Innovations en microfabrication pour la production de circuits a tres hautes frequences et ajustables

In recent years, the microwave field has seen two important trends: the increase in the operation frequency and the integration of several functions in one device. These changes have brought new challenges, mainly related to the use of integrated tunable elements and fabrication problems caused by the increasingly small critical dimensions required for high frequency operation. Two possible solutions are presented in this thesis: the use of ferroelectric-based adjustable elements integrated onto the substrate and the fabrication of three dimensional circuits using an innovative manufacturing process called photoimageable thick films.;The ferroelectric material chosen is barium and strontium titanate noted BaxSr1-xTiO3, or simply BST. As all ferroelectrics, its permittivity can be changed by applying an external electric field. RF sputtering is used to deposit this material. X-ray diffraction analysis confirms the crystalline nature of the BST thin films while a measurement by Rutherford backscattering spectroscopy suggests a slight deviation from the expected stoichiometry. A titanium deficiency is identified as the likely source of this variation. The addition of titanium as a dopant diffused into the BST film is shown to have important impact on its electrical properties..;Photoimageable pastes allow lateral resolutions of about 20 microns and thicknesses of the same order. Since this process is multi-layered in nature, it is suitable for the realization of millimeter wave circuits of complex geometry, such as waveguides. This approach has been explored by only one research group to this day. However, these materials were not designed for use with high frequency, so it is necessary to characterize their microwave properties. The permittivity of the dielectric layers is extracted using parallel plate capacitors and circular resonators. The dielectric constant is very stable in frequency with a measured value of 9,2 +/- 1% between 9 and 93 GHz. To reduce the fabrication time of these circuits, several changes to the manufacturing process are implemented. First, a method of drying in a controlled atmosphere allows to increase each layer thickness without cracking. Moreover, a pulsed electroplating of copper significantly reduces the cost and manufacturing time by filling up in one step the trenches that make the waveguide sidewalls. For example, a guide that would take 21 days to fabricate without these changes can be manufactured in only 7 days using electroplating.;The interest of this fabrication process using thick films of photoimageable paste is shown through a number of passive devices. First, the rectangular waveguides are presented. Their single-mode operating range is between 60 and 95 GHz. A transition to a microstrip line allows measurement using GSG probes. The measured losses of these guides are less than 0,4 dB / length up to 110 GHz. These results compare favorably with those of the other group working with photoimageable paste. Two rectangular waveguide band-pass filter of 3rd and 5th order are designed and fabricated. They show measured losses of 3,7 and 4,1 dB at 80 and 75 GHz respectively. These results are comparable to the best band-pass filters published at these frequencies. A 3 dB Riblet type coupler is then presented. This coupler has a very wide bandwidth of 26,6 %, and presents low loss measured at 0,9 dB. To properly characterize this circuit, a new approach to replace the matched loads is presented. Highly resistive titanium is used to terminate the unused ports. With sufficient attenuation, the signal reflected in the device is too small to disturb the measurements. Half-waveguides are also presented.;Finally, micro-coaxial guides are presented. These lines take the appearance of rectangular guides, but with a central conductor inside. The interest of these transmission lines is that they are not dispersive; all frequencies will travel at the same speed. This property enables the design of devices with very large bandwidth. A transition in the band from 1 to 110 GHz is presented for measurements with GSG probes. This allows extracting the guiding characteristics the micro-coaxial lines. The measured performance is very close to the simulated results. (Abstract shortened by UMI.)...