Juan Roldan | Universidad Simón Bolívar (Barranquilla) (original) (raw)
Papers by Juan Roldan
Applied Physics Letters
We show by Monte Carlo simulation that electron mobility is greater when strained-silicon inversi... more We show by Monte Carlo simulation that electron mobility is greater when strained-silicon inversion layers are grown on SiGe-on-insulator substrates than when unstrained-silicon-on-insulator devices are employed ͑as experimentally observed͒. However, the electron mobility in strained-Si/SiGe-on-insulator inversion layers is strongly dependent on the strained-silicon layer thickness, T Si , due to an increase of the phonon scattering, which partially counteracts the increase in the mobility achieved by the strain. This effect is less important as the germanium mole fraction, x, is reduced, and as the value of T Si increases.
Journal of Socio-Economics
Electron transport properties of strained-Si on relaxed Si1-xGex channel MOSFETs have been studie... more Electron transport properties of strained-Si on relaxed Si1-xGex channel MOSFETs have been studied using a Monte Carlo simulator. The steady- and non-steady-state high-longitudinal field transport regimes have been described in detail. Electron-velocity-overshoot effects are also studied in deep-submicron strained-Si MOSFETs, where they show an improvement over the performance of their normal silicon counterparts.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
ABSTRACT
Se presentan las características de un nuevo simulador didáctico de circuitos electrónicos multip... more Se presentan las características de un nuevo simulador didáctico de circuitos electrónicos multiplataforma, con interfaz gráfica avanzada GTK+, denominado ESPICE. El simulador basado en SPICE tiene nuevas funcionalidades que posibilitan el acceso a los datos internos de la simulación; el análisis e interpretación del fichero de simulación, las matrices de tensiones y corrientes en cada iteración; la inclusión de nuevas funciones de procesado de datos, tipos de análisis, modelos de dispositivos y obtención del ejecutable mediante la compilación en Windows y Linux previa descarga del código fuente del repositorio público. Así mismo, se presenta un conjunto de recursos multimedia que acompañan al simulador.
Radioengineering, 2015
We have measured the transition process from the high to low resistivity states, i.e., the reset ... more We have measured the transition process from the high to low resistivity states, i.e., the reset process of resistive switching based memristors based on Ni/HfO 2 /Si-n+ structures, and have also developed an analytical model for their electrical characteristics. When the characteristic curves are plotted in the current-voltage (I-V) domain a high variability is observed. In spite of that, when the same curves are plotted in the charge-flux domain (Q-), they can be described by a simple model containing only three parameters: the charge (Q rst ) and the flux ( rst ) at the reset point, and an exponent, n, relating the charge and the flux before the reset transition. The three parameters can be easily extracted from the Q- plots. There is a strong correlation between these three parameters, the origin of which is still under study.
Solid-State Electronics, 2015
The scaling of MOSFET transistors makes the use of new device geometries, such as multigate FETs,... more The scaling of MOSFET transistors makes the use of new device geometries, such as multigate FETs, a need to solve the limitations of the conventional bulk technology. In this context we introduce an analytical model for square Gate All Around (GAA) MOSFETs with rounded corners including quantum effects. The modeling of rounded corners in GAA and FinFET devices is imperative because there are no perfectly square corners in the cross-section of real devices. In this model the 2D inversion charge distribution function (ICDF) is described analytically for devices of different sizes and for different operation regimes. The model reproduces accurately simulated data obtained with a state-of-the-art simulator that solves self-consistently the Poisson and Schrödinger equations in the devices under consideration. The analytical ICDF is used to better understand the device physics and to calculate the inversion charge centroid and the gate-to-channel capacitance for different device geometries and biases for modeling purposes.
Solid-State Electronics, 2015
ABSTRACT Reset transitions in HfO2 based RRAMs operated at different temperatures have been studi... more ABSTRACT Reset transitions in HfO2 based RRAMs operated at different temperatures have been studied. Ni/HfO2/Si-n+ devices were fabricated and measured at temperatures ranging from 233 K to 473 K to characterize their reset features. In addition, a simulator including several coupled conductive filaments, series resistance and quantum effects was employed to analyze the same devices. The experimental results were correctly reproduced. It was found that the reset voltage and current show slight temperature dependence. To explain this fact, the roles of the out-diffusion of metallic species from the conductive filament and its conductance temperature dependence have been studied by simulation. The different conductive filament resistance components are also analyzed in the temperature range employed in our study. Finally, the thermal change in the energy barrier linked to quantum effects in the transport properties in the filament is modeled.
Microelectronics Journal, 2015
ABSTRACT DC thermal effects modelling for nanometric silicon-on-insulator (SOI) and bulk fin-shap... more ABSTRACT DC thermal effects modelling for nanometric silicon-on-insulator (SOI) and bulk fin-shaped field-effect transistors (FinFETs) is presented. Among other features, the model incorporates self-heating effects (SHEs), velocity saturation and short-channel effects. SHEs are analysed in depth by means of thermal resistances, which are determined through an equivalent thermal circuit, accounting for the degraded thermal conductivity of the ultrathin films within the device. Once the thermal resistance for single-fin devices has been validated for different gate lengths and biases, comparing the modelled output characteristics and device temperatures with numerical simulations obtained using Sentaurus Device, the thermal model is extended by circuital analysis to multi-fin devices with multiple fingers.
The transport properties of very thin double gate SOI MOSFETs, have been studied. W e have shown ... more The transport properties of very thin double gate SOI MOSFETs, have been studied. W e have shown the importance of volume inversion, which greatly reduces the dependence of the electron mobility on the surface scattering mechanisms, and enhances the mobility at high inversion charge concentrations. W e have also shown that if the silicon film is extremely thin, electron mobility abruptly decreases due to stronger phonon scattering.
This paper shows the relevance of mobility models to describe the carrier dynamics for the analys... more This paper shows the relevance of mobility models to describe the carrier dynamics for the analysis of radiative semiconductor photoconductive devices in the terahertz regime. We have built a simulator that self-consistently solves the device physics and Maxwell's equations to study the radiated fields. In particular, we show a significant influence of an accurate description of the steady-state regime of the semiconductor device for calculating radiated electromagnetic fields in the broadside direction. Comparison with measurements shows the accuracy of our simulator and demonstrates the superior performance of numerical schemes based not only on the description of the carrier, electric potential, and field distributions, but also on reliable local mobility models.
Journal of Computational Electronics, 2006
... L. Donetti ( ) · F. Gámiz · JB Roldán · A. Godoy Departamento de Electrónica y Tecnologıa de ... more ... L. Donetti ( ) · F. Gámiz · JB Roldán · A. Godoy Departamento de Electrónica y Tecnologıa de Computadores, Universidad de Granada, 18071 Granada ... TIC2001-3243 supported by the Spanish Government, and by EU (Network of Excellence SINANO, IST-1-506844-NoE). ...
Physics Letters a, 2014
We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an ... more We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an effective Hamiltonian, we have investigated the autocorrelation function and the density currents in this material. Moreover, we have analyzed other types of periodicities of the system (classical and revival times). Finally, the above results are compared with their counterparts in two other monolayer materials subject to a magnetic field: graphene and MoS 2
Journal of Applied Physics, 2014
ABSTRACT An in-depth study of reset processes in RRAMs (Resistive Random Access Memories) based o... more ABSTRACT An in-depth study of reset processes in RRAMs (Resistive Random Access Memories) based on Ni/HfO2/Si-n+ structures has been performed. To do so, we have developed a physically based simulator where both ohmic and tunneling based conduction regimes are considered along with the thermal description of the devices. The devices under study have been successfully fabricated and measured. The experimental data are correctly reproduced with the simulator for devices with a single conductive filament as well as for devices including several conductive filaments. The contribution of each conduction regime has been explained as well as the operation regimes where these ohmic and tunneling conduction processes dominate.
Page 1. Double Gate Silicon-on-Insulator transistors: + + n+-n+ gate versus n -p gate configurati... more Page 1. Double Gate Silicon-on-Insulator transistors: + + n+-n+ gate versus n -p gate configuration. F.Gamiz, JBRoldan, A.Godoy and F.Jimenez-Molinos ... TIC2001-3243 supported by the Spanish Government, and by EU (Network of Excellence SINANO, IST-1-506844-NoE). ...
Essderc 2003: Proceedings of the 33rd European Solid-State Device Research Conference, 2003
A model to study the effect of the roughness at the poly-Si/SiO 2 interface in silicon inversion ... more A model to study the effect of the roughness at the poly-Si/SiO 2 interface in silicon inversion layers on the electron mobility is obtained. Screening of the resulting perturbation potential by the channel carriers is taken into account, considering Green's functions for Metal-Oxide-Semiconductor (MOS) geometry, i.e. taking into account the finite thickness of the gate oxide. Mobility of electrons is evaluated at room temperature by the Monte Carlo method, taking into account the simultaneous contribution of phonon scattering, SiO 2 /Si interface roughness scattering, Coulomb scattering and remote surface roughness scattering. The contribution of excited subbands is considered. The resulting remote surface roughness scattering is shown to be strongly dependent on the oxide thickness, and degrades mobility curves at low inversion charge concentrations. The results obtained show that the effect of this scattering mechanism cannot be ignored when the oxide thickness is below 5nm, (as in actual devices), even when (as is usual) very high doping concentrations are used.
Semiconductor Science and Technology, 2006
The high field transport regime of single gate (SG) SOI MOSFETs has been the subject of an in-dep... more The high field transport regime of single gate (SG) SOI MOSFETs has been the subject of an in-depth characterization. To study this, we have used a Monte Carlo simulator where all the major features involved in the description of the transport of state-of-the-art SOI devices are taken into account: quantization, non-parabolic band structure, phonon and surface roughness scattering. It has been shown that the behaviour of stationary electron velocity curves versus the longitudinal electric field is different to what we found in standard bulk devices. Particularly, it is very interesting that different saturation velocity values show up in the simulations. We found different curves corresponding to different effective fields when both phonon and surface roughness scattering mechanisms are taken into consideration. In addition, it was observed that the electron velocity obtained was dependent on the silicon layer thickness even when the same effective field was taken into account. Clear dependence of the saturation velocity has also been depicted in the delta parameter (representing the abrupt variations of the oxide-semiconductor surface) used in the surface roughness scattering model. Finally, we have performed simulations on double gate (DG) MOSFETs and observed different saturation velocities when we change the thickness of the intrinsic silicon slab.
Journal of Computational Electronics, 2009
The Monte Carlo simulation method is used to analyze the behavior of electron and hole mobility i... more The Monte Carlo simulation method is used to analyze the behavior of electron and hole mobility in different nanoelectronic devices including double gate transistors and FinFETs. The impact of technological parameters on carrier mobility is broadly discussed, and its behavior physically explained. Our main goal is to show how mobility in multiple gate devices compares to that in single gate
2012 IEEE International Symposium on Circuits and Systems, 2012
ABSTRACT
2013 European Conference on Circuit Theory and Design (ECCTD), 2013
ABSTRACT With CMOS image sensors scaling down due to the resolution and miniaturization demands, ... more ABSTRACT With CMOS image sensors scaling down due to the resolution and miniaturization demands, compact models for these devices become essential. A physically based model can be used to optimize the device performance and allow circuit designers to use these sensors in integrated circuits. Among other capacities, this analytical model can be used to predict with high accuracy the best photodiode geometry to achieve the maximum photoresponse while optimizing the total layout area cost.
Applied Physics Letters
We show by Monte Carlo simulation that electron mobility is greater when strained-silicon inversi... more We show by Monte Carlo simulation that electron mobility is greater when strained-silicon inversion layers are grown on SiGe-on-insulator substrates than when unstrained-silicon-on-insulator devices are employed ͑as experimentally observed͒. However, the electron mobility in strained-Si/SiGe-on-insulator inversion layers is strongly dependent on the strained-silicon layer thickness, T Si , due to an increase of the phonon scattering, which partially counteracts the increase in the mobility achieved by the strain. This effect is less important as the germanium mole fraction, x, is reduced, and as the value of T Si increases.
Journal of Socio-Economics
Electron transport properties of strained-Si on relaxed Si1-xGex channel MOSFETs have been studie... more Electron transport properties of strained-Si on relaxed Si1-xGex channel MOSFETs have been studied using a Monte Carlo simulator. The steady- and non-steady-state high-longitudinal field transport regimes have been described in detail. Electron-velocity-overshoot effects are also studied in deep-submicron strained-Si MOSFETs, where they show an improvement over the performance of their normal silicon counterparts.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
ABSTRACT
Se presentan las características de un nuevo simulador didáctico de circuitos electrónicos multip... more Se presentan las características de un nuevo simulador didáctico de circuitos electrónicos multiplataforma, con interfaz gráfica avanzada GTK+, denominado ESPICE. El simulador basado en SPICE tiene nuevas funcionalidades que posibilitan el acceso a los datos internos de la simulación; el análisis e interpretación del fichero de simulación, las matrices de tensiones y corrientes en cada iteración; la inclusión de nuevas funciones de procesado de datos, tipos de análisis, modelos de dispositivos y obtención del ejecutable mediante la compilación en Windows y Linux previa descarga del código fuente del repositorio público. Así mismo, se presenta un conjunto de recursos multimedia que acompañan al simulador.
Radioengineering, 2015
We have measured the transition process from the high to low resistivity states, i.e., the reset ... more We have measured the transition process from the high to low resistivity states, i.e., the reset process of resistive switching based memristors based on Ni/HfO 2 /Si-n+ structures, and have also developed an analytical model for their electrical characteristics. When the characteristic curves are plotted in the current-voltage (I-V) domain a high variability is observed. In spite of that, when the same curves are plotted in the charge-flux domain (Q-), they can be described by a simple model containing only three parameters: the charge (Q rst ) and the flux ( rst ) at the reset point, and an exponent, n, relating the charge and the flux before the reset transition. The three parameters can be easily extracted from the Q- plots. There is a strong correlation between these three parameters, the origin of which is still under study.
Solid-State Electronics, 2015
The scaling of MOSFET transistors makes the use of new device geometries, such as multigate FETs,... more The scaling of MOSFET transistors makes the use of new device geometries, such as multigate FETs, a need to solve the limitations of the conventional bulk technology. In this context we introduce an analytical model for square Gate All Around (GAA) MOSFETs with rounded corners including quantum effects. The modeling of rounded corners in GAA and FinFET devices is imperative because there are no perfectly square corners in the cross-section of real devices. In this model the 2D inversion charge distribution function (ICDF) is described analytically for devices of different sizes and for different operation regimes. The model reproduces accurately simulated data obtained with a state-of-the-art simulator that solves self-consistently the Poisson and Schrödinger equations in the devices under consideration. The analytical ICDF is used to better understand the device physics and to calculate the inversion charge centroid and the gate-to-channel capacitance for different device geometries and biases for modeling purposes.
Solid-State Electronics, 2015
ABSTRACT Reset transitions in HfO2 based RRAMs operated at different temperatures have been studi... more ABSTRACT Reset transitions in HfO2 based RRAMs operated at different temperatures have been studied. Ni/HfO2/Si-n+ devices were fabricated and measured at temperatures ranging from 233 K to 473 K to characterize their reset features. In addition, a simulator including several coupled conductive filaments, series resistance and quantum effects was employed to analyze the same devices. The experimental results were correctly reproduced. It was found that the reset voltage and current show slight temperature dependence. To explain this fact, the roles of the out-diffusion of metallic species from the conductive filament and its conductance temperature dependence have been studied by simulation. The different conductive filament resistance components are also analyzed in the temperature range employed in our study. Finally, the thermal change in the energy barrier linked to quantum effects in the transport properties in the filament is modeled.
Microelectronics Journal, 2015
ABSTRACT DC thermal effects modelling for nanometric silicon-on-insulator (SOI) and bulk fin-shap... more ABSTRACT DC thermal effects modelling for nanometric silicon-on-insulator (SOI) and bulk fin-shaped field-effect transistors (FinFETs) is presented. Among other features, the model incorporates self-heating effects (SHEs), velocity saturation and short-channel effects. SHEs are analysed in depth by means of thermal resistances, which are determined through an equivalent thermal circuit, accounting for the degraded thermal conductivity of the ultrathin films within the device. Once the thermal resistance for single-fin devices has been validated for different gate lengths and biases, comparing the modelled output characteristics and device temperatures with numerical simulations obtained using Sentaurus Device, the thermal model is extended by circuital analysis to multi-fin devices with multiple fingers.
The transport properties of very thin double gate SOI MOSFETs, have been studied. W e have shown ... more The transport properties of very thin double gate SOI MOSFETs, have been studied. W e have shown the importance of volume inversion, which greatly reduces the dependence of the electron mobility on the surface scattering mechanisms, and enhances the mobility at high inversion charge concentrations. W e have also shown that if the silicon film is extremely thin, electron mobility abruptly decreases due to stronger phonon scattering.
This paper shows the relevance of mobility models to describe the carrier dynamics for the analys... more This paper shows the relevance of mobility models to describe the carrier dynamics for the analysis of radiative semiconductor photoconductive devices in the terahertz regime. We have built a simulator that self-consistently solves the device physics and Maxwell's equations to study the radiated fields. In particular, we show a significant influence of an accurate description of the steady-state regime of the semiconductor device for calculating radiated electromagnetic fields in the broadside direction. Comparison with measurements shows the accuracy of our simulator and demonstrates the superior performance of numerical schemes based not only on the description of the carrier, electric potential, and field distributions, but also on reliable local mobility models.
Journal of Computational Electronics, 2006
... L. Donetti ( ) · F. Gámiz · JB Roldán · A. Godoy Departamento de Electrónica y Tecnologıa de ... more ... L. Donetti ( ) · F. Gámiz · JB Roldán · A. Godoy Departamento de Electrónica y Tecnologıa de Computadores, Universidad de Granada, 18071 Granada ... TIC2001-3243 supported by the Spanish Government, and by EU (Network of Excellence SINANO, IST-1-506844-NoE). ...
Physics Letters a, 2014
We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an ... more We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an effective Hamiltonian, we have investigated the autocorrelation function and the density currents in this material. Moreover, we have analyzed other types of periodicities of the system (classical and revival times). Finally, the above results are compared with their counterparts in two other monolayer materials subject to a magnetic field: graphene and MoS 2
Journal of Applied Physics, 2014
ABSTRACT An in-depth study of reset processes in RRAMs (Resistive Random Access Memories) based o... more ABSTRACT An in-depth study of reset processes in RRAMs (Resistive Random Access Memories) based on Ni/HfO2/Si-n+ structures has been performed. To do so, we have developed a physically based simulator where both ohmic and tunneling based conduction regimes are considered along with the thermal description of the devices. The devices under study have been successfully fabricated and measured. The experimental data are correctly reproduced with the simulator for devices with a single conductive filament as well as for devices including several conductive filaments. The contribution of each conduction regime has been explained as well as the operation regimes where these ohmic and tunneling conduction processes dominate.
Page 1. Double Gate Silicon-on-Insulator transistors: + + n+-n+ gate versus n -p gate configurati... more Page 1. Double Gate Silicon-on-Insulator transistors: + + n+-n+ gate versus n -p gate configuration. F.Gamiz, JBRoldan, A.Godoy and F.Jimenez-Molinos ... TIC2001-3243 supported by the Spanish Government, and by EU (Network of Excellence SINANO, IST-1-506844-NoE). ...
Essderc 2003: Proceedings of the 33rd European Solid-State Device Research Conference, 2003
A model to study the effect of the roughness at the poly-Si/SiO 2 interface in silicon inversion ... more A model to study the effect of the roughness at the poly-Si/SiO 2 interface in silicon inversion layers on the electron mobility is obtained. Screening of the resulting perturbation potential by the channel carriers is taken into account, considering Green's functions for Metal-Oxide-Semiconductor (MOS) geometry, i.e. taking into account the finite thickness of the gate oxide. Mobility of electrons is evaluated at room temperature by the Monte Carlo method, taking into account the simultaneous contribution of phonon scattering, SiO 2 /Si interface roughness scattering, Coulomb scattering and remote surface roughness scattering. The contribution of excited subbands is considered. The resulting remote surface roughness scattering is shown to be strongly dependent on the oxide thickness, and degrades mobility curves at low inversion charge concentrations. The results obtained show that the effect of this scattering mechanism cannot be ignored when the oxide thickness is below 5nm, (as in actual devices), even when (as is usual) very high doping concentrations are used.
Semiconductor Science and Technology, 2006
The high field transport regime of single gate (SG) SOI MOSFETs has been the subject of an in-dep... more The high field transport regime of single gate (SG) SOI MOSFETs has been the subject of an in-depth characterization. To study this, we have used a Monte Carlo simulator where all the major features involved in the description of the transport of state-of-the-art SOI devices are taken into account: quantization, non-parabolic band structure, phonon and surface roughness scattering. It has been shown that the behaviour of stationary electron velocity curves versus the longitudinal electric field is different to what we found in standard bulk devices. Particularly, it is very interesting that different saturation velocity values show up in the simulations. We found different curves corresponding to different effective fields when both phonon and surface roughness scattering mechanisms are taken into consideration. In addition, it was observed that the electron velocity obtained was dependent on the silicon layer thickness even when the same effective field was taken into account. Clear dependence of the saturation velocity has also been depicted in the delta parameter (representing the abrupt variations of the oxide-semiconductor surface) used in the surface roughness scattering model. Finally, we have performed simulations on double gate (DG) MOSFETs and observed different saturation velocities when we change the thickness of the intrinsic silicon slab.
Journal of Computational Electronics, 2009
The Monte Carlo simulation method is used to analyze the behavior of electron and hole mobility i... more The Monte Carlo simulation method is used to analyze the behavior of electron and hole mobility in different nanoelectronic devices including double gate transistors and FinFETs. The impact of technological parameters on carrier mobility is broadly discussed, and its behavior physically explained. Our main goal is to show how mobility in multiple gate devices compares to that in single gate
2012 IEEE International Symposium on Circuits and Systems, 2012
ABSTRACT
2013 European Conference on Circuit Theory and Design (ECCTD), 2013
ABSTRACT With CMOS image sensors scaling down due to the resolution and miniaturization demands, ... more ABSTRACT With CMOS image sensors scaling down due to the resolution and miniaturization demands, compact models for these devices become essential. A physically based model can be used to optimize the device performance and allow circuit designers to use these sensors in integrated circuits. Among other capacities, this analytical model can be used to predict with high accuracy the best photodiode geometry to achieve the maximum photoresponse while optimizing the total layout area cost.