In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical Semiconductor devices are Electronic components that exploit the electronic properties of Semiconductor materials principally Silicon, Germanium An electronic amplifier is a device for increasing the power and/or Amplitude of a signal. The transistor is the fundamental building block of computers, and all other modern electronic devices. A computer is a Machine that manipulates data according to a list of instructions. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical Some transistors are packaged individually but most are found in integrated circuits. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside
An electrical signal can be amplified by using a device that allows a small current or voltage to control the flow of a much larger current. Transistors are the basic devices providing control of this kind. Modern transistors are divided into two main categories: bipolar junction transistors (BJTs) and field effect transistors (FETs). A bipolar (junction transistor ( BJT) is a type of Transistor. The field-effect transistor (FET is a type of Transistor that relies on an Electric field to control the shape and hence the conductivity of a 'channel' Applying current in BJTs and voltage in FETs between the input and common terminals increases the conductivity between the common and output terminals, thereby controlling current flow between them. Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. The characteristics of a transistor depend on its type.
The term "transistor" originally referred to the point contact type, which saw very limited commercial application, being replaced by the much more practical bipolar junction types in the early 1950s. A point-contact transistor was the first type of solid-state electronic Transistor ever constructed A bipolar (junction transistor ( BJT) is a type of Transistor. Today's most widely used schematic symbol, like the term "transistor", originally referred to these long-obsolete devices. An electronic symbol is a Pictogram used to represent various Electrical and electronic devices (such as Wires batteries, Resistors 
In analog circuits, transistors are used in amplifiers, (direct current amplifiers, audio amplifiers, radio frequency amplifiers), and linear regulated power supplies. Analogue electronics (or analog in American English) are those electronic systems with a continuously Variable signal An electronic amplifier is a device for increasing the power and/or Amplitude of a signal. In electronics a linear regulator is a Voltage regulator based on an active device (such as a Bipolar junction transistor, Field effect transistor Transistors are also used in digital circuits where they function as electronic switches, but rarely as discrete devices, almost always being incorporated in monolithic Integrated Circuits. Digital electronics are Electronics systems that use Digital signals Digital electronics are representations of Boolean algebra also see A discrete device (or discrete component) is an Electronic component with just one Circuit element, either passive ( Resistor, Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Digital circuits include logic gates, random access memory (RAM), microprocessors, and digital signal processors (DSPs). A logic gate performs a logical operation on one or more logic inputs and produces a single logic output A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated A digital signal processor ( DSP or DSP micro) is a specialized Microprocessor designed specifically for Digital signal processing, generally
The first patent for the field-effect transistor principle was filed in Canada by Austrian-Hungarian physicist Julius Edgar Lilienfeld on October 22, 1925, but Lilienfeld did not publish any research articles about his devices, and they were ignored by industry. Julius Edgar Lilienfeld ( April 18, 1881 &ndash August 28, 1963) was an Austrian-Hungarian physicist In 1934 German physicist Dr. Oskar Heil patented another field-effect transistor. Oskar Heil (1908 in Langwieden / Rhineland-Palatinate – 1994 was a German electrical engineer and inventor There is no direct evidence that these devices were built, but later work in the 1990s shows that one of Lilienfeld's designs worked as described and gave substantial gain. Legal papers from the Bell Labs patent show that Shockley and Pearson had built operational versions from Lilienfeld's patents, yet they never referenced this work in any of their later research papers or historical articles
The transistor is considered by many to be the greatest invention of the twentieth century.  It is the key active component in practically all modern electronics. Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical Its importance in today's society rests on its ability to be mass produced using a highly automated process (fabrication) that achieves astonishingly low per-transistor costs. Mass production (also called flow production, repetitive flow production, series production, or serial production) is the production of Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic
Although several companies each produce over a billion individually-packaged (known as discrete) transistors every year , the vast majority of transistors produced are in integrated circuits (often abbreviated as IC and also called microchips or simply chips) along with diodes, resistors, capacitors and other electronic components to produce complete electronic circuits. Transistor-photoJPG|right|thumb|250px|Through-hole transistors (tape measure marked in centimetres]] Discrete transistors are Transistors that are individually packaged Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads A logic gate consists of about twenty transistors whereas an advanced microprocessor, as of 2006, can use as many as 1. A logic gate performs a logical operation on one or more logic inputs and produces a single logic output 7 billion transistors (MOSFETs). The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals  "About 60 million transistors were built this year  . . . for [each] man, woman, and child on Earth. " 
The transistor's low cost, flexibility and reliability have made it a universal device for non-mechanical tasks, such as digital computing. Transistorized mechatronics circuits have replaced electromechanical devices for the control of appliances and machinery as well. Mechatronics (or Mecha nical and Elec' tronics' Engineering) is the combination of Mechanical engineering, Electronic engineering In Engineering, electromechanics combines the Sciences of Electromagnetism of Electrical engineering and mechanics. 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 control function. A microcontroller (also MCU or µC is a functional Computer system-on-a- chip. Computer programs (also software programs, or just programs) are instructions for a Computer.
Because of the low cost of transistors and hence digital computers, there is a trend to digitize information, such as the Internet Archive. The Internet Archive ( IA) is a Nonprofit organization dedicated to maintaining an on-line Library and archive of Web and With digital computers offering the ability to quickly find, sort and process digital information, more and more effort has been put into making information digital. A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for As a result, today, much media data is delivered in digital form, finally being converted and presented in analog form to the user. Areas influenced by the Digital Revolution include television, radio, and newspapers. This article presents a Timeline of events in the history of Computing from 1990 to the present Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. A newspaper is a written Publication containing News, information and Advertising, usually printed on low-cost paper called Newsprint.
Prior to the development of transistors, vacuum (electron) tubes (or in the UK "thermionic valves" or just "valves") were the main active components in electronic equipment. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall.
The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are:
Transistors are categorized by:
Thus, a particular transistor may be described as: silicon, surface mount, BJT, NPN, low power, high frequency switch. Through-hole technology, also spelled "thru-hole" refers to the mounting scheme used for Pin-through-hole ( PTH) Electronic components that Surface-mount technology ( SMT) is a method for constructing electronic circuits in which the components (SMC or Surface Mounted Components are mounted directly onto Transistors are complicated devices In order to ensure the reliable operation of circuits employing transistors it is necessary to scientifically model the physical phenomena
The bipolar junction transistor (BJT) was the first type of transistor to be mass-produced. A bipolar (junction transistor ( BJT) is a type of Transistor. A bipolar (junction transistor ( BJT) is a type of Transistor. Bipolar transistors are so named because they conduct by using both majority and minority carriers. The three terminals of the BJT are named emitter, base and collector. Two p-n junctions exist inside a BJT: the base/emitter junction and base/collector junction. A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact "The [BJT] is useful in amplifiers because the currents at the emitter and collector are controllable by the relatively small base current. " In an NPN transistor operating in the active region, the emitter-base junction is forward biased, 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. By controlling the number of electrons that can leave the base, the number of electrons entering the collector can be controlled. 
Unlike the FET, 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. In Electronics, diode modeling refers to the mathematical models used to approximate the actual behavior of real diodes to enable calculations and circuit analysis A bipolar (junction transistor ( BJT) is a type of Transistor. Because of this exponential relationship, the BJT has a higher transconductance than the FET. Transconductance, also known as mutual conductance, is a property of certain electronic components
Bipolar transistors can be made to conduct by exposure to light, since absorption of photons in the base region generates a photocurrent that acts as a base current; the collector current is approximately beta times the photocurrent. Devices designed for this purpose have a transparent window in the package and are called phototransistors. A photodiode is a type of Photodetector capable of converting Light into either current or Voltage, depending upon the mode of operation
The field-effect transistor (FET), sometimes called a unipolar transistor, uses either electrons (in N-channel FET) or holes (in P-channel FET) for conduction. The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals The junction gate field-effect transistor ( JFET or JUGFET) is the simplest type of Field effect transistor. The field-effect transistor (FET is a type of Transistor that relies on an Electric field to control the shape and hence the conductivity of a 'channel' The four terminals of the FET are named source, gate, drain, and body (substrate). On most FETs, the body is connected to the source inside the package, and this will be assumed for the following description.
In FETs, 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 (Vgs) is increased, the drain–source current (Ids) increases exponentially for Vgs below threshold, and then at a roughly quadratic rate () (where VT is the threshold voltage at which drain current begins) in the "space-charge-limited" region above threshold. Space charge is a concept in which excess Electric charge is treated as being a Continuum of charge distributed over a region of space (either a volume or an area A quadratic behavior is not observed in modern devices, for example, at the 65nm technology node. The 65 nanometer (65 nm process is an advanced lithographic node used in volume CMOS Semiconductor fabrication. 
To turn on a transistor it has to be charged like a capacitor. One polarity of charge is responsible for conduction, the other serves for charge neutrality. In the BJT, both types of charge carriers come close together and so the capacitance is high, therefore only low voltages are needed to produce a given amount of charge. In a FET both types of charges are separated by the dielectric and additionally the Debye length, thus reducing the capacity and increasing the voltage needed for switching. In Plasma physics, the Debye length (also called Debye radius) named after the Dutch physicist and physical chemist Peter Debye, is the scale over which Above zero Kelvin, the exponential curve is convoluted with the hard turn on of the BJT and the parabolic turn on of the FET.
For low noise at narrow bandwidth the higher input resistance of the FET is advantageous. Bandwidth is the difference between the upper and lower Cutoff frequencies of for example a filter, a Communication channel, or a Signal spectrum
FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET). The junction gate field-effect transistor ( JFET or JUGFET) is the simplest type of Field effect transistor. The IGFET is more commonly known as metal–oxide–semiconductor FET (MOSFET), from their original construction as a layer of metal (the gate), a layer of oxide (the insulation), and a layer of semiconductor. The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals Unlike IGFETs, the JFET gate forms a PN diode with the channel which lies between the source and drain. Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes Functionally, this makes the N-channel JFET the solid state equivalent of the vacuum tube triode which, similarly, forms a diode between its grid and cathode. A triode is an electronic amplification device having three active electrodes A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device 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 (MESFETs) are JFETs in which the reverse biased PN junction is replaced by a metal–semiconductor Schottky-junction. A p-n junction is a junction formed by combining P-type and N-type Semiconductors together in very close contact Walter Hermann Schottky ( 23 July 1886, Zürich, Switzerland – 4 March 1976, Pretzfeld, West Germany 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 (microwave frequencies; several GHz).
Unlike bipolar transistors, FETs do not inherently amplify a photocurrent. Nevertheless, there are ways to use them, especially JFETs, as light-sensitive devices, by exploiting the photocurrents in channel–gate or channel–body junctions.
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 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 as the diode junctions would forward bias and conduct if they were enhancement mode devices; most IGFETs are enhancement-mode types.
The first BJTs were made from germanium (Ge) and some high power types still are. A FREDFET (sometimes FredFET) is a fast-reverse or fast-recovery epitaxial diode field-effect transistor. An EOSFET or electrolyte-oxide-semiconductor field effect transistor is a FET, like a MOSFET, but with the metal replaced by Electrolyte solution A neurochip is a chip ( Integrated circuit / Microprocessor) that is designed for the interaction with Neuronal cells An Organic Field-Effect Transistor (OFET is a Field effect transistor using an Organic semiconductor in its channel A DNA field-effect transistor (DNAFET is a Field-effect transistor which uses the field-effect due to the partial charges of DNA molecules to function as a Biosensor Germanium (dʒɚˈmeɪniəm is a Chemical element with the symbol Ge and Atomic number 32 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). Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. SiGe (ˈsɪɡɪː ˈsaɪdʒɪ or silicon-germanium, is a general term for the Alloy Si1-xGex which consists of any molar ratio of Silicon SiGe (ˈsɪɡɪː ˈsaɪdʒɪ or silicon-germanium, is a general term for the Alloy Si1-xGex which consists of any molar ratio of Silicon 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 table below; it must be noted that these parameters will vary with increase in temperature, electric field, impurity level, strain and various other factors:
V @ 25 °C
m²/(V·s) @ 25 °C
m²/(V·s) @ 25 °C
|Max. junction temp. |
|Ge||0. 27||0. 39||0. 19||70 to 100|
|Si||0. 71||0. 14||0. 05||150 to 200|
|GaAs||1. 03||0. 85||0. 05||150 to 200|
|Al-Si junction||0. 3||—||—||150 to 200|
The junction forward voltage is the voltage applied to the emitter-base junction of a BJT in order 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 increase in temperature. For a typical silicon junction the change is approximately −2. 1 mV/°C. 
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 Physics, electron mobility (or simply mobility) is a quantity relating the Drift velocity of Electrons to the applied Electric field In Physics, electron mobility (or simply mobility) is a quantity relating the Drift velocity of Electrons to the applied Electric field In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can In general, the higher the electron mobility the faster the transistor. 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:
Because the electron mobility is higher than the hole mobility for all semiconductor materials, a given bipolar NPN transistor tends to be faster than an equivalent PNP transistor type. Reverse leakage current in a semiconductor device is the current flowing from that semiconductor device when the device is reverse biased The term is particularly applicable A bipolar (junction transistor ( BJT) is a type of Transistor. A bipolar (junction transistor ( BJT) is a type of 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 heterostructure (junction between different semiconductor materials) of aluminium gallium arsenide (AlGaAs)-gallium arsenide (GaAs) which has double the electron mobility of a GaAs-metal barrier junction. A heterojunction is the interface that occurs between two layers or regions of dissimilar Crystalline Semiconductors These semiconducting materials have unequal Because of their high speed and low noise, HEMTs are used in satellite receivers working at frequencies around 12 GHz.
Max. junction temperature values represent a cross section taken from various manufacturers' data sheets. This temperature should not be exceeded or the transistor may be damaged.
Al-Si junction refers to the high-speed (aluminum-silicon) semiconductor-metal barrier diode, commonly known as a Schottky diode. The Schottky diode (named after German physicist Walter H Schottky; also known as hot carrier diode) is a Semiconductor Diode with 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 packages (chip carriers) (see images). A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth The two main categories are through-hole (or leaded), and surface-mount, also known as surface mount device (SMD). Through-hole technology, also spelled "thru-hole" refers to the mounting scheme used for Pin-through-hole ( PTH) Electronic components that Surface-mount technology ( SMT) is a method for constructing electronic circuits in which the components (SMC or Surface Mounted Components are mounted directly onto The ball grid array (BGA) is the latest surface mount package (currently only for large transistor arrays). A ball grid array ( BGA) is a type of Surface-mount packaging used for Integrated circuits BGA The BGA is descended from the 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 rating.
Transistor packages are made of glass, metal, ceramic or plastic. The package often dictates the power rating and frequency characteristics. Power transistors have large packages that can be clamped to heat sinks for enhanced cooling. A heat sink (or heatsink) is an environment or object that absorbs and dissipates heat from another object using Thermal contact (either direct or radiant Additionally, most power transistors have the collector or drain physically connected to the metal can/metal plate. At the other extreme, some surface-mount microwave transistors are as small as grains of sand.
Often a given transistor type is available in different packages. Transistor packages are mainly standardized, but the assignment of a transistor's functions to the terminals is not: different transistor types can assign different 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- i. e. BC212L and BC212K).
For a basic guide to the operation of transistors, see How a transistor works. A transistor may be used to switch or to amplify. The image to the right represents a typical transistor in a circuit
In the early days of transistor circuit design, the bipolar junction transistor, or BJT, was the most commonly used transistor. A bipolar (junction transistor ( BJT) is a type of Transistor. Even after MOSFETs became available, the BJT remained the transistor of choice for digital and analog circuits because of their ease of manufacture and speed. The metal–oxide–semiconductor field-effect transistor ( MOSFET, MOS-FET, or MOS FET) is a device used to amplify or switch electronic signals However, desirable properties of MOSFETs, such as their utility in low-power devices, have made them the ubiquitous choice for use in digital circuits and a very common choice for use in analog circuits.
Transistors are commonly used as electronic switches, for both high power applications including switched-mode power supplies and low power applications such as logic gates. A switched-mode power supply, switching-mode power supply or SMPS, is an electronic Power supply unit (PSU that incorporates a switching regulator A logic gate performs a logical operation on one or more logic inputs and produces a single logic output
From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. For biologic transmitters see Transmitter substance. A transmitter is an electronic device which usually with the aid of an antenna Signal processing is the analysis interpretation and manipulation of signals Signals of interest include sound, images, biological signals such as 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.
Transistors are commonly used in modern musical instrument amplifiers, in which circuits up to a few hundred watts are common and relatively cheap. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. Transistors have largely replaced valves (electron tubes) in instrument amplifiers. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. Some musical instrument amplifier manufacturers mix transistors and vacuum tubes in the same circuit, to utilize the inherent benefits of both devices.
The "first generation" of electronic computers used vacuum tubes, which generated large amounts of heat, were bulky, and were unreliable. The development of the transistor was key to computer miniaturization and reliability. The "second generation" of computers, through the late 1950s and 1960s featured boards filled with individual transistors and magnetic memory cores. Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory. Subsequently, transistors, other components, and their necessary wiring were integrated into a single, mass-manufactured component: the integrated circuit. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside
A wide range of transistors has been available since the 1960s and manufacturers continually introduce improved types. A few examples from the main families are noted below. Unless otherwise stated, all types are made from silicon semiconductor. Complementary pairs are shown as NPN/PNP or N/P channel. Links go to manufacturer datasheets, which are in PDF format. (On some datasheets the accuracy of the stated transistor category is a matter of debate. )
Part numbers starting with "2S" are from Japan. Transistors with part numbers beginning with 2SA or 2SB are PNP BJTs. Transistors with part numbers beginning with 2SC or 2SD are NPN BJTs. Transistors with part numbers beginning with 2SJ are P-channel FETs (both JFETs and MOSFETs). Transistors with part numbers beginning with 2SK are N-channel FETs (both JFETs and MOSFETs).