JPH02172201A - Humidity sensor - Google Patents

Abstract

PURPOSE:To improve the humidity detection sensitivity and reduce the cost by a method wherein humidity-sensitive resistance elements made of predetermined contents of Bi2O3 and M2O3 and a heater which is made of heat-resistant metal and heats the humidity-sensitive resistance elements are provided. CONSTITUTION:Humidity-sensitive resistance elements 12 are made of 65-98mol% Bi2O3 and 2.0-35mol% M2O3, wherein M denotes at least one among In and group IIIa elements except actinoids. A heater 14 is formed in the humidity- sensitive resistance elements 12. The heater 14 is made of heat-resistant metal and heats the humidity-sensitive resistance elements 12. A humidity sensor 10 composed like this can measure a humidity in a wide temperature range and the humidity-sensing characteristics are stable in course of time. Further, as the humidity-sensitive resistance elements 12 are heated by the heater 14 to a temperature at which they show good characteristics, the humidity detection sensitivity can be high and a humidity from a low humidity range to a high humidity range can be detected.

Description

[Detailed description of the invention] (Industrial application field) This invention relates to a humidity sensor.

(Prior Art) Conventional humidity sensors include those using polymer materials and those using ceramics. In addition, as a device that measures humidity by heating a humidity-sensitive resistor using a heater,
There was one using ZrO.

(Problems to be Solved by the Invention) However, with humidity sensors using polymeric materials, the temperature range in which humidity can be measured is limited to room temperature to 100°C. Furthermore, humidity sensors using ceramics utilize the adsorption of water molecules onto porous ceramics, but there are problems with the temperature range for measuring humidity and the stability over time of moisture sensitivity characteristics. Furthermore, the humidity sensor using ZrO has problems in that it requires firing at a high temperature, which increases the cost and also has low temperature measurement sensitivity.

Therefore, the main object of the present invention is to provide a low-cost humidity sensor that can measure humidity over a wide temperature range, has good stability of humidity-sensitive characteristics over time, has high temperature measurement sensitivity, and is low-cost. .

(Means for Solving the Problems) This invention includes 65 to 98 mol% Bi, 0. and 2.0~
A moisture-sensitive resistor consisting of 35 mol% MzOx (where M excludes actinides (at least one type selected from Illa group elements and In) and a heat-resistant metal for heating the humidity-sensitive resistor. This is a humidity sensor that includes a heater.

(Function) The temperature of the humidity-sensitive resistor is maintained by the heater at a temperature at which the humidity-sensitive characteristics of the humidity-sensitive sensor are good.

(Effects of the Invention) According to the present invention, it is possible to obtain a humidity sensor that has a wide temperature range in which humidity can be measured and has good stability of humidity sensitivity characteristics over time. Furthermore, a humidity sensor with high temperature detection sensitivity and low cost can be obtained.

The above object, other object 2 features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Embodiment) FIG. 1 is an illustrative diagram showing an embodiment of the present invention. This humidity sensor 10 includes a rectangular humidity sensitive resistor 12. This moisture sensitive resistor 12 contains 65 to 98 mol% BlzOs and 2.
It is formed with 0 to 35 mol% M2O3. Here, M
is at least one type selected from group IIIa elements and In, excluding actinides.

A heater 14 is formed inside the humidity sensitive resistor 12 .

This heater 14 is made of heat-resistant metal, and the moisture-sensitive resistor 12
It is for heating. This heater 14
As shown in the figure, it is formed, for example, in a meandering manner so that the entire moisture sensitive resistor 12 can be heated. Then, an insulating layer 16 is formed around the heater 14.

Furthermore, electrodes 18 and 20 are formed on the bidirectional surfaces of the humidity-sensitive resistor 12. Between these electrodes 18 and 20,
A change in the resistance value of the humidity-sensitive resistor 12 in response to a change in humidity is detected.

Furthermore, a cap 22 having a diffusion hole formed therein is sealed on one main surface of the humidity-sensitive resistor 12 using, for example, glass. In this way, the humidity sensor 10 is obtained.

In such a humidity sensor 10, the temperature range in which humidity can be measured is wide, and the humidity sensitivity characteristics are stable over time. Furthermore, by the heater 14, %? Since the W resistor 12 is heated to a suitable temperature, its temperature measurement sensitivity is high. In addition, this humidity sensor 10 can measure temperatures in a wide range from low humidity ranges to high humidity ranges. Furthermore, this humidity sensor 10 can be fired at a lower temperature than that using ZrO□, and manufacturing costs can be reduced.

Experimental Example I Using BtzOs as the basic material, Aj! , Ga, YIn
and rare earth oxides were mixed in an amount of 0 to 50 mol% in terms of M2O. An organic binder was added to this mixture, and the mixture was molded into a disk shape with a diameter of 10 mm and a thickness of 1 mm. This molded product was heated to 850 to 11
Sintering was carried out at 00°C for 2 hours. Then, both sides of this sintered body were polished and evaluated.

First, this humidity-sensitive resistor was heated to 600° C., and the conductivity and oxide ion transfer number were measured and shown in the attached table. Furthermore, the relationship between the composition of the moisture-sensitive resistor and the oxide ion axis ratio is shown in FIG. From these results, M2O, is 1 to 35 mol%
It can be seen that in the range of , the oxide ion transfer number is large and the electrical conductivity is also large.

Experimental Example 2 Using the humidity sensor shown in FIGS. 1 and 2, a predetermined voltage (2 .mu.) was applied between the electrodes in the circuit shown in FIG. 4, and the relationship between relative humidity and current was investigated. The results are shown in FIG. Also, relative humidity 10%RH, 50%RH
FIG. 6 shows the relationship between voltage and current at 90% RH. In addition, when performing this experiment, the temperature of the humidity sensitive resistor 12 was set to 500° C. by energizing the heater 14 of the humidity sensor IO, and the measurement was performed under the condition that the ambient temperature was 25° C.

Here, when Bi,03 is less than 65 mol%, it is desirable that the oxide ion transfer number is large.

On the other hand, when Bi, 01 is more than 99 mol %, the strength of the moisture sensitive resistor becomes weak and unstable.

[Brief explanation of the drawing]

FIG. 1 is an illustrative view showing an embodiment of the present invention. FIG. 2 is an illustrative diagram showing the shape of the heater of the humidity sensor shown in FIG. 1. FIG. 3 is a graph showing the relationship between the composition of the humidity-sensitive resistor and the oxide ion transfer number. FIG. 4 is a circuit diagram showing a measurement circuit used in Experimental Example 2. FIG. 5 is a graph showing the relationship between relative humidity and current of the humidity sensor of the present invention. Figure 6 shows the relative humidity of the humidity sensor of this invention at 10% RH.
It is a graph showing the relationship between voltage and current at 50% RH and 90% RH. In the figure, 10 is a humidity sensor, 12 is a temperature-sensitive resistor, 1
4 indicates a heater. Patent applicant: Murata Manufacturing Co., Ltd. Representative: Patent attorney Oka 1) Zenkei Omote-ku, Dimension-ku, Qurihoshima- 1ml

Claims (1)

[Claims] 65-98 mol% Bi_2O_3 and 2.0-35 mol% M_2O_3 (where M is I excluding actinides)
At least one selected from group IIa elements and In
1. A humidity sensor comprising: a humidity-sensitive resistor made of a heat-sensitive resistor; and a heater made of a heat-resistant metal for heating the humidity-sensitive resistor.