Slot Routing as a Solution for Optically Transparent Scalable WDM Wide Area Networks*

All-optical Wavelength Division Multiplexing (WDM) backbones are believed to be a fundamental component in future high speed networks. Currently, the most pursued approach for Wide Area Networks (WANs) is wavelength routing, in which communication circuits are established between node pairs by means of lightpaths (paths of light) spanning one or more fiber-optic links. This approach has, however, two drawbacks. Since the number of wavelengths and links in a network is finite, not all node pairs can be connected via a dedicated lightpath directly. Consequently, some node pairs will communicate using a concatenation of lightpaths, which requires electronic switching of in transit information, loosing the advantages of optical transparency. Secondly, typically some form of (electronic) traffic grooming will be necessary to make efficient use of the fixed lightpath capacity. This paper proposes to design all-optical WANs using a novel approach, called photonic slot routing. With photonic slot routing, entire slots, each carrying multiple packets on distinct wavelengths, are switched transparently and individually, using available fast and wavelength non-sensitive devices. The advantage of using photonic slot routing is threefold. All node pairs in the network communicate all-optically. Traffic aggregation necessary to efficiently use the capacity of the wavelength channels is optically achieved. The solution is practical as it is based on proven optical technologies. In addition, through the use of wavelength non-sensitive devices the proposed WAN design yields intrinsic scalability in the number of wavelengths.     

Integration of InGaP/GaAs/Ge triple‐junction solar cells on deeply patterned silicon substrates

We report preliminary results on InGaP/InGaAs/Ge photovoltaic cells for concentrated terrestrial applications, monolithically integrated on engineered Si(001) substrates. Cells deposited on planar Ge/Si(001) epilayers, grown by plasma‐enhanced chemical vapor deposition, provide good efficiency and spectral response, despite the small thickness of the Ge epilayers and a threading dislocation density as large as 10⁷/cm². The presence of microcracks generated by the thermal misfit is compensated by a dense collection grid that avoids insulated areas. In order to avoid the excessive shadowing introduced by the use of a dense grid, the crack density needs to be lowered. Here, we show that deep patterning of the Si substrate in blocks can be an option, provided that a continuous Ge layer is formed at the top, and it is suitably planarized before the metalorganic chemical vapor deposition. The crack density is effectively decreased, despite that the efficiency is also lowered with respect to unpatterned devices. The reasons of this efficiency reduction are discussed, and a strategy for improvement is proposed and explored. Full morphological analysis of the coalesced Ge blocks is reported, and the final devices are tested under concentrated AM1.5D spectrum. Copyright © 2016 John Wiley & Sons, Ltd.     

A 1.0-mW, 71-dB SNDR,fourth-order ΣΔ interface circuit for MEMS microphones

In this paper an integrated interface circuit for condenser MEMS microphones is presented. It consists of an input buffer followed by a multi-bit (12-levels), analog, second-order ΣΔ modulator and a fully-digital, single-bit, fourth-order ΣΔ modulator, thus providing a single-bit output signal with fourth order noise shaping, compatible with standard audio chipsets. The circuit, supplied with 3.3 V, exhibits a current consumption of 215 μA for the analog part and 95 μA for the digital part. The measured signal-to-noise and distortion ratio (SNDR) is 71 dB, with an input signal amplitude as large as −1.8 dB with respect to full-scale, obtained thanks to the use of a feed-forward architecture in the analog ΣΔ modulator, which relaxes the voltage swing requirements of the operational amplifiers. The test chip, fabricated in a 0.35-μm CMOS process, occupies an area of 3 mm², including pads.     

Discovering Homophily in Online Social Networks

Mobile Networks and Applications - During the last ten years, Online Social Networks (OSNs) have increased their popularity by becoming part of the real life of users. Despite their tremendous...     

Characterization of transient currents in HfO2 capacitors in the short timescale

We present a detailed experimental investigation of transient currents in HfO₂ capacitors in the short timescale. We show that the transient currents flowing through the capacitor plates when the gate voltage is reset to zero after a low voltage stress period follow a power-law time dependence t^−α (with α ? 1) over more than eight decades of time and down to the μs timescale. As transient currents in HfO₂ are largely increased with respect to the SiO₂ case, these results confirm that transient effects can be a severe issue for the successful integration of high-k dielectrics.     

Comparative analysis of the outdoor performance of a dye solar cell mini‐panel for building integrated photovoltaics applications

New generation photovoltaic (PV) devices such as polymer and dye sensitized solar cells (DSC) have now reached a more mature stage of development, and among their various applications, building integrated PVs seems to have the most promising future, especially for DSC devices. This new generation technology has attracted an increasing interest because of its low cost due to the use of cheap printable materials and simple manufacturing techniques, easy production, and relatively high efficiency. As for the more consolidated PV technologies, DSCs need to be tested in real operating conditions and their performance compared with other PV technologies to put into evidence the real potential. This work presents the results of a 3 months outdoor monitoring activity performed on a DSC mini‐panel made by the Dyepower Consortium, positioned on a south oriented vertical plane together with a double junction amorphous silicon (a‐Si) device and a multi‐crystalline silicon (m‐Si) device at the ESTER station of the University of Rome Tor Vergata. Good performance of the DSC mini‐panel has been observed for this particular configuration, where the DSC energy production compares favorably with that of a‐Si and m‐Si especially at high solar angles of incidence confirming the suitability of this technology for the integration into building facades. This assumption is confirmed by the energy produced per nominal watt‐peak for the duration of the measurement campaign by the DSC that is 12% higher than that by a‐Si and only 3% lower than that by m‐Si for these operating conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Low‐Cost Post‐Growth Treatments of Crystalline Silicon Nanoparticles Improving Surface and Electronic Properties

Freestanding silicon nanocrystals (Si‐ncs) offer unique optical and electronic properties for new photovoltaic, thermoelectric, and other electronic devices. A method to fabricate Si‐ncs which is scalable to industrial usage has been developed in recent years. However, barriers to the widespread utilization of these nanocrystals are the presence of charge‐trapping defects and an oxide shell formed upon ambient atmosphere exposure hindering the charge transport. Here, we exploit low‐cost post‐growth treatment routes based on wet‐etching in hydrofluoric acid plus surface hydrosilylation or annealing enabling a complete native oxide removal and a reduction of the defect density by up to two orders of magnitude. Moreover, when compared with only H‐terminated Si‐ncs we report an enhancement of the conductivity by up to a factor of 400 for films of HF etched and annealed Si‐ncs, which retain a defect density below that of untreated Si‐ncs even after several months of air exposure. Further, we demonstrate that HF etched and hydrosilylated Si‐ncs are extremely stable against oxidation and maintain a very low defect density after a long‐term storage in air, opening the possibility of device processing in ambient atmosphere.     

Nanostructured Metallo‐Dielectric Quasi‐Crystals: Towards Photonic‐Plasmonic Resonance Engineering

The first evidence of out‐of‐plane resonances in hybrid metallo‐dielectric quasi‐crystal (QC) nanostructures composed of metal‐backed aperiodically patterned low‐contrast dielectric layers is reported. Via experimental measurements and full‐wave numerical simulations, these resonant phenomena are characterized with specific reference to the Ammann‐Beenker (quasi‐ periodic, octagonal) tiling lattice geometry and the underlying physics is investigated. In particular, it is shown that, by comparison with standard periodic structures, a moderately richer spectrum of resonant modes may be excited, due to the easier achievement of phase‐matching conditions endowed by its denser Bragg spectrum. Such modes are characterized by a distinctive plasmonic or photonic behavior, discriminated by their field distribution and dependence on the metal film thickness. Moreover, the response is accurately predicted via computationally affordable periodic‐approximant‐based numerical modeling. The enhanced capability of QCs to control number, spectral position, and mode distribution of hybrid resonances may be exploited in a variety of possible applications. To assess this aspect, label‐free biosensing is studied via characterization of the surface sensitivity of the proposed structures with respect to local refractive index changes. Moreover, it is also shown that the resonance‐engineering capabilities of QC nanostructures may be effectively exploited in order to enhance the absorption efficiency of thin‐film solar cells.     

Physical Mechanisms behind the Field‐Cycling Behavior of HfO2‐Based Ferroelectric Capacitors

Novel hafnium oxide (HfO₂)‐based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite‐based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake‐up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake‐up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake‐up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.