 2(a)
Figures 2(d) and 2(d) are X-ray diffraction spectra showing the crystal structure at each stage from γ-alumina to α-alumina, and Figure 3 is a graph showing the sensitivity of the detection unit at different sintering temperatures. 4 is a graph showing changes in sensitivity over time according to relative temperature, FIGS. 5 and 6 are perspective views showing several other embodiments of the present invention, and FIG. 7 is a graph showing changes in sensitivity over time. FIG. 2 is a graph diagram showing the frequency dependence of . (Explanation of symbols) 1, 3. 7: Detection part 1a, 1b, 3a, 3b, 7a, 7b: Electrode 2θ [degrees] Figure 3 Relative humidity [%] Figure 4 Number of days elapsed [8] Figure 5

Claims (1)

[Claims] 1. A sintered body obtained from one substance or a mixture of two or more substances selected from the group consisting of ammonium alum, aluminum hydroxide, aluminum chloride, and aluminum sulfate is used as the detection part, and the detection 1 with a lead wire in the part
A humidity sensor characterized by having a pair of electrodes and detecting humidity by a change in capacitance according to a change in atmospheric humidity. 2. The humidity sensor according to item 1 above, characterized in that the detection section is fixed on a heating body. 3. The humidity sensor according to item 1 above, characterized in that a heating element is embedded inside the detection section. 4. After dissolving one substance or a mixture of two or more selected from the group consisting of ammonium alum, aluminum hydroxide, aluminum chloride, and aluminum sulfate in water, a basic precipitation reagent is added to adjust the hydrogen ion concentration. a step of precipitating the dissolved material with a weak base; a step of filtering and washing the precipitate and then pulverizing it to powder; a firing step of heating and dehydrating the powdered precipitate at a predetermined temperature; and a step of heating and dehydrating the powdered precipitate at a predetermined temperature; A method for manufacturing a humidity sensor, comprising a sintering step of further firing at a high temperature to form a sintered body. 5. The method for manufacturing a humidity sensor according to item 4 above, wherein the precipitation reagent is ammonia water or urea water. 6. The method for manufacturing a humidity sensor according to item 4 above, wherein the predetermined temperature in the firing step is 200 to 600°C. 7. The method for manufacturing a humidity sensor according to item 4 above, wherein the high temperature in the sintering step is 800 to 1,100°C.