JP4205601B2 - Carbon monoxide gas sensor and method for manufacturing P-type semiconductor - Google Patents

Description

  The present invention relates to a carbon monoxide gas sensor that detects carbon monoxide gas (CO gas) with high selectivity, and a method of manufacturing a P-type semiconductor that constitutes the sensor.

  Conventionally, a semiconductor type gas sensor has been used to detect gas in the environment (for example, see Patent Document 1). This sensor keeps the N-type semiconductor made of metal oxide and P-type semiconductor in contact with each other at a high temperature, and the resistance value of the sensor changes when the environmental gas contacts the contact part of both semiconductors. This change in resistance value is detected electrically (PN sensor).

  This sensor can detect various organic gases such as methane, ethanol, and ethyl acetate in addition to carbon monoxide gas at the same time with good sensitivity, and is preferable as a general-purpose sensor. Not suitable for.

  For example, carbon monoxide gas is a toxic gas that has a significant effect on the human body even when present at about 1000 ppm. Therefore, when measuring carbon monoxide gas for the environmental safety of the human body, a sensor capable of detecting carbon monoxide gas with a concentration of about several hundred ppm is required.

  The conventional gas sensor has a performance capable of detecting carbon monoxide gas of about several hundred ppm. However, as described above, the conventional gas sensor is also sensitive to the organic gas at the same time. Therefore, in the environment where the organic gas is present, the carbon monoxide gas is present even if the carbon monoxide gas is not present. Cause malfunction. In particular, since ethanol or the like may be present in a room at a high concentration, there are many opportunities for malfunction due to this, and there is a problem that accurate detection of carbon monoxide gas cannot be performed.

Patent No. 3081244 (Claim 1)

  While the inventors have made various studies to solve the above problem, when a La compound is added to a P-type semiconductor of a PN-type sensor configured by contacting an N-type semiconductor and a P-type semiconductor. The present inventors have found that carbon monoxide gas can be selectively detected with high sensitivity. As a result of further investigation, it was found that the selectivity of carbon monoxide gas can be further improved when a Bi compound is used in combination with the La compound.

  The present invention has been completed on the basis of the above discovery, and its object is to have high selectivity for detecting carbon monoxide gas, and to accurately control the concentration of carbon monoxide gas even in the presence of organic gas. An object of the present invention is to provide a carbon monoxide gas sensor that can be detected and a method for manufacturing a P-type semiconductor for manufacturing the sensor.

  In order to achieve the above object, the present invention is configured as follows.

  [1] A carbon monoxide gas sensor formed by press-contacting a P-type semiconductor containing CuO containing 1 to 10 mol% of La element as a base material and an N-type semiconductor containing ZnO as a base material.

  [2] A P-type semiconductor containing CuO containing 1 to 10 mol% of La element and Bi element as a base material and an N-type semiconductor containing ZnO as a base material, respectively. Carbon monoxide gas sensor.

  [3] The carbon monoxide gas sensor according to [2], wherein the molar ratio of La element to Bi element is 6: 4 to 4: 6.

  [4] The carbon monoxide gas sensor according to any one of [1] to [3], wherein the La element is contained as a LaOCl compound.

[5] Carbon monoxide which is pressure-molded by adding LaCl ₃ or LaOCl corresponding to 1 to 10 mol% of La element to Cu element and then firing at 650 to 950 ° C. in an oxidizing atmosphere Manufacturing method of P-type semiconductor for gas sensor.

[6] to CuO, were added and LaCl ₃ or LaOCl equivalent to 10 mol% of La element relative to Cu, the BiCl ₃ of Bi element corresponds to 1 to 10 mol% based on Cu element A method for producing a P-type semiconductor for a carbon monoxide gas sensor, which is pressure-molded and then fired at 650 to 950 ° C. in an oxidizing atmosphere.

  In the carbon monoxide gas sensor according to the present invention, the La compound is added to the P-type semiconductor of the PN sensor configured by press-contacting the N-type semiconductor and the P-type semiconductor, so that the detection selectivity of the carbon monoxide gas is high. . Furthermore, when a Bi compound is added to the P-type semiconductor in addition to the La compound, the selectivity for detecting carbon monoxide gas can be further improved.

  Hereinafter, an embodiment of the carbon monoxide gas sensor of the present invention will be described in detail with reference to the drawings.

  In FIG. 1A, 2 is a side view showing an example of the carbon monoxide gas sensor of the present invention, and 4 and 6 are ceramic substrates having heat resistance and insulation properties such as alumina. Element electrodes 8 and 10 are formed on the surfaces of the ceramic substrates 4 and 6 facing each other.

  A P-type semiconductor element 12 is formed on the element electrode 8. An N-type semiconductor element 14 is formed on the element electrode 10. The P-type semiconductor element 12 and the N-type semiconductor element 14 are in pressure contact with each other at the pressure contact surface 16. The pressing pressure is preferably 30 KPa or more.

  On the surface of the ceramic substrates 4 and 6 opposite to the surface on which the device electrodes 8 and 10 are formed, heaters 18 and 20 are formed by meandering and sintering an electric resistor thin film such as platinum, and both ends of the heaters 18 and 20 are formed. Are connected to the heater electrodes 22, 24, 26, 28, respectively. FIG. 1B is a plan view of the carbon monoxide gas sensor.

  In the carbon monoxide gas sensor having the above configuration, the P-type semiconductor element 12 has CuO as a base material. The P-type semiconductor element 12 further contains La element in an amount of 1 to 10 mol%, preferably 3 to 7 mol% with respect to the Cu element. As the compound containing La element, LaOCl is preferable. When the addition amount of La element is less than 1 mol%, the selectivity of the obtained carbon monoxide gas sensor to carbon monoxide is low. When the addition amount of La element exceeds 10 mol%, the moldability at the time of manufacturing a P-type semiconductor is deteriorated.

An example of a method for manufacturing the P-type semiconductor element 12 is a method in which the calculated amount of LaCl ₃ .7H ₂ O or LaOCl is added to CuO and molded, and then fired in an oxidizing atmosphere at 650 to 950 ° C. The firing time is preferably 10 minutes to 1 hour. It has been confirmed by the analysis by μ-X-ray diffraction that the La compound is changed to LaOCl by firing. Since LaCl ₃ is water-soluble, it can be easily dispersed uniformly in CuO and is a preferred P-type semiconductor material. On the other hand, since LaOCl is water-insoluble, it is inferior to LaCl3 from the viewpoint of being uniformly dispersed in CuO. However, when using LaOCl, the resulting sensor is highly selective.

The P-type semiconductor element 12 may further contain Bi element in an amount of 1 to 10 mol%, preferably 3 to 7 mol% with respect to the Cu element. By containing Bi element, the detection selectivity of the sensor with respect to carbon monoxide gas further increases.
BiCl ₃ is preferred as the compound containing Bi element. When the amount of Bi element added is less than 1 mol%, the selectivity of the obtained carbon monoxide gas sensor to carbon monoxide is low. When the addition amount of Bi element exceeds 10 mol%, the moldability at the time of manufacturing a P-type semiconductor is deteriorated.

  When the Bi element is contained in the P-type semiconductor element, the molar ratio of the La element to the Bi element is preferably 6: 4 to 4: 6.

  The N-type semiconductor element 14 uses ZnO as a base material. As a method for manufacturing the N-type semiconductor element 14 and an additive metal, conventionally known ones can be arbitrarily adopted.

  FIG. 2 shows a configuration of a carbon monoxide gas measuring apparatus in which the carbon monoxide gas sensor 2 is incorporated. The case where carbon monoxide gas is detected using this measuring apparatus will be described.

  A predetermined power is supplied to the heater electrodes 22, 24 and 26, 28 from a power source (not shown), whereby the heaters 18, 20 generate heat and the sensor 2 is heated to 200 to 400 ° C.

  On the other hand, the power of the power supply 30 is adjusted by the variable resistor 32 and applied to the element electrodes 8 and 10 of the carbon monoxide gas sensor 2. When carbon monoxide gas comes into contact with the vicinity of the pressure contact surface 16, the height and width of the potential barrier on the pressure contact surface 16 change, and the value of the current flowing through the sensor 2 changes. By measuring this change in the current value with the ammeter 34, the concentration of the carbon monoxide gas is detected. Reference numeral 36 denotes a voltmeter for measuring a voltage applied to the element electrode.

  Usually, in the case of the carbon monoxide gas sensor having the above-described configuration, when the applied voltage is set to about 0.1 V, a current of several μA flows.

Example 1
As a P-type semiconductor base material, CuO (trade name: nanotecCuO, manufactured by CI Kasei Co., Ltd.), 0.25 g of LaCl ₃ .7H ₂ O mixed with 5 mol% of Cu element, 10 mm in diameter and 1.0 mm in thickness It was press-molded into a disk shape. The molding pressure was 120 MPa. The molded product was baked at 800 ° C. for 1 hour to obtain a P-type semiconductor element.

  On the other hand, 0.25 g of ZnO (trade name nanotecZnO manufactured by CI Kasei Co., Ltd.) powder as an N-type semiconductor base material was press-molded into a disk shape having a diameter of 10 mm and a thickness of 1.0 mm. The molding pressure was 120 MPa. The molded product was baked at 1000 ° C. for 1 hour to obtain an N-type semiconductor element.

  Next, a device electrode pattern was printed on a 12.7 × 12.7 × 0.635 mm Kyocera alumina substrate by screen printing using Ag paste (Sylvest P-603 manufactured by Tokoku Chemical Laboratories Co., Ltd.), and at 550 ° C. for 10 minutes. By firing, an element electrode was formed on the alumina substrate.

  The Ag paste was applied to the element electrode of the alumina substrate on which the element electrode was formed, and the manufactured P-type semiconductor element was stuck thereon. Then, it baked for 10 minutes at 550 degreeC, and obtained the P-type semiconductor.

  Similarly, an N-type semiconductor was obtained.

  Finally, the P and N type semiconductors obtained above were pressure-fixed with clips with the semiconductor surfaces facing each other to obtain a carbon monoxide gas sensor.

  This sensor is inserted into a cylindrical heating furnace, and air containing carbon monoxide gas, ethanol, and ethyl acetate gas in the concentrations shown in Table 1 is kept in the heating furnace while maintaining the heating furnace at 260 ° C. (= detection temperature). Supplied.

  The detection sensitivity of the obtained sensor is summarized in Table 1.

Comparative Example 1
A sensor was manufactured in the same manner as in Example 1 except that LaCl ₃ .7H ₂ O was not added as a P-type semiconductor element. Using this, the same detection test as in Example 1 was performed, and the results are shown in Table 1.

Comparative Example 2
A sensor was manufactured in the same manner as in Example 1 except that 0.1 mol% of LaCl ₃ .7H ₂ O was added as a P-type semiconductor element. Using this, the same detection test as in Example 1 was performed, and the results are shown in Table 1. According to the data of Comparative Example 2 in Table 1, the gas detection sensitivities of ethanol and ethyl acetate are slightly higher than those of Comparative Example 1. This is based on variations in sensor characteristics, and the sensors of Comparative Example 1 and Comparative Example 2 are substantially equivalent as gas selection characteristics.

表１中、ガス検出感度（*1）は、ΔＩ_gas／ΔＩ_CO1000 で定義されるものである。ここで、ΔＩ_gas＝Ｉ_gas−Ｉ_air、 ΔＩ_CO1000＝Ｉ_CO1000−Ｉ_air
但し、Ｉ_air：空気雰囲気中における検出電流値、Ｉ_gas：供給ガス中における検出電流値、Ｉ_CO1000：ＣＯガス１０００ｐｐｍ雰囲気中における検出電流値

実施例２
Ｐ型半導体素子の製造において、ＬａＣｌ₃・７Ｈ₂Ｏの代りにＬａＯＣｌ粉末を使用した以外は実施例１と同様に操作して一酸化炭素ガスセンサを製造した。その結果を表２に示した。

実施例３
Ｐ型半導体素子の製造において、ＬａＣｌ₃・７Ｈ₂Ｏを１０モル％添加する代りにＬａＣｌ₃・７Ｈ₂Ｏを５モル％と、ＢｉＣｌ₃を５モル％添加した以外は実施例１と同様に操作して一酸化炭素ガスセンサを製造した。検出温度３４０℃で求めたガス検出感度を表２に示した。

In Table 1, the gas detection sensitivity (* 1) is defined by ΔI _gas / ΔI _CO1000 . Here, ΔI _gas = I _gas −I _air , ΔI _CO1000 = I _CO1000 −I _air
Where I _air : detected current value in air atmosphere, I _gas : detected current value in supply gas, I _CO1000 : detected current value in CO gas 1000 ppm atmosphere

Example 2
A carbon monoxide gas sensor was produced in the same manner as in Example 1 except that LaOCl powder was used instead of LaCl ₃ .7H ₂ O in the production of the P-type semiconductor element. The results are shown in Table 2.

Example 3
In the production of P-type semiconductor element, similarly to 5 mol% of LaCl ₃ · 7H ₂ O instead of adding LaCl ₃ · 7H ₂ O 10 mole%, except for adding BiCl ₃ 5 mol% from Example 1 A carbon monoxide gas sensor was manufactured by operating. Table 2 shows gas detection sensitivities determined at a detection temperature of 340 ° C.

  As Reference Example 1, Table 2 shows the gas detection sensitivities obtained by the same measurement method as in Example 3 (however, the detection temperature is 260 ° C.) using the carbon monoxide gas sensor of Example 1.

表２中、ガス検出感度（*2）は、ΔＩ_gas／ΔＩ_CO500 で定義されるものである。ここで、ΔＩ_CO500＝Ｉ_CO500−Ｉ_air、
但し、Ｉ_air：空気雰囲気中における検出電流値、Ｉ_gas：供給ガス中における検出電流値、Ｉ_CO500：ＣＯガス５００ｐｐｍ雰囲気中における検出電流値

実施例１、２、比較例１、２のデータの比較から、本発明の一酸化炭素ガスセンサは、一酸化炭素に対する選択性に優れていることが解る。

In Table 2, the gas detection sensitivity (* 2) is defined by ΔI _gas / ΔI _CO500 . Where ΔI _CO500 = I _CO500 −I _air ,
However, I _air : detected current value in air atmosphere, I _gas : detected current value in supply gas, I _CO500 : detected current value in CO gas 500 ppm atmosphere

From the comparison of the data of Examples 1 and 2 and Comparative Examples 1 and 2, it can be seen that the carbon monoxide gas sensor of the present invention is excellent in selectivity to carbon monoxide.

  Further, it can be seen from the data of Example 3 and Reference Example 1 that the selectivity of the carbon monoxide gas is further enhanced when the P-type semiconductor element coexists with the Bi element in addition to the La element.

(A) which shows an example of the carbon monoxide gas sensor of this invention is a schematic side view, (B) is a schematic plan view. It is explanatory drawing which shows an example of the circuit structure of a carbon monoxide measuring apparatus.

Explanation of symbols

2 Carbon monoxide gas sensor 4, 6 Ceramic substrate 8, 10 Element electrode 12 P-type semiconductor element 14 N-type semiconductor element 16 Pressure contact surface 18, 20 Heater 22, 24, 26, 28 Heater electrode 30 Power supply 32 Variable resistance 34 Ammeter 36 voltmeter

Claims (6)

A carbon monoxide gas sensor formed by press-contacting a P-type semiconductor containing CuO containing 1 to 10 mol% of La element with respect to Cu element as a base material and an N-type semiconductor containing ZnO as a base material. Carbon monoxide formed by pressure-contacting a P-type semiconductor containing CuO containing 1 to 10 mol% of La element and Bi element with respect to Cu element and an N-type semiconductor containing ZnO as a base material Gas sensor. The carbon monoxide gas sensor according to claim 2, wherein a molar ratio of La element to Bi element is 6: 4 to 4: 6. The carbon monoxide gas sensor according to any one of claims 1 to 3, wherein La element is contained as a LaOCl compound. P for carbon monoxide gas sensor, in which LaCl ₃ or LaOCl corresponding to 1 to 10 mol% of La element is added to CuO and subjected to pressure molding, and then fired at 650 to 950 ° C. in an oxidizing atmosphere. Type semiconductor manufacturing method. To CuO, corresponding to 10 mol% of La element relative to Cu element LaCl ₃ or LaOCl and with the addition of BiCl ₃ of Bi element corresponds to 1 to 10 mol% based on Cu element pressing Then, a method for manufacturing a P-type semiconductor for a carbon monoxide gas sensor, which is fired at 650 to 950 ° C. in an oxidizing atmosphere.

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