JP2018036062A - Gas detection element and gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detection element which is joined to a wiring more strongly and can stably detect a detection target gas.SOLUTION: The gas detection element includes: a gas sensing layer 107b having electric characteristics which vary by contacting with a detection target gas; an electrode 107a connected to the gas sensing layer; and sensing electrode layers 108 and 109 on the surface of the electrode, to which the wiring is connected.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a gas detection element and a gas detection device.

  Conventionally, a gas detection element that detects fuel gas, carbon monoxide gas generated by incomplete combustion of the fuel gas, and the like is known. As such a gas detection element, a detection element having a gas sensitive part whose resistance value changes according to the concentration of the detection target gas is known (see, for example, Patent Document 1).

  In the detection element according to Patent Document 1, the concentration of the detection target gas can be measured based on a change in the resistance value of the gas sensitive part obtained by applying a voltage to a pair of electrodes connected to the gas sensitive part. .

JP-A-10-197470

  In the sensing element according to Patent Document 1, a voltage is applied to the gas sensitive part through wiring connected to the electrode. Here, if the bonding strength between the electrode and the wiring is low, the bonding interface between the electrode and the wiring is peeled off due to a minute impact, vibration, etc., and the resistance value of the gas sensitive part fluctuates and the measurement accuracy of the gas concentration decreases. there is a possibility. Further, there is a possibility that the electrode and the wiring are completely separated and disconnected, and the detection target gas cannot be detected.

  The present invention has been made in view of the above, and an object of the present invention is to provide a gas detection element capable of detecting a detection target gas stably by improving the bonding strength with a wiring.

  According to the gas detection element of one aspect of the present invention, the gas detection layer is formed on the surface of the gas sensing layer whose electrical characteristics change by contact with the detection target gas, the electrode connected to the gas sensing layer, and the electrode. And a sensing electrode layer to which the wiring is bonded.

  According to the embodiment of the present invention, a gas detection element capable of detecting a detection target gas stably by improving the bonding strength with a wiring is provided.

It is a figure which illustrates schematic structure of the gas detection apparatus in embodiment. It is a section schematic diagram of a gas sensor in an embodiment. It is a section schematic diagram of a gas detection element in an embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

  FIG. 1 is a diagram illustrating a configuration of a gas detection device 100 according to the embodiment.

  As shown in FIG. 1, the gas detection device 100 includes a gas sensor 1, a control unit 2, and an alarm device 3.

  The gas sensor 1 includes a gas detection element 10 and detects a detection target gas. The detection target gas is, for example, fuel gas (main component is methane), carbon monoxide gas, hydrogen gas, or the like generated when the fuel gas is incompletely burned.

  The control unit 2 includes a drive unit 21 and a detection unit 22 and is connected to the gas sensor 1. The function of each unit included in the control unit 2 is realized by, for example, a program that the CPU reads from the ROM and executes in cooperation with the RAM, a plurality of circuits, and the like.

  The drive unit 21 heats the gas sensing layer by energizing the heater layer of the gas sensing element 10 to generate heat, and the gas sensing element 10 can detect the detection target gas based on a change in electrical characteristics of the gas sensing layer. Drive.

  The detection unit 22 detects a change in electrical characteristics of the gas sensing layer of the gas detection element 10 and detects the concentration of the detection target gas in the ambient atmosphere of the gas sensor 1. More specifically, the detection unit 22 detects the concentration of the detection target gas based on the resistance value of the gas sensing layer of the gas detection element 10. The detection unit 22 transmits a detection signal to the alarm device 3 when the concentration of the detection target gas is equal to or higher than a predetermined value.

  The alarm device 3 is connected to the control unit 2, and notifies that the detection target gas has been detected by emitting a sound or turning on a lamp when a detection signal is received from the detection unit 22.

  In addition, the gas detection apparatus 100 may be provided with an operation input unit that performs an operation input, a display unit that displays a detection result by the detection unit 22 of the control unit 2, and the like.

  FIG. 2 is a schematic cross-sectional view of the gas sensor 1 according to the embodiment.

  As shown in FIG. 2, the gas sensor 1 includes a gas detection element 10, a case 12, a filter body 18, and lead terminals 19. In the following description, the opening 13 side of the case 12 in the gas sensor 1 is described as the upper side, and the lead terminal 19 side is the lower side, but the mounting posture of the gas sensor 1 is not limited.

  The gas detection element 10 is fixed to the upper surface of a stepped disk-shaped sensor base 11. The configuration of the gas detection element 10 will be described later. The lead terminal 19 is provided so as to protrude downward from the sensor base 11, and its upper end is connected to the gas detection element 10 by a wiring (not shown). By joining the lead terminal 19 to the printed circuit board on which the control unit 2 is provided, the gas detection element 10 of the gas sensor 1 and the drive unit 21 and the detection unit 22 of the control unit 2 are connected.

  The case 12 is formed in a cylindrical shape, and the lower end side is fixed to the periphery of the sensor base 11 and covers the periphery of the gas detection element 10. An opening 13 through which gas flows is formed in the upper wall of the case 12.

  The first mesh 15 is attached to the inside of the case 12 so as to close the opening 13. The second mesh 16 is attached to the inside of the case 12 with a predetermined interval below the first mesh 15. The third mesh 17 is attached to the inside of the case 20 with a predetermined interval below the second mesh 16. The third mesh 17 is a double mesh for explosion protection.

  Each of the first mesh 15, the second mesh 16, and the third mesh 17 is a stainless steel net, and functions as a presser for the first filter 18a and the second filter 18b. The second mesh 16 functions as a partition between the first filter 18a and the second filter 18b.

  The filter body 18 is provided between the opening 13 of the case 12 and the gas detection element 10. The filter body 18 allows the detection target gas flowing from the opening 13 to pass to the gas detection element 10 side, and adsorbs the non-detection target gas. The filter body 18 includes a first filter 18a and a second filter 18b.

  The first filter 18a is provided between the first mesh 15 and the second mesh 16, and allows the detection target gas flowing from the opening 13 to pass therethrough and adsorbs the non-detection target gas. The first filter 18a has a filter case (not shown) in which an infinite number of air holes are formed, and granular (powder, spherical, crushed) activated carbon filled in the filter case as an adsorbent.

  The second filter 18b is provided between the second mesh 16 and the third mesh 17 so as to be stacked below the first filter 18a. The second filter 18b passes the detection target gas flowing from the opening 13 and adsorbs the non-detection target gas that has passed through the first filter 18a. The second filter 18b has a filter case (not shown) in which an infinite number of air holes are formed, and granular (powder, spherical, crushed) activated carbon filled in the filter case as an adsorbent.

  The activated carbon provided as an adsorbent in the first filter 18a and the second filter 18b performs physical adsorption by van der Waals force in the gas phase. Activated carbon adsorbs non-detection target gases such as alcohol vapor, siloxane compounds, SOx, NOx, VOCs, etc., and detection targets such as methane, propane, butane, carbon monoxide, and hydrogen, which are the main components of fuel gas Gas does not adsorb.

  For this reason, most of the non-detection target gas that has flowed into the case 12 from the opening 13 is adsorbed by the first filter 18 a and the second filter 18 b and reaches the gas detection element 10 in a very small amount. In addition, the detection target gas that has flowed into the case 12 through the opening 13 is adsorbed by the first filter 18a and the second filter 18b, but most of the detection target gas passes through the first filter 18a and the second filter 18b. The gas detection element 10 is reached.

  As described above, in the gas sensor 1, the first filter 18a and the second filter 18b remove the non-detection target gas, so that the gas detection element 10 can detect the detection target gas with high accuracy.

  In addition, in the gas sensor 1 in this embodiment, the filter body 18 is comprised by two filters, the 1st filter 18a and the 2nd filter 18b, However, You may be comprised by 1 or 3 or more filters. Further, the adsorbent for the first filter 18a and the second filter 18b is not limited to activated carbon, and may be silica gel, for example. Further, different adsorbents may be used for the first filter 18a and the second filter 18b, respectively.

  FIG. 3 is a schematic cross-sectional view of the gas detection element 10 in the embodiment.

  As shown in FIG. 3, the gas detection element 10 includes a silicon substrate 101, a thermal insulation support layer 102, a heater layer 103, an electrical insulation layer 106, and a gas detection unit 107. Note that the size and thickness of each part of the gas detection element 10 shown in FIG. 3 are appropriately changed for the sake of explanation.

  In the silicon substrate 101, a through hole 101 a is formed in a portion corresponding to the gas detection unit 107.

The heat insulating support layer 102 is formed on the upper surface of the silicon substrate 101 so as to cover the through hole 101a of the silicon substrate 101 and to have a diaphragm structure. The thermally insulating support layer 102 has a three-layer structure of a thermally oxidized SiO ₂ layer 102a, a CVD-Si ₃ N ₄ layer 102b, and a CVD-SiO ₂ layer 102c.

The thermally oxidized SiO ₂ layer 102a is a heat insulating layer. The thermal oxide SiO ₂ layer 102 a makes it difficult for heat generated in the heater layer 103 to be transmitted to the silicon substrate 101. Further, the thermally oxidized SiO ₂ layer 102a exhibits high resistance to plasma etching, and facilitates formation of the through hole 101a of the silicon substrate 101 by plasma etching.

The CVD-Si ₃ N ₄ layer 102b is stacked on the upper surface side of the thermally oxidized SiO ₂ layer 102a. The CVD-SiO ₂ layer 102c is an electrically insulating layer and is laminated on the upper surface side of the CVD-Si ₃ N ₄ layer 102b.

The heater layer 103 is a Ta / PtW / Ta film, and is formed by continuously forming a Ta film, a PtW film, and a Ta film in this order on the upper surface of the CVD-SiO ₂ layer 102c by sputtering.

  On the surface of the heater layer 103, a heater electrode layer 105 to which wiring is bonded is formed. For example, wires are bonded to the heater electrode layer 105 by wire bonding. A heater intermediate layer 104 that joins the heater layer 103 and the heater electrode layer 105 is formed between the heater layer 103 and the heater electrode layer 105.

  The heater layer 103 is connected to the drive unit 21 of the control unit 2 through the wiring joined to the heater electrode layer 105, the lead terminal 19 and the like, and heats the gas detection unit 107 when energized from the drive unit 21 to generate heat.

The electrical insulating layer 106 is, for example, a SiO ₂ film, and is formed on the upper surface of the thermal insulating support layer 102 so as to cover the heater layer 103, the heater intermediate layer 104, and the heater electrode layer 105. In the electrical insulating layer 106, an opening 106a is formed at a joint portion between the wiring and the heater electrode layer 105, for example, by photolithography.

  The gas detection unit 107 includes a pair of electrodes 107a, a gas sensing layer 107b, and a gas selective combustion layer 107c.

  The electrode 107a is a Ta / Pt film, and is formed by continuously forming a Ta film and a Pt film in this order on the upper surface of the electrical insulating layer 106 by sputtering. The bonding strength between the Pt film and the electrical insulating layer 106 is increased by the Ta film.

  A sensing electrode layer 109 to which the wiring is bonded is formed on the surface of the electrode 107a. For example, wiring is bonded to the sensing electrode layer 109 by wire bonding. A sensing intermediate layer 108 that joins the electrode 107 a and the sensing electrode layer 109 is formed between the electrode 107 a and the sensing electrode layer 109. The electrode 107 a is connected to the detection unit 22 of the control unit 2 through a wiring joined to the sensing electrode layer 109, the lead terminal 19, and the like.

The gas sensing layer 107b is formed on the upper surface of the electrical insulating layer 106 so as to cover at least a part of each electrode 107a. The gas sensing layer 107b is formed, for example, using a metal oxide such as SnO ₂ , In ₂ O ₃ , WO ₃ , ZnO, or TiO ₂ as a main component.

The gas selective combustion layer 107c is a sintered body supporting at least one kind of catalyst such as Pd, PdO, or Pt. The gas selective combustion layer 107c is, for example, a catalyst-supported Al ₂ O ₃ sintered body, and is formed so as to cover the gas sensing layer 107b.

The gas selective combustion layer 107c can oxidize and remove the detection target gas by accelerating the combustion reaction of the reducing non-detection target gas having a higher oxidation activity than the detection target gas. The concentration of the detection target gas that reaches the gas sensing layer 107b is increased by the gas selective combustion layer 107c, and the detection target gas can be detected with higher sensitivity. Note that the gas selective combustion layer 107c may be formed using, for example, a metal oxide such as Cr ₂ O ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , ZrO ₂ , SiO ₂ , or zeolite as a main component.

The gas sensing layer 107b is, for example, an SnO ₂ layer of an n-type metal oxide semiconductor and adsorbs oxygen on the surface. Oxygen has a strong electron-accepting property and adsorbs negative charges, so when oxygen is adsorbed on the surface of the gas sensing layer 107b, it takes in electrons from the gas sensing layer 107b. For this reason, when oxygen is adsorbed on the surface of the gas sensing layer 107b, the internal electron density decreases, the conductivity decreases, and the resistance increases.

When the gas sensing layer 107b to which oxygen is adsorbed is heated to about 300 ° C. to 500 ° C. by the heater layer 103, a combustion reaction such as CH ₄ , H ₂ , and CO of the detection target gas occurs. By the combustion reaction of these combustible gases, oxygen (O ²⁻ ) adsorbed on the surface of the gas sensing layer 107b is consumed, and the adsorbed oxygen electrons trapped in the adsorbed oxygen become free electrons in the gas sensing layer 107b. Returned to For this reason, the gas sensing layer 107b increases in internal electron density, increases in conductivity, and decreases in resistance.

The combustion reaction formula of the detection target gas (CH ₄ , H ₂ , CO) is as follows.

CH ₄ + 4O ²⁻ (ad) ⇒CO ₂ + 2H ₂ O + 8e
H ₂ + O ²⁻ (ad) ⇒H ₂ O + 2e
CO + O ²⁻ (ad) ⇒CO ₂ + 2e
The drive unit 21 of the gas detection device 100 heats the gas sensing layer 107b at a predetermined cycle by energizing the heater layer 103 intermittently through the wiring joined to the heater electrode layer 105. The detection unit 22 detects a resistance value as an electrical characteristic of the gas sensing layer 107b through a wiring joined to the sensing electrode layer 109, and obtains the concentration of the detection target gas based on the detected resistance value.

The gas selective combustion layer 107c covers the gas sensing layer 107b and is heated by the heater layer 103 to burn the non-detection target gas, thereby increasing the concentration of the detection target gas reaching the gas sensing layer 107b. The gas selective combustion layer 107c selectively burns a high-boiling point hydrocarbon gas, a non-detection target gas such as ethanol or VOC, and allows a detection target gas such as CH _{4 to} pass therethrough.

  In the gas sensor 1 according to the present embodiment, as described above, the non-detection target gas is adsorbed and removed by the filter body 18, but the non-detection target gas that has passed through the filter body 18 is burned in the gas selective combustion layer 107c. For this reason, in the gas sensor 1, the non-detection target gas reaching the gas sensing layer 107b of the gas detection element 10 is reduced, and the detection target gas can be detected with high accuracy.

  Moreover, in the gas detection element 10 in this embodiment, the heater electrode layer 105 to which wiring is joined is formed on the surface of the heater layer 103. In addition, a sensing electrode layer 109 is formed on the surface of the electrode 107a to which wiring is bonded. The heater electrode layer 105 and the sensing electrode layer 109 to which the wiring is joined are preferably formed of a material capable of forming an alloy with the wiring material, for example. For example, when the wiring material is Au, an Au film, a Pt film, an Au alloy film, or the like is formed as the heater electrode layer 105 and the sensing electrode layer 109. When the wiring material is Cu, a Cu film, a Cu alloy film, or the like is formed as the heater electrode layer 105 and the sensing electrode layer 109. When the wiring material is Al, an Al film, an AlSi film, an Al alloy film, or the like is formed as the heater electrode layer 105 and the sensing electrode layer 109. For the heater electrode layer 105, the sensing electrode layer 109, and the wiring material, it is preferable to use Au having high bonding strength and thermal conductivity. Moreover, cost can be reduced by using Cu.

  The heater intermediate layer 104 and the sensing intermediate layer 108 are, for example, a Ti film, a Cr film, a Ni film, a Ta film, or the like. The heater layer 103 and the heater electrode layer 105 are joined by the heater intermediate layer 104. Similarly, the electrode 107 a and the sensing electrode layer 109 are joined by the sensing intermediate layer 108.

  In the gas detection element 10 in the present embodiment, the heater layer 103 and the wiring are connected via the heater electrode layer 105 as described above. Further, the electrode 107 a and the wiring are connected through the sensing electrode layer 109. By forming the heater electrode layer 105 and the sensing electrode layer 109 using a material having higher bonding strength to the wiring than the heater layer 103 and the electrode 107a, respectively, the connection reliability between the wiring and the heater layer 103 and the electrode 107a is achieved. Can be increased.

  For this reason, separation or disconnection between the wiring and the heater electrode layer 105 due to impact or vibration is reduced, and the gas sensing layer 107b can be heated to a desired temperature by energizing the heater layer 103 stably. Similarly, the separation and disconnection between the wiring and the sensing electrode layer 109 can be reduced, and the concentration of the detection target gas can be detected stably and with high accuracy based on the detection result of the resistance change in the gas sensing layer 107b. Is possible.

  As described above, according to the gas detection element 10 in the present embodiment, the bonding strength with the wiring is improved, and the detection target gas can be stably detected.

  Although the gas detection element and the gas detection device according to the embodiments have been described above, the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made within the scope of the present invention.

  For example, the heater intermediate layer 104 and the heater electrode layer 105 do not have to be provided on the entire upper surface of the heater layer 103, and may be partially formed as electrode pads at the junction with the wiring. Similarly, the sensing intermediate layer 108 and the sensing electrode layer 109 may not be provided on the entire upper surface of the electrode 107a, and may be partially formed as an electrode pad at a junction with the wiring.

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Control part 10 Gas detection element 21 Drive part 22 Detection part 100 Gas detection apparatus 103 Heater layer 104 Heater intermediate layer 105 Heater electrode layer 107 Gas detection part 107a Electrode 107b Gas sensing layer 107c Gas selective combustion layer 108 Sensing intermediate layer 109 Sensing electrode layer

Claims (4)

A gas sensing layer whose electrical characteristics change upon contact with the gas to be detected;
An electrode connected to the gas sensing layer;
And a sensing electrode layer formed on a surface of the electrode to which wiring is joined. A heater layer that heats the gas sensing layer so that the detection target gas can be selectively detected;
The gas detection element according to claim 1, further comprising: a heater electrode layer formed on a surface of the heater layer to which wiring is joined. Between the electrode and the sensing electrode layer, a sensing intermediate layer that joins the electrode and the sensing electrode layer is formed,
The gas detection element according to claim 2, wherein a heater intermediate layer that joins the heater layer and the heater electrode layer is formed between the heater layer and the heater electrode layer. A gas detection element according to any one of claims 1 to 3,
A gas detection apparatus comprising: a detection unit that detects the detection target gas based on a change in electrical characteristics of the gas sensing layer.

Images