Patent Publication Number: US-2019172821-A1

Title: In-package photonics integration and assembly architecture

Description:
CLAIM OF PRIORITY 
     This application is a divisional application, which claims the benefit of and priority to U.S. application Ser. No. 15/396,467, filed Dec. 31, 2016, entitled IN-PACKAGE PHOTONICS INTEGRATION AND ASSEMBLY ARCHITECTURE, by Myung Jin Yim, and the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The subject matter described herein relates generally to the field of electronic devices and more particularly to an in-package photonics integration and assembly architecture. 
     Technical advances such as increases in connectivity technologies and the growth of processing loads are generating ever-increasing demands on bandwidth and transmission speeds. Data centers are considering optical interconnects which rely on photons instead of electrons to send data between servers, racks, and boards, and how best to make high speed photonic connections between chips as well. 
     Wide adoption of photonics links depends on connecting optics to electronics by optics module miniaturization technologies which provide low power consumption and high bandwidth throughput and which can be manufactures using high volume and low cost manufacturing techniques. There has been lots of progress including integration of photonics on silicon, and integration of chips on interposers for standard IC packaging. Highly integrated optical module at small form factor is critical in enabling high bandwidth and low power optical interconnect between chips. Accordingly additional architectures for in-package photonics integration for electronic components may find utility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is described with reference to the accompanying figures. 
         FIG. 1  is a side view, schematic illustration of an in-package optics-based co-package architecture, in accordance with some embodiments. 
         FIG. 2  is a side view, schematic illustration of a photonic engine integration on an electronic integrated circuit (IC) wafer, in accordance with some embodiments. 
         FIG. 3  is a flowchart illustrating operations in a method to make an in-package photonic integration architecture, according to embodiments. 
         FIGS. 4A-4E  illustrate an in-package photonic integration architecture in various stages of formation, according to embodiments. 
         FIG. 5  is a flowchart illustrating operations in a method to assemble an in-package photonic integration architecture, according to embodiments. 
         FIGS. 6A-6F  illustrate an in-package photonic integration architecture in various stages of formation, according to embodiments. 
         FIG. 7  is a schematic illustration of a universal integrated circuit (IC) based photonic engine block, according to embodiments. 
         FIG. 8A  is a top view, schematic illustration of a co-package optics interconnect, in accordance with some embodiments. 
         FIG. 8B  is a top view, schematic illustration of a co-package optics interconnect, in accordance with some embodiments. 
         FIG. 9  represents a schematic of a computing device according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the methods and structures may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments. It is to be understood that the various embodiments, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein, in connection with one embodiment, may be implemented within other embodiments without departing from the spirit and scope of the embodiments. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the embodiments. 
     The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the embodiments is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals may refer to the same or similar functionality throughout the several views. The terms “over”, “to”, “between” and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “over” or “on” another layer or bonded “to” another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. Layers and/or structures “adjacent” to one another may or may not have intervening structures/layers between them. A layer(s)/structure(s) that is/arc directly on/directly in contact with another layer(s)/structure(s) may have no intervening layer(s)/structure(s) between them. 
     Various implementations of the embodiments herein may be formed or carried out on a substrate, such as a package substrate. A package substrate may comprise any suitable type of substrate capable of providing electrical communications between a die, such as an integrated circuit (IC) die, and a next-level component to which an IC package may be coupled (e.g., a circuit board). In another embodiment, the substrate may comprise any suitable type of substrate capable of providing electrical communication between an IC die and an upper IC package coupled with a lower IC/die package, and in a further embodiment a substrate may comprise any suitable type of substrate capable of providing electrical communication between an upper IC package and a next-level component to which an IC package is coupled. 
     A substrate may also provide structural support for a die. By way of example, in one embodiment, a substrate may comprise a multi-layer substrate—including alternating layers of a dielectric material and metal—built-up around a core layer (either a dielectric or a metal core). In another embodiment, a substrate may comprise a coreless multi-layer substrate. Other types of substrates and substrate materials may also find use with the disclosed embodiments (e.g., ceramics, sapphire, glass, etc.). Further, according to one embodiment, a substrate may comprise alternating layers of dielectric material and metal that are built-up over a die itself—this process is sometimes referred to as a “bumpless build-up process.” Where such an approach is utilized, conductive interconnects may or may not be needed (as the build-up layers may be disposed directly over a die, in some cases). 
     In accordance with aspects described herein, a photonic integrated circuit (IC) may be integrated on electronic integrated circuit (IC) using a wafer level package structure to provide an effective thermal, electrical and optical coupling structure which may assembled using high throughput manufacturing techniques. By using wafer level packaging infrastructure, the optical module itself becomes fully integrated photonic engine enabling that the optical path and electrical paths downward, and thermal path upward, and then co-packaging assembly process is fully compatible with conventional multi-die flip chip BGA assembly process with heat spreader, and further optics assembly afterward either by passive alignment or active alignment. 
     The invention also details the process flow that can enable the integration of photonic IC on UIC integration by wafer level package to make the photonic engine die and optical/electrical interconnect by using it for in-package photonics assembly to be compatible the electrical and optical assembly requirement and high volume manufacturability. 
     Described herein are techniques and architectures to integrate a photonic integrated circuit (IC) on electronic IC using a wafer-level package structure. The architecture may provide an effective thermal, electrical and optical coupling structure which may be assembled using high throughput manufacturing techniques. Further, the architecture described herein provides packaging-level optic system integration for photonics in package assembly solution. 
     By using a wafer-level packaging infrastructure, an optical module may be implemented as a fully integrated photonic engine on the electronic integrated circuit (IC). In some examples described herein the optical path and electrical paths are disposed in a first orientation (i.e., downward), and the thermal path is disposed in a second orientation (i.e., upward). The co-packaging assembly process is fully compatible with conventional multi-die flip chip BGA assembly processes, with heat spreaders, and further optics assembly afterward either by passive alignment or active alignment. Also described herein are techniques to enable the integration of photonic integrated circuit (IC) on a universal integrated circuit (IC) by wafer-level package to make the photonic engine die and optical/electrical interconnect compatible. 
       FIG. 1  is a side view, schematic illustration of an in-package optics-based co-package architecture, and  FIG. 2  is a side view, schematic illustration of a photonic engine integration on an electronic integrated circuit (IC) wafer, in accordance with some embodiments. Referring to  FIG. 1  and  FIG. 2 , in some examples a microelectronic package structure  100 , comprises a substrate  110  comprising at least one waveguide  112 , a first instrument integrated circuit  120  coupled to the substrate  100 , a photonic engine  130  coupled to the substrate and comprising an integrated circuit body  131 , a transmit die  140 , and a receive die  150 . 
     In some examples the microelectronic package structure  100  of claim may comprise a memory device  180  coupled to the substrate  110 . A thermal interface material (TIM)  160  layer may be formed in thermal communication with the photonic engine  130 , the first integrated circuit  120 , the photonic engine  130  and the memory device  180 . An integrate heat spreader (IHS) is  170  in thermal communication with the thermal interface material  160 . 
     In some examples the microelectronic package structure  100  may further comprise a ball grid array  106  positioned proximate a surface of the substrate  110  to provide electrical connections with an underlying device. e.g., a printed circuit board. 
     Referring to  FIG. 2 , in some examples the a photonic engine  130  comprises an integrated circuit body  131 , a transmit die  140 , and a receive die  150 . In some examples the transmit die  140  and the receive die  150  are coupled to the photonic engine  130  by a first plurality of bumps  132  having a first height and one or more solder balls  108  are coupled to the photonic engine  130  by a second plurality of bumps  134  having a second height, greater than the first height. One or more solder balls  108  are coupled to the second plurality of bumps  134 . The photonic engine  130  is coupled to the substrate  110  via the one or more solder balls  108 , which are at least partially covered by a mold material  136 . 
     Referring back to  FIG. 1 , the photonic engine  130  is positioned adjacent the at least one waveguide  112  such that optical signals may be exchanged between the at least one waveguide  112  and the transmit die  140  and the at least one waveguide  112  and the receive die  150 . In some examples the mold material  136  defines an air gap  148  between the transmit die  140  and the at least one waveguide  112  and the receive die  150  and the at least one waveguide  112  through which optical signals may be transmitted. The microelectronic package structure  100  further comprises an optical coupling  190  coupled to the at least one waveguide  112 . 
     In some examples the photonic engine  130  is coupled to the substrate  110  via one or more solder balls  108 , which the are at least partially covered by a mold material  136  such that the mold material  136  defines an air gap  148  between the transmit die  140  and the at least one waveguide  112  and the receive die  150  and the at least one waveguide  112 . In the example depicted in  FIG. 1  the photonic engine  130  is positioned adjacent the at least one waveguide  112  such that optical signals may be exchanged between the at least one waveguide  112  and the transmit die  140  and the at least one waveguide  112  and the receive die  150 . 
     In some examples the first integrated circuit  120  may comprise any type of device suitable for a particular application, such as but not limited to a microprocessor, a graphics processor, a signal processor, a network processor, a chipset, etc. In one embodiment, the integrated circuit  120  may comprise a system-on-chip (SoC) having one or more functional units (e.g., one or more processing units, one or more graphics units, one or more communications units, one or more signal processing units, one or more security units, etc.). However, it should be understood that the disclosed embodiments are not limited to any particular type or class of die/devices. An active side (which may comprise various circuit components such as transistors, for example) of the integrated circuit  120  may be electrically and physically coupled with the substrate  110  by solder balls/conductive structures  108 . 
     The conductive structures  108  may comprise any type of structure and materials capable of providing electrical communication between the integrated circuit  120  and substrate  110 . In the embodiment, each of the interconnects  108  comprises an electrically conductive terminal on the die (e.g., a pad, bump, stud bump, column, pillar, or other suitable structure or combination of structures) and a corresponding electrically conductive terminal on the substrate  110  (e.g., a pad, bump, stud bump, column, pillar, or other suitable structure or combination of structures). Solder (e.g., in the form of balls or bumps) may be disposed on the terminals of the substrate and/or die, and these terminals may then be joined using a solder reflow process. Of course, it should be understood that many other types of interconnects and materials are possible (e.g., wirebonds extending between the integrated circuit  120  and substrate  110 ). 
     The terminals on integrated circuit  120  may comprise any suitable material or any suitable combination of materials, whether disposed in multiple layers or combined to form one or more alloys and/or one or more intermetallic compounds. For example, the terminals on integrated circuit  120  may include copper, aluminum, gold, silver, nickel, titanium, tungsten, as well as any combination of these and/or other metals. In other embodiments, a terminal may comprise one or more non-metallic materials (e.g., a conductive polymer). Similarly, terminals on substrate  110  may also comprise any suitable material or any suitable combination of materials, whether disposed in multiple layers or combined to form one or more alloys and/or one or more intermetallic compounds. For example, the terminals on substrate  110  may include copper, aluminum, gold, silver, nickel, titanium, tungsten, as well as any combination of these and/or other metals. Any suitable solder material may be used to join the mating terminals of the integrated circuit  120  and substrate  110 , respectively. For example, the solder material may comprise any one or more of tin, copper, silver, gold, lead, nickel, indium, as well as any combination of these and/or other metals. The solder may also include one or more additives and/or filler materials to alter a characteristic of the solder (e.g., to alter the reflow temperature). 
       FIG. 3  is a flowchart illustrating operations in a method to make an in-package photonic integration architecture, and  FIGS. 4A-4E  illustrate an in-package photonic integration architecture in various stages of formation on a wafer  400 , according to embodiments. Referring to  FIG. 3A  and  FIGS. 4A-4E , at operation  310  the dual height bumps  132 ,  134  are formed on a surface of the IC body  131  ( FIG. 4A ). In some examples the first plurality of bumps  132  and the second plurality of bumps  134  may be fabricated in a region of a die to which the Tx die  140  and the Rx die  150  are to be attached. 
     At operation  315  the photonic Tx die  140  and the Rx die  150  are attached to the IC body  131  and may be underfilled with a molding material as shown in  FIG. 4B . The Tx die  140  and Rx die  150  have front-side micro-bumping and backside optical coupling path by backside lens array formation. 
     At operation  320  the wafer is leveled by applying a molding material  136  as illustrated in  FIG. 4C . The Tx die  140  and Rx die  140  are exposed. Similarly the second plurality of bumps  134  are exposed. At operation  325  the solder balls  108  are attached to the exposed second plurality of bumps  134 , as illustrated in  FIG. 4D . Finally, at operation  330  the wafer may be diced to separate the discrete photonic engine  130  integrated circuits, as illustrated in  FIG. 4E . 
       FIG. 5  is a flowchart illustrating operations in a method to assemble an in-package photonic integration architecture, and  FIGS. 6A-6F  illustrate an in-package photonic integration architecture in various stages of formation, according to embodiments. Referring to  FIG. 5  and  FIGS. 6A-6F , at operation  510  the substrate  110  is prepared ( FIG. 6A ). In some examples the substrate  110  may be prepared with electrical and/or optical routing on a first surface  114  thereof. For example, a patterning material such as a resist material may be formed on the first surface  112  of the substrate  112 . The resist material may be patterned to form channels that circuit trace paths and paths for one or more waveguides. A conductive material may be formed within the channels to define circuit traces. The conductive material may comprise any suitable conductive material, such as copper, for example, and may be formed using any suitable process, such as a plating process, for example. Similarly, an optically transmissive material, e.g., an optical fiber, may be formed within the channel to define the waveguide  112 . Further, the ball grid array  106  may be formed on a second surface  116  of the substrate  110 . 
     At operation  515  one or more integrated circuits may be attached to the substrate  110 . For example, referring to  FIG. 6B , the integrated circuit  120  and the memory device  180  may be attached to the substrate  110  using solder balls  108 . At operation  520  the photonic engine  130  is attached to the substrate  110  using solder balls  108 . As described above and illustrated in  FIG. 6C , the photonic engine  130  may be attached by solder balls  106  which the are at least partially covered by a mold material  136  such that the mold material  136  defines an air gap  148  between the transmit die  140  and the at least one waveguide  112  and the receive die  150  and the at least one waveguide  112 . 
     At operation  525  the thermal interface material (TIM)  160  is applied to the memory device  180 , the integrated circuit  120 , and the photonic engine  160 , as illustrated in  FIG. 6D . Suitable thermal interface materials may include a silicon-based oil doped with aluminum oxide, zinc oxide, or the like. 
     At operation  530  the integrated heat spreader (IHS)  170  is attached to the thermal interface material  160  ( FIG. 6E ), and at operation  535  the optical coupling  190  is attached ( FIG. 6F ). 
       FIG. 7  is a schematic illustration of a universal integrated circuit (IC) based photonic engine block  700 , according to embodiments. Referring to  FIG. 7 , in some examples the Tx die  140  and the Rx die  150  are mounted on photonic engine  130  and are coupled to respective first and second optical couplings  190 . 
       FIG. 8A  is a top view, schematic illustration of a co-package optics interconnect, and  FIG. 8B  is a top view, schematic illustration of a co-package optics interconnect, in accordance with some embodiments. As illustrated in  FIGS. 8A and 8B , microelectronic package structure  100  may be provided with a plurality of photonic engine blocks  700  to provide a corresponding plurality of optical interconnects with the integrated circuit  120 . 
     Thus, as described herein one or more photonic engine blocks  700  may be attached to an integrated circuit package  100  to provide an electrical path in a first direction (i.e., down) via solder bump array bonding and underfilling and an optical path via a lens to substrate waveguide connecting to substrate edge coupling  190 , which in turn may connect to a single mode fiber (SMF) array. The architecture further provides a thermal dissipation path in a second direction (i.e., upward) via the thermal interface material (TIM)  160  and the integrated heat spreader (IHS)  170 . All components such as integrated circuit  120 , memory device  180  and photonic engine  130  may be assembled to substrate  110  where electrical routing and optical waveguide may be fabricated in the same plane. The heat spreader attach process and optical coupling assembly can be done as last step to avoid a high temperature process on the optical coupling structure  190  and an SMF array. 
       FIG. 9  is a schematic of a computing device  900  that may be implemented incorporating embodiments of the package structures described herein. For example, any suitable ones of the components of the computing device  900  may include, or be included in, a stacked die/PoP assembly in accordance with any of the embodiments disclosed herein. In an embodiment, the computing device  900  houses a board  902 , such as a motherboard  902  for example. The board  902  may include a number of components, including but not limited to a processor  904 , an on-die memory  906 , and at least one communication chip  908 . The processor  904  may be physically and electrically coupled to the board  902 . In some implementations the at least one communication chip  908  may be physically and electrically coupled to the board  902 . In further implementations, the communication chip  908  is part of the processor  904 . 
     Depending on its applications, computing device  900  may include other components that may or may not be physically and electrically coupled to the board  902 , and may or may not be communicatively coupled to each other. These other components include, but are not limited to, volatile memory (e.g., DRAM)  909 , non-volatile memory (e.g., ROM)  910 , flash memory (not shown), a graphics processor unit (GPU)  912 , a chipset  914 , an antenna  916 , a display  918  such as a touchscreen display, a touchscreen controller  920 , a battery  922 , an audio codec (not shown), a video codec (not shown), a global positioning system (GPS) device  926 , a speaker  930 , a camera  932 , compact disk (CD) (not shown), digital versatile disk (DVD) (not shown), and so forth). These components may be connected to the system board  902 , mounted to the system board, or combined with any of the other components. 
     The communication chip  908  enables wireless and/or wired communications for the transfer of data to and from the computing device  900 . The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The communication chip  908  may implement any of a number of wireless or wired standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family). IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, Ethernet derivatives thereof, as well as any other wireless and wired protocols that are designated as 3G, 4G, 5G, and beyond. The computing device  900  may include a plurality of communication chips  908 . For instance, a first communication chip may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS. CDMA, WiMAX. LTE, Ev-DO, and others. The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. 
     In various implementations, the computing device  900  may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultra mobile PC, a wearable device, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, the computing device  900  may be any other electronic device that processes data. 
     Embodiments of the package structures described herein may be implemented as a part of one or more memory chips, controllers, CPUs (Central Processing Unit), microchips or integrated circuits interconnected using a motherboard, an application specific integrated circuit (ASIC), and/or a field programmable gate array (FPGA). 
     The following pertains to various examples. 
     Example 1 is a microelectronic package structure, comprising a substrate comprising at least one waveguide; a first instrument integrated circuit coupled to the substrate; a photonic engine coupled to the substrate and comprising an integrated circuit body, a transmit die; and a receive die; wherein the photonic engine is positioned adjacent the at least one waveguide such that optical signals may be exchanged between the at least one waveguide and the transmit die and the at least one waveguide and the receive die. 
     Example 2 may optionally include the subject matter of example 1, wherein the photonic engine is coupled to the substrate via one or more solder balls; and the one or more solder balls are at least partially covered by a mold material, wherein the mold material defines an air gap between the transmit die and the at least one waveguide and the receive die and the at least one waveguide. 
     Example 3 may optionally include the subject matter of any one of examples 1-2, wherein the transmit die and the receive die are coupled to the photonic engine by a first plurality of bumps having a first height; and the one or more solder balls are coupled to the photonic engine by a second plurality of bumps having a second height, greater than the first height. 
     Example 4 may optionally include the subject matter of any one of examples 1-3, further comprising an optical coupling coupled to the at least one waveguide. 
     Example 5 may optionally include the subject matter of any one of examples 1-4, further comprising a thermal interface material (TIM) in thermal communication with the photonic engine. 
     Example 6 may optionally include the subject matter of any one of examples 1-5, further comprising a heat spreader in thermal communication with the thermal interface material. 
     Example 7 may optionally include the subject matter of any one of examples 1-6, further comprising a ball grid array positioned proximate a surface of the substrate. 
     Example 8 may optionally include the subject matter of any one of examples 1-7, further comprising a memory device coupled to the substrate. 
     Example 9 may optionally include the subject matter of any one of examples 1-8, further comprising a thermal interface material (TIM) in thermal communication with the memory device. 
     Example 10 may optionally include the subject matter of any one of examples 1-9, further comprising a heat spreader in thermal communication with the thermal interface material. 
     Example 11 is a photonic engine, comprising an integrated circuit body; a transmit die; and a receive die; wherein the transmit die and the receive die are coupled to the photonic engine by a first plurality of bumps having a first height; and the one or more solder balls are coupled to the photonic engine by a second plurality of bumps having a second height, greater than the first height. 
     Example 12 may optionally include the subject matter of any one of example 11, wherein the photonic engine is coupled to a substrate via the one or more solder balls; and the one or more solder balls are at least partially covered by a mold material, wherein the mold material defines an air gap between the transmit die and at least one waveguide on the substrate and the receive die and the at least one waveguide on the substrate. 
     Example 13 may optionally include the subject matter of any one of examples 11-12, further comprising a thermal interface material (TIM) in thermal communication with the photonic engine. 
     Example 14 may optionally include the subject matter of any one of examples 11-13, further comprising a heat spreader in thermal communication with the thermal interface material. 
     Example 15 may optionally include the subject matter of any one of examples 11-14, further comprising a ball grid array positioned proximate a surface of the substrate. 
     Example 16 is a method to form a microelectronic package structure, comprising forming a first plurality of bumps having a first height and a second plurality of bumps having a second height on an integrated circuit body of a photonic engine; mounting a transmit die and a receive die to the first plurality of bumps; coupling one or more solder balls to the second plurality of bumps having a second height, greater than the first height; mounting the photonic engine on a substrate adjacent at least one waveguide such that optical signals may be exchanged between the at least one waveguide and the transmit die and the at least one waveguide and the receive die; and mounting a first instrument integrated circuit to the substrate. 
     Example 17 may optionally include the subject matter of example 16, further comprising applying a fill layer in a region surrounding the first plurality of bumps. 
     Example 18 may optionally include the subject matter of any one of examples 16-17, wherein an air gap is formed in an area proximate the transmit die and the receive die. 
     Example 19 may optionally include the subject matter of any one of examples 16-18, further comprising applying a thermal interface material (TIM) to the photonic engine. 
     Example 20 may optionally include the subject matter of any one of examples 16-19, further comprising positioning a heat spreader in thermal communication with the thermal interface material. 
     Example 21 may optionally include the subject matter of any one of examples 16-20, further comprising positioning a ball grid array positioned proximate a surface of the substrate. 
     The terms “logic instructions” as referred to herein relates to expressions which may be understood by one or more machines for performing one or more logical operations. For example, logic instructions may comprise instructions which are interpretable by a processor compiler for executing one or more operations on one or more data objects. However, this is merely an example of machine-readable instructions and embodiments are not limited in this respect. 
     The terms “computer readable medium” as referred to herein relates to media capable of maintaining expressions which are perceivable by one or more machines. For example, a computer readable medium may comprise one or more storage devices for storing computer readable instructions or data. Such storage devices may comprise storage media such as, for example, optical, magnetic or semiconductor storage media. However, this is merely an example of a computer readable medium and embodiments are not limited in this respect. 
     The term “logic” as referred to herein relates to structure for performing one or more logical operations. For example, logic may comprise circuitry which provides one or more output signals based upon one or more input signals. Such circuitry may comprise a finite state machine which receives a digital input and provides a digital output, or circuitry which provides one or more analog output signals in response to one or more analog input signals. Such circuitry may be provided in an application specific integrated circuit (ASIC) or field programmable gate array (FPGA). Also, logic may comprise machine-readable instructions stored in a memory in combination with processing circuitry to execute such machine-readable instructions. However, these are merely examples of structures which may provide logic and embodiments are not limited in this respect. 
     Some of the methods described herein may be embodied as logic instructions on a computer-readable medium. When executed on a processor, the logic instructions cause a processor to be programmed as a special-purpose machine that implements the described methods. The processor, when configured by the logic instructions to execute the methods described herein, constitutes structure for performing the described methods. Alternatively, the methods described herein may be reduced to logic on, e.g., a field programmable gate array (FPGA), an application specific integrated circuit (ASIC) or the like. 
     In the description and claims, the terms coupled and connected, along with their derivatives, may be used. In particular embodiments, connected may be used to indicate that two or more elements are in direct physical or electrical contact with each other. Coupled may mean that two or more elements are in direct physical or electrical contact. However, coupled may also mean that two or more elements may not be in direct contact with each other, but yet may still cooperate or interact with each other. 
     Reference in the specification to “one embodiment” or “some embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an implementation. The appearances of the phrase “in one embodiment” in various places in the specification may or may not be all referring to the same embodiment. 
     Although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that claimed subject matter may not be limited to the specific features or acts described. Rather, the specific features and acts are disclosed as sample forms of implementing the claimed subject matter.