Gas sensor

Abstract

Provided is a gas sensor that makes it possible to improve durability.　The gas sensor (10) comprises a substrate (30) and a gas sensor element (20). The gas sensor element (20) has a heater (24). The gas sensor element (20) and the substrate (30) are bonded via a bond section (40), a first adhesion layer (50) disposed in contact with the gas sensor element (20) between the bond section (40) and the gas sensor element (20), and a second adhesion layer (60) disposed in contact with the substrate (30) between the bond section (40) and the substrate (30). A first surface (20A) which is the surface of the gas sensor element (20) in contact with the first adhesion layer (50) and a second surface (30A) which is the surface of the substrate (30) in contact with the second adhesion layer (60) consist of surfaces containing an oxide or a nitride. The bond section (40) contains gold (Au) as a main component. The first adhesion layer (50) and the second adhesion layer (60) contain tantalum oxide (Ta2O5).

Description

gas sensor

[0001] This disclosure relates to a gas sensor.

[0002] The gas sensor disclosed in Patent Document 1 comprises a substrate on which a heater is provided, and a sensor portion disposed on the substrate. The sensor portion has a solid electrolyte layer and a lower electrode and an upper electrode sandwiching the solid electrolyte layer.

[0003] International Publication No. 2017 / 014033, Japanese Patent Publication No. 2000-146884

[0004] In the gas sensor described in Patent Document 1, there is a concern that the temperature of the substrate will rise due to the heat generated from the heater. Therefore, it is conceivable to provide a heater in the sensor portion and separate the substrate and the sensor portion by joining them via a joint. When gold (Au) is used for the joint, it is necessary to provide an adhesion layer between the joint and the sensor portion, and between the joint and the substrate, to improve adhesion. However, when the adhesion layer is composed of tantalum (Ta), titanium (Ti), molybdenum (Mo), etc., as in Patent Document 2, there is a concern that diffusion is likely to occur between the joint and the sensor portion at high temperatures, reducing the bonding strength. Therefore, there is a need for a gas sensor that can suppress delamination between the joint and the sensor portion, and between the joint and the substrate, and thereby improve durability.

[0005] This disclosure is made in view of the above circumstances and aims to provide a gas sensor that can improve durability. This disclosure can be implemented in the following forms.

[0006] The gas sensor of the first invention of this disclosure is a gas sensor comprising a substrate and a gas sensor element disposed on the substrate, wherein the gas sensor element has a heater, the gas sensor element and the substrate are joined via a joint, a first adhesion layer disposed between the joint and the gas sensor element and in contact with the gas sensor element, and a second adhesion layer disposed between the joint and the substrate and in contact with the substrate, the first surface of the gas sensor element which is in contact with the first adhesion layer and the second surface of the substrate which is in contact with the second adhesion layer are composed of surfaces containing oxide or nitride, the joint mainly contains gold (Au), and the first and second adhesion layers are composed of tantalum oxide (Ta ２ O ５ ) includes.

[0007] The gas sensor of the second invention of this disclosure is a gas sensor comprising a substrate and a gas sensor element disposed on the substrate, wherein the gas sensor element has a heater, the gas sensor element and the substrate are joined via a joint, a first contact portion disposed between the joint and the gas sensor element and in contact with the gas sensor element, and a second contact portion disposed between the joint and the substrate and in contact with the substrate, the first surface of the gas sensor element which is the surface in contact with the first contact portion, and the second surface of the substrate which is the surface in contact with the second contact portion are composed of a surface containing an oxide or nitride, the joint mainly contains gold (Au), and the first contact portion is composed of tantalum oxide (Ta) on the joint side ２ O ５ The second adhesion portion has a first intermediate layer containing ) and a first adhesion layer in contact with the first surface and containing tantalum (Ta), and the second adhesion portion has tantalum oxide (Ta) on the joint side ２ O ５ It has a second intermediate layer containing ) and a second adhesion layer that is in contact with the second surface and contains tantalum (Ta).

[0008] This disclosure can provide a gas sensor that may have improved durability.

[0009] It is a side cross-sectional view of the gas sensor according to the first embodiment of the present disclosure. It is a plan view of the gas sensor of FIG. 1. It is a figure showing experimental results relating to the strength reduction rate using the gas sensor of the example and the gas sensor of the comparative example. It is a side cross-sectional view of the gas sensor element portion of the gas sensor according to the second embodiment of the present disclosure. It is a side cross-sectional view of the gas sensor element portion of the gas sensor according to the third embodiment of the present disclosure. It is a side cross-sectional view of the gas sensor element portion of the gas sensor according to the fourth embodiment of the present disclosure. It is a side cross-sectional view of the gas sensor element portion of the gas sensor according to the fifth embodiment of the present disclosure. It is a plan view of the gas sensor of FIG. 7.

[0010] Hereinafter, embodiments of the present disclosure are listed and illustrated. [1] A gas sensor comprising a substrate and a gas sensor element disposed on the substrate, wherein the gas sensor element has a heater, and the gas sensor element and the substrate are bonded to each other via: a bonding portion; a first adhesion layer disposed between the bonding portion and the gas sensor element and in contact with the gas sensor element; and a second adhesion layer disposed between the bonding portion and the substrate and in contact with the substrate, wherein a first surface of the gas sensor element that is a surface in contact with the first adhesion layer, and a second surface of the substrate that is a surface in contact with the second adhesion layer are each constituted by a surface containing an oxide or a nitride, the bonding portion contains gold (Au) as a main component, and the first adhesion layer and the second adhesion layer are made of tantalum oxide (Ta ２ O ５ ), a gas sensor.

[0011] According to the gas sensor of [1] above, since the gas sensor element having a heater is separated from the substrate via the bonding portion, conduction of heat generated by the heater to the substrate can be suppressed. Further, since the first adhesion layer is disposed between the bonding portion and the gas sensor element, the adhesion between the bonding portion and the gas sensor element can be enhanced. Further, since the second adhesion layer is disposed between the bonding portion and the substrate, the adhesion between the bonding portion and the substrate can be enhanced. Furthermore, for the bonding portion containing gold (Au) as a main component, the first adhesion layer and the second adhesion layer are made of tantalum oxide (Ta ２ O ５Because it contains ), diffusion is less likely to occur between the joint and the first and second adhesion layers, a decrease in bonding strength between the joint and the gas sensor element and substrate can be suppressed, and the gas sensor element is less likely to peel off from the substrate. Therefore, the durability of the gas sensor can be improved.

[0012] [2] A gas sensor comprising a substrate and a gas sensor element disposed on the substrate, wherein the gas sensor element has a heater, the gas sensor element and the substrate are joined via a joint, a first contact portion disposed between the joint and the gas sensor element and in contact with the gas sensor element, and a second contact portion disposed between the joint and the substrate and in contact with the substrate, the first surface of the gas sensor element which is the surface in contact with the first contact portion, and the second surface of the substrate which is the surface in contact with the second contact portion are composed of a surface containing an oxide or nitride, the joint mainly contains gold (Au), and the first contact portion is composed of tantalum oxide (Ta) on the joint side ２ O ５ The second adhesion portion has a first intermediate layer containing ) and a first adhesion layer in contact with the first surface and containing tantalum (Ta), and the second adhesion portion has tantalum oxide (Ta) on the joint side ２ O ５ A gas sensor having a second intermediate layer containing ) and a second adhesion layer in contact with the second surface and containing tantalum (Ta).

[0013] According to the gas sensor described in [2] above, since the gas sensor element having a heater is separated from the substrate via a joint, the conduction of heat generated by the heater to the substrate can be suppressed. Furthermore, since a first contact portion is provided between the joint and the gas sensor element, the adhesion between the joint and the gas sensor element can be improved. Furthermore, since a second contact portion is provided between the joint and the substrate, the adhesion between the joint and the substrate can be improved. In addition, the first contact portion and the second contact portion are provided on the joint side of the joint, with respect to the joint portion mainly composed of gold (Au). ２ O ５Since the first intermediate layer and the second intermediate layer including ) are provided, diffusion is less likely to occur between the joint portion, the first adhesion portion and the second adhesion portion, a decrease in bonding strength between the joint portion, the gas sensor element and the substrate can be suppressed, and the gas sensor element is less likely to peel off from the substrate. Therefore, the durability of the gas sensor can be improved.

[0014] [3] The gas sensor according to [1] or [2], wherein the joint portion is composed only of gold (Au).

[0015] According to the gas sensor of [3] above, the physical properties of gold (Au) can be stably exhibited in the joint portion.

[0016] [4] The gas sensor according to any one of [1] to [3], wherein the joint portion includes a joint body and bonding pads disposed at both ends in the lamination direction of the joint body, the bonding pads being mainly composed of gold (Au) or platinum (Pt).

[0017] According to the gas sensor of [4] above, by using the bonding pads, it is possible to realize a configuration that facilitates bonding between the joint body, the configuration on the substrate side and the configuration on the gas sensor element side.

[0018] [5] The gas sensor according to [4], wherein the bonding pad is a vapor-deposited film.

[0019] According to the gas sensor of [5] above, the adhesion between the bonding pads, the gas sensor element and the substrate can be improved.

[0020] <First Embodiment> 1. Configuration of Gas Sensor 10 Hereinafter, a gas sensor 10 according to a first embodiment embodying the present invention will be described with reference to FIGS. 1 and 2. The gas sensor 10 of the first embodiment shown in FIG. 1 is an example of the gas sensor of the present disclosure. For convenience of explanation, in the following description, the vertical direction shown in FIG. 1 is directly defined as the vertical direction, but this does not need to match the vertical direction in the actual arrangement state of the gas sensor 10. The vertical direction corresponds to the thickness direction of the substrate 30.

[0021] The gas sensor 10 measures the gas concentration of a target gas, such as oxygen. As shown in Figures 1 and 2, the gas sensor 10 comprises a gas sensor element 20, a substrate 30, a joint 40, a first adhesion layer 50, and a second adhesion layer 60. The gas sensor element 20 is arranged on the substrate 30. The gas sensor element 20 and the substrate 30 are joined via the joint 40, the first adhesion layer 50, and the second adhesion layer 60. The first adhesion layer 50 is located between the joint 40 and the gas sensor element 20. The second adhesion layer 60 is located between the joint 40 and the substrate 30.

[0022] When viewed from above in the thickness direction (vertical direction) of the substrate 30, the gas sensor 10 (specifically, the gas sensor element 20 and the substrate 30) has a rotationally symmetrical configuration with the center line C (a line passing through the center of gravity and parallel to the vertical direction) as the center of rotation.

[0023] 1-1. Configuration of Substrate 30 The substrate 30 shown in Figures 1 and 2 is, for example, a MEMS (Micro Electro Mechanical Systems) chip. Figure 1 is a cross-section of line A-A in Figure 2. The substrate 30 has a frame 31 and a membrane 32. The frame 31 is, for example, a rectangular ring. A rectangular parallelepiped cavity 33 is formed inside the frame 31. The membrane 32 is fixed to the upper surface of the frame 31. The membrane 32 is a plate-like structure with a rectangular (for example, square) shape in plan view. The membrane 32 has a diaphragm structure that covers the cavity 33 surrounded by the frame 31 from above.

[0024] Specifically, as shown in Figure 1, the substrate 30 has a semiconductor substrate 34 and an insulating layer 35. The semiconductor substrate 34 is, for example, a silicon (Si) substrate. The semiconductor substrate 34 has openings 34A that penetrate through both the upper and lower surfaces. The shape of the openings 34A is, for example, a rectangle in plan view. A part of the insulating layer 35 is exposed inside the openings 34A.

[0025] The insulating layer 35 only needs to have sufficient insulating properties, and its material is not particularly limited. The insulating layer 35 is laminated on the upper surface of the semiconductor substrate 34. The insulating layer 35 has, for example, a plurality of insulating films. The material of the insulating film is, for example, silicon oxide (SiO₂ ２ ), silicon nitride (Si ３ N ４ ) etc. Silicon oxide (SiO) on semiconductor substrate 34 ２ Silicon oxide (SiO₂) is formed, for example, by thermal oxidation (thermal oxidation of silicon substrates, etc.). ２ ) is, for example, TEOS (Si(OC ２ H ５ ) ４ It is formed by plasma CVD using silicon nitride (Si) as a liquid source. ３ N ４ ) is formed, for example, by reduced-pressure CVD.

[0026] The surface (bottom surface) of the substrate 30 (more specifically, the insulating layer 35) that is in contact with the second adhesion layer 60, which will be described later, is referred to as the second surface 30A. The second surface 30A is made of oxide (for example, silicon oxide (SiO2)). ２ ), aluminum oxide (Al ２ O ３ ) etc.) or nitrides (for example, silicon nitride (Si ３ N ４ It is composed of a surface containing (such as aluminum nitride (AlN)).

[0027] As shown in Figure 2, a pair of substrate-side signal pads 36 and a pair of substrate-side heater pads 37 are provided on the substrate 30. The substrate-side signal pads 36 and the substrate-side heater pads 37 have a two-layer structure, for example, a layer made of chromium (Cr) and a layer made of gold (Au) formed on top of it. Wiring (not shown) for exchanging power with an external circuit is connected to the substrate-side signal pads 36 and the substrate-side heater pads 37.

[0028] The frame 31 is made of a semiconductor substrate 34. The membrane 32 is made of an insulating layer 35.

[0029] 1-2. Configuration of the gas sensor element 20 As shown in Figure 1, the gas sensor element 20 is positioned on the side (top side) of the membrane 32 opposite to the cavity 33. The gas sensor element 20 shown in Figures 1 and 2 comprises a main body 21, a pair of element-side signal electrode pads 22, and a pair of element-side heater electrode pads 23. The main body 21 is formed using a ceramic material. The gas sensor element 20 is, for example, a rectangular (square) plate in plan view.

[0030] The main body 21 includes, for example, a solid electrolyte (not shown), a sensing electrode, and a reference electrode. The solid electrolyte contains a material that becomes activated and exhibits ionic conductivity when heated to a high temperature. The solid electrolyte is zirconia (ZrO ２ It is preferable that the solid electrolyte is made of ) material. The solid electrolyte includes, for example, stabilized zirconia. The stabilized zirconia is, for example, yttria-stabilized zirconia (YSZ). The detection electrode and the reference electrode are electrodes mainly composed of metal formed on the surface of the solid electrolyte. The material of the detection electrode and the reference electrode is, for example, platinum (Pt). The solid electrolyte is sandwiched between the detection electrode and the reference electrode. The detection electrode is exposed to the gas to be measured. A reference gas (oxygen, etc.) of a predetermined concentration is introduced into the reference electrode.

[0031] The main body portion 21 includes, for example, an insulating layer (not shown). The insulating layer constitutes, for example, the lower end portion of the main body portion 21. The material of the insulating layer is, for example, a metal oxide, such as aluminum oxide (Al ２ O ３ ) etc.

[0032] The surface (bottom surface) of the gas sensor element 20 (more specifically, the main body portion 21) that is in contact with the first adhesion layer 50, which will be described later, is referred to as the first surface 20A. The first surface 20A is made of an oxide (for example, aluminum oxide (Al ２ O ３ It is composed of a surface that includes ).

[0033] The main body 21 is equipped with a heater 24. The heater 24 is embedded in an insulating layer, for example. The heater 24 is, for example, in the shape of a strip. When viewed from above or below, the heater 24 has a shape such as a square spiral or a meandering shape (meanda shape). The material of the heater 24 is, for example, platinum (Pt). The heater 24 generates heat to activate the solid electrolyte when an electric current is passed through it.

[0034] As shown in Figure 2, the pair of element-side signal electrode pads 22 and the pair of element-side heater electrode pads 23 are arranged, for example, at the four corners on the upper surface of the gas sensor element 20. The element-side signal electrode pads 22 and the element-side heater electrode pads 23 are, for example, made of a material mainly composed of platinum (Pt), or have a two-layer structure consisting of a gold (Au) layer and a platinum (Pt) layer formed beneath it.

[0035] One of the element-side signal electrode pads 22 is a pad that extracts the signal obtained from the detection electrode (not shown). Although not shown, one of the element-side signal electrode pads 22 is connected to the detection electrode (not shown) for example through a through-hole formed in the gas sensor element 20 (insulating layer, etc.).

[0036] The other element-side signal electrode pad 22 is a pad that extracts the signal obtained from the reference electrode (not shown). Although not shown, the other element-side signal electrode pad 22 is connected to the reference electrode (not shown) for example through a through-hole formed in the gas sensor element 20 (insulating layer, etc.).

[0037] The pair of element-side heater electrode pads 23 are electrodes for supplying current to the heater 24. One element-side heater electrode pad 23 is connected to one end of the heater 24. The other element-side heater electrode pad 23 is connected to the other end of the heater 24. The pair of element-side heater electrode pads 23 are connected to the heater 24, for example, through through holes formed in the gas sensor element 20 (insulating layer, etc.).

[0038] The gas sensor 10 includes conductive portions 25 that connect the gas sensor element 20 and the substrate 30. The conductive portions 25 are, for example, conductive wires. The material of the conductive portions 25 is, for example, gold (Au), copper (Cu), aluminum (Al), etc. One pair of conductive portions 25 are connected to the substrate-side signal pad 36 of the substrate 30 and the element-side signal electrode pad 22 of the gas sensor element 20, respectively. The other pair of conductive portions 25 are connected to the substrate-side heater pad 37 of the substrate 30 and the element-side heater electrode pad 23 of the gas sensor element 20, respectively.

[0039] The gas sensor element 20 outputs a signal (voltage signal) based on the difference between the concentration of the target gas to which the detection electrode (not shown) is exposed and the concentration of the reference gas introduced to the reference electrode (not shown). For example, if the target gas is oxygen, the solid electrolyte (not shown) can be made ionic conductive by keeping it at a high temperature, and oxygen ions conduct from the reference electrode side, where the oxygen concentration is high, to the detection electrode side, generating an electric current. Since oxygen ions have a negative charge, an electromotive force is generated between the two electrodes.

[0040] The driving temperature of the gas sensor element 20 (surface temperature of the solid electrolyte when heated by the heater 24) is preferably, for example, 500°C to 800°C, more preferably 550°C to 750°C, and even more preferably 600°C to 700°C. The surface temperature of the frame 31 (semiconductor substrate 34) when the gas sensor element 20 is driven is preferably, for example, room temperature (e.g., 25°C) to 50°C.

[0041] 1-3. Joint 40 As shown in Figure 1, the joint 40 joins the gas sensor element 20 and the substrate 30. The gas sensor element 20 and the substrate 30 are connected via the joint 40, and the entire gas sensor element 20, excluding the portion in contact with the joint 40, is positioned to face and be separated from the substrate 30.

[0042] The joint portion 40 is, for example, a rectangular parallelepiped. The joint portion 40 is, for example, solid. The joint portion 40 contains gold (Au) as its main component. Here, "main component" refers to a component whose content in the joint portion 40 is 50% or more. Preferably, the joint portion 40 consists only of gold (Au).

[0043] Here, the composition of the joint 40, the lower surface of the gas sensor element 20 (first surface 20A), the upper surface of the substrate 30 (second surface 30A), and the first and second adhesion layers 50 and 60, which will be described later, can be measured by SEM-EDS and TEM-EDS.

[0044] The joint portion 40 includes a joint body portion 41, a first joining pad 42, and a second joining pad 43. The first joining pad 42 and the second joining pad 43 correspond to examples of "joining pads" in this disclosure. The joint body portion 41 mainly contains gold (Au). Preferably, the joint body portion 41 consists only of gold (Au). The joint body portion 41 is, for example, bump-shaped (block-shaped). The joint body portion 41 is, for example, solid.

[0045] The first bonding pad 42 and the second bonding pad 43 are positioned at both ends of the bonding body 41 in the stacking direction (vertical direction). Specifically, the first bonding pad 42 is in contact with the upper end of the bonding body 41. The second bonding pad 43 is in contact with the lower end of the bonding body 41. The first bonding pad 42 and the second bonding pad 43 mainly contain gold (Au). Preferably, the first bonding pad 42 and the second bonding pad 43 consist only of gold (Au). The first bonding pad 42 and the second bonding pad 43 are, for example, rectangular plates. The shape of the first bonding pad 42 and the second bonding pad 43 when viewed from the vertical direction is the same rectangular shape as the bonding body 41.

[0046] The first bonding pad 42 and the second bonding pad 43 are vapor-deposited films. For example, the first bonding pad 42 and the second bonding pad 43 are sputtered films formed by sputtering.

[0047] 1-4. First Adhesion Layer 50 As shown in Figure 1, the first adhesion layer 50 is positioned between the joint 40 and the gas sensor element 20 (more specifically, the main body 21), and is in close contact with the joint 40 and the gas sensor element 20. The upper surface of the first adhesion layer 50 is in contact with the gas sensor element 20 (more specifically, the main body 21). The surface (lower surface) of the gas sensor element 20 (more specifically, the main body 21) that the first adhesion layer 50 is in contact with is the first surface 20A. The lower surface of the first adhesion layer 50 is in contact with the upper surface of the joint 40 (more specifically, the first bonding pad 42).

[0048] The first adhesion layer 50 is made of tantalum oxide (Ta ２ O ５ The first adhesion layer 50 is a vapor-deposited film. For example, the first adhesion layer 50 is a sputtered film formed by sputtering.

[0049] The first adhesion layer 50 is, for example, a rectangular plate. The shape of the first adhesion layer 50 when viewed from above or below is the same rectangular shape as the first bonding pad 42.

[0050] 1-5. Second Adhesion Layer 60 As shown in Figure 1, the second adhesion layer 60 is positioned between the joint 40 and the substrate 30 (more specifically, the insulating layer 35), and is in close contact with the joint 40 and the substrate 30. The lower surface of the second adhesion layer 60 is in contact with the substrate 30 (more specifically, the insulating layer 35). The surface (upper surface) of the substrate 30 (more specifically, the insulating layer 35) in contact with the second adhesion layer 60 is the second surface 30A. The upper surface of the second adhesion layer 60 is in contact with the lower surface of the joint 40 (more specifically, the second bonding pad 43).

[0051] The second adhesion layer 60 is made of tantalum oxide (Ta ２ O ５ The second adhesion layer 60 is a vapor-deposited film. For example, the second adhesion layer 60 is a sputtered film formed by sputtering.

[0052] The second adhesion layer 60 is, for example, a rectangular plate. The shape of the second adhesion layer 60 when viewed from above or below is the same rectangular shape as the second bonding pad 43.

[0053] 1-6. Method for Manufacturing the Gas Sensor 10 The method for manufacturing the gas sensor 10 will be described below. The method for manufacturing the gas sensor 10 includes an element formation step, a substrate formation step, and a bonding step.

[0054] 1-6-1. Element Formation Process In the element formation process, the main body 21 is formed using, for example, a sheet molding process and a printing process. For example, the main body 21 can be formed by preparing a sheet made from ceramic raw materials that will serve as the base for the solid electrolyte, a sheet that will serve as the base for the insulating layer, printing various electrodes on it, and then sintering it.

[0055] Next, a pair of element-side signal electrode pads 22 and a pair of element-side heater electrode pads 23 are formed on the upper surface of the main body 21. The element-side signal electrode pads 22 and element-side heater electrode pads 23 are mainly composed of, for example, platinum (Pt). The element-side signal electrode pads 22 and element-side heater electrode pads 23 are formed, for example, by paste printing and sintering or vapor deposition (sputtering, etc.). This forms the gas sensor element 20.

[0056] Next, a first adhesion layer 50 is formed on the lower surface of the main body 21. The first adhesion layer 50 is made of tantalum oxide (Ta ２ O ５ ) is included. The first adhesion layer 50 is formed, for example, by vapor deposition (sputtering, etc.).

[0057] Next, a first bonding pad 42 is formed on the lower surface of the first adhesion layer 50. The first bonding pad 42 is mainly composed of, for example, gold (Au). The first bonding pad 42 is formed by, for example, vapor deposition (sputtering, etc.).

[0058] 1-6-2. Substrate Forming Process In the substrate forming process, a semiconductor substrate (for example, a silicon (Si) substrate) that will serve as the base for the semiconductor substrate 34 is prepared. An insulating layer 35 is formed on the upper surface of the semiconductor substrate. Furthermore, a substrate-side signal pad 36 and a substrate-side heater pad 37 are formed on the insulating layer 35. The substrate-side signal pad 36 and the substrate-side heater pad 37 are mainly composed of gold (Au), for example. The substrate-side signal pad 36 and the substrate-side heater pad 37 are formed by, for example, vapor deposition (sputtering, etc.).

[0059] A second adhesion layer 60 is formed on the insulating layer 35. The second adhesion layer 60 is made of tantalum oxide (Ta ２ O ５ ) is included. The second adhesion layer 60 is formed, for example, by vapor deposition (sputtering, etc.).

[0060] Next, a second bonding pad 43 is formed on the upper surface of the second adhesion layer 60. The second bonding pad 43 is mainly composed of, for example, gold (Au). The second bonding pad 43 is formed by, for example, vapor deposition (sputtering, etc.).

[0061] Next, a bonding body portion 41 is formed on the upper surface of the second bonding pad 43. The bonding body portion 41 is mainly composed of gold (Au). The bonding body portion 41 is formed using the wire bonding method.

[0062] 1-6-3. Bonding Process In the bonding process, the gas sensor element 20, which is provided with a first adhesion layer 50 and a first bonding pad 42, is bonded to a substrate (the base substrate for the substrate 30) on which a second adhesion layer 60, a second bonding pad 43, and a bonding body portion 41 are formed. The first bonding pad 42 and the bonding body portion 41 are bonded, for example, using a flip-chip bonding method.

[0063] Furthermore, using a wire bonding method, the substrate-side signal pad 36 of the substrate 30 and the element-side signal electrode pad 22 of the gas sensor element 20 are connected by a conductive portion 25. The conductive portion 25 is, for example, a gold (Au) wire. Similarly, the substrate-side heater pad 37 of the substrate 30 and the element-side heater electrode pad 23 of the gas sensor element 20 are connected by a conductive portion 25. The conductive portion 25 is, for example, a gold (Au) wire.

[0064] Furthermore, an opening 34A (cavity 33) is formed in the semiconductor substrate (for example, a silicon (Si) substrate) that will serve as the base for the semiconductor substrate 34 by etching or the like to create a diaphragm structure, which then forms the substrate 30. This completes the manufacturing of the gas sensor 10.

[0065] In the above manufacturing method, the bonding body portion 41 is formed on the substrate side (the substrate that forms the base of the substrate 30), but it may also be formed on the gas sensor element 20 side. Furthermore, the bonding body portion 41 may be formed by printing. In this case, it is preferable to bond the first bonding pad 42 and the bonding body portion 41 by pressurized firing.

[0066] 1-7. An experiment was conducted to evaluate the strength (durability) of the experimental gas sensor. The example used the gas sensor 10 of the first embodiment. The comparative example used the gas sensor 10 of the first embodiment in which the first adhesion layer 50 and the second adhesion layer 60 are made of tantalum oxide (Ta ２ O ５ The difference is that it contains tantalum (Ta) instead of .

[0067] With the substrate 30 fixed, the gas sensor element 20 is pressed horizontally, and as the pressing force is increased, the pressing force (delamination pressure) at which delamination occurs between the substrate 30 and the gas sensor element 20 is measured. The above pressing force was measured for the gas sensors of the example and comparative example in the following states: without heat treatment, after heat treatment at 700°C for 10 hours, and after heat treatment at 700°C for 100 hours.

[0068] Figure 3 shows the measured strength reduction rate for each state for the example and comparative example, with the peel pressure in the untreated state set as 100% strength reduction rate. A smaller percentage value in the table indicates a greater decrease in strength. In the example, it can be seen that the decrease in strength in the heat-treated state is suppressed compared to the comparative example. Therefore, tantalum oxide (Ta) is used in the adhesion layer. ２ O ５ It can be seen that the configuration using () is less prone to delamination between the gas sensor element and the substrate and has higher durability than the configuration using tantalum (Ta).

[0069] 2. Effects of the First Embodiment The gas sensor 10 of the first embodiment comprises a substrate 30 and a gas sensor element 20 disposed on the substrate 30. The gas sensor element 20 has a heater 24. The gas sensor element 20 and the substrate 30 are joined via a joint 40, a first adhesion layer 50 disposed between the joint 40 and the gas sensor element 20 and in contact with the gas sensor element 20, and a second adhesion layer 60 disposed between the joint 40 and the substrate 30 and in contact with the substrate 30. The first surface 20A of the gas sensor element 20, which is the surface in contact with the first adhesion layer 50, and the second surface 30A of the substrate 30, which is the surface in contact with the second adhesion layer 60, are composed of surfaces containing oxides or nitrides. The joint 40 mainly contains gold (Au). The first adhesion layer 50 and the second adhesion layer 60 are composed of tantalum oxide (Ta ２ O ５ It includes ).

[0070] With this gas sensor 10, since the gas sensor element 20 having a heater 24 is separated from the substrate 30 via a bonding portion 40, the conduction of heat generated by the heater 24 to the substrate 30 can be suppressed. Furthermore, since a first adhesion layer 50 is disposed between the bonding portion 40 and the gas sensor element 20, the adhesion between the bonding portion 40 and the gas sensor element 20 can be improved. Furthermore, since a second adhesion layer 60 is disposed between the bonding portion 40 and the substrate 30, the adhesion between the bonding portion 40 and the substrate 30 can be improved. In addition, the bonding portion 40 mainly contains gold (Au), and the first adhesion layer 50 and the second adhesion layer 60 contain tantalum oxide (Ta ２ O ５ Because it includes ), diffusion is less likely to occur between the joint 40 and the first adhesion layer 50 and the second adhesion layer 60, a decrease in bonding strength between the joint 40 and the gas sensor element 20 and the substrate 30 can be suppressed, and the gas sensor element 20 is less likely to peel off from the substrate 30. Therefore, the durability of the gas sensor 10 can be improved.

[0071] In the gas sensor 10 of the first embodiment, the joint portion 40 is made solely of gold (Au). This allows the physical properties of gold (Au) to be stably generated in the joint portion 40.

[0072] In the gas sensor 10 of the first embodiment, the bonding portion 40 includes a bonding body portion 41 and a first bonding pad 42 and a second bonding pad 43, which are arranged at both ends of the bonding body portion 41 in the stacking direction (up and down direction) and are mainly composed of gold (Au) or platinum (Pt). This makes it possible to realize a configuration that facilitates bonding between the bonding body portion 41 and the configuration on the substrate 30 side and the configuration on the gas sensor element 20 side by utilizing the first bonding pad 42 and the second bonding pad 43.

[0073] In the gas sensor 10 of the first embodiment, the first bonding pad 42 and the second bonding pad 43 are vapor-deposited films. This improves the adhesion between the first bonding pad 42 and the second bonding pad 43 and the gas sensor element 20 and the substrate 30.

[0074] <Second Embodiment> A second embodiment embodying the present disclosure will be described below with reference to Figure 4. The gas sensor of the second embodiment differs from that of the first embodiment in the configuration of the adhesion layer, but is otherwise common. Components identical to those of the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted.

[0075] As shown in Figure 4, the gas sensor 210 of the second embodiment comprises a gas sensor element 20, a substrate 30, a joint 40, a first contact portion 250, and a second contact portion 260. The gas sensor element 20 and the substrate 30 are joined via the joint 40, the first contact portion 250, and the second contact portion 260. The first contact portion 250 is positioned between the joint 40 and the gas sensor element 20. The second contact portion 260 is positioned between the joint 40 and the substrate 30.

[0076] 1-1. First contact portion 250 As shown in Figure 4, the surface (bottom surface) of the gas sensor element 20 (more specifically, the main body portion 21) that the first contact portion 250 contacts is the first surface 20A. The bottom surface of the first contact portion 250 is in contact with the top surface of the joint portion 40 (more specifically, the first joining pad 42).

[0077] The first adhesion portion 250 has a first intermediate layer 251 and a first adhesion layer 252. The first intermediate layer 251 is located on the joint portion 40 side of the first adhesion portion 250. The first intermediate layer 251 is in contact with the joint portion 40. The first intermediate layer 251 is made of tantalum oxide (Ta２ O ５ The first intermediate layer 251 is, for example, a vapor-deposited film. For example, the first intermediate layer 251 is a sputtered film formed by sputtering.

[0078] The first adhesion layer 252 is in contact with the first surface 20A. The first adhesion layer 252 contains tantalum (Ta). The first adhesion layer 252 is, for example, a vapor-deposited film. For example, the first adhesion layer 252 is a sputtered film formed by sputtering.

[0079] The first intermediate layer 251 and the first adhesion layer 252 are, for example, rectangular plates. The shape of the first intermediate layer 251 when viewed from above and the shape of the first adhesion layer 252 when viewed from above and the same rectangular shape as the first bonding pad 42.

[0080] 1-2. Second contact portion 260 As shown in Figure 4, the surface (upper surface) of the substrate 30 (more specifically, the insulating layer 35) that the second contact portion 260 contacts is the second surface 30A. The upper surface of the second contact portion 260 is in contact with the lower surface of the bonding portion 40 (more specifically, the second bonding pad 43).

[0081] The second adhesion portion 260 has a second intermediate layer 261 and a second adhesion layer 262. The second intermediate layer 261 is located on the joint portion 40 side of the second adhesion portion 260. The second intermediate layer 261 is in contact with the joint portion 40. The second intermediate layer 261 is made of tantalum oxide (Ta ２ O ５ The second intermediate layer 261 is, for example, a vapor-deposited film. For example, the second intermediate layer 261 is a sputtered film formed by sputtering.

[0082] The second adhesion layer 262 is in contact with the second surface 30A. The second adhesion layer 262 contains tantalum (Ta). The second adhesion layer 262 is, for example, a vapor-deposited film. For example, the second adhesion layer 262 is a sputtered film formed by sputtering.

[0083] The second intermediate layer 261 and the second adhesion layer 262 are, for example, rectangular plates. The shape of the second intermediate layer 261 when viewed from above and the shape of the second adhesion layer 262 when viewed from above and the other side are the same rectangular shape as the second bonding pad 43.

[0084] 2. Effects of the second embodiment In the gas sensor 210 of the second embodiment, the first contact portion 250 is made of tantalum oxide (Ta) on the joint portion 40 side. ２ O ５ The first intermediate layer 251 contains ) and the first adhesion layer 252 which is in contact with the first surface 20A and contains tantalum (Ta). The second adhesion portion 260 has tantalum oxide (Ta) on the joint portion 40 side ２ O ５ It has a second intermediate layer 261 containing ) and a second adhesion layer 262 that is in contact with the second surface 30A and contains tantalum (Ta).

[0085] With this gas sensor 210, a first contact portion 250 is provided between the joint portion 40 and the gas sensor element 20, thereby improving the adhesion between the joint portion 40 and the gas sensor element 20. Furthermore, a second contact portion 260 is provided between the joint portion 40 and the substrate 30, thereby improving the adhesion between the joint portion 40 and the substrate 30. In addition, the first contact portion 250 and the second contact portion 260 are provided on the joint portion 40 side of the joint portion 40, with gold (Au) as the main component. ２ O ５ Because it has a first intermediate layer 251 and a second intermediate layer 261 containing ), diffusion is less likely to occur between the joint 40 and the first and second adhesion portions 250 and 260, a decrease in bonding strength between the joint 40 and the gas sensor element 20 and the substrate 30 can be suppressed, and the gas sensor element 20 is less likely to peel off from the substrate 30. Therefore, the durability of the gas sensor 210 can be improved.

[0086] <Third Embodiment> A third embodiment embodying the present disclosure will be described below with reference to Figure 5. The gas sensor of the third embodiment differs from that of the first embodiment in the configuration of the joint, but is otherwise common. Components identical to those of the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted.

[0087] As shown in Figure 5, the gas sensor 310 of the third embodiment is equipped with a joint 340 instead of the joint 40 of the first embodiment.

[0088] The joint portion 340 includes a joint body portion 41, a first joining pad 42, a second joining pad 43, a third joining pad 344, and a fourth joining pad 345. The third joining pad 344 and the fourth joining pad 345 correspond to examples of "joining pads" in this disclosure.

[0089] The third bonding pad 344 and the fourth bonding pad 345 are positioned at both ends of the bonding body 41 in the stacking direction (up and down direction). Specifically, the third bonding pad 344 is positioned at the upper end of the bonding portion 340 and is in contact with the upper surface of the first bonding pad 42. The fourth bonding pad 345 is positioned at the lower end of the bonding portion 340 and is in contact with the lower surface of the second bonding pad 43. The third bonding pad 344 and the fourth bonding pad 345 contain platinum (Pt) as their main component. Preferably, the third bonding pad 344 and the fourth bonding pad 345 consist only of platinum (Pt). The third bonding pad 344 and the fourth bonding pad 345 are, for example, rectangular plates. The shape of the third bonding pad 344 and the fourth bonding pad 345 when viewed from the up and down direction is the same rectangular shape as the bonding body 41.

[0090] The third bonding pad 344 and the fourth bonding pad 345 are vapor-deposited films. For example, the third bonding pad 344 and the fourth bonding pad 345 are sputtered films formed by sputtering.

[0091] <Fourth Embodiment> A fourth embodiment embodying the present disclosure will be described below with reference to Figure 6. The gas sensor of the fourth embodiment differs from that of the first embodiment in the configuration of the adhesion layer and the joint, but is otherwise common. Components identical to those of the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted.

[0092] As shown in Figure 6, the gas sensor 410 of the fourth embodiment includes the first adhesion portion 250 and the second adhesion portion 260 of the second embodiment instead of the first adhesion layer 50 and the second adhesion layer 60 of the first embodiment. In addition, the gas sensor 410 includes the joint portion 340 of the third embodiment instead of the joint portion 40 of the first embodiment.

[0093] <Fifth Embodiment> A fifth embodiment embodying the present disclosure will be described below with reference to Figures 7 and 8. The gas sensor of the fifth embodiment differs from that of the first embodiment in the configuration of the conductive portion between the gas sensor element 20 and the substrate 30, but is otherwise common. Components identical to those of the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted.

[0094] 1-1. Configuration of the substrate 530 As shown in Figures 7 and 8, the substrate 530 of the gas sensor 510 of the fifth embodiment has a semiconductor substrate 34, an insulating layer 35, a pair of signal leads 538A, a pair of substrate-side signal pads 538B, a pair of heater leads 539A, and a pair of substrate-side heater pads 539B. Figure 7 is a cross-sectional view of Figure 8 along line B-B. In Figure 7, one signal lead 538A, one substrate-side signal pad 538B, one heater lead 539A, and one substrate-side heater pad 539B are visible.

[0095] A pair of signal leads 538A are embedded in the insulating layer 35. A substrate-side signal pad 538B is formed on one end of each signal lead 538A. Wiring (not shown) for exchanging power with an external circuit is connected to the substrate-side signal pad 538B. The other end of each signal lead 538A is exposed through a hole provided in the insulating layer 35. A fourth adhesion layer 590, described later, is connected to the other end of each signal lead 538A.

[0096] A pair of heater leads 539A are embedded in the insulating layer 35. A substrate-side heater pad 539B is formed at one end of the heater leads 539A. Wiring (not shown) for exchanging power with an external circuit is connected to the substrate-side heater pad 539B. The other end of the heater leads 539A is exposed through a hole provided in the insulating layer 35. A fourth contact layer 590, described later, is connected to the other end of the heater leads 539A.

[0097] 1-2. Configuration of the gas sensor element 20 In the gas sensor element 20, instead of the element-side signal electrode pad 22 and element-side heater electrode pad 23 of the first embodiment, an element-side signal electrode pad 522 (see Figure 8) and an element-side heater electrode pad 523 (see Figure 8) are provided on the lower surface of the main body 21.

[0098] 1-3. Conduction configuration between the gas sensor element 20 and the substrate 30 As shown in Figures 7 and 8, the gas sensor 510 includes four sets of second bonding portions 570, third adhesion layers 580, and fourth adhesion layers 590. The second bonding portion 570 is mainly composed of, for example, gold (Au). The second bonding portion 570 has a bonding body portion 571, a third bonding pad 572, and a fourth bonding pad 573. The bonding body portion 571 is sandwiched above and below by the third bonding pad 572 and the fourth bonding pad 573. The third adhesion layer 580 and the fourth adhesion layer 590 contain, for example, tantalum (Ta).

[0099] The element-side signal electrode pad 522 of the gas sensor element 20 and the other end of the signal lead 538A are connected via a second joint 570, a third contact layer 580, and a fourth contact layer 590. The third contact layer 580 is positioned between the second joint 570 and the element-side signal electrode pad 522. The fourth contact layer 590 is positioned between the second joint 570 and the other end of the signal lead 538A.

[0100] The element-side heater electrode pad 523 of the gas sensor element 20 and the other end of the heater lead 539A are connected via a second joint 570, a third contact layer 580, and a fourth contact layer 590. The third contact layer 580 is positioned between the second joint 570 and the element-side heater electrode pad 523. The fourth contact layer 590 is positioned between the second joint 570 and the other end of the heater lead 539A.

[0101] <Other Embodiments> This disclosure is not limited to the embodiments described above and in the drawings. For example, any combination of the features of the embodiments described above or below is possible as long as it does not contradict the original. Furthermore, any feature of the embodiments described above or below may be omitted unless explicitly stated as essential. In addition, the embodiments described above may be modified as follows.

[0102] In the first to fifth embodiments described above, one bonding configuration (bonding portion, first adhesion layer, second adhesion layer, etc.) was provided between the gas sensor element and the substrate, but multiple bonding configurations may be provided.

[0103] In the first to fifth embodiments described above, a configuration was shown in which the horizontal width of the joining body and the horizontal width of the joining pads (first joining pad, second joining pad, etc.) are the same, but they may be different. For example, the horizontal width of the joining pads (first joining pad, second joining pad, etc.) may be larger than the horizontal width of the joining body.

[0104] In the first to fifth embodiments described above, a configuration was shown in which the horizontal width of the bonding pad (first bonding pad, second bonding pad, etc.) and the horizontal width of the adhesive layer (first adhesive layer, second adhesive layer, etc.) are the same, but they may be different. For example, the horizontal width of the adhesive layer (first adhesive layer, second adhesive layer, etc.) may be greater than the horizontal width of the bonding pad (first bonding pad, second bonding pad, etc.).

[0105] In the first to fifth embodiments described above, a total of four electrode pads (electrode pads for the element-side signal and electrode pads for the element-side heater) were provided, but there are no need to be four. For example, in addition to the electrode pads for the element-side signal and the electrode pads for the element-side heater, an electrode pad for temperature measurement may be provided.

[0106] 10: Gas sensor 20: Gas sensor element 20A: First surface 21: Main body 22: Electrode pad for element-side signal 23: Electrode pad for element-side heater 24: Heater 25: Conductive part 30: Substrate 30A: Second surface 31: Frame 32: Membrane 33: Cavity 34: Semiconductor substrate 34A: Opening 35: Insulating layer 36: Substrate-side signal pad 37: Substrate-side heater pad 40: Bonding part 41: Bonding main body 42: First bonding pad (bonding pad) 43: Second bonding pad (bonding pad) 50: First adhesion layer 60: Second adhesion layer 210: Gas sensor 250: First adhesion part 251: First intermediate layer 252: First adhesion layer 260: 261: Second contact section 262: Second intermediate layer 262: Second contact layer 310: Gas sensor 340: Bonding section 344: Third bonding pad (bonding pad) 345: Fourth bonding pad (bonding pad) 410: Gas sensor 510: Gas sensor 522: Electrode pad for element-side signal 523: Electrode pad for element-side heater 530: Substrate 538A: Signal lead 538B: Substrate-side signal pad 539A: Heater lead 539B: Substrate-side heater pad 570: Second bonding section 571: Bonding body section 572: Third bonding pad 573: Fourth bonding pad 580: Third contact layer 590: Fourth contact layer C: Centerline

Claims

1. A gas sensor comprising a substrate and a gas sensor element disposed on the substrate, wherein the gas sensor element has a heater, the gas sensor element and the substrate are joined via a joint, a first adhesion layer disposed between the joint and the gas sensor element and in contact with the gas sensor element, and a second adhesion layer disposed between the joint and the substrate and in contact with the substrate, the first surface of the gas sensor element which is in contact with the first adhesion layer and the second surface of the substrate which is in contact with the second adhesion layer are composed of surfaces containing oxide or nitride, the joint mainly contains gold (Au), and the first and second adhesion layers are composed of tantalum oxide (Ta ２ O ５ Gas sensors, including ).

2. A gas sensor comprising a substrate and a gas sensor element disposed on the substrate, wherein the gas sensor element has a heater, the gas sensor element and the substrate are joined via a joint, a first contact portion disposed between the joint and the gas sensor element and in contact with the gas sensor element, and a second contact portion disposed between the joint and the substrate and in contact with the substrate, the first surface of the gas sensor element which is the surface in contact with the first contact portion, and the second surface of the substrate which is the surface in contact with the second contact portion are composed of a surface containing an oxide or nitride, the joint mainly contains gold (Au), and the first contact portion is composed of tantalum oxide (Ta) on the joint side ２ O ５ The second adhesion portion has a first intermediate layer containing ) and a first adhesion layer in contact with the first surface and containing tantalum (Ta), and the second adhesion portion has tantalum oxide (Ta) on the joint side ２ O ５ A gas sensor having a second intermediate layer containing ) and a second adhesion layer in contact with the second surface and containing tantalum (Ta).

3. The gas sensor according to claim 1 or claim 2, wherein the joint portion is made of gold (Au) only.

4. The gas sensor according to claim 1 or claim 2, wherein the joint portion comprises a joint body portion and joint pads disposed at both ends of the joint body portion in the stacking direction, the joint pads being mainly composed of gold (Au) or platinum (Pt).

5. The gas sensor according to claim 4, wherein the bonding pad is a vapor-deposited film.

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