MODFET


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MODFET

[′mäd‚fet]

FET

(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.

MOSFETs
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.
References in periodicals archive ?
Ahlawat, "Analysis of small-signal parameters of 2-D MODFET with polarization effects for microwave analysis," International Journal of VLSI Design & Communication, vol.
Another recent development shows that Si/SiGe MODFETs are capable of operation above 10 GHz.[7,8] in devices with
The FET model generator is general because the same calculation procedure applies to any device for which the model equivalent-circuit is valid, including MESFETs and MODFETs from a wide variety of processes.
Based on our experience with 0.5 [micrometer] MESFETs technology, it was apperceived that the 300 [micrometer] MODFET would be an excellent choice for the forestated requirements.
Schlechtweg, et al., "Coplanar Millimeter-wave ICs for W-band Applications Using 0.15 [micro]m Pseudomorphic MODFETs," IEEE Journal of Solid-state Circuits, Vol.
Seeger, "Low Noise High Speed [Ga.sub..47][In.sub..53]As/[Al.sub..48][In.sub..52]As 0.1-[micro]m MODFETS and High Gain/Bandwidth Three-stage Amplifier Fabricated on GaAs Substrate," Seventh International Conference on Indium Phosphide and Related Materials, 1995, pp.