Integració 3D de detectors de píxels híbrids

La miniaturització de la industria microelectrònica és un fet del tot inqüestionables i la tecnologia CMOS no n'és una excepció. En conseqüència la comunitat científica s'ha plantejat dos grans reptes: En primer lloc portar la tecnologia CMOS el més lluny possible ('Beyond CMOS') tot desenvolupant sistemes d'altes prestacions com microprocessadors, micro - nanosistemes o bé sistemes de píxels. I en segon lloc encetar una nova generació electrònica basada en tecnologies totalment diferents dins l'àmbit de les Nanotecnologies. Tots aquests avanços exigeixen una recerca i innovació constant en la resta d'àrees complementaries com són les d'encapsulat. L'encapsulat ha de satisfer bàsicament tres funcions: Interfície elèctrica del sistema amb l'exterior, Proporcionar un suport mecànic al sistema i Proporcionar un camí de dissipació de calor. Per tant, si tenim en compte que la majoria d'aquests dispositius d'altes prestacions demanden un alt nombre d'entrades i sortides, els mòduls multixip (MCMs) i la tecnologia flip chip es presenten com una solució molt interessant per aquests tipus de dispositiu. L'objectiu d'aquesta tesi és la de desenvolupar una tecnologia de mòduls multixip basada en interconnexions flip chip per a la integració de detectors de píxels híbrids, que inclou: 1) El desenvolupament d'una tecnologia de bumping basada en bumps de soldadura Sn/Ag eutèctics dipositats per electrodeposició amb un pitch de 50µm, i 2) El desenvolupament d'una tecnologia de vies d'or en silici que permet interconnectar i apilar xips verticalment (3D packaging) amb un pitch de 100µm. Finalment aquesta alta capacitat d'interconnexió dels encapsulats flip chip ha permès que sistemes de píxels tradicionalment monolítics puguin evolucionar cap a sistemes híbrids més compactes i complexes, i que en aquesta tesi s'ha vist reflectit transferint la tecnologia desenvolupada al camp de la física d'altes energies, en concret implantant el sistema de bump bonding d'un mamògraf digital. Addicionalment s'ha implantat també un dispositiu detector híbrid modular per a la reconstrucció d'imatges 3D en temps real, que ha donat lloc a una patent.

On the performance of near-far resistant CDMA detectors in the presence of synchronization errors

Little has so far been reported on the performance of the near-far resistant CDMA detectors in the presence of the synchronization errors. Starting with the general mathematical model of matched filters, this paper examines the effects of three classes of synchronization errors (i.e. time-delay errors, carrier phase errors, and carrier frequency errors) on the performance (bit error rate and near-far resistance) of an emerging type of near-far resistant coherent DS/SSMA detectors, i.e. the linear decorrelating detector (LDD). For comparison, the corresponding results for the conventional detector are also presented. It is shown that the LDD can still maintain a considerable performance advantage over the conventional detector even when some synchronization errors exist. Finally, several computer simulations are carried out to verify the theoretical conclusions.

Power control requirements in linear decorrelating detectors for CDMA

This paper addresses the effects of synchronisation errors (time delay, carrier phase, and carrier frequency) on the performance of linear decorrelating detectors (LDDs). A major effect is that all LDDs require certain degree of power control in the presence of synchronisation errors. The multi-shot sliding window algorithm (SLWA) and hard decision method (HDM) are analysed and their power control requirements are examined. Also, a more efficient one-shot detection scheme, called “hard-decision based coupling cancellation”, is proposed and analysed. These schemes are then compared with the isolation bit insertion (IBI) approach in terms of power control requirements.

Performance analysis of near-far resistant CDMA detectors-influence of system parameter estimation errors

Little has been reported on the performance of near-far resistant CDMA detectors in the presence of system parameter estimation errors (SPEEs). Starting with the general mathematical model of matched filters, the paper examines the effects of three classes of SPEEs, i.e., time-delay, carrier phase, and carrier frequency errors, on the performance (BER) of an emerging type of near-far resistant coherent DS/SSMA detector, i.e., the linear decorrelating detector. For comparison, the corresponding results for the conventional detector are also presented. It is shown that the linear decorrelating detector can still maintain a considerable performance advantage over the conventional detector even when some SPEEs exist.

Convergence analysis of chip- and fractionally spaced LMS adaptive multiuser CDMA detectors

This paper analyzes the convergence behavior of the least mean square (LMS) filter when used in an adaptive code division multiple access (CDMA) detector consisting of a tapped delay line with adjustable tap weights. The sampling rate may be equal to or higher than the chip rate, and these correspond to chip-spaced (CS) and fractionally spaced (FS) detection, respectively. It is shown that CS and FS detectors with the same time-span exhibit identical convergence behavior if the baseband received signal is strictly bandlimited to half the chip rate. Even in the practical case when this condition is not met, deviations from this observation are imperceptible unless the initial tap-weight vector gives an extremely large mean squared error (MSE). This phenomenon is carefully explained with reference to the eigenvalues of the correlation matrix when the input signal is not perfectly bandlimited. The inadequacy of the eigenvalue spread of the tap-input correlation matrix as an indicator of the transient behavior and the influence of the initial tap weight vector on convergence speed are highlighted. Specifically, a initialization within the signal subspace or to the origin leads to very much faster convergence compared with initialization in the a noise subspace.

Variable step-size LMS blind CDMA multiuser detectors

Adaptive least mean square (LMS) filters with or without training sequences, which are known as training-based and blind detectors respectively, have been formulated to counter interference in CDMA systems. The convergence characteristics of these two LMS detectors are analyzed and compared in this paper. We show that the blind detector is superior to the training-based detector with respect to convergence rate. On the other hand, the training-based detector performs better in the steady state, giving a lower excess mean-square error (MSE) for a given adaptation step size. A novel decision-directed LMS detector which achieves the low excess MSE of the training-based detector and the superior convergence performance of the blind detector is proposed.

Nickel hydroxide electrodes as amperometric detectors for carbohydrates in flow injection analysis and liquid chromatography

The present paper describes the utilization of nickel hydroxide modified electrodes toward the catalytic oxidation of carbohydrates (glucose, fructose, lactose and sucrose) and their utilization as electrochemical sensor. The modified electrodes were employed as a detector in flow injection analysis for individual carbohydrate detection, and to an ionic column chromatography system for multi-analyte samples aiming a prior separation step. Kinetic studies were performed on a rotating disk electrode (RDE) in order to determine both the heterogeneous rate constant and number of electrons transferred for each carbohydrate. Many advantages were found for the proposed system including fast and easy handling of the electrode modification, low cost procedure, a wide range of linearity (0.5-50 ppm), low detection limits (ppb level) and high sensitivities. (C) 2009 Elsevier B.V. All rights reserved.

Sequential IRMPD of XGe(OEt)(4)(-) ions: Gas-phase synthesis of novel oxy-germanium anions

The gas-phase ion/molecule reactions of F(-) and EtO(-) with Ge(OEt)(4) yield readily and exclusively pentacoordinated complexes XGe(OEt)(4)(-) (X = F, EtO) at pressures in the 10(-8) T range as observed by FT-ICR techniques. These hypervalent species are prone to undergo sequential fragmentations induced by infrared multiphoton excitation that lead to a variety of germyl and germanate anions. In the case of FGe(OEt)(4)(-), three primary competitive channels are observed in the IRMPD process that can be identified as (EtO)(3)GeO(-), F(EtO)(2)GeO(-) and (EtO)(3)Ge(-). Ab initio calculations have been carried out to characterize the primary fragmentation paths induced by IRMPD and the most favorable structure of the resulting anions. The gas-phase acidity of a number of these germanium-containing ions have been estimated by bracketing experiments and by theoretical calculations. Germanate anions such as (EtO)(3)GeO(-) undergo some interesting reactions with H(2)S to give rise to anions such as (EtO)(3)GeS(-) and (EtO)(2)Ge(OH)S(-). (C) 2010 Elsevier B.V. All rights reserved.

Modified LPE system used to diffuse Cd to obtain InSb infrared detectors

We are presenting here p/n junctions obtained with a modified opened liquid-phase epitaxy (LPE) system, used to diffuse indium antimonide (InSb) doped with Cd over InSb doped with Te wafers, in order to make InSb infrared (IR) sensors. This technique has several advantages: the diffusion can be performed in bigger substrate areas improving the device production; this method decreases the device manipulation, decreasing human mistakes and increasing the process reproducibility. The opened LPE in this work produced sensors in the first case with vapor of the diffusion material, coming from a microholed carbon boat full of the diffusion material, over which is positioned the substrate at atmospheric pressure. In the second, the diffusion material is on the bottom of a quartz recipient, and the InSb/Te wafer works as its cover, and vacuum was used. The IR sensors produced with the first method measured 8.9 x 10(7) cm Hz(1/2)/W as detectivity value and higher IR spectral response at 4.6 mu m, and those produced with the second 2.8 x 10(9) cm Hz(1/2)/W, at 4.4 mu m. Besides the electrical-optical properties, the structural properties of diffused layers were investigated by X-ray diffraction (XRD), scanning electron and atomic force microscopy (SEM, AFM), energy-dispersive and secondary ion mass spectroscopy (EDS, SIMS). (C) 2007 Elsevier B.V. All rights reserved.

UNIFORMLY ACCELERATED FINITE-TIME DETECTORS

The behavior of uniformly accelerated detectors in the Minkowski and Rindler vacua is analyzed when the detector is coupled to a scalar field during a finite amount of time T. We point out that the logarithmic ultraviolet divergences reported in the literature are due to the instantaneous switching of the detector. We explicitly show this by considering a detector switched on and off continuously. The usual Planckian spectrum for the excitation probability is recovered in the limit T --> infinity.

Femtosecond nonlinear optical properties of lead-germanium oxide amorphous films

The nonlinear (NL) response of lead-germanium oxide amorphous films was investigated using a Ti:saphire laser delivering pulses of approximate to 150 fs at 800 nm. The Kerr shutter technique was employed to reveal the time response of the nonlinearity that is smaller than 150 fs. The sign and magnitude of the nonlinearity were obtained using a novel technique called thermally managed eclipse Z scan which allows the simultaneous characterization of cumulative and noncumulative NL effects. The NL refractive index of electronic origin, n(2)approximate to 2x10(-17) m(2)/W, and the NL absorption coefficient, alpha(2)approximate to 3x10(3) cm/GW, were determined. (c) 2007 American Institute of Physics.

Local order around of germanium atoms in Ga10Ge25S65 glass by EXAFS

Irreversible photoexpansion effect has been observed in amorphous Ga10Ge2S65 glasses when its surface was exposed to light with energy greater than the band gap, 3.52 eV. A volume change of about 5% was reached in bulk samples by controlling illumination time and the laser power density. To understand the atomic scale processes of the photoexpansion effect, extended X-ray absorption fine structure (EXAFS) spectroscopy has been used as a local probe of the germanium environment in the glass samples before and after illumination. Modifications are observed in the average coordination shell around Ge atoms in the illuminated sample compared to the non-illuminated one. For the non-illuminated sample, the Ge coordination shell is described by a distorted tetrahedron of sulfur atoms at around 2.20 Angstrom. After illumination, the EXAFS signal can be explained by introducing an additional contribution to this average environment. Based on an analysis of the EXAFS data we proposed a two-shell model of 0.5 oxygen atoms at 2.01 Angstrom and 3.6 sulfur atoms at a 2.20 Angstrom. The existence of Ge-O bonds in the glass after illumination was confirmed by infrared measurements. (C) 2002 Elsevier B.V. B.V. All rights reserved.