Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
  • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
  • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid

Definitions

• the present invention relates to a gas sensor element provided with an oxide thin film having semiconductor characteristics.
• 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.
• 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 ⁇ 0 2 method for doping ⁇ or ⁇ the silicon substrate obtained by forming an insulating film (JP 5 7 1 7 8 4 9 JP> like proposed
• the desired effect has not been obtained because dopant atoms are difficult to dope uniformly.
• 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.
• 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 ⁇ 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,
• I! , I 2 and I 3 are the line intensities of the (110), (101) and (211) planes, respectively.
• (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 / ⁇ .5, Is / 1 2 ⁇ 0.6 and 0! Has a half width of ⁇ .3 or more
• a silicon substrate, a ceramic substrate, a glass substrate, or the like is used as a substrate of the gas sensor of the present invention.
• 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.
• 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 ⁇ 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. ⁇
• the sputtering method belonging to the VD method for example, at a substrate temperature of 0 to 500, the distance ⁇ ⁇ 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 -' ⁇ ⁇ ⁇ 1 0- 4 Bok Oxygen partial pressure in atmospheric gas: 0 to 1 X ⁇ 0 to 3 torr, applied voltage: 10 to 200 V, high frequency output: about 10 W to 10 KW
• metal tin is used as a vapor deposition material source.
• the oxygen partial pressure in the atmospheric gas 1 ⁇ ⁇ ⁇ - 5 ⁇ 1 ⁇ . ⁇ 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.
• 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.
• 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.
• 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.
• 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
• 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.
• 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.
• 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 ⁇ ⁇ ⁇ ) 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 ⁇ film layer, (7) denotes a platinum electrode.
• 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.
• 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.
• each curve shows the results for the following gases, respectively.
• Curve (G) Dry air
• Curve (E) Dry air containing 0.35% of methane
• Curve ( ⁇ ) Dry air containing 0.3% of hydrogen
• Curve (IV) 0.35% of hydrogen
• 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.
• FIGS. 4 to 3 and 25 X-ray diffraction patterns of the obtained oxide thin films are shown in FIGS. 4 to 3 and 25.
• the gas sensor element of the present invention is excellent in the ability to detect methane and hydrogen.
• 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.

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• Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)

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• 1985
  • 1985-02-20 JP JP60032228A patent/JPS61191954A/ja active Granted
• 1986
  • 1986-02-19 WO PCT/JP1986/000077 patent/WO1986004989A1/ja unknown
  • 1986-02-19 KR KR1019860700721A patent/KR940002511B1/ko not_active Expired - Fee Related
  • 1986-02-19 GB GB08624904A patent/GB2182448B/en not_active Expired
  • 1986-10-18 GB GB868625006A patent/GB8625006D0/en active Pending

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