Advantages of Transistor

 Lower cost and smaller in size.

 Smaller mechanical sensitivity.
 Low operating voltage.
 Extremely long life.
 No power consumption.
 Fast switching.
 Better efficiency circuits can be developed.
 Used to develop a single integrated circuit.

Limitations of Transistors
Transistors have a few limitations, and they are as follows:

 Transistors lack higher electron mobility.

 Transistors can be easily damaged when electrical and thermal events arise. For example,
electrostatic discharge in handling.
 Transistors are affected by cosmic rays and radiation.

Frequently Asked Questions on Transistor

Q1

Which region of the transistor is lightly doped?

The base of the transistor is lightly doped.

Q2

How is the emitter region of the transistor different from the collector region?

The emitter is more heavily doped than the collector.

Q3

What is the normal biasing of the diodes of the transistor?

The emitter-base junction is forward-biased, and the collector-base junction is reversed-biased.

Q4

How many depletion regions does a transistor have?

The transistor has two depletion regions.

Transistor

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From Wikipedia, the free encyclopedia

For other uses, see Transistor (disambiguation).

 Size comparison of bipolar junction transistor packages, including

(from left to right): SOT-23, TO-92, TO-126, and TO-3 Metal–oxide–

semiconductor field-effect transistor (MOSFET), showing gate (G), body (B), source (S) and drain (D)
terminals. The gate is separated from the body by an insulating layer (white).

A transistor is a semiconductor device used to amplify or switch electrical signals and power. It
is one of the basic building blocks of modern electronics.[1] It is composed of semiconductor
material, usually with at least three terminals for connection to an electronic circuit. A voltage or
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.[2]

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.[3] 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.[4] 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.[5][6][7] Transistors revolutionized the field of electronics and paved the way for smaller and
cheaper radios, calculators, computers, 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 Gyrotrons.
Many types of transistors are made to standardized specifications by multiple manufacturers.

History
Main article: History of the transistor

Julius Edgar Lilienfeld proposed the concept of a field-effect

transistor in 1925.

The thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and
long-distance telephony. The triode, however, was a fragile device that consumed a substantial
amount of power. In 1909, physicist William Eccles discovered the crystal diode oscillator.[8]
Physicist Julius Edgar Lilienfeld filed a patent for a field-effect transistor (FET) in Canada in
1925,[9] intended as a solid-state replacement for the triode.[10][11] He filed identical patents in the
United States in 1926[12] and 1928.[13][14] However, he did not publish any research articles about
his devices nor did his patents cite any specific examples of a working prototype. Because the
production of high-quality semiconductor materials was still decades away, Lilienfeld's solid-
state amplifier ideas would not have found practical use in the 1920s and 1930s, even if such a
device had been built.[15] In 1934, inventor Oskar Heil patented a similar device in Europe.[16]

Bipolar transistors
Further information: Point-contact transistor and Bipolar junction transistor

John Bardeen, William Shockley, and Walter Brattain at Bell Labs in

1948; Bardeen and Brattain invented the point-contact transistor in 1947 and Shockley invented the
bipolar junction transistor in 1948. A replica of the first working

transistor, a point-contact transistor invented in 1947 Herbert

Mataré (pictured in 1950) independently invented a point-contact transistor in June 1948.

A Philco surface-barrier transistor developed and produced in 1953

From November 17 to December 23, 1947, John Bardeen and Walter Brattain at AT&T's Bell
Labs in Murray Hill, New Jersey, performed experiments and observed that when two gold point
contacts were applied to a crystal of germanium, a signal was produced with the output power
greater than the input.[17] Solid State Physics Group leader William Shockley saw the potential in
this, and over the next few months worked to greatly expand the knowledge of semiconductors.
The term transistor was coined by John R. Pierce as a contraction of the term transresistance.[18]
[19][20]
According to Lillian Hoddeson and Vicki Daitch, Shockley proposed that Bell Labs' first
patent for a transistor should be based on the field-effect and that he be named as the inventor.
Having unearthed Lilienfeld's patents that went into obscurity years earlier, lawyers at Bell Labs
advised against Shockley's proposal because the idea of a field-effect transistor that used an
electric field as a "grid" was not new. Instead, what Bardeen, Brattain, and Shockley invented in
1947 was the first point-contact transistor.[15] To acknowledge this accomplishment, Shockley,
Bardeen and Brattain jointly received the 1956 Nobel Prize in Physics "for their researches on
semiconductors and their discovery of the transistor effect".[21][22]

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.[23][24]

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
rectifiers 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.[25][26][27]

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.[28][29]

The first high-frequency transistor was the surface-barrier germanium transistor developed by
Philco in 1953, capable of operating at frequencies up to 60 MHz.[30] 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.[31][32]

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.[33] 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.[34][35] The first production-model pocket transistor radio was the Regency TR-
1, released in October 1954.[22] 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.[36][37][38]

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.[39][40]

The Sony TR-63, released in 1957, was the first mass-produced transistor radio, leading to the
widespread adoption of transistor radios.[41] Seven million TR-63s were sold worldwide by the
mid-1960s.[42] Sony's success with transistor radios led to transistors replacing vacuum tubes as
the dominant electronic technology in the late 1950s.[43]

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.[44][45][46]

Field effect transistors

Main article: Field-effect transistor

The basic principle of the field-effect transistor (FET) was first proposed by physicist Julius
Edgar Lilienfeld when he filed a patent for a device similar to MESFET in 1926, and for an
insulated-gate field-effect transistor in 1928.[11][47] The FET concept was later also theorized by
engineer Oskar Heil in the 1930s and by William Shockley in the 1940s.

In 1945 JFET was patented by Heinrich Welker.[48] 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.[49]

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.[50]

MOSFET (MOS transistor)

Main article: MOSFET
Mohamed Atalla (left) and Dawon Kahng (right) invented the MOSFET (MOS transistor) at Bell Labs in
1959.

In the early years of the semiconductor industry, companies focused on the junction transistor, a
relatively bulky device that was difficult to mass-produce, limiting it to several specialized
applications. Field-effect transistors (FETs) were theorized as potential alternatives, but
researchers could not get them to work properly, largely due to the surface state barrier that
prevented the external electric field from penetrating the material.[51]

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.[52][53][54] Building on the method, he
developed the metal–oxide–semiconductor (MOS) process,[52] 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,[52][5][6] the first transistor that could be
miniaturized and mass-produced for a wide range of uses.[51] In a self-aligned CMOS process, a
transistor is formed wherever the gate layer (polysilicon or metal) crosses a diffusion layer. [55]: p.1
(see Fig. 1.1)
With its high scalability,[56] much lower power consumption, and higher density than
bipolar junction transistors,[57] the MOSFET made it possible to build high-density integrated
circuits,[7] allowing the integration of more than 10,000 transistors in a single IC.[58]

CMOS (complementary MOS) was invented by Chih-Tang Sah and Frank Wanlass at Fairchild
Semiconductor in 1963.[59] The first report of a floating-gate MOSFET was made by Dawon
Kahng and Simon Sze in 1967.[60] A double-gate MOSFET was first demonstrated in 1984 by
Electrotechnical Laboratory researchers Toshihiro Sekigawa and Yutaka Hayashi.[61][62] FinFET
(fin field-effect transistor), a type of 3D non-planar multi-gate MOSFET, originated from the
research of Digh Hisamoto and his team at Hitachi Central Research Laboratory in 1989.[63][64]

Importance
Because transistors are the key active components in practically all modern electronics, many
people consider them one of the 20th century's greatest inventions.[2]

The invention of the first transistor at Bell Labs was named an IEEE Milestone in 2009.[65] Other
Milestones include the inventions of the junction transistor in 1948 and the MOSFET in 1959.[66]

The MOSFET is by far the most widely used transistor, in applications ranging from computers
and electronics[53] to communications technology such as smartphones.[67] It has been considered
the most important transistor,[68] possibly the most important invention in electronics,[69] and the
device that enabled modern electronics.[70] It has been the basis of modern digital electronics
since the late 20th century, paving the way for the digital age.[71] The US Patent and Trademark
Office calls it a "groundbreaking invention that transformed life and culture around the world". [67]
Its ability to be mass-produced 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.[72]

Although several companies each produce over a billion individually packaged (known as
discrete) MOS transistors every year,[73] the vast majority are produced in integrated circuits
(also known as ICs, microchips, or simply chips), along with diodes, resistors, capacitors 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.[74] Transistors are often organized into logic gates in microprocessors to
perform computation.[75]

The transistor's low cost, flexibility and reliability have made it ubiquitous. Transistorized
mechatronic circuits have replaced electromechanical devices 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.

Simplified operation

A simple circuit diagram showing the labels of an n–p–n bipolar

transistor
A transistor can use a small signal applied between one pair of its terminals to control a much
larger signal at another pair of terminals, a property called gain. It can produce a stronger output
signal, a voltage or current, proportional to a weaker input signal, acting as an amplifier. It can
also be used as an electrically controlled switch, where the amount of current is determined by
other circuit elements.[76]

There are two types of transistors, with slight differences in how they are used:

 A bipolar junction transistor (BJT) has terminals labeled base, collector and emitter. A small
current at the base terminal, flowing between the base and the emitter, can control or switch a
much larger current between the collector and emitter.

 A field-effect transistor (FET) has terminals labeled gate, source and drain. A voltage at the gate
can control a current between source and drain.[77]

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.[77]

Transistor as a switch

BJT used as an electronic switch in grounded-emitter configuration

Transistors are commonly used in digital circuits as electronic switches which can be either in an
"on" or "off" state, both for high-power applications such as switched-mode power supplies and
for low-power applications such as logic gates. Important parameters for this application include
the current switched, the voltage handled, and the switching speed, characterized by the rise and
fall times.[77]

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.[77]

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.[78]

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.[77] The base
resistor value is calculated from the supply voltage, transistor C-E junction voltage drop,
collector current, and amplification factor beta.[79]

Transistor as an amplifier

An amplifier circuit, a common-emitter configuration with a

voltage-divider bias circuit

The common-emitter amplifier is designed so that a small change in voltage (Vin) changes the
small current through the base of the transistor whose current amplification combined with the
properties of the circuit means that small swings in Vin produce large changes in Vout.[77]

Various configurations of single transistor amplifiers are possible, with some providing current
gain, some voltage gain, and some both.

From mobile phones to televisions, vast numbers of products include amplifiers for sound
reproduction, radio transmission, 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. [77]

Modern transistor audio amplifiers of up to a few hundred watts are common and relatively
inexpensive.
Comparison with vacuum tubes
Before transistors were developed, vacuum (electron) tubes (or in the UK "thermionic valves" or
just "valves") were the main active components in electronic equipment.

Advantages

The key advantages that have allowed transistors to replace vacuum tubes in most applications
are

 No cathode heater (which produces the characteristic orange glow of tubes), reducing power
consumption, eliminating delay as tube heaters warm up, and immune from cathode poisoning
and depletion.
 Very small size and weight, reducing equipment size.
 Large numbers of extremely small transistors can be manufactured as a single integrated circuit.
 Low operating voltages compatible with batteries of only a few cells.
 Circuits with greater energy efficiency are usually possible. For low-power applications (for
example, voltage amplification) in particular, energy consumption can be very much less than
for tubes.
 Complementary devices available, providing design flexibility including complementary-
symmetry circuits, not possible with vacuum tubes.
 Very low sensitivity to mechanical shock and vibration, providing physical ruggedness and
virtually eliminating shock-induced spurious signals (for example, microphonics in audio
applications).
 Not susceptible to breakage of a glass envelope, leakage, outgassing, and other physical
damage.

Limitations

Transistors may have the following limitations:

 They lack the higher electron mobility afforded by the vacuum of vacuum tubes, which is
desirable for high-power, high-frequency operation – such as that used in some over-the-air
television transmitters and in travelling wave tubes used as amplifiers in some satellites
 Transistors and other solid-state devices are susceptible to damage from very brief electrical
and thermal events, including electrostatic discharge in handling. Vacuum tubes are electrically
much more rugged.
 They are sensitive to radiation and cosmic rays (special radiation-hardened chips are used for
spacecraft devices).
 In audio applications, transistors lack the lower-harmonic distortion – the so-called tube sound –
which is characteristic of vacuum tubes, and is preferred by some.[80]