Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application (and claims the benefit of priority under 35 USC 120) of U.S. application Ser. No. 13/192,388, filed Jul. 27, 2011, now U.S. Pat. No. 8,537,524, which is a divisional application (and claims the benefit of priority under 35 USC 120) of U.S. application Ser. No. 12/536,237, filed Aug. 5, 2009, now U.S. Pat. No. 7,988,744, which is a divisional application (and claims the benefit of priority under 35 USC 120) of U.S. application Ser. No. 11/474,246, filed Jun. 23, 2006, now U.S. Pat. No. 7,578,858, which is a divisional application (and claims the benefit of priority under 35 USC 120) of U.S. application Ser. No. 11/179,133, filed Jul. 11, 2005, now U.S. Pat. No. 7,116,544, which is a continuation application (and claims the benefit of priority under 35 USC 120) of U.S. application Ser. No. 10/870,579, filed Jun. 16, 2004, now U.S. Pat. No. 6,980,414. The disclosure of these prior applications is considered part of (and is incorporated by reference in) the disclosure of this application. The present application is related to U.S. application Ser. No. 10/601,286, filed on Jun. 20, 2003, now U.S. Pat. No. 6,885,543, which is a continuation of U.S. application Ser. No. 09/765,200, filed Jan. 18, 2001, now U.S. Pat. No. 6,625,006 (the &#39;006 patent), the entire contents of which are incorporated by reference herein. 
     The present application is also related to U.S. application Ser. No. 10/372,617, filed on Feb. 21, 2003 which is a divisional of the &#39;006 patent and is now U.S. Pat. No. 6,784,050, the entire contents of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     The following disclosure relates to semiconductor devices. 
     In integrated circuit design there are many applications that include high performance, on-chip capacitors. These applications include, for example, voltage control oscillators, phase-lock loops, operational amplifiers, and switching capacitors. On-chip capacitors can be used, e.g., to isolate digital and analog integrated circuits from noise created within an integrated circuit system or to store charge within an integrated circuit system. 
     Conventional on-chip capacitors can be configured as Metal-Oxide-Metal capacitors (MOMs). Referring to  FIG. 1 , the construction of a conventional MOM capacitor  100  is illustrated. MOM capacitor  100  includes two nodes  102  and  104  that are formed on conductor layers  106  and  108 , respectively. A substrate  110  forms a base for MOM capacitor  100 . Conductor layers  106  and  108  are separated by a dielectric  112  (e.g., silicon dioxide). Substrate  110  and conductor layer  108  can also be separated by a dielectric (not shown). In addition to a device (parallel plate) capacitance (Cpp) that is formed between nodes  102  and  104 , an undesirable parasitic capacitance (Cs) may also be formed between substrate  110  and node  104  in a conventional MOM structure. 
     SUMMARY 
     In general, in one aspect, this specification describes a capacitor structure. The capacitor structure includes a substrate, a first group of conducting strips, a second group of conducting strips, a third group of conducting strips, and a fourth group of conducting strips. 
     The first group of conducting strips are arranged substantially parallel to each other within a first layer disposed on the substrate. The first group of conducting strips are also connected to a first node and are in electrical communication with each other. The second group of conducting strips are arranged substantially parallel to each other and alternate with the first group of conducting strips within the first layer. The second group of conducting strips are connected to a second node and are in electrical communication with each other. The third group of conducting strips are arranged substantially parallel to each other within a second layer that at least partially overlies the first layer. The third group of conducting strips are in electrical communication with each other and with the first group of conducting strips. The third group of conducting strips are further substantially perpendicular to the first group of conducting strips and the second group of conducting strips. The fourth group of conducting strips are arranged substantially parallel to each other and alternate with the third group of conducting strips within the second layer. The fourth group of conducting strips are in electrical communication with each other and with the second group of conducting strips. The fourth group of conducting strips are further substantially perpendicular to the first group of conducting strips and the second group of conducting strips. 
     Particular implementations can include one or more of the following. The capacitor structure can further include a dielectric interposed between the first and second layers. The dielectric can be a layer of silicon dioxide. The capacitor structure can further include a guardband spaced from the first and second nodes. The guardband can be comprised of a conductive material—e.g., aluminum, polysilicon, or copper. The guardband can be spaced approximately a predetermined distance (dg) from the first and second nodes, in which adjacent conducting strips of the first and second layers are spaced apart approximately a predetermined distance (dh), and the distance (dg) is selected to be substantially twice the distance (dh). The guardband can be located on a single layer or distributed over multiple layers. The guardband can encircle the first and second layers of conducting strips. At least one of the first, second, third and fourth groups of conducting strips can be connected by a corresponding base strip. The first group of conducting strips can be connected to the third group of conducting strips by vertical vias. The second group of conducting strips can be connected to the fourth group of conducting strips by vertical vias. The second layer can substantially overlie the first layer. 
     In general, in another aspect, this specification describes a capacitor structure that includes a substrate, a first group of conducting strips, a second group of conducting strips, a third group of conducting strips, a fourth group of conducting strips, a first set of vertical vias, a second set of vertical vias, a third set of vertical vias, and a fourth set of vertical vias. 
     The first group of conducting strips are arranged substantially parallel to each other within a first layer disposed on the substrate. The first group of conducting strips are connected to a first node and are connected to a first base strip. The second group of conducting strips are arranged substantially parallel to each other and alternate with the first group of conducting strips within the first layer. The second group of conducting strips are connected to a second node and are connected to a second base strip. The third group of conducting strips are arranged substantially parallel to each other within a second layer that at least partially overlies the first layer. The third group of conducting strips are connected to the first node and are connected to a third base strip. The third group of conducting strips are substantially parallel to and substantially overlie the first group of conducting strips. The fourth group of conducting strips are arranged substantially parallel to each other and alternate with the third group of conducting strips within the second layer. The fourth group of conducting strips are connected to the second node and are connected to a fourth base strip. The fourth group of conducting strips are also substantially parallel to and substantially overlie the second group of conducting strips. The first set of vertical vias interconnect the first group of conducting strips to the third group of conducting strips. The second set of vertical vias interconnect the second group of conducting strips to the fourth group of conducting strips. The third set of vertical vias interconnect the first base strip to the third base strip. The fourth set of vertical vias interconnect the second base strip to the fourth base strip. 
     Particular implementations can include one or more of the following. The third set and fourth set of vertical vias can be each placed at locations along a respective base strip substantially adjacent to vertical vias of an opposite node that are located on one or more of the first, second, third or fourth groups of conducting strips. 
     Implementations can include one or more of the following advantages. On-chip capacitance structures are provided that are highly immune to noise fluctuations that may be present on a substrate. In addition, the on-chip capacitance structures provide a high capacitance-per-volume. In one implementation, vertical vias are used within a base strip to form base strip via capacitances that further increase the overall capacitance-per-volume of the capacitance structure. On-chip capacitance structures are provided that also have an efficient use of space. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a conventional on-chip capacitor structure. 
         FIG. 2  is a perspective view of an on-chip capacitor structure. 
         FIG. 3  is a side view of the A-A cross-section of the on-chip capacitor structure in  FIG. 2 , showing associated capacitances. 
         FIG. 4  is a top view of the on-chip capacitor structure of  FIG. 2 . 
         FIG. 5  is a side view of the on-chip capacitor structure of  FIG. 2 , including guard bands. 
         FIG. 6  is a top view of an on-chip capacitor structure. 
         FIG. 7A  is a side view of an on-chip capacitor structure, including vertical vias. 
         FIG. 7B  is a perspective view of the on-chip capacitor structure of  FIG. 7A . 
         FIG. 7C  is a top view of the on-chip capacitor structure of  FIG. 7A . 
         FIG. 8  is a side view of the on-chip capacitor structure of  FIG. 7A , including guardbands. 
         FIG. 9  is a perspective view of a split-capacitor configuration. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 2  illustrates one implementation of an on-chip capacitor  200 . On-chip capacitor  200  includes two layers  201 ,  203  of conducting strips formed upon a substrate  202 . Substrate  202  can be a p-type substrate or an n-type substrate. A first layer  201  is formed by two sets of conducting strips  204 A and  204 B. Conducting strips  204 A and  204 B are arranged alternately and substantially in parallel to each other (i.e., a conducting strip  204 A is next to a conducting strip  204 B, which, in turn, is located next to a second conducting strip  204 A, and so on). A second layer  203  is formed by two sets of conducting strips  206 A and  206 B. Second layer  203  can be separated from first layer  201  by an insulating layer (not shown). The insulating layer can be a silicon dioxide layer. Second layer  203  at least partially overlies first layer  201 —e.g., at least one conducting strip of the second layer overlies at least a portion of a conducting strip in the first layer. Conducting strips  206 A and  206 B are also arranged alternately and substantially in parallel to each other. In one implementation, conducting strips  206 A and  206 B overlie and are substantially perpendicular to conducting strips  204 A and  204 B. 
     Conducting strips  204 A of first layer  201  and conducting strips  206 A of second layer  203  are connected to form a first common node. In one implementation, conducting strips  204 A and conducting strips  206 A are connected by vertical vias. Likewise, conducting strips  204 B of first layer  201  and conducting strips  206 B of second layer  203  are connected to form a second common node. The first common node and the second common node form opposing nodes of on-chip capacitor  200 . Each conducting strip  204 A connected to the first common node has one or more overlying conducting strips  206 B and one or more overlying conducting strips  206 A. Likewise, each conducting strip  204 B connected to the second common node has one or more overlying conducting strips  206 A and one or more overlying conducting strips  206 A. In one implementation, the number of “A” and “B” conducting strips are equal within each layer. 
       FIG. 3 . shows a cross-section of on-chip capacitor  200  ( FIG. 2 ). A parallel plate capacitance (Cpp) is present between each conducting strip  204 B and conducting strip  206 A. Furthermore, a sidewall capacitance (Csw) is present between each adjacent pair of conducting strips (e.g., conducting strips  204 A and  204 B) within each layer. In addition, a substrate capacitance (Cb) is formed between conducting strips in first layer  201  (e.g., conducting strips  204 A and  204 B) and substrate  202 . As shown in  FIG. 3 , substrate  202  can be at ground (or a low voltage potential). 
       FIG. 4  illustrates a top view of how conducting strips  204 A and  204 B of first (lower) layer  201  and conducting strips  206 A and  206 B of second (upper) layer  203  are laid out in one implementation. Conducting strips  204 A and  204 B of the lower layer are shown in solid lines. In one implementation, conducting strips  204 A are connected by a base strip  208 A and conducting strips  204 B are connected by a base strip  208 B. Alternatively, each of conducting strips  204 A and conducting strips  204 B can be respectively connected by vertical vias (not shown). Base strips  208 A and  208 B are located at opposing ends of conducting strips  204 A and  204 B so that conducting strips  204 A and  204 B are interdigitated. In one implementation, base strips  208 A and  208 B are sized to be narrow—e.g., as wide as conducting strips  204 A and  204 B—to minimize space occupied by on-chip capacitor  200 . 
     Conducting strips  206 A and  206 B of the upper layer are shown by dotted lines and are displaced to distinguish the upper layer conducting strips  206 A and  206 B from the lower layer conducting strips  204 A and  204 B. In general, conducting strips  206 A and  206 B substantially lie perpendicularly directly over conducting strips  204 A and  2043 . In one implementation, conducting strips  206 A are connected by a base strip  210 A and conducting strips  206 B are connected by a base strip  210 B. Alternatively, each of conducting strips  206 A and conducting strips  2063  can be respectively connected by vertical vias (not shown). As shown in  FIG. 4 , base strips  210 A and  210 B are at opposing ends of conducting strips  206 A and  206 B. In one implementation, the second layer pattern of interdigitated conducting strips  206 A and  206 B is substantially perpendicular to the first layer pattern. 
     The interconnections between the “A” conducting strips—i.e., conducting strips  204 A and  206 A, and the “B” conducting strips—i.e., conducting strips  204 B and  206 B, are not shown. In one implementation, the interconnections are made by vertical vias (not shown) through the insulating layer between first layer  201  and second layer  203  of on-chip capacitor  200 . 
       FIG. 5 . shows a cross-section of one implementation of on-chip capacitor  200  ( FIG. 2 ). As shown in  FIG. 5 , on-chip capacitor  200  includes a guardband  500  for attenuating coupling between on-chip capacitor  200  and external electromagnetic fields. Guardband  500  can be formed from a conductive material, for example, polysilicon, aluminum, and copper. In one implementation, guardband  500  is provided on each of first layer  201  and second layer  203  and substantially encircles the first and second common nodes of on-chip capacitor  200 . Guardband  500  can encircle less than all of first layer  201  and second layer  203 . Guardband  500  can only run along one side of on-chip capacitor  200 . In addition, guardband  500  can be included on other layers either above or below first layer  201  and second layer  203  of on-chip capacitor  200 . In one implementation, guardband  500  is spaced from the conducting strips a distance (dg) that is approximately twice the distance (dh) between adjacent conducting strips. Distance (dg) can be selected to minimize the parasitic fringing capacitance that is formed between guardband  500  and an adjacent conducting strip or base strip, while at the same time maintaining a volumetrically efficient on-chip capacitor  200 . 
     In one implementation, to maintain a predetermined ratio between the capacitance of on-chip capacitor  200  and the parasitic capacitance formed from guardband  500 , distance (dg) is increased when there are fewer conducting layers or conducting strips, and distance (dg) is decreased when there are more conducting layers or conducting strips. In one implementation, a line width of guardband  500  is selected to be the same as a line width of a conducting strip—e.g., conducting strip  206 A or  206 B. However, other line widths can be selected. In one implementation, guardband  500  is coupled through a low impedance (not shown) to a voltage potential such as ground. In one implementation, guardband  500  floats with respect to system voltage potentials. 
       FIG. 6  illustrates a top view of one implementation of a path configuration for an on-chip capacitor  600 . On-chip capacitor  600  contains conducting strips that are laid out a path configuration that is substantially spiral. In particular, on-chip capacitor  600  includes lower layer conducting strips  602 A and  602 B and upper layer conducting strips  604 A and  604 B. Conducting strips  602 A and  602 B of the lower layer are shown in solid lines and conducting strips  604 A and  604 B of the upper layer are shown in dotted lines. Conducting strips  604 A and  604 B of the upper layer are displaced to distinguish the upper layer conducting strips  604 A and  604 B from the lower layer conducting strips  602 A and  602 B. In one implementation, conducting strips  604 A and  604 B respectively lie substantially directly over conducting strips  602 B and  602 A. Other path configurations can be implemented, e.g., L-shaped paths and S-shaped paths. 
       FIG. 7A . shows a cross-section B-B ( FIG. 7B ) of an on-chip capacitor  700 . On-chip capacitor  700  includes two layers  701 ,  703  of conducting strips formed upon a substrate  702 . A first layer  701  is formed by two sets of conducting strips  704 A and  704 B. Conducting strips  704 A and  704 B are arranged alternately and substantially in parallel to each other so that a conducting strip  704 A is located next to a conducting strip  704 B, as shown in  FIG. 7B . 
     Referring to  FIGS. 7A and 7B , a second layer  703  is formed by two sets of conducting strips  706 A and  706 B. Conducting strips  706 A and  706 B are also arranged alternately and substantially in parallel to each other so that a conducting strip  706 A is located next to a conducting strip  706 B. Conducting strips  706 A and  706 B respectively overlie and are substantially parallel to conducting strips  704 A and  704 B, such that conducting strips of a same polarity overlie one another. For example, conducting strip  706 A—shown as having a “+” polarity—substantially overlies conducting strip  704 A—also shown as having a “+” polarity. On-chip capacitor  700  further includes vertical vias  708 A that interconnect conducting strips  706 A and  704 A, and vertical vias  708 B that interconnect conducting strips  706 B and  704 B. 
     A parallel plate capacitance (Cpp) is present between each adjacent pair of conducting strips (e.g., conducting strips  706 A and  706 B) within each layer. Furthermore, a via capacitance (Cv) is present between each adjacent pair of vertical vias (e.g., vertical vias  708 A and  708 B). 
       FIG. 7C  shows a top view of on-chip capacitor  700 . In one implementation, conducting strips  706 A are connected by a base strip  710 A and conducting strips  706 B are connected by a base strip  710 B. Base strips  710 A and  710 B are located at opposing ends of conducting strips  706 A and  706 B so that conducting strips  706 A and  7063  are interdigitated. In one implementation, base strips  710 A and  710 B are sized as wide as conducting strips  706 A and  706 B. 
     In one implementation, base strips  710 A and  710 B include vertical vias  712 A and  712 B, respectively. Vertical vias  712 A and  712 B interconnect with corresponding base strips (not shown) underlying base strips  710 A and  710 B. Vertical vias  712 A can be placed along base strip  710 A at locations substantially adjacent to one or more vertical vias  708 B that are located on conducting strips  706 B. Likewise, vertical vias  712 B can be placed along base strip  710 B at locations substantially adjacent to one or more vertical vias  708 A that are located on conducting strips  706 A. 
     In addition to the parallel plate capacitance (Cpp) ( FIG. 7A ), and the via capacitance (Cv) ( FIG. 7A ), a base strip via capacitance (Cvb) is present between each adjacent pair of base strip vertical via and conducting strip vertical via (e.g., vertical vias  712 A and  708 B). 
       FIG. 8 . shows a cross-section of one implementation of on-chip capacitor  700  ( FIG. 7A ). As shown in  FIG. 8 , on-chip capacitor  700  includes a guardband  800  for attenuating coupling between on-chip capacitor  700  and external electromagnetic fields. In one implementation, guardband  800  is provided on each of first layer  701  and second layer  703  and substantially encircles the first and second common nodes of on-chip capacitor  700 . Guardband  700  can encircle less than all of first layer  701  and second layer  703 . Guardband  800  can only run along one side of on-chip capacitor  700 . In addition, guardband  800  can be included on other layers either above or below first layer  701  and second layer  703  of on-chip capacitor  700 . 
     A number of implementations have been described. Nevertheless, various modifications to the implementations may be made. For example, an on-chip capacitor can be formed in a split-capacitor configuration  900  as shown in  FIG. 9 . Split-capacitor configuration  900  includes a first on-chip capacitor  902  and a second on-chip capacitor  904  formed upon a substrate  906 . Each of first on-chip capacitor  902  and second on-chip capacitor  904  can have any one of the capacitor structures described in the implementations above. In addition, each of the capacitor structures described above can have any number of conducting layers, e.g. more than two layers. Accordingly, other implementations are within the scope of the following claims.

Technology Category: h