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Integrated circuit

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Integrated circuit showing memory blocks, logic and input/output pads around the periphery
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Integrated circuit showing memory blocks, logic and input/output pads around the periphery

A monolithic integrated circuit (also known as IC, microchip, silicon chip, computer chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) which 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.

Contents

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Introduction

The integrated circuit was 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 vacuum tubes and circuits using discrete components. The integrated circuit's mass production capability, reliability, and ease of adding complexity prompted the use of standardized ICs in place of designs using discrete transistors which quickly pushed vacuum tubes into obsolescence. There are two main advantages of ICs over discrete circuits - cost and performance. The 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. As of 2006, chip areas range from a few square mm to around 250 mm2, with up to 1 million transistors per mm2.

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Advances in integrated circuits

Among the most advanced integrated circuits are the microprocessors, which control everything from computers to cellular phones to digital microwave ovens. Digital memory chips are another family of integrated circuit that is crucially important to the modern information society. While the 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 - see Moore's law. 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, IC's 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, or ITRS.

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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.

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Classification and complexity

A CMOS 4000 IC
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A CMOS 4000 IC

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 one 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. Analog integrated circuits perform analog functions like amplification, active filtering, demodulation, mixing, etc. ADCs and DACs are the key elements of mixed signal ICs. They convert signals between analog and digital formats. Analog ICs ease the burden on circuit designers by having expertly designed analog circuits available instead of designing a difficult analog circuit from scratch.

The growth of complexity of integrated circuits follows a trend called "Moore's Law", first observed by Gordon Moore of Intel. Moore's Law in its modern interpretation states that the number of transistors in an integrated circuit doubles every two years. By the year 2000 the largest integrated circuits contained hundreds of millions of transistors. It is difficult to say whether the trend will continue (see technological singularity).

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Manufacture

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Fabrication

Main article: Semiconductor fabrication.

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, 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.

Criss-crossing geometry of the layers of an IC
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Criss-crossing geometry of the layers of an IC
  • For a CMOS process, for example, a transistor is formed by the criss-crossing intersection of striped layers. The stripes can be monocrystalline substrate, doped layers, perhaps insulator layers or polysilicon layers. Some etched vias to the doped layers might interconnect layers with metal conducting tracks.
  • The criss-crossed checkerboard-like (see image above) transistors are the most common part of the circuit, each checker forming a transistor.
  • 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 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 memory device 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.

SEM image of an integrated circuit showing defects in the aluminium layer deposition (shown in cyan).
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SEM image of an integrated circuit showing defects in the aluminium layer deposition (shown in cyan).

Each device is tested before packaging using very expensive automated test equipment (ATE), a process known as wafer testing, or wafer probing. The wafer is then cut into small rectangles called dice. Each good die (N.B. die is the singular form of dice, although dies is also used as the plural) 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:

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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.

Ball grid array (BGA) packages have existed since the 1970s.

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 die are put in one package, it is called SiP, for System In Package. When multiple die 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.

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History, origins and generations

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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.

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 US3138743, US3138747, US3261081, and US3434015. 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.Lehovec

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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).

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.

LSI circuits began to be produced in large quantities around 1970, for computer main memories and pocket calculators.

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VLSI

Main article: Very-large-scale integration.

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.)

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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 industry.

The WSI technique failed commercially, but advances in semiconductor manufacturing allowed for another attack on the 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.

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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 defense applications, including projectors, ink jet printers, and accelerometers used to deploy the airbag in car accidents.

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.

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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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Key industrial and academic data

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Notable ICs

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Manufacturers

A list of notable manufacturers; some operating, some defunct:

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VLSI conferences

  • ISSCC – IEEE International Solid-State Circuits Conference
  • CICC – IEEE Custom Integrated Circuit Conference
  • ISCAS – IEEE International Symposium on Circuits and Systems
  • VLSI – IEEE International Conference on VLSI Design
  • DAC – Design Automation Conference
  • ICCAD – International Conference on Computer Aided Design
  • ESSCIRC – European Solid-State Circuits Conference
  • ISLPED – International Symposium on Low Power and Design
  • ISPD – International Symposium on Physical Design
  • ISQED – International Symposium on Quality Electronic Design
  • DATE – Design and Test in Europe
  • ICCD – International Conference on Computer Design
  • IEDM – IEEE International Electron Devices Meeting
  • GLSVLSI – IEEE Great Lakes Symposium on VLSI
  • ASP-DAC – Asia and South Pacific Design Automation Conference
  • MWSCAS – IEEE Midwest Symposium on Circuits and Systems
  • ICSVLSI – IEEE Computer Society Annual Symposium on VLSI
  • EDS – IEEE EDS Meetings Calendar
  • EDS – IEEE EDS Sponsored, Cosponsored & Topical Conferences
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VLSI journals

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Branch pages

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See also

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References

Academic:

Patents:

  • ↑  Kurt Lehovec's patent on the isolation p-n junction: US patent 3 029 366 awarded on April 10, 1962, filed April 22, 1959. Robert Noyce credits Lehovec in his article – "Microelectronics", Scientific American, September 1977, Volume 23, Number 3, pp. 63–9.
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External links

Wikimedia Commons has media related to:
Patents
  • US3138743 – Miniaturized electronic circuit – J. S. Kilby
  • US3138747 – Integrated semiconductor circuit device – J. S. Kilby
  • US3261081 – Method of making miniaturized electronic circuits – J. S. Kilby
  • US3434015 – Capacitor for miniaturized electronic circuits or the like – J. S. Kilby
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