Abstract:
A layered capacitor device with high capacitance per unit area is realized by alternating in the vertical direction first layers (FL 1 , FL 2 , FL 3 , FL 4 , FL 5 ) and second layers (SL 1 , SL 2 , SL 3 , SL 4 ). A first layer (FL 2 ) consists of horizontally alternating electrically conducting tracks (T 2,2 ; T 2,3 ) and electrically insulating tracks, whereas a second layer includes of electrically insulating material, e.g. an oxide. In this way top-bottom capacitors (C TB ) and side-wall capacitors (C SW ) are constituted that are parallel coupled to form the layered capacitor device. In a preferred embodiment of the invention, this parallel coupling is realized by conductively interconnecting diagonally neighboring electrically conducting tracks (T 1,2 ; T 2,3 ).

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a layered capacitor device and an integrated circuit comprising such a capacitor device. 
     Such a layered capacitor device is already known in the art, e.g. from the U.S. Pat. No. 4,656,557, entitled ‘ Electrical Layer Capacitor and Method for the Manufacture Thereof’ . Therein, a layered capacitor device is described that is formed by an alternating superposition of electrically conducting layers, called metal coatings in the cited U.S. Patent, and electrically insulating layers, called plastic films in the cited U.S. Patent. In this way, a longitudinal stack of individual capacitors is constructed. Metal coatings of a same polarisation are interconnected so that the individual capacitors become parallel coupled. In case a layered capacitor which forms part of an integrated circuit is given the structure known from U.S. Pat. No. 4,656,557 by alternating superposition of metal layers and oxide layers, the realised capacitance per unit chip area is small. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a layered capacitor device similar to the known one but through which the realised capacitance per unit area increases significantly. 
     According to the invention, this object is achieved by a layered capacitor device comprising the parallel coupling of a plurality of capacitors constituted by vertically alternating first and second layers, the second layers consisting of electrically insulating material, wherein the first layers consist of horizontally alternating electrically conducting tracks and electrically insulating tracks, whereby top-bottom capacitors are constituted by two vertically neighboring electrically conducting tracks and a second layer of said second layers therebetween, and whereby side-wall capacitors are constituted by two horizontally neighboring said electrically conducting tracks and an electrically insulating track of said electrically insulating tracks therebetween, said top-bottom capacitors and said side-wall capacitors constituting said plurality of capacitors. 
     In this way, the realised capacitance is the superposition of vertically oriented or top-bottom capacitors and horizontally oriented or side-wall capacitors. The latter side-wall capacitors are bigger than the top-bottom capacitors because the spacing between horizontally neighbouring metal tracks typically is smaller than the spacing between vertically neighbouring metal tracks as a result of the thickness of the insulating layers. Moreover, fringing electrical fields between side-walls of a metal track and top or bottom plates of other metal tracks also have an increasing effect on the realised capacitance per unit area. 
     It is to be noticed that the term ‘comprising’, used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression ‘a device comprising means A and B’ should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. 
     An additional feature of the layered capacitor device according to the present invention is defined by claim  2 . 
     In this way, by electrically interconnecting all diagonally neighbouring metal tracks, all top-bottom capacitors and all side-wall capacitors become parallel coupled between two contact points of the capacitor device. If the metal tracks are supposed to be labelled with a row index and column index in accordance with their position in the capacitor device, the first contact point is electrically connected to all metal tracks whose row index and column index, when added together, constitute an odd number and the second contact point is electrically connected to all metal tracks whose row index and column index, when added together, constitute an even number. 
     As described by claim  3 , a capacitor device with a structure according to the present invention is suitable for integration in an integrated circuit, because the area occupied by the integrated circuit is reduced significantly in comparison with an integrated circuit wherein the same aggregate capacitance is realised via a capacitor device with the known structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned and other objects and features of the invention will become more apparent and the invention itself will be best understood by referring to the following description of an embodiment taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 represents a three dimensional illustration of the structure of an embodiment of the known capacitor device; and 
     FIG. 2 represents a three dimensional illustration of the structure of an embodiment of the capacitor device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The capacitor device drawn in FIG. 1 consists of five metal layers ML 1 , ML 2 , ML 3 , ML 4  and ML 5 , four oxide layers OL 1 , OL 2 , OL 3  and OL 4 , a first electrically conductive path E 1  and a second electrically conductive path E 2 . The metal layers ML 1 , ML 2 , ML 3 , ML 4  and ML 5  have a rectangular surface S. The oxide layers have a thickness d. The metal layers ML 1 , ML 2 , ML 3 , ML 4  and ML 5  and the oxide layers OL 1 , OL 2 , OL 3  and OL 4  are alternatingly superimposed to form a vertical stack. The first electrically conductive path E 1  interconnects the second metal layer ML 2  with the fourth metal layer ML 4  and constitutes a first terminal of the capacitor device. The second electrically conductive path E 2  interconnects the first metal layer ML 1 , the third metal layer ML 3  and the fifth metal layer ML 5 , and constitutes a second terminal of the capacitor device. 
     The capacitor device of FIG. 1, which is for example manufactured via a 5 layer submicron CMOS technology, has a well-known structure: a longitudinal stack of parallel coupled capacitors C 1 , C 2 , C 3  and C 4 . The capacitor C 1 , formed by the first metal layer ML 1 , the first oxide layer OL 1  and the second metal layer ML 2  has a capacitance value given by the formula:        C1   =       ɛ   0     ·     ɛ   r     ·     S   d                              
     Herein, ε 0  represents the permittivity of air and ε r  represents the relative permittivity of the oxide where the first oxide layer OL 1  is made of. The second capacitor C 2 , formed by the second metal layer ML 2 , the second oxide layer OL 2  and the third metal layer ML 3 , the third capacitor C 3  formed by the third metal layer ML 3 , the third oxide layer OL 3  and the fourth metal layer ML 4 , and the fourth capacitor C 4  formed by the fourth metal layer ML 4 , the fourth oxide layer OL 4  and the fifth metal layer ML 5  each have a capacitance value equal to that of the first capacitor C 1  since the thickness d is supposed to be equal for all oxide layers OL 1 , OL 2 , OL 3  and OL 4 , each oxide layer OL 1 , OL 2 , OL 3  and OL 4  is supposed to be made of the same oxide, and each metal layer ML 1 , ML 2 , ML 3 , ML 4  and ML 5  is supposed to have the same horizontal surface area S. As a result, the capacitor device of FIG. 1 realises between its first terminal and its second terminal a capacitance value given by:        C   =       C1   +   C2   +   C3   +   C4     =       4   ·   C1     =     4   ·     ɛ   0     ·     ɛ   r     ·     S   d                                  
     The capacity per unit silicon area or capacitor density obtained for the capacitor device of FIG. 1 with the known longitudinal stacked structure consequently equals:          D   C     =       C   S     =       4   ·     ɛ   0     ·     ɛ   r       d                              
     The capacitor device drawn in FIG. 2 also contains five metal layers FL 1 , FL 2 , FL 3 , FL 4  and FL 5 , four oxide layers SL 1 , SL 2 , SL 3  and SL 4 , a first electrically conductive path E 1  and a second electrically conductive path E 2 . The metal layers FL 1 , FL 2 , FL 3 , FL 4  and FL 5  and the oxide layers SL 1 , SL 2 , SL 3  and SL 4  are alternatingly superimposed to constitute the capacitor device. The metal layers FL 1 , FL 2 , FL 3 , FL 4  and FL 5  in the capacitor device of FIG. 2 however contain spacings filled with the oxide where also the oxide layers SL 1 , SL 2 , SL 3  and SL 4  are made of. More particularly, each metal layer FL 1 , FL 2 , FL 3 , FL 4  and FL 5  in lateral direction consists alternatingly of metal tracks and oxide tracks. Each metal track has a top surface and a bottom surface area S TB , and two side-wall surface areas S LAT . The metal tracks T 1 , 1 , T 1 , 2 , T 1 , 3 , T 1 , 4 , T 1 , 5 , T 2 , 1 , T 2 , 2 , T 2 , 3 , T 2 , 4 , T 2 , 5 , T 3 , 1 , T 3 , 2 , T 3 , 3 , T 3 , 4 , T 3 , 5 , T 4 , 1 , T 4 , 2 , T 4 , 3 , T 4 , 4 , T 4 , 5 , T 5 , 1 , T 5 , 2 , T 5 , 3 , T 5 , 4  and T 5 , 5  in the capacitor device of FIG. 2 are labelled with two indices, the first index being indicative for the metal layer FL 1 , FL 2 , FL 3 , FL 4  or FL 5  where the metal track forms part of, and the second index being indicative for the lateral position of the metal track in the respective metal layer FL 1 , FL 2 , FL 3 , FL 4  or FL 5 . If the capacitor device is so oriented that the metal layers FL 1 , FL 2 , FL 3 , FL 4  or FL 5  form horizontal planes, the front sides of the metal tracks T 1 , 1 , T 1 , 2 , T 1 , 3 , T 1 , 4 , T 1 , 5 , T 2 , 1 , T 2 , 2 , T 2 , 3 , T 2 , 4 , T 2 , 5 , T 3 , 1 , T 3 , 2 , T 3 , 3 , T 3 , 4 , T 3 , 5 , T 4 , 1 , T 4 , 2 , T 4 , 3 , T 4 , 4 , T 4 , 5 , T 5 , 1 , T 5 , 2 , T 5 , 3 , T 5 , 4  and T 5 , 5  form an array as drawn in FIG.  2 . The first index r of each metal track Tr,s than corresponds to the row and the second index s to the column of the metal track in the array. Metal tracks like T 2 , 2  and T 2 , 3 , forming part of the same metal layer FL 2  and separated from each other by a single oxide track are named horizontally neighbouring tracks in this patent application. Such metal tracks have equal first indices, and second indices that differ by 1. Metal tracks like T 1 , 2  and T 2 , 2 , forming part of metal layers FL 1  and FL 2  separated from each other by a single oxide layer SL 1 , and having respectively a bottom surface and top surface facing towards each other, are named vertically neighbouring tracks in this patent application. Such metal tracks have equal second indices, and first indices that differ by 1. Metal tracks like T 1 , 2  and T 2 , 3 , that are in vertical direction separated by an oxide layer SL 1  and in horizontal direction by an oxide track are named diagonally neighbouring tracks in this application. Such metal tracks have first indices that differ by 1 and second indices that differ by 1. The first electrically conductive path E 1  interconnects all diagonally neighbouring metal tracks starting from the leftmost metal track T 2 , 1  in the second metal layer FL 2  and so constitutes a first terminal of the capacitor device. The sum of the first index r and the second index s for each metal track Tr,s coupled to this first terminal is odd. The second electrically conductive path E 2  interconnects all diagonally neighbouring metal tracks starting from the leftmost metal track T 1 , 1  of the first metal layer FL 1  and so constitutes a second terminal of the capacitor device. The sum of the first index r and the second index s for each metal track Tr,s coupled to this second terminal is even. To reduce the number of connections to be made between metal tracks in the capacitor device, each metal track Tr,s is connected via an electrical conductor to the metal track Tr+1,s+1 whose first index r+1 and second index s+1 are 1 higher than its own first index r and second index s respectively. The first electrically conductive path E 1  than is realised by interconnecting the leftmost metal tracks T 2 , 1  and T 4 , 1  of respectively the second metal layer FL 2  and fourth metal layer FL 4 , and the second metal track T 1 , 2  and fourth metal track T 1 , 4  in the first metal layer FL 1 . The second electrically conductive path is realised by interconnecting the leftmost metal tracks T 1 , 1 , T 3 , 1  and T 5 , 1  of respectively the first metal layer FL 1 , the third metal layer FL 3  and the fifth metal layer FL 5 , and the first metal track T 1 , 1 , the third metal track T 1 , 3  and the fifth metal track T 1 , 5  in the first metal layer FL 1 . 
     The capacitor device of FIG. 2, which may also be manufactured for example via a 5 layer submicron CMOS technology, is an array of parallel coupled top-bottom capacitors C TB  and side-wall capacitors C SW . Each top-bottom capacitor C TB  is constituted by two vertically neighbouring metal tracks, for instance T 1 , 2  and T 2 , 2 , and the intermediate oxide layer, for instance SL 1  and has a capacitance value given by:          C   TB     =       ɛ   0     ·     ɛ   r     ·       S   TB       d   TB                                
     Herein S TB  represents the top and bottom surface area of a metal track and d TB  represents the thickness of the oxide layers SL 1 , SL 2 , SL 3  and SL 4  which is supposed to be equal for all oxide layers SL 1 , SL 2 , SL 3  and SL 4 . This thickness d TB  for 0.35 μm CMOS technology typically equals 0.8 {grave over (a)} 0.9 μm. Each side-wall capacitor C SW  is constituted by two horizontally neighbouring metal tracks, for instance T 1 , 1  and T 1 , 2 , and the intermediate oxide track in the same metal layer, for instance FL 1 , and has a capacitance value given by:          C   SW     =       ɛ   0     ·     ɛ   r     ·       S   LAT       d   LAT                                
     Herein, S LAT  represents the lateral side-wall surface area of the metal tracks and d LAT  represents the horizontal spacing between two horizontally neighbouring metal tracks. This horizontal spacing d LAT  for 0.35 μm CMOS technology typically equals 0.6 {grave over (a)} 0.7 μm. Because the spacing d LAT  between horizontally neighbouring tracks typically is smaller than the spacing d TB  between vertically neighbouring metal tracks the capacitance realised by side-wall capacitors C SW  is bigger than that realised by top-bottom capacitors C TB . Moreover, fringing electrical fields FF, for example between side-wall surfaces S LAT  of a metal track T 1 , 5  and top or bottom surfaces S TB  of vertically neighbouring tracks T 2 , 5  increase the aggregate capacitance value between the first terminal E 1  and second terminal E 2  of the capacitor device of FIG.  2 . If these fringing fields FF are not taken into account and if it is supposed that all metal tracks T 1 , 1 , T 1 , 2 , T 1 , 3 , T 1 , 4 , TI, 5 , T 2 , 1 , T 2 , 2 , T 2 , 3 , T 2 , 4 , T 2 , 5 , T 3 , 1 , T 3 , 2 , T 3 , 3 , T 3 , 4 , T 3 , 5 , T 4 , 1 , T 4 , 2 , T 4 , 3 , T 4 , 4 , T 4 , 5 , T 5 , 1 , T 5 , 2 , T 5 , 3 , T 5 , 4  and T 5 , 5  have the same dimensions, that all oxide layers SL 1 , SL 2 , SL 3  and SL 4  have the same thickness d TB , that all horizontal oxide tracks between metal tracks have the same width d LAT , and that one and the same oxide is used for the oxide layers SL 1 , SL 2 , SL 3 , SL 4  and oxide tracks, the aggregate capacitance value realised between the first terminal E 1  and second terminal E 2  is given by:        C   =         20   ·     C   TB       +     20   ·     C   SW         =       20   ·     ɛ   0     ·     ɛ   r     ·       S   TB       d   TB         +     20   ·     ɛ   0     ·     ɛ   r     ·       S   LAT       d   LAT                                    
     If it is assumed that the capacitor device of FIG. 2 occupies the same aggregate silicon area S as the capacitor device of FIG. 1, the capacity per unit silicon area or capacitor density obtained for the capacitor device of FIG. 2 with the new array-like structure equals:          D   C     =       C   S     =       20   ·     ɛ   0     ·     ɛ   r     ·       S   TB         d   TB     ·   S         +     20   ·     ɛ   0     ·     ɛ   r     ·       S   LAT         d   LAT     ·   S                                    
     Because the width d LAT  of the oxide tracks is smaller than the thickness d TB  of the oxide layers, the contribution of the side-wall capacitors C SW  significantly increases the capacitor density in comparison with capacitor devices with the known stacked structure. With the submicron CMOS technologies available at the time the invention was made, a capacity increase per unit area of 30%, or an area gain per unit capacitance of 30% is obtainable. The linearity of the capacitors, i.e. the fact the capacitance value is independent of the voltage drop over the capacitor, does not decrease for a capacitor with the structure according to the present invention in comparison with a capacitor with the known stacked structure. 
     It is noticed that in the above given description of the structure of the capacitor device according to the present invention, the terms horizontal, vertical, and diagonal are relative terms, assuming that the capacitor device is turned in a position wherein the metal layers FL 1 , FL 2 , FL 3 , FL 4  and FL 5  and oxide layers SL 1 , SL 2 , SL 3  and SL 4  constitute horizontal planes. 
     It is further remarked that the technology used to manufacture the capacitor device, i.e. the submicron CMOS technology, is only given by way of example. A person skilled in the art of microelectronics will appreciate that several multi-layer technologies are suitable to manufacture a capacitor device wherein horizontally oriented side-wall capacitors and vertically oriented top-bottom capacitors are parallel coupled to reduce the required area to realise a given aggregate capacitance value. 
     Another remark is that in the above described embodiment, the number of metal layers, oxide layers, and the number of metal tracks within one metal layer are given as an example. Any skilled person appreciates that the selected technology to manufacture the capacitor device puts constraints on the number of layers and on the number of tracks that can be realised on a certain given area. As technology evolves, these numbers typically increase, so that it may be expected that the currently proposed structure for a capacitor device will become more and more interesting. 
     While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.