Editing MOSFET (section)

== Applications ==
Digital [[integrated circuit]]s such as [[microprocessor]]s and memory devices contain thousands to billions of integrated MOSFETs on each device, providing the basic switching functions required to implement [[logic gate]]s and [[data storage]]. Discrete devices are widely used in applications such as [[switch mode power supplies]], [[variable-frequency drive]]s and other [[power electronics]] applications where each device may be switching thousands of watts. Radio-frequency amplifiers up to the [[UHF]] spectrum use MOSFET transistors as analog signal and power amplifiers. Radio systems also use MOSFETs as oscillators, or [[frequency mixer|mixer]]s to convert frequencies. MOSFET devices are also applied in audio-frequency power amplifiers for public address systems, [[sound reinforcement]] and home and automobile sound systems{{citation needed |date=December 2015}}

=== MOS integrated circuits ===
Following the development of [[clean room]]s to reduce contamination to levels never before thought necessary, and of [[photolithography]]<ref>{{ cite web | url = http://www.computerhistory.org/semiconductor/timeline/1955-Photolithography.html |publisher=Computer History Museum |title=1955&nbsp;– Photolithography Techniques Are Used to Make Silicon Devices |access-date=2012-06-02}}</ref> and the [[planar process]] to allow circuits to be made in very few steps, the Si–SiO<sub>2</sub> system possessed the technical attractions of low cost of production (on a per circuit basis) and ease of integration. Largely because of these two factors, the MOSFET has become the most widely used type of transistor in the [[Institution of Engineering and Technology]] (IET).{{citation needed|date=March 2023}}

General Microelectronics introduced the first commercial MOS integrated circuit in 1964.<ref>{{cite web|url=http://www.computerhistory.org/semiconductor/timeline/1964-Commecial.htm|title=1964 – First Commercial MOS IC Introduced}}{{Dead link|date=August 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
Additionally, the method of coupling two complementary MOSFETs (P-channel and N-channel) into one high/low switch, known as CMOS, means that digital circuits dissipate very little power except when actually switched.

The [[microprocessor chronology|earliest microprocessors]] starting in 1970 were all ''MOS microprocessors''; i.e., fabricated entirely from [[PMOS logic]] or fabricated entirely from [[NMOS logic]]. In the 1970s, ''MOS microprocessors'' were often contrasted with ''CMOS microprocessors'' and ''bipolar bit-slice processors''.<ref name="cushman">{{cite web|first=Robert H.|last=Cushman|url=http://www.swtpc.com/mholley/Microprocessors/EDN_Sep_20_1975_6502.pdf|title=2-1/2-generation μP's-$10 parts that perform like low-end mini's|publisher=EDN|date=20 September 1975|access-date=8 August 2013|archive-date=24 April 2016|archive-url=https://web.archive.org/web/20160424050556/http://www.swtpc.com/mholley/Microprocessors/EDN_Sep_20_1975_6502.pdf|url-status=dead}}</ref>

=== CMOS circuits ===
The MOSFET is used in digital complementary metal–oxide–semiconductor ([[CMOS]]) logic,<ref>{{cite web|url=http://www.computerhistory.org/semiconductor/timeline/1963-CMOS.html |title=Computer History Museum&nbsp;– The Silicon Engine &#124; 1963&nbsp;– Complementary MOS Circuit Configuration is Invented |publisher=Computerhistory.org |accessdate=2012-06-02}}</ref> which uses p- and n-channel MOSFETs as building blocks. Overheating is a major concern in [[integrated circuit]]s since ever more transistors are packed into ever smaller chips. CMOS logic reduces power consumption because no current flows (ideally), and thus no [[Power (physics)|power]] is consumed, except when the inputs to [[logic gate]]s are being switched. CMOS accomplishes this current reduction by complementing every nMOSFET with a pMOSFET and connecting both gates and both drains together. A high voltage on the gates will cause the nMOSFET to conduct and the pMOSFET not to conduct and a low voltage on the gates causes the reverse. During the switching time as the voltage goes from one state to another, both MOSFETs will conduct briefly. This arrangement greatly reduces power consumption and heat generation.

==== Digital ====
The growth of digital technologies like the [[microprocessor]] has provided the motivation to advance MOSFET technology faster than any other type of silicon-based transistor.<ref>{{cite web|url=http://www.computerhistory.org/microprocessors/ |title=Computer History Museum&nbsp;– Exhibits&nbsp;– Microprocessors |publisher=Computerhistory.org |accessdate=2012-06-02}}</ref> A big advantage of MOSFETs for digital switching is that the oxide layer between the gate and the channel prevents DC current from flowing through the gate, further reducing power consumption and giving a very large input impedance. The insulating oxide between the gate and channel effectively isolates a MOSFET in one logic stage from earlier and later stages, which allows a single MOSFET output to drive a considerable number of MOSFET inputs. Bipolar transistor-based logic (such as [[transistor-transistor logic|TTL]]) does not have such a high fanout capacity. This isolation also makes it easier for the designers to ignore to some extent loading effects between logic stages independently. That extent is defined by the operating frequency: as frequencies increase, the input impedance of the MOSFETs decreases.

==== Analog ====
The MOSFET's advantages in digital circuits do not translate into supremacy in all [[analog circuit]]s. The two types of circuit draw upon different features of transistor behavior. Digital circuits switch, spending most of their time either fully on or fully off. The transition from one to the other is only of concern with regards to speed and charge required. Analog circuits depend on operation in the transition region where small changes to ''V''{{sub|gs}} can modulate the output (drain) current. The JFET and [[bipolar junction transistor]] (BJT) are preferred for accurate matching (of adjacent devices in integrated circuits), higher [[transconductance]] and certain temperature characteristics which simplify keeping performance predictable as circuit temperature varies.

Nevertheless, MOSFETs are widely used in many types of analog circuits because of their own advantages (zero gate current, high and adjustable output impedance and improved robustness vs. BJTs which can be permanently degraded by even lightly breaking down the emitter-base).{{Vague|date=January 2016}} The characteristics and performance of many analog circuits can be scaled up or down by changing the sizes (length and width) of the MOSFETs used. By comparison, in bipolar transistors follow a different [[scaling law]]. MOSFETs' ideal characteristics regarding gate current (zero) and drain-source offset voltage (zero) also make them nearly ideal switch elements, and also make [[switched capacitor]] analog circuits practical. In their linear region, MOSFETs can be used as precision resistors, which can have a much higher controlled resistance than BJTs. In high power circuits, MOSFETs sometimes have the advantage of not suffering from [[thermal runaway]] as BJTs do.{{Dubious|reason=Depends on circuit topology?|date=January 2016}} This means that complete analog circuits can be made on a silicon chip in a much smaller space and with simpler fabrication techniques. MOSFETS are ideally suited to switch inductive loads because of tolerance to [[Counter-electromotive force|inductive kickback]].

Some ICs combine analog and digital MOSFET circuitry on a single [[mixed-signal integrated circuit]], making the needed board space even smaller. This creates a need to isolate the analog circuits from the digital circuits on a chip level, leading to the use of isolation rings and [[silicon on insulator]] (SOI). Since MOSFETs require more space to handle a given amount of power than a BJT, fabrication processes can incorporate BJTs and MOSFETs into a single device. Mixed-transistor devices are called bi-FETs (bipolar FETs) if they contain just one BJT-FET and [[BiCMOS]] (bipolar-CMOS) if they contain complementary BJT-FETs. Such devices have the advantages of both insulated gates and higher current density.

=== Analog switches ===
{{Unreferenced section|date=September 2016}}

MOSFET analog switches use the MOSFET to pass analog signals when on, and as a high impedance when off. Signals flow in both directions across a MOSFET switch. In this application, the drain and source of a MOSFET exchange places depending on the relative voltages of the source and drain electrodes. The source is the more negative side for an N-MOS or the more positive side for a P-MOS. All of these switches are limited on what signals they can pass or stop by their gate-source, gate-drain and source–drain voltages; exceeding the voltage, current, or power limits will potentially damage the switch. See [[MOSFET#Power MOSFET|Power MOSFET]] subsection down below.

==== Single-type ====
This analog switch uses a four-terminal simple MOSFET of either P or N type.

In the case of an n-type switch, the body is connected to the most negative supply (usually GND) and the gate is used as the switch control. Whenever the gate voltage exceeds the source voltage by at least a threshold voltage, the MOSFET conducts. The higher the voltage, the more the MOSFET can conduct. An N-MOS switch passes all voltages less than ''V''{{sub|gate}} − ''V''{{sub|tn}}. When the switch is conducting, it typically operates in the linear (or ohmic) mode of operation, since the source and drain voltages will typically be nearly equal.

In the case of a P-MOS, the body is connected to the most positive voltage, and the gate is brought to a lower potential to turn the switch on. The P-MOS switch passes all voltages higher than ''V''{{sub|gate}} − ''V''{{sub|tp}} (threshold voltage ''V''{{sub|tp}} is negative in the case of enhancement-mode P-MOS).

==== Dual-type (CMOS) ====
This "complementary" or CMOS type of switch uses one P-MOS and one N-MOS FET to counteract the limitations of the single-type switch. The FETs have their drains and sources connected in parallel, the body of the P-MOS is connected to the high potential (''V''<sub>DD</sub>) and the body of the N-MOS is connected to the low potential (''gnd''). To turn the switch on, the gate of the P-MOS is driven to the low potential and the gate of the N-MOS is driven to the high potential. For voltages between ''V''<sub>DD</sub> − ''V''<sub>tn</sub> and ''gnd'' − ''V''<sub>tp</sub>, both FETs conduct the signal; for voltages less than ''gnd'' − ''V''<sub>tp</sub>, the N-MOS conducts alone; and for voltages greater than ''V''<sub>DD</sub> − ''V''<sub>tn</sub>, the P-MOS conducts alone.

The voltage limits for this switch are the gate-source, gate-drain and source-drain voltage limits for both FETs. Also, the P-MOS is typically two to three times wider than the N-MOS, so the switch will be balanced for speed in the two directions.

[[Three-state logic|Tri-state circuitry]] sometimes incorporates a CMOS MOSFET switch on its output to provide for a low-ohmic, full-range output when on, and a high-ohmic, mid-level signal when off.