Tubes continue to amaze
Stanford professor sees new role for vacuum tubes
(06/14/2005 5:49 AM EDT)
LONG BEACH, Calif. — The vacuum tube amplifier — or a nano-scale version — may be the best means of exploiting terahertz spectra, according to Stanford University Professor Thomas Lee in a presentation at the IEEE Microwave Technology and Techniques Symposium here.
Semiconductor scaling makes CMOS a useful technology for building RF transmitters and power amplifiers, said Lee. The utility of silicon decreases exponentially with increasing frequency, he said, becoming almost useless at high GHz frequencies.
This is unfortunate, he suggested, since terahertz broadcasting offers two previously underutilized applications: a short-distance, high-data rate wireless communications technique called Extreme Wideband (EWB) and the ability to identify the molecular structure of unknown and frequently hidden materials. This would have utility for medical diagnosis as well as security applications.
Based on antenna research, parallel energy accumulators like phased-array antennas have the best potential for launching carriers at terahertz frequencies. Also needed is a "free-air" radiator like the cathode of a vacuum tube, rather than the inherently resistive material of a semiconductor. "Bashing electrons through a solid is not a good way to go," he said.
Semiconductor technology, however, has given us the ability to scale vacuum tube components down to the submicron level, Lee projected. With MEMS technology, it becomes possible to bond tube-like structures [cathodes, gate screens and plates] onto a semiconductor substrate.