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McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


(Field Effect Transistor) One of two major categories of transistor; the other is bipolar. FETs use a gate element that, when charged, creates an electromagnetic field that changes the conductivity of a silicon channel and turns the transistor on or off. FETs are fabricated as individually packaged discrete components as well as by the hundreds of millions on a single chip.

FETs vs. Bipolar
FET-based silcon chips are easier to construct than their bipolar counterparts. FETs switch a little slower than bipolar transistors, but use less power. Once the gate terminal on an FET has been charged, no more current is needed to keep that transistor on (closed) for the duration of time required. By comparison, a bipolar transistor requires a small amount of current flowing to keep the transistor on. While the current for one transistor may be negligible, it adds up when millions are switching simultaneously. The heat dissipated on bipolar limits the total number of transistors that can be built on the chip, which is why CMOS logic (based on FETs) is used to build chips with millions of transistors.

The most widely used and widely known FETs are MOSFETs (metal oxide semiconductor FETs), which come in NMOS (n-channel) and PMOS (p-channel) varieties. On a chip, NMOS and PMOS transistors are wired together in a complementary fashion to create CMOS logic, which is the most predominant and used in almost every electronic device today. See MOSFET and n-type silicon.

There Are Many Kinds of FETs
Similar to MOSFETs are JFETs (junction FETs), which use a PN junction gate rather than a poly-crystalline gate. Used for microwave communications, MESFETs (metal semiconductor FETs) are similar to JFETs, but use a Schottky metal gate and are made from gallium arsenide or indium phosphide, not silicon. Evolving from MESFETs for higher-frequency applications are HEMTs and PHEMTs (high electron mobility transistors and pseudomorphic high electron mobility transistors). HEMTs are also called MODFETs, TEGFETs and SDHTs (modulation doped FETs, two-dimensional electron gas FETs and selectively doped heterojunction transistors).

Another high-frequency FET is the gallium arsenide-based CHFET (complementary heterostructure FET), which uses a complementary architecture similar to CMOS.

FETs vs. Bipolar
After the gate is charged in an FET, no more current flows, but the transistor remains closed (turned on) during the required time period. Bipolar transistors (BJTs) require current the entire time the transistor must be closed.
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References in periodicals archive ?
The introduction of photoexcitation now serves to increase the available minority carriers, augmenting the inversion layer and shifting more of the voltage drop to the BOX and the embedded MESFET. The channel thus constricts incrementally, and [I.sub.DS] drops accordingly.
As with the previous case, in this section we demonstrate the accuracy of the modeling approach with a lower power GaAs MESFET. In Table 2, the parameters associated with the [I.sub.ds] current source are shown.
Pedro, "Physics Based MESFET Empirical Model," IEEE International Microwave Symposium Digest, San Diego, CA, 1994, pp.
Three typical microwave amplifier designs were then used as illustration examples, covering various transistor technologies (Si BJT, GaAs MESFET and GaN HEMT) and applications (low noise and power amplifiers).
Currently, low-noise MESFETs with device size in the 75-[micro]m region are capable of producing up to 8 dB of gain, with 2.7-dB noise figures at 60 GHz.
To examine the variation of IV measurements with dwell time and sweep rate, the DC IV characteristics of a commercial 1 W GaAs MESFET and a 7 W power Si MOSFET were measured using a Keithley 4200 Semiconductor Characterization System.
The performance of the TQTRX MESFET process is contrasted against the TQPED pHEMT technology in Table 1.
Advances in GaAs MESFET technology require accurate large-signal MESFET models to correctly predict the circuit performance of power amplifiers and oscillators utilized in RF applications and communication systems.
A new automated system for observing the dependence of the IV characteristics of GaAs MESFET devices on electric field, frequency and thermal effects is presented.
The GENESYS Advanced Modeling Kit includes device models for a range of new MOSFET, MESFET, BJT and other device models (see Table 1).
The model AM 100MX-CU GaAs FET is part of a series of GaAs MESFET power products.