High Electron Mobility Transistors (HEMT) BY: Aaron Buehler & Jason Vanderlinde
Outline • Brief History • What are they? • How they Work • Different Types • Band Structure and Diagrams • Applications • Key Points • References
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
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
Different Types • Material: AlGaAs-GaAs • Pseudomorphic HEMT (pHEMT) • Metamorphic HEMT (mHEMT) • Indium Phosphide (InP) • Galium Nitride (GaN)
pHEMT • GaAspHEMT • < .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
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.
InP HEMT Cross section using a scanning electron micrograph
GaN HEMT • Based on GaN/AlGaNheterojunctions • 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
Applications • Originally for high speed applications • High power/ high temperature microwave applications • Power amplifiers • Oscillators • Cell Phones • Radar • Most MMIC’s radio frequency applications
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
Sources • "GaAsPseudomorphic 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>.
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=98996 1&tag=1>.