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MOS-FETs

Most of today's transistors are "MOS-FETs", or Metal Oxide Semiconductor Field Effect Transistors. They were developed mainly by Bell Labs, Fairchild Semiconductor, and hundreds of Silicon Valley, Japanese and other electronics companies.

СField-effect transistors are so named because a weak electrical signal coming in through one electrode creates an electrical field through the rest of the transistor. This field flips from positive to negative when the incoming signal does, and controls a second current traveling through the rest of theиtransistor. The field modulates the second current to mimic the first one

– but it can be substantially larger. How it works

On the bottom of the transistor is a U-shaped section (though it's flatter than a trueбА"U") of N-type semiconductor with an excess of electrons. In the center of the U is a section known as the "base" made of P-type (positively charged) semiconductor with too few electrons. (Actually, the N- and P-types can be reversed and the device will work in exactly the same way, except that holes, not electrons, would cause the current.)

Three electrodes are attached to the top of this semiconductor crystal: one to the middle positive section and one to each arm of the U. By applying a voltage to the electrodes on the U, current will flow through it. The side where the electrons come in is known as the source, and the side where the electrons come out is calledДthe drain.

If nothing else happens, current will flow from one side to the other. Due to the way electrons behave at the junction between N- and P-type semiconductors, however, the current won't flow particularly close to the base. It travels only through a thin channel down the middle of the U.

There's also an electrode attached to theИbase, a wedge of P-type semiconductor in the middle, separated from the rest of the transistor by a thin layer of metal-oxide such as silicon dioxide (which plays the role of an insulator). This electrode is called the "gate." The weak electrical signal we'd like to amplify is fed through the gate. If the charge coming through the gate is negative, it adds more electrons to the base. Since electrons repel each other, the electrons in the U move as far away from the base as possible. This creates a depletion zone around the base – a whole area where electrons cannot travel. The channel down the middle of the U through which current can flow becomes even thinner. Add enough negative charge to the base and the channel will pinch off completely, stopping all current. It's like stepping on a garden hose to stop the flow of water.

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(Earlier transistors controlled this depletion zone by making use of how electrons move when two semiconductor slabs are put next to each other, creating what is known as a P-N junction. In a MOS-FET, the P-N junction is replaced with metal-oxide, which turned out to be easier to mass produce in microchips.)

СNow imagine if the charge coming through the gate is positive. The

positive base attracts many electrons – suddenly the area around the base which used to be a no-man's-land opens up. The channel for current through the U becomes larger than it was originally and much more electricity can flow through.

Alternating charge on the base, therefore, changes how much current goes through the U. The incoming current can be used as a faucet to turn

current on or off as it moves through the rest of the transistor.

и On theбАother hand, the transistor can be used in a more complex

manner as well – as an amplifier. Current traveling through the U gets larger or smaller in perfect synch with the charge coming into the base, meaning it has the identical pattern as that original weak signal. And, since the second current is connected to a different voltage supply, it can be made to be larger. The current coming through the U is a perfect replica of the original, only amplified. The transistor is used this way for stereo amplification in speakers and microphones, as well as to boost telephone signals as they travel around the world.

Other transistor types: Д

Point-Contact Transistor; Junction ("Sandwich") Transistor.

Resources:

Footnote on Shockley

Shockley watched as Silicon Valley grew but could not seem to enter

The Promised Land he had envisioned. He never was able to make field effect transistors, while other companies designed, grew, and prospered. Fred

Seitz called Shockley "The Moses of Silicon Valley." И

The Way Things Work by David Macaulay; Van Nostrand's Scientific Encyclopedia; The Field Effect Transistor; Interview, Walter Brown, May 3, 1999

http://www.pbs.org

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THE HISTORY OF ELECTRIC MEASURING INSTRUMENTS

AND ACTIVE COMPONENTS

Society of Historical Metrology, Japan

Eiju Matsumoto

Abstract:

СPrecision electric meters are indispensable to the development of

technology in this age. The first electric measuring instruments, however, were physically impossible to transport, and were functionally inadequate for use in a laboratory. The measuring instruments of today have evolved into sturdy, easy-to-use instruments with higher performance, adopting new active components which have appeared one after another.

и After бАVolta's battery was invented in 1600, the first utilization of

(1) Practical electric measuring instrument: Weston moving-coil DC

ammeter: electromagnetic mechanism

electricity was in telegraphic communication. What kind of measuring instrument was required for telegraphic communication? Probably, neither voltage nor current needed to be measured regularly. Measurement was necessary only at times of failure or in preparation. In other words, a measuring instrument as an electric component was not independently used.

When the electric power industry began to develop in the second half of the 19th century, current and voltage needed to be measured regularly. One of the engineers who put the precision DC ammeter into practical use

voltage value read immediately fromДa scale. He used a permanent magnet for the DC meter, and realized the equal magnetic field in the coil moving portion. A square frame type coil, pivot supports, and two hair springs were then used, making a current pass through the coil. An indicator was attached to the tip of the coil.

was Edward Weston (1850-1936). He named the meter the Portable Instrument, as the electric meters until then could be used only in the laboratory, and could not be transported anywhere to make measurements.

Weston aimed at making a highly reliable infallible meter, rather

than a sensitive meter, which could be used by anybody, anywhere, with a И

In 1886 Weston completed a portable DC ammeter with an accuracy of 0.5%, and subsequently aimed at creating an ammeter for large currents and an AC meter. For that purpose, he invented stable resistance Manganin. In fact, the key component of the meter was a stable permanent magnet and the supporting mechanism of the pivot.

(2) The advent of the Fleming Valve and the prototype of AC measurement: Measurement of high-voltage-high frequency

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In 1892, J. A. Fleming (1849-1945), Edison's British adviser, became interested in the "Edison effect." Later, he became an adviser for the Marconi Telegraphy Co., searching for an application of chemical action for a wave detector to replace a coherer. It is said that he started his research because he remembered the "Edison effect," and attempted to carry out sup-

Сplementary examinations. In contrast to Edison’s method, he put a metal plate, then a cylinder into the electric bulb, naming the equipment an "Oscillation Valve." It was known as the "Valve," a device that lets the flow move in one direction only, because current flows in the cylinder only whenиa positive voltage is applied. Later, since the shape resembled the electric bulb, it was also known simply as a "Bulb."

E. Doyle and L. Chubb applied this valve to the measurement of high voltages. This was the first step in adopting the use of an active element in the voltmeter.бАThe valve was filled with mercury or rare gas, and for both the anode plate and the cathode plate, tungsten was used. The meter operated stably as a voltmeter in both cases.

(3) De Forest Audion (Audion Vacuum Tube) and BARUBORU (Vacuum Tube Voltmeter): High sensitivity measurement

Hoping first to improve the characteristics of the valve used in the wave detector, L. De Forest (1873-1961) also put a third electrode in the electric bulb. The electrode was made of a zigzag platinum line, and was put in between the filament and the plate. The effect was more than expected, and it turned out that plateДcurrentcould be controlled by the voltage applied to the grid.

The triode vacuum tube, called Audion, is categorized from present eyes, as a tube containing gas. It was filled with a small amount of gas. Argon and Cesium steam were injected with a low degree of vacuum first. The injection of gas was thought to improve detectionИsensitivity. However, when high voltage was applied to the tube, a flaw, causing an internal electric discharge, was found. Later, I. Langmuir of GE realized a tube with a long life and high power, using a high vacuum.

The vacuum-tube voltmeter incorporated this tube as an amplifier or a wave detector, being called a Valve-Voltmeter or Vacuum-Tube Voltmeter. In Japan it was uniquely called BARUBORU. The first vacuum-tube voltmeter was invented by E.B. Moullin of the University of Cambridge in 1922, and was put on the market as the product of the Cambridge Scientific Instrument Company. Several kinds of voltmeters were then manufactured, varying from an A-type voltmeter for AC and DC use, the technology of

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which was most fundamentally on the plate detector, to a B, D-type (AC), a C-type (double range), and a P-type (with a probe).

The scale of the BARUBORU of those days was not linear because the nonlinear nature of the tube appeared as it was.

(4) Challenge to Digital: High precision measurement

The dual slope analog-to-digital conversion circuit, developed in С1957, was an excellent circuit for measuring instruments. This circuit was

characterized by dramatically reducing the noise of the commercial frequency existing in the vicinity, and being capable of performing stable digital measurement. Rosewell Gilbert of Weston invented the circuit, but could not put it into practical use in those days, because the A/D converter assembled with tubes was as big as the drawer of a desk. Weston Corp, a prestigious company specializing in measurement, was absorbed by a company not specializing in measurement.

иIn the 1970s, when the price of semiconductors went down, the circuit was put into practical use for the first time. The size of the complicated electrical circuit was shrunk by the use of transistors and ICs.

In the 1980s especially, complicated electrical circuits became small and cheap and very reliable. The digital voltmeter uses many small electronic parts as supporting components, including resistors, capacitors, tran-

When mechanism parts, the tube, transistor, and A/D converter were developed, they were soon adopted to create the necessary measuring instruments. New technology requires not only invention, but also supporting technology to be incorporated in the measuring instruments, thus allowing the hardware to be realized. A measuring instrument will choose technology, and the technology that can satisfy the instrument will survive. Technology is useless if it is too early or too late. History chooses inventions and people, and so does the world of electric measuring instruments.

Tracing the history of the change in the quantity of production of electronic parts, one is occasionally able to see changes in industry and technology. For example, from around 1960, the tubes began to decrease in number, and on the other hand, semiconductor passive components, transistors, ICs, increased rapidly; making clear the change in technology.

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