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Content archived on 2024-05-24



Most long range telecommunication systems are based on microwave links including high power transmitters on ground stations and on satellites. These satellites will be equipped with 50 to 100 travelling wave tubes (TWTs) within a few years. Due to the rapid growth of telecommunications and saturation of the present frequency bands, new bands will have to be allocated at higher frequencies (30-100 GHz) bringing the present technology close to its limit. Manufacturers are looking for a technological breakthrough to satisfy the need for low cost microwave amplifiers, which will operate at higher frequencies. Cold cathodes using carbon Nanotubes (CNTs) are considered as an ideal starting point. The overall objective of this three years project is to demonstrate that the use of CNT-based cold cathodes (instead of today's hot thermionic cathodes) will lead to a new generation of high frequency (30-100 GHz) compact and low cost vacuum microwave amplifier.

The overall objective of this three years project is to demonstrate that CNT-based cold cathodes can satisfy the future telecommunications requirement for high frequency (30-100 GHz) compact and low cost microwave amplifier. The project itself aims to achieve an emission current density of 1 A/cm2 modulated at 30GHz from a CNT-based cold cathode. The cold cathode will consist of an array of CNTs with an integral extraction grid positioned 5-10 µm from the CNT emitters. The intermediate objectives are the fabrication of arrays of identical and vertically-aligned CNTs and the design/fabrication of low capacitance CNT based field emission cathodes. We shall verify that 1A/cm2 of emission current can be obtained in DC mode from the cathodes, and using a RF modulated input, validate that our device delivers 30 GHz modulated current at a density of 1A/cm2.

This project is divided into 7 WPs, namely nanolithographically defined growth of aligned nanotubes (WP1), design and fabrication of cathodes (WP2), field emission properties of cathodes (WP3), properties of nanotube based microwave amplifier (WP4), assessment and evaluation (WP5), dissemination and implementation (WP6), and project management (WP7). WP1 aims to produce arrays of identical and vertically-aligned CNTs. This will be achieved by using a three-pronged approach - precise control of the size and the position of the catalyst dot by nanolithography, selection of a high temperature diffusion barrier for high yield and uniformity, and optimisation of growth parameters to obtain selective growth of nanotubes. The objective of WP2 is to fabricate a cathode that integrates the array of CNTs with an extraction grid positioned 5-10 µm away from array. This includes the design of a low capacitance and high transparency extraction grid, and the determination of a suitable technology to integrate the CNTs with the grid to form the compact cathode.WP3 relates to the emission properties of the cathodes. We shall determine the emission current density (~1 A/cm2), emission uniformity, energy distribution of the emitted electrons, and stability/lifetime of the cathodes. WP4 provides the simulations and modelling support for the preliminary design of the microwave vacuum amplifier. An experimental test system will also be set up to measure the emission current density modulated at 30 GHz. WP7 ensures that the project shall be executed in the most effective fashion and the results are fully exploited technologically and commercially. The progress of the project will be measured using the main deliverables: nanolithographically defined growth of aligned CNTs, design and fabrication of CNT-based cathode with capacitance 2-3 pF/mm2, and cathodes delivering 1 A/cm2 emission current densities modulated at 30 GHz.


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