Paolo Nenzi

On-chip THz 3D antennas

In this work a new class of integrated 3D antennas is presented: the u-helix antenna class. U-helix is a truncated conical helix built using a novel MEMS (micro electro mechanical systems) technology directly realized on a silicon substrate, extruded from a planar spiral. The antenna is characterized by high gain (>;6 dBi) and wide fractional bandwidth (0.4) in the 100 GHz to 1 THz frequency range. Fabrication processes of the antenna and simulated performances are reported, and its possible use in a THz rectifying device is presented.

Biological effects of in vitro THz radiation exposure in human foetal fibroblasts

In recent years, terahertz (THz) radiation has been widely used in a variety of applications: medical, security, telecommunications and military areas. However, few data are available on the biological effects of this type of electromagnetic radiation and the reported results, using different genetic or cellular assays, are quite discordant. This multidisciplinary study focuses on potential genotoxic and cytotoxic effects, evaluated by several end-points, associated with THz radiation. For this purpose, in vitro exposure of human foetal fibroblasts to low frequency THz radiation (0.1-0.15THz) was performed using a Compact Free Electron Laser. We did not observe an induction of DNA damage evaluated by Comet assay, phosphorylation of H2AX histone or telomere length modulation. In addiction, no induction of apoptosis or changes in pro-survival signalling proteins were detected. Moreover, our results indicated an increase in the total number of micronuclei and centromere positive micronuclei induction evaluated by CREST analysis, indicating that THz radiation could induce aneugenic rather than clastogenic effects, probably leading to chromosome loss. Furthermore, an increase of actin polymerization observed by ultrastructural analysis after THz irradiation, supports the hypothesis that an abnormal assembly of spindle proteins could lead to the observed chromosomal malsegregation.

Nanostructures formed by displacement of porous silicon with copper: from nanoparticles to porous membranes

The application of porous silicon as a template for the fabrication of nanosized copper objects is reported. Three different types of nanostructures were formed by displacement deposition of copper on porous silicon from hydrofluoric acid-based solutions of copper sulphate: (1) copper nanoparticles, (2) quasi-continuous copper films, and (3) free porous copper membranes. Managing the parameters of porous silicon (pore sizes, porosity), deposition time, and wettability of the copper sulphate solution has allowed to achieve such variety of the copper structures. Elemental and structural analyses of the obtained structures are presented. Young modulus measurements of the porous copper membrane have been carried out and its modest activity in surface enhanced Raman spectroscopy is declared.

Electric Field Enhancement in 3-D Tapered Helix Antenna for Terahertz Applications

A tapered helix monopole as a part of a rectenna for the detection of terahertz radiation is proposed. The antenna consists of a truncated conical helix extruded from a planar spiral and in a nanometric metallic whisker connected to one of its edges. The whisker faces a semiconductor substrate constituting the antenna ground plane. The structure is designed to be combined with a rectifying junction, realized just below the whisker base, which produces the direct conversion of terahertz electromagnetic field into dc current. The figure of merit of the structure is the electric field enhancement factor at the metallic whisker/semiconductor interface. Numerical full-wave simulations show that, for the tapered helix monopole, the field enhancement factor value can be higher than 26 000, which is approximately one order of magnitude greater than previously reported values in the literature. Detailed description of the fabrication process and investigation of antenna performances for different values of geometrical parameters are presented.

Comparative study of initial stages of copper immersion deposition on bulk and porous silicon

Initial stages of Cu immersion deposition in the presence of hydrofluoric acid on bulk and porous silicon were studied. Cu was found to deposit both on bulk and porous silicon as a layer of nanoparticles which grew according to the Volmer-Weber mechanism. It was revealed that at the initial stages of immersion deposition, Cu nanoparticles consisted of crystals with a maximum size of 10 nm and inherited the orientation of the original silicon substrate. Deposited Cu nanoparticles were found to be partially oxidized to Cu2O while CuO was not detected for all samples. In contrast to porous silicon, the crystal orientation of the original silicon substrate significantly affected the sizes, density, and oxidation level of Cu nanoparticles deposited on bulk silicon.

New selective wet processing

A new selective processing technique based on a confined dynamic liquid drop\meniscus is presented. This approach is represented by the localized wet treatment of silicon wafers using dynamic liquid drop that while is in contact with the wafer forms a dynamic liquid meniscus. The main scientific innovation and relevance introduced by this work have been applied to industrial solar cell production and on silicon wafer metal bumps formation for the IC interconnection (i.e. copper pillars). Such new technique allows to touch in specific defined positions the silicon wafer in order to perform any kind of wet processing (e.g. etching, cleaning and/or plating) without the need of any protective resist. To investigate on pendant dynamic liquid drops and dynamic liquid meniscus use of computational fluid dynamic technique (i.e. numerical techniques to accurately predict fluid flows) was followed and is presented. An experimental setup has been built to validate the calculations. Numerical results showed a good agreement with experimental ones. Prototypes heads, using stereo-lithography systems, were developed and localized selective plating without the need of lithography step was performed on silicon.

Transfer layer technology for the packaging of high power modules

Most power electronic modules are specifically designed for the customer and this entails intense labour during the production phase. The monolithic integration for power electronic devices in the form of power IC has not proven to be efficient, neither from a technical, nor from an economic point of view. In a typical high power module the power devices are assembled on a heatsink and, driver, sensor and protection circuits are mounted on separate PCBs assembled to the power devices. This results in low performance and high cost. Higher integrated power modules are produced assembling power devices in die format onto a DCB (Direct Copper Bonding) substrate and interconnect them by wire bonding technique [1]. The relative driver, sensor and protection circuits are surface mounted on a separate PCB assembled with the former.

First integration of MOSFET band-to-band-tunneling current in BSIM4

Static leakage currents represent a major issue in nano-scale CMOS. In digital VLSI circuits, the most relevant contributions to the overall leakage current are subthreshold conduction, gate current and band-to-band-tunneling (BTBT) current, which flows from drain/source to bulk through the reverse biased diffusion junctions. While the latter has been recognized as an important effect in digital nano-CMOS, yet no compact model of it has ever been included in the industry-standard device model BSIM4. In this work, we show that the lack of a BTBT current model leads to discrepancies between SPICE and device-level simulations and that adding a BTBT current source into BSIM4 DC model can correct this. The new current source follows a widely accepted physical model of the BTBT phenomenon with a rectangular junction approximation. Test case results show a good agreement between the new circuit-level simulations and the device-level extracted currents.

Technology and design of innovative flexible electrode for biomedical applications

The electrochemotherapy is an effective treatment that requires the application of an intense electric field to the tumoral tissue to open the cellular membrane and deliver drugs. This work will present the results of the ongoing research project, showing a new technology and design geometry that allows to realize flexible electrodes able to wrap biological tissues bringing the necessary electric field intensity for the electroporation of cells to reach a unique penetration depth to the centimeter range. The flexible electrode is realized by conversion of porous silicon into nano-porous metals (copper and/or gold) filled by a biocompatible thermoplastic polymer.

First acceleration of a proton beam in a side coupled drift tube linac

We report the first experiment aimed at the demonstration of low-energy protons acceleration by a high-efficiency S-band RF linear accelerator. The proton beam has been accelerated from 7 to 11.6 MeV by a 1 meter long SCDTL (Side Coupled Drift Tube Linac) module powered with 1.3 MW. The experiment has been done in the framework of the Italian TOP-IMPLART (Oncological Therapy with Protons-Intensity Modulated Proton Therapy Linear Accelerator for Radio-Therapy) project devoted to the realization of a proton therapy centre based on a proton linear accelerator for intensity modulated cancer treatments to be installed at IRE-IFO, the largest oncological hospital in Rome. It is the first proton therapy facility employing a full linear accelerator scheme based on high-frequency technology.