Session chairperson and summary author: W. Devereux Palmer
There is no argument that vacuum microelectronics has the power to transform the field of vacuum electronics. As operating frequency increases, tolerance limits in standard manufacturing techniques will force the move to photolihtographic definition and chemical machining of interaction structures. Moreover, field-emission or cold cathodes hold the promise of low-power, fast-turn-on, and high-frequency modulation of the electron beam at the cathode. The people presenting papers in this session are part of the community that will bring about this transformation.
The first session paper, given by Dr. Charles Hunt with the University of California at Davis, presented an overview of the 14th International Vacuum Microelectronics Conference (IVMC-2001). This paper showcased the progress of the field of vacuum microelectronics from its initial focus on microwave amplifiers, through a period of development in flat-panel displays, to the wide-ranging and sometimes novel application areas of current interest. Summaries of papers on spacecraft propulsion systems and other space applications, terabit mass storage devices, high-resolution high-throughput lithography systems, lighting, power control, and applications in analytical instrumentation were shown. The technologies represented included carbon-based emitters (nanotubes, micro- and nano-crystalline surfaces, and structured diamond-like tips) and Spindt-type emitters made from various materials including carbides and nitrides.
The second paper, given by Dr. Takiguchi of NHK Science and Technical Research Laboratories in Japan, presented work on a High-gain Avalanche Rushing amorphous Photoconductor, or HARP, camera tube. In the presented device, icident light generates electric charges that are multiplied by the HARP target. These charges recombine with electrons emitted from the underlying field emitter array to produce an output signal current. The technology is under development at NHK and Futaba as a high-sensitivity, high-resolution replacement for current CCD image sensors. Several example monochrome images were shown in the paper, including a short movie.
The third paper, given by Dr. Capp Spindt of SRI International, explained a method of heat treatment to achieve more uniform emission from individual tips and thus a higher total current output for a given array. Cathodes fabricated at SRI and conditioned using this technique generated significant RF output power using cathode current modulation in a Northrup-Grumman TWT as reported in paper number 11.1 of this conference: "Characterization of Field Emitter Arrays Operating In A Traveling Wave Tube Amplifier" by Whaley et al.
The fourth paper, given by Dr. Robert Espinosa of Microwave Power Technology in Campbell CA, showed a commercial hand-held X-ray spectroscopy instrument that uses a nanostructured carbon cold cathode. The instrument is currently available from Oxford X-Ray Technology in Scotts Valley CA. The cold cathode yielded a reduction in size, weight, and power requirements for the unit, in addition to eliminating the complications associated with radioactive isotope sources.
The fifth and final paper of the session presented work done jointly by Saratov State University in Russia and Seoul National University in Korea on micromachined microwave devices using cold cathodes. The speaker, Dr. Ryskin of Saratov State University, gave results from numerical simulations of micromachined analogs to the traveling-wave klystron, klystrode, and crossed-field amplifier structures, in addition to a novel proposed structure with a distributed field emission cathode.
The abundance of commercial applications and the range of new ideas presented in the Vacuum Microelectronics session of IVEC 2002 reinforces the view that the field of vacuum microelectronics continues to grow both in participation and technical diversity.