The field-effect transistor (FET) is an electronic device which uses an electric field to control the flow of current. FETs are devices with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source.
FETs are also known as unipolar transistors since they involve single-carrier-type operation. That is, FETs use electrons or holes as charge carriers in their operation, but not both. Many different types of field effect transistors exist. Field effect transistors generally display very high input impedance at low frequencies.
- 1 History
- 2 Basic information
- 3 More about terminals
- 4 Composition
- 5 Types
- 6 Advantages
- 7 Disadvantages
- 8 Failure modes
- 9 Uses
- 10 Source-gated transistor
- 11 See also
- 12 References
- 13 External links
The concept of a field-effect transistor (FET) was first patented by Julius Edgar Lilienfeld in 1925 and by Oskar Heil in 1934, but they were unable to build a working practical semiconducting device based on the concept. The transistor effect was later observed and explained by the team of William Shockley at Bell Labs in 1947, shortly after the 17-year patent expired. Shockley initially attempted to build a working FET, by trying to modulate the conductivity of a semiconductor, but was unsuccessful, mainly due to problems with their materials, copper compounds and germanium. In the course of trying to understand the mysterious reasons behind their failure to build a working FET, this led them to instead inventing the bipolar point-contact and junction transistors.
The first FET device to be successfully demonstrated was the junction field-effect transistor (JFET) in 1950. The first type of JFET was the static induction transistor (SIT), invented by Japanese engineers Jun-ichi Nishizawa and Y. Watanabe in 1950. The SIT is a type of JFET with a short channel. However, while the JFET was a useful device, it was not what Shockley had originally sought to build.
In the 1950s, Mohamed Atalla investigated the surface properties of silicon semiconductors at Bell Labs, where he proposed a new method of semiconductor device fabrication, coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below, overcoming the surface states that prevented electricity from reaching the semiconducting layer. This is known as surface passivation, a method that became critical to the semiconductor industry as it made possible the mass-production of silicon integrated circuits (ICs). Building on his surface passivation method, he developed the metal–oxide–semiconductor (MOS) process, which he presented in 1957, and later proposed could be used to build the first working silicon FET. The led to the invention of the metal–oxide–semiconductor field-effect transistor (MOSFET) by Mohamed Atalla and Dawon Kahng in 1959.
The MOSFET largely superseded the JFET, and had a profound effect on digital electronic development. With its high scalability, and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuit chips. The MOSFET thus became the most common type of transistor in computers, electronics, and communications technology (such as smartphones). The US Patent and Trademark Office calls the MOSFET a "groundbreaking invention that transformed life and culture around the world".
CMOS (complementary MOS) was invented by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor in 1963. The first report of a floating-gate MOSFET was made by Dawon Kahng and Simon Sze in 1967. A double-gate MOSFET was first demonstrated in 1984 by Electrotechnical Laboratory researchers Toshihiro Sekigawa and Yutaka Hayashi. FinFET (fin field-effect transistor), a type of 3D non-planar multi-gate MOSFET, originated from the research of Digh Hisamoto and his team at Hitachi Central Research Laboratory in 1989.
FETs can be majority-charge-carrier devices, in which the current is carried predominantly by majority carriers, or minority-charge-carrier devices, in which the current is mainly due to a flow of minority carriers. The device consists of an active channel through which charge carriers, electrons or holes, flow from the source to the drain. Source and drain terminal conductors are connected to the semiconductor through ohmic contacts. The conductivity of the channel is a function of the potential applied across the gate and source terminals.
The FET's three terminals are:
- source (S), through which the carriers enter the channel. Conventionally, current entering the channel at S is designated by IS.
- drain (D), through which the carriers leave the channel. Conventionally, current entering the channel at D is designated by ID. Drain-to-source voltage is VDS.
- gate (G), the terminal that modulates the channel conductivity. By applying voltage to G, one can control ID.
More about terminals
All FETs have source, drain, and gate terminals that correspond roughly to the emitter, collector, and base of BJTs. Most FETs have a fourth terminal called the body, base, bulk, or substrate. This fourth terminal serves to bias the transistor into operation; it is rare to make non-trivial use of the body terminal in circuit designs, but its presence is important when setting up the physical layout of an integrated circuit. The size of the gate, length L in the diagram, is the distance between source and drain. The width is the extension of the transistor, in the direction perpendicular to the cross section in the diagram (i.e., into/out of the screen). Typically the width is much larger than the length of the gate. A gate length of 1 µm limits the upper frequency to about 5 GHz, 0.2 µm to about 30 GHz.
The names of the terminals refer to their functions. The gate terminal may be thought of as controlling the opening and closing of a physical gate. This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain. Electron-flow from the source terminal towards the drain terminal is influenced by an applied voltage. The body simply refers to the bulk of the semiconductor in which the gate, source and drain lie. Usually the body terminal is connected to the highest or lowest voltage within the circuit, depending on the type of the FET. The body terminal and the source terminal are sometimes connected together since the source is often connected to the highest or lowest voltage within the circuit, although there are several uses of FETs which do not have such a configuration, such as transmission gates and cascode circuits.
Effect of gate voltage on current
The FET controls the flow of electrons (or electron holes) from the source to drain by affecting the size and shape of a "conductive channel" created and influenced by voltage (or lack of voltage) applied across the gate and source terminals. (For simplicity, this discussion assumes that the body and source are connected.) This conductive channel is the "stream" through which electrons flow from source to drain.
In an n-channel "depletion-mode" device, a negative gate-to-source voltage causes a depletion region to expand in width and encroach on the channel from the sides, narrowing the channel. If the active region expands to completely close the channel, the resistance of the channel from source to drain becomes large, and the FET is effectively turned off like a switch (see right figure, when there is very small current). This is called "pinch-off", and the voltage at which it occurs is called the "pinch-off voltage". Conversely, a positive gate-to-source voltage increases the channel size and allows electrons to flow easily (see right figure, when there is a conduction channel and current is large).
In an n-channel "enhancement-mode" device, a conductive channel does not exist naturally within the transistor, and a positive gate-to-source voltage is necessary to create one. The positive voltage attracts free-floating electrons within the body towards the gate, forming a conductive channel. But first, enough electrons must be attracted near the gate to counter the dopant ions added to the body of the FET; this forms a region with no mobile carriers called a depletion region, and the voltage at which this occurs is referred to as the threshold voltage of the FET. Further gate-to-source voltage increase will attract even more electrons towards the gate which are able to create a conductive channel from source to drain; this process is called inversion.
In a p-channel "depletion-mode" device, a positive voltage from gate to body widens the depletion layer by forcing electrons to the gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile, positively charged acceptor ions.
Conversely, in a p-channel "enhancement-mode" device, a conductive region does not exist and negative voltage must be used to generate a conduction channel.
Effect of drain-to-source voltage on channel
For either enhancement- or depletion-mode devices, at drain-to-source voltages much less than gate-to-source voltages, changing the gate voltage will alter the channel resistance, and drain current will be proportional to drain voltage (referenced to source voltage). In this mode the FET operates like a variable resistor and the FET is said to be operating in a linear mode or ohmic mode.
If drain-to-source voltage is increased, this creates a significant asymmetrical change in the shape of the channel due to a gradient of voltage potential from source to drain. The shape of the inversion region becomes "pinched-off" near the drain end of the channel. If drain-to-source voltage is increased further, the pinch-off point of the channel begins to move away from the drain towards the source. The FET is said to be in saturation mode; although some authors refer to it as active mode, for a better analogy with bipolar transistor operating regions. The saturation mode, or the region between ohmic and saturation, is used when amplification is needed. The in-between region is sometimes considered to be part of the ohmic or linear region, even where drain current is not approximately linear with drain voltage.
Even though the conductive channel formed by gate-to-source voltage no longer connects source to drain during saturation mode, carriers are not blocked from flowing. Considering again an n-channel enhancement-mode device, a depletion region exists in the p-type body, surrounding the conductive channel and drain and source regions. The electrons which comprise the channel are free to move out of the channel through the depletion region if attracted to the drain by drain-to-source voltage. The depletion region is free of carriers and has a resistance similar to silicon. Any increase of the drain-to-source voltage will increase the distance from drain to the pinch-off point, increasing the resistance of the depletion region in proportion to the drain-to-source voltage applied. This proportional change causes the drain-to-source current to remain relatively fixed, independent of changes to the drain-to-source voltage, quite unlike its ohmic behavior in the linear mode of operation. Thus, in saturation mode, the FET behaves as a constant-current source rather than as a resistor, and can effectively be used as a voltage amplifier. In this case, the gate-to-source voltage determines the level of constant current through the channel.
FETs can be constructed from various semiconductors -- silicon is by far the most common. Most FETs are made by using conventional bulk semiconductor processing techniques, using a single crystal semiconductor wafer as the active region, or channel.
Among the more unusual body materials are amorphous silicon, polycrystalline silicon or other amorphous semiconductors in thin-film transistors or organic field-effect transistors (OFETs) that are based on organic semiconductors; often, OFET gate insulators and electrodes are made of organic materials, as well. Such FETs are manufactured using a variety of materials such as silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), and indium gallium arsenide (InGaAs).
In June 2011, IBM announced that it had successfully used graphene-based FETs in an integrated circuit. These transistors are capable of about 2.23 GHz cutoff frequency, much higher than standard silicon FETs.
The channel of a FET is doped to produce either an n-type semiconductor or a p-type semiconductor. The drain and source may be doped of opposite type to the channel, in the case of enhancement mode FETs, or doped of similar type to the channel as in depletion mode FETs. Field-effect transistors are also distinguished by the method of insulation between channel and gate. Types of FETs include:
- The JFET (junction field-effect transistor) uses a reverse biased p–n junction to separate the gate from the body.
- The MOSFET (metal–oxide–semiconductor field-effect transistor) utilizes an insulator (typically SiO2) between the gate and the body.
- The MNOS metal–nitride–oxide–semiconductor transistor utilizes an nitride-oxide layer insulator between the gate and the body.
- The DGMOSFET (dual-gate MOSFET), a FET with two insulated gates.
- The DEPFET is a FET formed in a fully depleted substrate and acts as a sensor, amplifier and memory node at the same time. It can be used as an image (photon) sensor.
- The FREDFET (fast-reverse or fast-recovery epitaxial diode FET) is a specialized FET designed to provide a very fast recovery (turn-off) of the body diode.
- The HIGFET (heterostructure insulated-gate field-effect transistor) is now used mainly in research.
- The MODFET (modulation-doped field-effect transistor) is a high-electron-mobility transistor using a quantum well structure formed by graded doping of the active region.
- The TFET (tunnel field-effect transistor) is based on band-to-band tunneling.
- The IGBT (insulated-gate bipolar transistor) is a device for power control. It has a structure akin to a MOSFET coupled with a bipolar-like main conduction channel. These are commonly used for the 200–3000 V drain-to-source voltage range of operation. Power MOSFETs are still the device of choice for drain-to-source voltages of 1 to 200 V.
- The HEMT (high-electron-mobility transistor), also called a HFET (heterostructure FET), can be made using bandgap engineering in a ternary semiconductor such as AlGaAs. The fully depleted wide-band-gap material forms the isolation between gate and body.
- The ISFET (ion-sensitive field-effect transistor) can be used to measure ion concentrations in a solution; when the ion concentration (such as H+, see pH electrode) changes, the current through the transistor will change accordingly.
- The BioFET (Biologically sensitive field-effect transistor) is a class of sensors/biosensors based on ISFET technology which are utilized to detect charged molecules; when a charged molecule is present, changes in the electrostatic field at the BioFET surface result in a measurable change in current through the transistor. These include EnFETs, ImmunoFETs, GenFETs, DNAFETs, CPFETs, BeetleFETs, and FETs based on ion-channels/protein binding.
- The MESFET (metal–semiconductor field-effect transistor) substitutes the p–n junction of the JFET with a Schottky barrier; and is used in GaAs and other III-V semiconductor materials.
- The NOMFET is a nanoparticle organic memory field-effect transistor.
- The GNRFET (graphene nanoribbon field-effect transistor) uses a graphene nanoribbon for its channel.
- The VeSFET (vertical-slit field-effect transistor) is a square-shaped junctionless FET with a narrow slit connecting the source and drain at opposite corners. Two gates occupy the other corners, and control the current through the slit.
- The CNTFET (carbon nanotube field-effect transistor).
- The OFET (organic field-effect transistor) uses an organic semiconductor in its channel.
- The DNAFET (DNA field-effect transistor) is a specialized FET that acts as a biosensor, by using a gate made of single-strand DNA molecules to detect matching DNA strands.
- The QFET (quantum field effect transistor) takes advantage of quantum tunneling to greatly increase the speed of transistor operation by eliminating the traditional transistor's area of electron conduction.
- The SB-FET (Schottky-barrier field-effect transistor) is a field-effect transistor with metallic source and drain contact electrodes, which create Schottky barriers at both the source-channel and drain-channel interfaces.
- The GFET is a highly sensitive graphene-based field effect transistor used as biosensors and chemical sensors. Due to the 2 dimensional structure of graphene, along with its physical properties, GFETs offer increased sensitivity, and reduced instances of 'false positives' in sensing applications
- The Fe FET uses a ferroelectric between the gate, allowing the transistor to retain its state in the absence of bias - such devices may have application as non-volatile memory.
The FET has high gate-to-main current resistance, on the order of 100 MΩ or more, providing a high degree of isolation between control and flow. Because base current noise will increase with shaping time, a FET typically produces less noise than a bipolar junction transistor (BJT), and is found in noise-sensitive electronics such as tuners and low-noise amplifiers for VHF and satellite receivers. It is relatively immune to radiation. It exhibits no offset voltage at zero drain current and makes an excellent signal chopper. It typically has better thermal stability than a BJT. Because they are controlled by gate charge, once the gate is closed or open, there is no additional power draw, as there would be with a bipolar junction transistor or with non-latching relays in some states. This allows extremely low-power switching, which in turn allows greater miniaturization of circuits because heat dissipation needs are reduced compared to other types of switches.
A field-effect transistor has a relatively low gain–bandwidth product compared to a BJT. The MOSFET is very susceptible to overload voltages, thus requiring special handling during installation. The fragile insulating layer of the MOSFET between the gate and channel makes it vulnerable to electrostatic discharge or changes to threshold voltage during handling. This is not usually a problem after the device has been installed in a properly designed circuit.
FETs often have a very low "on" resistance and have a high "off" resistance. However, the intermediate resistances are significant, and so FETs can dissipate large amounts of power while switching. Thus efficiency can put a premium on switching quickly, but this can cause transients that can excite stray inductances and generate significant voltages that can couple to the gate and cause unintentional switching. FET circuits can therefore require very careful layout and can involve trades between switching speed and power dissipation. There is also a trade-off between voltage rating and "on" resistance, so high-voltage FETs have a relatively high "on" resistance and hence conduction losses.
FETs are relatively robust, especially when operated within the temperature and electrical limitations defined by the manufacturer (proper derating). However, modern FET devices can often incorporate a body diode. If the characteristics of the body diode are not taken into consideration, the FET can experience slow body diode behavior, where a parasitic transistor will turn on and allow high current to be drawn from drain to source when the FET is off.
This section does not cite any sources. (September 2018) (Learn how and when to remove this template message)
The most commonly used FET is the MOSFET. The CMOS (complementary metal oxide semiconductor) process technology is the basis for modern digital integrated circuits. This process technology uses an arrangement where the (usually "enhancement-mode") p-channel MOSFET and n-channel MOSFET are connected in series such that when one is on, the other is off.
In FETs, electrons can flow in either direction through the channel when operated in the linear mode. The naming convention of drain terminal and source terminal is somewhat arbitrary, as the devices are typically (but not always) built symmetrical from source to drain. This makes FETs suitable for switching analog signals between paths (multiplexing). With this concept, one can construct a solid-state mixing board, for example. FET is commonly used as an amplifier. For example, due to its large input resistance and low output resistance, it is effective as a buffer in common-drain (source follower) configuration.
IGBTs are used in switching internal combustion engine ignition coils, where fast switching and voltage blocking capabilities are important.
Source-gated transistors are more robust to manufacturing and environmental issues in large-area electronics such as display screens, but are slower in operation than FETs.
- Lee, Thomas H. (2003). The Design of CMOS Radio-Frequency Integrated Circuits (PDF). Cambridge University Press. ISBN 9781139643771.
- Jun-Ichi Nishizawa (1982). Junction Field-Effect Devices. Semiconductor Devices for Power Conditioning. Springer. pp. 241–272. doi:10.1007/978-1-4684-7263-9_11. ISBN 978-1-4684-7265-3.
- "Martin Atalla in Inventors Hall of Fame, 2009". Retrieved 21 June 2013.
- "Dawon Kahng". National Inventors Hall of Fame. Retrieved 27 June 2019.
- Lojek, Bo (2007). History of Semiconductor Engineering. Springer Science & Business Media. p. 120. ISBN 9783540342588.
- "1960 - Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine. Computer History Museum.
- Lojek, Bo (2007). History of Semiconductor Engineering. Springer Science & Business Media. pp. 321–3. ISBN 9783540342588.
- "960 - Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine. Computer History Museum.
- Motoyoshi, M. (2009). "Through-Silicon Via (TSV)" (PDF). Proceedings of the IEEE. 97 (1): 43–48. doi:10.1109/JPROC.2008.2007462. ISSN 0018-9219.
- "Transistors Keep Moore's Law Alive". EETimes. 12 December 2018. Retrieved 18 July 2019.
- "Who Invented the Transistor?". Computer History Museum. 4 December 2013. Retrieved 20 July 2019.
- "Remarks by Director Iancu at the 2019 International Intellectual Property Conference". United States Patent and Trademark Office. June 10, 2019. Retrieved 20 July 2019.
- "1963: Complementary MOS Circuit Configuration is Invented". Computer History Museum. Retrieved 6 July 2019.
- U.S. Patent 3,102,230, filed in 1960, issued in 1963
- D. Kahng and S. M. Sze, "A floating gate and its application to memory devices", The Bell System Technical Journal, vol. 46, no. 4, 1967, pp. 1288–1295
- Colinge, J.P. (2008). FinFETs and Other Multi-Gate Transistors. Springer Science & Business Media. p. 11. ISBN 9780387717517.
- Sekigawa, Toshihiro; Hayashi, Yutaka (1 August 1984). "Calculated threshold-voltage characteristics of an XMOS transistor having an additional bottom gate". Solid-State Electronics. 27 (8): 827–828. doi:10.1016/0038-1101(84)90036-4. ISSN 0038-1101.
- "IEEE Andrew S. Grove Award Recipients". IEEE Andrew S. Grove Award. Institute of Electrical and Electronics Engineers. Retrieved 4 July 2019.
- "The Breakthrough Advantage for FPGAs with Tri-Gate Technology" (PDF). Intel. 2014. Retrieved 4 July 2019.
- Jacob Millman (1985). Electronic devices and circuits. Singapore: McGraw-Hill International. p. 397. ISBN 978-0-07-085505-2.
- Jacob Millman (1985). Electronic devices and circuits. Singapore: McGraw-Hill. pp. 384–385. ISBN 978-0-07-085505-2.
- Galup-Montoro, C.; Schneider, M.C. (2007). MOSFET modeling for circuit analysis and design. London/Singapore: World Scientific. p. 83. ISBN 978-981-256-810-6.
- Norbert R Malik (1995). Electronic circuits: analysis, simulation, and design. Englewood Cliffs, NJ: Prentice Hall. pp. 315–316. ISBN 978-0-02-374910-0.
- Spencer, R.R.; Ghausi, M.S. (2001). Microelectronic circuits. Upper Saddle River NJ: Pearson Education/Prentice-Hall. p. 102. ISBN 978-0-201-36183-4.
- Sedra, A. S.; Smith, K.C. (2004). Microelectronic circuits (Fifth ed.). New York: Oxford University Press. p. 552. ISBN 978-0-19-514251-8.
- PR Gray; PJ Hurst; SH Lewis; RG Meyer (2001). Analysis and design of analog integrated circuits (Fourth ed.). New York: Wiley. pp. §1.5.2 p. 45. ISBN 978-0-471-32168-2.
- Bob Yirka (10 January 2011). "IBM creates first graphene based integrated circuit". Phys.org. Retrieved 14 January 2019.
- Lin, Y.-M.; Valdes-Garcia, A.; Han, S.-J.; Farmer, D. B.; Sun, Y.; Wu, Y.; Dimitrakopoulos, C.; Grill, A; Avouris, P; Jenkins, K. A. (2011). "Wafer-Scale Graphene Integrated Circuit". Science. 332 (6035): 1294–1297. doi:10.1126/science.1204428. PMID 21659599.
- Belle Dumé (10 December 2012). "Flexible graphene transistor sets new records". Physics World. Retrieved 14 January 2019.
- freepatentsonline.com, HIGFET and method - Motorola]
- Ionescu, A. M.; Riel, H. (2011). "Tunnel field-effect transistors as energy-efficient electronic switches". Nature. 479 (7373): 329–337. doi:10.1038/nature10679. PMID 22094693.
- Schöning, Michael J.; Poghossian, Arshak (2002). "Recent advances in biologically sensitive field-effect transistors (BioFETs)" (PDF). Analyst. 127 (9): 1137–1151. doi:10.1039/B204444G.
- "Organic transistor paves way for new generations of neuro-inspired computers". ScienceDaily. January 29, 2010. Retrieved January 14, 2019.
- Sarvari H.; Ghayour, R.; Dastjerdy, E. (2011). "Frequency analysis of graphene nanoribbon FET by Non-Equilibrium Green's Function in mode space". Physica E: Low-dimensional Systems and Nanostructures. 43 (8): 1509–1513. doi:10.1016/j.physe.2011.04.018.
- Jerzy Ruzyllo (2016). Semiconductor Glossary: A Resource for Semiconductor Community. World Scientific. p. 244. ISBN 978-981-4749-56-5.
- Appenzeller, J, et al. (November 2008). "Toward Nanowire Electronics". IEEE Transactions on Electron Devices. 55 (11): 2827–2845. doi:10.1109/ted.2008.2008011. ISSN 0018-9383. OCLC 755663637.
- Prakash, Abhijith; Ilatikhameneh, Hesameddin; Wu, Peng; Appenzeller, Joerg (2017). "Understanding contact gating in Schottky barrier transistors from 2D channels". Scientific Reports. 7 (1): 12596. doi:10.1038/s41598-017-12816-3. ISSN 2045-2322. OCLC 1010581463. PMC 5626721. PMID 28974712.
- Miklos, Bolza. "What Are Graphene Field Effect Transistors (GFETs)?". Graphenea. Retrieved 14 January 2019.
- VIII.5. Noise in Transistors
- Allen Mottershead (2004). Electronic devices and circuits. New Delhi: Prentice-Hall of India. ISBN 978-81-203-0124-5.
- Slow Body Diode Failures of Field Effect Transistors (FETs): A Case Study.
- Sporea, R.A.; Trainor, M.J.; Young, N.D.; Silva, S.R.P. (2014). "Source-gated transistors for order-of-magnitude performance improvements in thin-film digital circuits". Scientific Reports. 4: 4295. doi:10.1038/srep04295. PMC 3944386. PMID 24599023.
|Wikimedia Commons has media related to Field-effect Transistors.|
- PBS The Field Effect Transistor
- How Semiconductors and Transistors Work (MOSFETs) WeCanFigureThisOut.org
- Junction Field Effect Transistor
- CMOS gate circuitry
- Winning the Battle Against Latchup in CMOS Analog Switches
- Field Effect Transistors in Theory and Practice
- The Field Effect Transistor as a Voltage Controlled Resistor
- "The FET (field effect transistor)". rolinychupetin (L.R.Linares). March 30, 2013 – via YouTube.