Vacuum Nanoelectronics Integrated with Silicon: Vacuum electronics technology may sound like ancient
history but a team from MIT has used a modern variant to make some very futuristic devices. They are
nanoscale cold cathodes (tiny electron guns) built from arrays of nanowire field emitters that can be integrated
with traditional silicon technology. The integrated devices may enable compact new RF amplifiers and sources
of terahertz, infrared and X-ray energy. They combine the positive aspects of solid state semiconductors (high
gain and low noise) with those of vacuum electronics (high power and efficiency). They demonstrated a current
density of >100 A/cm2, more than a hundredfold greater than any other field-emission cathode operated in
continuous wave mode. At the same time, the devices also exhibited long lifetimes and low-voltage operation.
Each emitter (6-8nm tip diameter) sits atop a vertical silicon nanowire (10µm tall, 100-200nm in diameter). The
nanowire acts as a current limiter to protect the emitter from possible damage from heating and arcing. The
team built emitter arrays as large as 1,000 x 1,000.
The top view is a schematic of the device structure.
The two bottom images are, at left, a scanning electron microscope cross-sectional view of the silicon
nanowire current limiter with the gate oxide removed to show details. At right, the emitters are shown
with 1µm spacing and with a gate aperture of 350nm.
(Paper33.1, High Performance and Reliable Silicon Field Emission Arrays Enabled by Silicon Nanowire Current Limiters; Stephen
Guerrera et al, MIT)