Search

The purpose of this thesis is to develop a microwave device architecture combining the technology of metallic nanowires aligned in a nanoporous medium and that of Substrate Integrated Waveguide (SIW). This multidisciplinary research aims to realize and characterize original microwave components based on nanowires, promising structures for modern applications. Indeed, nanowire-based microwave components represent an interesting alternative for high frequency electronics, in a context of ever-increasing miniaturization and concentration of devices, where traditional design strategies may prove ineffective, particularly because of the size of the components to be implemented, which are not compatible with the new micro- and nano-electronics standards. Two innovative laser-etching processes were developed for the precise location of areas hosting the growth of nanowires in a porous alumina membrane. Both were used to fabricate microwave devices in SIW topology. These fabrication methods allow to control the composition, height and diameter of the nanowires and secondly, the location of nanowired areas. Using those processes, various devices have been characterized. Simple nanowired SIW have been first realized as well as nanowire-based SIW band-pass filter using electromagnetic band-gap effect and nanowire-based SIW resonance isolator. This research paves to road towards the conception of a wide range of smart and versatile microwave devices offering immunity to radiation losses, excellent temperature stability and increased miniaturization compatible with high-frequency monolithic integrated circuits technology., (FSA - Sciences de l'ingénieur) -- UCL, 2019

This paper compares two laser-assisted processes developed by the authors for the fabrication of microwave devices based on nanowire arrays loaded inside porous alumina templates. Pros and cons of each process are discussed in terms of accuracy, reproducibility and ease of fabrication. A comparison with lithography technique is also provided. The efficiency of the laser-assisted process is demonstrated through the realization of substrate integrated waveguide (SIW) based devices. A Nanowired SIW line is firstly presented. It operates between 8.5 and 17 GHz, corresponding to the first and second cut-off frequency of the waveguide, respectively. Next, a Nanowired SIW isolator is demonstrated. It shows a nonreciprocal isolation of 12 dB (corresponding to 4.4 dB/cm), observed in absence of a DC magnetic field, and achieved through an adequate positioning of ferromagnetic nanowires inside the waveguide cavity.

An experimental process for the fabrication of microwave devices made of nanowire arrays embedded in a dielectric template is presented. A pulse laser process is used to produce a patterned surface mask on alumina templates, defining precisely the wire growing areas during electroplating. This technique makes it possible to finely position multiple nanowire arrays in the template, as well as produce large areas and complex structures, combining transmission line sections with various nanowire heights. The efficiency of this process is demonstrated through the realisation of a microstrip electromagnetic band-gap filter and a substrate-integrated waveguide.

We demonstrate the operation of a fully integrated and miniaturized waveguide based on ferromagnetic nanowires as a promising alternative to macroscopic ferrite slab-loaded metallic rectangular waveguides used as microwave isolators. Nanowires of various heights are selectively grown at dedicated areas into a low-loss nanoporous alumina template in order to create the shielding walls of a Substrate Integrated Waveguide (SIW) topology and the ferromagnetic slab supporting a circularly polarized nonreciprocal propagation. A model is proposed for the microwave response of the SIW and its non-reciprocity, which takes into account the substrate permittivity and the tensorial permeability of the ferromagnetic nanowires, and its predictions are validated by measurements. A significant isolation of 7 dB/cm is obtained experimentally at 13.5 GHz, without the need of a DC biasing magnetic field.