the various types of transistors

7/28/2019 The Various Types of Transistors

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Transistor s

The two main types of transistors are the bipolar junction transistor (BJT) and the field-effect transistor (FET).

Bipolar J unction Transistors

BJTs can have two different polarities, NPN and PNP. An NPN BJT is one where a positively-doped (P-type) semiconductor

is sandwiched between two negatively-doped (N-type) semiconductors. A PNP BJT is, obviously, one where an N-type

semiconductor is sandwiched between two P-types. Both types of BJTs have an exponential dependence between the

input voltage and the current output. For the record, I should state that a semiconductor is basically a material with

conductance between that of an insulator and a conductor. Silicon and germanium are the two most well-known

semiconductors. Also, doping just means the addition of impurities into a semiconducting material in order for it to either:

increase its electron acceptance (P-type) or increase its electron conductance (N-type).

Some specific types of BJ Ts:

HBT - heterojunction bipolar transistor - These types of transistors are very similar to BJTs except that the two P-type

semiconductors in the PNP polarity, or the two N-type semiconductors in the NPN polarity, are doped differently relative

to each other. The reason for doing this, simply stated, is to make it more difficult for a transistor to operate in the

reverse direction from which is was intended.

Grown-junction transistor - This was the first type of BJT and is self-explanatory. The PN or NP junctions, depending

on whether it's of NPN or PNP polarity, respectively, are grown onto a single, solid crystal of semiconductor material.

Grown, in this case, means slowly attached, chemically.

Alloy-junction transistor - Similar to a grown-junction transistor except the semiconducting material onto which the PN

or NP junctions are grown is specifically germanium.

MA T - micro-alloy transistor - An improved, speedier version of the alloy-junction transistor. The materials of the PN or

NP junctions of a MAT are metal-semiconductor, as opposed to semiconductor-semiconductor.

MADT - micro-alloy diffused transistor - An improved, speedier version of the MAT. The dopant material of a MADT is

diffused (thinly spread) accross the entire germanium crystal prior to PN or NP growth, as opposed to a MAT where the

doping material is only on the metallic side of the PN or NP junction.

PADT - post-alloy diffused transistor - An improved, speedier version of the MADT. A thin, diffused dopant layer of

germanium is grown onto the germanium crystal, as opposed to the entire germanium crystal being diffused, which

allows the germanium crystal to be as thick as necessary for mechanical strength purposes. The PN or NP junctions are

then grown onto this thin layer.

Schottky transistor - These are alloy-junction transistors with a Schottky barrier between the metal-semiconductor

junction. All metal-semiconductor junctions act sort of like capacitors with a voltage between the junctions. Often, you'd

like to minimize this voltage in order to minimize the saturation (the amount of the germanium crystal) needed for the

transistor to work. Minimizing the saturation effectively speeds up the transistor's performance, which is great for things

like switches. Schottky barriers use various materials to do exactly this.

Electronics Engineering Questions

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What are the various types oftransistors?

are the various types of transistors http://wiki.answers.com/Q/What_are_the_various_types_of_t

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Surface-barrier transistor - These are just like Schottky transistors except that both junctions are metal-

semiconductor as opposed to only one.

Drift-field transistor - The doping agent of these transistors is engineered to produce a specific electric field. This

effectually reduces the electrons' transit time between the junctions of the transistor, thereby making it work faster.

Avalanche transistor - These transistors can operate in the breakdown voltage region of a transistor's junctions. The

breakdown voltage is simply the minimum voltage in which an insulator starts acting like a conductor. Thus, these

transistors allow for higher currents to be applied to them than their normal counterparts.

Darlington transistor - These are simply two BJTs connected together to further increase the gain of the current

output.

IGBT - insulated-gate bipolar transistor - These transistors combine the use of BJTs as switches with an isolated-gate FET

(see below) as the input. IGBTs provide much more efficient and faster switching than regular BJTs and are thus some of

the most common transistors found in modern appliances.

Photo transistor - These transistors convert electromagnetic radiation in the form of visible light, UV-rays, or X-rays

into current or voltage. As opposed to the normal PN junctions found in many transistors, photo transistors use PIN

junctions. PIN junctions are similar to PN junctions except that they have an additional intrinsic semiconductor between

the P-type and N-type semiconducting regions. This intrinsic semiconductor is a very lightly doped semiconductor which

exists, at least for the purposes of photo transistors, to supply a region within the junction where a photon (a particle of

electromagnetic radiation with a specific energy) can ionize (knock an electron out of via the photoelectric effect) an

atom of this semiconducting material. Because of the electric field caused from the surrounding P-type and N-type

semiconducting regions, this ionization causes the photoelectron to move toward one end of the junction, thereby

producing what's known as a photocurrent, which is then amplified in the same manner as all other BJTs. I promise that

the rest of my answer won't get more complicated than this.

Field-Effect Transistors

FETs use electric fields to control only one-type of charge carrier, as opposed to BJTs which control both types. Now's as

good a time as any to introduce the concept ofelectron holes. Intuitively, electrons carry negative charge and are thus

referred to as negative charge carriers. Well, the absence of an electron where one used to be is called an electron hole.

These holes act exactly as electrons do in transistors except that they carry positive charge, in the form of missing

negative charge, and are thus called positive charge carriers. FETs are designed to control either positive or negative

charge carriers, in the form of holes or electrons, but not both. The flow of positive or negative charge carriers occurs

through what's called the channel of an FET. FET channels are created within the bulk material of the FET, which is usually

silicon. If you find this idea more complicated than what I wrote about photo transistors, that's only because you haven't

looked up the physics behind the photoelectric effect yet.

Some specific types of FETs:

CNTFET - carbon nanotube field-effect transistor - These FETs use carbon nanotubes instead of silicon as their channel

material. Carbon nanotubes are needed as FETs continue to get smaller in size. They help reduce effects, such as

quantum tunneling and overheating, which are beginning to become real problems in small, silicon-based FETs.

J FET - junction gate field-effect transistor - This FET supplies a voltage accross the charge-carrying channel that can

pinch it shut, effectively stopping the current through the channel.

MESFET - metal semiconductor field-effect transistor - Similar to, but faster than, JFETs, MESFETs use a Schottky barrier

(see above) instead of a PN junction.

HEMT - high electron mobility transistor - The FET version of an HBT (see above). Faster than a MESFET, the charge-

carrying channel is between two different materials instead of within a single, doped region. Also known as a

heterostructure FET (HFET) or a modulation-doped FET (MODFET).

MOSFET - metal-oxide-semiconductor field-effect transistor - This is the most basic, and most common, type of FET,

analogous to the standard BJT (see above). Instead of pinching its charge-carrying channel shut as in a JFET, a MOSFET

has an insulator attached to its input electrode which can be turned on or off depending on whether a voltage is supplied

accross it. The channel can be N-type (nMOS) or P-type (pMOS), as explained above under the "bipolar junction

transistors" heading.

I TFET - inverted-T field-effect transistor - This is simply any type of FET that extends vertically out from the horizontal

plane in a T-shape, hence the name.

MuGFET - multiple gate field-effect transistor - A MOSFET where more than one input shares the bulk material of the

FET. The idea is to use the same FET, thus the same sized object, for multiple things. This concept came about due to the

ever shrinking sizes of transistors.

MI GFET - multiple independent gate field-effect transistor - A MuGFET where the multiple inputs are independently

controlled.

Flexfet - A MIGFET with two inputs, one on a JFET and the other on a MOSFET. The JFET and MOSFET are then "stacked"

on top of each other. Due to its design, the JFET and MOSFET are coupled to each other; i.e. the channel through one

effects the channel through the other and vice versa.

FinFET - A MuGFET where the charge-carrying channel is wrapped around a piece of silicon, called a fin. The reason for


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doing this is similar to that of a PADT (see above); i.e. mechanical strength.

FREDFET - fast-recovery (or reverse) epitaxial diode field-effect transistor - A cute name for a transistor which is

basically designed to quickly turn off when no more voltage is being supplied to it.

TFT - thin-film transistor - An FET where the semiconducting material is placed via thin films over the bulk of the device.

This is opposed to the bulk of the device being the semiconductor itself, as in most FETs. The bulk material used in TFTs is

often glass. The reason being so that the transistors can work behind a clear display in applications like liquid crystal

display (LCD) monitors.

OFET - organic field-effect transistor - An FET with an organic polymer semiconductor as its channel. These are like TFTs

except the bulk of the device is plastic, allowing for very cool, flexible LCD monitors.

FGMOS - floating gate MOSFET - A MOSFET with a "floating gate" input; i.e. an electrically isolated input that can store

charge, like a capacitor, to be used later. These are the transistors behind flash drives.

I SFET - ion-sensitive field-effect transistor - An FET that changes its current depending on the ion concentration of a

solution. The solution itself is used as the input electrode in an ISFET.

EOSFET - electrolyte-oxide-semiconductor field-effect transistor - A MOSFET with the metal replaced by an electrolyte

solution. EOSFETs are used to in neurochips to detect brain activity.

DNAFET - Deoxyribonucleic acid (DNA) field-effect transistor - A MOSFET with its input electrode being a layer of

immobilized, single-stranded DNA. The current through the MOSFET is modulated by the varying charge distributions that

occur when complimentary DNA strands hybridize to the layer of single-stranded DNA on the input electrode. DNAFETs

are used, not surprisingly, in DNA sequencing.

My sources all stem from the link below which is also a great place to learn more about transistors.

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the various types of transistors

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