Development of Vertical Nanodiamond Vacuum Field Emission Microelectronic Integrated Devices
Recent development of nanocrystalline diamonds has demonstrated the potential use of diamond material for vacuum microelectronics. Apart from the advantages of conventional microcrystalline diamond, nanodiamond with smaller grain size and smoother surface morphology possesses unique properties including the insertion of deliberate amounts of sp2-carbon into the sp3-diamond matrix and controlled electrical conductivity, expanding its utility for practical applications. This research is focused on the design, fabrication, and characterization of nitrogen-incorporated nanodiamond vacuum field emission (VFE) functional devices and integrated circuits, specifically on vertically configured VFE transistors, triodes, and differential amplifiers (diff-amps). A well-controlled and IC-compatible fabrication process has been developed to achieve three-terminal nanodiamond VFE integrated devices for vacuum micro/nanoelectronics. The nanodiamond pyramidal sharpened nanotips built with self-aligned silicon gate and anode electrodes were fabricated by employing a dual-mask microfabrication process which involved a silicon-on-insulator (SOI) mold transfer technique in collaboration with chemical vapor deposition (CVD) of nanodiamond and silicon gate partitioning. With proper design of the electrodes placement, the fabricated VFE functional devices have achieved transistor and triode characteristics, and they have been further implemented into vacuum integrated circuit building block – differential amplifiers. The nanodiamond VFE transistors and triodes demonstrate efficient gate-modulated electron field emission behavior with low operating voltages, high emission current, and negligible gate intercepted current. The dc characteristics of the transistor demonstrate distinct linear, saturation and cutoff regions with low turn-on gate voltage and high amplification factor. The triode demonstrates high emission current with efficient current modulation by low gate voltages. The ac signal amplification performance has been evaluated, indicating the applicability of nanodiamond VFE transistors and triodes as signal amplifiers and buffer amplifiers, respectively. An identical pair of nanodiamond VFE transistors with well-matched field emission characteristics was constructed and employed to accomplish a nanodiamond VFE diff-amp for the first time. A large common-mode-rejection ratio (~ 60 dB) was realized, demonstrating a viable approach to vacuum-based IC technology. These achievements signify the fundamental step for further development of vacuum integrated micro/nanoelectronics for practical applications, including high-speed, high-power and extreme-environment electronics.