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nents. A more serious shortcoming was that it was once the universal practice to manufacture each of the components separately and then assemble the complete device by wiring the components together with metallic conductors. It was no go d: the more components and interactions, the less reliable the system. The development of rockets and space vehicles provided the final impetus to study the problem. However, many attempts were largely unsuccessful. What ultimately provided the solution was the semiconductor integrated circuit, the concept of which has begun to take shape a few years after the invention of the transistor. Roughly between 1960 and 1963 a new circuit technology became a reality. It was microelectronics development that solved the problem. The advent of microelectronic circuits has not, for the most part, changed the nature of the basic functional units: microelectronic devices are also made up of transistors, resistors, capacitors, and similar components. The major difference is that all these elements and their interconnections are now fabricated on single substrate in single series of operations. Several key developments were required before the exciting potential of integrated circuits could be realized. The development of microelectronics depended on the invention of techniques for making the various functional units on or in a crystal of semiconductor materials. In particular, a growing number of functions have been given over the circuit elements that perform best: transistors. Several kinds of microelectronic transistors have been developed, and for each of them families of associated circuit elements and circuit patterns have evolved. It was the bipolar transistor that was invented in 1948 by John Bardeen, Walter H. Brattain and William Shockley of the Bell Telephone Laboratories. In bipolar transistors charge carries of both polarities are involved in their operation. They are also known as junction transistors. The npn and pnp transistors make up the class of devices called junction transistors. A second kind of transistor was actually conceived almost 25 years before the bipolar devices, but its fabrication in quantity did not become practical until the early 1960 's. This is the field-effect transistor. The one that is common in microelectronics is the metal-oxide-semiconductor field-effect transistor. The term refers to the three materials employed in its construction and is abbreviated MOSFET. The two basic types of transistor, bipolar and MOSFET, divide microelectronic circuits into two large families. Today the greatest density of circuit elements per chip can be achieved with the newer MOSFET technology. An individual integrated circuit (IC) on a chip now can embrace more electronic elements than most complex piece of electronic equipment that could be built in 1950. In the first 15 years since the inception of integrated circuits, the number of transistors that could be placed on a single chip (with tolerable yield) has doubled every year. The 1980 state of art is about 70K density per chip. Nowadays we can put a million transistors on a single chip. The first generation of commercially produced microelectronic devices is now referred to as small-scale integrated circuits (SSI). They included a few gates.
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