An assembly process allows mixing and matching of different types of electrode and dielectric layers assembled in a stack to create multi-electrode vacuum devices.

Field-emission electron sources using carbon nanotubes (CNTs) are being targeted for low-power vacuum microelectronic applications for harsh-environment operation (high temperature, pressure, and corrosive atmosphere). While CNTs have demonstrated excellent properties in terms of low threshold field, low-power operation, and high-current densities, one of the problems that has persisted for vacuum electronic applications is the low yield of multi-electrode vacuum devices such as diodes, triodes, tetrodes, pentodes, etc.

A hybrid micro assembly process has been developed that allows mixing and matching of different types of electrode and dielectric layers assembled in a stack to create multi-electrode vacuum devices. The cathode, anode, extraction grid electrode, gate electrodes, and focusing electrodes all can be made from different materials micromachined to specific thickness. Following this, the electrodes are stacked. The electrode and dielectric layers are machined to contain alignment slots (similar to kinematic alignment structures) into which microspheres that function as precision spacers are placed. The stack is held in place using either vacuum-compatible epoxy or hard-mounted mechanical fixtures (such as assembly slots, alignment pin fasteners, etc.). This creates a hybrid vacuum device that is then placed inside standard vacuum packages, evacuated to high vacuums, and hermetically sealed.

The assembly process, when automated, is conducive for mass manufacturing of vacuum devices. The precision stages used in this development can be programmed to perform pick-and-place of different layers in an automated fashion, thus enhancing the speed of device fabrication. Hybrid assembly is modular by nature and allows selection of best-suited materials and dimensions for a given layer. This also allows for repairing the stacks with assembly or layer errors, and makes such a process easier. Most importantly, this assembly process helps to achieve a high degree of reproducibility among vacuum devices.

This work was done by Harish Manohara, Risaku Toda, Linda Y. Del Castillo, and Rakesh Murthy of Caltech for NASA’s Jet Propulsion Laboratory.

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Refer to NPO-48958.

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Assembly and Packaging to Mass-Produce Carbon Nanotube Vacuum Microdevices and Circuits (reference NPO-48958) is currently available for download from the TSP library.

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