Patent Publication Number: US-2022230807-A1

Title: Multilayer capacitor

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims benefit of priority to Korean Patent Application No. 10-2021-0006205 filed on Jan. 15, 2021 and Korean Patent Application No. 10-2021-0064091 filed on May 18, 2021 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     Example embodiments of the present disclosure relate to a multilayer capacitor. 
     BACKGROUND 
     A capacitor is a device for storing electricity, and when two electrodes are disposed to oppose each other, and a voltage is applied thereto, electricity may be accumulated in each electrode. When a DC voltage is applied, a current may flow in the capacitor as electricity is stored, but when the accumulation is completed, the current may stop flowing. When an AC voltage is applied, an AC current may flow while a polarity of the electrode changes. 
     Such a capacitor may include, depending on a type of insulator provided between electrodes, an aluminum electrolytic capacitor having an electrode formed of aluminum and having a thin oxide film between the aluminum electrodes, a tantalum capacitor using tantalum as an electrode material, a ceramic capacitor using a dielectric having a high dielectric constant such as barium oxide, a multilayer ceramic capacitor (MLCC) using a ceramic having a high dielectric constant as a dielectric provided between electrodes, and a film capacitor using a polystyrene film as a dielectric between electrodes. 
     Among the capacitors, a multilayer ceramic capacitor may have excellent temperature and frequency properties, and may be implemented in a small size such that a multilayer ceramic capacitor has been widely applied in various fields such as a high-frequency circuit. Recently, there have been attempts to implement a multilayer ceramic capacitor to have a smaller size, and to this end, a dielectric layer and an internal electrode may be configured to have a reduced thickness. When the dielectric layer has a reduced thickness, however, high-temperature reliability and withstand voltage properties may deteriorate, and there have been attempts to address such issues. 
     SUMMARY 
     An example embodiment of the present disclosure is to provide a multilayer capacitor which may have improved high-temperature reliability and withstand voltage properties. 
     According to an example embodiment of the present disclosure, a multilayer capacitor includes a body including a plurality of dielectric layers and a plurality of internal electrodes laminated with the dielectric layers interposed therebetween, and an external electrode disposed externally on the body and connected to one or more of the internal electrodes. One of the plurality of dielectric layers include a barium titanate composition including a Sn component. One of the plurality of internal electrodes includes a Sn component. The one of the plurality of dielectric layers has a Sn content equal to at least twice a Sn content of the one of the plurality of internal electrodes adjacent to the one of the plurality of dielectric layers. 
     The one of the plurality of dielectric layers may include a first Sn-rich region disposed on an interfacial surface with the one of the plurality of internal electrodes, and the one of the plurality of internal electrodes may include a second Sn-rich region disposed on the interfacial surface with the one of the plurality of dielectric layers. 
     A sum of thicknesses of the first and second Sn-rich regions may be 5 nm or less. 
     A thickness of the first Sn rich region may be greater than a thickness of the second Sn rich region. 
     A thickness of the second Sn rich region may be greater than a thickness of the first Sn rich region. 
     A sum of contents of Sn included in the first and second Sn-rich regions may be 0.8 mol or more based on 100 mol of a Ti content of the one of the plurality of dielectric layers. 
     A content of Sn included in the first Sn-rich region may be greater than a content of Sn included in a region of the one of the plurality of dielectric layers other than the first Sn-rich region. 
     A content of Sn included in the second Sn-rich region may be greater than a content of Sn included in a region of the one of the plurality of internal electrodes other than the second Sn-rich region. 
     In the first Sn-rich region, a content of Sn may decrease from the interfacial surface toward a center of the one of the plurality of dielectric layers. 
     In the second Sn-rich region, a content of Sn may decrease from the interfacial surface toward a center of the one of the plurality of internal electrodes. 
     In the interfacial surface, the first and second Sn-rich regions may have the same Sn content. 
     An average thickness of the one of the plurality of dielectric layers may be 500 nm or less. 
     An average thickness of the one of the plurality of internal electrodes may be 400 nm or less. 
     According to an example embodiment of the present disclosure, a multilayer capacitor includes a body including a plurality of dielectric layers and a plurality of internal electrodes laminated with the dielectric layers interposed therebetween, and an external electrode disposed externally on the body and connected to one or more of the plurality of internal electrodes. One of the plurality of dielectric layers includes a barium titanate composition including Sn. One of the plurality of the internal electrodes includes Sn. The one of the plurality of dielectric layers includes a first Sn-rich region disposed on an interfacial surface with the internal electrode. One of the plurality of internal electrodes includes a second Sn-rich region disposed on the interfacial surface with the one of the plurality of dielectric layers. A sum of thicknesses of the first and second Sn-rich regions is 5 nm or less. 
     According to an example embodiment of the present disclosure, a multilayer capacitor includes a body including a plurality of dielectric layers and a plurality of internal electrodes laminated with the dielectric layers interposed therebetween; and an external electrode disposed externally on the body and connected to one or more of the plurality of internal electrodes. One of the plurality of dielectric layers includes a first Sn-rich region disposed on an interfacial surface with one of the plurality of internal electrodes. The one of the plurality of internal electrodes includes a second Sn-rich region disposed on the interfacial surface with the one of the plurality of dielectric layers. A sum of contents of Sn included in the first and second Sn-rich regions is 0.8 mol or more based on 100 mol of a Ti content of the one of the plurality of dielectric layers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective diagram illustrating an exterior of a multilayer capacitor according to an example embodiment of the present disclosure; 
         FIG. 2  is a cross-sectional diagram illustrating the multilayer capacitor taken along line I-I′ in  FIG. 1 ; 
         FIG. 3  is a cross-sectional diagram illustrating the multilayer capacitor taken along line II-II′ in  FIG. 1 ; 
         FIG. 4  is an enlarged diagram illustrating a portion of a dielectric layer and a portion of an internal electrode; and 
         FIGS. 5 and 6  are graphs illustrating a content of Sn in a dielectric layer and an internal electrode. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described as follows with reference to the attached drawings. 
     The present disclosure may, however, be exemplified in many different forms and should not be construed as being limited to the specific embodiments set forth herein. Rather, these embodiments are provided such that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Accordingly, shapes and sizes of the elements in the drawings may be exaggerated for clarity of description. Also, elements having the same function within the scope of the same concept represented in the drawing of each example embodiment will be described using the same reference numeral. 
     In the drawings, same elements will be indicated by the same reference numerals. Also, redundant descriptions and detailed descriptions of known functions and elements that may unnecessarily make the gist of the present invention obscure will be omitted. In the accompanying drawings, some elements may be exaggerated, omitted or briefly illustrated, and the sizes of the elements do not necessarily reflect the actual sizes of these elements. Also, it will be understood that when a portion “includes” an element, it may further include another element, not excluding another element, unless otherwise indicated. 
       FIG. 1  is a perspective diagram illustrating an exterior of a multilayer capacitor according to an example embodiment of the present disclosure.  FIG. 2  is a cross-sectional diagram illustrating the multilayer capacitor taken along line I-I′ in  FIG. 1 .  FIG. 3  is a cross-sectional diagram illustrating the multilayer capacitor taken along line II-II′ in  FIG. 1 .  FIG. 4  is an enlarged diagram illustrating a portion of a dielectric layer and a portion of an internal electrode.  FIGS. 5 and 6  are graphs illustrating a content of Sn in a dielectric layer and an internal electrode. 
     Referring to  FIGS. 1 to 3 , a multilayer capacitor  100  according to an example embodiment may include a body  110  including a dielectric layer  111  and a plurality of internal electrodes  121  and  122  laminated with the dielectric layer  111  interposed therebetween and external electrodes  131  and  132 . The plurality of dielectric layers  111  may include a barium titanate composition including a Sn component, and the internal electrodes  121  and  122  may include a Sn component. Also, at least one of the plurality of dielectric layers  111  may have a Sn content equal to at least twice a Sn content of an adjacent internal electrode among the internal electrodes  121  and  122 . 
     The body  110  may include a lamination structure in which a plurality of dielectric layers  111  are laminated in a first direction (X direction), and may be obtained by, for example, laminating a plurality of green sheets and sintering the plurality of green sheets. Two directions perpendicular to the first direction (X direction) and perpendicular to each other may be defined as a second direction (Y direction) and a third direction (Z direction), respectively. As illustrated in FIG.  1 , the body  110  may have a shape similar to a rectangular parallelepiped. The dielectric layer  111  included in the body  110  may include a ceramic material having a high dielectric constant, and may include a barium titanate (BaTiO 3 ) composition. Specifically, the dielectric layer  111  may include a base material main component including Ba and Ti, where the base material main component may include a main component represented as (Ba, Ca) (Ti,Ca)O 3 , (Ba, Ca) (Ti,Zr)O 3 , Ba (Ti, Zr) O 3  in which BaTiO 3  or Ca, Zr, and the like, is partially solid solute. Also, the dielectric layer  111  may further include additives, organic solvents, plasticizers, binders and dispersants if necessary, in addition to the ceramic material, a main component. Further, the above-described barium titanate composition of the plurality of dielectric layers  111  may include a Sn component, and may be added in the form of Sn oxide when the dielectric layer  111  is manufactured. The Sn component present in the dielectric layer  111  may strengthen a Schottky barrier at a grain boundary after baking, and may also control grain growth of dielectric grains. Accordingly, even when the dielectric layer  111  is formed to have a thin thickness, high-temperature reliability and withstand voltage properties may improve. 
     The plurality of internal electrodes  121  and  122  may form capacitance and may be obtained by, for example, printing a paste including a conductive metal by a predetermined thickness on one surface of a ceramic green sheet and sintering the paste. In this case, as illustrated in  FIG. 2 , the plurality of internal electrodes  121  and  122  may include first and second internal electrodes  121  and  121  exposed in the third direction (Z direction) of the body  110  to oppose each other. The first and second internal electrodes  121  and  122  may be connected to different external electrodes  131  and  132  and may have different polarities when driven, and may be electrically separated from each other by the dielectric layer  111  disposed therebetween. However, the number of the external electrodes  131  and  132  or the connection method with the internal electrodes  121  and  122  may be varied in example embodiments. 
     The main component material for forming the internal electrodes  121  and  122  may include nickel (Ni), copper (Cu), palladium (Pd), silver (Ag), or the like, and alloys thereof may also be used. As described above, the internal electrodes  121  and  122  may include a Sn component. The Sn component present in the internal electrodes  121  and  122  may form an alloy with other metals or may be present as a single body (e.g., a Sn layer), and may be diffused and segregated on an interfacial surface between the internal electrodes  121  and  122  and the dielectric layer  111  such that a second Sn-rich region  221  may be formed. Since the Sn-rich region  221  has a large electrical resistance as compared to the main component (e.g., Ni) of the internal electrodes  121  and  122 , when a DC voltage is applied, a voltage decrease may more greatly occur than in the example in which the second Sn-rich region  221  is not provided. Due to this action, an electric field in the dielectric layer  111  may be weakened, and accordingly, DC bias capacitance properties and reliability of the multilayer capacitor  100  may improve. 
     The external electrodes  131  and  132  may be formed externally on the body  110 , and may include the first and second external electrodes  131  and  132  connected to the first and second internal electrodes  121  and  122 , respectively. The external electrodes  131  and  132  may be formed by preparing a paste of a material including a conductive metal and applying the paste to the body  110 . Examples of the conductive metal may include nickel (Ni), copper (Cu), palladium (Pd), gold (Au), or alloys thereof. The external electrodes  131  and  132  may further include a plating layer including Ni, Sn, or the like. 
     In the example embodiment, the internal electrodes  121  and  122  may have a Sn content smaller than that of the adjacent dielectric layer  111 , and specifically, at least one of the plurality of dielectric layers  111  may have a Sn content at least twice a Sn content of the adjacent internal electrodes  121  and  122 . Such a configuration may be obtained when a Sn component is added to the dielectric layer  111  during a manufacturing process and the added Sn component is diffused into the internal electrodes  121  and  122 , for example. In this case, most of the Sn components present in the internal electrodes  121  and  122  may be derived from the dielectric layer  111 , which will be described in greater detail with reference to  FIGS. 4 to 6 . 
     As illustrated in  FIG. 4 , the dielectric layer  111  may include a first Sn-rich region  211  formed on an interfacial surface with the internal electrodes  121  and  122 . Also, the internal electrodes  121  and  122  may include a second Sn-rich region  221  formed on an interfacial surface with the dielectric layer  111 . The first and second Sn-rich regions  211  and  221  may correspond to regions in which the Sn component added to the dielectric layer  111  diffuses and locally has a high Sn content, and a sum of thicknesses t 1  and t 2  thereof may be 5 nm or less. In this case, a thickness of the first Sn-rich region  211  may be greater than that of the second Sn-rich region  221  (t 1 &gt;t 2 ). According to the research of the present inventors, when the Sn component is diffused from the internal electrodes  121  and  122  into the dielectric layer  111 , the dielectric layer  111  does not include Sn in a sufficient content, and the Sn-rich region present in the dielectric layer  111  may be present in less than 20% of the entire Sn-rich region in terms of a thickness ratio. In the example embodiment, the Sn content of the dielectric layer  111  may be at least twice a Sn content of the internal electrodes  121  and  122 , such that the Sn component may be sufficiently secured. However, according to example embodiments, the Sn content of the dielectric layer  111  may not be necessarily at least twice the Sn content of the internal electrodes  121  and  122 . In this case, a sum of the thicknesses t 1  and t 2  of the first and second Sn-rich regions  211  and  221  may be adjusted to be 5 nm or less, and under this thickness condition, high-temperature reliability and withstand voltage properties may be secured without greatly degrading the electrical properties of the dielectric layer  111  and the internal electrodes  121  and  122 . 
     The above-described thickness conditions of the first and second Sn-rich regions  211  and  221  may be obtained by, for example, allowing the Sn component to be derived from the dielectric layer  111  while controlling the baking conditions. For example, when a reducing atmosphere during baking is strong, that is, when an oxygen partial pressure is lowered, the Sn oxide may be reduced and the amount of the Sn component diffused from the dielectric layer  111  to the internal electrodes  121  and  122  may increase, and the thickness of the second Sn-rich region of  221  may increase. Thus, the overall thickness of the first and second Sn-rich regions  211  and  221  and the ratio of each thickness may be adjusted as above. 
     A sum of the contents of Sn included in the first and second Sn-rich regions  211  and  221  may be 0.8 mol or more based on 100 mol of the Ti content of the dielectric layer  111 . In this case, the Sn component may be present in the dielectric layer  111  and the internal electrodes  121  and  122  in a sufficient amount such that high-temperature reliability and withstand voltage properties may improve. Also, the content of Sn included in the first Sn-rich region  211  may be greater than the content of Sn included in a region of the dielectric layer  111  other than the first Sn-rich region  211 , which may indicate that a large amount of Sn may be present in the first Sn-rich region  211 . Also, the content of Sn included in the second Sn-rich region  221  may be greater than the content of Sn included in a region of the internal electrodes  121  and  122  other than the second Sn-rich region  221 , and as the Sn content is sufficiently secured in the Sn-rich region  221 , withstand voltage characteristics may improve. 
     An example of a method of measuring the content of each element in the dielectric layer  111  and the internal electrodes  121  and  122  will be described. In a region including the dielectric layer  111  and the internal electrodes  121  and  122  of one cross-sectional surface of the sintered body  110 , a thinned analysis sample may be prepared using a focused ion beam (FIB) device. A damaged layer on the surface of the thinned sample may be removed using Ar ion milling, and mapping and quantitative analysis of each component may be performed on the image obtained using STEM-EDX. In this case, the quantitative analysis graph of each component may be obtained as a mass fraction of each element, which may also be represented by a mole fraction.  FIGS. 5 and 6  illustrate the Sn content in the dielectric layer  111  and the internal electrode  121  in the form of a line profile. Although the Sn content of the first internal electrode  121  and the dielectric layer  111  is illustrated in  FIGS. 5 and 6 , a line profile similar to the above example may be obtained on the interfacial surface between the second internal electrode  122  and the dielectric layer  111 . 
     Referring to  FIG. 5 , on the interfacial surface B between the dielectric layer  111  and the internal electrode  121 , the Sn content of the first Sn-rich region  211  may decrease toward a center of the dielectric layer  111 . Similarly, the content of Sn of the second Sn-rich region  221  may decrease toward a center of the internal electrode  121  on the interfacial surface. Also, on the interfacial surface B between the dielectric layer  111  and the internal electrode  121 , the first and second Sn-rich regions  211  and  221  may have the same Sn content. 
     The ranges of the first and second Sn-rich regions  211  and  221  may be determined in consideration of the Sn content of central regions of the dielectric layer  111  and the internal electrodes  121  and  122 , respectively. For example, the first Sn-rich region  211  may be defined up to a region A 1  in which a value of the Sn content may be firstly exhibited the same as that of the Sn content of the central region of the dielectric layer  111  from the interfacial surface B. In this case, considering that the Sn content in a region other than the first Sn-rich region  211  is relatively low while the degree of change caused by noise is large, the Sn content in the central region of the dielectric layer  111  may be calculated as an average value in a section C 1  at ¼ to ½ of a thickness of the dielectric layer  111  in a thickness direction from the interfacial surface B. Similarly, the second Sn-rich region  221  may be defined from the interfacial surface B to a region A 2  in which a value of the Sn content may be firstly exhibited the same as that of the Sn content in the central region of the internal electrode  121  from the interfacial surface B. In this case, considering that the Sn content in a region other than the second Sn-rich region  221  is relatively low while the degree of change caused by noise is large, the Sn content in the central region of the internal electrode  121  may be calculated as an average value in a section C 2  at ¼ to ½ of a thickness of the internal electrode  121  in a thickness direction from the interfacial surface B. In addition to these methods, the first and second Sn-rich regions  211  and  221  may be defined by a more simplified method, and may be, for example, from the interfacial surface B up to a region in which the Sn content decreases and starts to increase. 
     In the graph in  FIG. 5 , the first Sn-rich region  211  may have a thickness greater than that of the second Sn-rich region  221 , but an example embodiment thereof is not limited thereto. In example embodiments, as illustrated in the graph in  FIG. 6 , the second Sn-rich region  221  may have a thickness greater than that of the first Sn-rich region  211  in the graph, and by increasing the thickness of the second Sn-rich region  221 , electrical insulation on the interfacial surface between the internal electrode  121  and the dielectric layer  111  may increase. The Sn content distribution in  FIG. 6  may be obtained by lowering the oxygen partial pressure during baking and allowing the Sn component to more greatly diffuse into the internal electrode  121 . 
     The effect of the improved withstand voltage properties obtained as above may be more prominent when the dielectric layer  111  and the internal electrodes  121  and  122  have a reduced thickness. The thickness of the dielectric layer  111  may be 500 nm or less, and the thickness of the internal electrodes  121  and  122  may be 400 nm or less. The thickness of the dielectric layer  111  may refer to an average thickness of the dielectric layer  111  disposed between the internal electrodes  121  and  122 . As an example of the measurement standard, the average thickness of the dielectric layer  111  may be measured by obtaining an image by scanning a cross-sectional surface of the body  110  in the first direction (X direction) and the third direction (Z direction). For example, in an arbitrary dielectric layer extracted from an image obtained by scanning a cross-sectional surface of a central portion of the body  110  in the second direction (Y direction), taken along the first and third directions, using a scanning electron microscope (SEM), thicknesses of 30 points equally spaced in the third direction may be measured and an average value thereof may be measured. The thicknesses measured at the 30 points equally spaced may be measured in a capacitor forming portion, which may refer to a region in which the internal electrodes  121  and  122  overlap each other. 
     Similarly, the thickness of the internal electrodes  121  and  122  may refer to an average thickness. In this case, the average thickness of the internal electrodes  121  and  122  may be measured by obtaining an image by scanning a cross-sectional surface of the body  110  in the first direction (X direction) and the third direction (Z direction). For example, in the arbitrary internal electrodes  121  and  122  extracted from an image obtained by scanning a cross-sectional surface of a central portion of the body  110  in the second direction (Y direction), taken along the first and third directions, using a scanning electron microscope (SEM), thicknesses of 30 points equally spaced in the third direction may be measured and an average value thereof may be measured. The thicknesses measured at the 30 points equally spaced may be measured in a capacitor forming portion, which may refer to a region in which the internal electrodes  121  and  122  overlap each other. 
     According to the aforementioned example embodiments, the multilayer capacitor may have improved high-temperature reliability and withstand voltage properties. 
     While the example embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present disclosure as defined by the appended claims.