JP2008053278A - Laminated capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated capacitor improving the dielectric constant of ceramics without lowering an insulation resistance capable of obtaining a large electrostatic capacity and having an excellent reliability. <P>SOLUTION: In the laminated capacitor 1, a plurality of internal electrodes 3a, 3b, 4a and 4b are formed so as to be superposed through ceramic layers in a ceramics sintered body 2 composed of (Ba, Ca)(Ti, Zr)O<SB>3</SB>ceramics as a main component and ceramics containing Ni and an rare earth element R as by-components at a mol ratio Ni/R at a value from 0.05 to 0.25. In the laminated capacitor 1, sections superposing a plurality of the internal electrodes 3a, 3b, 4a and 4b through the ceramic layers are used as an internal layer 2W and ceramics formed outside the laminating direction of the internal layer 2W and laminating no internal electrode through ceramics are used as external layers 2V. In the laminated capacitor 1, B/A is set in 0.5 or less when the thickness of the internal layer 2W is represented by A and the whole thickness of the external layers 2V and 2V by B. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multilayer capacitor using a ceramic sintered body obtained by a technique of integrally firing ceramics and internal electrodes using dielectric ceramics.

  A multilayer capacitor is required to have a small size and a large capacity in order to reduce the size. Depending on the application, a large-capacity multilayer capacitor using a dielectric ceramic having a dielectric constant of 10,000 or more is also used. In such a multilayer capacitor, for example, the capacitance temperature characteristic satisfies the F characteristic of JIS standard, and the capacitance temperature characteristic is not so good. That is, priority is given to a capacity larger than the capacitance temperature characteristic.

As dielectric ceramics having a dielectric constant of 10,000 or more, as described in Patent Document 1 below, BaTiO ₃ of BaTiO ₃ is substituted with Ca and Zr, respectively (Ba, Ca) (Ti, Zr). O ₃ ceramics are known. In Patent Document 1, a main component represented by (Ba _1-x Ca _x ) (Ti _1-y Zr _y ) O ₃ (however, 0.01 ≦ x ≦ 0.10, 0.1 <y <0. 26) 0.2 to 1.0 part by weight of Y ₂ O ₃ , 0.06 to 0.6 part by weight of MnO ₂ , and 0.1 to 1 part of Al ₂ O ₃ as subcomponents with respect to 100 parts by weight. A multilayer capacitor using a dielectric ceramic having a composition containing 0 part by weight and 0.1 to 1.0 part by weight of NiO is disclosed.

  However, in recent years, a further increase in capacitance has been demanded. In order to increase the capacitance, (1) a method of devising a laminated structure or (2) a method of increasing the dielectric constant of the dielectric ceramic layer can be considered.

  (2) In order to increase the dielectric constant of the dielectric ceramic layer, a method of improving the ceramic composition is effective. However, when the dielectric constant is increased, it is difficult to achieve compatibility with other characteristics, for example, compatibility with dielectric temperature characteristics and high temperature load reliability. Therefore, there is a limit to increasing only the dielectric constant without sacrificing other characteristics.

  On the other hand, in Patent Document 2 below, a multilayer capacitor using a dielectric ceramic having a composition in which MgO and rare earth oxides are added to barium titanate as subcomponents by 2 mol% or less is sandwiched between internal electrodes. It has been shown that the dielectric constant of the ceramic layer is increased by reducing the thickness of the ceramic layer to 2 μm or less, the thickness of the internal electrode to 1 μm or more, and the number of stacked internal electrodes to 100 or more.

  Here, when the internal electrode and the dielectric ceramic layer were integrally fired, the internal electrode was sandwiched between the internal electrodes due to the difference between the shrinkage rate during firing of the internal electrode and the shrinkage rate during firing of the dielectric ceramic layer. It is said that the dielectric constant is increased by applying stress to the dielectric ceramic layer.

Further, in Patent Document 2, in the conventional multilayer ceramic capacitor, the relative dielectric constant hardly changed even when the number of dielectric layers was changed, whereas in the configuration described in Patent Document 2, the dielectric layer Has a core-shell structure particle in which barium titanate is the core and MgO and rare earth oxide subcomponents form a shell. Therefore, the dielectric ceramic layer is thinned and the number of layers is increased, so that the stress is applied. It is said that the distortion increases and the dielectric constant is increased.
JP-A-10-139538 JP 2004-111461 A

  As described above, in the multilayer capacitor described in Patent Document 2, in the multilayer capacitor using the core-shell dielectric ceramic having the specific composition, the thickness of the ceramic layer sandwiched between the internal electrodes is reduced, and the number of stacked layers By increasing the stress, stress is applied to the ceramic layer due to the difference in shrinkage during firing, and the dielectric constant is increased. Accordingly, it is said that a dielectric capacitor can be increased and a large-capacity multilayer capacitor can be obtained without changing the composition of the dielectric ceramic.

  However, in the multilayer capacitor, in order to increase the number of layers while maintaining the outer diameter, it is necessary to reduce the thickness of the ceramic layer sandwiched between the internal electrodes. If the thickness of the ceramic layer sandwiched between the internal electrodes is too thin, there is a risk that a short circuit will occur between the internal electrodes that overlap with each other via the ceramic layer, and the insulation resistance of the multilayer capacitor may be reduced.

  The object of the present invention is to increase the dielectric constant without changing the composition of the dielectric ceramics in view of the above-described state of the prior art, and is therefore suitable for increasing the capacity and being sandwiched between the internal electrodes. Therefore, it is not necessary to reduce the thickness of the ceramic layer so much, and it is therefore an object of the present invention to provide a multilayer capacitor excellent in reliability in which a decrease in insulation resistance hardly occurs.

In the present invention, the main component is a (Ba, Ca) (Ti, Zr) O ₃ based ceramic layer, and Ni and rare earth elements R (where R is Y, Sc, La, Ce, Pr, Nd) as subcomponents. , Sm, Eu, Tb, Gd, Dy, Ho, Er, Tm, Yb, Lu), a ceramic sintered body made of ceramics, and the ceramic sintered body, A multilayer capacitor comprising a plurality of internal electrode layers arranged so as to overlap with each other via a ceramic layer, wherein the molar ratio Ni / R is 0.05 or more and less than 0.2, and in the ceramic sintered body, A portion in which a plurality of internal electrodes overlap with each other through a ceramic layer is provided on the inner layer portion and on the outer side in the stacking direction of the inner layer portion. B / A is set to 0.5 or less, where the hook portion is the outer layer portion, the thickness of the inner layer portion is A, and the total thickness of the outer layer portion is B.

In the multilayer capacitor according to the present invention, preferably, 0.01 ≦ x ≦ 0.05 when the main component of the ceramic is expressed as (Ba _1−x Ca _x ) (Ti _1−y Zr _y ) O _3. Moreover, 0.05 ≦ y ≦ 0.15, and in this case, the shrinkage rate difference upon firing with the internal electrode can be further increased, and a larger capacitance can be obtained.

  In the present invention, preferably, the internal electrode is mainly composed of Ni, and in this case, the shrinkage rate of the internal electrode during firing is sufficiently large, and the inner layer portion is caused by a shrinkage difference from the dielectric ceramic layer. As a result, a large stress is applied to the dielectric ceramic, thereby further effectively increasing the dielectric constant of the dielectric ceramic of the inner layer portion.

  In the multilayer capacitor according to the present invention, the outer layer portion is disposed on both sides of the inner layer portion in the stacking direction, but the thicknesses of the outer layer portions on both sides are preferably equal, but are slightly different as long as the object of the present invention is not impaired. It may be.

In the multilayer capacitor according to the present invention, a ceramic sintered body is formed using a dielectric ceramic having a composition that includes (Ba, Ca) (Ti, Zr) O ₃ ceramics as a main component and includes rare earth elements and Ni as subcomponents. Since it is configured, it is easy to increase the capacity, and when the thickness of the inner layer portion is A and the total thickness of the outer layer portion is B, B / A is 0.5 or less and the molar ratio is When Ni / R is 0.05 or more and less than 0.20, if a large stress is applied to the inner layer due to the difference in shrinkage between the internal electrode and the dielectric ceramic layer during firing, the dielectric ceramic layer of the inner layer The dielectric constant is effectively increased.

  In this case, since the dielectric constant of the dielectric ceramic layer of the inner layer portion is increased by the stress generated by the difference in shrinkage rate between the inner layer portion and the outer layer portion, the thickness of one ceramic layer sandwiched between the inner electrodes in the inner layer portion. There is no need to make it too thin. Therefore, it is possible to provide a large-capacity multilayer capacitor without causing a decrease in insulation resistance.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1 is a schematic front sectional view for explaining a multilayer capacitor according to an embodiment of the present invention.

  The multilayer capacitor 1 has a ceramic sintered body 2. The ceramic sintered body 2 has a rectangular parallelepiped shape, and includes a first end surface 2a, a second end surface 2b facing the first end surface 2a, an upper surface 2c, and a lower surface 2d.

  In the ceramic sintered body 2, a plurality of first internal electrodes 3 a and 3 b and second internal electrodes 4 a and 4 b are provided so as to overlap with each other via a ceramic layer. For ease of illustration, it should be pointed out that in FIG. 1, the number of internal electrodes is considerably smaller than the actual number.

  The ceramic sintered body 2 is obtained by a known ceramic-metal integrated firing technique. That is, it is obtained by laminating a plurality of ceramic green sheets mainly composed of dielectric ceramics via internal electrodes, laminating plain ceramic green sheets on the top and bottom, and firing the obtained laminate.

  The plurality of first internal electrodes 3a and 3b extend in a direction parallel to the upper surface 2c and the lower surface 2d of the ceramic sintered body 2, and are drawn out to the first end surface 2a. The second inner electrodes 4a and 4b extend in a direction parallel to the upper surface 2c and the lower surface 2d, and are drawn out to the second end surface 2b.

  A first external electrode 5 is formed so as to cover the first end face 2a of the ceramic sintered body 2, and a second external electrode 6 is formed so as to cover the second end face 2b.

In the multilayer capacitor 1 of the present embodiment, the ceramic sintered body 2 is mainly composed of (Ba, Ca) (Ti, Zr) O ₃ -based ceramics, contains Ni and a rare earth element R as subcomponents, and has a molar ratio. It is made of dielectric ceramics having Ni / R of 0.05 or more and less than 0.2. The rare earth element R is specifically at least one selected from Y, Sc, La, Ce, Pr, Nd, Sm, Eu, Tb, Gd, Dy, Ho, Er, Tm, Yb, and Lu. It is. That is, as the rare earth element R, two or more kinds of rare earth elements may be blended.

The (Ba, Ca) (Ti, Zr) O ₃ ceramics as the main component is preferably _x when expressed as (Ba _1-x Ca _x ) (Ti _1-y Zr _y ) O _3. Is 0.01 or more and 0.05 or less, and y is in the range of 0.05 or more and 0.15 or less.

  The first and second internal electrodes 3a, 3b, 4a, 4b are made of an appropriate metal. Examples of such metals include appropriate metals such as Ni, Ag, Cu, Pt, and Ac—Pd. Or an alloy can be mentioned. Preferably, Ni having a larger firing shrinkage rate than the firing shrinkage rate at the time of firing the dielectric ceramic is used.

  The external electrodes 5 and 6 can be formed of an appropriate metal or alloy. For example, the external electrodes 5 and 6 can be formed of Cu, Ag, or an alloy thereof. The external electrodes 5 and 6 can be formed by various methods such as application of a conductive paste and baking. A plating film such as a Sn plating film may be formed on the surface of the external electrode.

  The multilayer capacitor 1 is characterized in that the ceramic sintered body 2 is made of dielectric ceramics having the above-mentioned specific composition, and the first and second internal electrodes 3a, 3b, 4a, 4b are overlapped via the ceramic layer. That is, the portion where the capacitance is taken out is the inner layer portion 2W, the ceramic portions located on both sides of the inner layer portion 2W in the stacking direction are the outer layer portions 2V, the thickness of the inner layer portion 2W is A, the two outer layer portions 2V and 2V. When the total thickness is B, B / A is 0.5 or less. Thereby, the dielectric constant of the ceramic layer sandwiched between the internal electrodes 3a, 3b, 4a, 4b can be increased without causing a decrease in insulation resistance, and a large capacitance can be obtained. This is because, during firing, the shrinkage rate of the internal electrodes 3a, 3b, 4a, 4b is much larger than the shrinkage rate of the dielectric ceramics, and the stress due to the shrinkage rate difference is applied to the ceramic layer located in the inner layer portion 2W. This is because the dielectric constant of the ceramic in the inner layer portion 2W is increased.

  That is, in Patent Document 2 described above, it is said that the dielectric constant of the ceramic layer can be increased by applying stress due to the difference in shrinkage ratio during firing to the ceramic layer sandwiched between internal electrodes connected to different potentials. It was. For this reason, in order to increase the dielectric constant by applying a large stress to the ceramic layer, the thickness of the ceramic layer sandwiched between the internal electrodes has been reduced.

  In contrast, the inventor of the present application further examined the phenomenon in which the dielectric constant is increased by the stress on the ceramic layer due to the difference in shrinkage rate during firing, and as a result, the shrinkage rate during firing of the internal electrode and the firing of the ceramic layer. Although the stress due to the difference from the shrinkage rate of the material acts to increase the dielectric constant, this effect is achieved when a specific dielectric ceramic is used without reducing the thickness of the ceramic layer sandwiched between the internal electrodes. Has found for the first time that the dielectric constant can be effectively increased by controlling the thickness of the inner layer portion 2W and the outer layer portions 2V and 2V, and has achieved the present invention.

  That is, if a ceramic sintered body is constituted by using the specific dielectric ceramic, and the ratio B / A of the total thickness of the outer layer portions 2V and 2V to the thickness of the inner layer portion 2W is 0.5 or less, the internal electrode The dielectric constant of the ceramic layer sandwiched between them can be effectively increased, that is, the dielectric constant can be effectively increased without reducing the thickness of the ceramic layer sandwiched between internal electrodes connected to different potentials. And a large capacitance can be obtained.

  In particular, as the dielectric ceramic, as described above, in the above structural formula, when x is in the range of 0.01 to 0.05 and y is in the range of 0.05 to 0.15, the shrinkage rate difference This is because the stress due to is more effectively applied, so that the dielectric constant can be increased more effectively, and a larger capacitance can be realized.

  Further, when an internal electrode containing Ni as a main component is formed as the internal electrode, the shrinkage rate upon firing of the internal electrode becomes sufficiently large, and the dielectric constant can be further effectively increased.

  The total thickness B of the outer layer portion is the sum of the thicknesses of the two outer layer portions 2V and 2V in the embodiment shown in FIG.

  Next, based on a specific experimental example, it will be clarified that the present invention can surely increase the capacitance without causing a decrease in insulation resistance.

(Experimental example 1)
BaTiO ₃ , BaZrO ₃ , CaZrO ₃ , MnCO ₃ , SiO _2, and rare earth element oxide powders are prepared, and these powders are expressed by the formula (Ba _1-X Ca _X ) _m (Ti _1-y Zr _y ) O. ₃ were mixed so that x = 0.04, y = 0.10, m = 1.003, and calcined to obtain a calcined raw material for constituting the main component.

MnCO ₃ , SiO ₂ so that Mn is 0.05 mol, Si is 0.2 mol part, and Y and Ni are in the ratio (molar ratio) shown in Table 1 below with respect to 100 mol of the calcined raw material. , Y ₂ O ₃ and NiO powders were added, wet mixed by a ball mill, and pulverized. In this way, a slurry was obtained.

  The obtained slurry was dried and then pulverized to obtain a ceramic raw material. A polyvinyl butyral binder resin and ethanol as an organic solvent were added to the ceramic raw material, and wet mixed by a ball mill to obtain a ceramic slurry.

  The ceramic slurry was molded by a doctor blade method to obtain a mother ceramic green sheet. A conductive paste mainly composed of Ni was printed on the mother ceramic green sheet. Sixty mother ceramic green sheets printed with conductive paste were laminated to obtain an inner layer portion of the laminate. With respect to this inner layer portion, on both sides in the stacking direction, a plurality of plain mother ceramic green sheets prepared in the same manner as described above except that the conductive paste is not printed are stacked, and above and below the inner layer portion, An outer layer portion was provided to obtain a mother laminate. Note that the number of plain mother ceramic green sheets laminated to constitute the outer layer portion was the number that achieved B / A in Table 1 below.

After the mother laminate obtained as described above is cut into laminate chips of individual multilayer capacitors, the binder is removed at a temperature of 250 ° C. in the atmosphere, and then mixed with humidified N ₂ + H _2. Firing was performed in a gas atmosphere under conditions of a temperature rising rate of 5 ° C./min and a maximum temperature of 1250 ° C. In this way, the length of 2.0 × width 1.2 × thickness 0.3 to 0.6 mm, the thickness of the ceramic layer sandwiched between the internal electrodes is 5.0 μm, and one internal electrode A ceramic sintered body having a thickness of 1.7 μm was obtained. A conductive paste mainly composed of Cu powder and glass frit was applied to both end faces of these ceramic sintered bodies and baked, and then multilayer capacitors of sample numbers 1 to 21 shown in Table 1 below were obtained.

  About each said multilayer capacitor, the electrostatic capacitance in 25 degreeC, 1 kHz, and 1 Vrms was measured. Further, from the capacitance, the area where the first and second internal electrodes overlap through the ceramic layer, and the thickness of the ceramic layer sandwiched between the first and second internal electrodes, the relative dielectric constant of the ceramic layer εr was determined. In addition, an acceleration test was performed under a direct current electric field of 150 ° C. and 60 V, and the time until the insulation resistance IR became 0.1 MΩ or less was determined as the lifetime. The number of tests for the acceleration test was 30. The results are shown in Table 1 below.

  As is apparent from Table 1, since Ni / R is 0.2 or more in sample numbers 1, 2, 5 to 8, and 9 to 12, even if the thickness ratio B / A is changed, the relative dielectric constant εr Almost no change was observed, and no effect of improving the dielectric constant was observed.

  Moreover, in sample numbers 13, 14, 17-18, and 19-20, when the molar ratio Ni / R is less than 0.2 and B / A is 0.5 or less, the dielectric constant can be increased. Recognize.

  On the other hand, in Sample No. 21, rare earth elements are not used and Ni / R is not required. However, if the rare earth elements are too small, the relative permittivity εr cannot be improved, and the lifetime is also reduced. It can be seen that the time is short and the insulation resistance is significantly reduced. Similarly, in Sample Nos. 3 and 4, the molar ratio Ni / R was as high as 1.90, and the life time was very short, probably because the blending ratio of the rare earth element R was too small.

  Further, in Sample Nos. 15 and 16, Ni / R is 0.16, but since the thickness ratio B / A is as large as 0.99 and 0.74, the relative dielectric constant εr remains large at 13328 and 13358. The effect of improving the dielectric constant could not be obtained.

  On the other hand, in sample numbers 13, 14, 17, 18, 19, and 20, the molar ratio Ni / R is in the range of 0.05 or more and less than 0.2, and the thickness ratio B / A is 0.5. Therefore, the relative dielectric constant εr could be increased to 17791 or more, and the lifetime was sufficiently long as 14.2 hours or more.

(Experimental example 2)
Ceramics different from those in Experimental Example 1 were used. As composition a, Dy is 2.5 mol, Mg is 1.0 mol, Mn is 0.5 mol, and Si is 1.2 mol with respect to 100 mol of BaTiO ₃ as the main component. A multilayer capacitor was fabricated in the same manner as in Experimental Example 1 except that a ceramic composition to which Dy ₂ O ₃ , MgCO ₃ , MnCO ₃ , and SiO ₂ were added was used.

A multilayer capacitor was prepared in the same manner as in Experimental Example 1 except that (Mg _0.88 Ca _0.10 Sr _0.02 ) O—SiO ₂ was used as the main component as the composition b.

  In these two types of multilayer capacitors, B / A was changed and the relative dielectric constant εr was evaluated in the same manner as in Experimental Example 1. The results are shown in Table 2 below.

  As can be seen from Table 2, the relative dielectric constant εr was not particularly increased even when the ceramics of composition a and composition b were used, even if the thickness ratio B / A was changed.

  Therefore, from the results of Experimental Example 1 and Experimental Example 2, the effect of increasing the relative permittivity εr when the thickness ratio B / A is changed is effective in the specific composition system used in Experimental Example 1. It can be seen that similar effects cannot be obtained with other compositions.

(Experimental example 3)
A multilayer capacitor was prepared and evaluated in the same manner as in Experimental Example 1 except that the type and amount of rare earth elements were varied. The results are shown in Table 3 below.

  Note that the addition ratios of Mn, Y, and Ni as subcomponents were the same as in Experimental Example 1.

  As can be seen from Table 3, even when various rare earth elements are used as the rare earth elements instead of Y, the relative dielectric constant εr is increased as in the case of Sample Nos. 13, 14, and 17 to 20 in Experimental Example 1. It can also be seen that the lifetime is sufficiently long.

  In Sample Nos. 51 and 52, Dy is used as the rare earth element. Since B / A is 0.99 and 0.74, which is outside the scope of the present invention, the relative dielectric constant εr must be sufficiently high. I couldn't.

In Experimental Examples 1 to 3, (Ba _1−x Ca _x ) _m (Ti _1−y Zr _y ) O ₃ is used as the main component constituting the dielectric ceramic, and x = 0.04, y = 0. 01, m = 1.003, but the present invention is not limited to the above, and in (Ba _1-x Ca _x ) _m (Ti _1-y Zr _y ) O ₃ , x is 0.01 or more. 0.05 or less, and y is 0.05 or more and 0.15 or less, the thickness ratio B / A is set to 0.5 or less in the same manner as in the experiment numbers 13, 14, 17 to 20, In addition, it has been confirmed that by setting Ni / R to be 0.05 or more and less than 0.2, the relative dielectric constant εr is effectively increased and the lifetime is extended.

  Similarly, when x is 0.01 or less, when it exceeds 0.05, when y is 0.05 or less, or when it exceeds 0.15, the relative permittivity is similarly increased and the lifetime is increased. It has been confirmed. However, preferably, by setting 0.01 ≦ x ≦ 0.05 and 0.05 ≦ y ≦ 0.15, the relative permittivity can be increased more effectively.

  In addition, as long as the said specific composition is satisfy | filled, it does not specifically limit about the manufacturing method of a ceramic sintered compact. For example, the production method of various oxides used as the ceramic raw material is not limited to the production method shown in Experimental Example 1, and an oxalate method, a sol-gel method, a hydrothermal combination method, and the like can be used.

  Further, the method for producing the ceramic green sheet and the binder resin and solvent used for obtaining the ceramic green sheet are not limited to those shown in Experimental Example 1.

1 is a schematic front cross-sectional view for explaining a multilayer capacitor according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multilayer capacitor 2 ... Ceramic sintered compact 2a ... Terminal 2b ... Terminal 2c ... Upper surface 2d ... Lower surface 2W ... Inner layer part 2V ... Outer layer part 3a, 3b ... 1st internal electrode 4a, 4b ... 2nd internal electrode 5, 6 ... External electrode

Claims (4)

The main component is (Ba, Ca) (Ti, Zr) O ₃ -based ceramics, and Ni and rare earth elements R (where R is Y, Sc, La, Ce, Pr, Nd, Sm, Eu, A ceramic sintered body made of ceramics containing at least one element selected from the group consisting of Tb, Gd, Dy, Ho, Er, Tm, Yb, and Lu;
In the ceramic sintered body, a multilayer capacitor comprising a plurality of internal electrodes arranged to overlap with each other via a ceramic layer,
The portion in which the molar ratio Ni / R is 0.05 or more and less than 0.2 and the plurality of internal electrodes overlap with each other through the ceramic layer in the ceramic sintered body is the inner layer portion, and the inner layer portion is positioned outside the stacking direction. The ratio B / A is 0 when the ceramic portion in which the internal electrodes are not laminated via the ceramic layer is the outer layer portion, the thickness of the inner layer portion is A, and the total thickness of the outer layer portion is B. A multilayer capacitor characterized by having a thickness of 5 or less. When the main component of the ceramic is expressed as (Ba _1-x Ca _x ) (Ti _1-y Zr _y ) O ₃ , 0.01 ≦ x ≦ 0.05 and 0.05 ≦ y ≦ 0.15 The multilayer capacitor according to claim 1, wherein:   The multilayer capacitor according to claim 1, wherein the internal electrode contains Ni as a main component. The multilayer capacitor according to claim 1, wherein the outer layer portion is located on both sides of the inner layer portion in the stacking direction.

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