EE PhD Oral Examination - Justin Snapp, Thursday May 3, 3pm CISX 101 Auditorium
jsnapp at stanford.edu
Mon Apr 30 10:06:11 PDT 2012
Sidewall Silicon Carbide Emitters for Integrated Terahertz Vacuum Microelectronics
Department of Electrical Engineering
Advisor: Prof. Thomas H. Lee
Co-Advisor: Prof. Roger T. Howe
Thursday, May 3, 2012
3:00 pm (refreshments at 2:45 pm)
Paul G. Allen Auditorium (Allen CIS-X 101)
The frequency band from 250 GHz to 2.5 THz is rich in potential applications, but suffers from a lack of efficient sources. This “THz gap” arises from the sharp decrease in the efficiency of solid-state electronic amplifiers at frequencies above 100 GHz and the unavailability of compact, uncooled optical sources for wavelengths longer than the infrared. Future THz systems hold great promise for leveraging the unique properties of THz waves, which are long enough in wavelength to be penetrating through clothing and skin, but short enough to be useful for imaging, resonant with complex molecular bonds, and low enough in energy to be safe and non-ionizing. In additions to applications in security screening and medical imaging, continuous wave THz systems would also enable short-range extreme wideband communications.
We propose a micro-fabricated Barkhausen-Kurz (u-BK) oscillator as a promising candidate source. The u-BK oscillator has significant advantages over other vacuum electronic devices, promising high DC-to-THz efficiency and low startup current requirements. This device achieves low impedance, even when operated at harmonics of the electron orbit frequency, by extracting energy over multiple passes of favorably phased electrons confined within a potential well. The need for an emitter integrated into a parabolic potential well poses a major fabrication challenge. The basic fabrication process for the cavity and integrated poly-silicon carbide thermionic cathode has been demonstrated, providing the foundation for developing stable cathodes for injecting a sheet electron beam and for optimizing the electrode geometry for defining a parabolic potential well.
The talk will discuss why the proposed u-BK oscillator is a promising candidate for future efficient integrated THz circuits. The fabrication process and results for the sidewall lateral emitter integratable into a silicon u-BK cavity process will be presented. Experimental results from emission testing on integrated diode test structures under testing in a vacuum chamber will be shown. Additionally future work towards the development of a fully realized integrated THz source will be discussed. The demonstrated sidewall filament emitters allow the design of radically new vacuum electronics that combine electron emitters, coupled resonant cavities and lithographically shaped electrodes in a single substrate. This will enable a new class of efficient THz vacuum electronic integrated circuits.
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