1、Integrated circuit In electronics, an 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 o
2、f semiconductor material. Integrated circuits are used in almost all electronic equipment in use today and have revolutionized the world of electronics. Integrated circuits were made possible by experimental discoveries which showed that semiconductor devices could perform the functions of vacuum tu
3、bes, 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 electronic components. The integrated circuits mass production capab
4、ility, 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
5、, are printed as a unit by photolithography and not constructed one transistor at a time. Furthermore, much less material is used to construct a circuit as a packaged IC die than as a discrete circuit. Performance is high since the components switch quickly and consume little power (compared to thei
6、r discrete counterparts) because the components are small and close together. As of 2006, chip areas range from a few square millimeters to around 350 mm2, with up to 1 million transistors per mm2. Among the most advanced integrated circuits are the microprocessors or cores, which control everything
7、 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 the cost of designing and developing a complex integrated circuit is quite high, when spread
8、 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 siz
9、es 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 functionalitysee Moores law which, in its modern interpretation, states that the number of transistors in an integrated circuit doubles every two y
10、ears. In general, as the 第 页 共 页 feature size shrinks, almost everything improvesthe 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
11、leakage 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 manufacture
12、rs 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). Only a half century after their development was initiated, integrated circuits have become ubiquitous. Computers, cellular
13、 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. Integrated circuits can be classified int
14、o 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
15、 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 amplifi
16、ers, work by processing continuous signals. They perform functions like amplification, active filtering, demodulation, mixing, etc. 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 lo
17、wer cost, but must carefully account for signal interference. 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 co
18、pper 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 special
19、ized 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 第 页 共 页 semiconducting material. Semiconductor ICs are fabricated in a layer process which includes
20、these key process steps: Imaging Deposition Etching The main process steps are supplemented by doping and cleaning. Integrated circuits are composed of many overlapping layers, each defined by photolithography, and normally shown in different colors. Some layers mark where various dopants are diffus
21、ed 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 sp
22、ecific 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. Since a CMOS device only draws current on the transition between logic states, CMOS devices consume much less current than bipolar devi
23、ces. 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. Although the structures are intricate with widths which have been shrinking for decades the layers remain much thinner th
24、an 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
25、 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. The earliest integrated circuits were packaged in ceramic flat packs, which continued to be used by the military for th
26、eir 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 ch
27、ip 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.
