Photonic packaging: transforming silicon photonic integrated circuits into photonic devices

Dedicated multi-project wafer (MPW) runs for photonic integrated circuits (PICs) from Si foundries mean that researchers and small-to-medium enterprises (SMEs) can now afford to design and fabricate Si photonic chips. While these bare Si-PICs are adequate for testing new device and circuit designs on a probe-station, they cannot be developed into prototype devices, or tested outside of the laboratory, without first packaging them into a durable module. Photonic packaging of PICs is significantly more challenging, and currently orders of magnitude more expensive, than electronic packaging, because it calls for robust micron-level alignment of optical components, precise real-time temperature control, and often a high degree of vertical and horizontal electrical integration. Photonic packaging is perhaps the most significant bottleneck in the development of commercially relevant integrated photonic devices. This article describes how the key optical, electrical, and thermal requirements of Si-PIC packaging can be met, and what further progress is needed before industrial scale-up can be achieved.

La innovación dentro del entorno de Silicon Valley

En este artículo se presentan los resultados de la visita a las empresas ubicadas en Silicon Valley, cuna de la innovación, con el fin de obtener un entendimiento integral del funcionamiento y factores claves de éxito de las starups y organizaciones que conforman este conglomerado empresarial.

Cálculo de constantes ópticas de películas delgadas de Cu3BiS3 a través del método de Wolfe

Se calculó la obtención de las constantes ópticas usando el método de Wolfe. Dichas contantes: coeficiente de absorción (α), índice de refracción (n) y espesor de una película delgada (d ), son de importancia en el proceso de caracterización óptica del material. Se realizó una comparación del método del Wolfe con el método empleado por R. Swanepoel. Se desarrolló un modelo de programación no lineal con restricciones, de manera que fue posible estimar las constantes ópticas de películas delgadas semiconductoras, a partir únicamente, de datos de transmisión conocidos. Se presentó una solución al modelo de programación no lineal para programación cuadrática. Se demostró la confiabilidad del método propuesto, obteniendo valores de α = 10378.34 cm−1, n = 2.4595, d =989.71 nm y Eg = 1.39 Ev, a través de experimentos numéricos con datos de medidas de transmitancia espectral en películas delgadas de Cu3BiS3.

Effect of silicon application to Eucalyptus camaldulensis on the population of Glycaspis brimblecombei (Hemiptera: Aphalaridae).

O uso do silício na área florestal tem aumentado recentemente, pois o elemento está relacionado a uma melhoria na resistência a insetos pragas. O psilídeo de concha, Glycaspis brimblecombei é encontrado em todas as regiões produtoras de eucalipto no Brasil. O efeito do silício aplicado em Eucalyptus camaldulensis, na população do psilídeo, foi estudado em dois ensaios. No primeiro experimento, as aplicações foram via solo (silicato de cálcio) e foliar (silicato de potássio) em uma plantação de nove meses. No segundo experimento, este mineral foi aplicado em mudas de eucalipto, no substrato ou sobre as folhas. Mensalmente, durante 24 meses, ovos e imaturos de G. brimblecombei foram amostrados nas folhas. A altura das plantas foi medida com 9, 12, 16 e 24 meses (experimento 1) e, aos 4, 8, 12 e 24 meses (experimento 2) após a aplicação dos tratamentos. O número de ovos e de imaturos foram menores nos períodos de maior precipitação, indicando menos ataque dos psilídeos durante a estação chuvosa. A população psilídeo foi menor nos tratamentos com aplicação de silício tanto foliar como via solo. Nenhuma diferença significativa foi encontrada na altura de plantas de E. camaldulensis.

Silicon nanocrystals tailored for bioimaging and energy conversion

This thesis focus is the development of hybrid organic-inorganic systems based on Silicon Nanocrystals (SiNCs) with possible applications in the field of bioimaging and solar energy conversion. SiNCs were engineered thanks to the realization of a strong covalent Si-C bond on their surface, which allowed us to disperse them in different solvents with different final purpose. Chapter 1 introduces the basic properties of nanomaterials. Chapter 2 describes all the synthetic procedures to obtain the organic molecules-functionalized SiNCs. Chapter 3 illustrates an organic-inorganic antenna system based on SiNCs conjugated with diphenylanthracene (DPA) photoactive molecules, which was also embedded into Luminescent Solar Concentrators (LSC) made of a polymeric matrix. The optical and photovoltaic performances of this device were compared with the ones of a LSC embedded with a physical mixture made of SiNCs plus DPA at the same concentrations of the two components in the covalent system. Chapter 4 shows many different techniques to functionalize SiNCs with polyethylene glycol (PEG) chains in order to make them dispersible in water, for biomedical imaging applications. Chapter 5 presents the synthesis of dyes and/or SiNCs loaded Polymer Nanoparticles (PNPs) capable of excitation energy transfer (EET) mechanism. Chapter 6 is focused on the realization of photo-switchable systems based on azobenzene derivatives-functionalized SiNCs. These organic-inorganic hybrid materials were studied to possibly obtain a new light-driven response of SiNCs. In the end, chapter 7 reports the activity I followed in America, at The University of Texas at Austin, in the laboratory led by the professor Brian Korgel. Here I studied and compared the properties of high temperature hydrosilylated SiNCs and room temperature, radical promoted, hydrosilylated SiNCs.

Charge accumulation and transport in degenerately doped semiconducting polymers with mixed ionic and electronic conductivity

This thesis is part of the fields of Material Physics and Organic Electronics and aims to determine the charge carrier density and mobility in the hydrated conducting polymer–polyelectrolyte blend PEDOT:PSS. This kind of material combines electronic semiconductor functionality with selective ionic transport, biocompatibility and electrochemical stability in water. This advantageous material properties combination makes PEDOT:PSS a unique material to build organic electrochemical transistors (OECTs), which have relevant application as amplifying transducers for bioelectronic signals. In order to measure charge carrier density and mobility, an innovative 4-wire, contact independent characterization technique was introduced, the electrolyte-gated van der Pauw (EgVDP) method, which was combined with electrochemical impedance spectroscopy. The technique was applied to macroscopic thin film samples and micro-structured PEDOT:PSS thin film devices fabricated using photolithography. The EgVDP method revealed to be effective for the measurements of holes’ mobility in hydrated PEDOT:PSS thin films, which resulted to be <μ>=(0.67±0.02) cm^2/(V*s). By comparing this result with 2-point-probe measurements, we found that contact resistance effects led to a mobility overestimation in the latter. Ion accumulation at the drain contact creates a gate-dependent potential barrier and is discussed as a probable reason for the overestimation in 2-point-probe measurements. The measured charge transport properties of PEDOT:PSS were analyzed in the framework of an extended drift-diffusion model. The extended model fits well also to the non-linear response in the transport characterization and results suggest a Gaussian DOS for PEDOT:PSS. The PEDOT:PSS-electrolyte interface capacitance resulted to be voltage-independent, confirming the hypothesis of its morphological origin, related to the separation between the electronic (PEDOT) and ionic (PSS) phases in the blend.

Optoelectronic investigation of defects in hybrid metal halide perovskites

The growing demand for flexible and low-cost electronics has driven research towards the study of novel semiconducting materials to replace traditional semiconductors like silicon and germanium, which are limited by mechanical rigidity and high production cost. Some of the most promising semiconductors in this sense are metal halide perovskites (MHPs), which combine low-cost fabrication and solution processability with exceptional optoelectronic properties like high absorption coefficient, long charge carrier lifetime, and high mobility. These properties, combined with an impressive effort by many research groups around the world, have enabled the fabrication of solar cells with record-breaking efficiencies, and photodetectors with better performance than commercial ones. However, MHP devices are still affected by issues that are hindering their commercialization, such as degradation under humidity and illumination, ion migration, electronic defects, and limited resistance to mechanical stress. The aim of this thesis work is the experimental characterization of these phenomena. We investigated the effects of several factors, such as X-ray irradiation, exposure to environmental gases, and atmosphere during synthesis, on the optoelectronic properties of MHP single crystals. We achieved this by means of optical spectroscopy, electrical measurements, and chemical analyses. We identified the cause of mechanical delamination in MHP/silicon tandem solar cells by atomic force microscopy measurements. We characterized electronic defects and ion migration in MHP single crystals by applying for the first time the photo-induced current transient spectroscopy technique to this class of materials. This research allowed to gain insight into both intrinsic defects, like ion migration and electron trapping, and extrinsic defects, induced by X-ray irradiation, mechanical stress, and exposure to humidity. This research paves the way to the development of methods that heal and passivate these defects, enabling improved performance and stability of MHP optoelectronic devices.

Studio e caratterizzazione di sensori Silicon PhotoMultiplier (SiPM) per applicazioni di timing nell'esperimento ALICE 3

Lo studio che verrà presentato in questo lavoro di tesi riguarda la caratterizzazione di Silicon PhotoMultiplier (SiPM): essi sono sensori a semiconduttore che sono stati proposti per la realizzazione del layer Time-Of-Flight (TOF) del nuovo esperimento proposto ad LHC, ALICE 3. Sono stati testati sensori diversi, sia in termini di casa di fabbricazione (FBK o HPK), sia in termini di struttura; in particolare, i modelli a disposizione di produzione FBK sono singoli SPAD, singoli SiPM e mini-array di SiPM, mentre i modelli HPK sono tutti singoli SiPM. La caratterizzazione è avvenuta mediante misure di corrente e capacità del sensore al variare della tensione (curve IV e curve CV); l'obiettivo primario è studiare e confrontare tali andamenti, in modo da poter selezionare i sensori con caratteristiche simili per la costruzione del layer del TOF. Si è osservato che sensori della stessa casa produttrice e con la stessa struttura interna esibiscono comportamenti quasi sovrapponibili, dimostrando in generale una ottima uniformità.

Characterization of innovative kerfless cutting of monocrystalline silicon wafers for photovoltaic applications

Nowadays renewable energies are a hot research topic, and the goal is to improve cell efficiency and reduce production costs, aiming to make the use of photovoltaics increasingly widespread and convenient. Monocrystalline silicon solar cells are leaders in the photovoltaic market. However, market-established cutting techniques produce a consistent amount of material waste when cutting ingots into wafers. The“Stress-induced LIft-Off Method” (SLIM) is emerging in recent years as an alternative, more sustainable separation technique, which reduces material loss and can lead to obtaining increasingly thinner wafers, further reducing the required amount of silicon. This thesis presents the micro-characterization of the separated wafers with the SLIM technique. The wafers were obtained with a two-step procedure. First, a layer of defects was induced in the silicon using ultra-short medium-infrared laser pulses. Then, the material was deposited on one of the sides and induced stress in the silicon, such as to further weaken it. In this way, only rapid cooling is required for detachment to occur. The obtained results indicate that the SLIM-cut technique halves the minority carriers’ lifetime. There is no amorphization, crystal disorder or high-pressure phases. However, changes in the Raman spectra suggest that tensile stress may have been produced on these surface layers by the separation process. The AFM topography highlights surface irregularities, which may be removed with a polishing step. The surface also shows laser-modified regions, which are evident in SEM images, but not in AFM topographies, suggesting a charging effect due to electron bombardment. Lastly, the electrical characterization by conductive AFM lacks any changes in the conductive behaviour of the material where the laser-modified areas should be located. In conclusion, these preliminary results are promising to carry out a systematic characterization of this technique of this innovative SLIM technique.

The Applicability Of Ordered Mesoporous Sba-15 And Its Hydrophobic Glutaraldehyde-bridge Derivative To Improve Ibuprofen-loading In Releasing System.

The mesoporous SBA-15 silica with uniform hexagonal pore, narrow pore size distribution and tuneable pore diameter was organofunctionalized with glutaraldehyde-bridged silylating agent. The precursor and its derivative silicas were ibuprofen-loaded for controlled delivery in simulated biological fluids. The synthesized silicas were characterized by elemental analysis, infrared spectroscopy, (13)C and (29)Si solid state NMR spectroscopy, nitrogen adsorption, X-ray diffractometry, thermogravimetry and scanning electron microscopy. Surface functionalization with amine containing bridged hydrophobic structure resulted in significantly decreased surface area from 802.4 to 63.0 m(2) g(-1) and pore diameter 8.0-6.0 nm, which ultimately increased the drug-loading capacity from 18.0% up to 28.3% and a very slow release rate of ibuprofen over the period of 72.5h. The in vitro drug release demonstrated that SBA-15 presented the fastest release from 25% to 27% and SBA-15GA gave near 10% of drug release in all fluids during 72.5 h. The Korsmeyer-Peppas model better fits the release data with the Fickian diffusion mechanism and zero order kinetics for synthesized mesoporous silicas. Both pore sizes and hydrophobicity influenced the rate of the release process, indicating that the chemically modified silica can be suggested to design formulation of slow and constant release over a defined period, to avoid repeated administration.

Evaluation Of The Effect Of Different Methods Of Microabrasion And Polishing On Surface Roughness Of Dental Enamel.

The microabrasion technique of enamel consists of selectively abrading the discolored areas or causing superficial structural changes in a selective way. In microabrasion technique, abrasive products associated with acids are used, and the evaluation of enamel roughness after this treatment, as well as surface polishing, is necessary. This in-vitro study evaluated the enamel roughness after microabrasion, followed by different polishing techniques. Roughness analyses were performed before microabrasion (L1), after microabrasion (L2), and after polishing (L3).Thus, 60 bovine incisive teeth divided into two groups were selected (n=30): G1- 37% phosphoric acid (37%) (Dentsply) and pumice; G2- hydrochloric acid (6.6%) associated with silicon carbide (Opalustre - Ultradent). Thereafter, the groups were divided into three sub-groups (n=10), according to the system of polishing: A - Fine and superfine granulation aluminum oxide discs (SofLex 3M); B - Diamond Paste (FGM) associated with felt discs (FGM); C - Silicone tips (Enhance - Dentsply). A PROC MIXED procedure was applied after data exploratory analysis, as well as the Tukey-Kramer test (5%). No statistical differences were found between G1 and G2 groups. L2 differed statistically from L1 and showed superior amounts of roughness. Differences in the amounts of post-polishing roughness for specific groups (1A, 2B, and 1C) arose, which demonstrated less roughness in L3 and differed statistically from L2 in the polishing system. All products increased enamel roughness, and the effectiveness of the polishing systems was dependent upon the abrasive used.

Mechanical Properties And Fracture Dynamics Of Silicene Membranes.

As graphene has become one of the most important materials, there is renewed interest in other similar structures. One example is silicene, the silicon analogue of graphene. It shares some of the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair.

Characterization Of Morphology And Composition Of Inorganic Fillers In Dental Alginates.

Energy dispersive X-ray spectroscopy microanalysis (EDX), scanning electron microscopy (SEM), and Archimedes' Principle were used to determine the characteristics of inorganic filler particles in five dental alginates, including Cavex ColorChange (C), Hydrogum 5 (H5), Hydrogum (H), Orthoprint (O), and Jeltrate Plus (JP). The different alginate powders (0.5 mg) were fixed on plastic stubs (n = 5) and sputter coated with carbon for EDX analysis, then coated with gold, and observed using SEM. Volume fractions were determined by weighing a sample of each material in water before and after calcining at 450(°)C for 3 h. The alginate materials were mainly composed of silicon (Si) by weight (C-81.59%, H-79.89%, O-78.87%, H5-77.95%, JP-66.88%, wt). The filler fractions in volume (vt) were as follows: H5-84.85%, JP-74.76%, H-70.03%, O-68.31%, and C-56.10%. The tested materials demonstrated important differences in the inorganic elemental composition, filler fraction, and particle morphology.

Lymphocyte Activation In Silica-exposed Workers.

Exposure to silica dust has been examined as a possible risk factor for autoimmune diseases, including systemic sclerosis, rheumatoid arthritis, systemic lupus erythematosus and ANCA-associated vasculitis. However, the underlying cellular and molecular mechanisms resulting in the increased prevalence of autoimmunity remain elusive. To clarify these mechanisms, we studied various markers of immune activation in individuals occupationally exposed to silica dust, i.e., serum levels of soluble IL-2 receptor (sIL-2R), levels of IL-2, other pro- and anti-inflammatory cytokines and lymphoproliferation. Our results demonstrate that silica-exposed individuals present important alterations in their immune response when compared to controls, as shown by increased serum sIL-2R levels, decreased production of IL-2 and increased levels of the pro-inflammatory (IFN-γ, IL-1α, TNF-α, IL-6) as well as anti-inflammatory (IL-10 and TGF-β) cytokines. Furthermore, silica-exposed individuals presented enhanced lymphoproliferative responses. Our findings provide evidence that the maintenance of immune homeostasis may be disturbed in silica-exposed individuals, possibly resulting in autoimmune disorders.