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Integrated circuit

An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. As of 2004, typical chips are of size 1 cm2 or smaller, and contain millions of interconnected devices, but larger ones exist as well.

Among the most advanced integrated circuits are the microprocessors, which drive everything from computers to cellular phones to digital microwave ovens. Digital memory chips are another family of integrated circuits that are crucially important in modern society.

The integrated circuit was made possible by mid-20th-century technology advancements in semiconductor device fabrication and experimental discoveries that showed that semiconductor devices could perform the functions performed by vacuum tubes at the time. The integration of large numbers of tiny transistors onto a small chip was an enormous improvement to the manual assembly of finger-sized vacuum tubes. The integrated circuit's small size, reliability, fast switching speeds, low power consumption, mass production capability, and ease of adding complexity quickly pushed vacuum tubes into obsolescence.

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. 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.

 image of an integrated circuit showing defects in the  layer deposition.
Optical Microscope image of an integrated circuit showing defects in the aluminium layer deposition.

Fabrication

Main article: Fabrication (semiconductor).

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. (Some III-V compounds of the periodic table of the elements such as gallium arsenide are used for specialised applications like LEDs, night vision, and the highest-speed integrated circuits.) Today, silicon monocrystals are the main substrate used for integrated circuits (ICs). It took decades to perfect methods of creating crystals without defects in the crystalline structure of the semiconducting material.

Semiconductor ICs are fabricated in an almost two-dimensional bottom-up layer process which includes these key process steps: -

  • Imaging
  • Deposition
  • Etching

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

A mono-crystal silicon wafer (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 or aluminum tracks sputtered on them.

Cris-crossing geometry of the layers of an IC
Cris-crossing geometry of the layers of an IC
  • For a CMOS process, for example, a transistor is formed by the cris-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 cris-crossed checkerboard-like (see image above) transistors are the cheapest part of the circuit, each checker forming a transistor.
    • 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.
    • Resistive structures, meandering stripes of varying lengths, form the loads on the circuit. The resistors are the most expensive part of a typical integrated circuit. The total length of the resistive structure, and not its width, determines the resistance.
    • More rarely, inductive structures can be simulated by gyrators.
    • Since a CMOS device only draws current on the transition between logic states, CMOS devices are stressed at a much lower level than a bipolar device.
    • 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, they are largely two-dimensional in nature, with widths which have been shrinking for decades. The layers of material are fabricated much like a photographic process, although light waves in the visible spectrum can no longer be used to "expose" a layer of material, as they be would too large for the features. Thus photons of even higher frequencies are used to build the "photomasks" for each layer.
    • Electron microscopes are an essential tool for a process engineer who might be debugging a fabrication process.

Each device is tested, before packaging. The wafer is then diced into small rectangles called die. The die is then connected into a package using gold or aluminum wires which are welded to pads, usually found around the edge of the die. After packaging, the devices go through final test on very expensive automated testers, which account for over 25 percent of the cost of fabrication. A fabrication facility, commonly known as a semiconductor fab, currently costs over a billion US Dollars to construct, because much of the operation is automated. In the most advanced processes, the wafers exceed 30 centimeters in diameter (wider than a common dinner plate).

Significance

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, etc. 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.

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 eventually slow down (see technological singularity).

The integrated circuit is one of the most important inventions of the 20th century. Modern computing, communications, manufacturing and transport systems, including the Internet, all depend on its existence.

History

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 DC 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 (http://www.ti.com/corp/docs/kilbyctr/jackbuilt.shtml) for more information.)

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

SSI

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).

MSI

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.

LSI

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.

VLSI

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 or even an entire microprocessor on a single integrated circuit. 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

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.

WSI

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.

SOC

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, etc., i.e., 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 defense applications, including projectors, ink jet printers, and are 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.

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 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...

Notable integrated circuits

Notable manufacturers

See also

Conferences related to VLSI

  • IEDM - IEEE International Electron Devices Meeting
  • DAC - Design Automation Conference
  • EDS - IEEE EDS Meetings Calendar
  • EDS - IEEE EDS Sponsored, Cosponsored & Topical Conferences
  • CAS - IEEE Circuits and Systems Conferences

VLSI Journals

  • ED - IEEE Transactions on Electron Devices
  • EDL - IEEE Electron Device Letters
  • CAD - IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
  • JSSC - IEEE Journal of Solid-State Circuits
  • VLSI - IEEE Transactions on Very Large Scale Integration (VLSI) Systems
  • CAS II - IEEE Transactions on Circuits and Systems II: Analogy and Digital Signal Processing
  • SM - IEEE Transactions on Semiconductor Manufacturing
  • SSE - Solid-State Electronics
  • SST - Solid-State Technology
  • TCAD - Journal of Technology Computer-Aided Design

References

  • Mead, C. and Conway, L. (1980). Introduction to VLSI Systems. Addison-Wesley. ISBN 0-201-04358-0.
  • Kang, S. and Leblebici, Y. (2002). CMOS Digital Integrated Circuits Analysis & Design. McGraw-Hill. ISBN 0072460539.
  • Weste, Neil H.E. and Harris, David (2004). CMOS VLSI Design : A Circuits and Systems Perspective. Addison Wesley. ISBN 0321149017.
  • Hodges, D.A., Jackson H.G. and Saleh, R. (2003). Analysis and Design of Digital Integrated Circuits. McGraw-Hill. ISBN 0072283653.
  • Uyemura, John P. (2001). Introduction to VLSI Circuits and Systems. Wiley. ISBN 0471127043.

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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