JP2010091501A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor which excellently senses a variation in concentration of a specific gas, while preventing any gas sensing layer from delaminating and without affecting its gas sensitivity. <P>SOLUTION: In the gas sensor 1 having the gas sensing layer 4 which is formed on a substrate 15 and made of a metal oxide semiconductor as the principal component varying its electric property in accordance with the variation in concentration of the specific gas in an environmental atmosphere, the gas sensing layer 4 is configured to conjoin a plurality of particles such that a gas-permeable property in the thickness direction of the gas sensing layer 4 is obtained through voids existing among the plurality of particles. Furthermore, the gas sensor 1 includes: a pair of sensing electrodes 6 which contain an inorganic oxide differing from the metal oxide semiconductor, and are disposed on the substrate 15 and used for sensing a variation in the electric property of the gas sensing layer 4 while contacting the gas sensing layer 4; and a contact layer 7 which contacts with the gas sensing layer 4, wherein a middle region 22 containing the inorganic oxide exists in at least a portion of an interface between the gas sensing layer 4 and the contact layer 7, so as to connect between the contact layer 7 and a particle being inward in regard to the outermost-side particle of the gas sensing layer 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas sensor having a gas detection layer mainly composed of a metal oxide semiconductor.

Conventionally, a precious metal such as platinum is supported on a metal oxide semiconductor such as tin oxide (SnO ₂ ) as a catalyst, and electrical characteristics (for example, resistance value) change depending on the concentration change of a specific gas in the environmental atmosphere. A gas sensor that detects a change in the concentration of a specific gas by using it is known. In the gas detection layer of such a gas sensor, the precious metal was dispersed on the surface of the metal oxide semiconductor by impregnating the metal oxide semiconductor powder in the solution containing the precious metal element in the manufacturing process and then firing. It is carried in a state (see, for example, Patent Document 1).
In addition, when a gas detection layer in which a basic metal oxide is supported as a catalyst on a metal oxide semiconductor is used, high gas sensitivity against various odors (especially bad odors) that may be caused by hydrogen sulfide, mercaptans, etc. (For example, refer to Patent Document 2).

  On the other hand, the gas detection layer of such a gas sensor does not react with the specific gas at room temperature, but is activated by being heated to, for example, 200 to 400 ° C. and reacts with the specific gas. For this reason, a heating resistor is generally provided in a substrate such as a semiconductor substrate on which a gas detection layer is formed. However, when the gas sensor is driven at a high temperature using the heating resistor, there is a possibility that separation at the interface may occur due to a difference in thermal expansion between the gas detection layer and the substrate. Further, in such a gas sensor, in order to obtain high reliability, it is naturally required to increase the mechanical adhesion strength between the gas detection layer and the substrate.

Therefore, in order to improve the adhesion between the gas detection layer and the substrate, a technique of interposing an adhesion layer having irregularities between them has been proposed (see, for example, Patent Document 3). This adhesion layer ensures adhesion by an anchor effect due to unevenness. In addition, since the adhesion layer is formed by oxidizing a thin film made of a metal element that is the main component of the gas detection layer, the thermal expansion coefficient is almost equal to that of the gas detection layer, and the gas detection is caused by the difference in thermal expansion coefficient. Peeling from the layer can be prevented.
In addition, when a gas detector and a selective combustion film are sequentially formed on a silicon substrate, a technique has been proposed in which silica is contained in the selective combustion film to improve the adhesion between the selective combustion film and the substrate ( For example, see Patent Document 4). According to this technique, the silica in the selective combustion film is combined with the silicon oxide film on the silicon substrate during sintering, and the adhesion strength is increased.
Furthermore, a gas sensor has been proposed that has a detection electrode on a substrate and an uneven adhesion layer provided between the detection electrodes, and the detection electrode and the adhesion layer are covered with a gas detection layer (for example, Patent Document 5). reference).

JP-A 63-279150 Japanese Patent Publication No. 6-27719 JP 2007-333676 A Japanese Patent Laid-Open No. 2002-5865 European Patent Publication No. EP1953539

However, in the case of the technique described in Patent Document 3, although the adhesion is improved, the adhesion layer is interposed between the gas detection layer and the substrate (specifically, the detection electrode on the substrate side). The gas sensitivity tends to be lower than the structure in which the electrode and the detection electrode are in direct contact with each other.
Further, in the case of the technique described in Patent Document 4, since the silicon substrate has a smooth mirror surface, the effect of improving the adhesion cannot be said to be sufficient. Further, even in the case of the technique described in Patent Document 5, the effect of improving the adhesion may not be sufficiently obtained.
Therefore, an object of the present invention is to provide a gas sensor that prevents a gas detection layer from being peeled off from a substrate and that can favorably detect a change in the concentration of a specific gas without affecting the gas sensitivity.

In order to solve the above problems, the gas sensor of the present invention is a gas sensor mainly composed of a metal oxide semiconductor which is formed on a substrate and whose electrical characteristics change according to a change in the concentration of a specific gas in an environmental atmosphere. In the gas sensor having a layer, the gas detection layer is configured to have gas permeability in the thickness direction of the gas detection layer through a gap existing between the plurality of particles while a plurality of particles are combined. And a pair of sensing electrodes for detecting a change in electrical characteristics of the gas sensing layer while contacting the gas sensing layer on the substrate, including an inorganic oxide different from the metal oxide semiconductor, An adhesion layer that is in contact with the gas detection layer, and at least part of the interface between the gas detection layer and the adhesion layer includes a particle inside the outermost particle of the gas detection layer and the adhesion And as to connect between the intermediate region portion containing the inorganic oxide is present.
If it does in this way, since the gas detection layer and the detection electrode are contacting, the gas reaction in the interface of a gas detection layer and a detection electrode will not be inhibited by other members including a contact | adherence layer. The detection electrode and the adhesion layer are preferably formed directly on the surface of the substrate, and provided on the substrate so as not to contact the detection electrode and the adhesion layer. As a result, the surface including the side peripheral surface of the detection electrode and the gas detection layer are in contact with each other over almost the entire surface, and a good contact area is ensured, so that the gas reaction at the interface between the gas detection layer and the detection electrode is good. Will be brought.
Further, according to the gas sensor of the present invention, not only the adhesion layer and the gas detection layer are bonded on the surface (anchor effect, etc.), but also the intermediate region made of an inorganic oxide in the gas detection layer has the gas detection layer. In the form of entering the voids existing between the plurality of particles constituting the gas, the inner particles of the gas detection layer and the adhesion layer are connected to each other, so that the inside of the gas detection layer and the adhesion layer are It is firmly connected, and the adhesion between the adhesion layer and the gas detection layer is further improved.

The adhesion layer may contain the same element as the inorganic oxide.
If it does in this way, since the inorganic oxide in a gas detection layer and the contact | adherence layer contain the same element, both bond strength improves further. In addition, since the adhesion layer contains the same element as the inorganic oxide in the gas detection layer, the difference in thermal expansion between the gas detection layer and the adhesion layer is mitigated by the intermediate region portion. Peeling between them becomes difficult to occur.

The detection electrode is formed in a comb-like shape, and the comb-teeth of the other electrode are inserted between the comb-teeth of one electrode, and at least between the comb-teeth of the one electrode and the comb-teeth of the other electrode Further, the adhesion layer may be provided.
In this case, the comb teeth of the other electrode are inserted between the comb teeth of one electrode, and an adhesion layer is provided between the comb teeth of the one electrode and the comb teeth of the other electrode. The contact area between the electrode and the gas detection layer can be increased, and the adhesion between the surface of the substrate positioned between the pair of detection electrodes and the gas detection layer can be more effectively enhanced.

The base is formed on the semiconductor substrate having an opening formed in a plate thickness direction, an insulating layer formed on the semiconductor substrate and having a partition wall at a portion corresponding to the opening, and the partition wall. A heating layer and a protective layer formed on the insulating layer so as to cover the heating resistor, and the detection electrode, the adhesion layer, and the gas detection layer are formed on the protective layer of the substrate. It may be formed.
If it does in this way, since a gas detection layer will be heated quickly and favorably with a heating resistor, and it will activate, the gas sensitivity of a gas sensor can be raised.

In addition, a porous coating layer that covers at least the surface of the gas detection layer may be formed.
In this way, the gas detection layer mainly composed of a metal oxide semiconductor is protected from poisonous substances such as organic silicon, the deterioration of the gas detection layer can be prevented, and the durability of the gas sensor is improved.

  According to the present invention, it is possible to prevent the gas detection layer from being peeled off from the substrate, and to satisfactorily detect a change in the concentration of the specific gas without affecting the gas sensitivity.

Hereinafter, a first embodiment of the present invention will be described.
FIG. 1 shows a plan view of a gas sensor according to a first embodiment of the present invention.
The gas sensor 1 has a rectangular shape in plan view with a length of 2.6 mm and a width of 2 mm, and an adhesion layer 7 is formed on the upper surface of the center of the base body 15. A pair of detection electrodes 6 are formed on the upper surface of the substrate 15 so as not to contact the adhesion layer 7. Further, the gas detection layer 4 is formed so as to cover the detection electrode 6 and the adhesion layer 7 around the detection electrode 6. And the porous coating layer 20 is formed so that the gas detection layer 4 may be covered completely, and the adhesion layer 7 of the gas detection layer 4 periphery may be covered.
Further, as will be described in detail later, a heating resistor 5 is embedded in the base body 15 located almost immediately below the gas detection layer 4.

Then, the two lead portions 12 are drawn from the heat generating resistor 5 to the outside of the adhesion layer 7 when the gas sensor 1 is viewed in plan, and each lead portion 12 further extends to one side of the base body 15 (the lower side in FIG. 1). A contact pad 9 is formed at the end of each lead portion 12.
Further, two electrode lead portions 10 are drawn from the detection electrode 6 to the outside of the adhesion layer 7 when the gas sensor 1 is viewed in a plan view, and each electrode lead portion 10 further extends to the one side of the base body 15. An oxide semiconductor contact portion 8 is formed at the end of the portion 10.
Here, each lead portion 12 is for energizing the heating resistor 5. Each electrode lead portion 10 is for energizing each comb-like detection electrode 6.
In this embodiment, the two oxide semiconductor contact portions 8 are arranged adjacent to the central side of the one side, and the two contact pads 9 are arranged outside the one side so as to sandwich the oxide semiconductor contact portion 8. Respectively. The oxide semiconductor contact portion 8 and the contact pad 9 are connected to an external circuit of the gas sensor 1.
In addition, the planar shape of the produced gas sensor 1 is not limited to a rectangle, and may be a polygon or a circle. The size, thickness, and arrangement of each member are not limited.

2 is a cross-sectional view taken along line AA in FIG. In FIG. 2, the base 15 is composed of a silicon substrate 2 and an insulating coating layer 3 formed on the surface of the silicon substrate 2. Further, when the central portion of the lower surface of the silicon substrate 2 is viewed in a section along the thickness direction of the silicon substrate 2, it is removed in a trapezoidal shape to form an opening 21, and the insulating coating layer 3 is exposed from the opening 21. ing. That is, the base body 15 forms a diaphragm structure by the silicon substrate 2 having the opening 21 and the insulating coating layer 3. Here, the opening 21 is positioned so as to overlap the position where the heating resistor 5 is disposed.
The silicon substrate 2 and the insulating coating layer 3 correspond to the “base” in the present invention, and the silicon substrate 2 corresponds to the “semiconductor substrate” in the present invention. The insulating coating layer 3 corresponds to the “insulating layer” in the present invention.
Further, a substrate insulating layer 232 is formed on the lower surface of the silicon substrate 2 (the surface opposite to the side on which the insulating coating layer 3 is formed).
The base 15 is not limited to that of the present embodiment using the silicon substrate 2 and may be made of alumina (Al ₂ O ₃ ) or a semiconductor material.

The insulating coating layer 3 is configured by laminating insulating layers 32 and 33 and a protective layer 35 in this order, and the insulating layer 32 is located on the silicon substrate 2 side. Inside the insulating layer 33, the heating resistor 5 and each lead portion 12 are formed, and the protective layer 35 covers the insulating layer 33. In the insulating layer 32 on the silicon substrate 2 side, a portion exposed from the opening 21 is referred to as a partition wall 39.
The insulating layer 32 and the protective layer 35 are silicon nitride (Si ₃ O ₄ ) films having a predetermined thickness, and the insulating layer 33 is a silicon oxide (SiO ₂ ) film having a predetermined thickness.

On the upper surface of the insulating coating layer 3, a detection electrode 6, an adhesion layer 7, and a gas detection layer 4 are formed.
The gas detection layer 4 is formed by combining a plurality of particles, and has a property that its own resistance value changes depending on a specific gas in the gas to be detected. The gas sensor detection layer 4 is also configured to have gas permeability in the thickness direction of the gas detection layer 4 through voids existing between a plurality of particles. Here, in the gas sensor 1, the gas detection layer 4 is provided by containing 0.2 wt% calcium oxide as a catalyst in tin oxide (SnO ₂ ). Tin oxide containing calcium oxide is a metal oxide semiconductor that exhibits gas detection ability. And using this gas detection layer 4, ammonia (NH ₃ ), hydrogen sulfide (H ₂ S), methyl disulfide ((CH ₃ ) ₂ S ₂ ), methyl mercaptan (CH ₃ SH) in the gas to be detected And a specific gas such as trimethylamine ((CH ₃ ) ₃ N). The “detection” in the present invention includes not only detecting the presence or absence of a specific gas contained in the gas to be detected, but also detecting a change in the concentration of the specific gas.

  As another example of the metal oxide semiconductor, a configuration in which Ir, P, and Pt are contained after the content of tin oxide in the gas detection layer 4 is set to 90% by mass or more can be employed. More specifically, it contains 0.50% by mass of Ir in terms of Ir, 0.01% by mass of P in terms of P, and 0.05% by mass of Pt in terms of Pt, with the balance being tin oxide. A metal oxide semiconductor can also be used.

Furthermore, the gas detection layer 4 contains an inorganic oxide different from the metal oxide semiconductor. As will be described later, this inorganic oxide forms an intermediate region that improves the adhesion to the adhesion layer 7. Examples of the inorganic oxide include insulating oxides such as alumina (Al ₂ O ₃ ) and silica (SiO ₂ ), and the same element as the adhesion layer 7 may be used.
The blending ratio of the inorganic oxide is preferably 0.2 to 5.0% by mass with respect to the entire gas detection layer 4. If the blending ratio of the inorganic oxide is too small, the adhesion effect described later is small, and if the blending ratio is too large, the gas detection ability may be lowered.
In addition, this inorganic oxide can be mix | blended with the form of the inorganic oxide sol (alumina sol, silica sol, etc.) in the said metal oxide semiconductor paste used when forming the gas detection layer 4, and gas detection Layer 4 becomes an inorganic oxide after firing.

  Further, the porous coating layer 20 covering the gas detection layer 4 is not an essential component of the present invention, but by providing the coating layer 20, the gas detection layer 4 is prevented from being poisoned by organic silicon or the like. And durability is improved. As the coating layer 20, a ceramic porous layer such as alumina, a porous layer made of titanium oxide, or the like can be used.

  As shown in FIG. 3, the heating resistor 5 is formed in a spiral shape in plan view, and is disposed at a position corresponding to the upper portion of the opening 21 of the silicon substrate 2. The heating resistor 5 has a two-layer structure composed of a platinum (Pt) layer and a tantalum (Ta) layer.

4 is a cross-sectional view taken along line BB in FIG. In FIG. 4, each electrode lead portion 10 is provided on the protective layer 35. Further, a contact pad 11 is formed on the surface of the terminal end of each electrode lead portion 10 to constitute the oxide semiconductor contact portion 8 as a whole.
On the other hand, the lead portion 12 is embedded in the insulating layer 33, and the contact pad 9 is formed on the surface of the end of the lead portion 12. The contact pad 9 is formed so as to be exposed to the protective layer 35.
The electrode lead part 10 and the lead part 12 are composed of a tantalum (Ta) layer and a platinum (Pt) layer formed on the surface thereof. The contact pads 9 and 11 are made of Au.

  As an example, as shown in FIG. 5 which is a plan view, each of the pair of detection electrodes 6 has a comb-like planar shape, and between the comb teeth 67 of one electrode, the comb teeth 67 of the other electrode. Has been inserted. In addition, the adhesion layer 7 is continuously provided between the comb teeth 67 of one electrode and the comb teeth 67 of the other electrode in a meandering manner in a non-contact manner with the comb teeth 67. The detection electrodes 6 are a pair of electrodes for detecting changes in electrical characteristics in the gas detection layer 4. Further, as shown in FIG. 5, the adhesion layer 7 is continuously formed not only between the comb teeth 67 of the detection electrode 6 but also around the detection electrode 6 (outer periphery). Note that the adhesion layer 7 is also formed on the outer edge portion of the detection electrode 6 at a non-contact interval.

  As shown in FIG. 2, the surface 61 of the detection electrode 6 facing the gas detection layer 4 and both side surfaces thereof are in contact with the gas detection layer 4 over the entire surface, and the gas detection layer 4 and the detection electrode 6 are in contact with each other. And are electrically connected. Thus, since the gas detection layer 4 and the surface 61 of the detection electrode 6 and both side surfaces thereof are in contact with each other to ensure a contact area, the gas reaction at the interface between the gas detection layer 4 and the detection electrode 6 is ensured. However, it is not hindered by other members including the adhesion layer 7. In addition, the gas sensitivity of the gas sensor 1 (gas detection layer 4) can be increased because the gas detection layer 4 is heated by the heating resistor 5 and activated quickly and satisfactorily.

  On the other hand, as shown in FIG. 2, the surface 62 of the detection electrode 6 facing the protective layer 35 is in contact with the protective layer 35. An adhesion layer 7 for improving the adhesion between the base 15 and the gas detection layer 4 and preventing the gas detection layer 4 from peeling from the base 15 is provided between the detection electrodes 6 adjacent to each other. It is provided in non-contact with the electrode 6. That is, the detection electrode 6 is in contact with the gas detection layer 4 and is not in contact with the adhesion layer 7.

As schematically shown in FIG. 6, the adhesion layer 7 is a layer for improving the adhesion between the substrate 15 and the gas detection layer 4, and includes a plurality of particles made of an insulating metal oxide. Has an agglomerated structure. Therefore, the adhesion layer 7 has an uneven surface 71 on its own surface. On the other hand, the gas detection layer 4 also has a structure in which a plurality of particles are bonded (aggregated) as described above.
Therefore, the substance constituting the gas detection layer 4 physically enters the uneven surface 71 of the adhesion layer 7, and this anchor effect increases the adhesion between the base 15 and the gas detection layer 4 formed in a thick film shape. It has been.

The adhesion layer 7 can be formed by, for example, forming a hillock Al film by sputtering and then oxidizing it. The hillock Al film is a substantially hemispherical protrusion-like film obtained by sputtering Al.
Further, since the adhesion layer 7 is not in contact with the detection electrode 6, it can also be formed of a conductive material. However, the adhesion layer 7 is made of an insulating oxide such as alumina (Al ₂ O ₃ ) or silica (SiO ₂ ) so as not to affect the gas reaction occurring at the interface between the detection electrode 6 and the gas detection layer 4. It is preferable to configure.
In this embodiment, the adhesion layer 7 is made of alumina (Al ₂ O ₃ ).

Furthermore, in the present invention, in order to further improve the adhesion between the adhesion layer 7 and the gas detection layer 4, a metal oxide semiconductor (in this embodiment, an oxidation oxide) that exhibits its gas detection capability is included in the gas detection layer 4. An inorganic oxide (in this embodiment, alumina (Al ₂ O ₃ )) different from tin is included. If it does in this way, the inorganic oxide in gas detection layer 4 will flow to adhesion layer 7 through the gap which exists between a plurality of particles which consist of metal oxide semiconductors, and adhesion layer 7 (uneven surface 71) and gas detection layer 4 The intermediate region 22 is present between the two. In addition to the anchor effect, the adhesion region 7 and the gas detection layer 4 are firmly connected to each other by the intermediate region 22. Therefore, in the gas sensor 1 of the present embodiment, the adhesion between the gas detection layer 4 and the adhesion layer 7 is improved. Further improve.
In particular, as described above, when the base body 15 has a diaphragm structure, the diaphragm portion is bent due to heat, and the gas detection layer 4 is easily peeled off from the adhesion layer 7, but the intermediate region portion 22 is interposed. Separation can be prevented.
Furthermore, in this embodiment, since the inorganic oxide in the gas detection layer 4 is composed of the same alumina as the inorganic oxide (metal oxide) constituting the adhesion layer 7, the coefficient of thermal expansion is very close. Therefore, when the diaphragm portion is bent due to heat, the intermediate region portion 22 reduces the difference in thermal expansion coefficient between the gas detection layer 4 and the adhesion layer 7, and this effect also reduces the difference between the two. Separation can be prevented.

FIG. 7 shows a STEM (scanning transmission electron microscope) image of the interface between the adhesion layer 7 and the gas detection layer 4 in the embodiment of the present invention. In this figure, it can be seen that the gas detection layer 4 is formed by combining a plurality of particles. Moreover, it turns out that a clearance gap exists between several particle | grains. The metal oxide semiconductor composing the gas detection layer 4 is shown in a dark color in FIG. 7 (the element distribution obtained by EDX attached to the STEM expresses the difference in composition by shading). On the other hand, in the adhesion layer 7, a plurality of particles aggregate to form an uneven surface 71.
Then, the gas detection layer 4 is connected to the interface between the adhesion layer 7 and the gas detection layer 4 such that the particles 4b inside the outermost particles 4a of the gas detection layer 4 and the adhesion layer 7 are connected. A light colored intermediate region 22 is formed. The hues of the intermediate region portion 22 and the adhesion layer 7 are the same, and the intermediate region portion 22 extends from the surface of the adhesion layer 7 to the void on the back surface of the outermost particle 4a of the gas detection layer 4 (that is, the outermost region). The intermediate region portion 22 is formed up to the particle 4b inside the particle 4a).

Usually, since the uneven surface 71 of the adhesion layer 7 is only physically in contact with the surface of the gas detection layer 4, the adhesion layer 7 itself may not be in contact with the outermost surface (outermost particle 4a) of the gas detection layer 4. However, the adhesion layer 7 does not enter the back surface (particles 4b) of the outermost particles 4a. Therefore, it is considered that the intermediate region portion 22 is not derived from the adhesion layer 7 but is formed by the inorganic oxide in the gas detection layer 4 flowing during firing. This is supported by the fact that the hues of the intermediate region 22 and the adhesion layer 7 are the same, and both are made of alumina (Al ₂ O ₃ ).

On the other hand, as shown in the STEM image of FIG. 8, when the gas detection layer 4 does not contain an inorganic oxide, the uneven surface 71 of the adhesion layer 7 only physically contacts the surface of the gas detection layer 4. Although the adhesion layer 7 itself contacts the outermost surface (outermost particle 4a) of the gas detection layer 4, it can be seen that the adhesion layer 7 does not enter the back surface (inner particle 4b) of the outermost particle 4a.
In addition, when the STEM (scanning transmission electron microscope) image of the interface between the adhesion layer 7 and the gas detection layer 4 of the actual gas sensor is viewed, a light and dark intermediate region portion different from the metal oxide semiconductor constituting the gas detection layer 4 It is observed that 22 is interposed up to the inner particle 4b of the outermost particle 4a and the intermediate region 22 is connected to the adhesion layer 7.
Further, when the adhesion layer 7 contains an inorganic oxide contained in the gas detection layer 4, when the STEM (scanning transmission electron microscope) image of the interface between the adhesion layer 7 and the gas detection layer 4 is viewed, the intermediate region portion 22 and the adhesion layer 7 are observed to be integrated (see FIG. 7).

  Next, an example of a manufacturing process of the gas sensor 1 having the above structure will be described with reference to FIGS. 9 to 15 are longitudinal sectional views of the gas sensor 1 during the manufacturing process of the gas sensor 1. In addition, the intermediate body of the gas sensor 1 in the middle of manufacture is called a board | substrate.

(1) Cleaning of the silicon substrate 2 First, the silicon substrate 2 having a thickness of 400 μm is immersed in a cleaning solution to perform a cleaning process.
(2) Formation of Insulating Layer 32 and Substrate Insulating Layer 232 Next, dichlorosilane (SiH ₂ Cl ₂ ) and ammonia (NH ₃ ) are used as source gases by LP-CVD, as shown in FIG. An insulating layer 32 made of a silicon nitride film (Si ₃ N ₄ ) having a thickness of 200 nm and a substrate insulating layer 232 are formed on the upper and lower surfaces of the substrate.
(3) Formation of Insulating Layer 33 Next, silicon oxide (SiO ₂ ) having a thickness of 100 nm is formed on the surface of the insulating layer 32 using tetraethoxysilane (TEOS) and oxygen (O ₂ ) as a source gas by plasma CVD. An insulating layer 33 made of a film is formed.

(4) Formation of heating resistor 5 and lead portion 12 Thereafter, using a DC sputtering apparatus, a tantalum (Ta) layer having a thickness of 20 nm is formed on the surface of the insulating layer 33, and platinum having a thickness of 220 nm is formed on the layer. A (Pt) layer is formed. After sputtering, the resist is patterned by photolithography, and a pattern of the heating resistor 5 and the lead portion 12 is formed by wet etching using aqua regia as shown in FIG.

(5) Further film formation of the insulating layer 33 And, as in (3), tetraethoxysilane (TEOS) and oxygen (O ₂ ) are used as a source gas by plasma CVD, and the insulating layer 33, the heating resistor 5 and A new insulating layer made of a silicon oxide (SiO ₂ ) film having a thickness of 100 nm is formed on the surface of the lead portion 12 as shown in FIG. 11 to increase the thickness of the insulating layer 33. In this manner, the heating resistor 5 and the lead portion 12 are embedded in the insulating layer 33 having a thickness of 200 nm.
(6) Formation of Protective Layer 35 Further, as in (2), dichlorosilane (SiH ₂ Cl ₂ ) and ammonia (NH ₃ ) are used as source gases by LP-CVD, and the thickness is increased on the upper surface of the insulating layer 33. A protective layer 35 made of a 200 nm silicon nitride (Si ₃ N ₄ ) film is formed.
(7) Formation of Opening of Contact Pad 9 Next, resist is patterned by photolithography, and the protective layer 35 and the insulating layer 33 are etched by a dry etching method to form the contact pad 9 as shown in FIG. A contact hole 13 is opened in the portion, and a part of the end of the lead portion 12 is exposed.

(8) Formation of Detection Electrode 6 and Electrode Lead 10 Next, using a DC sputtering apparatus, a tantalum (Ta) layer having a thickness of 20 nm is formed on the surface of the protective layer 35, and further a thickness of 40 nm is formed on the surface. The platinum (Pt) layer is formed. After sputtering, resist is patterned by photolithography, and a pattern of detection electrodes 6, electrode lead portions 10 and the like having a comb-like planar shape is formed by wet etching with aqua regia as shown in FIG. .

(9) Formation of Adhesion Layer 7 A hillock Al film to be the adhesion layer 7 is formed on the detection electrode 6 and the protective layer 35 by a sputtering method. Next, after resist patterning by photolithography, an unnecessary Al film on and around the detection electrode 6 is removed by a wet etching process mainly including phosphoric acid, and then Al ₂ O ₃ is formed by anodic oxidation, and the adhesion layer 7 is formed. It is formed on the protective layer 35 between and around the comb-like detection electrodes 6.

(10) Formation of Contact Pads 9 and 11 Using a DC sputtering apparatus, a gold (Au) layer having a thickness of 400 nm is formed on the electrode-side surface of the substrate on which the electrode portion is formed. After sputtering, as shown in FIG. 13, resist patterning is performed by photolithography, and contact pads 9 and 11 are formed by wet etching.

(11) Formation of Opening 21 Next, resist is patterned by photolithography, and an insulating film serving as a mask is formed by dry etching. Then, the bottom surface is opened by immersing the substrate in tetramethylammonium hydroxide (TMAH) solution and performing anisotropic etching of the silicon substrate 2, and corresponds to the position of the heating resistor 5 as shown in FIG. The opening 21 is formed so that a portion to be the partition wall 39 of the insulating layer 32 is exposed.

(12) Formation of gas detection layer 4 Further, on the surfaces of the detection electrode 6 and the adhesion layer 7, tin oxide (tin oxide particles) is the main component, calcium oxide is added, and alumina (inorganic oxide) sol is further added. An oxide semiconductor paste added in an amount of 1.0% by mass in terms of alumina is applied by thick film printing to form a paste layer having a thickness of 20 μm as shown in FIG. 4 is formed.
The oxide semiconductor paste can be manufactured, for example, by the following procedure. First, tin chloride (SnCl ₂ ) is added to pure water, and after sufficiently stirring and dissolving, ammonia water is added dropwise to precipitate tin hydroxide. Thereafter, the precipitated powder is washed several times with pure water to remove ammonium ions and chlorine ions and dried. After drying, the precipitated powder and calcium hydroxide (Ca (OH) ₂ ) are dispersed in pure water, sufficiently stirred, and then dried. At this time, the addition amount of calcium hydroxide is 0.2 wt% in terms of calcium oxide (CaO). After drying, calcining under conditions of 800 ° C. for 5 hours, pulverizing 4.95 g of the obtained powder and 0.25 g of alumina (inorganic oxide) sol (20 mass% solution) for 1 hour with a cracking machine Then, the organic solvent is mixed and pulverized for 4 hours with a roughing machine (or a pot mill). Further, a binder and a viscosity adjusting agent are added and pulverized for 4 hours to prepare a paste having a viscosity of 140 Pa · s at 25 ° C.

(13) Firing of the substrate The substrate is inserted into a heat treatment furnace and baked, for example, at 650 ° C. for 1 hour. By this treatment, a substrate on which the detection electrode 6, the gas detection layer 4, and the adhesion layer 7 are formed can be obtained. In addition, it is considered that the inorganic oxide in the gas detection layer 4 flows and the intermediate region 22 is formed by this treatment.
(14) Formation of coating layer 20 Next, a paste containing titanium oxide particles is applied to the fired substrate by thick film so as to cover the gas detection layer 4 to form a coating layer 20 in an unfired state. To do. Then, this substrate is inserted into a heat treatment furnace and baked, for example, at 500 ° C. under baking conditions for 1 hour. By the treatment, a substrate on which the coating layer 20 is formed can be obtained.
(15) Cutting the substrate The substrate is cut using a dicing saw to obtain the gas sensor 1 having a size of, for example, 2.6 mm × 2 mm in plan view.

Note that a thermal oxide film may be formed on the silicon substrate 2 before “(2) formation of the insulating layer 32 and the insulating layer 232”. Further, the contact hole 13 is formed in “(7) Formation of the opening of the contact pad 9”, but the contact hole 13 may be formed after “(8) Formation of the detection electrode 6 and the electrode lead portion 10”. Further, “(9) formation of adhesion layer 7” may be performed after “(11) formation of opening 21”.
Further, in “(9) Formation of adhesion layer 7”, the step of converting hillock Al to Al ₂ O ₃ by oxidation may be omitted (as metal Al remains). Further, the adhesion layer 7 may be formed by other methods such as a screen printing method and a spin coating method.
Moreover, in the said embodiment, although the contact | adherence layer 7 is produced after formation of the detection electrode 6 and the electrode lead part 10, you may produce the adhesion layer 7 before formation of the detection electrode 6 and the electrode lead part 10. FIG. . In that case, for example, after forming a sol solution layer to be the adhesion layer 7 on the protective layer 35 in a film shape, the portions where the detection electrodes 6 and the electrode lead portions 10 are formed are removed by etching or the like. Then, the detection electrode 6 and the electrode lead portion 10 may be formed in the removed portion.

Next, a gas sensor according to a second embodiment of the present invention will be described. Since the gas sensor according to the second embodiment has the same configuration as that of the first embodiment except that the shape of the adhesion layer 7B is different, only the shape of the adhesion layer 7B will be described with reference to FIG.
FIG. 16 is a plan view of the adhesion layer 7B. As shown in FIG. 16, the adhesion layer 7 </ b> B is formed in a strip shape in a plan view, and includes a plurality of adhesion layers 7 </ b> B that are separated from each other. The plurality of adhesion layers 7 </ b> B are spaced apart from each other and are arranged between the comb teeth 67 of one detection electrode 6 and the comb teeth 67 of the other detection electrode 6. The adhesion layer 7B is arranged in non-contact with the comb teeth 67.

Next, a gas sensor according to a third embodiment of the present invention will be described. Since the gas sensor according to the third embodiment has the same configuration as that of the first embodiment except that the shape of the adhesion layer 7C is different, only the shape of the adhesion layer 7C will be described with reference to FIG.
FIG. 17 is a plan view of the adhesion layer 7C. The adhesion layer 7C is formed in a strip shape in a plan view, and is composed of a plurality of adhesion layers 7C spaced apart from each other. The adhesion layer 7C is arranged so as to surround the periphery of one detection electrode 6 and the other detection electrode 6. Yes. The adhesion layer 7 </ b> C is arranged in non-contact with the detection electrode 6.

Next, a gas sensor according to a fourth embodiment of the present invention will be described. Since the gas sensor according to the fourth embodiment has the same configuration as that of the first embodiment except that the shape of the detection electrode 6D is different, only the shape of the detection electrode 6D will be described with reference to a plan view 18. . In FIG. 18, the adhesion layer 7 is omitted.
As shown in FIG. 18, the detection electrode 6 </ b> D is not a detection electrode formed in a comb shape as in the first embodiment, but is formed by bending a T-shaped base portion parallel to the top side. The parallel electrodes are prepared in parallel and arranged symmetrically so that the tops of the T-shapes face each other at a predetermined interval. In this case, the adhesion layer 7 may have any shape of the first to third embodiments.

  In the first to fourth embodiments, the projected area when the contact surface between the gas detection layer 4 and the adhesion layer 7 is projected when viewed from above (when viewed from the upper side of the sheet of FIG. 1) is as follows. It is desirable to occupy 50% or more of the projected area when the contact surface between the gas detection layer 4 and the adhesion layer 7 and the detection electrode 6 is projected. With this configuration, the adhesion between the substrate 15 and the gas detection layer 4 can be obtained more reliably. In the first embodiment described above, the projected area when the contact surface between the gas detection layer 4 and the adhesion layer 7 is projected is the contact area between the gas detection layer 4, the adhesion layer 7 and the detection electrode 6. The gas sensor 1 is configured to be 68% of the projected area when projected.

  It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention.

  EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these.

The gas sensor 1 shown in FIGS. 1 and 2 was manufactured by the method shown in FIGS. However, the gas detection layer 4 was formed by printing the following paste.
In this paste, first, tin chloride (SnCl ₂ ) was added to pure water and dissolved with sufficient stirring, and then ammonia water was added dropwise to precipitate tin hydroxide. Thereafter, the precipitated powder is washed several times with pure water to remove ammonium ions and chlorine ions and dried. After drying, the precipitated powder and calcium hydroxide (Ca (OH) ₂ ) were dispersed in pure water, sufficiently stirred, and then dried. The amount of calcium hydroxide added at this time was 0.2 wt% in terms of calcium oxide (CaO). After drying, calcined at 800 ° C. for 5 hours, pulverized 5 g of the obtained powder for 0.5 hour with a rake machine, mixed with an organic solvent, and crushed for 1 hour with a rake machine (or a pot mill). did. Furthermore, an alumina (inorganic oxide) sol, a binder, and a viscosity modifier were added and pulverized for 3 hours to prepare a paste having a viscosity of 140 Pa · s at 25 ° C.

The alumina sol was added to the paste so as to be 1.0 mass% with respect to the weight of the gas detection layer 4 in terms of alumina (after firing).
Further, a thick film of TiO ₂ was printed on the fired gas detection layer 4 and fired at 500 ° C. for 1 hour to form the coating layer 20.

The gas sensor 1 manufactured as described above is an example.
As Comparative Example 1, a gas sensor was manufactured in exactly the same manner as in Example except that the adhesion layer 7 was not formed and the gas detection layer 4 did not contain an inorganic oxide (alumina).
As Comparative Example 2, a gas sensor was manufactured in exactly the same manner as in Example except that the adhesion layer 7 was not formed.
As Comparative Example 3, a gas sensor was manufactured in exactly the same manner as in Example except that the gas detection layer 4 did not contain an inorganic oxide (alumina).

The STEM (scanning transmission electron microscope) image of the interface between the adhesion layer 7 and the gas detection layer 4 of the gas sensor of the example is as shown in FIG.
Further, the STEM (scanning transmission electron microscope) image of the interface between the adhesion layer 7 and the gas detection layer 4 of the gas sensor of Comparative Example 3 is as shown in FIG.

  For the gas sensors of Examples and Comparative Examples 1 to 3, an impact test was performed in which the impact acceleration G was applied in a direction in which the surface (upper surface) of the gas detection layer 4 (coating layer 20) faces downward. Specifically, when the impact acceleration is applied 3 times at 500 G, and further applied 3 times at 1000 G, the impact acceleration is increased by 1000 G and applied 3 times each. When the impact acceleration is applied 3 times, the number of peeled gas detection layers 4 in the gas sensor (gas It was visually confirmed that a state where a part or all of the detection layer was dropped was defined as being peeled. (Peeling occurrence rate: number of peeling / total number of inputs (10)).

The obtained result is shown in FIG.
As is clear from FIG. 19, in the case of the embodiment in which the adhesion layer 7 is formed and the gas detection layer 4 contains an inorganic oxide (alumina), the gas detection layer can be used even if an impact test is performed with an impact acceleration of 2000 G or less. No peeling of 4 occurred. This is presumably because the intermediate region 22 exists so as to be connected to the adhesion layer 7 from within the gas detection layer 4 as shown in FIG.
On the other hand, in the case of Comparative Examples 1 and 3 in which the gas detection layer 4 did not contain an inorganic oxide (alumina), and the gas detection layer 4 contained an inorganic oxide (alumina), the adhesion layer 7 was not formed. In the case of Comparative Example 2, peeling of the gas detection layer 4 occurred at a rate (%) when the impact test was performed at the initial impact acceleration (500 G). This is as described above as shown in FIG. It is considered that the intermediate region portion 22 does not exist (Comparative Examples 1 and 3), or the other party is the base body 15 without unevenness even if the intermediate region portion 22 is interposed (Comparative Example 2).

It is a top view of the gas sensor which concerns on the 1st Embodiment of this invention. FIG. 2 is a cross-sectional view in the direction of the arrow in the line AA shown in FIG. It is a top view of the heating resistor with which a gas sensor is provided. It is arrow direction sectional drawing in the BB line shown in FIG. It is a top view which shows a detection electrode and a contact | adherence layer when it sees from the plane direction of a gas sensor. It is the elements on larger scale of the arrow direction cross section of the gas detection layer vicinity in the AA line shown in FIG. It is a figure which shows the STEM (scanning transmission electron microscope) image of the interface of the contact | adherence layer and gas detection layer in the 1st Embodiment of this invention. It is a figure which shows the STEM (scanning transmission electron microscope) image of the interface of a contact | adherence layer and a gas detection layer in case an inorganic oxide is not included in a gas detection layer. It is a longitudinal cross-section of the gas sensor in the middle of the manufacturing process of a gas sensor. FIG. 10 is a longitudinal cross-sectional view of the gas sensor in the middle of the gas sensor manufacturing process continued from FIG. 9; FIG. 11 is a longitudinal cross-sectional view of the gas sensor in the middle of the gas sensor manufacturing process continued from FIG. 10. FIG. 12 is a longitudinal cross-sectional view of the gas sensor in the middle of the gas sensor manufacturing process continued from FIG. 11. FIG. 13 is a longitudinal sectional view of the gas sensor in the middle of the gas sensor manufacturing process following FIG. 12. FIG. 14 is a longitudinal cross-sectional view of the gas sensor in the middle of the gas sensor manufacturing process continued from FIG. 13. FIG. 15 is a longitudinal cross-sectional view of the gas sensor in the middle of the gas sensor manufacturing process continued from FIG. 14. It is a top view which shows the contact | adherence layer which the gas sensor which concerns on the 2nd Embodiment of this invention has. It is a top view which shows the contact | adherence layer which the gas sensor which concerns on the 3rd Embodiment of this invention has. It is a top view which shows the detection electrode which the gas sensor which concerns on the 4th Embodiment of this invention has. It is a figure which shows the peeling incidence rate of a gas detection layer when an impact test is given to a gas sensor.

Explanation of symbols

1 Gas sensor 2 Silicon substrate (semiconductor substrate)
3 Insulating coating layer 4 Gas detection layer 4a Outermost particles of gas detection layer 4b Particles inside innermost particles 5 Heating resistor 6, 6D Detection electrodes 7, 7B, 7C Adhesion layer 15 Base 20 Covering layer 21 Opening 22 Intermediate region portion 32, 33 Insulating layer 35 Protective layer 39 Partition portion 67 Comb teeth

Claims (5)

In a gas sensor having a gas detection layer mainly composed of a metal oxide semiconductor that is formed on a substrate and whose electrical characteristics change according to a change in concentration of a specific gas in an environmental atmosphere.
The gas detection layer is configured to have gas permeability in the thickness direction of the gas detection layer through a gap existing between the plurality of particles while the plurality of particles are bonded, and the metal oxide semiconductor. A pair of detection electrodes for detecting a change in electrical characteristics of the gas detection layer while being in contact with the gas detection layer, and in contact with the gas detection layer. An adhesion layer,
At least part of the interface between the gas detection layer and the adhesion layer connects the particles inside the outermost particles of the gas detection layer and the adhesion layer, and the inorganic oxide A gas sensor in which an intermediate region portion is present.   The gas sensor according to claim 1, wherein the adhesion layer contains the same element as the inorganic oxide. The detection electrode is formed in a comb-like shape, and the comb tooth of the other electrode is inserted between the comb teeth of one electrode,
The gas sensor according to claim 1, wherein the adhesion layer is provided at least between the comb teeth of the one electrode and the comb teeth of the other electrode. The base is a semiconductor substrate having an opening formed in the thickness direction;
An insulating layer formed on the semiconductor substrate and having a partition wall at a portion corresponding to the opening;
A heating resistor formed on the partition wall of the insulating layer;
A protective layer formed on the insulating layer so as to cover the heating resistor,
The gas sensor according to claim 1, wherein the detection electrode, the adhesion layer, and the gas detection layer are formed on the protective layer of the base.   The gas sensor according to claim 1, wherein a porous coating layer that covers at least a surface of the gas detection layer is formed.