Abstract:
An electrical component includes a first varistor and a second varistor. The first varistor includes first electrodes and ceramic between the first electrodes. At least part of the first electrodes overlap vertically. The second varistor includes second electrodes and ceramic between the second electrodes. The second electrodes are in a substantially same horizontal plane.

Description:
TECHNICAL FIELD 
     This patent application relates to an electrical multi-layer component comprising ESD (electrostatic discharge) protective elements. 
     BACKGROUND 
     From publication DE 19931056 A1, a ceramic multi-layer varistor is known, which has internal electrodes opposite each other. Internal electrodes connected to the same electrical potential are arranged one above the other. Electrode stacks connected to different electrical potentials are arranged one alongside the other. This component is used as ESD protection for high-frequency circuits and data lines. 
     SUMMARY 
     Described herein is a multi-layer component, which has ESD protective elements. The component is suitable both as ESD protection for high-frequency circuits and data lines, and also as ESD protection for power-supply lines. 
     An electrical component is specified, in which a first varistor (with relatively large capacitance and power capacity) is formed by two overlapping electrodes and a varistor ceramic arranged therebetween, and in which a second varistor (with a relatively small capacitance due to its small active volume) is formed by two internal electrodes lying in one plane and a varistor ceramic arranged therebetween. 
     In this way it is possible to implement varistors that can be used for ESD protection for different lines of an electric circuit, with different capacitance values and power capacities in a basic element. 
     In one implementation, a multi-layer component is specified with a base body, on whose side surfaces are arranged external contacts, which are connected to internal electrodes arranged in the base body. The base body has several layers made from varistor ceramic (e.g., ZnO—Bi, ZnO—Pr), between which metallization layers are arranged with electrode structures embodied therein. 
     A first varistor is formed by a pair of internal electrodes arranged one above the other and the varistor ceramic arranged therebetween. A second varistor is formed by two internal electrodes arranged one alongside the other and the varistor ceramic arranged between its side surfaces facing each other. 
     The second varistor, which has a low capacitance, is suitable as ESD protection for a high-frequency line or data line and can be connected between this high-speed signal line and ground. The first varistor, which has a higher current-pulse capacity and also a significantly higher capacitance, can be connected between a current or voltage supply line and ground. 
     More than just one or two internal electrodes can be provided in one plane of the component. 
     Two main surfaces of the internal electrodes which are arranged one above the other, and which face each other in the vertical direction, span an active volume of the first varistor. The active volume of the first varistor may be least 0.001 mm 3 . Two side surfaces of the internal electrodes, which face each other in the horizontal direction, and which are arranged one alongside the other, span an active volume of the second varistor. The active volume of the second varistor may be a maximum of 10% of the active volume of the first varistor. 
     The distance between the internal electrodes arranged one alongside the other may equal at least 20 μm. 
     The first and the second varistor may share the same internal electrode, which may be connected to ground, which represents, e.g., a common reference potential for high-frequency lines or data lines and power-supply lines. 
     The internal electrode connected to ground—e.g., the electrode with the largest surface area in the corresponding plane—may also be designated as the first electrode and the internal electrodes arranged in the same plane and lying alongside the first electrode may be designated as second electrodes. The internal electrode arranged in the other plane and lying opposite the first electrode may be designated as the third electrode and the internal electrodes arranged in the same plane and lying alongside the third electrode may be designated as fourth electrodes. 
     Second varistors arranged in the first plane are each formed by the first electrode, one of the second electrodes, and the varistor ceramic lying therebetween. Other second varistors arranged in the second plane are each formed by the third electrode, one of the fourth electrodes, and the varistor ceramic lying therebetween. 
     The first electrode may be arranged in a center of an appropriate plane. However, it is also possible for the first electrode to be arranged to one side of the first plane and the second electrodes are arranged to the opposite side of this plane. 
     The internal electrodes arranged one above the other may have substantially equal surface areas. 
     The distance between two second electrodes may be at least twice as large as the distance between the first and one of the second electrodes. 
     All of the features related to the first plane, first electrode, and second electrode can be transferred—as much as technically useful—to the second plane, third electrode, and fourth electrodes. 
     In the first plane, several first electrodes or a shared first electrode can also be provided. 
     The first plane may be divided in a lateral direction into two edge areas and a middle area arranged therebetween. The first electrode is arranged in the middle area and the second electrodes are arranged in the edge areas, the middle area being free of second electrodes. 
     The terminals of the first and third electrode may run outwards to opposing side surfaces of the base body. The terminals of the first and third electrode can alternatively run outwards to the same side of the base body or to different side surfaces arranged at a right angle to each other in the base body. 
     The terminals of the second or fourth electrodes can run outwards to the same side surfaces of the base body as the first or third electrode. In this example, only two side surfaces of the base body are occupied with external contacts. However, it is also possible to occupy all of the side surfaces of the base body with at least one external contact. 
     The first and second planes may have electrode structures that are dimensioned and arranged essentially equally. 
     Second and fourth electrodes allocated to each other can be arranged one above the other or offset relative to each other and can be connected to the same external contact. 
     The second varistors, which are constructed in different planes and whose electrodes are arranged one above the other, are connected on one side, e.g., to the same external contact. The second varistors constructed in the same plane may be connected to different external contacts, wherein each external contact can be connected to a unique signal line. In this way it is possible to eliminate interference on several high-speed signal lines with a single compact component. 
     In one variant, more than only one first varistor with high capacitance can be constructed, which is formed by another first electrode, another third electrode lying opposite it in the vertical direction, and a varistor ceramic arranged therebetween. Two first varistors can also have a common electrode, which can be connected to ground, wherein these varistors are each connected on the other side to a separate external contact or can each be connected to a separate power-supply line. 
     The first varistor can be realized in one variant by a stack of electrodes arranged one above the other (instead of only one pair of internal electrodes arranged one above the other). Here, first and third electrodes are arranged alternately in the vertical direction. Several alternately arranged first and second planes (with second or fourth electrodes) can also be provided. 
     The multi-layer component may be suitable for surface mounting. The external contacts are also constructed so that they each extend past the side surface of the base body and are arranged partially at least on the bottom main surface of the base body. 
     The switching voltage of a varistor formed in the vertical direction, i.e., the varistor voltage between the internal electrodes lying one above the other, may be at least 5 V at a current load of 1 mA. The varistor voltage may be a maximum of 250 V. 
     The switching voltage of a varistor formed in the horizontal direction, i.e., the varistor voltage between the internal electrodes lying one alongside the other, may be at least 10 V at a current load of 1 mA. The varistor voltage may be a maximum of 500 V. 
     In the following, embodiments are explained in more detail on the basis of associated figures. The figures show different embodiments on the basis of schematic representations not true to scale. Parts that are identical or that have an identical function are designated with the identical reference symbols. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1A , a varistor component with one first and two second varistors in cross section, 
         FIG. 1B , the plan view onto the first plane of the component from  FIG. 1A , 
         FIG. 1C , the plan view onto the second plane of the component from  FIG. 1A , 
         FIG. 1D , the plan view onto the component from  FIG. 1A  from above (left), onto a first side surface (in the middle), and onto a second side surface (right), 
         FIG. 1E , the equivalent circuit diagram of the component from  FIGS. 1A to 1D , 
         FIG. 2A , a component with one first varistor and four second varistors in cross section, 
         FIG. 2B , the plan view onto the first plane of the component from  FIG. 2A , 
         FIG. 2C , the plan view onto the second plane of the component from  FIG. 2A , 
         FIG. 2D , a view of the component according to  FIGS. 2A to 2C  from above, 
         FIG. 3A , a varistor component with one first varistor and four second varistors constructed in each plane, 
         FIG. 3B , the plan view onto the first plane of the component from  FIG. 3A , 
         FIG. 3C , the plan view onto the second plane of the component from  FIG. 3A , 
         FIG. 3D , the view of the component from  FIGS. 3A to 3C  from above (left) and from the side (right), and 
         FIG. 3E , an electrical equivalent circuit diagram of the component from  FIGS. 3A to 3D . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A to 1D  show different views of a component with a base body GK that has several layers made from varistor ceramic. Between layers there is a first metallization plane E 1  with internal electrodes IE 10 , IE 11  formed therein and also a second metallization plane E 2  with internal electrodes IE 20 , IE 21  formed therein. 
       FIG. 1A  corresponds to a cross section through the component along the line A-A′ shown in  FIGS. 1B and 1C .  FIG. 1B  shows the first plane E 1  and  FIG. 1C  shows the second plane E 2  of the component from  FIG. 1A . The first internal electrode IE 10  has a larger surface area than the second internal electrode IE 11  arranged next to it. The third internal electrode IE 20  arranged underneath the first internal electrode IE 10  has a larger surface area than the fourth internal electrode IE 21  arranged next to it or underneath the second internal electrode IE 11 . 
     The internal electrode IE 10  is connected to an external contact  1  and the internal electrode IE 20  is connected to an external contact  2 . The internal electrodes IE 11 , IE 21  are connected to another external contact  3 . The external contacts  1  and  2  are arranged on opposite first side surfaces of the base body GK. The external contact  3  is arranged on a second side surface of the base body GK, which is at a right angle to the first side surfaces. In this variant, only three side surfaces are occupied with external contacts. 
     A first varistor (varistor V 1  in  FIG. 1E ) is formed by the opposing internal electrodes IE 10 , IE 20  and a varistor ceramic arranged therebetween. The first internal electrode IE 10  and the third internal electrode IE 20  may have the same surface areas. 
     A second varistor V 21  is formed by the internal electrodes IE 10 , IE 11  arranged one alongside the other in the first plane E 1  and a varistor ceramic arranged therebetween. Another second varistor V 25  is formed by the internal electrodes IE 20 , IE 21  arranged one alongside the other in the second plane E 2  and a varistor ceramic arranged therebetween. 
     The active volume of a varistor is understood to be the volume of a varistor material arranged between two electrodes. The active volume of the first varistor V 1  is spanned between the main surfaces of the internal electrodes IE 10  and IE 20  facing each other and equals at least 0.001 mm 3 . The active volume of the second varistor V 21  is spanned between opposing side surfaces of the first internal electrode IE 10  and the second internal electrode IE 11 . The active volume of the second varistor V 21  is significantly smaller than the active volume of the first varistor V 1 —e.g., by at least one order of magnitude, e.g., by at least two orders of magnitude. 
     At the left, in  FIG. 1D , a view of the component from  FIGS. 1A to 1C  is shown from above, in the middle the plan view onto the first side surface is shown, and at the right, the plan view onto the second side surface of the component is shown. The external contacts  1 ,  2 ,  3  extend past the corresponding side surface and are partially arranged on a main surface (e.g., the bottom side) of the base body, where they form electrical connections of the component that are suitable for surface mounting. 
     In this example, the internal electrodes IE 11  and IE 21  connected to the same electrical potential are arranged one above the other. In one implementation, it is possible for these electrodes to be offset laterally relative to each other. 
     It is advantageous if the first and the third internal electrodes IE 10 , IE 20  are connected to the external contacts arranged on opposing side surfaces. It is also possible, however, to connect the internal electrodes IE 10 , IE 20  to the external contacts that are arranged on the side surfaces at right angles to each other, or on the same side surface. 
     All of the external contacts of the component can be arranged as in  FIG. 3D  on opposing first side surfaces of the component, with the second side surfaces of the base body at right angles to the first surfaces being free of external contacts. It is also possible, however, for all of the side surfaces of the base body to be occupied with external contacts, as in the variant from  FIG. 2D . 
     In  FIG. 2A , another variant is shown, in which the first internal electrode IE 10  in the first plane E 1  is arranged between two second internal electrodes IE 11 , IE 12 , and the third internal electrode IE 20  in the second plane E 2  is arranged between two fourth internal electrodes IE 21 , IE 22 . The first varistor V 1  and the second varistors V 21 , V 25  are formed here and in the variant presented in  FIGS. 3A to 3E  as in  FIGS. 1A to 1E . 
     In the plane E 1 , another second varistor is formed by the internal electrodes IE 10 , IE 12  and a varistor ceramic arranged therebetween. In the second plane E 2 , another second varistor is formed by the internal electrodes IE 20 , IE 22  and a varistor ceramic arranged therebetween. 
     In  FIGS. 3A to 3D , different views are shown of another varistor component, which comprises a total of eight second varistors.  FIG. 3A  shows this component in a schematic cross section along line A-A′.  FIGS. 3B ,  3 C show the plan view onto the first plane E 1  and second plane E 2  of the component, respectively. In the first plane E 1 , a first internal electrode IE 10  and four second internal electrodes IE 11 , IE 12 , IE 13 , and IE 14  are arranged. The first internal electrode IE 10  is arranged in the plane E 1  in the center between two groups of second internal electrodes. In the second plane E 2  there is a third internal electrode IE 20  and four fourth internal electrodes IE 21 , IE 22 , IE 23 , and IE 24 . The third internal electrode IE 20  is arranged in the plane E 2  in the center between two groups of fourth internal electrodes. 
     The second varistors are formed in the first plane E 1  by a second internal electrode, the side surface of the first internal electrode IE 10  opposite it, and the varistor ceramic arranged therebetween. The additional second varistors are formed in the second plane E 2  by a fourth internal electrode, the side surface of the third internal electrode IE 20  opposite it, and the varistor ceramic arranged therebetween. 
     The equivalent circuit diagram of the component presented in  FIGS. 3A to 3D  is shown in  FIG. 3E . The first varistor V 1  is connected between the external contacts  2  and  5 . The external contact  2  is set to ground. All of the second varistors V 21  to V 28  are connected to the external contact  2 . The second varistor V 21  defined by the internal electrodes IE 10  and IE 11  is connected to the external contact  1 . The second varistor V 22  defined by the internal electrodes IE 10  and IE 12  is connected to the external contact  3 . The second varistor V 23  defined by the internal electrodes IE 10  and IE 13  is connected to the external contact  4 , and the second varistor V 24  defined by the internal electrodes IE 10  and IE 14  is connected to the external contact  6 . The other second varistors V 25  to V 28  are formed in a manner corresponding to the second varistors V 21  to V 24  in the second plane E 2  of the component. 
     The claims are not limited to the embodiments shown in this publication or to the number of illustrated elements. It is possible to arrange the electrode pair formed by the first and third internal electrodes arbitrarily in the corresponding metallization planes. It is possible to divide the first or third internal electrode into, e.g., two equal-area sub-electrodes and to connect these sub-electrodes to a separate electrical external contact.