Abstract:
A method and apparatus is provided that pertains to a low inductance capacitor. The capacitor has a first surface electrically interconnected to a plurality of conductive electrodes and one or more second surfaces electrically interconnected to a plurality of electrodes interposed between the electrodes electrically interconnected to the first conductive surface. A dielectric layer separates the layered plurality of electrodes. The one or more second conductive surfaces are positioned within the body of the layered electrodes, such that the distance between the terminations of the first conductive surface and the one or more second conductive surfaces is shortened to lower inductance.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to capacitors and the manufacture thereof, and more particularly, to low inductance capacitors suitable for use with microelectronic circuits.  
         BACKGROUND OF INVENTION  
         [0002]    Microelectronic devices are continually becoming smaller, and the circuit density, operating speeds and switching rates are continually increasing. This trend has impacted the design and manufacture of a variety of components that support the operation of microelectronic devices, such as voltage regulation devices, inductors, capacitors, and the like. In regard to capacitors, the decreased size and increased speed trend has amplified issues with respect to the inductance of capacitors, which have not previously been a critical concern.  
           [0003]    Capacitors can be used for a variety of reasons, including as a means to store energy for use by microelectronic devices during periods of non-steady state or transient current demands, or to manage noise problems that occur in microelectronic circuit applications. Inductance is a capacitor limitation that is becoming more critical as microelectronic devices get smaller and faster. The higher the inductance, the slower the capacitor, as a power source, responds to a transient current demand. Accordingly, it is one goal of the industry to reduce inductance in capacitors, so as to allow them to timely respond to the energy demands as required by a microelectronic device (e.g. within the first few cycles).  
           [0004]    [0004]FIG. 1 is a side view of an example of a capacitor of the prior art design. Capacitors commonly consist of a first conductive plate  10  and a second conductive plate  12 . The first conductive plate  10  is electrically interconnected to a plurality of conductive first electrodes  14 . The second conductive plate  12  is electrically interconnected to a plurality of conductive second electrodes  16 . Dielectric material  18  is dispersed between the plurality of first electrodes and the plurality of second electrodes. The dielectric material  18  can be any nonconductive material, including, but not limited to air, aluminum oxide, ceramics, mica, and the like.  
           [0005]    The charge or polarity of the first conductive plate  10  and the first electrodes  14  is opposite to the charge of the second conductive plate  12  and the second electrodes  16 , such that the electrical energy of the charged system then is stored in the polarized dielectric. First conductive plate  10  terminates at first terminal  20  and second conductive plate  12  terminates at second terminal  22 . First and second terminals  20  and  22  can then be electrically interconnected to a conductive path, such as a power trace in a printed circuit board that electrically interconnects a power source with a microelectronic device (not shown).  
           [0006]    Inductance is dependent on factors such as the separation distance between first and second electrodes  14  and  16 , as well as the first and second conductive plates  10  and  14 . Generally, inductance is directly proportional to the distance between the oppositely charged surfaces, i.e. first and second electrodes  14  and  16  and first and second conductive plates  10  and  14 , show by terminal distance arrow  24 . As such, industry has attempted to reduce both distances, in order to reduce inductance. As new dielectric materials  18  with higher dielectric constants are developed, the distance between the conductive plates may be reduced.  
           [0007]    New configurations and methods for reducing the distance between the conductive surfaces  10  and  12  are needed to reduce inductance of capacitors, which will increase the capacitor response time to the energy demands of the smaller, yet higher speed microelectronic devices. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 is a cross-sectional view of an example of a current capacitor;  
         [0009]    [0009]FIG. 2 is a cross-sectional view of a capacitor in accordance with an embodiment of the present invention;  
         [0010]    [0010]FIG. 3 is a perspective view of the embodiment of FIG. 2;  
         [0011]    [0011]FIG. 4 is a cross-sectional view of a capacitor in accordance with another embodiment of the present invention; and  
         [0012]    [0012]FIG. 5 is a perspective view of the embodiment of FIG. 4.  
     
    
     DESCRIPTION  
       [0013]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.  
         [0014]    [0014]FIG. 2 is a cross-sectional view of a capacitor  30  in accordance with an embodiment of the present invention. A plurality of conductive first electrodes  34  and a corresponding plurality of conductive second electrodes  38  are layered or interleaved to a predetermined number of layers. A dielectric material  40  separates each layered first electrode  34  and second electrode  38 . The layered first and second electrodes  34  and  38 , and the dielectric material  40 , generally comprise the body of capacitor  30  defining a certain shape and size. A first conductive surface  32  is positioned about the perimeter of the capacitor  30 . The first electrodes  34  are electrically interconnected to the first conductive surface  32  and extend generally perpendicular to the first conductive surface  32 . The first conductive surface  32  and the first electrodes  34  have a predetermined charge or polarity.  
         [0015]    The second conductive surface  36  is disposed in the body of the capacitor  30 , generally penetrating the layers of the first and second electrodes  34  and  38 . The second electrodes  38  are electrically interconnected to the second conductive surface  36  and extend substantially perpendicular to the second conductive surface  36 , but are not electrically interconnected with the first conductive surface  32 . The second conductive surface  36  and the second electrodes  38  electrically interconnected thereto have a charge that is opposite to the charge of the first conductive surface  32  and the first electrodes  34 . The first conductive surface  32  terminates at the first terminal  42  and the second conductive surface  36  terminates at the second terminal  44 . The terminals  42  and  44  can be configured to electrically interconnect to, for example, the power and ground plane of a power delivery path for a microelectronic device. The capacitor  30  can be encapsulated with a dielectric material to prevent grounding or electromagnetic influence from other devices (not shown).  
         [0016]    Though first conductive surface  32  is shown in the illustrated embodiment to surround the perimeter of capacitor  30 , the first conductive surface  32  may segmented and electrically interconnected to first electrodes  34  at different positions around the perimeter of capacitor  30 .  
         [0017]    The inductance of the capacitor  30  is influenced by the separation distance between the first and second electrodes  34  and  38 . The separation distance between first conductive surface  32  and second conductive surface  36 , shown by termination distance arrow  46 , directly impacts the inductance. Comparing termination distance  46  of FIG. 2 with the termination distance  24  of FIG. 1, the inductance of capacitor  30  will be lower as the terminal distance  46  is reduced, in this case to approximately one half in reference to FIG. 1. This reduction is due to the positioning the second conductive surface  36  into the body of capacitor  30 , such that it is no longer on the opposite edge of the perimeter. The lower inductance allows the capacitor  30  to respond more quickly to the increased energy demand of a microelectronic device.  
         [0018]    [0018]FIG. 3 is a perspective view of the capacitor  30  shown in the embodiment of FIG. 2. The first conductive surface  32  is electrically interconnected to the first electrodes  34  (not shown), and comprises at least a portion of the perimeter of the capacitor  30 . The first conductive surface  32  terminates at first terminal  42  and has a charge. The second conductive surface  36  extends into the layers of the first and second electrodes  34  and  38  (not shown), and is electrically interconnected with the second electrodes  38  (not shown). The second conductive surface  36  terminates at the second terminal  44  and is opposite in polarity to the first terminal  42  and the first conductive surface  32 . As shown, the termination distance  46 , again, is roughly half what it would be if the capacitor  30  was of conventional design.  
         [0019]    The capacitor  30  can be constructed in a variety of ways. In one embodiment in accordance with the present invention, individual sheets of the first electrodes  34  and the second electrodes  38  in the form of sheets can be layered with inserting a dielectric material  40  between each first electrode  34  and second electrode  38 . Once the desired number of first and second electrode layers is reached, the capacitor  30  can be cut to any desired shape or size. The first conductive surface  32  can then be secured to the perimeter of the body of the capacitor  30  and electrically interconnected to the first electrodes  34 . An opening within the body of the capacitor  30  can be created, for example but not limited to by drilling, and a second conductive surface  36  can be inserted in the opening and electrically interconnected with the second electrodes  38 .  
         [0020]    Alternatively, in another embodiment of the present invention, the first conductive surface  32  and the second conductive surface  36  can be pre-positioned. Pre-sized first electrodes  34  and second electrodes  38  can be alternately layered, with placing a dielectric material  40  between each electrode layer. As each first electrode  34  is placed it can be electrically interconnected with first conductive surface  32  and as each second electrode  38  is placed, it can be electrically interconnected with second conductive surface  36 .  
         [0021]    [0021]FIG. 4 is a side view of a capacitor  50  in accordance with another embodiment of the present invention. A plurality of first electrodes  54  and a corresponding plurality of second electrodes  58  are interleaved or layered with a dielectric material  60  placed between each first and second electrode  54  and  58 , such that the body of capacitor  50  is defined. The first electrodes  54  are electrically interconnected to first conductive surface  52  in a substantially perpendicular manner. A plurality of second conductive surfaces  56  are disposed within the body of capacitor  50  in the layered first and second electrodes  54  and  58 . The second electrodes  58  electrically interconnect to the plurality of first conductive surfaces  56  and have an opposite charge as that of the first conductive surface  52  and first electrodes  54 . First conductive surface  52  terminates at first terminal  62  and second conductive surfaces  56  terminate at second terminal  64 .  
         [0022]    Termination distance  66  is reduced by the plurality of second conductive surfaces  56  disposed within the capacitor  50 , which in turn proportionally decreases the inductance. Like the embodiment described in FIG. 2, first conductive surface  52  need not entirely surround the perimeter of capacitor  50 , but can be at a portion or multiple portions at spaced apart intervals.  
         [0023]    [0023]FIG. 5 is a perspective view of the capacitor shown in the embodiment of FIG. 4. The first conductive surface  52  is electrically interconnected to the first electrodes  54  (not shown), and comprises at least a portion of the perimeter of the capacitor  50 . The first conductive surface  52  terminates at first terminal  62 . The second conductive surfaces  56  are disposed through the layers of first and second electrodes  54  and  58  (shown in FIG. 4), and only electrically interconnect with the second electrodes  58  (shown in FIG. 4). The second conductive surfaces  56  terminate at the second terminals  64 , and are oppositely charged to the first terminal  62  and first conductive surface  52 . Termination distances  66 , again, are roughly half what it would be if the second conductive surface  56  was on the perimeter at a position opposite to the first conductive surface  52 .  
         [0024]    The terminals  62  and  64  can be configured to electrically interconnect to, for example but not limited to, the power and ground plane of a power delivery path for a microelectronic device, or any other electronic device. Though not shown, the capacitor  50  can be encapsulated with a dielectric material to prevent grounding or influence from other devices. Methods of manufacturing the capacitor  50  or capacitors having a plurality of second conductive surfaces disposed within the body of the capacitor is the same as those methods described in regards to the embodiments of FIGS. 2 and 3, except multiple second conductive surfaces  56  are provided.  
         [0025]    Though the second conductive surfaces  36  and  56  in the embodiments described herein in FIGS. 2 through 5 are cylindrical in shape with a hollow core, which helps with heat dissipation, it is within the scope of the invention for the second conductive surfaces  36  and  56  to be a polygonal, oblong or any other shape that allows for the second conductive surfaces to be disposed in the plurality of layered first electrodes  34  and  54  and second electrodes  38  and  58 , such that the second electrodes  38  and  58  are electrically interconnected to the second conductive surfaces  36  and  56 , and the second conductive electrodes  38  and  58  are electrically interconnected to the second conductive surfaces  36  and  56 . The second conductive surfaces  36  and  56  can be solid, and their shape, as well as the shape and size of the capacitor itself can be varied depending on the desired configuration and taking into account manufacturing constraints.  
         [0026]    Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.