Field-effect transistor
The field-effect transistor (FET) is a type of
FETs are also known as unipolar transistors since they involve single-carrier-type operation. That is, FETs use either
History
The concept of a field-effect transistor (FET) was first patented by the Austro-Hungarian born physicist Julius Edgar Lilienfeld in 1925[1] 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 John Bardeen and Walter Houser Brattain while working under 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 the surface states, the dangling bond, and the germanium and copper compound materials. In the course of trying to understand the mysterious reasons behind their failure to build a working FET, it led to Bardeen and Brattain instead inventing the point-contact transistor in 1947, which was followed by Shockley's bipolar junction transistor in 1948.[2][3]
The first FET device to be successfully built was the
The foundations of MOSFET technology were laid down by the work of
After Bardeen's surface state theory the trio tried to overcome the effect of surface states. In late 1947, Robert Gibney and Brattain suggested the use of electrolyte placed between metal and semiconductor to overcome the effects of surface states. Their FET device worked, but amplification was poor. Bardeen went further and suggested to rather focus on the conductivity of the inversion layer. Further experiments led them to replace electrolyte with a solid oxide layer in the hope of getting better results. Their goal was to penetrate the oxide layer and get to the inversion layer. However, Bardeen suggested they switch from silicon to germanium and in the process their oxide got inadvertently washed off. They stumbled upon a completely different transistor, the point-contact transistor. Lillian Hoddeson argues that "had Brattain and Bardeen been working with silicon instead of germanium they would have stumbled across a successful field effect transistor".[8][9][10][11][12]
By the end of the first half of the 1950s, following theoretical and experimental work of Bardeen, Brattain, Kingston, Morrison and others, it became more clear that there were two types of surface states. Fast surface states were found to be associated with the bulk and a semiconductor/oxide interface. Slow surface states were found to be associated with the oxide layer because of adsorption of atoms, molecules and ions by the oxide from the ambient. The latter were found to be much more numerous and to have much longer relaxation times. At the time Philo Farnsworth and others came up with various methods of producing atomically clean semiconductor surfaces.
In 1955, Carl Frosch and Lincoln Derrick accidentally covered the surface of silicon wafer with a layer of silicon dioxide. They showed that oxide layer prevented certain dopants into the silicon wafer, while allowing for others, thus discovering the passivating effect of oxidation on the semiconductor surface. Their further work demonstrated how to etch small openings in the oxide layer to diffuse dopants into selected areas of the silicon wafer. In 1957, they published a research paper and patented their technique summarizing their work. The technique they developed is known as oxide diffusion masking, which would later be used in the fabrication of MOSFET devices. At Bell Labs, the importance of Frosch's technique was immediately realized. Results of their work circulated around Bell Labs in the form of BTL memos before being published in 1957. At Shockley Semiconductor, Shockley had circulated the preprint of their article in December 1956 to all his senior staff, including Jean Hoerni.[6][13][14]
In 1955,
Metal-oxide-semiconductor FET (MOSFET)
A breakthrough in FET research came with the work of Egyptian engineer
The
Basic information
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.[36] 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:[37]
- 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 leaving 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
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.
Unlike BJTs, the vast majority of FETs are electrically symmetrical. The source and drain terminals can thus be interchanged in practical circuits with no change in operating characteristics or function. This can be confusing when FET's appear to be connected "backwards" in schematic diagrams and circuits because the physical orientation of the FET was decided for other reasons, such as printed circuit layout considerations.
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.
n-channel FET
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 an active channel from source to drain; this process is called inversion.
p-channel FET
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.[38][39]
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;[40] although some authors refer to it as active mode, for a better analogy with bipolar transistor operating regions.[41][42] 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,
Composition
FETs can be constructed from various semiconductors, out of which silicon is by far the most common. Most FETs are made by using conventional bulk
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.[43][44] These transistors are capable of about 2.23 GHz cutoff frequency, much higher than standard silicon FETs.[45]
Types
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 insulator (typically SiO2) between the gate and the body. This is by far the most common type of FET.
- The DGMOSFET (dual-gate MOSFET) or DGMOS, a MOSFET with two insulated gates.
- 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 JLNT (Junctionless nanowire transistor) is a type of Field-effect transistor (FET) which channel is one or multiple nanowires and does not present any junction.
- The MNOS (insulatorbetween the gate and the body.
- The pH electrode) changes, the current through the transistor will change accordingly.
- The DNAFETs, cell-based BioFETs (CPFETs), beetle/chip FETs (BeetleFETs), and FETs based on ion-channels/protein binding.[46]
- 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.
- GAAFETor gate-all-around FET, used on high density processor chips
- The DGMOSFET (
- The JFET (junction field-effect transistor) uses a reverse biased p–n junction to separate the gate from the body.
- The static induction transistor (SIT) is a type of JFET with a short channel.
- 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, making it convenient for driving inductive loads such as electric motors, especially medium-powered brushless DC motors.
- The HIGFET (heterostructure insulated-gate field-effect transistor) is now used mainly in research.[47]
- 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.[48]
- The TQFET (topological quantum field-effect transistor) switches a 2D material from dissipationless topological insulator ('on' state) to conventional insulator ('off' state) using an applied electric field.[49]
- The AlGaAs. The fully depleted wide-band-gap material forms the isolation between gate and body.
- The III-V semiconductormaterials.
- The NOMFET is a nanoparticle organic memory field-effect transistor.[50]
- The GNRFET (graphene nanoribbon field-effect transistor) uses a graphene nanoribbon for its channel.[51]
- 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.[52]
- The CNTFET (carbon nanotube field-effect transistor).
- The OFET (organic field-effect transistor) uses an organic semiconductor in its channel.
- 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.[53][54]
- 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[55]
- The 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.
- VTFET, or finFET to allow higher density and lower power.[56]
Advantages
Field-effect transistors have high gate-to-drain current resistance, of 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[
Because the FETs 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.
Disadvantages
A field-effect transistor has a relatively low gain–bandwidth product compared to a bipolar junction transistor. MOSFETs are very susceptible to overload voltages, thus requiring special handling during installation.[58] The fragile insulating layer of the MOSFET between the gate and the 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.[59]
Failure modes
Field-effect transistors are relatively robust, especially when operated within the temperature and electrical limitations defined by the manufacturer (proper
Uses
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 (
IGBTs are used in switching internal combustion engine ignition coils, where fast switching and voltage blocking capabilities are important.
Source-gated transistor
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.[61]
See also
- Chemical field-effect transistor
- CMOS
- FET amplifier
- Field effect (semiconductor)
- FinFET
- FlowFET
- Multigate device
References
- ^ Lilienfeld, J.E. "Method and apparatus for controlling electric current" Archived 2022-04-09 at the Wayback Machine US Patent no. 1,745,175 (filed: 8 October 1926 ; issued: 28 January 1930).
- ^ ISBN 978-1-139-64377-1. Archived from the original(PDF) on 2019-12-09. Retrieved 2019-07-20.
- ^ ISBN 978-3-527-34053-8.
- ISBN 978-3-642-13884-3.
- ISBN 978-1-4684-7265-3.
- ^ ISBN 978-0-470-50892-3.
- ^ "The Foundation of Today's Digital World: The Triumph of the MOS Transistor". Computer History Museum. 13 July 2010. Retrieved 21 July 2019.
- ^ .
- ^ Hans Camenzind (2005). Designing Analog Chips.
- ISBN 978-1-56677-130-6.
- .
- ISBN 978-0-393-04124-8.
- ISBN 978-0-262-01424-3.
- ISBN 978-1-56677-376-8.
- ISBN 978-3-540-34258-8.
- ISBN 978-3-7392-4894-3.
- ISBN 978-1-4665-5401-6.
- ISBN 978-0-8018-8639-3.
- ^ "Martin Atalla in Inventors Hall of Fame, 2009". Retrieved 21 June 2013.
- ^ a b "Dawon Kahng". National Inventors Hall of Fame. Retrieved 27 June 2019.
- ^ "1960 - Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine. Computer History Museum.
- ^ ISBN 978-3-540-34258-8.
- ^ "960 - Metal Oxide Semiconductor (MOS) Transistor Demonstrated". The Silicon Engine. Computer History Museum.
- S2CID 29105721.
- EETimes. 12 December 2018. Retrieved 18 July 2019.
- ^ "Who Invented the Transistor?". Computer History Museum. 4 December 2013. Retrieved 20 July 2019.
- ISBN 978-0-08-050804-7.
- ^ a b "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
- ISBN 978-0-387-71751-7.
- 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.
- ISBN 978-0-07-085505-2.
- ^ ISBN 978-0-07-085505-2.
- ^
Galup-Montoro, C.; Schneider, M.C. (2007). MOSFET modeling for circuit analysis and design. London/Singapore: ISBN 978-981-256-810-6.
- 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.
- S2CID 3020496.
- ^ Belle Dumé (10 December 2012). "Flexible graphene transistor sets new records". Physics World. Retrieved 14 January 2019.
- PMID 12375833.
- ^ freepatentsonline.com, HIGFET and method - Motorola]
- S2CID 4322368.
- ^ Dumé, Isabelle (12 December 2018). "Topological off-on switch could make new type of transistor". Physics World. IOP Publishing. Retrieved 16 January 2022.
- ^ "Organic transistor paves way for new generations of neuro-inspired computers". ScienceDaily. January 29, 2010. Retrieved January 14, 2019.
- .
- ISBN 978-981-4749-56-5.
- S2CID 703393.
- PMID 28974712.
- ^ Miklos, Bolza. "What Are Graphene Field Effect Transistors (GFETs)?". Graphenea. Retrieved 14 January 2019.
- ^ IBM Research Unveils 'VTFET': A Revolutionary New Chip Architecture Which is Two Times the Performance finFET Dec 2021
- ^ VIII.5. Noise in Transistors
- ISBN 978-81-203-0124-5.
- ^ Bhalla, Anup (2021-09-17). "Origins of SiC FETs and Their Evolution Toward the Perfect Switch". Power Electronics News. Retrieved 2022-01-21.
- ^ Slow Body Diode Failures of Field Effect Transistors (FETs): A Case Study.
- PMID 24599023.
External links
- 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.