JP3677479B2 - Oxygen sensor element - Google Patents

Description

【００５５】
表１の結果によれば、本発明に基づき、一対の発熱体パターンを絶縁層を介して設けると、素子の幅を発熱体パターンの幅ｘに対して、２．５ｘ以下に狭めることができ、素子の小型化を図ることができるとともに、活性化時間も短縮することができた。しかも、小型化によって、ヒータの耐久性も向上することがわかった。
【００５６】
【発明の効果】
以上詳述したとおり、本発明によれば、センサ部と一体的に設けられるヒータ部における一対の発熱体をセラミック絶縁層を介して形成することによって、小型で、且つガス応答性の優れ急速昇温が可能な酸素センサ素子を得ることができる。
【図面の簡単な説明】
【図１】本発明の酸素センサ素子の一例を説明するための概略断面図である。
【図２】本発明の酸素センサ素子の他の例を説明するために概略断面図である。
【図３】本発明における発熱体パターンの構造を説明するための概略透過図である。
【図４】本発明における発熱体パターンの他の構造を説明するための透過図である。
【図５】図１の酸素センサ素子の製造方法を説明するための分解斜視図である。
【図６】活性化時間の測定方法を説明するためのグラフである。
【図７】従来のヒータ一体型酸素センサ素子の構造を説明するための概略断面図である。
【図８】従来の他のヒータ一体型酸素センサ素子の構造を説明するための概略断面図である。
【符号の説明】
１ センサ部
２ ヒータ部
３ 固体電解質
４ 基準電極
５ 測定電極
６ セラミック多孔質層
７ セラミック絶縁層
８ 白金ヒータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxygen sensor element, and more particularly to an oxygen sensor element for controlling a ratio of air and fuel in an internal combustion engine such as an automobile.
[0002]
[Prior art]
Currently, in an internal combustion engine such as an automobile, by detecting the oxygen concentration in the exhaust gas and controlling the amount of air and fuel supplied to the internal combustion engine based on the detected value, harmful substances from the internal combustion engine, For example, a method of reducing CO, HC, and NOx is adopted.
[0003]
As this detection element, a solid electrolyte type oxygen mainly composed of a solid electrolyte mainly composed of zirconia having oxygen ion conductivity and having a pair of electrode layers formed on the outer surface and the inner surface of a cylindrical tube sealed at one end. A sensor is used. As a typical example of this oxygen sensor, as shown in the schematic cross-sectional view of FIG. 7, the inner surface of a cylindrical tube 31 made of a ZrO ₂ solid electrolyte and sealed at the tip is made of platinum as a sensor part and made of air. A reference electrode 32 that comes into contact with a reference gas such as the above, and a measurement electrode 33 that comes into contact with a measured gas such as exhaust gas are formed on the outer surface of the cylindrical tube 31.
[0004]
In such an oxygen sensor, a so-called theoretical air-fuel ratio sensor (λ sensor) that is generally used for controlling the ratio of air to fuel near 1 is a ceramic porous as a protective layer on the surface of the measurement electrode 33. A layer 34 is provided, and an oxygen concentration difference generated on both sides of the cylindrical tube 31 at a predetermined temperature is detected to control the air-fuel ratio of the engine intake system. At this time, the theoretical air-fuel ratio sensor needs to be heated up to an operating temperature of about 700 ° C. For this reason, a rod heater 35 is inserted inside the cylindrical tube 31 to heat the sensor unit to the operating temperature. Yes.
[0005]
[Problems to be solved by the invention]
However, in recent years, exhaust gas regulations have been strengthened, and it has become necessary to detect CO, HC, and NOx immediately after the engine is started. In response to such a request, in the indirect heating type cylindrical oxygen sensor formed by inserting the heater 35 into the cylindrical tube 31 as described above, the time required for the sensor unit to reach the activation temperature (hereinafter, There is a problem that exhaust gas regulations cannot be fully met because the activation time is slow.
[0006]
In recent years, as a method for avoiding this problem, a reference electrode 37 and a measurement electrode 38 are provided on the outer surface and the inner surface of a flat solid electrolyte substrate 36 as shown in the schematic cross-sectional view of FIG. A heater-integrated oxygen sensor element in which a heating element 40 is embedded is proposed.
[0007]
However, unlike the conventional indirect heating method described above, the conventional heater-integrated oxygen sensor is a direct heating method, so that rapid temperature increase is possible. However, it is desired to further increase the rate of temperature increase. However, since the element itself is large, there is a limit to rapid temperature increase, and as a result, there is a problem that the activation time cannot be shortened.
[0008]
An object of the present invention is to provide an oxygen sensor element that is small in size and excellent in gas responsiveness and capable of rapid temperature increase.
[0009]
[Means for Solving the Problems]
The present inventor has examined the above problem, and one of the factors that hinders the downsizing of the element is the arrangement of the heating element in the heater portion. By downsizing this, the design for downsizing of the element is performed. As a result of repeated investigations based on the knowledge that the degree of freedom can be improved, a pair of heating elements in a cross section perpendicular to the longitudinal direction of the heater portion can be formed through a ceramic insulating layer to reduce the size. As a result, the present invention has been found.
[0010]
That is, in the oxygen sensor element of the present invention, a sensor part provided with a measurement electrode and a reference electrode on at least opposite surfaces of a long ceramic solid electrolyte substrate flat plate, and a heating element embedded in the ceramic insulating layer. In an oxygen sensor element having an overall thickness of 0.8 to 1.5 mm provided with a heater portion, a pair of heating elements in a cross section in a direction orthogonal to the longitudinal direction of the heater portion has a ceramic insulation having a thickness of 1 to 300 μm. The maximum width x in the direction orthogonal to the longitudinal direction of the heating element and the maximum width w in the direction orthogonal to the longitudinal direction of the oxygen sensor element are w ≦ 2. It has a 5x relationship .
[0013]
The sensor unit and the heater unit may be formed by simultaneous firing, or may be formed separately from the sensor unit and the heater unit, and then bonded and integrated with a bonding material. Good.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of the basic structure of the oxygen sensor element of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining an example of the oxygen sensor element of the present invention, and FIG. 2 is a schematic cross-sectional view for explaining another example. These are generally referred to as theoretical air-twist ratio sensor elements, and both include the sensor unit 1 and the heater unit 2 in the examples of FIGS.
[0015]
In the oxygen sensor element of FIG. 1, a ceramic solid electrolyte substrate 3 made of zirconia and having oxygen ion conductivity, a reference electrode 4 that is in contact with air, and a measurement that is in contact with exhaust gas are provided on both opposing surfaces of the solid electrolyte substrate 3. The electrode 5 is formed, and the sensor unit 1 having a function of detecting the oxygen concentration is formed.
[0016]
That is, the solid electrolyte substrate 3 has a flat hollow shape with the tip sealed, and the hollow portion forms the air introduction hole 3a. A reference electrode 4 in contact with a reference gas such as air is deposited on the hollow inner wall, and measurement is performed on the outer surface of the solid electrolyte substrate 3 facing the reference electrode 4 with a measured gas such as exhaust gas. An electrode 5 is formed.
[0017]
Further, from the viewpoint of preventing electrode poisoning by exhaust gas, a ceramic porous layer 6 is formed on the surface of the measurement electrode 5 as an electrode protective layer.
[0018]
On the other hand, the heater unit 2 has a structure in which a heating element 8 is embedded in a ceramic insulating layer 7 having electrical insulation. In the oxygen sensor element of FIG. 1, the heater unit 2 is integrated with the sensor unit 1 by firing. In the oxygen sensor element of FIG. 2, the sensor unit 1 and the heater unit 2 are formed separately from each other and joined by a joining material 10.
[0019]
In particular, when the difference in thermal expansion coefficient between the solid electrolyte substrate 3 of the sensor unit 1 and the ceramic insulating layer 7 of the heater unit 2 is large, it is desirable to have the structure of FIG. It is desirable to join at a low temperature part in use in which 8 and electrodes 4 and 5 are not formed. Further, in the case of bonding over the entire surface, for example, the zirconia solid electrolyte substrate 3 of the sensor unit 1 and the alumina ceramic insulation of the heater unit 2 are alleviated in order to relieve stress due to the difference in thermal expansion coefficient between the sensor unit 1 and the heater unit 2. A composite material with the layer 7, alumina and zirconia may be interposed between the composite compound layers.
[0020]
In FIG. 1, the heater unit 2 is a sensor unit in order to increase the heating efficiency of the heater unit 2 and to increase the heating efficiency of the heater unit 2. It is desirable to form a ceramic layer 9 having the same or similar thermal expansion coefficient as that of the solid electrolyte substrate 3 on the side opposite to the side in contact with 1.
[0021]
In the present invention, as shown in FIGS. 1 and 2, it is important that the pair of heating elements 8 in the cross section in the direction orthogonal to the longitudinal direction of the heater portion 2 is formed via the ceramic insulating layer 7a. is there. In other words, the main feature is that the pair of heating elements 8 are formed in different planes, not in the same plane.
[0022]
More specifically, as shown in the schematic transmission diagram for explaining the structure of the heating element pattern in FIG. 3, the lead 8 a 1 extends in the longitudinal direction from one end side in the long ceramic insulating layer 7, and the ceramic insulating layer 7 is formed in a portion facing the electrode forming portion of the sensor portion 1 near the other end portion of the sensor 7, and after being folded at the other end portion of the element, connected to the lead 8a2 via the heat generating portion 8b2. Yes. In the present invention, at least the heat generating portions 8b1 and 8b2 are formed above and below via the ceramic insulating layer 7a, and the heat generating portions 8b1 and 8b2 are formed of vias 8c penetrating the ceramic insulating layer 7a at the other end. It is electrically connected by a connection body.
[0023]
The heating element pattern of FIG. 3 is composed of a meander structure (waveform) pattern. When the width of the heating element is x, in the meander structure of FIG. 3, the width x of the heating element 8 has the maximum amplitude of the waveform. Equivalent to. When the heat generating portions 8b1 and 8b2 each have a predetermined width x, generally, when they are formed in the same plane, the width w of the entire element is a margin for embedding the heat generating portions 8b1 and 8b2 in the insulating layer 7. In order to prevent a short circuit between the portions and the heating elements 8b1 and 8b2, the width w of the entire element needs to be about w ≧ 3x.
[0024]
On the other hand, when the heat generating portions 8b1 and 8b2 are formed between different layers according to the present invention, the insulating properties are maintained by the ceramic insulating layer 7a even when the heat generating portions 8b1 and 8b2 overlap each other in plan view. In addition, the overall width w of the device can be smaller than 3x. In particular, in order to reduce the size, it is desirable to satisfy w ≦ 2.5x, and further w ≦ 2x.
[0025]
The thickness of the ceramic insulating layer 7a between the upper and lower heat generating portions 8a1 and 8b2 is required to be 1 to 300 μm or more, particularly 5 to 100 μm, and further 5 to 50 μm from the viewpoint of electrical insulation .
[0026]
In the example of FIG. 3, the heating element 8 has a meandering (waveform) pattern that is folded in a direction orthogonal to the longitudinal direction of the element. However, the heating element pattern is limited to this. For example, as shown in the pattern diagram of the heating element in FIG. 4, a meander pattern having a folding in the longitudinal direction of the element may be used.
[0027]
The solid electrolyte used in the oxygen sensor element of the present invention is made of a ceramic containing ZrO ₂ , and Y ₂ O ₃ and Yb ₂ O ₃ , Sc ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O are used as stabilizers. _3, Dy ₂ O ₃ or the like 1 to 30 mol% of rare earth oxide in terms of oxide, preferably the partially stabilized ZrO ₂ or stabilized ZrO ₂ containing 3 to 15 mol% are used. Further, by using ZrO ₂ in which 1 to 20 atomic% of Zr in ZrO ₂ is substituted with Ce, there is an effect that the ionic conductivity is increased and the responsiveness is further improved. Furthermore, for the purpose of improving the sinterability, Al ₂ O ₃ and SiO ₂ can be added to the ZrO ₂ , but if it is contained in a large amount, the creep properties at high temperatures are deteriorated. The total amount of Al ₂ O ₃ and SiO ₂ is preferably 5% by weight or less, particularly 2% by weight or less.
[0028]
The reference electrode 4 and the measurement electrode 5 deposited on the surface of the solid electrolyte substrate 3 are both platinum or an alloy of platinum and one selected from the group of rhodium, palladium, ruthenium and gold. In addition, for the purpose of preventing the grain growth of the metal in the electrode during the operation of the sensor and for the purpose of increasing the contact at the so-called three-phase interface between the platinum particles, the solid electrolyte and the gas related to the responsiveness, The components may be mixed in the electrodes 4 and 5 at a ratio of 1 to 50% by volume, particularly 10 to 30% by volume. Further, the electrode shape may be a quadrangle or an ellipse. The thickness of the electrodes 4 and 5 is preferably 3 to 20 μm, particularly preferably 5 to 10 μm.
[0029]
On the other hand, the ceramic insulating layer 7 in which the heating element 8 is embedded is preferably composed of a dense ceramic made of alumina ceramics having a relative density of 80% or more and an open porosity of 5% or less. At this time, Mg, Ca and Si may be contained in total in an amount of 1 to 10% by mass for the purpose of improving sinterability. However, the content of alkali metals such as Na and K is migrated to the heater part. In order to deteriorate the electrical insulation between the pair of heaters in No. 2, it is desirable to control to 50 ppm or less in terms of oxide weight. In addition, by setting the relative density within the above range, the substrate strength increases, and as a result, the mechanical strength of the oxygen sensor itself can be increased.
[0030]
The ceramic porous layer 6 formed on the surface of the measuring electrode 5 is at least one selected from the group consisting of zirconia, alumina, γ-alumina and spinel having a thickness of 10 to 800 μm and a porosity of 10 to 50%. It is desirable to be formed by. When the thickness of the porous layer 6 is less than 10 μm or the porosity exceeds 50%, the electrode poisoning substance P, Si, etc. easily reach the electrode and the electrode performance is deteriorated. On the other hand, when the thickness of the porous layer 6 exceeds 800 μm or the porosity is less than 10%, the diffusion rate of the gas in the porous layer 6 becomes slow, and the gas responsiveness of the electrode is deteriorated. In particular, the thickness of the porous layer 6 is suitably 100 to 500 μm, although it depends on the porosity.
[0031]
The heating element 8 and the leads 8a1 and 8a2 embedded in the ceramic insulating layer 7 in the heater section 2 use platinum as a metal or an alloy of platinum and one selected from the group of rhodium, palladium, and ruthenium. Can do. In this case, the resistance ratio between the heating element 8 and the leads 8a1 and 8a2 is preferably controlled in the range of 9: 1 to 7: 3 at room temperature.
[0032]
In addition, the oxygen sensor element of the present invention needs to have a total thickness of 0.8 to 1.5 mm, particularly 1.0 to 1.2 mm. 55 mm, particularly 45 to 50 mm, is preferable from the relationship between the rapid temperature rise property and how the element is mounted in the engine.
[0033]
Next, a method for manufacturing the oxygen sensor element of the present invention will be described with reference to the exploded perspective view of FIG. 5, taking the method of manufacturing the oxygen sensor element of FIG. 1 as an example.
[0034]
First, a solid electrolyte green sheet 11 is prepared. For example, the green sheet 11 may be formed by appropriately adding a forming organic binder to a ceramic solid electrolyte powder having oxygen ion conductivity of zirconia, and by a doctor blade method, extrusion molding, or isostatic pressing (rubber press). Or it produces by well-known methods, such as press formation.
[0035]
Next, a pattern 12, a lead pattern 13, a through hole (not shown), etc., which become the measurement electrode 5 and the reference electrode 4, respectively, are slurried on both surfaces of the green sheet 11 using, for example, a conductive paste containing platinum. After printing by dipping , screen printing, pad printing, or roll transfer, the green sheet 15 and the green sheet 16 in which the air introduction hole 14 is formed are interposed with an adhesive such as an acrylic resin or an organic solvent, or a roller or the like The laminated body A of the sensor part 1 is produced by mechanically adhering while applying pressure.
[0036]
At this time, a porous slurry for forming the ceramic porous layer 6 of FIG. 1 may be formed by printing on the surface of the pattern 12 to be the measurement electrode 5.
[0037]
Next, as shown in FIG. 5, a paste made of alumina powder is printed on the surface of the zirconia green sheet 17 by a slurry dipping method, screen printing, pad printing, or roll transfer to form a ceramic insulating layer 18a.
[0038]
Next, as shown in FIG. 1, when the platinum heater is formed up and down via the ceramic insulating layer, first, the lower heater pattern 19a and the lead pattern 20a are printed on the surface of the ceramic insulating layer 18a. . Then, an insulating paste such as alumina is applied to form the ceramic insulating layer 18b, and the upper heater pattern 19b and the lead pattern 20b are printed on the surface of the ceramic insulating layer 18b. Then, the laminated body B of the heater unit 2 is manufactured by printing the ceramic insulating layer 18c again using an insulating paste.
[0039]
At this time, in order to connect the lower heater pattern 19a and the upper heater pattern 20b, a through hole extending from the surface to the lower heater pattern is formed in the ceramic insulating layer 18b after the ceramic insulating layer 18b is formed. When the upper heater pattern is formed, the via conductor 21 is formed by filling the through hole with a conductive paste. Alternatively, the front end portion of the ceramic insulating layer 18b is cut out so that a part of the lower heater pattern 19a is exposed, and a conductive paste is applied to the cutout portion to connect the upper and lower heater patterns. A connected heating element can be formed.
[0040]
In preparing the laminate B of the heater section, the ceramic insulating layers 18a, 18b, and 18c are formed by printing and applying an insulating paste as described above, and using a ceramic slurry such as alumina. An insulating sheet can be formed and laminated by a sheet forming method such as a blade method.
[0041]
Thereafter, the laminated body A of the sensor part and the laminated body B of the heater part are bonded together by interposing an adhesive such as an acrylic resin or an organic solvent, or by mechanically bonding the two while applying pressure with a roller or the like. These are fired. Firing is performed in the air or in an inert gas atmosphere at a temperature range of 1300 ° C to 1700 ° C for 1 to 10 hours. At the time of firing, in order to suppress warping of the sensor part A at the time of firing, the amount of warpage can be reduced by placing a smooth substrate such as alumina on the laminate as a weight.
[0042]
Further, when the laminated body A of the sensor part and the laminated body B of the heater part are simultaneously fired and integrated, for example, a sensor part is formed in order to reduce the generation of stress due to the difference in thermal expansion coefficient between them. It is desirable to interpose a composite material of the solid electrolyte component to be formed and the insulating component forming the ceramic insulating layer of the heater portion.
[0043]
Thereafter, if necessary, the heater part was integrated by forming at least one ceramic selected from the group consisting of alumina, zirconia, and spinel on the surface of the measurement electrode 12 after firing by a plasma spraying method or the like. An oxygen sensor element can be formed.
[0044]
In the above method, the heater part is described as being formed by simultaneous firing with the sensor part. However, after the sensor part and the heater part are separately fired, they are joined with a suitable inorganic adhesive such as glass. It is also possible to integrate them.
[0045]
【Example】
The λ sensor shown in FIG. 1 was produced as follows according to FIG.
First, it consists of a commercially available 99.9% alumina powder, 0.1 mol% Si-containing 5 mol% Y ₂ O ₃ zirconia powder, and an average particle diameter of 0.1 μm and 8 mol% yttria. Platinum powders containing 30% by volume of zirconia in crystals were prepared.
[0046]
First, a polyvinyl alcohol solution is added to zirconia powder containing 5 mol% Y ₂ O ₃ to prepare a slurry, and a zirconia green sheet 11 having a thickness after sintering of 0.4 mm is manufactured by extrusion molding. did.
[0047]
Thereafter, the conductive paste containing the platinum powder is screen-printed on both surfaces of the green sheet 11 to form the measurement electrode and the reference electrode pattern 12 and the lead pattern 13, and then the green in which the air introduction hole 14 is formed. The sheet 15 and the green sheet 16 were laminated with an acrylic resin adhesion material to obtain a sensor laminate A. At this time, the measurement electrode was formed to be 10 mm ² after firing.
[0048]
Next, the surface of the zirconia green sheet 17 is screen-printed using the above-mentioned paste made of alumina powder to form the ceramic insulating layer 18a so as to have a thickness of about 10 μm after firing, and then one heater pattern 19a and lead pattern 20a are formed. Then, a conductive paste containing a platinum powder containing alumina was printed by screen printing, and a paste made of alumina powder was screen printed once again on this surface to form a ceramic insulating layer 18b. Thereafter, the other heater pattern 19b and the lead pattern 20b are formed by screen printing using the same conductive paste as described above, and the ceramic insulating layer 18c is formed again, whereby the heater substrate laminate B is manufactured. did. The heater patterns 19a and 19b were connected by via conductors 21 formed in the ceramic insulating layer 18b.
[0049]
The heater patterns 19a and 19b have a meander structure pattern with a width of 1.1 mm as shown in FIG.
[0050]
Thereafter, the laminate obtained by joining the laminate A for sensor substrates and the laminate B for heater substrates was baked at 1500 ° C. for 1 hour to produce a heater integrated oxygen sensor element.
[0051]
In addition, by changing the widths of the sensor substrate laminate A and the heater substrate laminate B, the stoichiometric air-fuel ratio (λ type) heater integrated oxygen sensor element having a width of Table 1 was manufactured.
[0052]
Thereafter, a mixed gas of hydrogen, methane, nitrogen, and oxygen is used to blow the mixed gas of air-fuel ratio 11 and 23 alternately to the sensor element at intervals of 0.5 seconds, and 12 V is applied to the heater of the element to apply the element. The activation time was measured. At this time, as shown in FIG. 6, the time during which the voltage is applied to the heater is set to zero. First, the element shows 0.6 V at the air-fuel ratio 11 and then the time t until it shows 0.3 V at the air-fuel ratio 11 Activation time.
[0053]
Further, as a heater durability test, 18 V was applied to the heater of the element in the atmosphere, and the time until the heater was disconnected was measured. The results are shown in Table 1.
[0054]
[Table 1]

[0055]
According to the results in Table 1, when a pair of heating element patterns are provided via an insulating layer according to the present invention, the width of the element can be reduced to 2.5x or less with respect to the width x of the heating element pattern. The element can be miniaturized and the activation time can be shortened. Moreover, it has been found that the durability of the heater is improved by downsizing.
[0056]
【The invention's effect】
As described above in detail, according to the present invention, the pair of heating elements in the heater unit provided integrally with the sensor unit is formed via the ceramic insulating layer, thereby reducing the size and increasing the gas response rapidly. An oxygen sensor element capable of temperature can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view for explaining an example of an oxygen sensor element of the present invention.
FIG. 2 is a schematic sectional view for explaining another example of the oxygen sensor element of the present invention.
FIG. 3 is a schematic transmission diagram for explaining a structure of a heating element pattern in the present invention.
FIG. 4 is a transmission diagram for explaining another structure of the heating element pattern in the present invention.
5 is an exploded perspective view for explaining a method for manufacturing the oxygen sensor element of FIG. 1. FIG.
FIG. 6 is a graph for explaining a method for measuring activation time.
FIG. 7 is a schematic cross-sectional view for explaining the structure of a conventional heater-integrated oxygen sensor element.
FIG. 8 is a schematic cross-sectional view for explaining the structure of another conventional oxygen sensor element integrated with a heater.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sensor part 2 Heater part 3 Solid electrolyte 4 Reference electrode 5 Measuring electrode 6 Ceramic porous layer 7 Ceramic insulating layer 8 Platinum heater

Claims (3)

The overall thickness of the sensor is such that a sensor part provided with a measurement electrode and a reference electrode on at least both opposing surfaces of a long ceramic solid electrolyte substrate plate, and a heater part in which a heating element is embedded in a ceramic insulating layer. In the oxygen sensor element of 0.8 to 1.5 mm, a pair of heating elements in a cross section in a direction orthogonal to the longitudinal direction of the heater portion is formed via a ceramic insulating layer having a thickness of 1 to 300 μm , The maximum width x in the direction orthogonal to the longitudinal direction of the heating element and the maximum width w in the direction orthogonal to the longitudinal direction of the oxygen sensor element have a relationship of w ≦ 2.5x. Oxygen sensor element. The oxygen sensor element according to claim 1, wherein the sensor unit and the heater unit are formed by simultaneous firing. 2. The oxygen sensor element according to claim 1, wherein the sensor unit and the heater unit are formed separately from each other, and are bonded and integrated by a bonding material.

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