WO1986004989A1

WO1986004989A1 - Gas sensor element of tin oxide film

Info

Publication number: WO1986004989A1
Application number: PCT/JP1986/000077
Authority: WO
Inventors: Takeshi Matsumoto; Osamu Okada; Yuuji Nakamura
Original assignee: Osaka Gas Company Limited
Priority date: 1985-02-20
Filing date: 1986-02-19
Publication date: 1986-08-28
Also published as: GB2182448A; JPS61191954A; GB8625006D0; GB2182448B; KR940002511B1; GB8624904D0; JPH053895B2; KR880700261A

Abstract

A gas sensor element of a tin oxide film in a gas sensor using a tin oxide film. In this element, a special relation is established between the numerical values of two or three of the highest intensity I1?, second highest intensity I2?, third highest intensity I3?, fourth highest intensity I4? and fifth highest intensity I5? of diffraction rays, which are obtained when the crystalline orientation and crystallinity of the surface of an object to be gas-detected are determined by carrying out an X-ray diffraction operation using Cuk as a ray source; and a half-value width of the highest intensity of diffraction rays is in a level not lower than a predetermined level.

Description

Specification

Tin oxide thin film gas sensor element

Technical field

The present invention relates to a gas sensor element provided with an oxide thin film having semiconductor characteristics.

Background technology

Currently used semiconductor gas sensors are mainly manufactured by sintering. However, the production method by sintering is a complex process and includes various fluctuation factors that affect the performance of the product. Therefore, it is not satisfactory in terms of product religion, stability, durability, etc. Hard to say. In addition, products obtained by sintering have a drawback of low sensitivity because their dimensions cannot be reduced below a certain level. Therefore, thin-film semiconductor sensors are being developed to replace sintered products, but no viable alternative to sintered products has been obtained.

One reason that thin-film semiconductor sensors are difficult to put into practical use is that thin-film semiconductor sensors are generally very good at detecting hydrogen, but hardly detect methane. For this reason, for example, a method of oxidizing a substrate made of silicon to form an insulating film made of SiO ₂ and then forming a Pt-doped Sn 02 film thereon (see Japanese Patent Application Laid-Open No. 5 4 2 4 0 9 4 JP>, S ί 0 ₂ method for doping ρ or Β the silicon substrate obtained by forming an insulating film (JP 5 7 1 7 8 4 9 JP> like proposed However, the desired effect has not been obtained because dopant atoms are difficult to dope uniformly.

Disclosure of the invention

The present inventor has conducted various experiments and studies in view of the current state of the technology as described above, and as a result, using a metal powder and at least one of tin oxide as a vapor deposition material source, a physical vapor deposition (PVD) or When a vapor deposition layer is formed on a substrate under specific conditions by chemical vapor deposition (CVD), a thin film with a specific crystal orientation is formed at the interface with the gas phase. The resulting thin film was found to exhibit excellent characteristics as a sensor not only for hydrogen but also for gas phase components such as hydrocarbons such as methane, ethane, propane, and butane, and oxygen. That is, the present invention provides the following gas sensor element.

`` In the thin-film oxide gas sensor element, the crystal orientation and crystallinity of the gas detection surface are defined as I, the strongest diffraction line intensity when X-ray diffraction is performed using Cu 線 as the source, and the second, third, fourth, and The fifth strongest diffraction line intensities are I ₂ , I 3, When 4 and 55 I2 are taken,

(a) Whether the line intensity of the (211) plane or the (110) plane is the strongest, I 2 / I 1 ≤ 0.6, and the half-width of I〗 is 0.58 or more;

(b) I! There (110) plane or (101) plane is and the line strength of E ₂ (101) plane or (110) plane in the line strength _{of, 1 2 / ≥0. 5,} I 3 / I a <0. 6 And the half-value width of h is 0.54 or more,

(c) I! Is the line intensity of the (110) plane or the (211) plane, and I ₂ is the line intensity of the (101) plane or the (110) plane. I ₂ / ≥ 0.5, I 3 / I a And the half-value width of ιι is 0,58 or more,

(d) I! , I ₂ and I ₃ are the line intensities of the (110), (101) and (211) planes, respectively.

Ι ₃ / ί 1 ≥ 0.5, ΐ 4 / I 3 〇, 6 and the half width of I is 0.61 or more,

(E> I〗, I _2, I ₃ and I 4 respectively (110) plane, (101) plane, is any line strength of (211) plane and (301) plane, It ZI ≥0. 5 , Is / d and 0.6, and if the half width of I is 0.73 or more,

(f) 1 1 is the line intensity of the (301) plane, and _{2 2} / I 1 ≤ Or the half-value width of and I i in 0.6 is 0.60 or more, (g) E 1 (211) plane or (301) and a line intensity of surface E ₂ (301) plane or (211) It is the line intensity of the surface, _{2 2} / 〇 .5, Is / 1 ₂く 0.6 and 0! Has a half width of 〇 .3 or more

A tin oxide thin film gas sensor element characterized by the above-mentioned. "

As a substrate of the gas sensor of the present invention, a silicon substrate, a ceramic substrate, a glass substrate, or the like is used. When a silicon substrate is used, an SiO ₂ insulating layer is formed on the surface thereof in accordance with a conventional method. A tin oxide layer is formed as a thin film semiconductor layer on a substrate. In order for tin oxide to exhibit its properties as a semiconductor, some oxygen atoms were lost from the complete oxide. That is, it is necessary to take a form having lattice defects. The presence of such lattice defects can be confirmed by measuring the conductivity.

In the case of Si 〇 ₂ having lattice defects, the plane orientations of the crystals involved in gas detection are (110), (101), (211) and (30). Table II shows some examples of the relationship. No. 'Ί

The crystal in the tin oxide thin film semiconductor layer in the sensor of the present invention is

The half-width of the strongest diffraction line (I i) from the X-ray diffraction spectrum using Cu K rays as the source is 80% or more of the experimental value, and multiple diffraction lines appearing according to the number of plane orientations If the half-value width of (d) is less than the above-mentioned value, the crystal and the particle diameter become large, so that the sensitivity is increased. Decreases and cannot be used as a sensor. The gas sensor element of the present invention is manufactured, for example, as follows. First, therefore the formation of the oxide insulating layer such as S ί 0 ₂ in a conventional manner on the surface of the silicon of the substrate to form a tin oxide thin film semiconductor layer by PVD or CVD. The conditions for the vapor deposition operation can vary widely depending on the material of the substrate, the type of tin metal and tin oxide as the source of the vapor deposition material, the vapor deposition method, and the like.Ρ In the case of the sputtering method belonging to the VD method, for example, at a substrate temperature of 0 to 500, the distance Ί ~ 500 thighs of target Bok and the substrate, a ', H e, an inert gas atmosphere gas pressure 1 x 1 0, such as N ₂ -'~ Ί Χ 1 0- ⁴ Bok Oxygen partial pressure in atmospheric gas: 0 to 1 X Ί 0 to ³ torr, applied voltage: 10 to 200 V, high frequency output: about 10 W to 10 KW In particular, metal tin is used as a vapor deposition material source. If used, the oxygen partial pressure in the atmospheric gas 1 Χ Ί Ο- 5 ~1 Χ.Ί 0 -. and ³ Bokuru the proportion of inert gas and oxygen in the atmospheric gas, the former It is preferable that the amount of oxygen is too small, and if the proportion of oxygen is too small, the oxygen in the thin film becomes insufficient and S n 0 ₂ is not obtained. If the ratio is too high, the lattice defects will decrease, and the conductivity will be too low to use as a sensor.If the substrate temperature exceeds 500, the crystal grain size becomes coarse and the gas Detection _The performance is reduced. Note that if the crystal grains are coarsened, the half width will decrease, so it is easily checked. If the other conditions are out of the above range, a thin film is not formed or a crystal having a specific plane orientation is not generated, so that the gas detection ability is lost.

Metal tin and tin oxide are used as vapor deposition material sources. The gas sensor element of the present invention formed by vapor deposition can be further improved in stability and durability by annealing if necessary. The annealing treatment is performed, for example, by maintaining the temperature in a dry air atmosphere at 50 ° C. for about 4 hours.

When the device of the present invention is used as a gas sensor, for example, a platinum electrode may be formed on the thin film semiconductor layer and a predetermined lead wire may be connected according to a conventional method.

According to the present invention, the following effects are achieved.

(1) A thin-film semiconductor gas sensor can be obtained without a doping step. The resulting gas sensor has the ability to detect not only hydrogen but also hydrocarbons such as methane and oxygen. Also, its gas sensitivity is extremely high, and it can detect even small amounts of gas.

(2) The manufacturing process is simpler than when sintering (3) An element with uniform performance can be obtained compared to the case of sintering.

(4) The obtained device has better mechanical strength than the device manufactured by the sintering method, so that the sensor characteristics hardly change even during long-term use.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1, 4 to 9 and 25 show X-ray diffraction patterns of the tin oxide thin film semiconductor layer formed according to the embodiment of the present invention, and FIGS. FIG. 24 shows a similar X-ray diffraction pattern according to the comparative example. FIG. 2 is a schematic sectional view showing an example of the gas sensor element according to the present invention. FIGS. 3, 14 to 19 and 26 are graphs showing the gas detecting ability of the gas sensor element according to the embodiment of the present invention, and FIGS. 20 to 23 are comparative figures. 5 is a graph showing the gas detection ability of a gas sensor according to an example. Each number in FIG. 2 indicates the following components.

(1) ······· Silicon wafer

(3) '

(5) ...... Tin oxide thin film layer

(7) Platinum electrode

Example Hereinafter, the features of the present invention will be described in more detail with reference to Examples.

Example 1

A silicon wafer (2 x X 3 Restaurant) as a substrate is ripened in an atmosphere containing oxygen and water vapor for 2 hours with OOOO CTC to form a SiO ₂ insulating layer on the surface, and then a parallel plate type high-frequency magnet Using a tron sputtering equipment,

The evaporation operation was rows summer as targets Bok material to S n 0 ₂ sintered body. The conditions at the time of vapor deposition are as shown in Table 2 below.

Table 2

High frequency output about 300 W

Atmosphere Α Ί Ί. 8 Χ Ί 0 ^-2 Torr +

0 ₂ 0. ₂ X Ί 0 one ² Bokuru

Assault temperature 200

Circuit board 50

Get distance

Approx. 240 minutes

Speed

The line diffraction diagram of the thus-obtained oxide thin film (140) is shown in Fig. 1. It is clear that the intensity of the diffraction line corresponding to the orientation plane (211) is particularly large. A platinum electrode (thickness: about Ί ^ ΓΤΊ) was formed by sputtering on the vapor-deposited thin film formed above to obtain a gas sensor element shown in FIG. In FIG. 2, (1> silicon wafer, (3) 3! 0 ₂ insulating layer, (5> oxide鍚薄film layer, (7) denotes a platinum electrode.

Next, the above gas sensor element is placed in a cell in an electric furnace, and is annealed while flowing at 500 ° C. for 4 hours while flowing dry air. (A) Dry air, (a) Methane-containing dry air or (又は) The hydrogen-containing dry air was flowed, and the electrical resistance between the electrodes at each temperature was measured, and the results are as shown in Fig. 3. As is clear from Fig. 3, the gas sensor of the present invention only has a hydrogen detecting ability. However, it is clear that it has methane detection capability at 40 ° C or higher.

In FIG. 3 and the graphs showing the results of the following examples, each curve shows the results for the following gases, respectively.

Curve (G): Dry air, Curve (E): Dry air containing 0.35% of methane, Curve (ΠΙ): Dry air containing 0.3% of hydrogen, Curve (IV): 0.35% of hydrogen Curve (V)… dry air containing 0.1% of methane it Lyair.

Examples 2 to 8 and Comparative Examples 1 to 4

A thin oxide film was formed on a substrate in the same manner as in Example 1 except that vapor deposition was performed under the conditions shown in Table 3 below, and then a gas sensor element was obtained.

Table 3 also shows the peak intensity of each diffraction line corresponding to each orientation plane and the intensity ratio to the highest peak intensity.

X-ray diffraction patterns of the obtained oxide thin films are shown in FIGS. 4 to 3 and 25.

Further, the characteristics of the obtained gas sensors are shown in FIGS. 4 to 23 and 26.

Three

Table 3 (continued)

As is clear from the results shown in FIGS. 3, 4 to 23 and 26, the gas sensor element of the present invention is excellent in the ability to detect methane and hydrogen.

Comparative Example 5

A gas sensor element was obtained by forming an oxide thin film on a substrate according to Comparative Example II. The X-ray diffraction pattern of the obtained tin oxide thin film (using the Cu K line as the source) is as shown in Fig. 24, showing that the (200) plane has a single strong line intensity. I have.

Using the obtained gas sensor element, various gas detection tests were carried out in the same manner as in Example 1. However, it was found that the gas sensor element did not show sensitivity to gas and could not be put to practical use.

Claims

The scope of the claims

In the tin oxide thin film gas sensor, the crystal orientation and crystallinity of the gas detection surface are the strongest diffraction line intensity when X-ray diffraction is performed using Cu K as a source, and the second, third, fourth, and When the fifth strongest diffraction line intensities are ェ 2, I 3, 及び 4 and ₁₅ respectively,

(a) The line intensity of the (211) plane or the (110) plane is the strongest, and I 2 / I 1 ≤ 0.6 and I! Is greater than or equal to 0.58,

(b) I 1 is the linear strength of the (110) plane or the (101) plane, and E 2 is the linear strength of the (101) or (110) plane,

If I 2 / I 1 ≥ 0.5, I 3 / I 2 and 0.6, and if the half width of I 1 is 〇0.54 or more,

(c) I ^ Intensity of the 10) or (211) plane and

I 2 is the line intensity of the (101) plane or the (110) plane,

I ₂ / I i ≥0.5, l 3 / I ₂ <0.6 and the half-value width of I 1 is 0.58 or more,

I s / I 1 ≥ 0.5, I 4 / Ϊ 3 <0.6 and

If the half-width of I 1 is 0.61 or more, _{(E> I,, I 2} , I 3 and I ₄ respectively (110) plane (101) plane, a (211) plane and (301) plane or the line strength of the, 14 Roh 11 ≥ 0. 5, Is ェ 4 0.6, and the half width of I i is 0.73 or more,

(ΐ) I 1 is the line intensity of the (301) plane, 12/1 ^ 0.6 and the half-width of D 1 is 0.60 or more

(G) I 1 is (211) plane or (301) is a line intensity of and E ₂ (301) plane or (211) plane in the line strength of the surface, E ₂ E 1 ≥0. 5, I ₃ ZI _{2 and} 0.6, and the half-value width of E1 is 0.3 or more

A tin oxide thin film gas sensor element characterized in that: