Patrick Poveda

N-Type Porous Silicon Substrates for Integrated RF Inductors

To study the effect of various n-type substrates on high-frequency inductor performances, several devices were integrated on porous silicon (PS), silicon (Si), and glass. Both n-type mesoporous Si and mesoporous/macroporous Si bilayers were fabricated. The analysis further shows that PS reduces significantly the substrate losses. Indeed, higher quality factors have been obtained for the inductors integrated on PS than on the Si substrate and particularly in the case of bilayer structures. These original results can be added to p-type PS performances already shown in the literature. Then, this work demonstrates that PS can also be a promising candidate for the integration of passive and active devices on n-type silicon.

RF performances of inductors integrated on localized p + -type porous silicon regions

To study the influence of localized porous silicon regions on radiofrequency performances of passive devices, inductors were integrated on localized porous silicon regions, full porous silicon sheet, bulk silicon and glass substrates. In this work, a novel strong, resistant fluoropolymer mask is introduced to localize the porous silicon on the silicon wafer. Then, the quality factors and resonant frequencies obtained with the different substrates are presented. A first comparison is done between the performances of inductors integrated on same-thickness localized and full porous silicon sheet layers. The effect of the silicon regions in the decrease of performances of localized porous silicon is discussed. Then, the study shows that the localized porous silicon substrate significantly reduces losses in comparison with high-resistivity silicon or highly doped silicon bulks. These results are promising for the integration of both passive and active devices on the same silicon/porous silicon hybrid substrate.

Porous Silicon/Silicon Hybrid Substrate Applied to the Monolithic Integration of Common-Mode and Bandpass RF Filters

In order to develop high performances and miniaturized devices for RF communications, monolithic integration becomes an important challenge for microelectronics industries. Bandpass filters and common-mode filter have been integrated on 6-in porous silicon (PS)/silicon hybrid substrates with PS regions under passive devices. An improvement of the rejection level on common mode was demonstrated on PS regards to low-resistivity silicon. Furthermore, the bandwidth differential was increased regards to bulk silicon and, thus, allows the development of devices for high-speed communications systems.

RF Planar Inductor Electrical Performances on n-Type Porous 4H Silicon Carbide

For the first time, inductors were integrated on porous silicon carbide to study the effect of this substrate on radio-frequency (RF) performances. n-Type heavily doped 4H-SiC substrates were anodized in an HF-based electrolyte to produce 6- and 15-μm-thick porous layers. An improvement of the quality factor was demonstrated on porous SiC with regard to SiC bulk. This promising result shows the decrease of substrate losses at the high frequencies with the porous SiC substrate. Thus, porous SiC could have an interest for the integration of RF power devices.

Shape-controlled electrochemical synthesis of mesoporous Si/Fe nanocomposites with tailored ferromagnetic properties

This study reports on an original and efficient way to synthesize iron nanowires and cubic-shaped nanoparticles by electrochemical deposition on a mesoporous silicon host and its impact on magnetic properties. The selective growth of iron nanostructures inside the pores can be achieved, thanks to the presence of a native oxide layer on the pore walls, suggesting a surface-state assisted electrochemical process. Because of hydrogen coevolution, the pH of the solution controls the shape of the iron nanostructures (particles or wires) while the electrodeposition current density can be adjusted to suppress the parasitic deposition on top of the structure. Under optimal conditions, nanowires with lengths up to 2 μm are synthesized after 15 seconds of deposition. Magnetic characterization of the ferromagnetic nanowire composite exhibits an easy axis of magnetization in the pore direction due to shape anisotropy with a remanence ratio of 0.6. The shape anisotropy of the nanoparticle composite is weaker than for the nanowire composite because of the homogeneous dispersion of the particles. The versatility of the mesoporous silicon framework is thus a considerable asset to tune the nanocomposite’s magnetic properties.