Electronics Information needs to be received, processed to derive useful information, stored and

7.4.3 Electronics Information needs to be received, processed to derive useful information, stored and

retrieved, and communicated to others. With digital information, electronic signals may need magnification when they are received from a great distance, and when they should be presented by public address to a large audience. When there is a large volume of signals and symbols to handle, it becomes necessary to have infor- mation processing machines to handle them. Modern information equipment, com- puters, and networks are built on electronic components and devices.

The beginning of electronics was based on the observation that a hot metal fila- ment has the tendency to eject electrons, especially toward a positively charged anode, in a phenomenon that is called “thermionic emission of electrons.” When the filament is placed in air, it has a tendency to burn out after a while, and the ejected electrons meet resistance from air molecules. When the hot filament is encased in a vacuum tube, it is called the cathode tube and can have a longer life, and the electrons flow as

a straight line to the anode, which is a cool metallic plate. John Ambrose Fleming invented the first vacuum tube in 1904, which is now called the diode. Electrons can pass from the heated filament cathode to the cool plate anode, but the flow of elec- trons is not reversed when the voltage difference is reversed, as the plate is not heated and cannot emit electrons. Thus, the diode can be used for a number of functions, such as “rectification” to convert alternating currents AC into direct currents DC. It can also be used as a logic gate to do logical and arithmetic operations.

269 The more elaborate triode was invented by Lee de Forest in 1907, who added

7.4 INFORMATION TOOLS

a wire grid between the cathode and the anode. The flow of electrons from the nega- tively charged cathode to the positively charged anode can be controlled by adjust- ing the voltage on the grid. When the grid is negatively charged, some of the electron flow from the filament would be repelled and diminished; a positive charge on the grid would lead to a higher flow. So if an alternating signal is placed on the grid, the flow of electrons from the cathode to the anode would be an amplified alternating signal. The triode found usage in switching a signal on or off, as well as in amplifying signals in music for microphones and loudspeakers, and in the long distance transmission of signals. The initial applications were driven by military and government needs, followed by consumer needs when simpler devices that cost much less became available. In 1944, the ENIAC computer operated with 17,000 vacuum tubes and weighed 27,000 kg; the electric power requirements and periodic replacement of burnt tubes made it unsuitable for many practical applications. A great incentive for miniaturization was created.

The semiconductor arrived in 1947, and was based on entirely different princi- ples than hot wires emitting electrons in vacuum tubes. The electrical properties of most materials can be classified as either conductors like copper, or as insulators like rubber. There is a class of elements with conductivities that depend on impurities and external conditions. The middle of the periodic table has these elements:

Group III

IV V

First row Boron Carbon

Nitrogen

Second row Aluminum Silicon

Phosphorous

Third row Gallium Germanium Arsenic Fourth row

The group IV elements carbon, silicon, and germanium are insulators when they are very pure, but they become conductive when they contain a small amount of impurities. Germanium with contaminants from group V are donors of electrons, which become mobile and carry electricity; but contaminants from group III are donors of holes or deficiencies of electrons, which can also be mobile and carry electricity.

The invention of the transistor was made at Bell Laboratories by John Bardeen, William Shockley, and Walter Brattain in 1947, which was based on the element germanium. Bardeen and Shockley added small amounts of antimony to germanium at the level of 10 ppm, and discovered that the conductivity of germa- nium increased 200 times. This is called “doping,” and the addition of electron-rich group V elements give the N-type semiconductor, and the addition of electron-poor group III elements give the P-type semiconductor. The conductivity is also very dependent on the surrounding electrical field, which gives rise to the method called “field effect” to control conductivity. The team also discovered the point-contact method, by using “cat’s whisker,” which is a wire contact touching the germanium surface that injects electrons or holes, and thus controls electron flow. It is now pos- sible to do most of the work formerly done by the vacuum tube with the transistor, which is much smaller in size and weight, uses lower voltage and power, can be kept at room temperature, has a longer life, and can be mass produced in a factory.

270 CHAPTER 7 INFORMATION

The transistor is often mentioned as the greatest invention of the twentieth century, for which Bardeen, Shockley, and Brattain won the 1956 Nobel Prize in Physics. In 1972, Bardeen became the only person to win two Nobel Prizes in Physics when

he shared the prize with Cooper and Schrieffer for a theory on superconductivity. The first silicon transistor was the next important invention, made by Gordon Teal in 1954, based on the inexhaustible and inexpensive element of silicon. This was the beginning of the phenomenon called “Silicon Valley,” of start-up companies creat- ing irresistible products and young pioneers becoming billionaires.

The task of amplifying sound needs an electronic circuit, which consists of vacuum tubes or transistors connected to the input and the output signals, as well as many components including resistors, inductors, and capacitors. Resistors are pas- sive elements that diminish electric flow, and are often made of carbon powder mixed with ceramic powder and resin; capacitors are also passive elements that store electricity, and are made of metal plates sandwiched with a dielectric insulator such as paper and glass; and the connecting wires are made of copper. The manu- facturing of an electronic circuit requires the assembly of hundreds of thousands of tubes or transistors as well as passive elements, which requires a great deal of hand labor and time, and is subject to errors in an assembly line.

The integrated circuit, or IC, was invented independently in 1958 by Jack Kilby of Texas Instruments based on germanium, and by Robert Noyce of Fairchild Semi- conductor based on silicon. Instead of using copper as conductors and ceramics as insu- lators, the integrated circuit is made entirely of a single block or chip of silicon that has different regions doped by different N- or P-type material. The electronic circuit is designed on a piece of paper, and then photolithographed or printed onto the silicon surface like a photograph. The idea was a compromise: silicon is not as good a conduc- tor as copper, and not as bad an insulator as ceramic, but the benefits of integration were so great that it overcame these objections. Speed increased and power consump- tion dropped since the elements are very small and are located very near each other. A chip can be a few square millimeters in area, with up to a million transistors per square millimeter. Robert Noyce went on to found the Intel Corporation together with Gordon Moore, but Noyce died in 1990. Jack Kilby received the 2000 Nobel Prize in Physics, and he noted the crucial role of Robert Noyce in his acceptance speech.

VLSI is very large-scale integration, which combines thousands of transistors into a single chip. The microprocessor incorporates most or all of the functions of a central processing unit (CPU) in a computer, placed on a single integrated circuit. They were first made by Noyce and Moore in 1971 for electronic calculators. Forty years later, the company Nvidia has a computer that uses 1.4 billion transistors for logic. Progress was so rapid that it inspired Moore’s Law: that the long-term trend of progress in electronics is to double the capabilities of electronic devices every 18–

24 months, including processing speed, memory capacity, and cost per unit of mem- ory. There are many forecasts that there is a limit to Moore’s Law, and that sooner or later this torrid pace will have to slow down.