DIELECTRIC CERAMIC MATERIAL COMPOSITION FOR CAPACITOR

Abstract

A dielectric ceramic material composition for a capacitor, which can be particularly a multilayer ceramic capacitor manufactured by a base-metal-electrode process, is provided. The dielectric ceramic material composition includes a main component BaTiO.sub.3 and at least one sub-component Sc.sub.2O.sub.3. BaTiO.sub.3 can be modified by controlling an addition amount of Sc.sub.2O.sub.3, and during the sintering reaction process, the addition of Sc.sub.2O.sub.3 can cause BaTiO.sub.3 to form a core-shell structure, thereby inhibiting grain growth of BaTiO.sub.3 and effectively improving insulation characteristic and capacitance temperature characteristic, and the stability to DC bias electric field. In an embodiment, MgO can be appropriately added to improve the stability of the TCC curve within an interval of 55 C. to 25 C. Therefore, the production process can be simplified and the usage amount of Sc.sub.2O.sub.3 can be reduced, thereby obtaining the dielectric ceramic material satisfying X8R characteristics regulated by EIA, at a low cost.

Claims

1. A dielectric ceramic material composition applied to capacitor, and the dielectric ceramic material composition comprising: a main component comprising BaTiO.sub.3; and a sub-component Sc.sub.2O.sub.3, wherein a content of the sub-component Sc.sub.2O.sub.3 per 100 mol of the main component BaTiO.sub.3 is in range of 0.05 mol to 1.00 mol, and a TCC curve of the dielectric ceramic material composition formed by sintering the sub-component Sc.sub.2O.sub.3 and the main component BaTiO.sub.3 satisfies X8R characteristics regulated by EIA.

2. The dielectric ceramic material composition according to claim 1, wherein the content of the sub-component Sc.sub.2O.sub.3 is in range of 0.45 mol to 1.00 mol.

3. The dielectric ceramic material composition according to claim 2, further comprising a secondary sub-component MgO.

4. The dielectric ceramic material composition according to claim 3, wherein a content of the secondary sub-component MgO per 100 mol of the main component BaTiO.sub.3 is in range of 0.10 mol to 2.00 mol.

5. The dielectric ceramic material composition according to claim 2, further comprising a core-shell structure formed on grain structure.

6. The dielectric ceramic material composition according to claim 5, further comprising a secondary sub-component MgO.

7. The dielectric ceramic material composition according to claim 6, wherein a content of the secondary sub-component MgO per 100 mol of the main component BaTiO.sub.3 is in range of 0.10 mol to 2.00 mol.

8. The dielectric ceramic material composition according to claim 5, wherein the content of the sub-component Sc.sub.2O.sub.3 is in range of 0.45 mol to 0.60 mol.

9. The dielectric ceramic material composition according to claim 8, further comprising a secondary sub-component MgO.

10. The dielectric ceramic material composition according to claim 9, wherein a content of the secondary sub-component MgO per 100 mol of the main component BaTiO.sub.3 is in range of 0.10 mol to 2.00 mol.

11. The dielectric ceramic material composition according to claim 5, wherein the content of the sub-component Sc.sub.2O.sub.3 is in range of 0.60 mol to 1.00 mol.

12. The dielectric ceramic material composition according to claim 11, further comprising a secondary sub-component MgO.

13. The dielectric ceramic material composition according to claim 12, wherein a content of the secondary sub-component MgO per 100 mol of the main component BaTiO.sub.3 is in range of 0.10 mol to 2.00 mol.

14. The dielectric ceramic material composition according to claim 1, wherein the content of the sub-component Sc.sub.2O.sub.3 is lower than 0.45 mol, and the dielectric ceramic material composition further comprises a secondary sub-component MgO.

15. The dielectric ceramic material composition according to claim 14, wherein a content of the secondary sub-component MgO per 100 mol of the main component BaTiO.sub.3 is in range of 0.10 mol to 2.00 mol.

16. The dielectric ceramic material composition according to claim 15, wherein the content of the sub-component Sc.sub.2O.sub.3 is in range of 0.05 mol to 0.30 mol, and the content of the second sub-component MgO is in range of 0.10 mol to 1.00 mol.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The structure, operating principle and effects of the present invention will be described in detail by way of various embodiments which are illustrated in the accompanying drawings.

[0009] FIG. 1 is a flowchart of preparing a multilayer ceramic capacitor by using dielectric ceramic material, according to an embodiment of the present invention.

[0010] FIG. 2 is a first data table of composition proportions and characteristics of the dielectric ceramic material according to an embodiment of the present invention.

[0011] FIG. 3 is a first diagram showing measured data of dielectric temperature characteristic according to an embodiment of the present invention.

[0012] FIG. 4 is a second data table of composition proportions and dielectric characteristics of the dielectric ceramic material according to an embodiment of the present invention.

[0013] FIG. 5 is a second diagram showing measured data of dielectric temperature characteristic according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The following embodiments of the present invention are herein described in detail with reference to the accompanying drawings. These drawings show specific examples of the embodiments of the present invention. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is to be acknowledged that these embodiments are exemplary implementations and are not to be construed as limiting the scope of the present invention in any way. Further modifications to the disclosed embodiments, as well as other embodiments, are also included within the scope of the appended claims. These embodiments are provided so that this disclosure is thorough and complete, and fully conveys the inventive concept to those skilled in the art. Regarding the drawings, the relative proportions and ratios of elements in the drawings may be exaggerated or diminished in size for the sake of clarity and convenience. Such arbitrary proportions are only illustrative and not limiting in any way. The same reference numbers are used in the drawings and description to refer to the same or like parts.

[0015] It is to be acknowledged that although the terms first, second, third, and so on, may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only for the purpose of distinguishing one component from another component. Thus, a first element discussed herein could be termed a second element without altering the description of the present disclosure. As used herein, the term or includes any and all combinations of one or more of the associated listed items.

[0016] It will be acknowledged that when an element or layer is referred to as being on, connected to or coupled to another element or layer, it can be directly on, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being directly on, directly connected to or directly coupled to another element or layer, there are no intervening elements or layers present.

[0017] In addition, unless explicitly described to the contrary, the word comprise and variations such as comprises or comprising, will be acknowledged to imply the inclusion of stated elements but not the exclusion of any other elements.

[0018] Please refer to FIG. 1, which shows a flowchart of preparing a multilayer ceramic capacitor by using dielectric ceramic material according to an embodiment of the present invention. As shown in FIG. 1, the method of preparing the multilayer ceramic capacitor according to the embodiment of the present invention can be implemented by following steps 101 to 109, but the present invention is not limited to this example, and any method of preparing the multilayer ceramic capacitor well known to those skilled in the art can be used in the present invention, and other types of products applying the ceramic capacitor are also included the present invention. The method of preparing the multilayer ceramic capacitor includes the steps 101 to 109.

[0019] In a step 101, main component powder and sub-component powder are mixed upon a composition proportion, to prepare ceramic slurry.

[0020] In a step 102, a ceramic thin tape is prepared.

[0021] In a step 103, screen printing is performed to form electrode patterns.

[0022] In a step 104, multilayer ceramic embryo is prepared.

[0023] In a step 105, an oxidation heat treatment is performed to burn off organic matter.

[0024] In a step 106, a sintering process is performed under reduction atmosphere.

[0025] In a step 107, the oxidation heat treatment is performed again.

[0026] In a step 108, outer electrodes are prepared.

[0027] In a step 109, electrical measurement is performed.

[0028] According to above-mentioned implementation steps, the high-purity (>99%) BaTiO.sub.3 powder is heated to 1150 C. in air by a heating rate of 5 C./min for 4 hours, the heated BaTiO.sub.3 powder is used as the initial BaTiO.sub.3 powder. Next, the main component including BaTiO.sub.3 powder, 0.05 mol % manganese carbonate (MnCO.sub.3), 1.37 mol % barium silicate (BaSiO.sub.3), and at least one sub-component including 0.301.00 mol % scandium oxide (Sc.sub.2O.sub.3), and 02.00 mol % magnesium oxide (MgO), are mixed upon a composition formula. Next, toluene, waterfree alcohol, binder, dispersant and plasticizer are added in the above-mentioned mixture and zirconia balls are used to grind for uniformly mixing, so as to prepare the ceramic slurry. Next, the ceramic slurry is shaped to form the ceramic thin tape by using scraper, and the screen printing process is then performed to form metal electrode patterns including nickel (Ni), copper (Cu), silver (Ag) or palladium (Pd), on the ceramic thin tape. The ceramic thin tape is then stacked in a staggered manner, and a thermocompression process is performed on the stacked ceramic thin tape to form the compact multilayer ceramic embryo. Next, the compact multilayer ceramic embryo can be cut according to a designed size of the multilayer ceramic capacitor.

[0029] Before the sintering process, the oxidation heat treatment is performed on the multilayer ceramic embryo at 350 C. to 550 C. for 4 hours under a pure nitrogen (N.sub.2) atmosphere, and heating and cooling rates are maintained at 2 C./min, thereby burning off the previously-added organic matter in the multilayer ceramic embryo, and the multilayer ceramic embryo is then sintered at 1200 C.1300 C. for 2 hours under the reduction atmosphere composed of 97% pure nitrogen, 3% hydrogen (H.sub.2), and 35 C. saturated vapor, wherein heating and cooling rates are maintained at 5 C./min. Next, the oxidation heat treatment is performed on the sintered samples at 950 C. for 2 hours under low oxygen partial pressure atmosphere composed of pure nitrogen and 35 C. saturated vapor. After the heated sample is slowly cooled to room temperature, the mature multilayer ceramic embryo can be obtained.

[0030] Next, two ends of the mature multilayer ceramic embryo are coated by immersing into Cu electrode coating, to form the outer electrodes in contact with the inner Ni electrodes. The outer electrodes are sintered at 900 C. under the pure nitrogen atmosphere, to combine with the inner Ni electrodes. Next, Ni and Sn are plated on the Cu electrodes at the two ends of the semi-finished multilayer ceramic capacitor. As a result, preparation of all samples of the embodiments of the present invention is completed. After the preparation of the samples is completed, the microstructure of the multilayer ceramic capacitor can be observed by using a scanning electron microscope (SEM), a transmission electron microscope (TEM) and an X-ray diffractometer (XRD). The resistance-capacitance inductance (TLC) measuring instrument can be used to measure dielectric characteristic of the multilayer ceramic capacitor.

[0031] Please refer to FIGS. 2 and 3, which are a first data table showing composition proportion and dielectric characteristic of the dielectric ceramic material of an embodiment of the present invention, respectively, and a first diagram showing measured data of dielectric temperature characteristic of an embodiment according to the present invention. As shown in FIGS. 2 and 3, the dielectric ceramic material, used to manufacture the multilayer ceramic capacitor of the present invention, mainly includes BaTiO.sub.3, 0.05 mol % MnCO.sub.3, and 1.37 mol % BaSiO.sub.3 as main components; however, in practical application, other compounds can be appropriately added to mix with BaTiO.sub.3. The main components can be further added with sub-components including different contents of Sc.sub.2O.sub.3 (0.300.60 mol %) and MgO (02.00 mol %), for modifying BaTiO.sub.3.

[0032] According to observation results of using the SEM to observe cross-sectional microstructure of the multilayer ceramic capacitor of each embodiment of the present invention, the multilayer ceramic capacitor formed by adding 0.30 mol % Sc.sub.2O.sub.3 has less apertures and higher sinter density than the multilayer ceramic capacitor formed by adding 0.60 mol % Sc.sub.2O.sub.3. As the addition amount of Sc.sub.2O.sub.3 increases, the grain sizes of BaTiO.sub.3 become tinier and particle sizes of BaTiO.sub.3 are more uniform, but during the sintering process Sc.sub.2O.sub.3 tends to inhibit the grain boundary migration rate of BaTiO.sub.3. As a result, excessive addition of Sc.sub.2O.sub.3 results in a decrease in the compactness of BaTiO.sub.3 and an increase of the sintering dense temperature. Furthermore, because of the grain size reduction of BaTiO.sub.3, the increase of the addition amount of Sc.sub.2O.sub.3 makes the dielectric constant and dielectric loss of BaTiO.sub.3 lower, and the insulation characteristic is significantly improved because of the increase of grain BET surface area. Furthermore, according to the changes of the TCC corresponding to the addition amount of Sc.sub.2O.sub.3 changed from 0.30 mol % to 0.60 mol %, it can be found that the increase of the addition amount of Sc.sub.2O.sub.3 is significantly beneficial to the stability of the TCC curve of BaTiO.sub.3.

[0033] The effect of different addition amount of Sc.sub.2O.sub.3 for the crystal structure and dielectric characteristic of BaTiO.sub.3 in the microstructure of multilayer ceramic capacitor is described in following paragraphs. The observation result of using the TEM shows that when the addition amount of Sc.sub.2O.sub.3 is increased to 0.45 mol % or more, the grain of BaTiO.sub.3 forms a core-shell structure with uneven chemical compositions. According to the analysis for the compositions of the grain by using the energy dispersive X-Ray spectroscopy (EDS), it can be found that the grain shell has a higher content of scandium (Sc) (for example, higher than 1.0 at %) and the grain core has a lower content of Sc element (for example, lower than 0.5 at %), and the phenomenon is due to the difference in concentration gradient caused by the lower diffusion rate of Sc. The higher content of Sc causes that the core-shell structure having a concentration gradient can be formed on the grain of BaTiO.sub.3. The grain shell is less tetragonal and has a paraelectric state of the approximate cubic crystal structure, and grain core is more tetragonal and has a spontaneously polarized ferroelectric tetragonal structure. Furthermore, the diffusion rate of Mg is relatively fast, so contents of Mg in the grain shell and the grain core are not different greatly. However, when the addition amount of Sc.sub.2O.sub.3 reaches 0.30 mol %, the core-shell structure with the uneven chemical composition is not found in the crystal grain.

[0034] As shown in FIGS. 2 and 3, the dielectric characteristics of the capacitors added with different contents of Sc.sub.2O.sub.3 and MgO and sintered in the reduction atmosphere are listed and temperature coefficient of capacitance (TCC) versus temperature curves are provided, respectively. As shown in FIGS. 2 and 3, when the content of Sc.sub.2O.sub.3 added with BaTiO.sub.3 is increased from 0.30 mol %, the TCC curve within the interval of 55 C. to 150 C. can become flatter, more particularly for the multilayer ceramic capacitors added with 0.45 mol % and 0.60 mol % of Sc.sub.2O.sub.3. When the addition amount of MgO is 1.00 mol %, the stability of the TCC curve within the interval of 55 C. to 25 C. interval is improved. As a result, the addition of Sc.sub.2O.sub.3 can provide a good effect of stabilizing the dielectric temperature characteristics of BaTiO.sub.3, especially for the TCC curve within the interval of 25 C. to 150 C.

[0035] As shown in FIGS. 2 and 3, when the addition amounts of Sc.sub.2O.sub.3 are 0.45 mol % and 0.60 mol %, dielectric constants are 1744 and 1675, the dielectric losses (tan ) are 0.58% and 0.59%, the TCCs at 55 C. are 3.9% and 2.1%, TCCs at 150 C. are 8.5% and 11.6%, the resistivity at room temperature 25 C. can reach 2.810.sup.12 -cm and 3.310.sup.12 -cm, and the resistivity at high-temperature 150 C. can reach 1.710.sup.11 -cm and 4.310.sup.11 -cm, respectively. As a result, all TCC curves corresponding to relevant composition proportions can satisfy the X8R characteristics regulated by EIA, and the material composition of the present invention also has good insulation characteristic.

[0036] In an preferred embodiment, the dielectric ceramic material used for multilayer ceramic capacitor is doped with 0.45 mol % Sc.sub.2O.sub.3 and 1.00 mol % MgO, and such dielectric ceramic material has the best dielectric characteristic, and a variation rate of the dielectric constant (K value) of the dielectric ceramic material at a temperature of 55 C. to 150 C. can be stable within 10%, which satisfies the X8R characteristics regulated by EIA, wherein the dielectric constant is 1744, the dielectric loss (tan ) is 0.58%, the TCC at 55 C. is 3.9%, and the TCC at 150 C. is 8.5%, the resistivity at room temperature 25 C. reaches 2.810.sup.12 -cm, and the resistivity at high temperature 150 C. reaches 1.710.sup.11 -cm. Furthermore, in the process of manufacturing the multilayer ceramic capacitor of the embodiment of the present invention, the BaTiO.sub.3 substrate can be modified by controlling the addition amount of Sc.sub.2O.sub.3, to make BaTiO.sub.3 grains have the core-shell structure, and addition of Sc.sub.2O.sub.3 has the effect of inhibiting grain growth of BaTiO.sub.3 during the sintering reaction process, so as to effectively improve the insulation characteristic. Furthermore, the addition amount of Sc.sub.2O.sub.3 is very tiny and not more than 1.00 mol %, the composition of the material composition is simple and the proportion of the additive component is scarce, so the production process can be simplified, and the usage amount of Sc.sub.2O.sub.3 can be reduced. As a result, the dielectric ceramic material composition of the present invention can be applied to the base-metal-electrode process at a low cost and satisfy the X8R characteristics regulated by EIA.

[0037] Please also refer to FIGS. 4 and 5, which are a second data table of the composition proportions and dielectric characteristics of the dielectric ceramic material used in the embodiment of the present invention, and a second diagram showing the dielectric temperature characteristic of the embodiment, respectively. As shown in FIGS. 4 and 5, when the addition amount of Sc.sub.2O.sub.3 is in range of 0.60 mol % to 1.00 mol %, the multilayer ceramic capacitor added with 0 mol % MgO still can have the TCC curves corresponding to relevant compositions and satisfying X8R characteristics regulated by EIA. Since the addition of 0.45 mol % or more Sc.sub.2O.sub.3 can cause BaTiO.sub.3 grain to form the core-shell structure, the peak of TCC curve at a temperature ranging from 55 C. to 150 C. can be effectively suppressed. The addition of MgO has an effect of enhancing stabilization of the TCC curve within the interval of 55 C. to 25 C. When the addition amount of MgO is in a range of 0.50 mol % to 2.00 mol %, the addition of MgO causes the effect with same trend. The dielectric loss (tan ) of the multilayer ceramic capacitor is rapidly dropped from 0.76% when the addition amount of MgO is 0 mol %, to 0.56% when the addition amount of MgO is 2.00 mol %. Obviously, the addition of Sc.sub.2O.sub.3 is critical for the stability of dielectric temperature characteristics (such as the dielectric constant and the TCC curve) of the multilayer ceramic capacitor. The addition of MgO is beneficial to enhance compactness of BaTiO.sub.3 and reduce dielectric loss, and increase the TCC value at low temperature 55 C., for example, the TCC value is increased from 2.1% to 0.2%. More particularly, when the addition amount of Sc.sub.2O.sub.3 is 0.60 mol % or more, the effect of different content of MgO on the TCC curve becomes non-obvious, and it also indicates that the addition of Sc.sub.2O.sub.3 can improve the stability of the dielectric characteristic of BaTiO.sub.3 to temperature, and also improve the stability of BaTiO.sub.3 to chemical composition. Obviously, the content of the present invention is extremely valuable for industrial applicability.

[0038] In order to solve the convention problem that the preparation of the dielectric ceramic has various difficulty in adding Sc.sub.2O.sub.3 for modifying BaTiO.sub.3 and especially in adding other compounds such as La.sub.2O.sub.3, Co.sub.3O.sub.4 or NiO, and the convention problem that addition of the other compounds causes manufacturing variation, the inventors use a tiny amount of Sc.sub.2O.sub.3 (0.31.00 mol %) and MgO (02.0 mol %) to effectively control the micro-diffusion in the crystal lattice, so as to simplify the production process and finally satisfy requirements defined in X8R characteristics regulated by EIA. When the addition amount of Sc.sub.2O.sub.3 is in a range of 0.45 mol % to 1.00 mol %, BaTiO.sub.3 grain can form the core-shell structure with a concentration gradient, and have the stable dielectric characteristic. For example, when the content of Sc.sub.2O.sub.3 is 0.60 mol %, the TCC curves corresponding to different addition amounts of MgO almost overlap within the interval of 55 C. to 150 C.; furthermore, the low-temperature part (55 C. to 25 C.) or high-temperature part (25 C. to 150 C.) of each of the TCC curves is very smooth. However, when the addition amount of Sc.sub.2O.sub.3 is less than 0.45 mol %, BaTiO.sub.3 grain does not form the core-shell structure with the concentration gradient, so it is necessary to skillfully control the composition proportion of Sc.sub.2O.sub.3 and MgO, to make the dielectric ceramic satisfy the X8R characteristics regulated by EIA. For example, when the content of Sc.sub.2O.sub.3 is 0.30 mol %, the addition of MgO has a stabilizing effect on the TCC curve within the interval of 55 C. to 25 C., so that dielectric ceramic can satisfy to the X8R characteristics regulated by EIA, and the dielectric ceramic has a dielectric constant superior to other dielectric ceramic having the core-shell structure with concentration gradient. Furthermore, the present invention is not limited to the experimental values shown in figures or data tables disclosed above, and in particular, those skilled in the art can extrapolate the relationship between the data values obtained by the present invention, to further calculate, through statistical logic or trend derivation, some specific test values not described in the present invention, but the effect and modification do not depart from the spirit and scope of the disclosure set forth in the claims. For example, through extrapolation manner, it can be found that the same effect can be obtained when the tiny amount of Sc.sub.2O.sub.3 is decreased to 0.05 mol %. The present invention does not propose the specific test values and explain the experimental values in detail, but any result obtained by controlling the contents of Sc.sub.2O.sub.3 or MgO disclosed in the present invention and further using common scientific methods, such as interpolation, does not depart from the spirit and scope of the disclosure set forth in the claims.

[0039] According to above-mentioned contents, compared with conventional dielectric ceramic material, the dielectric ceramic material of the present invention has following advantages.

[0040] First, the dielectric ceramic material of the multilayer ceramic capacitor of the embodiment of the present invention includes BaSiO.sub.3 as main component, and different content of Sc.sub.2O.sub.3 (such as 0.301.00 mol %) as sub-component for modifying BaTiO.sub.3; during the sintering reaction process Sc.sub.2O.sub.3 can make the grain size of BaTiO.sub.3 smaller and make particle sizes of BaTiO.sub.3 more uniform, and the addition of Sc.sub.2O.sub.3 also has the effect of inhibiting grain growth of BaTiO.sub.3 and effectively improving insulation characteristic; when the content of Sc.sub.2O.sub.3 reaches 0.45 mol % or more, BaTiO.sub.3 grain can form the core-shell structure having the concentration gradient, so as to greatly improve the stability of the TCC curve of BaTiO.sub.3 within the interval of 55 C. to 150 C., and all TCC curves corresponding to relevant compositions can satisfy the X8R characteristics regulated by EIA.

[0041] Secondly, according to the dielectric ceramic material of the multilayer ceramic capacitor of the present invention, BaSiO.sub.3 can be modified by adding different content of Sc.sub.2O.sub.3 in BaSiO.sub.3, and the appropriate addition of MgO (0 to 2.00 mol %) in BaSiO.sub.3 also can enhance the stability of the TCC curve within the interval of 55 C. to 25 C. The composition proportion of the dielectric ceramic material is simple and the proportion of additive component is scarce, so that the usage amount of Sc.sub.2O.sub.3 can be reduced and the usage of La.sub.2O.sub.3, Co.sub.3O.sub.4 and NiO can be omitted, thereby effectively reducing the complexity of the compositions of the material formula, the production cost, and the risk of manufacturing variation. As a result, the dielectric ceramic material of the present invention can be applied to the base-metal-electrode process and satisfy the X8R characteristics regulated by EIA.

[0042] Thirdly, the dielectric ceramic material disclosed in the present invention can preferably be BaTiO.sub.3 doped with 0.45 mol % Sc.sub.2O.sub.3 and 1.00 mol % MgO, and the dielectric constant is 1744, the dielectric loss is 0.58%, the TCC at 55 C. is 3.9% and the TCC at 150 C. is 8.5%, and the resistivity at room temperature reaches 2.810.sup.12 -cm and the resistivity at high temperature 150 C. reaches 1.710.sup.11 -cm. Obviously, the stability of the dielectric temperature characteristics of the multilayer ceramic capacitor can be effectively improved.

[0043] The present invention disclosed herein has been described by means of specific embodiments. However, numerous modifications, variations and enhancements can be made thereto by those skilled in the art without departing from the spirit and scope of the disclosure set forth in the claims.