Field of the Invention
Examples of the present disclosure generally relate to integrated circuits and, in particular, to capacitor structures in integrated circuits.
Description of the Related Art
Capacitors are used in integrated circuits (ICs) for a variety of purposes. Metal finger capacitors (“finger capacitors”) are example capacitor structures used in ICs. An LC tank or resonator is one type of circuit integrated in an IC that can utilize a finger capacitor. At low frequencies, such as frequencies less than 10 Gigahertz (GHz), the inductor (L) is normally the dominant factor for LC tank performance, since the quality factor (Q) of the inductor is typically 2-3 times lower than the Q of the finger capacitor (C). For higher frequencies, such as frequencies greater than 30 GHz, the Q of the finger capacitor drops dramatically, becoming less than the Q of the inductor. For such higher frequencies, the Q of the finger capacitor becomes the dominant limiting factor. As technology scaling continues, achieving a higher Q in finger capacitors without increasing surface area required in the IC remains a challenge.
Capacitor structures in integrated circuits (ICs) are described. In an example implementation, a capacitor in an integrated circuit (IC), includes: a first finger capacitor formed in at least one layer of the IC having a first bus and a second bus; a second finger capacitor formed in the at least one layer of the IC having a first bus and a second bus, where a longitudinal edge of the second bus of the second finger capacitor is adjacent a longitudinal edge of the first bus of the first finger capacitor and separated by a dielectric gap; and a first metal segment formed on a first layer above the at least one layer, the first metal segment being electrically coupled to the first bus of the first finger capacitor and increasing a width and a height of the first bus of the first finger capacitor.
In another example implementation, an integrated circuit (IC), comprises: a substrate; at least one layer on the substrate including finger capacitors formed therein separated by dielectric gaps, each of the finger capacitors having a first bus and a second bus where: for each adjacent pair of the finger capacitors, a longitudinal edge of the first bus of a first finger capacitor is adjacent a longitudinal edge of the second bus of an adjacent finger capacitor separated by a respective one of the dielectric gaps; the first busses of the finger capacitors are electrically coupled to provide a first node of a capacitor, and the second busses of the finger capacitors are electrically coupled to provide a second node of a capacitor; and a first layer above the at least one layer having first metal segments formed therein, each of the first metal segments being electrically coupled to, and increasing a width and a height of, the first bus of a respective one of the finger capacitors.
In another example implementation, a method of forming a capacitor in an integrated circuit (IC), comprises: forming a first finger capacitor having first and second busses in at least one layer of the IC; forming a second finger capacitor having first and second busses in the at least one layer, a longitudinal edge of the second bus of the second finger capacitor being adjacent to a longitudinal edge of the first bus of the first finger capacitor separated by a dielectric gap; and forming a first metal segment on a first layer above the at least one layer of the IC, the first metal segment being electrically coupled to the first bus in the first finger capacitor, the first metal segment increasing a width and a height of the first bus of the first finger capacitor.
These and other aspects and features will be evident from reading the following Detailed Description.
So that the manner in which the above recited features can be understood in detail, a more particular description, briefly summarized above, may be had by reference to example implementations, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical example implementations and are therefore not to be considered limiting of its scope.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements of one example may be beneficially incorporated in other examples.
Capacitor structures in integrated circuits (ICs) are described. In an example implementation, finger capacitors are formed in at least one layer of an IC separated by dielectric gaps. Each finger capacitor includes a pair of busses coupled to interdigitated metal fingers. For example, the finger capacitors include first busses electrically coupled to provide a first node of a capacitor, and second busses electrically coupled to provide a second node of the capacitor. For a given adjacent pair of finger capacitors, a longitudinal edge of a first bus in a first finger capacitor is adjacent to a longitudinal edge of a second bus in an adjacent finger capacitor separated by a dielectric gap. Metal segments are formed in a first layer above the at least one layer of the IC and are electrically coupled to the first busses of the finger capacitors. The metal segments increase the widths and heights of the first busses. In an example, a metal segment overlaps at least a portion of a first bus and at least a portion of a dielectric gap. In another example, a metal segment overlaps at least a portion of a first bus and at least a portion of a second bus of an adjacent finger capacitor. In yet another example, a metal segment is coextensive with a first bus of a first finger capacitor, a dielectric gap, and a second bus of an adjacent finger capacitor.
In this manner, the width and height of the first bus in each finger capacitor is increased without increasing surface area of the finger capacitor in the IC. The increase in both width and height of the first bus reduces series resistance (e.g., parasitic resistance of the capacitor), which results in a higher quality factor (Q) for the capacitor. Also, since the metal segments are on another layer within the existing capacitor area, no additional surface area is used to improve Q of the capacitor.
In another example implementation, one or more additional layers can be formed over the first layer in the IC. Each additional layer can include a metal segment electrically coupled to the first metal segments in the first layer. Each metal segment formed in an additional layer above the first layer further increases the width and height of the first busses of the finger capacitors. In general, each metal segment formed in an additional layer above the first layer can overlap at least a portion of the area of the finger capacitors. In an example, each metal segment formed in an additional layer above the first layer can be coextensive with the area of the finger capacitors. In this manner, the width and height of the first bus in each finger capacitor is further increased without increasing surface area of the finger capacitor in the IC. The additional metal segment(s) provide for a further increase in Q for the capacitor. These and additional aspects of example capacitor structures can be understood with reference to the following drawings and description.
The finger capacitors 104 are separated by dielectric gaps 118 each having a width 112. No metal is formed in the layer(s) comprising the capacitive structures 104 within the volume defined by each of the gaps 118. Rather, the dielectric gaps 118 comprise dielectric material between metal portions of adjacent finger capacitors. The finger capacitors 104 collectively provide the capacitor 120 having a width 108 and the length 114. The capacitor 120 can be repeated in the IC to provide multiple such capacitors 120.
At least one additional layer (generally shown by 106) is disposed over the finger capacitors 104. The additional layer(s) 106 include metal segments (examples described below) that extend both a width and a height of busses (described below) in the capacitive structures 104. The increased width and height of the busses decreases series resistance of the capacitor 120 and increases Q for the capacitor 120. Since the metal segments are formed on layer(s) above the finger capacitors 104, the metal segments do not increase the surface area or footprint of the capacitor 120 in the x-y plane of the substrate 102.
The finger capacitors 104 are disposed on the substrate 102 such that a longitudinal edge of the first bus in a one capacitive structure is adjacent a longitudinal edge of the second bus in an adjacent capacitive structure and separated by a dielectric gap. In the example, a longitudinal edge of the bus 202a is adjacent a longitudinal edge of the bus 204b, and the longitudinal edge of the bus 202b is adjacent a longitudinal edge of the bus 204c. A dielectric gap 118-1 separates the busses 202a and 204b, and a dielectric gap 118-2 separates the busses 202b and 204c. While the dielectric gaps 118 are shown generally as having equal widths, in other examples some gaps between capacitive structures can have greater width than other gaps.
In an example, the first busses of the finger capacitors 104 can be electrically coupled to provide a first node of the capacitor 120a, and the second busses of the finger capacitors 104 can be electrically coupled to provide a second node of the capacitor 120a. The conductors electrically coupling the first busses and electrically coupling the second busses are represented by dashed lines in
Metal segments 214-1 and 214-2 are formed on a layer above the layer(s) having the finger capacitors 104a through 104c. In
The bus 202a includes portions on layers M6, M7, and M8 electrically coupled by vias 218. The bus 204b includes portions on layers M6, M7, and M8 electrically coupled by vias 220. The bus 202b includes portions on layers M6, M7, and M8 electrically coupled by vias 222. The bus 202a includes a left longitudinal edge 228L and a right longitudinal edge 228R. The bus 202b includes a left longitudinal edge 230L and a right longitudinal edge 230R. The right longitudinal edge 228R of the bus 202a is adjacent to the left longitudinal edge 230L of the bus 202b separated by the dielectric gap 118-1.
The fingers 210b include segments on the layer M8 and the layer M6. The fingers 208b include segments on the layer M7. In general, the fingers 208b and 210b can be formed on any of the layers M6-M8 in an interdigitated fashion. Fingers 208 and 210 of other capacitive structures 104 can be configured similarly.
The metal segment 214-1 is formed in a layer M9 above the layer M8 and is electrically coupled to the bus 202a by vias 216. Likewise, the metal segment 214-2 is formed in the layer M9 and is electrically coupled to the bus 202b by vias 224. The metal segment 214-1 overlaps the bus 202a, the bus 204b, and the gap 118-1 between the bus 202a and 204b. In the example, the metal segment 214-1 is shown as being coextensive with the bus 202a, the gap 118-1, and the bus 204b. That is, a left longitudinal edge 226L of the metal segment 214-1 is aligned with the left longitudinal edge 228L of the bus 202a, and a right longitudinal edge 226R of the metal segment 214-1 is aligned with a right longitudinal edge 230R of the bus 204b. The parasitic capacitance between the metal segment 214-1 and the substrate 102 or other metal layers on the substrate 102 through the dielectric gap 118-1 is small and can be ignored in most applications. By being coextensive with the bus 202a, the dielectric gap 118-1, and the bus 204b, the metal segment 214-1 provides largest decrease in series resistance and adds the least parasitic capacitance. The term “aligned” is meant to encompass substantially aligned or approximately aligned within tolerances of IC fabrication technology.
Other configurations are possible depending on design specifications and fabrication constraints. For example, the metal segment 214-1 can overlap all or a portion of the bus 202a, all or a portion of the dielectric gap 118-1, or all or a portion of the bus 204b. In general, the left longitudinal edge 226L of the metal segment 214-1 can be aligned with the left longitudinal edge 228L of the bus 202a, or can be offset either to the left or the right of the left longitudinal edge 228L of the bus 202a. The right longitudinal edge 226R of the metal segment 214-1 can be aligned with the left longitudinal edge 230L of the bus 204b, or can be offset either to the left or the right of the left longitudinal edge 230L of the bus 204b. Other metal segments on the layer M9 can be configured similar to the metal segment 214-1.
While the foregoing is directed to specific examples, other and further examples may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
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Number | Date | Country | |
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20160049393 A1 | Feb 2016 | US |