A transistor is a semiconductor device used to amplify or switch electrical signals and electric power. It is one of the basic building blocks of modern electronics. It is composed of semiconductor material, usually with at least three terminals for connection to an electronic circuit. A voltage or Electric current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Some transistors are packaged individually, but many more in miniature form are found embedded in integrated circuits. Because transistors are the key active components in practically all modern electronics, many people consider them one of the 20th century's greatest inventions.
Physicist Julius Edgar Lilienfeld proposed the concept of a field-effect transistor (FET) in 1926, but it was not possible to construct a working device at that time. The first working device was a point-contact transistor invented in 1947 by physicists John Bardeen, Walter Brattain, and William Shockley at Bell Labs; the three shared the 1956 Nobel Prize in Physics for their achievement. The most widely used type of transistor is the metal–oxide–semiconductor field-effect transistor (MOSFET), invented by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959. Transistors revolutionized the field of electronics and paved the way for smaller and cheaper radio receiver, , , and other electronic devices.
Most transistors are made from very pure silicon, and some from germanium, but certain other semiconductor materials are sometimes used. A transistor may have only one kind of charge carrier in a field-effect transistor, or may have two kinds of charge carriers in bipolar junction transistor devices. Compared with the vacuum tube, transistors are generally smaller and require less power to operate. Certain vacuum tubes have advantages over transistors at very high operating frequencies or high operating voltages, such as Traveling-wave tubes and . Many types of transistors are made to standardized specifications by multiple manufacturers.
Shockley's team initially attempted to build a field-effect transistor (FET) by trying to modulate the conductivity of a semiconductor, but was unsuccessful, mainly due to problems with the surface states, the dangling bond, and the germanium and copper compound materials. Trying to understand the mysterious reasons behind this failure led them instead to invent the bipolar point-contact and junction transistors.
In 1948, the point-contact transistor was independently invented by physicists Herbert Mataré and Heinrich Welker while working at the Compagnie des Freins et Signaux Westinghouse, a Westinghouse subsidiary in Paris. Mataré had previous experience in developing Crystal detector from silicon and germanium in the German radar effort during World War II. With this knowledge, he began researching the phenomenon of "interference" in 1947. By June 1948, witnessing currents flowing through point-contacts, he produced consistent results using samples of germanium produced by Welker, similar to what Bardeen and Brattain had accomplished earlier in December 1947. Realizing that Bell Labs' scientists had already invented the transistor, the company rushed to get its "transistron" into production for amplified use in France's telephone network, filing his first transistor patent application on August 13, 1948.
The first bipolar junction transistors were invented by Bell Labs' William Shockley, who applied for patent (2,569,347) on June 26, 1948. On April 12, 1950, Bell Labs chemists Gordon Teal and Morgan Sparks successfully produced a working bipolar NPN junction amplifying germanium transistor. Bell announced the discovery of this new "sandwich" transistor in a press release on July 4, 1951.
The first high-frequency transistor was the surface-barrier germanium transistor developed by Philco in 1953, capable of operating at frequencies up to . They were made by etching depressions into an n-type germanium base from both sides with jets of indium(III) sulfate until it was a few ten-thousandths of an inch thick. Indium electroplated into the depressions formed the collector and emitter. The Wall Street Journal, December 4, 1953, page 4, Article "Philco Claims Its Transistor Outperforms Others Now In Use"Electronics magazine, January 1954, Article "Electroplated Transistors Announced"
AT&T first used transistors in telecommunications equipment in the No. 4A Toll Crossbar Switching System in 1953, for selecting trunk circuits from routing information encoded on translator cards.P. Mallery, Transistors and Their Circuits in the 4A Toll Crossbar Switching System, AIEE Transactions, September 1953, p.388 Its predecessor, the Western Electric No. 3A phototransistor, read the mechanical encoding from punched metal cards.
The first prototype pocket transistor radio was shown by INTERMETALL, a company founded by Herbert Mataré in 1952, at the Internationale Funkausstellung Düsseldorf from August 29 to September 6, 1953.1953 Foreign Commerce Weekly; Volume 49; pp.23 The first production-model pocket transistor radio was the Regency TR-1, released in October 1954. Produced as a joint venture between the Regency Division of Industrial Development Engineering Associates, I.D.E.A. and Texas Instruments of Dallas, Texas, the TR-1 was manufactured in Indianapolis, Indiana. It was a near pocket-sized radio with four transistors and one germanium diode. The industrial design was outsourced to the Chicago firm of Painter, Teague and Petertil. It was initially released in one of six colours: black, ivory, mandarin red, cloud grey, mahogany and olive green. Other colours shortly followed.
The first production all-transistor car radio was developed by Chrysler and Philco corporations and was announced in the April 28, 1955, edition of The Wall Street Journal. Chrysler made the Mopar model 914HR available as an option starting in fall 1955 for its new line of 1956 Chrysler and Imperial cars, which reached dealership showrooms on October 21, 1955.Wall Street Journal, "Chrysler Promises Car Radio With Transistors Instead of Tubes in '56", April 28, 1955, page 1
The Sony TR-63, released in 1957, was the first mass-produced transistor radio, leading to the widespread adoption of transistor radios. Seven million TR-63s were sold worldwide by the mid-1960s. Sony's success with transistor radios led to transistors replacing vacuum tubes as the dominant electronic technology in the late 1950s.
The first working silicon transistor was developed at Bell Labs on January 26, 1954, by Morris Tanenbaum. The first production commercial silicon transistor was announced by Texas Instruments in May 1954. This was the work of Gordon Teal, an expert in growing crystals of high purity, who had previously worked at Bell Labs.Chelikowski, J. (2004) "Introduction: Silicon in all its Forms", p. 1 in Silicon: evolution and future of a technology. P. Siffert and E. F. Krimmel (eds.). Springer, .McFarland, Grant (2006) Microprocessor design: a practical guide from design planning to manufacturing. McGraw-Hill Professional. p. 10. .
In 1945 JFET was patented by Heinrich Welker. Following Shockley's theoretical treatment on JFET in 1952, a working practical JFET was made in 1953 by George C. Dacey and Ian M. Ross.
In 1948, Bardeen patented the progenitor of MOSFET, an insulated-gate FET (IGFET) with an inversion layer. Bardeen's patent, and the concept of an inversion layer, forms the basis of CMOS technology today.
In 1957, Bell Labs engineer Mohamed Atalla proposed a new method of semiconductor device fabrication: coating a silicon wafer with an insulating layer of silicon oxide so electricity could overcome the surface state and reliably penetrate to the semiconducting silicon below. The process, known as surface passivation, became critical to the semiconductor industry, as it enabled the mass-production of silicon integrated circuits. Building on the method, he developed the metal–oxide–semiconductor (MOS) process, and proposed that it could be used to build the first working silicon FET.
Atalla and his Korean colleague Dawon Kahng developed the metal–oxide–semiconductor field-effect transistor (MOSFET), or MOS transistor, in 1959, the first transistor that could be miniaturized and mass-produced for a wide range of uses. In a self-aligned CMOS process, a transistor is formed wherever the gate layer (polysilicon or metal) crosses a diffusion layer. With its MOSFET scaling, much lower power consumption, and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuits, allowing the integration of more than 10,000 transistors in a single IC.
CMOS (complementary MOSFET) was invented by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor in 1963. The first report of a floating-gate MOSFET was made by Dawon Kahng and Simon Sze in 1967.D. Kahng and S. M. Sze, "A floating gate and its application to memory devices", The Bell System Technical Journal, vol. 46, no. 4, 1967, pp. 1288–1295 A double-gate MOSFET was first demonstrated in 1984 by Electrotechnical Laboratory researchers Toshihiro Sekigawa and Yutaka Hayashi. FinFET (fin field-effect transistor), a type of 3D non-planar Multigate device MOSFET, originated from the research of Digh Hisamoto and his team at Hitachi in 1989.
The invention of the first transistor at Bell Labs was named an IEEE Milestone in 2009. Other Milestones include the inventions of the junction transistor in 1948 and the MOSFET in 1959.
The MOSFET is by far the most widely used transistor, in applications ranging from and electronics to communications technology such as . It has been considered the most important transistor, possibly the most important invention in electronics, and the device that enabled modern electronics. It has been the basis of modern digital electronics since the late 20th century, paving the way for the digital age. The US Patent and Trademark Office calls it a "groundbreaking invention that transformed life and culture around the world". Its ability to be mass production by a highly automated process (semiconductor device fabrication), from relatively basic materials, allows astonishingly low per-transistor costs. MOSFETs are the most numerously produced artificial objects in history, with more than 13 sextillion manufactured by 2018.
Although several companies each produce over a billion individually packaged (known as discrete) MOS transistors every year, FETs/MOSFETs: Smaller apps push up surface-mount supply. globalsources.com (April 18, 2007) the vast majority are produced in integrated circuits (also known as ICs, microchips, or simply chips), along with , , and other electronic components, to produce complete electronic circuits. A logic gate consists of up to about 20 transistors, whereas an advanced microprocessor, as of 2022, may contain as many as 57 billion MOSFETs. Transistors are often organized into logic gates in microprocessors to perform computation.
The transistor's low cost, flexibility and reliability have made it ubiquitous. Transistorized mechatronics circuits have replaced cam timer in controlling appliances and machinery. It is often easier and cheaper to use a standard microcontroller and write a computer program to carry out a control function than to design an equivalent mechanical system.
There are two types of transistors, with slight differences in how they are used:
The top image in this section represents a typical bipolar transistor in a circuit. A charge flows between emitter and collector terminals depending on the current in the base. Because the base and emitter connections behave like a semiconductor diode, a voltage drop develops between them. The amount of this drop, determined by the transistor's material, is referred to as VBE. (Base Emitter Voltage)
In a switching circuit, the goal is to simulate, as near as possible, the ideal switch having the properties of an open circuit when off, the short circuit when on, and an instantaneous transition between the two states. Parameters are chosen such that the "off" output is limited to leakage currents too small to affect connected circuitry, the resistance of the transistor in the "on" state is too small to affect circuitry, and the transition between the two states is fast enough not to have a detrimental effect.
In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the base voltage rises, the emitter and collector currents rise exponentially. The collector voltage drops because of reduced resistance from the collector to the emitter. If the voltage difference between the collector and emitter were zero (or near zero), the collector current would be limited only by the load resistance (light bulb) and the supply voltage. This is called saturation because the current is flowing from collector to emitter freely. When saturated, the switch is said to be on.
The use of bipolar transistors for switching applications requires biasing the transistor so that it operates between its cut-off region in the off-state and the saturation region ( on). This requires sufficient base drive current. As the transistor provides current gain, it facilitates the switching of a relatively large current in the collector by a much smaller current into the base terminal. The ratio of these currents varies depending on the type of transistor, and even for a particular type, varies depending on the collector current. In the example of a light-switch circuit, as shown, the resistor is chosen to provide enough base current to ensure the transistor is saturated. The base resistor value is calculated from the supply voltage, transistor C-E junction voltage drop, collector current, and amplification factor beta.
Various configurations of single transistor amplifiers are possible, with some providing current gain, some voltage gain, and some both.
From to , vast numbers of products include amplifiers for sound reproduction, Transmitter, and signal processing. The first discrete-transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved.
Modern transistor audio amplifiers of up to a few hundred are common and relatively inexpensive.
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Transistors are categorized by
Hence, a particular transistor may be described as silicon, surface-mount, BJT, NPN, low-power, high-frequency switch.
In a FET, the drain-to-source current flows via a conducting channel that connects the source region to the drain region. The conductivity is varied by the electric field that is produced when a voltage is applied between the gate and source terminals, hence the current flowing between the drain and source is controlled by the voltage applied between the gate and source. As the gate–source voltage () is increased, the drain–source current () increases exponentially for below threshold, and then at a roughly quadratic rate: (, where is the threshold voltage at which drain current begins) in the "space charge" region above threshold. A quadratic behavior is not observed in modern devices, for example, at the 65 nm technology node.
For low noise at narrow bandwidth, the higher input resistance of the FET is advantageous.
FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET). The IGFET is more commonly known as a metal–oxide–semiconductor FET (MOSFET), reflecting its original construction from layers of metal (the gate), oxide (the insulation), and semiconductor. Unlike IGFETs, the JFET gate forms a p–n diode with the channel which lies between the source and drains. Functionally, this makes the n-channel JFET the solid-state equivalent of the vacuum tube triode which, similarly, forms a diode between its Control grid and cathode. Also, both devices operate in the depletion-mode, they both have a high input impedance, and they both conduct current under the control of an input voltage.
Metal–semiconductor FETs () are JFETs in which the Reverse-biased p–n junction is replaced by a metal–semiconductor junction. These, and the HEMTs (high-electron-mobility transistors, or HFETs), in which a two-dimensional electron gas with very high carrier mobility is used for charge transport, are especially suitable for use at very high frequencies (several GHz).
FETs are further divided into depletion-mode and enhancement-mode types, depending on whether the channel is turned on or off with zero gate-to-source voltage. For enhancement mode, the channel is off at zero bias, and a gate potential can "enhance" the conduction. For the depletion mode, the channel is on at zero bias, and a gate potential (of the opposite polarity) can "deplete" the channel, reducing conduction. For either mode, a more positive gate voltage corresponds to a higher current for n-channel devices and a lower current for p-channel devices. Nearly all JFETs are depletion-mode because the diode junctions would forward bias and conduct if they were enhancement-mode devices, while most IGFETs are enhancement-mode types.
BJTs have three terminals, corresponding to the three layers of semiconductor—an emitter, a base, and a collector. They are useful in because the currents at the emitter and collector are controllable by a relatively small base current. In an n–p–n transistor operating in the active region, the emitter-base junction is forward-biased ( and electron hole recombine at the junction), and the base-collector junction is reverse-biased (electrons and holes are formed at, and move away from, the junction), and electrons are injected into the base region. Because the base is narrow, most of these electrons will diffuse into the reverse-biased base-collector junction and be swept into the collector; perhaps one-hundredth of the electrons will recombine in the base, which is the dominant mechanism in the base current. As well, as the base is lightly doped (in comparison to the emitter and collector regions), recombination rates are low, permitting more carriers to diffuse across the base region. By controlling the number of electrons that can leave the base, the number of electrons entering the collector can be controlled. Collector current is approximately β (common-emitter current gain) times the base current. It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for high-power applications.
Unlike the field-effect transistor (see below), the BJT is a low-input-impedance device. Also, as the base-emitter voltage ( VBE) is increased the base-emitter current and hence the collector-emitter current ( ICE) increase exponentially according to the Shockley diode model and the Ebers-Moll model. Because of this exponential relationship, the BJT has a higher transconductance than the FET.
Bipolar transistors can be made to conduct by exposure to light because the absorption of photons in the base region generates a photocurrent that acts as a base current; the collector current is approximately β times the photocurrent. Devices designed for this purpose have a transparent window in the package and are called .
Military part numbers sometimes are assigned their codes, such as the British Military CV Naming System.
Manufacturers buying large numbers of similar parts may have them supplied with "house numbers", identifying a particular purchasing specification and not necessarily a device with a standardized registered number. For example, an HP part 1854,0053 is a (JEDEC) 2N2218 transistor which is also assigned the CV number: CV7763
As older "through-hole" transistors are given surface-mount packaged counterparts, they tend to be assigned many different part numbers because manufacturers have their systems to cope with the variety in pinout arrangements and options for dual or matched n–p–n + p–n–p devices in one pack. So even when the original device (such as a 2N3904) may have been assigned by a standards authority, and well known by engineers over the years, the new versions are far from standardized in their naming.
The first BJTs were made from germanium (Ge). Silicon (Si) types currently predominate but certain advanced microwave and high-performance versions now employ the compound semiconductor material gallium arsenide (GaAs) and the semiconductor alloy silicon-germanium (SiGe). Single-element semiconductor material (Ge and Si) is described as elemental.
Rough parameters for the most common semiconductor materials used to make transistors are given in the adjacent table. These parameters will vary with an increase in temperature, electric field, impurity level, strain, and sundry other factors.
The junction forward voltage is the voltage applied to the emitter-base junction of a BJT to make the base conduct a specified current. The current increases exponentially as the junction forward voltage is increased. The values given in the table are typical for a current of 1 mA (the same values apply to semiconductor diodes). The lower the junction forward voltage the better, as this means that less power is required to "drive" the transistor. The junction forward voltage for a given current decreases with an increase in temperature. For a typical silicon junction, the change is −2.1 mV/°C. In some circuits special compensating elements () must be used to compensate for such changes.
The density of mobile carriers in the channel of a MOSFET is a function of the electric field forming the channel and of various other phenomena such as the impurity level in the channel. Some impurities, called dopants, are introduced deliberately in making a MOSFET, to control the MOSFET electrical behavior.
The electron mobility and hole mobility columns show the average speed that electrons and holes diffuse through the semiconductor material with an electric field of 1 volt per meter applied across the material. In general, the higher the electron mobility the faster the transistor can operate. The table indicates that Ge is a better material than Si in this respect. However, Ge has four major shortcomings compared to silicon and gallium arsenide:
Maximum junction temperature values represent a cross-section taken from various manufacturers' datasheets. This temperature should not be exceeded or the transistor may be damaged.
Al–Si junction refers to the high-speed (aluminum-silicon) metal–semiconductor barrier diode, commonly known as a Schottky diode. This is included in the table because some silicon power IGFETs have a parasitic reverse Schottky diode formed between the source and drain as part of the fabrication process. This diode can be a nuisance, but sometimes it is used in the circuit.
Transistors come in many different semiconductor packages (see image). The two main categories are through-hole (or leaded), and surface-mount, also known as surface-mount device (SMD). The ball grid array (BGA) is the latest surface-mount package. It has solder "balls" on the underside in place of leads. Because they are smaller and have shorter interconnections, SMDs have better high-frequency characteristics but lower power ratings.
Transistor packages are made of glass, metal, ceramic, or plastic. The package often dictates the power rating and frequency characteristics. Power transistors have larger packages that can be clamped to for enhanced cooling. Additionally, most power transistors have the collector or drain physically connected to the metal enclosure. At the other extreme, some surface-mount microwave transistors are as small as grains of sand.
Often a given transistor type is available in several packages. Transistor packages are mainly standardized, but the assignment of a transistor's functions to the terminals is not: other transistor types can assign other functions to the package's terminals. Even for the same transistor type the terminal assignment can vary (normally indicated by a suffix letter to the part number, q.e. BC212L and BC212K).
Nowadays most transistors come in a wide range of SMT packages. In comparison, the list of available through-hole packages is relatively small. Here is a short list of the most common through-hole transistors packages in alphabetical order:
ATV, E-line, MRT, HRT, SC-43, SC-72, TO-3, TO-18, TO-39, TO-92, TO-126, TO220, TO247, TO251, TO262, ZTX851.
Unpackaged transistor chips (die) may be assembled into hybrid devices. The IBM SLT module of the 1960s is one example of such a hybrid circuit module using glass passivated transistor (and diode) die. Other packaging techniques for discrete transistors as chips include direct chip attach (DCA) and chip-on-board (COB).
Usage of MOSFETs and BJTs
Other transistor types
Device identification
Joint Electron Device Engineering Council (JEDEC)
+ JEDEC prefix table two-terminal device, such as diodes three-terminal device, such as transistors or single-gate field-effect transistors four-terminal device, such as dual-gate field-effect transistors
Japanese Industrial Standard (JIS)
+ JIS transistor prefix table high-frequency p–n–p BJT audio-frequency p–n–p BJT high-frequency n–p–n BJT audio-frequency n–p–n BJT P-channel FET (both JFET and MOSFET) N-channel FET (both JFET and MOSFET)
European Electronic Component Manufacturers Association (EECA)
+ EECA transistor prefix table Datasheet Datasheet Datasheet Datasheet Datasheet Datasheet Datasheet Datasheet
Proprietary
Naming problems
Construction
Semiconductor material
+ Semiconductor material characteristics
Because the electron mobility is higher than the hole mobility for all semiconductor materials, a given bipolar n–p–n transistor tends to be swifter than an equivalent p–n–p transistor. GaAs has the highest electron mobility of the three semiconductors. It is for this reason that GaAs is used in high-frequency applications. A relatively recent FET development, the high-electron-mobility transistor (HEMT), has a heterojunction (junction between different semiconductor materials) of aluminium gallium arsenide (AlGaAs)-gallium arsenide (GaAs) which has twice the electron mobility of a GaAs-metal barrier junction. Because of their high speed and low noise, HEMTs are used in satellite receivers working at frequencies around 12 GHz. HEMTs based on gallium nitride and aluminum gallium nitride (AlGaN/GaN HEMTs) provide still higher electron mobility and are being developed for various applications.
Packaging
Flexible transistors
See also
Further reading
External links
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