Patent Publication Number: US-9431338-B2

Title: Bypass capacitor circuit and method of providing a bypass capacitance for an integrated circuit die

Description:
FIELD OF THE INVENTION 
     This invention in general relates to integrated circuits and more specifically to a bypass capacitor circuit for an integrated circuit, an integrated circuit die and a method of providing a bypass capacitance for an integrated circuit. 
     BACKGROUND OF THE INVENTION 
     Many integrated circuits, especially if arranged to work at high frequencies, use bypass capacitances for attenuation of unwanted frequency components. This capacitance can be provided for example within the integrated circuit itself, while increasing the required die area and accordingly costs of the integrated circuit. A different approach may include provision of external capacitors off-chip, e.g, in the package, that is not integrated on the same die, providing separate devices to be connected to the IC. However, this increases the overall footprint of the package and requires additional operations. 
     SUMMARY OF THE INVENTION 
     The present invention provides a bypass capacitor circuit for an integrated circuit, an integrated circuit die and a method of providing a bypass capacitance for an integrated circuit as described in the accompanying claims. 
     Specific embodiments of the invention are set forth in the dependent claims. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. 
         FIG. 1  schematically shows examples of two integrated circuit dies of a wafer, each with a seal ring area. 
         FIG. 2  schematically shows an example of an embodiment of a bypass capacitor circuit. 
         FIG. 3  schematically shows a flow diagram of an example of an embodiment of a method of providing a bypass capacitance for an integrated circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a schematic block diagram is provided showing two integrated circuit dies  12 ,  14  of a wafer  10 . An integrated circuit  20 ,  22  may be provided with each die  12 ,  14 . An integrated circuit die may comprise a bypass capacitor circuit as described below. In the shown example, each of the integrated circuits  20 ,  22  may comprise an input/output interface and may therefore comprise a circumferential area adjacent to the peripheral area of the IC, in this example a ring area  24 ,  26  for input/output (IO) which encloses the IC areas  20 ,  22 . The shown interfaces may for example be high frequency IO interfaces requiring a bypass capacitance for robust implementation. 
     After IC fabrication, the wafer may be diced, that is the dies with the integrated circuits are separated from each other. As shown, a scribe line is provided the two adjacent dies so that these dies can be separated by cutting the semiconductor wafer  10  along the scribe line. It will be apparent that additional scribe lines may be provided when the wafer includes more dies, e.g. which define a matrix of dies. 
     The dies  12 ,  14  each comprise a seal ring area  16 ,  18 . The seal ring area  16 ,  18  is provided between the scribe line(s) and the respective peripheral regions of the internal circuit. In this example the seal ring area  16 ,  18  is a perimeter at the edge of each die. The perimeter extends in the plane of the wafer surface, around the integrated circuit of the respective die and separates the ring areas  24 ,  26  from the scribe line. The ring areas  24 ,  26  in turn separate the peripheral regions from the seal ring area  16 ,  18 . The seal ring areas  16 ,  18  serve to protect the integrated circuit  20 ,  22  and components peripheral thereto, e.g. in this example the components in the ring area  24 ,  26  during dicing. Wafer dicing may damage the die areas close to their edges. Thus, the seal ring area, situated on the wafer between the integrated circuits of different dies in the area where the wafer is to be diced, is not occupied by the integrated circuit or peripheral components thereof and thus any damage in the seal ring area will not affect the performance of the integrated circuit. 
     Referring now also to  FIG. 2 , an example of an embodiment of a bypass capacitor circuit  30  for an integrated circuit  20  is shown. The bypass capacitor circuit  30  may comprise one or more capacitive devices  32 ,  34 ,  36 , each arranged in a segment of a seal ring area  16  of a die  12 , the die  12  comprising the integrated circuit. Since the capacitors are provided in the sea ring area  16  the need for enlarging the die area used for the integrated circuit  20  itself may be avoided or reduced. The seal ring area  16 , which may otherwise remain unused due to the probability of defects for example caused by cutting the wafer  10  into dies  12 ,  14 , may remain connected to the integrated circuit even after dies  12 ,  14  of wafer  10  have been separated. The capacitive devices  32 ,  34 ,  36  may be implemented on-chip, that is on the same die  12  as the integrated circuit. The shown approach may thus avoid or at least reduce a need for off-chip provision of bypass capacitances. It will be apparent that, in addition to the bypass capacitor circuit  30 , bypass capacitor circuits in the integrated circuits or off-chip bypass capacitor circuits may be provided. 
     The available size of the seal ring, that is the distance between the integrated circuit  20  and the nearest edge of the die  12  may depend on the fabrication process. The size may for example be about 50 μm. However, it may be smaller or larger. The seal ring may comprise one large segment or may be divided into a plurality of segments, for example hundreds, e.g. 300 or 400 segments, each segment comprising a capacitive device  32 ,  34 ,  36 , hence making use of a great part or all of the seal ring area  16  of the die  12 . A selection of a suitable number of segments may depend on parameters of the fabrication process or the substrate. Since there may be a non-zero probability of having damaged seal ring regions, a number of segments having capacitive devices may be chosen as high as possible, each capacitive device with low capacitance. This may result in an overall bypass capacitance close to a maximum available capacitance of undamaged capacitive devices  32 ,  34 ,  36 . A less damaging wafer dicing process may result in less seal ring regions damaged and may allow for usage of fewer segments, each with a capacitive device having a higher capacitance. Any damaged region may result in a smaller overall available bypass capacitance but may allow for less power consumption caused by connecting lines and additional devices used for configuring the bypass capacitor circuit. 
     As shown in  FIG. 2 , one or more of the capacitive devices  32 ,  34 ,  36  are connected to a power supply bus  38 ,  40 , each through an associated switch  42 ,  44 ,  46 . For example, supply line  38  may be connected to a reference potential such as ground and supply line  40  may be connected to voltage supply V CC  of the integrated circuit  20 . A switch may allow for connecting or disconnecting a particular capacitive device  32 ,  34 ,  36  to the supply bus, therefore changing the overall provided bypass capacitance or disconnecting defective capacitive devices. 
     A switch may for example be a transistor device such as a metal oxide semiconductor (MOS) transistor. However, other devices capable of coupling and decoupling a capacitive device to or from the bypass capacitor circuit may be used. 
     Each of the associated switches  42 ,  44 ,  46  may be arranged to disconnect the capacitive device  32 ,  34 ,  36  from the power supply bus  38 ,  40  when a value of an operability parameter of the capacitive device  32 ,  34 ,  36  is indicative of a defectiveness of the capacitive device. An operability parameter value may be any information indicative of the ability of the particular capacitive device  32 ,  34 ,  36  to function correctly. The operability parameter value may be a measured value of an electrical characteristic related to the capacitive device such as voltage or current, for example indicating a short circuit. The operability parameter indicative of defectiveness or normal operability of a particular capacitive device may for example be determined in a test mode by applying test values to the bypass capacitor circuit. Instead of electrical characteristics other operability information may be used, such as for example automatic visual inspection information. 
     One or more associated switches  42 ,  44 ,  46  may comprise a control input  48 ,  50 ,  52 , each connected to a corresponding memory device  54 ,  56 ,  58 , the memory device arranged to store a state of the associated switch. Depending on the state of the switch  42 ,  44 ,  46 , the particular capacitive device  32 ,  34 ,  36  may or may not be connected to the bypass capacitor circuit. The state of the switch may depend on the corresponding operability parameter value, allowing for disconnecting defective capacitive devices. Or it may for example depend on a target overall bypass capacitance. 
     In an embodiment of the bypass capacitor circuit  30  the memory device  54 ,  56 ,  58  may be a permanent memory device. A permanent memory device may be any memory device configured to preserve a stored value such as an operability parameter value without a need for frequent refresh or during periods without power supply available. This may for example enable the bypass capacitor circuit  30  to be configured during a test phase, wherein defective capacitive devices, for example damaged during wafer dicing, may be detected and permanently disabled. This may allow providing an operable bypass capacitor circuit  30  for the integrated circuit  20  during normal operation without any need for further test or configuration. The bypass capacitor circuit can be located in the seal ring area  16  of the die  12 , hence saving die area. The test phase may for example be performed during manufacturing prior to product delivery to a customer. 
     Any device capable of permanently memorizing a state may be used. For example, the memory device may be a fuse. Defective segments and capacitive devices may be permanently excluded from the bypass capacitor circuit by burning fuses. Other permanent memory devices may be used. Permanent memory devices may also comprise any nonvolatile memory storage media including semiconductor-based memory units such as FLASH memory, EEPROM, EPROM, ROM, ferromagnetic digital memories or MRAM. 
     In order to control the bypass capacitor circuit for example during testing and configuration, the bypass capacitor circuit  30  may comprise a controlling unit  60  connected to the one or more switches  42 ,  44 ,  46  and adapted to control a state of the one or more switches. The controlling unit  60  may perform testing of all connected capacitive devices  32 ,  34 ,  36 , may determine operability parameter values and may switch on or off a particular capacitive device depending on a corresponding operability parameter value. In an embodiment where memory devices  44 ,  46 ,  48  are used, the controlling unit may be configured to write operability parameter values into corresponding memory devices. The controlling unit  60  may for example be placed on the integrated circuit die. In another embodiment, the controlling unit  60  may be placed off-chip and connected to the bypass capacitor circuit for example only during a test phase. This may save die area and avoid delivery of the controlling unit with the final product having a pre-configured bypass capacitor circuit. 
     Bypass capacitor circuits  30  may be used with many different applications. For example, any logic circuitry, especially when operating at high processing speed, may be sensitive for unwanted high-frequency components in the supply voltage which may cause erroneous behaviour of the logic circuitry. Also interfaces dedicated to high-speed data transmission to and from the IC may use a bypass capacitor circuit  30  for robust design. In an embodiment of the circuit and as indicated in  FIG. 1 , the integrated circuit  20  may comprise an input/output interface circuit. An input/output interface may enable bi-directional signal transmission to and from the integrated circuit. It should be noted that it is also in the scope of the described system that the interface may be a unidirectional interface either for data input or output. 
     The bypass capacitor circuit as presented may for example be used when the described input/output interface circuit may be arranged to connect to an external unit using one or more bondwires. Wirebonding is a technology of making interconnections between an IC and for example a printed circuit board (PCB) or to other IC or other electronic circuits. When wirebonding is applied, it may be impossible or at least difficult to place bypass capacitors for the interface circuit over die. In any case, bypass capacitors implemented separately from the die may result in increased costs and connections may potentially cause erroneous behavior. 
     Any integrated circuit device, especially when operating at high processing frequencies may benefit from a bypass capacitor reducing unwanted frequency components. The integrated circuit  20  protected by the bypass capacitor circuit  30  may for example be a very large scale integrated (VLSI) circuit. Very-large-scale integration (VLSI) is the process of creating integrated circuits by combining thousands of transistor-based circuits into a single chip. Here, VLSI may refer to any IC having thousands or even millions or billions of transistor-based circuits. Any other naming, such as for example ULSI (ultra large scale integration) suggesting a device to comprise more transistor-based circuits than a VLSI device may be considered a sub-group and comprised in VLSI. Therefore, for example any ULSI device is a VLSI device. 
     The integrated circuit device may be a data processing device. Processing devices operate at high frequencies and are sensitive to disturbances caused by noisy signals and supply voltages. The data processing device may for example be a processor, a general purpose processor (GPP), a microcontroller unit (MCU), a central cprocessing unit (CPU), a graphics processing unit (GPU) or a digital signal processor (DSP). It may be a single core or a multi core processing device. 
     Referring now to  FIG. 3 , a schematic flow diagram of an example of an embodiment of a method of providing a bypass capacitance for an integrated circuit is shown. The illustrated method allows implementing the advantages and characteristics of the described bypass capacitor circuit as part of a method of providing a bypass capacitance for an integrated circuit. 
     The flow diagram comprises a start  62  and an end  64  state. The method may comprise providing  66  a semiconductor wafer device comprising a plurality of dies, each comprising an integrated circuit; arranging  68  one or more capacitive devices in a seal ring area of at least one of the integrated circuits; dicing  70  the semiconductor wafer device; in a test phase, for each  72  of the one or more capacitive devices, enabling  74  the capacitive device, determining  76  an operability parameter value indicative of an operability of the capacitive device, and storing  78  the operability parameter in a memory device; and in a normal operation phase, providing  80  a bypass capacitance to the integrated circuit depending on a capacitance of one or more of the capacitive devices having an associated operability parameter value indicative of a non-defectiveness of the corresponding capacitive device. It will be apparent that not all the stages need to be performed at the same time and the same location. For example the provision  66  of the semiconductor wafer device and arranging  68  of the capacitive devices may be performed at one location, then the processing of the thus obtained intermediate product may be paused, and the intermediate product for example shipped to another location to be diced. After dicing, the intermediate product may for example shipped further to a location where the integrated circuits are tested and the test phase is performed. 
     Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. 
     In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. 
     For example, the semiconductor substrate of the wafer  10  described herein can be any semiconductor material or combinations of materials, such as gallium arsenide, silicon germanium, silicon-on-insulator (SOI), silicon, monocrystalline silicon, the like, and combinations of the above. 
     The connections as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connection that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals. 
     Although specific conductivity types or polarity of potentials have been described in the examples, it will appreciated that conductivity types and polarities of potentials may be reversed. 
     Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. For example, the capacitive device  32 ,  34 ,  36  may be further divided into more capacitive devices or merged into fewer devices. The memory devices  54 ,  56 ,  58  are shown as separate devices. However, they may also be implemented as a single memory device. 
     Any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality. 
     Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments. 
     Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. For example, the controlling unit  60  may be implemented on the integrated circuit die  12 . Alternatively, the examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner. For example, the controller unit  60  may be a separate device only connected to the integrated circuit die for testing and permanently configuring the bypass capacitor circuit. 
     Also for example, the examples, or portions thereof, may implemented as soft or code representations of physical circuitry or of logical representations convertible into physical circuitry, such as in a hardware description language of any appropriate type. 
     However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. 
     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.