JP2005308529A - Manufacturing method of thin-film metal oxide ion conductor used for reducing gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a metal oxide ion conductor used for a reducing gas sensor having high stability of a detection output and a simple structure, and dispensing with reference gas. <P>SOLUTION: In this manufacturing method of the thin-film metal oxide ion conductor used for the reducing gas sensor, a metal oxide thin film 2 constituting the metal oxide ion conductor is deposited by a liquid-phase deposition method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a thin metal oxide ion conductor used in a reducing gas sensor capable of selectively detecting hydrogen gas.

  An electrochemical gas sensor using a solid electrolyte as an oxide ion conductor generally has a structure in which a detection electrode and a counter electrode are integrally joined to a solid electrolyte, and since the structure is entirely made of solid, it has excellent long-term stability and room temperature. Suitable for operation at higher temperatures. Electrochemical gas sensors using such a solid electrolyte are classified into a voltage detection type and a current detection type depending on the detection method.

  The voltage detection type is also called a concentration cell type. It supplies a detection gas of unknown concentration (partial pressure) to the detection electrode fixed on one side of the solid electrolyte, and known concentration (partial pressure) to the counter electrode fixed to the other side of the solid electrolyte. When these gases are separated from each other, a concentration cell is formed. When the electromotive force is measured, the concentration (partial pressure) of the detection gas is determined according to the Nernst equation shown in Equation 1 (1). It is based on the principle of knowing.

  As a specific example, an oxygen concentration sensor that operates at 500 to 1000 ° C. using oxide oxide conductive stabilized zirconium oxide as a solid electrolyte and air as a reference gas is well known (see Patent Document 1).

  The current detection type is said to be a constant potential electrolysis type or a limit current type.When a constant voltage is applied between the detection electrode and the counter electrode so that a limit current corresponding to the concentration of the detection gas flows, The concentration of gas supplied to the detection electrode is detected by detecting the current flowing between the counter electrode and the counter electrode. As a specific example, an oxygen-containing gas having an unknown concentration is supplied to the detection electrode side of an element in which a detection electrode made of platinum is bonded to one side of stabilized zirconium oxide and a counter electrode made of platinum is bonded to the other side. When a voltage is applied, the reaction shown in the chemical formula 1 (2) and (3) occurs, and a method for detecting the oxygen concentration of the detection gas from the current flowing at that time has been proposed.

  As the solid electrolyte to be applied, it is usually necessary to select a material that can conduct ions corresponding to the detection gas species. For example, as described above, when the detection gas is oxygen, an oxygen ion conductive electrolyte is used. When the detection gas is hydrogen, hydrogen ion conductivity such as cerium barium or strontium cerate is used. The electrolyte is selected.

JP 2003-279531 A

  In the case where the detection gas is a reducing gas such as hydrogen and various hydrocarbon gases, as described above, it has conventionally been essential to use a hydrogen ion conductive solid electrolyte. These barium cerate-based or strontium cerate-based electrolytes have a drawback in that they are unstable when carbon dioxide is contained in the detection gas atmosphere.

  In addition, when the sensor is a concentration cell type, it is necessary to use a reference gas that is the same as the detection gas and has a known concentration. However, such a measure is extremely complicated and practical. Not right.

  Furthermore, because of the fact that solid electrolytes generally exhibit sufficient ionic conductivity only at high temperatures, temperature-controllable heating, such as bonding a platinum resistor to a sensor and passing a current through this part, for example. It is necessary to take measures. However, as in the conventional case, when the detection electrode and the counter electrode are joined to both sides of the solid electrolyte and the detection gas and the reference gas are isolated via the solid electrolyte, In addition to the complexity of the structure for ensuring heat resistance, there is also a problem in that there is little room for heat treatment.

  For the above reasons, for example, a solid electrolyte type sensor for reducing gas suitable for general use except for a special use such as a hydrogen sensor in molten aluminum has not been put into practical use.

  In view of the above situation, an object of the present invention is to provide a method for producing a thin-film metal oxide ion conductor used in a reducing gas sensor that has a high detection output stability, a simpler structure, and does not require a reference gas. It is to provide.

Means and effects for solving the problems

  The method for producing a thin-film metal oxide ion conductor used in the reducing gas sensor of the present invention comprises a liquid phase deposition method (LPD method: Liquid Phase Deposition Method) for forming a metal oxide thin film constituting the metal oxide ion conductor. It is characterized by being deposited by

  According to the present invention, since the metal oxide thin film is deposited by the LPD method, it is possible to provide a reducing gas sensor that has a high response speed to hydrogen gas and selectively exhibits high sensitivity to hydrogen gas.

  In the present invention, the metal oxide thin film is preferably a polyvalent metal oxide thin film.

  In the present invention, the polyvalent metal oxide thin film is a liquid containing a polyvalent metal oxide formed by adding a rare earth metal oxide and / or an alkaline earth metal oxide based on a tetravalent metal oxide. It is preferable to cause phase precipitation.

  In the present invention, the tetravalent metal is a metal selected from the group of zircon, titanium, niobium, tantalum, tungsten, and molybdenum, or an alloy of these metals, and the rare earth metal is selected from the group of yttrium, europume, and lanthanum. It is preferable that the metal or an alloy of these metals or the alkaline earth metal is a metal selected from the group of barium, calcium and strontium or an alloy of these metals.

  In the present invention, the content of the tetravalent metal is preferably about 85% to 95% and the content of the rare earth metal and / or the alkaline earth metal is preferably about 5% to 15%. .

  In the present invention, the polyvalent metal oxide thin film is preferably a yttria-stabilized zirconia thin film of about 5 mol% to 15 mol%. According to this, it can be set as the polyvalent metal oxide thin film with high electrical conductivity.

In the present invention, in the liquid phase precipitation method, it is preferable to use a reaction solution obtained by mixing a H ₂ ZrF ₆ aqueous solution, a hydrochloric acid aqueous solution containing Y ions, EDTA (ethylenediaminetetraacetic acid) and distilled water.

In the present invention, in the liquid phase precipitation method, an aqueous H ₂ ZrF ₆ solution (about 0.06 mol% / L), an aqueous hydrochloric acid solution containing Y ions (about 0.02 mol% / L, pH = about 5) and EDTA ( It is preferable to use a reaction liquid in which ethylenediaminetetraacetic acid) and distilled water are mixed at a ratio of about 10: 1: 1: 38 vol%, respectively. According to this, a thin film of yttria-stabilized zirconia can be suitably deposited.

  In the present invention, it is preferred that the yttria-stabilized zirconia film is formed by vertically suspending the substrate from the reaction solution and reacting at about 30 ° C. for about 18 hours. According to this, the amount of cracks generated in the yttria-stabilized zirconia thin film can be suppressed. Further, the film thickness of the yttria-stabilized zirconia thin film can be about 500 nm or less, preferably about 150 nm to 300 nm, and more preferably about 200 nm to 250 nm, which is suitable as a polyvalent metal oxide thin film.

  In the present invention, it is preferable that the metal oxide thin film is a deposited laminated film of ultrafine crystal yttria stabilized zirconia of about 8 nm or less by the liquid phase deposition method, and has an ultrathin film structure of about 500 nm or less. According to this, the high responsiveness selectively shown with respect to hydrogen gas can be made remarkable.

  Hereinafter, embodiments of a method for producing a thin-film metal oxide ion conductor used in a reducing gas sensor according to the present invention will be described with reference to the drawings.

  A configuration of a reducing gas sensor according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1A is a front view of the reducing gas sensor, and FIG. 1B is a back view of the reducing gas sensor. FIG. 2 is a cross-sectional view taken along line A-A ′ of FIG. FIG. 3 is a schematic view showing an apparatus of the LPD method.

  A reducing gas sensor (hereinafter referred to as a sensor) 10 includes an insulating ceramic substrate 1, a heating resistor 6 bonded to one surface of the insulating ceramic substrate 1, and a liquid phase, as shown in FIG. A metal oxide thin film 2 deposited on one surface of an insulating ceramic substrate 1 by a deposition method and constituting an oxide ion conductor, and a detection electrode 4 and a reference electrode (counter electrode) 3 respectively joined to the metal oxide thin film 2; And a gas non-permeable film 5 covering the reference electrode 3.

  The insulating ceramic substrate 1 is appropriately selected in view of electrical insulation, thermal conductivity, heat resistance, etc., but alumina or silica-alumina sintered at high density is optimal. A heating resistor 6 described later is bonded to one side of the insulating ceramic substrate 1, and after the metal oxide thin film 2 is formed on one side of the insulating ceramic substrate 1 by a liquid phase deposition method (LPD method) described later, It is cut into a size of 1.0 mm × 1.5 mm with a laser. In the present embodiment, an alumina substrate (insulating ceramic substrate) 1 having a thickness t = 0.4 mm is used in consideration of electrical insulation, thermal conductivity, heat resistance, and the like.

  The heating resistor 6 is bonded to one surface of the alumina substrate 1 (a surface opposite to a surface on which a detection electrode 4 and a reference electrode 3 described later are provided) by a known sputtering method, paste method, or the like, and heats the sensor 10. In this embodiment, platinum is used as the heating resistor 6 and is formed by a sputtering method. After the patterning of the heating resistor (platinum thin film heater) 6, the surface of the platinum thin film heater 6 is masked with an acid-resistant tape and sealed from the metal oxide thin film 2 deposited by the LPD method described later. In addition, after the acid-resistant tape is peeled off, the platinum ribbon wires 13 and 14 are connected to the platinum ribbon wire attachment portion 7 on the surface of the platinum thin film heater 6 by spot welding.

  The metal oxide thin film 2 is a thin film oxide ion conductor deposited on the alumina substrate 1 by a liquid layer deposition method (LPD method). By using the metal oxide thin film 2 as the solid electrolyte, the sensor 10 can be operated in a temperature range of about 500 ° C. or more and 600 ° C. or less that can be heated and held even with a small heater.

  Here, the LPD method used for forming the metal oxide thin film 2 will be described.

  In the LPD method, an oxide dissolved in an acidic ammonium fluoride aqueous solution or an aqueous solution in which various metal hydroxides are dissolved is used as a ceramic precipitation reaction solution. By adding boric acid or the like that forms a more stable complex as a fluoride ion eater, the equilibrium in the reaction solution is shifted to the oxide deposition side, and the substrate is immersed in this reaction solution, so that This is a method for precipitating oxide or hydroxide.

  Usually, in the LPD method, ceramics or ceramic precursors can be deposited and laminated in a temperature range of about 10 ° C. to 80 ° C., preferably in a temperature range of about 20 ° C. to 40 ° C. Even in this temperature range, the precipitated ceramic or ceramic precursor forms anatase crystals having a relative density of about 90% or more with respect to the theoretical density. Furthermore, the crystallinity can be increased by heat treatment at a high temperature. Ceramics or ceramic precursors by the LPD method can have a relative density of about 90% or more at the stage of deposition and lamination, so that they hardly shrink even when fired at a high temperature. In particular, the metal oxide thin film 2 is a deposited laminated film of ultrafine crystal yttria stabilized zirconia of about 8 nm or less that is selective to reducing gas, and is about 500 nm or less, preferably about 150 nm to 300 nm, Preferably, a metal oxide ion conductor ultrathin film structure capable of selectively detecting hydrogen gas can be formed as an ultrathin film structure of approximately 200 nm to 250 nm.

  The ceramic thin film deposited by the LPD method can be made into a fine microstructure with high adhesion to the substrate surface, and the metal oxide ion conductor of a reducing gas sensor with a nano-order controlled microstructure can be easily obtained. Can be obtained. By controlling the microstructure, it is possible to obtain a reducing gas sensor having a high sensitivity and a fast response speed in a low concentration region of the reducing gas. Since the metal oxide ion conductor film by the LPD method can obtain a large number of highly uniform thin films, it is excellent in productivity, and a highly sensitive reducing gas sensor can be manufactured at low cost. In particular, the microstructure of ultrafine crystal yttria-stabilized zirconia is almost insensitive to carbon monoxide, isobutane and methane, which have been treated as interfering gases, and acts selectively on hydrogen gas, on the order of about 10 ppm. Hydrogen gas can be detected.

The metal oxide thin film 2 is deposited on the alumina substrate 1 by this LPD method. The metal oxide thin film 2 is preferably a polyvalent metal oxide thin film, and the polyvalent metal oxide thin film is a metal selected from the group consisting of zircon, titanium, niobium, tantalum, tungsten, and molybdenum, or an alloy of these metals. Using a tetravalent metal oxide as a base material, a rare earth metal oxide and / or an alkaline earth metal oxide is added to cause liquid phase precipitation. As the rare earth metal, a metal selected from the group of yttrium, europume and lanthanum or an alloy thereof, and as the alkaline earth metal, a metal selected from the group of barium, calcium and strontium or an alloy of these metals. Are preferably used. The ratio of the tetravalent metal to the metal to be added is preferably about 85% to 95% for the tetravalent metal and about 5% to 15% for the metal to be added. In this embodiment, among the yttria-stabilized zirconia (Y ₂ O ₃ —ZrO ₂ , hereinafter referred to as YSZ) thin film which is a polyvalent metal oxide thin film, a deposited laminated film of ultrafine crystal YSZ having a thickness of about 8 nm or less is used as the metal oxide. Used as the thin film 2, an ultra-thin film structure having a thickness of about 500 nm or less, preferably about 150 nm to 300 nm, more preferably about 200 nm to 250 nm. This YSZ is formed by adding an oxide of yttrium, which is a rare earth metal, based on an oxide of zircon. Moreover, it is preferable that YSZ is about 5 mol% or more and 15 mol% or less.

The YSZ thin film is deposited using the LPD method apparatus 21 shown in FIG. Specifically, an aqueous H ₂ ZrF ₆ solution (about 0.06 mol% / L) sucked up by the pump 24, an aqueous hydrochloric acid solution containing about Y ions (about 0.02 mol% / L, pH = about 5), and EDTA (ethylenediamine four _{acetate: Ethylen Diamine tetraacetic acid (C 10} H 14 O 8 N 2 Na · 2H 2 O)) and distilled water are about 10: 1: 1: 38vol% of YSZ deposition reaction mixture 26 obtained by mixing aluminum through the pipe 25 The plate is poured into the container 23 installed along the inner wall to make the processing liquid 22, and the alumina substrate 1 attached to the substrate holding metal fitting 29 of the vertical transport mechanism 27 is vertically suspended and quickly immersed in the container 23, about 30 YSZ is about 500 nm or less, preferably about 150 nm or more and 300 nm or less, more preferably about 200 nm or more and 250 nm or less over about 18 hours at ° C. To be deposited and formed by a body. FIG. 4 is a SEM photograph of a cross section of an 8 mol% YSZ thin film deposited and formed on the alumina substrate 1. FIG. 5 is an SEM photograph of the surface of an 8 mol% YSZ thin film deposited and formed on the alumina substrate 1. After forming the YSZ thin film, the alumina substrate 1 on which the YSZ thin film is deposited is baked in an electric furnace at about 1000 ° C. for about 2 hours. In the aqueous hydrochloric acid solution containing Y ions, about 0.01 mol% / L of Y ₂ O ₃ is added to the aqueous hydrochloric acid solution, and while stirring, wait until Y ₂ O ₃ is completely dissolved, and then the pH is about 5. Prepare by adding hydrochloric acid. Note that the longer the film formation time, the thicker the film thickness. As a result, cracks on the thin film as shown in FIG. 5 become obvious, and even when the film thickness is changed, a significant difference in the sensitivity of hydrogen gas is recognized. Therefore, it is preferable to set the film formation time to about 18 hours. Moreover, if the firing temperature is about 600 ° C. or higher, a solid electrolyte having sufficient conductivity can be obtained. The temperature for baking a gold electrode described later is about 900 ° C., and the temperature for firing a glass-like material described later is also set. Since it is about 950 ° C., it is preferable to bake at about 1000 ° C. in the previous stage of these processes.

  The detection electrode 4 and the reference electrode 3 are joined on the metal oxide thin film (YSZ thin film) 2 so as to be isolated from each other. Both electrodes are made of a noble metal selected from the group consisting of platinum, palladium, rhodium, ruthenium and gold or an alloy of these noble metals. Further, both electrodes are joined by a known method such as a sputtering method or a paste method. In the present embodiment, gold electrodes are used as the detection electrode 4 and the reference electrode 3. Further, after the alumina substrate 1 is cut to the size of the sensor chip, a gold wire having a diameter of 50 μm is fixed to the detection electrode 4 and the reference electrode 3 with gold paste as the lead wires 11 and 12 to the detection electrode 4 and the reference electrode 3. . After the lead wires 11 and 12 are connected, baking is performed at about 900 ° C. for about 30 minutes, and both the electrodes 3 and 4 and the lead wires 11 and 12 are fixed to the YSZ thin film 2.

  As the gas impermeable film 5, a glassy material that melts by heating is preferably used, and the reference electrode 3 is covered to make the gas impermeable. Thereby, the hydrogen concentration of the reference electrode 3 can be regarded as zero. The glassy material can be covered by commercially available materials. After application of the gas impermeable film (glass-like material) 5, baking is performed at about 950 ° C. for about 30 minutes, and the glass-like material 5 is completely melted to cover the reference electrode 3 to form the YSZ thin film 2 without gaps. Stick.

  In addition, the reducing gas sensor which concerns on the manufacturing method of the thin metal oxide ion conductor used for the reducing gas sensor of this embodiment is not limited to the structure of the sensor 10 mentioned above.

  In the above configuration, the manufacturing method of the reducing gas sensor will be described with reference to FIGS. 1 and 3 to 6 to describe the manufacturing method of the metal oxide ion conductor. FIG. 6 is a flowchart for creating a reducing gas sensor.

  First, in step 1 (S1) of FIG. 6, the surface of the alumina substrate 1 is polished. By this polishing, the YSZ thin film 2 grows and deposits uniformly on the surface of the alumina substrate 1. Next, the alumina substrate 1 is ultrasonically cleaned in acetone for about 15 minutes, then baked at about 900 ° C. for about 2 hours, and further ultrasonically cleaned in acetone for about 15 minutes.

  Next, in step 2 (S2), a platinum thin film heater 6 as shown in FIG. 1B is formed on one surface of the alumina substrate 1 by sputtering.

  Next, in step 3 (S3), the alumina substrate 1 is washed with alkali. Here, degreasing is performed by immersing the alumina substrate 1 in an alkaline treatment liquid obtained by diluting about 48% hydrofluoric acid about 10 times. Thereafter, at least the platinum ribbon wire attachment portion 7 on the surface of the platinum thin film heater 6 is masked with an acid resistant tape.

  Next, in step 4 (S4), the YSZ thin film 2 is deposited on the surface of the alumina substrate 1 by the LPD method. Specifically, using the apparatus 21 of the LPD deposition method shown in FIG. 3, the YSZ deposition reaction liquid 26 is poured into a container 23 in which an aluminum plate is installed along the inner wall to form a treatment liquid 22, and the alumina substrate 1 is suspended vertically. 4 and 5 on the opposite side of the surface of the alumina substrate 1 to which the platinum thin film heater 6 is bonded. The thin film 2 is deposited and deposited with a thickness of about 500 nm or less, preferably about 150 nm to 300 nm, more preferably about 200 nm to 250 nm. YSZ is preferably used at a concentration of about 5 mol% to 15 mol%. Then remove the acid-resistant tape.

  Next, in step 5 (S5), the alumina substrate 1 on which the YSZ thin film 2 is formed is heated at about 1000 ° C. for about 2 hours, and the YSZ thin film 2 is fired.

  Next, in step 6 (S6), the alumina substrate 1 is cut into a sensor chip having a size of 1.0 mm × 1.5 mm using a laser or the like.

  Next, in step 7 (S7), as shown in FIG. 2A, the YSZ film is formed on the surface opposite to the surface to which the platinum thin film heater 6 is bonded by the known sputtering method, paste method, or the like. On the thin film 2, the detection electrode 4 and the reference electrode 3 which are gold electrodes are isolated and joined. Then, the lead wires 11 and 12 are bonded to the reference electrode 3 and the detection electrode 4 with gold paste, respectively. After that, baking is performed at about 900 ° C. for about 30 minutes to fix the detection electrode 4 and the reference electrode 3 to the YSZ thin film 2 and harden the gold paste, so that the lead wires 11 and 12 are respectively connected to the reference electrode 3 and the detection electrode. 4 is fixed.

  Next, in step 8 (S8), the glassy material 5 is applied to the reference electrode 3 to cover the reference electrode 3. Thereafter, baking is performed at about 950 ° C. for about 30 minutes to completely melt the glassy material 5, and the YSZ thin film is fixed and cured without any gap.

  Next, in step 9 (S9), in FIG. 1 (b), the platinum ribbon wires 13 and 14 are spot welded to the platinum ribbon wire attachment portion 7 on the surface of the platinum thin film heater 6. Thereby, the sensor 10 is completed.

  Next, the operation of the reducing gas sensor using the oxide ion conductor in the above configuration will be described with reference to FIG. FIG. 7 is a functional diagram of the sensor 10.

  The sensor 10 of this embodiment is a voltage detection type that measures the voltage (potential difference) between a detection electrode and a reference electrode. In FIG. 7, a current is supplied to the platinum thin film heater 6 from an external power source via an input / output pin, the temperature of the YSZ thin film 2 that is an oxide ion conductor is maintained at about 600 ° C., and hydrogen gas is detected. The sensor 10 is installed in

  Strictly speaking, the sensor 10 according to the present embodiment is not a concentration cell type. Therefore, as one estimate, when the sensor 10 comes into contact with hydrogen gas, the detection electrode 4 becomes hydrogen based on the equilibrium reaction of the chemical formula (4). Since the equilibrium potential according to the concentration is obtained and the surface of the reference electrode 3 is in a form in which oxygen is adsorbed (Au (O)), the reference electrode 3 has an equilibrium potential due to the equilibrium reaction of Formula 2 (5). It is considered that the difference between the equilibrium potentials of both electrodes is detected as a voltage.

  When a voltage is generated between the detection electrode 4 and the reference electrode 3, the sensor 10 detects hydrogen gas.

  Next, in order to confirm the effect of the sensor in this embodiment, the following test was performed. The sensor using the YSZ thin film of this embodiment and the sensor using the thick YSZ formed by processing bulk crystal ceramics into pellets by mechanical polishing are prepared, and current is supplied from an external power source to the platinum thin film heaters of both sensors. Then, the temperature of the YSZ thin film or pellet-like YSZ was maintained at about 600 ° C., both sensors were installed in atmospheres of various gas types and concentrations, and the voltage (potential difference) between the detection electrode and the reference electrode was measured. However, the characteristics shown in FIGS. 8 and 9 were obtained. Here, FIG. 8 is a graph showing sensitivity characteristics of the sensor with respect to various gases. The vertical axis represents the sensor output change amount related to the detection electrode-reference electrode voltage, and the horizontal axis represents the logarithm of the gas concentration. FIG. 9 is a graph showing the response characteristics of the sensor to hydrogen gas. The vertical axis represents the sensor output change amount related to the detection electrode-reference electrode voltage, and the horizontal axis represents time (seconds). That is, in FIG. 8, for various reducing gases (hydrogen, carbon monoxide, isobutane, methane), from the relationship between the logarithm of gas concentration (ppm) and the sensor output variation, the pellet shown in FIG. When the characteristics of the sensor using the YSZ in the shape of the sensor and the characteristics of the sensor using the YSZ thin film of this embodiment shown in FIG. 8B are compared, the ultrafine crystal yttria stabilized zirconia of about 8 nm or less A sensor using a YSZ thin film having a super thin film structure of about 500 nm or less, preferably about 150 nm or more and 300 nm or less, more preferably about 200 nm or more and 250 nm or less is more selective to hydrogen gas. It was proved to show high sensitivity. Further, comparing the characteristics of the sensor using the pellet-shaped YSZ shown in FIG. 9A with the characteristics of the sensor using the YSZ thin film of this embodiment shown in FIG. The following is a deposited multilayer film of ultrafine crystal yttria stabilized zirconia, which is a YSZ thin film having an ultrathin structure of about 500 nm or less, preferably about 150 nm to 300 nm, more preferably about 200 nm to 250 nm. It was found that the response speed to hydrogen gas was faster.

  As described above, the method for producing a thin film metal oxide ion conductor used in the reducing gas sensor of the present embodiment deposits a metal oxide thin film by the LPD method, so that the response speed to hydrogen gas is high. A reducing gas sensor that is fast and selectively shows high sensitivity to hydrogen gas can be obtained. Further, the metal oxide thin film is a polyvalent metal oxide obtained by adding a rare earth metal oxide and / or an alkaline earth metal oxide based on a tetravalent metal oxide such as an yttria-stabilized zirconia thin film. Therefore, the electrical conductivity can be increased. Moreover, the manufacturing method of the thin-film-shaped metal oxide ion conductor used for the reducing gas sensor of this embodiment uses a reducing gas sensor in a temperature range of about 500 ° C. or more and 600 ° C. or less that can be heated and held with a small heater. Since a metal oxide ion conductor that can be operated is provided, a practical reducing gas sensor can be provided.

  Ensuring the safety of hydrogen production, transportation, storage, and filling is indispensable for the practical application of energy systems using fuel cells that use hydrogen energy, and the industrial value of sensors that detect hydrogen is great. The industrial value of the method for producing a thin-film metal oxide ion conductor used in a reducing gas sensor is also great.

(A) is a front view of the reducing gas sensor which uses the yttria stabilized zirconia thin film which concerns on the example of embodiment of this invention, (b) is a back view. It is A-A 'line sectional drawing of Fig.1 (a). It is the schematic diagram which showed the apparatus of the LPD method. It is a SEM photograph of the section of 8 mol% yttria stabilized zirconia thin film deposited by the LPD method. It is a SEM photograph of the surface of 8 mol% yttria stabilized zirconia thin film deposited by LPD method. It is a preparation flowchart of the reducible gas sensor using the yttria stabilized zirconia thin film concerning the example of an embodiment of the present invention. It is a functional diagram of a reducing gas sensor using a yttria-stabilized zirconia thin film according to an embodiment of the present invention. (A) is a graph which shows the sensitivity characteristic with respect to various gas of the reducing gas sensor which uses the pellet-form yttria stabilization zirconia, (b) is the reduction | restoration which uses the yttria stabilization zirconia thin film which concerns on the embodiment of this invention. It is a graph which shows the sensitivity characteristic with respect to various gas of a property gas sensor. (A) is a graph which shows the response characteristic with respect to the hydrogen gas of the reducing gas sensor using a pellet-form yttria stabilized zirconia, (b) is a reduction | restoration using the yttria stabilized zirconia thin film which concerns on the embodiment of this invention. It is a graph which shows the response characteristic with respect to hydrogen gas of a property gas sensor.

Explanation of symbols

1 Insulating ceramic substrate (alumina substrate)
2 Metal oxide thin film (YSZ thin film)
3 Reference electrode 4 Detection electrode 5 Gas impermeable film (glassy material)
6 Heating resistor (platinum thin film heater)
7 Platinum ribbon wire mounting part 10 Reducing gas sensor (sensor)
11 and 12 Lead wires 13 and 14 Platinum ribbon wire 21 Manufacturing apparatus 22 Treatment liquid 23 Container 24 Pump 25 Piping 26 YSZ precipitation reaction liquid 27 Vertical transport mechanism 29 Substrate holding bracket

Claims (10)

  A method for producing a thin-film metal oxide ion conductor for use in a reducing gas sensor, wherein a metal oxide thin film constituting a metal oxide ion conductor is deposited by a liquid phase deposition method.   The method for producing a thin metal oxide ion conductor used in the reducing gas sensor according to claim 1, wherein the metal oxide thin film is a polyvalent metal oxide thin film.   The polyvalent metal oxide thin film is formed by liquid phase deposition of a polyvalent metal oxide obtained by adding a rare earth metal oxide and / or an alkaline earth metal oxide based on a tetravalent metal oxide. A method for producing a thin-film metal oxide ion conductor used in the reducing gas sensor according to claim 2.   The tetravalent metal is a metal selected from the group of zircon, titanium, niobium, tantalum, tungsten, molybdenum, or an alloy of these metals, and the rare earth metal is a metal selected from the group of yttrium, europume, lanthanum, or of these metals. 4. A thin-film metal oxide ion conductor used in a reducing gas sensor according to claim 3, wherein the alloy, the alkaline earth metal is a metal selected from the group of barium, calcium and strontium, or an alloy of these metals. Manufacturing method.   The reducibility according to claim 3 or 4, wherein the content of the tetravalent metal is about 85% to 95%, and the content of the rare earth metal and / or the alkaline earth metal is about 5% to 15%. A method for producing a thin-film metal oxide ion conductor used in a gas sensor.   6. A thin metal oxide ion conductor for use in a reducing gas sensor according to claim 2, wherein the polyvalent metal oxide thin film is a yttria-stabilized zirconia thin film of about 5 mol% to 15 mol%. Manufacturing method. The thin film used for the reducing gas sensor according to claim 6, wherein in the liquid phase deposition method, a H ₂ ZrF ₆ aqueous solution, a hydrochloric acid aqueous solution containing Y ions, and a reaction liquid obtained by mixing EDTA (ethylenediaminetetraacetic acid) and distilled water are used. For producing a metal oxide ion conductor in the form of a metal. In the liquid phase precipitation method, an aqueous H ₂ ZrF ₆ solution (about 0.06 mol% / L), an aqueous hydrochloric acid solution containing Y ions (about 0.02 mol% / L, pH = about 5), EDTA (ethylenediaminetetraacetic acid) and The method for producing a thin-film metal oxide ion conductor for use in a reducing gas sensor according to claim 7, wherein a reaction liquid in which distilled water is mixed at a ratio of about 10: 1: 1: 38 vol% is used.   The thin-film metal oxide ion conduction used in the reducing gas sensor according to claim 8, wherein the yttria-stabilized zirconia film is formed by vertically suspending the substrate from the reaction solution and reacting at about 30 ° C. for about 18 hours. Body manufacturing method.   10. The metal oxide thin film is a deposited laminated film of ultrafine crystal yttria stabilized zirconia of about 8 nm or less by the liquid phase deposition method, and forms an ultrathin film structure of about 500 nm or less. Of thin film metal oxide ion conductor for use in a reducing gas sensor.