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Integrated circuit

2007 Schools Wikipedia Selection. Related subjects: Computing hardware and
infrastructure; Electricity and Electronics

   Integrated circuit showing memory blocks, logic and input/output pads
   around the periphery
   Integrated circuit showing memory blocks, logic and input/output pads
   around the periphery
   Microchips with a transparent window, showing the integrated circuit
   inside. Note the fine silver-colored wires that connect the integrated
   circuit to the pins of the package.
   Microchips with a transparent window, showing the integrated circuit
   inside. Note the fine silver-colored wires that connect the integrated
   circuit to the pins of the package.

   A monolithic integrated circuit (also known as IC, microcircuit,
   microchip, silicon chip, or chip) is a miniaturized electronic circuit
   (consisting mainly of semiconductor devices, as well as passive
   components) that has been manufactured in the surface of a thin
   substrate of semiconductor material.

   A hybrid integrated circuit is a miniaturized electronic circuit
   constructed of individual semiconductor devices, as well as passive
   components, bonded to a substrate or circuit board.

   This article is about monolithic integrated circuits.

Introduction

   Integrated circuits were made possible by experimental discoveries
   which showed that semiconductor devices could perform the functions of
   vacuum tubes, and by mid-20th-century technology advancements in
   semiconductor device fabrication. The integration of large numbers of
   tiny transistors into a small chip was an enormous improvement over the
   manual assembly of circuits using discrete electronic components. The
   integrated circuit's mass production capability, reliability, and
   building-block approach to circuit design ensured the rapid adoption of
   standardized ICs in place of designs using discrete transistors.

   There are two main advantages of ICs over discrete circuits: cost and
   performance. Cost is low because the chips, with all their components,
   are printed as a unit by photolithography and not constructed a
   transistor at a time. Performance is high since the components switch
   quickly and consume little power, because the components are small and
   close together. As of 2006, chip areas range from a few square mm to
   around 350 mm^2, with up to 1 million transistors per mm^2.

Advances in integrated circuits

   The integrated circuit from an Intel 8742, an 8-bit microcontroller
   that includes a CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes of
   EPROM, and I/O in the same chip.
   The integrated circuit from an Intel 8742, an 8-bit microcontroller
   that includes a CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes of
   EPROM, and I/O in the same chip.

   Among the most advanced integrated circuits are the microprocessors or
   "cores", which control everything from computers to cellular phones to
   digital microwave ovens. Digital memory chips and ASICs are examples of
   other families of integrated circuits that are important to the modern
   information society. While cost of designing and developing a complex
   integrated circuit is quite high, when spread across typically millions
   of production units the individual IC cost is minimized. The
   performance of ICs is high because the small size allows short traces
   which in turn allows low power logic (such as CMOS) to be used at fast
   switching speeds.

   ICs have consistently migrated to smaller feature sizes over the years,
   allowing more circuitry to be packed on each chip. This increased
   capacity per unit area can be used to decrease cost and/or increase
   functionality—see Moore's law which, in its modern interpretation,
   states that the number of transistors in an integrated circuit doubles
   every two years. In general, as the feature size shrinks, almost
   everything improves—the cost per unit and the switching power
   consumption go down, and the speed goes up. However, ICs with
   nanometer-scale devices are not without their problems, principal among
   which is leakage current (see subthreshold leakage and MOSFET for a
   discussion of this), although these problems are not insurmountable and
   will likely be solved or at least ameliorated by the introduction of
   high-k dielectrics. Since these speed and power consumption gains are
   apparent to the end user, there is fierce competition among the
   manufacturers to use finer geometries. This process, and the expected
   progress over the next few years, is well described by the
   International Technology Roadmap for Semiconductors (ITRS).

Popularity of ICs

   Only a half century after their development was initiated, integrated
   circuits have become ubiquitous. Computers, cellular phones, and other
   digital appliances are now inextricable parts of the structure of
   modern societies. That is, modern computing, communications,
   manufacturing and transport systems, including the Internet, all depend
   on the existence of integrated circuits. Indeed, many scholars believe
   that the digital revolution brought about by integrated circuits was
   one of the most significant occurrences in the history of mankind.

Classification

   A CMOS 4000 IC in a DIP
   A CMOS 4000 IC in a DIP

   Integrated circuits can be classified into analog, digital and mixed
   signal (both analog and digital on the same chip).

   Digital integrated circuits can contain anything from a few thousand to
   millions of logic gates, flip-flops, multiplexers, and other circuits
   in a few square millimeters. The small size of these circuits allows
   high speed, low power dissipation, and reduced manufacturing cost
   compared with board-level integration. These digital ICs, typically
   microprocessors, DSPs, and micro controllers work using binary
   mathematics to process "one" and "zero" signals.

   Analog ICs, such as sensors, power management circuits, and operational
   amplifiers, work by processing continuous signals. They perform
   functions like amplification, active filtering, demodulation, mixing,
   etc. Analog ICs ease the burden on circuit designers by having expertly
   designed analog circuits available instead of designing a difficult
   analog circuit from scratch.

   ICs can also combine analog and digital circuits on a single chip to
   create functions such as A/D converters and D/A converters. Such
   circuits offer smaller size and lower cost, but must carefully account
   for signal interference (see signal integrity).

Manufacture

Fabrication

   Rendering of a small standard cell with three metal layers (dielectric
   has been removed). The sand-colored structures are metal interconnect,
   with the vertical pillars being contacts, typically plugs of tungsten.
   The reddish structures are polysilicon gates, and the solid at the
   bottom is the crystalline silicon bulk.
   Rendering of a small standard cell with three metal layers ( dielectric
   has been removed). The sand-colored structures are metal interconnect,
   with the vertical pillars being contacts, typically plugs of tungsten.
   The reddish structures are polysilicon gates, and the solid at the
   bottom is the crystalline silicon bulk.

   The semiconductors of the periodic table of the chemical elements were
   identified as the most likely materials for a solid state vacuum tube
   by researchers like William Shockley at Bell Laboratories starting in
   the 1930s. Starting with copper oxide, proceeding to germanium, then
   silicon, the materials were systematically studied in the 1940s and
   1950s. Today, silicon monocrystals are the main substrate used for
   integrated circuits (ICs) although some III-V compounds of the periodic
   table such as gallium arsenide are used for specialised applications
   like LEDs, lasers, solar cells and the highest-speed integrated
   circuits. It took decades to perfect methods of creating crystals
   without defects in the crystalline structure of the semiconducting
   material.

   Semiconductor ICs are fabricated in a layer process which includes
   these key process steps:
     * Imaging
     * Deposition
     * Etching

   The main process steps are supplemented by doping, cleaning and
   planarisation steps.

   Mono-crystal silicon wafers (or for special applications, silicon on
   sapphire or gallium arsenide wafers) are used as the substrate.
   Photolithography is used to mark different areas of the substrate to be
   doped or to have polysilicon, insulators or metal (typically aluminium)
   tracks deposited on them.
     * Integrated circuits are composed of many ovelapping layers, each
       defined by photolithography, and normally shown in different
       colors. Some layers mark where various dopants are diffused into
       the substrate (called diffusion layers), some define where
       additional ions are implanted (implant layers), some define the
       conductors (polysilicon or metal layers), and some define the
       connections between the conducting layers (via or contact layers).
       All components are constructed from a specific combination of these
       layers.
     * In a self-aligned CMOS process, a transistor is formed wherever the
       gate layer (polysilicon or metal) crosses a diffusion layer.
     * Resistive structures, meandering stripes of varying lengths, form
       the loads on the circuit. The ratio of the length of the resistive
       structure to its width, combined with its sheet resistivity
       determines the resistance.
     * Capacitive structures, in form very much like the parallel
       conducting plates of a traditional electrical capacitor, are formed
       according to the area of the "plates", with insulating material
       between the plates. Owing to limitations in size, only very small
       capacitances can be created on an IC.
     * More rarely, inductive structures can be built as tiny on-chip
       coils, or simulated by gyrators.

   Since a CMOS device only draws current on the transition between logic
   states, CMOS devices consume much less current than bipolar devices.

   A random access memory is the most regular type of integrated circuit;
   the highest density devices are thus memories; but even a
   microprocessor will have memory on the chip. (See the regular array
   structure at the bottom of the first image.) Although the structures
   are intricate – with widths which have been shrinking for decades – the
   layers remain much thinner than the device widths. The layers of
   material are fabricated much like a photographic process, although
   light waves in the visible spectrum cannot be used to "expose" a layer
   of material, as they would be too large for the features. Thus photons
   of higher frequencies (typically ultraviolet) are used to create the
   patterns for each layer. Because each feature is so small, electron
   microscopes are essential tools for a process engineer who might be
   debugging a fabrication process.

   Each device is tested before packaging using automated test equipment
   (ATE), in a process known as wafer testing, or wafer probing. The wafer
   is then cut into rectangular blocks, each of which is called a die.
   Each good die (plural dice, dies, or die) is then connected into a
   package using aluminium (or gold) wires which are welded to pads,
   usually found around the edge of the die. After packaging, the devices
   go through final test on the same or similar ATE used during wafer
   probing. Test cost can account for over 25% of the cost of fabrication
   on lower cost products, but can be negligible on low yielding, larger,
   and/or higher cost devices.

   As of 2005, a fabrication facility (commonly known as a semiconductor
   fab) costs over a billion US Dollars to construct, because much of the
   operation is automated. The most advanced processes employ the
   following techniques:
     * The wafers are up to 300 mm in diameter (wider than a common dinner
       plate).
     * Use of 90 nanometer or smaller chip manufacturing process. Intel,
       IBM, NEC, and AMD are using 90 nanometers for their CPU chips, and
       AMD , Intel and NEC have started using a 65 nanometer process. IBM
       and AMD are in development of a 45-nm process using immersion
       lithography.
     * Copper interconnects where copper wiring replaces aluminium for
       interconnects.
     * Low-K dielectric insulators.
     * Silicon on insulator (SOI)
     * Strained silicon in a process used by IBM known as Strained silicon
       directly on insulator (SSDOI)

Packaging

   The earliest integrated circuits were packaged in ceramic flat packs,
   which continued to be used by the military for their reliability and
   small size for many years. Commercial circuit packaging quickly moved
   to the dual in-line package (DIP), first in ceramic and later in
   plastic. In the 1980s pin counts of VLSI circuits exceeded the
   practical limit for DIP packaging, leading to pin grid array (PGA) and
   leadless chip carrier (LCC) packages. Surface mount packaging appeared
   in the early 1980s and became popular in the late 1980s, using finer
   lead pitch with leads formed as either gull-wing or J-lead, as
   exemplified by Small-Outline Integrated Circuit. A carrier which
   occupies an area about 30 – 50% less than an equivalent DIP, with a
   typical thickness that is 70% less. This package has "gull wing" leads
   protruding from the two long sides and a lead spacing of 0.050 inches.

   Small-Outline Integrated Circuit (SOIC) and PLCC packages. In the late
   1990s, PQFP and TSOP packages became the most common for high pin count
   devices, though PGA packages are still often used for high-end
   microprocessors. Intel and AMD are currently transitioning from PGA
   packages on high-end microprocessors to land grid array (LGA) packages.

   Ball grid array (BGA) packages have existed since the 1970s. Flip-chip
   Ball Grid Array packages, which allow for much higher pin count than
   other package types, were developed in the 1990s. In an FCBGA package
   the die is mounted upside-down (flipped) and connects to the package
   balls via a package substrate that is similar to a printed-circuit
   board rather than by wires. FCBGA packages allow an array of
   input-output signals (called Area-I/O) to be distributed over the
   entire die rather than being confined to the die periphery.

   Traces out of the die, through the package, and into the printed
   circuit board have very different electrical properties, compared to
   on-chip signals. They require special design techniques and need much
   more electric power than signals confined to the chip itself.

   When multiple dies are put in one package, it is called SiP, for System
   In Package. When multiple dies are combined on a small substrate, often
   ceramic, it's called a MCM, or Multi-Chip Module. The boundary between
   a big MCM and a small printed circuit board is sometimes fuzzy.

History, origins, and generations

The birth of the IC

   The integrated circuit was first conceived by a radar scientist,
   Geoffrey W.A. Dummer (born 1909), working for the Royal Radar
   Establishment of the British Ministry of Defence, and published in
   Washington, D.C. on May 7, 1952. Dummer unsuccessfully attempted to
   build such a circuit in 1956.

   A precursor idea to the IC was to create small ceramic squares
   (wafers), each one containing a single miniaturized component.
   Components could then be integrated and wired into a bidimensional or
   tridimensional compact grid. This idea, which looked very promising in
   1957, was proposed to the US Army by Jack Kilby, and led to the
   short-lived Micromodule Program (similar to 1951's Project Tinkertoy).
   However, as the project was gaining momentum, Kilby came up with a new,
   revolutionary design: the IC.

   The first integrated circuits were manufactured independently by two
   scientists: Jack Kilby of Texas Instruments filed a patent for a "Solid
   Circuit" made of germanium on February 6, 1959. Kilby received patents
   U.S. Patent 3,138,743, U.S. Patent 3,138,747, U.S. Patent 3,261,081,
   and U.S. Patent 3,434,015. Robert Noyce of Fairchild Semiconductor was
   awarded a patent for a more complex "unitary circuit" made of Silicon
   on April 25, 1961. (See the Chip that Jack built for more information.)

   Noyce credited Kurt Lehovec of Sprague Electric for the principle of
   p-n junction isolation caused by the action of a biased p-n junction
   (the diode) as a key concept behind the IC.

   See: Other variations of vacuum tubes for precursor concepts such as
   the Loewe 3NF.

SSI, MSI, LSI

   The first integrated circuits contained only a few transistors. Called
   "Small-Scale Integration" (SSI), they used circuits containing
   transistors numbering in the tens.

   SSI circuits were crucial to early aerospace projects, and vice-versa.
   Both the Minuteman missile and Apollo program needed lightweight
   digital computers for their inertially-guided flight computers; the
   Apollo guidance computer led and motivated the integrated-circuit
   technology, while the Minuteman missile forced it into mass-production.

   These programs purchased almost all of the available integrated
   circuits from 1960 through 1963, and almost alone provided the demand
   that funded the production improvements to get the production costs
   from $1000/circuit (in 1960 dollars) to merely $25/circuit (in 1963
   dollars). They began to appear in consumer products at the turn of the
   decade, a typical application being FM inter-carrier sound processing
   in television receivers.

   The next step in the development of integrated circuits, taken in the
   late 1960s, introduced devices which contained hundreds of transistors
   on each chip, called "Medium-Scale Integration" (MSI).

   They were attractive economically because while they cost little more
   to produce than SSI devices, they allowed more complex systems to be
   produced using smaller circuit boards, less assembly work (because of
   fewer separate components), and a number of other advantages.

   Further development, driven by the same economic factors, led to
   "Large-Scale Integration" (LSI) in the mid 1970s, with tens of
   thousands of transistors per chip.

   Integrated circuits such as 1K-bit RAMs, calculator chips, and the
   first microprocessors, that began to be manufactured in moderate
   quantities in the early 1970s, had under 4000 transistors. True LSI
   circuits, approaching 10000 transistors, began to be produced around
   1974, for computer main memories and second-generation microprocessors.

VLSI

   Upper interconnect layers on an Intel 80486DX2 microprocessor die.
   Upper interconnect layers on an Intel 80486DX2 microprocessor die.

   The final step in the development process, starting in the 1980s and
   continuing on, was "Very Large-Scale Integration" ( VLSI), with
   hundreds of thousands of transistors, and beyond (well past several
   million in the latest stages).

   For the first time it became possible to fabricate a CPU on a single
   integrated circuit, to create a microprocessor. In 1986 the first one
   megabit RAM chips were introduced, which contained more than one
   million transistors. Microprocessor chips produced in 1994 contained
   more than three million transistors.

   This step was largely made possible by the codification of "design
   rules" for the CMOS technology used in VLSI chips, which made
   production of working devices much more of a systematic endeavour. (See
   the 1980 landmark text by Carver Mead and Lynn Conway referenced
   below.)

ULSI, WSI, SOC

   To reflect further growth of the complexity, the term ULSI that stands
   for "Ultra-Large Scale Integration" was proposed for chips of
   complexity more than 1 million of transistors. However, there is no
   qualitative leap between VLSI and ULSI, hence normally in technical
   texts the "VLSI" term covers ULSI as well, and "ULSI" is reserved only
   for cases when it is necessary to emphasize the chip complexity, e.g.
   in marketing.

   The most extreme integration technique is wafer-scale integration
   (WSI), which uses whole uncut wafers containing entire computers
   (processors as well as memory). Attempts to take this step commercially
   in the 1980s (e.g. by Gene Amdahl) failed, mostly because of
   defect-free manufacturability problems, and it does not now seem to be
   a high priority for the industry.

   The WSI technique failed commercially, but advances in semiconductor
   manufacturing allowed for another attack on IC complexity, known as
   System-on-Chip (SOC) design. In this approach, components traditionally
   manufactured as separate chips to be wired together on a printed
   circuit board are designed to occupy a single chip that contains
   memory, microprocessor(s), peripheral interfaces, Input/Output logic
   control, data converters, and other components, together composing the
   whole electronic system.

Other developments

   In the 1980s programmable integrated circuits were developed. These
   devices contain circuits whose logical function and connectivity can be
   programmed by the user, rather than being fixed by the integrated
   circuit manufacturer. This allows a single chip to be programmed to
   implement different LSI-type functions such as logic gates, adders, and
   registers. Current devices named FPGAs (Field Programmable Gate Arrays)
   can now implement tens of thousands of LSI circuits in parallel and
   operate up to 400 MHz.

   The techniques perfected by the integrated circuits industry over the
   last three decades have been used to create microscopic machines, known
   as MEMS. These devices are used in a variety of commercial and military
   applications. Example commercial applications include DLP projectors,
   inkjet printers, and accelerometers used to deploy automobile airbags.

   In the past, radios could not be fabricated in the same low-cost
   processes as microprocessors. But since 1998, a large number of radio
   chips have been developed using CMOS processes. Examples include
   Intel's DECT cordless phone, or Atheros's 802.11 card.

   Future developments seem to follow the multi-microprocessor paradigm,
   already used by the Intel and AMD dual-core processors. Intel recently
   unveiled a prototype, "not for commercial sale" chip that bears a
   staggering 80 microprocessors. Each core is capable of handling it's
   own task independently of the others. This is in resposnse to the heat
   vs speed limit that is about to be reached using existing transistor
   technology. This design provides a new challenge to chip programming.
   X10 is the new open-source programming language designed to assist with
   this task.

Silicon graffiti

   Ever since ICs were created, some chip designers have used the silicon
   surface area for surreptitious, non-functional images or words. These
   are sometimes referred to as Chip Art, or Silicon Art, or Silicon
   Graffiti, or Silicon Doodling. For an overview of this practice, see
   the article The Secret Art of Chip Graffiti, from the IEEE magazine
   Spectrum.

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