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High Electron Mobility Transistors (HEMT)
BY: AARON BUEHLER &
JASON VANDERLINDE
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Outline•Brief History
•What are they?•How they Work•Different Types• Band Structure and Diagrams
•Applications
•Key Points
•References
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Brief History•Developed by Takashi Mimura and colleagues at Fujitsu in Japan in 1979•Faced several issues along the way •Early Applications: • Low noise amplifiers• Installed in radio telescope•Other space and military applications• Commercialization began in 1987 for satellite broadcasting receivers• Commercial production took off in the 90’s
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What are they?•Referred to as heterojunction field-effect transistor (FET)•Abrupt discontinuities •Two layers of different semiconductor with two different band gap energies•Separating majority carriers and ionized impurities minimizes the degradation in mobility and peak velocity•The 2-D electron gas = less electron collisions = less noise
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Different Types•Material: AlGaAs-GaAs•Pseudomorphic HEMT (pHEMT)•Metamorphic HEMT (mHEMT)•Indium Phosphide (InP)•Galium Nitride (GaN)
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HEMT structure
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pHEMT• GaAs pHEMT•< .5 µm gate length•Low noise: 1dB at 12GHz•High gain: 10 dB at 12GHz•Range up to 26GHz•Thin layer so the crystal lattice stretches to fit the other material. •Larger bandgap differences = better performance
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mHEMT•.15 µm gate length•Low noise•High gain•Range up to 100GHz•Large lattice mismatch between the channel and substrate is accommodated by formation of dislocations within a metamorphic buffer.
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Band Structure
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AlGaAs-GaAs HEMT band diagrams
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InP HEMT
Cross section using a scanning electron micrograph
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GaN HEMT•Based on GaN/AlGaN heterojunctions
•Uses a Sapphire (Al3O2)/Silicon Carbonide(SiC) substrate because of the wide energy gap of 3.4 eV and 3.3 eV•Applicable to high power supply voltages because of the wide energy gaps•Can withstand high operating temperatures
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Applications•Originally for high speed applications•High power/ high temperature microwave applications•Power amplifiers•Oscillators•Cell Phones•Radar•Most MMIC’s radio frequency applications
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Key Points•Its two main features are low noise and high frequency capability•A heterojunction is two layers different semiconductors with different band gap energies•The 2-D electron gas is essential to the low noise feature•AlGaAs and GaAs are the most common materials for heterojunction•Used in MMIC’s and radio frequency applications for high performance
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Sources•"GaAs Pseudomorphic HEMT Transistor." Mimix Broadband, Inc. N.p., 19 July 2008. Web. 30 Apr. 2013. <http://www.richardsonrfpd.com/resources/RellDocuments/SYS_4/CF003-
03.pdf>.
•Grunenputt, Erik. "Pseudomorphic and Metamorphic HEMT-technologies for Industrial W-band Low-noise and Power Applications.” Youscribe. N.p., Dec. 2009. Web. 30 Apr. 2013. <http://www.youscribe.com/catalogue/rapports-et-theses/savoirs/pseudomorphic-
and- metamorphic-hemt-technologies-for-industrial-w-band-1426512>.
•Poole, Ian. "HEMT, High Electron Mobility Transistor." Radio-Electronics.com. Adrio Communications, June 2010. Web. 30 Apr. 2013. <http://www.radio-electronics.com/info/data/semicond/fet-field-effect-transistor/hemt-phemt- transistor.php>.
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Sources continued•"0.15-um LN MHEMT 3MI." TriQuint.com. N.p., 29 Nov. 2007. Web. <http://www.triquint.com/prodserv/foundry/docs/0.15.LN.mHEMT.3MI.pdf>.•Göran, Andersson, ed. "High Electron Mobility Transistors (HEMT)." Laboratory for Millimeter-Wave
Electronics. ETH Zurich, 2 Mar 2010. Web. 30 Apr 2013. <http://www.mwe.ee.ethz.ch/en/about-
mwe-group/research/vision-and-aim/high-electron-mobility-transistors-hemt.html>.•Neamen, Donald. Semiconductor Physics and Devices Basic Principles. 4th ed. New York: McGraw-Hill,
2012. 602-9. Print.•Mimura, Takashi. "The Early History of the High Electron Mobility Transistor (HEMT)." Early History of
the High Electron Mobility Transistor (HEMT). 50.3 (2002): 780-82. Web. 30 Apr. 2013. <http://ieeexplore.ieee.org.libpdb.d.umn.edu:2048/stamp/stamp.jsp?tp=&arnumber=989961&tag=1>.