J. Barbolla

Universidad de Valladolid, Valladolid, Castille and León, Spain

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Publications (146)190.83 Total impact

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    ABSTRACT: We present an experimental continuous-time complex delta-sigma multi-bit modulator, implemented in standard 0.25-μm CMOS technology and meeting all major requirements for application in IEEE 802.11a/b/g wireless LAN receivers. The clock frequency is 320 MHz, producing an oversampling ratio of 16 for 20 MHz channel bandwidths. The modulator supports two operation modes for zero-IF and low-IF receiver architectures respectively, requires a single 2.5-V power supply, and dissipates only 32 mW of power. The measured peak signal-to-noise ratio is 55 dB. Further experimental results using sine-wave and OFDM test signals are also presented.
    IEEE Journal of Solid-State Circuits 03/2006; · 3.06 Impact Factor
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    ABSTRACT: The energy levels and electrically active concentrations for platinum in n- and p-type Si, and for palladium in n-type silicon are measured by the dark transient capacitance technique, p+—n—p+ and n+—p—n+ structures have been platinum-diffused at low temperatures (820 to 844 °C). Two levels are found, a donor at Ev + 0.32 eV in p-type silicon and an acceptor at Ec — 0.24 eV in n-type silicon. These two levels are associated with the usual substitutional site (Pt(I)). The second usual site (Pt(II)) does not appear in samples, p+—n—p+ structures have been palladium-diffused at 898 °C. An acceptor level at Ec — 0.20 eV is found which is probably associated with the substitutional site of palladium in silicon.Nous avons déterminé, par la méthode des transitoires isothermes de capacité, les niveaux d'énergie et les densités d'atomes électriquement actifs pour le platine dans du silicium de type n et p et pour le palladium dans du silicium de type n. Des structures p+—n—p+ et n+—p—n+ ont été dopées au platine à basse température (820 à 844 °C). Nous trouvons deux niveaux, un donneur à Ev + 0.32 eV dans le type p et un accepteur à Ec — 0.24 eV dans le type n. Ces deux niveaux sont associés au site usuel substitutionnel (Pt(I)). Le second site couramment rencontré, (Pt(II)), n'est pas présent dans nos échantillons. Nous avons effectué des diffusions de palladium à 898 °C sur des structures p+—n—p+ et nous trouvons un niveau accepteur à Ec — 0,20 eV qui est probablement associé au site substitutionnel du palladium dans le silicium.
    physica status solidi (a) 02/2006; 35(2):533 - 543. · 1.21 Impact Factor
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    ABSTRACT: From capacitance measurements, the thermal capture cross-section of electrons at neutral gold centres is determined through the time dependence of the net ionized recombination centres concentration to σ = 1.24 × 10−16 (T/300)−(0.21 ± 0.03) cm2 in the temperature range 80 to 205 K.La section de capture thermique des électrons sur l'or neutre est déduite de la dépendance temporelle de la densité de centres profonds ionisés, mesurée par une technique capacitive. Pour le domaine de température 80 à 205 K le résultat est: σ = 1,24 × 10−16 (T/300)−(0,21 ± 0.03) cm2.
    physica status solidi (a) 02/2006; 36(2):495 - 498. · 1.21 Impact Factor
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    ABSTRACT: Atomistic process simulation is expected to play an important role for the development of next generations of integrated circuits. This work describes an approach for modeling electric charge effects in a three-dimensional atomistic kinetic Monte Carlo process simulator. The proposed model has been applied to the diffusion of electrically active boron and arsenic atoms in silicon. Several key aspects of the underlying physical mechanisms are discussed: (i) the use of the local Debye length to smooth out the atomistic point-charge distribution, (ii) algorithms to correctly update the charge state in a physically accurate and computationally efficient way, and (iii) an efficient implementation of the drift of charged particles in an electric field. High-concentration effects such as band-gap narrowing and degenerate statistics are also taken into account. The efficiency, accuracy, and relevance of the model are discussed.
    Journal of Applied Physics 10/2005; · 2.21 Impact Factor
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    ABSTRACT: We introduce a model for damage accumulation up to amorphization, based on the ion-implant damage structures commonly known as amorphous pockets. The model is able to reproduce the silicon amorphous-crystalline transition temperature for C, Si, and Ge ion implants. Its use as an analysis tool reveals an unexpected bimodal distribution of the defect population around a characteristic size, which is larger for heavier ions. The defect population is split in both size and composition, with small, pure interstitial and vacancy clusters below the characteristic size, and amorphous pockets with a balanced mixture of interstitials and vacancies beyond that size.
    Journal of Applied Physics 09/2005; · 2.21 Impact Factor
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    ABSTRACT: In this work, an approach for the simulation of the effect of noise sources in the performance of continuous-time DeltaSigma modulators is presented. Electrical noise including thermal noise, /f noise and clock jitter are included in a simulation program and their impact on the system performance is analyzed.
    08/2005;
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    ABSTRACT: An accurate physically-based Fermi-level modeling approach, amenable to be implemented in an atomistic device-size process simulator, is reported. The atomistic kinetic Monte Carlo method is used for point and extended defects, in conjunction with a quasi-atomistic, continuum approach treatment for carrier densities. The model implements charge reactions and electric bias according to the local Fermi-level, pairing and break-up reactions between particles, clustering-related dopant deactivation and Fermi level-dependent solubility. We derive expressions that can be used as a bridge between the continuum and the atomistic frameworks. We present the implementation of two common dopants, Boron and Arsenic, using parameters that are in agreement with both ab- initio calculations and experimental results. Current microelectronic technology is facing increas- ingly complex phenomena related to very high-doping, reduced thermal budget (non-equilibrium conditions), and three dimensional efiects. Such conditions require a deep insight into the underlying physical mechanisms in order to correctly model the material properties. In particular, high-doping concentrations demand a cor- rect description of difiusion under extrinsic conditions.1,2 Other charge-related issues are Fermi-level dependent solubility,3,4 clustering-related dopant deactivation,5 and high-damage electrical compensation. Continuum modeling, based on solving partial dif- ferential equations (PDE) discretized by the flnite el- ement method, has been used since the 1980's, but this method is limited by the number of equations that can be solved without running into convergence insta- bilities. Moreover, meshing issues and dimensionality make this approach extremely complicated in 3D. The International Roadmap for Semiconductors 20036 estab- lishes the \Modeling hierarchy from atomistic to con- tinuum" among the di-cult challenges that need to be solved before 2010. The atomistic kinetic Monte Carlo (kMC) method,7 has proven to be a powerful approach that allows the inclusion of comprehensive, physically based models without signiflcantly degrading the sim- ulator's performance. Some semiconductor companies8,9 and software vendors10,11 have already started to develop simulators based on this atomistic kMC approach. Mod- elling Fermi level efiects is one of the critical steps in developing a comprehensive kMC simulator. Here we will describe a detailed Fermi-level modeling approach specially designed to be included in this methodology, which has been implemented and tested in the atomistic kMC process simulator DADOS.12 We flrst describe in detail the basic physical models and then the particular implementation of point defects and of two representative dopants (boron and arsenic), and flnally show a simulation example.
    Physical Review B 07/2005; 72. · 3.66 Impact Factor
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    ABSTRACT: A comprehensive atomistic model for arsenic in silicon which includes charge effects and is consistent with first-principles calculations for arsenic-vacancy cluster energies has been developed. Emphasis has been put in reproducing the electrical deactivation and the annealed profiles in preamorphized silicon. The simulations performed with an atomistic kinetic Monte Carlo simulator suggest a predominant role of the mobile interstitial arsenic in deactivation experiments and provide a good understanding of the arsenic behavior in preamorphized silicon during annealing.
    Applied Physics Letters 07/2005; · 3.79 Impact Factor
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    ABSTRACT: This paper presents a digital correction technique for wide-band multibit error-feedback (EF) digital-to-analog converters (DACs). The integral nonlinearity (INL) error of the multibit DAC is estimated (on line or off line) by a calibration analog-to-digital converter (CADC) and stored in a random-access memory table. The INL values are then used to compensate for the multibit DAC's distortion by a simple digital addition. The accuracy requirements for the error estimates are derived. These requirements can be significantly relaxed when the correction is combined with data-weighted averaging (DWA). Simulation and discrete-component measurement results are presented for a fourth-order 5-bit EF DAC. The results show a 14-bit DAC operating at an oversampling ratio of 8, which is suitable for digital subscriber line applications. The correction uses simple digital circuitry and a 3-bit CADC enhanced by DWA.
    Circuits and Systems I: Regular Papers, IEEE Transactions on 07/2005; · 2.24 Impact Factor
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    ABSTRACT: In this work a dual-mode complex multibit continuous-time DS modulator for a standard 0.25µm CMOS technol- ogy is presented. This modulator is intended for the analog-to-digital conversion in multi-mode wireless-LAN receivers (802.11a/b/g) which require wide bandwidth and moderate resolution. Then, a low oversampling ratio of 16 along with a clock frequency of 320 MHz provides a signal bandwidth of 20 MHz for a 9-bit resolution with a second-order modulator. The modulator can be congured for two different modes of operation depending on the type of radio receiver chosen: "zero- IF" (ZIF) and "low-IF" (LIF). The former mode is better suited for 802.11b, while LIF mode is more adequate for 802.11a/g applications. The loop lter is based on transconductors and MOS-capacitors allowing for low power consumption and small chip area. The modulator also includes two 3-bit quantizers, both with their corresponding DWA scrambler. The supply volt- age is 2.5V and the measured power consumption is 32 mW. Experimental results using both sine-wave and OFDM signals are presented. The obtained SNR and SNDR are 55dB and 53.5dB, respectively. A high image rejection of 47dB is achieved owing to proper layout techniques. When using OFDM signals, a minimum error vector magnitude of 1.3% is obtained. Finally, the active chip area is 0:44mm2.
    Proc SPIE 06/2005;
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    ABSTRACT: We use kinetic nonlattice Monte Carlo atomistic simulations to investigate the physical mechanisms for boron cluster formation and dissolution in complementary metal-oxide semiconductor (MOS) processing, and the role of Si interstitials in the different processes. For this purpose, B implants in crystalline Si as well as B implants in preamorphized Si are analyzed. For subamorphizing B implants, a high concentration of Si interstitials overlaps with the B profile and this causes a very quick B deactivation for both low- and high-dose B implants. For B implants in preamorphized silicon, B is activated during the regrowth of the amorphous layer if the B concentration is lower than 1020 cm−3 and remains active upon annealing. However, if B concentrations higher than 1020 cm−3 are present, as occurs in the formation of extensions in p-channel MOS transistors, B atoms are not completely activated during the regrowth. Moreover, the injection of Si interstitials from the end-of-range defects leads to additional B deactivation in the regrown layer during subsequent annealing. If the end-of-range defects overlap with a B profile, even of relatively low concentration, as it occurs for B pockets in n-channel MOS transistors, very quick and local B deactivation occurs in the high Si-interstitial concentration region.
    Journal of Applied Physics 05/2005; 97(10):103520-103520-7. · 2.21 Impact Factor
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    ABSTRACT: The authors have analyzed the damage produced by 5 keV Si cascades in Si using molecular dynamics simulations. In order to make a statistical study of the features of the damage 283 independent cascades have been simulated. Relations between the number of displaced atoms and the size and morphology of produced damage have been studied. Using a criteria for identifying defects that eliminates thermal noise in atom positions, the distribution of the displaced atoms in the cascades were obtained. The mean number of displaced atoms per cascade is 346. About 50 % of the cascades generate between 300 and 400 displaced atoms, although significant deviations from the average values are found. The analysis of the 'deviated cascades' has revealed an interesting relation between the number of displaced atoms of the cascade and the size of the defects that it has produced. The correlations between the results and those predicted by the modified Kinchin-Pease formula are also discussed.
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: We analyze the effects of junction formation by low-temperature solid phase epitaxial regrowth in NMOS transistors. Atomistic simulations indicate that the high concentration of Si interstitials associated with the end of range (EOR) defects favors the local formation of boron clusters just beyond the amorphous/crystalline interface, in agreement to sheet resistance measurements. Thus, EOR defects locally deactivate B in the NMOS pockets. These boron clusters start dissolution, and thus B reactivates, when the high Si interstitial supersaturation produced by the EOR defects decays close to the equilibrium value. This occurs when EOR defects dissolve or evolve to very stable configurations, such us dislocation loops.
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: The authors have analyzed the main features regarding the recrystallization of amorphous regions, using an atomistic amorphization-recrystallization model that considers the interstitial-vacancy pair (IV pair) as the building block of the amorphous phase. In the model presented recrystallization is governed by the local rearrangement of atoms, being the local coordination what determines the recrystallization rate. This feature explains why the recrystallization velocity is independent of the depth of the amorphous layer (a-layer). The geometry, and not only the size, is the key factor of amorphous pockets (a-pockets) regrowth. The different annealing behavior of a continuous a-layer and the damage tail are also studied.
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: Experiments and simulations on B diffusion and activation in pre-amorphized Si are presented. B concentrations below 2×10<sup> 20</sup> cm<sup> -3</sup> experience significant diffusion while higher B concentration regions remain immobile forming electrically inactive B clusters during low temperature recrystallization. Subsequent annealing causes B redistribution. Uphill diffusion and B deactivation is followed by B clustering dissolution and tail diffusion during high temperature anneals.
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: A comparative electrical characterization of metal-insulator-semiconductor (MIS) structures fabricated from atomic layer deposited (ALD) Al<sub>2</sub>O<sub>3</sub>, Ta<sub>2</sub>O<sub>5</sub> and Nb<sub>2</sub>O<sub>5</sub>-Ta<sub>2</sub>O<sub>5</sub>-Nb<sub>2</sub>O<sub>5</sub> dielectric thin films on silicon substrates has been carried out. The interface states as well as defects inside the insulator bulk were measured by using capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) and conductance-transient (G-t) techniques. Interface quality is poorer in the case of Ta<sub>2</sub>O<sub>5</sub> (D<sub>it</sub> is about 6 × 10<sup>12</sup> cm<sup>-2</sup> eV<sup>-1</sup>) than in the Al<sub>2</sub>O<sub>3</sub> ones (D<sub>it</sub> values up to 1 × 10<sup>12</sup> cm<sup>-2</sup> eV<sup>-1</sup>). Also, the addition of Nb<sub>2</sub>O<sub>5</sub> buffer layers to Ta<sub>2</sub>O<sub>5</sub>-based MIS degrades the structure (D<sub>it</sub> reaches values of 1.2 × 10<sup>13</sup> cm<sup>-2</sup> eV<sup>-1</sup>).
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: The authors have used molecular dynamics simulation techniques to study the properties of the amorphous phase of silicon. Several amorphous silicon samples have been prepared at different temperatures. The changes in the density, internal energy, structure, diffusion coefficients and recrystallization behavior of the amorphous phase have been extracted from the simulations as a function of temperature. The analysis of the results showed that, for temperatures between the amorphous and crystal melting points, there exists an intermediate phase which shares some of the properties of the amorphous and liquid silicon.
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: A comparison between interface quality of several temperatures thermal annealed HPRS TiO<sub>2</sub> films and 750 °C annealed ALD TiO<sub>2</sub> films has been established. Our attention has been focused on the interfacial state and disordered induced gap state densities. From our results, HPRS films submitted to in situ 900 °C thermal annealing in oxygen atmosphere exhibit the best characteristics, with D<sub>it</sub> density being the lowest value measured in this work (5.6 × 10<sup>11</sup> cm<sup>-2</sup> eV<sup>-1</sup>), and undetectable conductance transients within our experimental limits.
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: An electrical characterization of Al/Hf-Si-O/n-Si samples has been carried out. Hafnium-rich silicate films have been grown by means of atomic layer deposition (ALD). Capacitance-voltage (C-V), deep level transient spectroscopy (DLTS) and conductance transient (G-t) techniques have been used. Although as-deposited samples exhibit high interfacial state and disordered induced gap state densities, a post-metallization thermal annealing in vacuum under N<sub>2</sub> flow for 1 min. at temperatures between 600 and 730 °C clearly improves the interface quality. Moreover, both as-deposited and annealed samples show low flat-band voltage shift and hysteresis effect. These results confirm Hf silicate as a suitable candidate to replace SiO<sub>2</sub> as gate dielectric in future CMOS technologies.
    Electron Devices, 2005 Spanish Conference on; 03/2005
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    ABSTRACT: We present kinetic nonlattice Monte Carlo atomistic simulations to investigate the role of Si interstitials in B cluster dissolution. We show that the presence of Si interstitials from an oxidizing anneal stabilize B clusters and slow down B cluster dissolution, compared to anneal in inert ambient. We have also analyzed the influence of injected Si interstitials from end of range defects, due to preamorphizing implants, on B deactivation and reactivation processes. We have observed that the B cluster evolution can be clearly correlated to the evolution of Si interstitial defects at the end of range. The minimum level of activation occurs when the Si interstitial supersaturation is low because the end of range defects have dissolved or reach very stable configurations, such as dislocation loops.
    Applied Physics Letters 01/2005; 86(3):031908-031908-3. · 3.79 Impact Factor

Publication Stats

778 Citations
190.83 Total Impact Points

Institutions

  • 1970–2006
    • Universidad de Valladolid
      • • Department of Electricity and Electronics
      • • Facultad de Ciencias
      Valladolid, Castille and León, Spain
  • 2003
    • Universidad de Sevilla
      Hispalis, Andalusia, Spain
  • 2000
    • University of Barcelona
      • Department of Electronics
      Barcino, Catalonia, Spain
  • 1997
    • Lund University
      Lund, Skåne, Sweden
  • 1982–1983
    • University of Zaragoza
      • Faculty of Sciences (CIENCIAS)
      Zaragoza, Aragon, Spain