Editing MOSFET (section)

== Other types ==

=== Dual-gate ===
[[file:FINFET MOSFET.png|thumb|upright=1.2|A [[FinFET]]]]
{{Main|Multigate device}}

The dual-gate MOSFET has a [[tetrode]] configuration, where both gates control the current in the device. It is commonly used for small-signal devices in radio frequency applications where biasing the drain-side gate at constant potential reduces the gain loss caused by [[Miller effect]], replacing two separate transistors in [[cascode]] configuration. Other common uses in RF circuits include gain control and mixing (frequency conversion). The ''tetrode'' description, though accurate, does not replicate the vacuum-tube tetrode. Vacuum-tube tetrodes, using a screen grid, exhibit much lower grid-plate capacitance and much higher output impedance and voltage gains than triode vacuum tubes. These improvements are commonly an order of magnitude (10 times) or considerably more. Tetrode transistors (whether bipolar junction or field-effect) do not exhibit improvements of such a great degree.

The [[FinFET]] is a double-gate [[silicon-on-insulator]] device, one of a number of geometries being introduced to mitigate the effects of short channels and reduce drain-induced barrier lowering. The ''fin'' refers to the narrow channel between source and drain. A thin insulating oxide layer on either side of the fin separates it from the gate. SOI FinFETs with a thick oxide on top of the fin are called ''double-gate'' and those with a thin oxide on top as well as on the sides are called ''triple-gate'' FinFETs.<ref name=SOI>{{cite book |title=Frontiers in electronics: future chips : proceedings of the 2002 Workshop on Frontiers in Electronics (WOFE-02), St Croix, Virgin Islands, USA, 6–11 January 2002 |year=2002|publisher=World Scientific |chapter=Figure 12: Simplified cross section of FinFET double-gate MOSFET |isbn=978-981-238-222-1|first1=P. M.|last1= Zeitzoff |first2=J. A.|last2= Hutchby |first3=H. R.|last3= Huff |editor1-first=Yoon-Soo|editor1-last=Park |editor2-first=Michael|editor2-last=Shur |editor3-first=William|editor3-last=Tang |chapter-url=https://books.google.com/books?id=uC6h4-OEWsMC&pg=PA82 |page=82}}</ref><ref>{{cite book |title=Silicon-on-Insulator Technology and Devices |chapter=Comparison of SOI FinFETs and bulk FinFETs: Figure 2 |first1=J.-H.|last1= Lee |first2=J.-W.|last2= Lee |first3=H.-A.-R.|last3= Jung |first4=B.-K.|last4= Choi |chapter-url=https://books.google.com/books?id=OVbb42PwZysC&pg=PA102 |page=102 |publisher=The Electrochemical Society |year=2009 |isbn=978-1-56677-712-4}}</ref>

=== Depletion-mode ===
There are ''depletion-mode'' MOSFET devices, which are less commonly used than the standard ''enhancement-mode'' devices already described. These are MOSFET devices that are doped so that a channel exists even with zero voltage from gate to source. To control the channel, a negative voltage is applied to the gate (for an n-channel device), depleting the channel, which reduces the current flow through the device. In essence, the depletion-mode device is equivalent to a [[normally closed]] (on) switch, while the enhancement-mode device is equivalent to a [[normally open]] (off) switch.<ref>{{cite encyclopedia
 | title= Depletion Mode
 | encyclopedia= Techweb
 | date= 29 January 2010
 | location= 
 | id= 
 | url= http://www.techweb.com/encyclopedia/imageFriendly.jhtml;?term=depletion+mode
 | accessdate= 27 November 2010
 | archive-date= 31 October 2010
 | archive-url= https://web.archive.org/web/20101031061941/http://www.techweb.com/encyclopedia/imageFriendly.jhtml;?term=depletion+mode
 | url-status= dead
 }}</ref>

Due to their low [[noise figure]] in the [[RF]] region, and better [[gain (electronics)#Power gain|gain]], these devices are often preferred to [[bipolar junction transistors|bipolars]] in [[RF front end|RF front-ends]] such as in [[TV]] sets.

Depletion-mode MOSFET families include the BF960 by [[Siemens]] and [[Telefunken]], and the BF980 in the 1980s by [[Philips]] (later to become [[NXP Semiconductors]]), whose derivatives are still used in [[automatic gain control|AGC]] and RF [[frequency mixer|mixer]] front-ends.

=== Metal–insulator–semiconductor field-effect transistor (MISFET) ===
Metal–insulator–semiconductor field-effect-transistor,<ref>{{cite web
 | url = http://www.semi1source.com/glossary/default.asp?searchterm=MIS
 | title = MIS
 | work = Semiconductor Glossary
 | access-date = 2017-05-14
 | archive-date = 2017-01-22
 | archive-url = https://web.archive.org/web/20170122153452/http://www.semi1source.com/glossary/default.asp?searchterm=MIS
 | url-status = dead
 }}</ref><ref>
{{cite book
 | title = Semiconducting polymers: chemistry, physics and engineering
 | first1= Georges | last1 = Hadziioannou
 | first2=George G. | last2=Malliaras
 | publisher = Wiley-VCH
 | year = 2007
 | isbn = 978-3-527-31271-9
 | url = https://books.google.com/books?id=D37RykvobWwC&dq=misfet+metal-insulator-semiconductor-field-effect-transistor&pg=PA532
}}</ref><ref name=Jones>
{{cite book
 | title = Organic Molecular Solids: Properties and Applications
 | first = William | last=Jones
 | publisher = CRC Press
 | year = 1997
 | isbn = 978-0-8493-9428-7
 | url = https://books.google.com/books?id=8sb1kwH6EgIC&dq=misfet+metal-insulator-semiconductor-field-effect-transistor&pg=PA350
}}</ref> or ''MISFET'', is a more general term than ''MOSFET'' and a synonym to ''insulated-gate field-effect transistor'' (IGFET). All MOSFETs are MISFETs, but not all MISFETs are MOSFETs.

The gate dielectric insulator in a MISFET is a substrate oxide (hence typically [[silicon dioxide]]) in a MOSFET, but other materials can also be employed. The [[gate dielectric]] lies directly below the [[gate electrode]] and above the [[channel (semiconductor)|channel]] of the MISFET. The term ''metal'' is historically used for the gate material, even though now it is usually [[doping (semiconductor)|highly doped]] [[polysilicon]] or some other [[non-metal]].

Insulator types may be:

* Silicon dioxide, in silicon MOSFETs 
* Organic insulators (e.g., undoped trans-[[polyacetylene]]; [[cyanoethyl]] [[pullulan]], CEP<ref>
{{cite journal
 | url=https://pubs.rsc.org/en/Content/ArticleLanding/2013/TC/C3TC30134F|title=High performance organic field-effect transistors using cyanoethyl pullulan (CEP) high-k polymer cross-linked with trimethylolpropane triglycidyl ether (TTE) at low temperatures
 | journal=Journal of Materials Chemistry C
|volume=1
 |issue=25
 |pages=3955
 |doi=10.1039/C3TC30134F
 |year=2013
 |last1=Xu
 |first1=Wentao
 |last2=Guo
 |first2=Chang
 |last3=Rhee
 |first3=Shi-Woo
 }}</ref>), for organic-based FETs.<ref name=Jones/>

=== NMOS logic ===
For devices of equal current driving capability, n-channel MOSFETs can be made smaller than p-channel MOSFETs, due to p-channel charge carriers ([[electron hole|holes]]) having lower [[electron mobility|mobility]] than do n-channel charge carriers ([[electrons]]), and producing only one type of MOSFET on a silicon substrate is cheaper and technically simpler. These were the driving principles in the design of [[NMOS logic]] which uses n-channel MOSFETs exclusively. However, neglecting [[leakage current]], unlike CMOS logic, NMOS logic consumes power even when no switching is taking place. With advances in technology, CMOS logic displaced NMOS logic in the mid-1980s to become the preferred process for digital chips.

=== Power MOSFET ===
[[file:Power mos cell layout.svg|thumb|upright=1.2|Cross section of a power MOSFET, with square cells. A typical transistor is constituted of several thousand cells.]]
{{Main|Power MOSFET}}

[[Power MOSFET]]s have a different structure.<ref>{{cite book|title=Power Semiconductor Devices|first=B. Jayant|last=Baliga|publisher=PWS publishing Company|location=Boston|isbn=978-0-534-94098-0|year=1996}}</ref> As with most power devices, the structure is vertical and not planar. Using a vertical structure, it is possible for the transistor to sustain both high blocking voltage and high current. The voltage rating of the transistor is a function of the doping and thickness of the N-[[epitaxial]] layer (see cross section), while the current rating is a function of the channel width (the wider the channel, the higher the current). In a planar structure, the current and breakdown voltage ratings are both a function of the channel dimensions (respectively width and length of the channel), resulting in inefficient use of the "silicon estate". With the vertical structure, the component area is roughly proportional to the current it can sustain, and the component thickness (actually the N-epitaxial layer thickness) is proportional to the breakdown voltage.<ref>{{cite web|url=http://www.element-14.com/community/docs/DOC-18273/l/power-mosfet-basics-understanding-mosfet-characteristics-associated-with-the-figure-of-merit|title=Power MOSFET Basics: Understanding MOSFET Characteristics Associated With The Figure of Merit|website=element14|accessdate=27 November 2010|archive-url=https://web.archive.org/web/20150405142659/http://www.element-14.com/community/docs/DOC-18273/l/power-mosfet-basics-understanding-mosfet-characteristics-associated-with-the-figure-of-merit |archive-date=5 April 2015 }}</ref>

Power MOSFETs with lateral structure are mainly used in high-end audio amplifiers and high-power PA systems. Their advantage is a better behaviour in the saturated region (corresponding to the linear region of a bipolar transistor) than the vertical MOSFETs. Vertical MOSFETs are designed for switching applications.<ref>{{cite web|url=http://www.element-14.com/community/docs/DOC-18275/l/power-mosfet-basics-understanding-gate-charge-and-using-it-to-assess-switching-performance|title=Power MOSFET Basics: Understanding Gate Charge and Using It To Assess Switching Performance|website=element14|accessdate=27 November 2010|archive-url=https://web.archive.org/web/20140630044120/http://www.element-14.com/community/docs/DOC-18275/l/power-mosfet-basics-understanding-gate-charge-and-using-it-to-assess-switching-performance |archive-date=30 June 2014 }}</ref>

=== Double-diffused metal–oxide–semiconductor ({{vanchor|DMOS}}) ===
There are ''[[LDMOS]]'' (lateral double-diffused metal oxide semiconductor) and ''VDMOS'' (vertical double-diffused metal oxide semiconductor). Most power MOSFETs are made using this technology.

=== Radiation-hardened-by-design (RHBD) ===
Semiconductor sub-micrometer and nanometer electronic circuits are the primary concern for operating within the normal tolerance in harsh [[radiation]] environments like [[outer space]]. One of the design approaches for making a [[radiation hardening|radiation-hardened-by-design]] (RHBD) device is enclosed-layout-transistor (ELT). Normally, the gate of the MOSFET surrounds the drain, which is placed in the center of the ELT. The source of the MOSFET surrounds the gate. Another RHBD MOSFET is called H-Gate. Both of these transistors have very low leakage currents with respect to radiation. However, they are large in size and take up more space on silicon than a standard MOSFET. In older STI (shallow trench isolation) designs, radiation strikes near the silicon oxide region cause the channel inversion at the corners of the standard MOSFET due to accumulation of radiation induced trapped charges. If the charges are large enough, the accumulated charges affect STI surface edges along the channel near the channel interface (gate) of the standard MOSFET. This causes a device channel inversion to occur along the channel edges, creating an off-state leakage path. Subsequently, the device turns on; this process severely degrades the reliability of circuits. The ELT offers many advantages, including an improvement of [[reliability (semiconductor)|reliability]] by reducing unwanted surface inversion at the gate edges which occurs in the standard MOSFET. Since the gate edges are enclosed in ELT, there is no gate oxide edge (STI at gate interface), and thus the transistor off-state leakage is reduced very much. Low-power microelectronic circuits including computers, communication devices, and monitoring systems in space shuttles and satellites are very different from what is used on earth. They are radiation (high-speed atomic particles like [[proton]] and [[neutron]], [[solar flare]] magnetic energy dissipation in Earth's space, energetic [[cosmic rays]] like [[X-ray]], [[gamma ray]] etc.) tolerant circuits. These special electronics are designed by applying different techniques using RHBD MOSFETs to ensure safe space journeys and safe space-walks of astronauts.