John R. Tucker, professor emeritus at the University of Illinois at Urbana-Champaign (UIUC), and IEEE Microwave Theory and Techniques Society (MTT-S) Microwave Pioneer Award winner, passed away at the age of 70 on 12 April 2014 at his home in Champaign, IL. Prof. Tucker's citation for the 2002 MTT-S Microwave Pioneer Award reads: "For generalizing microwave mixer theory to include photon-assisted tunneling and discovering new effects leading to quantum-noise-limited millimeter wave receivers." This theory is best known as the Tucker Quantum-Mixer Theory. In 2002, he was also named a Fellow of the American Physical Society.
Born in Seattle, he received his B.S. in physics in 1966 from the California Institute of Technology and his Ph.D. in physics in 1972 from Harvard University with a Ph.D. thesis titled, "The Resistive Transition in One-Dimensional Superconductors." During his last year at Harvard, he served as a resident visitor and consultant in the theoretical physics group at Bell Telephone Laboratories. He completed his postdoctoral research with Leo Kadanoff at Brown University.
Prof. Tucker began his work on microwave photon-assisted tunneling as a research scientist at the Aerospace Corporation in 1974. At that time 'Super-Schottky' diodes were being used to set new records for detector sensitivity at temperatures of 1 K. It was questioned if this device could be improved indefinitely at lower temperature and Prof. Tucker demonstrated that the current responsively would approach a fundamental limit as the I-V nonlinearity became sharp on the scale of the quantum energy. He subsequently developed a complete quantum mixer theory. The new phenomena predicted by his theory permitted noiseless amplification of incoming signals during heterodyne down-conversion, a process that was previously thought impossible for resistive mixers. The experiments of other researcher on superconductor-insulator-superconductor (SIS) tunnel junctions confirmed the noiseless amplification in heterodyne down-conversion and also demonstrated important aspects of the theory and SIS receivers.
The quantum mixer theory revolutionized millimeter and submillimeter astronomy through development of SIS tunnel junction receivers operating at or near the fundamental limit for sensitivity set by the Heisenberg uncertainty principle. SIS receivers of this type are currently installed on all major (sub)millimeter astronomical telescopes. Two key examples are the Altacama Large Millimeter Array (ALMA) in Chile, which started operation in March 2013 as one of the world's largest scientific instruments, and the operation of a suite of submillimeter SIS receivers in space for the first time as a part of the Herschel Space Telescope, launched in 2009 by the European Space Agency.
Prof. Tucker joined the faculty of the Department of Electrical and Computer Engineering at UIUC in 1981, recruited by Professor John Bardeen, the two-time Nobel Prize winner who worked at the same nexus of theoretical physics and circuit development as John Tucker. In fact, it is Bardeen's theory of superconductivity—recognized by Bardeen's second Nobel Prize—which underlies the Tucker Quantum-Mixer Theory. Tucker and Bardeen worked together for a number of years investigating the phenomenon of sliding charge density waves in quasi-one-dimensional materials, considering both classical and quantum-mechanical electronic transport mechanisms.
Starting in 1989, Prof. Tucker's work focused on new nanoelectric architectures in silicon. He collaborated with Dr. T.-C. Shen on ultra-high vacuum scanning tunneling microscope (STM) research. This work centered on developing a fabrication process for atom-scale electronic devices in silicon. The STM's low-energy electron beam was used to expose bare dangling bonds. Molecules could then be selectively absorbed onto these STM-exposed patterns to realize conducting pathways based on overlap of individual electron wavefunctions. This process of creating silicon nanoelectronics with atom-scale donor patterns became the focus of efforts to build a silicon-based quantum computer.
In a related research area, Prof. Tucker proposed a new metal silicide source/drain MOS transistor in 1994 that operated by gate-induced (field emission) tunneling and permitted scaling to sub-25nm gate length without impurity doping or non-planar architecture. A new high-frequency world record for an MOS transistor was established in 2004 with p-type silicide source/drain devices of this type fabricated by MIT Lincoln Laboratory. These devices remain among the smallest MOS transistors in overall dimension, and potentially the fastest CMOS technology.
Prof. Tucker was an NRC Senior Fellow at the NASA Institute for Space Studies in New York in 1980, and a Visiting Professor at Technical University of Delft in 1999. He was a member of the Review Panel of Laboratory Directed Research and Development Programs at Los Alamos National Laboratory in May 2001 and 2002. He was Chairman of the NASA/Caltech Jet Propulsion Laboratory MicroDevices Laboratory Visiting Committee starting in 2008.
He is survived by his wife, Mary (Greiner), his son, Ross Tucker of Springfield, IL, and his daughter and son-in-law, Laura (Joel) Furrer of Urbana, IL.
Principal contribution to this article by Greg Lyons. Edited by John Barr.