Gaël Gautier

Plasma-deposited fluoropolymer film mask for local porous silicon formation

The study of an innovative fluoropolymer masking layer for silicon anodization is proposed. Due to its high chemical resistance to hydrofluoric acid even under anodic bias, this thin film deposited by plasma has allowed the formation of deep porous silicon regions patterned on the silicon wafer. Unlike most of other masks, fluoropolymer removal after electrochemical etching is rapid and does not alter the porous layer. Local porous regions were thus fabricated both in p+-type and low-doped n-type silicon substrates.

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.

Monolithic integration of common mode filters with electrostatic discharge protection on silicon/porous silicon hybrid substrate

This work presents the integration of a common mode filter with ElectroStatic Discharge protection on a silicon/porous silicon hybrid substrate. The porous silicon fabrication was performed after the integration of active components. Thus, a fluoropolymer hard mask was used to protect the active devices during anodization and can be easily removed without damaging the porous silicon. Electrical characterization results have shown fully operational components and an increase of performance with the hybrid substrate regarding to p+-type silicon. Indeed, the cutoff frequency was increased by 8.8 GHz when porous silicon was fabricated below the bump pads and the inductors. This improvement is a promising result to extend the application of RF components for future communication standards with silicon technology.

Evaluation of mesoporous silicon thermal conductivity by electrothermal finite element simulation

The aim of this work is to determine the thermal conductivity of mesoporous silicon (PoSi) by fitting the experimental results with simulated ones. The electrothermal response (resistance versus applied current) of differently designed test lines integrated onto PoSi/silicon substrates and the bulk were compared to the simulations. The PoSi thermal conductivity was the single parameter used to fit the experimental results. The obtained thermal conductivity values were compared with those determined from Raman scattering measurements, and a good agreement between both methods was found. This methodology can be used to easily determine the thermal conductivity value for various porous silicon morphologies.

Thermal conductivity measurement of porous silicon by the pulsed-photothermal method

Thermal properties of two types of porous silicon are studied using the pulsed-photothermal method (PPT). This method is based on a pulsed-laser source in the nanosecond regime. A 1D analytical model is coupled with the PPT technique in order to determine thermal properties of the studied samples (thermal conductivity and volumetric heat capacity).At first, a bulk single crystal silicon sample and a titanium thin film deposited on a single crystal silicon substrate are studied in order to validate the PPT method. Porous silicon samples are elaborated with two different techniques, the sintering technique for macroporous silicon and the electrochemical etching method for mesoporous silicon. Metallic thin films are deposited on these two substrates by magnetron sputtering. Finally, the thermal properties of macroporous (30% of porosity and pores diameter between 100 and 1000 nm) and mesoporous silicon (30% and 15% of porosity and pores diameter between 5 and 10 nm) are determined in this work and it is found that thermal conductivity of macroporous (73 W m−1 K−1) and mesoporous (between 80 and 50 W m−1 K−1) silicon is two times lower than the single crystal silicon (140 W m−1 K−1).

Enhanced quantum yield of photoluminescent porous silicon prepared by supercritical drying

The effect of supercritical drying (SCD) on the preparation of porous silicon (pSi) powders has been investigated in terms of photoluminescence (PL) efficiency. Since the pSi contains closely spaced and possibly interconnected Si nanocrystals (<5 nm), pore collapse and morphological changes within the nanocrystalline structure after common drying processes can affect PL efficiency. We report the highly beneficial effects of using SCD for preparation of photoluminescent pSi powders. Significantly higher surface areas and pore volumes have been realized by utilizing SCD (with CO2 solvent) instead of air-drying. Correspondingly, the pSi powders better retain the porous structure and the nano-sized silicon grains, thus minimizing the formation of non-radiative defects during liquid evaporation (air drying). The SCD process also minimizes capillary-stress induced contact of neighboring nanocrystals, resulting in lower exciton migration levels within the network. A significant enhancement of the PL quantum yiel...

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.

Non-oxidized porous silicon-based power AC switch peripheries

We present in this paper a novel application of porous silicon (PS) for low-power alternating current (AC) switches such as triode alternating current devices (TRIACs) frequently used to control small appliances (fridge, vacuum cleaner, washing machine, coffee makers, etc.). More precisely, it seems possible to benefit from the PS electrical insulation properties to ensure the OFF state of the device. Based on the technological aspects of the most commonly used AC switch peripheries physically responsible of the TRIAC blocking performances (leakage current and breakdown voltage), we suggest to isolate upper and lower junctions through the addition of a PS layer anodically etched from existing AC switch diffusion profiles. Then, we comment the voltage capability of practical samples emanating from the proposed architecture. Thanks to the characterization results of simple Al-PS-Si(P) structures, the experimental observations are interpreted, thus opening new outlooks in the field of AC switch peripheries.

P type porous silicon resistivity and carrier transport

The resistivity of p type porous silicon (PS) is reported on a wide range of PS physical properties. Al/PS/Si/Al structures were used and a rigorous experimental protocol was followed. The PS porosity (P%) was found to be the major contributor to the PS resistivity (ρPS). ρPS increases exponentially with P%. Values of ρPS as high as 1 × 109 Ω cm at room temperature were obtained once P% exceeds 60%. ρPS was found to be thermally activated, in particular, when the temperature increases from 30 to 200 °C, a decrease of three decades is observed on ρPS. Based on these results, it was also possible to deduce the carrier transport mechanisms in PS. For P% lower than 45%, the conduction occurs through band tails and deep levels in the tissue surrounding the crystallites. When P% overpasses 45%, electrons at energy levels close to the Fermi level allow a hopping conduction from crystallite to crystallite to appear. This study confirms the potential of PS as an insulating material for applications such as power e...