HEMT


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HEMT

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

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.
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References in periodicals archive ?
Detailed optical and Scanning Electron Microscope pictures and cross-sections with energy-dispersive X-ray analysis are included to reveal Power Integrations' technical choices at the microscopic level of the IC and HEMT designs.
Fujitsu and Fujitsu Laboratories will conduct an evaluation of the heat resistance and output performance of GaN HEMT power amplifiers using this technology, with the goal of commercializing high output power, high frequency GaN HEMT power amplifiers for use in applications such as radar systems, including weather radar, and 5G wireless communication systems by fiscal 2020.
Made et al., "Role of two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistor (HEMT) ON-state degradation," Microelectronics Reliability, vol.
In short, the TD and HEMT as part of a cavity act as very sensitive cavity oscillations and resonance monitoring combination, which, if developed properly, may offer an extremely valuable and low-noise resonance detection system.
[3.] LuoE, ChenZ., XueL., MattavelliP, BoroyevichD., HughesB., "Design Considerations for GaN HEMT Multichip Half- bridge Module for High-Frequency Power Converters", Applied Power Electronics Conference, 2014, pp.537-544.
This evidences the ability of AlSb/InAs HEMT for RF performances in low drain bias regime.
[V.sub.th] is the threshold voltage of the HEMT given by
Lower gate and S-D leakage currents thus obtained both suggest that the pinch-off characteristics of HEMT could be substantially improved through the incorporation of the multi-[Mg.sub.x][N.sub.y]/GaN buffer.
Jeong, "A highly linear and efficient three-way Doherty amplifier using two-stage GaN HEMT cells for repeater systems," Microwave and Optical Technology Letters, Vol.
Wang, "Millimeter wave MMIC single-pole-double-throw passive HEMT switches using impedance-transformation networks," IEEE Transactions on Microwave Theory and Techniques, Vol.
The simulation of the DC and dynamic characteristics of MESFET and HEMT devices as a function of bias (whether they be static and/or dynamic), temperature and frequency has received much attention over recent years [1-11].