Transistor

qas: question: What is the use of a transistor?
answers: text: to amplify or switch electronic signals and electrical power

question: What is a transistor made of?
answers: text: semiconductor material

question: What is the minimum amount of external connection terminals to call an item a transistor?
answers: text: three

question: Why does a transistor increase a signal?
answers: text: the controlled (output) power can be higher than the controlling (input) power

question: Where are most transistors found?
answers: text: embedded in integrated circuits

question: What is an integrated circuit used for?

question: Where are most semiconductor devices found?

question: What are integrated circuits made of?

question: How many transistors are embedded in most integrated circuits?

question: What controls how strong a signal is?
context: A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes 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. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

qas: question: When was the first transistor created?
answers: text: 1926

question: Who invented the first transistor?
answers: text: Julius Lilienfeld

question: When was the first transistor implemented for practical use?
answers: text: 1947

question: When did the implementers receive a Nobel Prize for making the transistor?
answers: text: 1956

question: What list is the transistor on?
answers: text: list of IEEE milestones in electronics

question: When were smaller, cheaper radios introduced?

question: What besides the transistor is on the IEEE list of milestones in electronics?

question: What did Julius Lilienfeld receive for inventing the transistor?

question: Who was the first person to use transistors in calculators? 

question: Why were transistors in 1947 easier to practically implement than transistors in 1926?
context: The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. First conceived by Julius Lilienfeld in 1926 and practically implemented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley, the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their achievement.

qas: question: When was the thermionic triode invented?
answers: text: 1907

question: What was the purpose of the thermionic triode?
answers: text: amplified radio technology and long-distance telephony

question: Who filed a patent for the field-effect transistor?
answers: text: Physicist Julius Edgar Lilienfeld

question: Where did Lilienfeld file his patent?
answers: text: Canada

question: What year did Lilienfeld file his patent?
answers: text: 1925

question: Where did Oskar Heil file a patent?

question: How long would it take for a practical field-effect transistor be built?

question: Why did Oskar Heil invent a device similar to Lilienfeld's?

question: Why were field-effect transistors not practical without high quality semiconductor materials?

question: Where was the thermionic triode invented?
context: 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 lot of power. Physicist Julius Edgar Lilienfeld filed a patent for a field-effect transistor (FET) in Canada in 1925, which was intended to be a solid-state replacement for the triode. Lilienfeld also filed identical patents in the United States in 1926 and 1928. However, Lilienfeld 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. In 1934, German inventor Oskar Heil patented a similar device.

qas: question: At what time did Bardeen and Brattain experiment on increasing signal output?
answers: text: November 17, 1947 to December 23, 1947

question: What were gold contacts attached to to increase signal output?
answers: text: germanium

question: Who was the Solid State Physics Group Leader?
answers: text: William Shockley

question: Who came up with the term transistor?
answers: text: John R. Pierce

question: Why was the term transistor used?
answers: text: a contraction of the term transresistance

question: When did lawyers at Bell Labs find Lilienfeld's patents?

question: Who thought of the term semiconductor?

question: How many patents did Lilienfeld file?

question: When was the term transistor first used?

question: Where was the biography of John Bardeen written?
context: From November 17, 1947 to December 23, 1947, John Bardeen and Walter Brattain at AT&T's Bell Labs in the United States 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. 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. According to Lillian Hoddeson and Vicki Daitch, authors of a biography of John Bardeen, Shockley had 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. In acknowledgement of this accomplishment, Shockley, Bardeen, and Brattain were jointly awarded the 1956 Nobel Prize in Physics "for their researches on semiconductors and their discovery of the transistor effect."

qas: question: In what year was the point-contact transistor invented?
answers: text: 1948

question: Who invented the point-contact transistor?
answers: text: Herbert Mataré and Heinrich Welker

question: Where were Matare and Welker working when inventing the point-contact transistor?
answers: text: Compagnie des Freins et Signaux

question: What was the name of Matare and Welker's transistor?
answers: text: transistron

question: What was the transistron used for?
answers: text: amplified use in France's telephone network

question: What were Matare and Welker's transistors made of?

question: When did Heinrich Welker start researching electronics?

question: When did Matare and Welker realize that Bell Labs had invented a transistor?

question: Where were the "transistrons" produced?

question: Who was in charge of France's telephone network?
context: In 1948, the point-contact transistor was independently invented by German physicists Herbert Mataré and Heinrich Welker while working at the Compagnie des Freins et Signaux, a Westinghouse subsidiary located in Paris. Mataré had previous experience in developing crystal rectifiers from silicon and germanium in the German radar effort during World War II. Using this knowledge, he began researching the phenomenon of "interference" in 1947. By June 1948, witnessing currents flowing through point-contacts, Mataré 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 before them, the company rushed to get its "transistron" into production for amplified use in France's telephone network.

qas: question: How many transistors make up a logic gate?
answers: text: up to about twenty transistors

question: How many transistors make up a microprocessor?
answers: text: as many as 3 billion transistors

question: How many transistors were made in 2002?
answers: text: 60 million transistors were built in 2002… for [each] man, woman, and child

question: How many individually packaged transistors are produced each year?
answers: text: over a billion

question: What are some abbreviations for integrated circuits?
answers: text: IC, microchips or simply chips

question: How many integrated circuits are produced every year?

question: How many men, women, and children are on Earth?

question: How many logic gates are in a microchip?

question: What produces electronic components?

question: Where are transistors being produced?
context: Although several companies each produce over a billion individually packaged (known as discrete) transistors every year, the vast majority of transistors are now produced in integrated circuits (often shortened to IC, 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 twenty transistors whereas an advanced microprocessor, as of 2009, can use as many as 3 billion transistors (MOSFETs). "About 60 million transistors were built in 2002… for [each] man, woman, and child on Earth."

qas: question: Why is a transistor so useful?
answers: text: gain

question: What is gain?
answers: text: it can act as an amplifier

question: What is an additional use of the transistor?
answers: text: turn current on or off in a circuit

question: What determines the amount of current in an electrically controlled switch?
answers: text: other circuit elements

question: What controls how strong the output signal is?

question: Where are transistors located?

question: How large is a transistor in comparison to a terminal?

question: What does a signal become when the transistor does not work properly?

question: Where would an electrically controlled switch be located?
context: The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. It can produce a stronger output signal, a voltage or current, which is proportional to a weaker input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.

qas: question: How many types of transistors are there?
answers: text: two

question: What are the components of a bipolar transistor?
answers: text: base, collector, and emitter

question: What controls the large current between the collector and emitter?
answers: text: A small current at the base terminal

question: What are the components of a field-effect transistor?
answers: text: gate, source, and drain

question: In a field-effect transistor, what controls the current between the source and drain?
answers: text: a voltage at the gate

question: Why would someone use a bipolar transistor instead of a field-effect transistor?

question: What is the most common kind of transistor?

question: What controls the voltage at the gate of a field-effect transistor?

question: Where is the collector terminal located?

question: Where is the gate terminal located?
context: There are two types of transistors, which have slight differences in how they are used in a circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals. For a field-effect transistor, the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current between source and drain.

qas: question: Why does the collector voltage drop in grounded-emitter transistor circuits?
answers: text: reduced resistance from collector to emitter

question: What would happen if the voltage difference from collector and emitter were zero?
answers: text: the collector current would be limited only by the load resistance (light bulb) and the supply voltage

question: What is the term for a zero difference between collector and emitter?
answers: text: saturation

question: Why is the term saturation named as such?
answers: text: current is flowing from collector to emitter freely

question: What position is the switch in when saturated?
answers: text: on

question: What causes reduced resistance from collector to emitter?

question: Why does "current" have that name?

question: What changes the most in a grounded-emitter transistor circuit?

question: What is the load resistance in a light bulb?

question: What changes the amount of supply voltage?
context: 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 collector to 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 current is flowing from collector to emitter freely. When saturated, the switch is said to be on.

qas: question: What is a major problem with using bipolar transistors as switches?
answers: text: Providing sufficient base drive current

question: What does the transistor provide?
answers: text: current gain

question: What determines the current ratio in transistors?
answers: text: the type of transistor

question: If the type of transistor is the same what determines the current ratio?
answers: text: collector current

question: What controls how much gain a transistor provides?

question: How much current is needed to saturate a light-switch?

question: What determines how much collector current there is?

question: What fluctuates the most in a transistor?
context: Providing sufficient base drive current is a key problem in the use of bipolar transistors as switches. The transistor provides current gain, allowing a relatively large current in the collector to be switched 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 light-switch circuit shown, the resistor is chosen to provide enough base current to ensure the transistor will be saturated.

qas: question: How are parameters chosen in a switching circuit?
answers: text: the "off" output is limited to leakage currents too small to affect connected circuitry

question: What is a switching circuit trying to simulate when on?
answers: text: short circuit

question: What is a switching circuit trying to simulate when off?
answers: text: open circuit

question: How quickly does the change from open circuit to short circuit happen?
answers: text: instantaneous

question: What might stop a switch from transitioning quickly? 

question: What can help a switch work more efficiently?

question: What kind of circuit has the least amount of resistance?

question: What kind of circuit has the most resistance?

question: When is a circuit most likely to fail?
context: In a switching circuit, the idea is to simulate, as near as possible, the ideal switch having the properties of open circuit when off, 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.

qas: question: What gives bipolar transistors their name?
answers: text: they conduct by using both majority and minority carriers

question: What was the first mass-produced transistor?
answers: text: bipolar junction transistor

question: What is the bipolar junction transistor a combination of?
answers: text: two junction diodes

question: What is the name for a layer of p-type semiconductor set between two n-type semiconductors?
answers: text: n–p–n transistor

question: What is the name for a layer of n-type semiconductor set between two p-type semiconductors?
answers: text: p–n–p transistor

question: What kind of transistor is used the most?

question: Where do junction diodes get their name?

question: What is the most common type of bipolar transistor?

question: How are bipolar transistors mass produced?
context: Bipolar transistors are so named because they conduct by using both majority and minority carriers. The bipolar junction transistor, the first type of transistor to be mass-produced, is a combination of two junction diodes, and is formed of either a thin layer of p-type semiconductor sandwiched between two n-type semiconductors (an n–p–n transistor), or a thin layer of n-type semiconductor sandwiched between two p-type semiconductors (a p–n–p transistor). This construction produces two p–n junctions: a base–emitter junction and a base–collector junction, separated by a thin region of semiconductor known as the base region (two junction diodes wired together without sharing an intervening semiconducting region will not make a transistor).

qas: question: How many terminals do BJTs have?
answers: text: three

question: How many layers of semiconductor do BJTs have?
answers: text: three

question: What are the layers of semiconductor in a BJT?
answers: text: an emitter, a base, and a collector

question: How can one find the amount of collector current?
answers: text: β (common-emitter current gain) times the base current

question: What is the usual collector current for small-signal transistors?
answers: text: greater than 100

question: Why is the base of a BJT narrow?

question: Where are BJT amplifiers most commonly used?

question: What controls how many electrons are injected into the base region?

question: How many electrons are injected into the base region?
context: BJTs have three terminals, corresponding to the three layers of semiconductor—an emitter, a base, and a collector. They are useful in amplifiers 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 (electrons and holes recombine at 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 (electrons and holes are formed at, and move away from the junction) 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. 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.

qas: question: What determines the conductivity in a FET?
answers: text: electric field that is produced when a voltage is applied between the gate and source terminals

question: What controls the current between the drain and source?
answers: text: the voltage applied between the gate and source

question: At what rate is the drain-source current increased when the gate-source current is increased?
answers: text: a roughly quadratic rate

question: Where is a quadratic behavior not observed?
answers: text: in modern devices

question: What controls the voltage applied between the gate and the source terminals?

question: Why is quadratic behavior not observed in modern devices?

question: Where does current fluctuate the most?

question: How quickly does the voltage increase?
context: 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 (VGS) is increased, the drain–source current (IDS) increases exponentially for VGS below threshold, and then at a roughly quadratic rate (IGS ∝ (VGS − VT)2) (where VT is the threshold voltage at which drain current begins) in the "space-charge-limited" region above threshold. A quadratic behavior is not observed in modern devices, for example, at the 65 nm technology node.

qas: question: How many groups are FETs split into?
answers: text: two

question: What are the names of the groups of FETs
answers: text: junction FET (JFET) and insulated gate FET (IGFET)

question: What is the common term for an IFGET?
answers: text: a metal–oxide–semiconductor FET (MOSFET)

question: How is a JFET different from an IGFET?
answers: text: the JFET gate forms a p–n diode with the channel

question: What mode do both JFET and IGFET operate in?
answers: text: depletion mode

question: What is a vacuum tube triode made from?

question: What controls the amount of input voltage?

question: How many layers of metal are in the gate of an IGFET?

question: What kind of FET is mass produced?
context: 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 drain. 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. 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.

qas: question: How are FET's separated?
answers: text: depletion-mode and enhancement-mode types

question: At what point is a channel off in enhancement-mode?
answers: text: at zero bias

question: At what point is a channel on in depletion-mode?
answers: text: at zero bias

question: What channel corresponds with high current?
answers: text: n-channel devices

question: What channel corresponds with low current?
answers: text: p-channel devices

question: What type of FET is more common?

question: What controls how positive the gate voltage is?

question: What controls the gate potential of a FET?

question: What type of FET usually has a higher voltage?
context: 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; most IGFETs are enhancement-mode types.

qas: question: What was the most frequently used transistor in the 1960s and 70s?
answers: text: bipolar junction transistor

question: Why were BJTs so popular?
answers: text: their greater linearity and ease of manufacture

question: What are some applications of discrete MOSFETs?
answers: text: transistor applications, including analog circuits, voltage regulators, amplifiers, power transmitters and motor drivers

question: What were the most popular digital circuits of the time?
answers: text: MOSFETs

question: When did MOSFETs become widely available?

question: What are the desirable properties of MOSFETs?

question: What was the most common application of MOSFETs?

question: Which type of circuit is older?

question: What kind of circuit is used more in the present?
context: The bipolar junction transistor (BJT) was the most commonly used transistor in the 1960s and 70s. Even after MOSFETs became widely available, the BJT remained the transistor of choice for many analog circuits such as amplifiers because of their greater linearity and ease of manufacture. In integrated circuits, the desirable properties of MOSFETs allowed them to capture nearly all market share for digital circuits. Discrete MOSFETs can be applied in transistor applications, including analog circuits, voltage regulators, amplifiers, power transmitters and motor drivers.

qas: question: What is the Pro Electron standard?
answers: text: European Electronic Component Manufacturers Association part numbering scheme

question: How many letters does the part numbering scheme begin with?
answers: text: two letters

question: What is the first letter in the part numbering scheme?
answers: text: the semiconductor type

question: What is the second letter in the part numbering scheme?
answers: text: the intended use

question: What follows the 2 letters in the part numbering scheme?
answers: text: A 3-digit sequence number

question: What is the most common semiconductor type?

question: What is the most common intended use for transistors?

question: What kinds of transistor are more likely to use a suffix?

question: What devices are more likely to have a code with a voltage rating?

question: What is the most common reason to have a suffix on a device's number?
context: The Pro Electron standard, the European Electronic Component Manufacturers Association part numbering scheme, begins with two letters: the first gives the semiconductor type (A for germanium, B for silicon, and C for materials like GaAs); the second letter denotes the intended use (A for diode, C for general-purpose transistor, etc.). A 3-digit sequence number (or one letter then 2 digits, for industrial types) follows. With early devices this indicated the case type. Suffixes may be used, with a letter (e.g. "C" often means high hFE, such as in: BC549C) or other codes may follow to show gain (e.g. BC327-25) or voltage rating (e.g. BUK854-800A). The more common prefixes are:

qas: question: What does the JEDEC EIA370 transistor number start with?
answers: text: 2N

question: what does the 2N is the JEDEC EIA370 mean?
answers: text: a three-terminal device

question: What follows the 2N in a JEDEC EIA370?
answers: text: a 2, 3 or 4-digit sequential number with no significance as to device properties

question: What does a letter at the end of a device number mean?
answers: text: a newer variant

question: What does the number 2N1301 indicate?
answers: text: a p–n–p germanium switching transistor

question: What were most early devices made from?

question: What is the most common amount of extra digits in a device number?

question: Which devices usually have the shortest transistor device numbers?

question: What are most modern devices made from?

question: What is the most common letter suffix?
context: The JEDEC EIA370 transistor device numbers usually start with "2N", indicating a three-terminal device (dual-gate field-effect transistors are four-terminal devices, so begin with 3N), then a 2, 3 or 4-digit sequential number with no significance as to device properties (although early devices with low numbers tend to be germanium). For example, 2N3055 is a silicon n–p–n power transistor, 2N1301 is a p–n–p germanium switching transistor. A letter suffix (such as "A") is sometimes used to indicate a newer variant, but rarely gain groupings.

qas: question: What was once an indicator of the devices creator?
answers: text: a manufacturer's prefix

question: What makes a manufacturer's prefix less reliable?
answers: text: devices are second-sourced

question: What is the marking for a 2N2222A in a plastic case?
answers: text: PN2222A

question: What is a plastic version of a BC108?
answers: text: PN108

question: What manufacturer creates the most devices?

question: What is the marking for a 2N108 in a plastic case?

question: What kind of case is most common?

question: How many naming schemes use an accurate manufacturer's prefix?

question: Who decided what letters were in the manufacturer's prefixes?
context: Manufacturers of devices may have their own proprietary numbering system, for example CK722. Since devices are second-sourced, a manufacturer's prefix (like "MPF" in MPF102, which originally would denote a Motorola FET) now is an unreliable indicator of who made the device. Some proprietary naming schemes adopt parts of other naming schemes, for example a PN2222A is a (possibly Fairchild Semiconductor) 2N2222A in a plastic case (but a PN108 is a plastic version of a BC108, not a 2N108, while the PN100 is unrelated to other xx100 devices).

qas: question: What is the junction forward voltage?
answers: text: the voltage applied to the emitter–base junction of a BJT

question: What is the purpose of a junction forward voltage?
answers: text: to make the base conduct a specified current

question: What is the ideal junction forward voltage?
answers: text: lower

question: Why is the ideal junction forward voltage lower?
answers: text: less power is required to "drive" the transistor

question: When happens to the junction forward voltage when temperature is raised?
answers: text: decreases

question: What applies voltage to the emitter-base junction?

question: What are most BJTs made of?

question: What are sensistors made of?

question: What kind of circuit needs special compensating elements the most?
context: 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 −2.1 mV/°C. In some circuits special compensating elements (sensistors) must be used to compensate for such changes.

qas: question: What is quicker, a bipolar n-p-n transistor or a p-n-p transistor?
answers: text: a given bipolar n–p–n transistor

question: What semiconductor has the highest electron mobility?
answers: text: GaAs

question: What is the common application of GaAs?
answers: text: high-frequency applications

question: What does HEMT stand for?
answers: text: high-electron-mobility transistor

question: What are common applications of HEMT?
answers: text: satellite receivers

question: What is the most common kind of semiconductor?

question: What causes HEMTs to have high speed and low noise?

question: Which material has the highest electron mobility?

question: Where are HEMTs most commonly used?
context: 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 heterostructure (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 aluminium gallium nitride (AlGaN/GaN HEMTs) provide a still higher electron mobility and are being developed for various applications.

qas: question: What is a discrete transistor?
answers: text: individually packaged transistors

question: What are the two most common types of transistor?
answers: text: through-hole (or leaded), and surface-mount

question: What is another name for the surface-mount transistor?
answers: text: surface-mount device (SMD)

question: What is the newest surface-mount transistor?
answers: text: ball grid array (BGA)

question: What is a ball grid array composed of?
answers: text: solder "balls" on the underside in place of leads

question: What is the most common type of transistor?

question: How many solder "balls" does a Ball Grid Array have?

question: What is the most common type of semiconductor package?

question: What is the most important attribute for a transistor to have?

question: What is the oldest type of semiconductor package?
context: Discrete transistors are individually packaged transistors. 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 (currently only for large integrated circuits). 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.