Development of a micromachined THz nanoklystron: a status report

Abstract

Summary form only given. A novel monolithic micro-tube source for submillimeter-wave (0.3 THz, 0.6 THz, 1.2 THz) power generation is being developed at JPL. The tube takes the form of a simple reflex klystron with micrometer range dimensions, nanoklystron, fabricated monolithically in silicon. Nanoklystrons are to be used as local oscillator elements for high-resolution heterodyne spectroscopy instruments and as THz sources for bio-imagers and contraband detectors, high bandwidth communications and atmospheric chemical and biohazard probes. Initial estimates indicate power output in the range of milliwatts at 1.2 THz, which is significantly higher than that possible with other oscillators or multiplier based sources. The device requires an electron gun capable of providing up to a kA/cm/sup 2/. Both cold and hot cathodes are being developed, with cold cathodes being the preferred choice for the eventual stand-alone device. Through a systematic study, ropes of multi-walled carbon nanotubes (MWNTs) have been identified as the most suitable candidate for the electron source. Using MWNTs synthesized on e-beam patterned catalyst arrays with varying parameters (bundle diameter and inter-bundle spacing), a suitable arrangement for high emission currents at low fields has been determined. We can repeatedly generate >1.4 A/cm/sup 2/ at fields as low as <3 V//spl mu/m, prior to focusing. The raw emission density can be further increased and this, in combination with beam focusing optics, is expected to achieve the required target current densities. For initial testing, a very high-resolution crossover type hot electron gun has been developed. The gun was designed to deliver /spl sim/0.5 kA/cm/sup 2/ at the repeller of the nanoklystron. The source current density was designed for 16.2 A/cm2. The gun includes three grids, one electrostatic lens and a magnetic lens and is mounted with a 0.6 THz copper constructed nanoklystron with a phosphor screen at the back end. The electron beam was successfully focused onto the phosphor screen behind the device (through the empty repeller hole) in a tunnel of /spl sim/40 /spl mu/m diameter. A current of 3.4 mA was recorded at the phosphor screen amounting to a current density of /spl sim/270 A/cm/sup 2/. This gun will be used for device testing after a shaped repeller electrode has been installed.