Electronics and microelectronics

I. The intensive effort1 of electronics to increase the reliability2 and performance3 of its products while reducing their size and cost has led to the results that hardly anyone would have dared to predict.4

The evolution of electronic technology is sometimes called a revolution. What we have seen has been a steady quantitative evolution: smaller and smaller electronic components performing increasingly complex electronic functions at ever higher speeds. And yet there has been a true revolution: a quantitative change in technology has given rise to qualitative change in human capabilities.5

It all began with the development of the transistor.

Prior to6 the invention of the transistor in 1947 its function in an electronic circuit could be performed only by a vacuum tube. Tubes came in so many shapes and sizes and performed so many functions that in 1947 it seemed audacious ( ) to think that the transistor would be able to compete7 except in limited applications.

The first transistors had no striking advantage in size over the smallest tubes and they were more costly. The one great advantage the transistor had over the best vacuum tubes was exceedingly8 low power consumption. Besides they promised greater reliability and longer life. However it took years to demonstrate other transistor advantages.

With the invention of the transistor all essential circuit functions could be carried out9 inside solid10 bodies. The goal11 of creating electronic circuits with entirely solid-state components had finally been realized.12

Early transistors, which were often described as being a size of a pea (), were actually enormous on the scale13 at which electronic events14 take place, and therefore they were very slow. They could respond15 at a rate16 of a few million times a second; this was fast enough to serve in radio and hearing-aid ( ) circuits but far below the speed needed for high-speed computers or for microwave communication systems.

It was, in fact, the effort to reduce the size of transistors so that they could operate at higher speed that gave rise to the whole technology of microelectronics.

A microelectronic technology has shrunk17 transistors and other circuit elements to dimensions18 almost invisible to unaided eye ( ).

The point19 of this extraordinary miniaturization is not so much to make circuits small per se (. ) as to make circuits that are rugged (. ), long-lasting, low in cost and capable of performing electronic functions at extremely high speeds. It is known that the speed of response depends primarily on the size of transistor: the smaller the transistor, the faster it is.

The second performance benefit20 resulting from microelectronics stems directly from the reduction of distances between circuit components. If a circuit is to operate a few billion times a second the conductors that tie the circuit together must be measured in fractions of an inch. The microelectronics technology makes close coupling21 attainable.22

It may be helpful if we say a few words about four of the principal devices found in electronic circuits: resistors, capacitors, diodes and transistors. Each device has a particular23 role in controlling the flow of electrons so that the completed circuit performs some desired function.

During the past decade the performance of electronic systems increased manifold24 by the use of ever larger numbers of components and they continue to evolve. Modern scientific and business computers, for example, contain 109 elements; electronic switching25 systems contain more than a million components.

The tyrany of numbers - the problem of handling26 many discrete electronic devices began to concern27 the scientists as early as 1950. The overall28 reliability of the electronic system is universally related to the number of individual components.

A more serious shortcoming29 was that it was once30 the universal practice to manufacture31 each of the components separately and then assemble32 the complete device by wiring33 the components together with metallic conductors. It was no good (. ): the more components and interactions, the less reliable the system.

The development of rockets and space vehicles34 provided the final impetus65 to study the problem. However, many attempts were largely unsuccessful.

What ultimately36 provided the solution was the semiconductor integrated circuit, the concept37 of which had 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 advent38 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 similar39 components. The major difference is that all these elements and their interconnections are now fabricated on a single substrate40 in a single series of operations.

II. Several key41 developments were required before the exciting potential of integrated circuits could be realized.

The development of microelectronics depended on the invention of techniques42 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 to 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 patterns43 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 carriers of both polarities are involved44 in their operation. They are also known as junction45 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 refers46 to the three materials employed in its construction and is addreviated 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 chip47 can be achieved with the newer MOSFET technology.

An individual integrated circuit (1C) 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 tolerable48 yield49) has doubled every year. The 1980 state of art50 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 are now referred to as small-scale integrated circuits (SSI). They included a few gates.51 The circuitry defining52 a logic array53 had to be provided by external conductors.

Devices with more than about 10 gates on a chip but fewer than about 200 are medium-scale integrated circuits (MSI). The upper boundary54 of medium-scale integrated circuits technology is marked55 by chips that contain a complete arithmetic and logic unit. This unit accepts as inputs two operands and can perform any one of a dozen or so operations on them. The operations include additions, subtraction, comparison, logical "and" and "or" and shifting56 one bit to the left or right.

A large-scale integrated circuit (LSI) contains tens of thousands of elements, yet each element is so small that the complete circuit is typically less than a quarter of an inch on a side.

Integrated circuits are evolving from large scale to very-large-scale (VLSI) and wafer-scale integration (WSI).

The change in scale can be measured by counting the number of transistors that can be fitted57 onto a chip.

Continued evolution of the microcomputer will demand further increases in packing58 density.

There appeared a new mode59 of integrated circuits, microwave integrated circuits. In broadest sense,60 a microwave integrated circuit is any combination of circuit functions which are packed together without a user accessible61 interface.

The evolution of microwave integrated circuits must begin with the development of planar62 transmission lines.63

As we moved into the 1970's, stripline and microstrip assemblies became commonplace and accepted as the everyday method of building microwave integrated circuits. New forms of transmission lines were on the horizon, however. In 1974 new integratedcircuit components in a transmission line called fineline appeared. Other more exotic techniques, such as dielectric waveguide64 integrated circuits emerge.65 Major efforts currently are directed at such areas as image guide, co-planar waveguide, fineline and dielectric waveguide, all with emphasis on techniques which can be applied to monolithic integrated circuits. These monolithic circuits encompass all of the traditional microwave functions of analog circuits as well as new digital applications.

Microelectronic technique will continue to displace other modes. As the limit of optical resolution66 is now being reached, new lithographic and fabrication techniques will be required. Circuit patterns will have to be formed with radiation having wavelength shorter than those of light, and fabrication techniques capable of greater definition will be needed.

Electronics has extended67 man's intellectual power. Microelectronics extends that power still further.



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