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Advances in integrated circuits
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Advances in integrated circuits
Among the most advanced integrated circuits are the microprocessors, that 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. This increased capacity per unit area can be used to decrease cost and/or increase functionality. Moore's law, 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, although these problems are not insurmountable and will likely be improved 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 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).
Classification
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 (триггеры), 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, digital signal processors (DSPs), and microcontrollers 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 analog-to-digital converters and digital-to-analog converters. Such circuits offer smaller size and lower cost, but must carefully account for signal interference.
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Manufacture
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 specialized 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 aluminum) tracks deposited on them.
History, origins, and generations
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 and Robert Noyce of Fairchild Semiconductor. Kilby filed a patent application for a " Solid Circuit" made of germanium on February 6, 1959. Kilby received several patents. Noyce was awarded a patent for a more complex " unitary circuit" made of silicon on April 25, 1961. He credited Kurt Lehovec of Sprague Electric for a key concept behind the IC: the principle of p-n junction isolation by the action of a biased p-n junction (the diode).
The first integrated circuits contained only a few transistors. Called " Small-Scale Integration " ( SSI ), they used circuits containing transistors numbering in the tens.
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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