Thermionic energy converters (TECs) were conceived in 1915, demonstrated in 1939, and were the focus of huge investments during the Cold War by the U.S. and the Soviet Union. A 6 kW thermionic converter, fabricated using precision machining technology, was flown in 1987 by the Soviet Union. TEC research ramped down in the 1990s and the field withered to a few embers by 2005. I will review the simple physics of TECs and what the barriers have been to applying them to direct heat-to-electricity conversion for terrestrial applications.
Over the past decade, new materials, processes, and device architectures are being explored at Stanford, the Max Planck Institute, and other research groups around the world. I will provide an update on recent progress at Stanford on thermally isolated, suspended micro cathodes inspired by microbolometer infrared imagers. In order to reach useful efficiencies, both very high thermal isolation between the cathode and the anode and a much lower anode work function are needed. Over the past year, two approaches to fabricating anodes with work functions of 1 eV or less have been demonstrated at Stanford: the electrostatic doping of graphene and the surface photovoltage in a semiconductor anode.
Roger T. Howe is the William E. Ayer Professor in the Department of Electrical Engineering at Stanford University. He received a B.S. degree in physics from Harvey Mudd College and an M.S. and Ph.D. in electrical engineering from the University of California, Berkeley in 1981 and 1984. After faculty positions at CMU and MIT from 1984-1987, he returned to Berkeley where he was a Professor until 2005. His research group focuses on nano electromechanical system design and fabrication for a variety of applications. He was elected an IEEE Fellow in 1996, was co-recipient of the IEEE Cledo Brunetti Award in 1998, and was elected to the National Academy of Engineering in 2005, and is the co-recipient of the inaugural IEEE Robert Bosch Award for Micro and Nano Electromechanical Systems in 2015. He co-founded Silicon Clocks in 2004 to commercialize integrated MEMS resonator-based timing products, which was acquired by Silicon Labs in 2010. He is the Faculty Director of the Stanford Nanofabrication Facility since 2009 and was the Director of the NSF's National Nanotechnology Infrastructure Network (NNIN) from 2011-2015.