Milestones:High Electron Mobility Transistor, HEMT, 1979
High Electron Mobility Transistor, HEMT, 1979
The HEMT was the first transistor to incorporate an interface between two semiconductor materials with different energy gaps. HEMTs proved superior to previous transistor technologies because of their high mobility channel carriers, resulting in high speed and high frequency performance. They have been widely used in radio telescopes, satellite broadcasting receivers and cellular base stations, becoming a fundamental technology supporting the information and communication society.
Street address(es) and GPS coordinates of the Milestone Plaque Sites
10-1 Morinosato-Wakamiya, Atsugi 243-0197, Japan.GPS coordinates: 35.443405, 139.313921, 10-1 Morinosato-Wakamiya, Atsugi 243-0197, Japan.GPS coordinates: 35.443405, 139.313921
Details of the physical location of the plaque
The plaque will be displayed in the exhibition room on the grand floor of the Atsugi Office, Fujitsu Laboratories Ltd.
How the intended plaque site is protected/secured
The intended plaque site is on a premise of Atsugi Office, Fujitsu Laboratories Ltd. and it is protected by guards. Fujitsu Laboratories Ltd. welcomes any visitors; the prior notification is required before a visit.
Historical significance of the work
The major historical significance concerning High Electron Mobility Transistor (HEMT) is described in detail below.
1. Historical Background of the Birth of HEMT
The fastest transistor before HEMT’s invention was the GaAs Metal-Semiconductor Field Effect Transistor (MESFET) invented in 1966. At the time, the goals of high-speed device development were logic circuits for supercomputers, more powerful radio-wave emitters for microwave applications, and low-noise amplifiers to detect very weak radio signals. Reduction of device dimension was the main technique for improving high-speed performance. But with MESFET, impurities were added to supply electrons in the regions where electrons would travel, and scatterings by ionized impurities limit electron mobility. In 1978, a modulation-doped heterojunction superlattice was reported, which accumulated electrons in an undoped GaAs layer sandwiched between n-type AlGaAs layers. This, however, was not reported to function as a transistor capable of controlling electrons with high mobility.
2. Invention and demonstration of HEMT
Dr. Takashi Mimura of Fujitsu Laboratories conceived of HEMT and applied for a patent on it in 1979 (granted in Japan in 1987 and in the US in 1991). The key point of this design was, in a single heterojunction between n-type AlGaAs and GaAs, introducing a Schottky junction that creates a depletion layer at the surface of the n-type AlGaAs. When operated as a gate, a field effect could be exerted on the two-dimensional electron gas inside the GaAs layer, which can control electron density using the field effect. This resulted in a high-speed transistor that uses a two-dimensional electron gas, which is unaffected by dopant scattering. He published a paper in 1980 demonstrating the first operation of HEMT in which a structure with a single heterojunction of n-AlGaAs and GaAs was used to control a two-dimensional electron gas using the field effect . In this paper, high-speed performances of HEMT were shown to be superior to those of MESFET; the electron mobility and the transconductance at 77K were 5.5 times and 3 times higher, respectively. Research and development on HEMT moved quickly after that, in applications such as high-speed logic circuits and microwaves. Integrated circuits with record breaking switching delay , first HEMT low-noise amplifiers , and HEMT-LSIs for supercomputers  all were reported.
3. Commercialization of HEMT: Low-noise amplifier
The first commercial application of HEMT was a low-noise amplifier. Because of its outstanding low-noise performance, HEMT can be used to receive very weak signals from space. In 1985, HEMT was used in the 45-meter radio telescope at Nobeyama Radio Observatory (NRO), Nagano, Japan, and in 1986, the technology contributed to discoveries relating to the interstellar molecules in Taurus Molecular Cloud about 400 light year away . In the private sector, HEMT was used in satellite broadcasting receivers, and allowed parabolic antennas to be reduced to less than half the diameter, helping to popularize satellite broadcasts in Japan as well as in Europe around 1987. The market of HEMT low-noise amplifiers in 1990 was about one hundred million dollars.
4. Developments and Commercialization of HEMT to the present day
Developments and commercialization of HEMT are continuing to the present day as follows. This expandability supports the significance of HEMT.
(1) Millimeter-wave amplifier
Because HEMT can operate at high frequencies, it can be used to build amplifiers for the millimeter wave band. In the late 1990s, development moved forward on products based on millimeter-wave radar, which is used in vehicles to prevent or mitigate collisions by detecting the distance to and speed difference of the car ahead. At the time, HEMT was used in the transceivers as it is a solid-state device that can operate reliably in the millimeter wave band, allowing the radar hardware to be made smaller, no more than 700-g in weight, for practical use on passenger vehicles .
(2) High-efficiency amplifier
Thanks to the higher performance of HEMT, it can be used to make high-efficiency microwave high power amplifiers [8, 9]. Taking advantage of this characteristic, GaN-based HEMTs are used in high-gain amplifiers for cellular base stations, and has contributed to producing the world’s smallest base stations . In that way HEMT helps support the information and communication society by contributing to the buildout of wireless networks for coping with the explosive growth in communications volume. The market of GaN-based HEMT amplifiers was about three hundred million dollars in 2016, and is expected to increase to six hundred million dollars in 2020.
More recently, demonstration of wireless transmission was reported using InP-based HEMTs in transceivers for the as-yet unused 300-GHz frequency band , and won Best Industry Paper Award at 2016 International Microwave Symposium, IEEE Microwave Theory and Techniques Society, that holds the promise for accommodating future needs for communications volume.
(3) High-efficiency power devices
HEMT’s high efficiency has benefited power conversion devices, as well , leading to the development of the world’s smallest and most efficient AC adapter . Helping make hardware more efficient should contribute to reducing CO2 emissions. The market of GaN-based HEMT power conversion devices is expected to be six hundred million dollars in 2022.
Features that set this work apart from similar achievements
There are a number of distinctive features of HEMT as summarized below.
1. Unique device operation principle and excellent fabrication technologies of HEMT
As mentioned previously, this was the world’s first transistor that used the field effect to control the density of electrons having high mobility. In addition to the ideas for the device structure, it was because Fujitsu Laboratories had exceptional technologies for crystal growth as well as compound semiconductor device fabrication technology that it succeeded in the development of HEMT.
In 1990, Dr. Takashi Mimura, who conceived of HEMT, and Dr. Satoshi Hiyamizu, who was in charge of crystal growth, won the IEEE Morris N. Liebmann Memorial Award “for demonstration of the High Electron mobility Transistor (HEMT).”
In November 10, 2017, Dr. Takashi Mimura received the Kyoto Prize, which is an international award to honor those who have contributed significantly to the scientific, cultural, and spiritual betterment of mankind, in the advanced technology category for “Invention of the High Electron Mobility Transistor (HEMT) and Its Development for the Progress of Information and Communications Technology.”
2. Contribution to social life
HEMT low-noise amplifiers, which take advantage of the technology’s excellent low-noise performance, allowed for parabolic antennas used for satellite broadcasting receivers to be half the previous diameter, contributing to the popularization of satellite broadcasting in the late 1980s. Because radio signals travel without regard for national boundaries, the spread of satellite broadcasting promoted the globalization of information flows. Nowadays, it is widely believed that information transmitted from the West into Eastern Europe by satellite broadcast played an important role in bringing down the Berlin Wall, and HEMT can be said to have been a part of that indirectly.
Commercial applications of millimeter-wave radar in anti-collision systems for vehicles in the late 1990s and early 2000s would not have happened without HEMT, showing the technology’s contribution to public safety.
HEMT has also contributed to high-gain amplifiers in cellular base stations, supporting the massive growth in wireless communications that began in the late 2000s and continues to this day.
As mentioned above HEMT plays a distinguished role as a foundational technology supporting the information and communication society.
3. Contribution to environment
HEMT helps cellular base stations operate more efficiently. With the number of base stations installed around the world rising rapidly, those improvements in efficiency make a significant contribution to helping societies reduce their CO2 emissions. In addition, with HEMT being used in more power conversion devices in the future, that effect will be amplified by the spread of more efficient AC adapters and other products.
4. Contribution to science
Low-noise amplifiers based on HEMT can be used to detect very weak radio signals from space. In 1985, they were used in the radio telescope at NRO, where they contributed to the discoveries relating to the interstellar medium, and since then have been used in radio telescopes around the world to advance the field of astrophysics.
The number of technical papers concerning HEMT increased every year since the first publication of the paper of HEMT in 1980 , and there were 584 publications in 2016 according to the IEEE explore. HEMT has pioneered a new technical area of high frequency and high speed semiconductor devices.
 Japanese Patent, No. 1409643, “Semiconductor Device,” Nov. 24, 1987. [Filing date Dec. 28, 1979] (Equivalent U.S. Patent, No. Re 33584, “HIGH ELECTRON MOBILITY SINGLE HETEROSTRUCTURE DEVICES,” May 7. 1991)
 T. Mimura, S. Hiyamizu, T. Fujii, and K. Nanbu, “A New Field-Effect Transistor with Selectivity Doped GaAs/n-AlGaAs Heterojunctions,” Japan. J. Appl. Phys., vol. 19, 1980, pp. L225-L227.
 T. Mimura, S. Hiyamizu, H. Hashimoto, and M. Fukuta, “High Electron Mobility Transistors with Selectively Doped GaAs/n-AlGaAs Heterojunctions,” IEEE Trans. Electron Devices, vol. ED-27, No. 11, pp. 2197-2197, 1980. Citation: 886.
 M. Niori, T. Saito, K. Joshin, and T. Mimura, “A 20GHz High Electron Mobility Transistor Amplifier for Satellite Communications,” IEEE ISSCC Dig. Tech., 1983, pp. 198-199.
 Y. Watanabe, S. Saito, N. Kobayashi, M. Suzuki, T. Yokoyama, E. Mitani, K. Odani, T. Mimura, and M. Abe, “A HEMT LSI for Multibit Data Register, “ IEEE ISSCC Dig. Tech., 1988, pp. 86-87.
 H. Suzuki, M. Ohishi, N. Kaifu, S. Ishikawa, and T. Kasuga, “Detection of the interstellar C6H radical,” Publ. Astron. Soc. Japan, vol. 38, pp. 911-917, 1986.
 Y. Ohashi, Y. Hasegawa, N. Motoni, H. Yagi, and S. Yamano,” Development of 76 GHz Single Chip MMIC High Frequency Unit,” FUJITSU TEN TECH. J, No. 19, pp. 23 - 31, 2002.
 T. Kikkawa, M. Nagahara, N. Okamoto, Y. Tateno, Y. Yamaguchi, N. Hara, K. Joshin, and P. M. Asbeck, “Surface-charge controlled AlGaN/GaN-power HFET without current collapse and gm dispersion,” IEEE Int. Electron Devices Meeting. Tech. Dig., pp. 25.4.1-25.4.4, 2001.
 K. Joshin, T. Kikkawa, H. Hayashi, T. Maniwa, S. Yokokawa, M. Yokoyama, N. Adachi, and M. Takikawa, “A 174 W high-efficiency GaN HEMT power amplifier for W-CDMA base station applications,” IEEE Int. Electron Devices Meeting. Tech. Dig., pp. 12.6.1 - 12.6.3, 2003.
 Fujitsu Press Release, “Fujitsu Announces Global Launch of Mobile WiMAX Base Stations; BroadOne™ WX300 is world's most compact all-in-one base station,” Feb. 6, 2008. http://www.fujitsu.com/global/about/resources/news/press-releases/2008/0206-01.html,
 H. Song, T. Kosugi, H. Hamada, T. Tajima. A. El Moutaouakil, H. Matsuzaki, M. Yaita, K. Kawano, T. Takahashi, Y. Nakasha, N. Hara, K. Fujii, I. Watanabe, and A. Kasamatsu, “Demonstration of 20-Gbps Wireless Data Transmission at 300 GHz for KIOSK Instant Data Downloading Applications with InP MMIC,” IEEE International Microwave Symposium, Interactive Forum, WEIF2-29, 2016.
 T. Hirose, M. Imai, K. Joshin and K. Watanabe, “Dynamic Performances of GaN-HEMT on Si in Cascode Configuration,” IEEE 29th Applied Power Electronics Conference and Exposition (APEC), pp. 174-181, 2014.
 Fujitsu Press Release, “Fujitsu Wins Grand Prize in 26th Global Environment Award; Recognized for development of the world's smallest and most efficient AC adapter,” March. 3, 2017. http://www.fujitsu.com/global/about/resources/news/press-releases/2017/0303-01.html