Paolo Ciampolini

A new discretization strategy of the semiconductor equations comprising momentum and energy balance

A discretization scheme is applied to the hydrodynamic model for semiconductor devices that generalizes the Scharfetter-Gummel method to both the momentum-conservation and the energy-conservation equations. The major advantages of the scheme are: (1) the discretization is carried out without neglecting any terms, thus providing a satisfactory description of such effects as velocity overshoot and carrier heating; and (2) the resulting equations lend themselves to a self-consistent solution procedure similar to those currently used to solve the simpler drift-diffusion equations. Two-dimensional steady-state simulations of an n-channel MOSFET and of an n-p-n BJT (bipolar junction transistor) have been carried out by means of an improved version of the program HFIELDS. Carrier-temperature plots have been obtained with a reasonable computational effort, demonstrating the efficiency of this technique. The results have been compared with those obtained with the standard drift-diffusion model and significant differences in the electron concentration have been found, especially at the drain end of the MOSFET channel. >

Numerical simulation of polycrystalline-Silicon MOSFET's

In this paper we investigate polycrystalline-silicon MOSFET operation by means of a two-dimensional device-analysis program developed at the University of Bologna. The grain-boundary model used in this study allows for both donor and acceptor states at the interface, and assumes a drift-diffusion transport mechanism, consistently with the general structure of the code. Results achieved thus far allow us to interpret the increased threshold voltage experimentally observed in polycrystalline-silicon MOSFETs and the device transconductance in strong inversion; on the other hand, the current increase occurring at negative gate voltages is not justified by the numerical model so far implemented. It is believed that field-enhanced emission rates and impact ionization are possible mechanims to interpret the above conduction increase.

Comprehensive modeling of bulk-damage effects in silicon radiation detectors

In this paper, the issue of numerical modeling of radiation-damaged silicon devices is discussed, with reference to radiation detectors employed in high-energy physics experiments. Since the actual physical picture is far too complex to be accounted for at a first-principle (i.e., defect kinetics) level and not yet fully understood, a hierarchical approach has been followed looking for a suitable approximation of macroscopic changes of the electrical behavior of silicon device induced by radiation damage. In particular, a three deep-level trapping mechanism is accounted for by means of Shockley-Read-Hall theory, whereas the shallow-level sensitivity on the radiation is considered by means of a donor-removal model.

Adaptive mesh generation preserving the quality of the initial grid

An algorithm allowing the automatic generation of a mesh and accounting for the main physical features of the problem is presented. The adaptivity is provided by a refinement strategy which preserves the characteristics of the initial grid, inserting nodes only in the regions where the solution deviates from a linear behavior. A geometrical interpretation in terms of a monitor surface is given, and various different approaches to the problem are discussed. The efficiency of the algorithm is enhanced by a local solution scheme, which uses previously computed values of all the unknown quantities as boundary conditions for the newly generated nodes. A few examples illustrate the performance of the algorithm. >

Food Image Recognition Using Very Deep Convolutional Networks

We evaluated the effectiveness in classifying food images of a deep-learning approach based on the specifications of Googles image recognition architecture Inception. The architecture is a deep convolutional neural network (DCNN) having a depth of 54 layers. In this study, we fine-tuned this architecture for classifying food images from three well-known food image datasets: ETH Food-101, UEC FOOD 100, and UEC FOOD 256. On these datasets we achieved, respectively, 88.28%, 81.45%, and 76.17% as top-1 accuracy and 96.88%, 97.27%, and 92.58% as top-5 accuracy. To the best of our knowledge, these results significantly improve the best published results obtained on the same datasets, while requiring less computation power, since the number of parameters and the computational complexity are much smaller than the competitors?. Because of this, even if it is still rather large, the deep network based on this architecture appears to be at least closer to the requirements for mobile systems.

Three-dimensional simulation of semiconductor devices: state of the art and prospects

Abstract In this paper we present a generalized model for electron transport in semiconductors accounting for three separate energy balance equations. Such a model generalizes the hydrodynamic and the electrothermal models, and comprises six partial differential equations, to be solved within the device domain with suitable boundary conditions. Next, we present simulation results obtained with a 3D code implementing a partial set of the above equations, which leads to a modified electrothermal model, and discuss the current status and future trends in multidimensional device simulation.

Sensitivity Analysis for Device Design

In this paper we propose a sensitivity-analysis technique for device design. By this method, we determine the linearized variations of the device terminal characteristics following some change either in the impurity distribution, or in device geometry, such as channel length and oxide thickness. This technique has been implemented in our general-purpose two-dimensional device-analysis program (HFIELDS) and proved to be very efficient, as only the assembly of the RHS and one back-substituton is required in order to achieve the final result. It is believed that the present method can be profitably used for both deterministic and statistical device design.

Numerical analysis of ISFET and LAPS devices

Abstract In this paper, a numerical simulation technique suitable for device-level analysis of ion-sensitive devices (ion-sensitive field-effect-transistor (ISFET) and light-addressable potentiometric sensor (LAPS)) is presented. Models of the charge layers which develop at the electrolyte–insulator interface of an electrolyte insulator-semiconductor (EIS) system are incorporated into the device equations, thus providing a self-consistent picture of charge and field distribution within the semiconductor domain. To accomplish the simulation of LAPS devices, an AC-modulated optical generation rate has been introduced as well. A TCAD tool, based on the proposed approach, has been developed, which allows for the electrical characterization and for the extraction of circuit-simulation parameters of ion-sensitive devices. Validation of the device-analysis technique comes from the comparison between predicted electrical responses and actual device measurements.

A BCI Platform Supporting AAL Applications

Brain Computer Interface (BCI) technology can provide users lacking voluntary muscle control with an augmentative communication channel, based on the interpretation of her/his brain activity. Such technologies, combined with AAL (Ambient Assisted Living) systems, can potentially have a great impact on daily living, extending the scope of the ageing at home paradigm also to individuals affected by severe motor impairments, for whom interacting with the environment is troublesome. In this paper, a low cost BCI development platform is presented; it consists of a customized EEG acquisition unit and a Matlab-based signal processing environment. An application example using SSVEP paradigm is discussed.

Modeling of light-addressable potentiometric sensors

In this paper, the extension of numerical simulation techniques to the analysis of light-addressable potentiometric sensors (LAPS) is discussed in detail. To this purpose, proper physical models of both the ion-sensitive and the photo-sensitive transduction mechanisms have been incorporated into the framework of a general-purpose device simulator. A self-consistent, accurate picture of charge transport within the device under the combined action of electrolyte ion layers and of luminous stimulus is recovered, which in turn allows for detailed analysis of the device behavior and for fine-tuning of the fabrication process. Extensive comparison with actual LAPS measurement has been performed, validating the tool and illustrating its flexibility and application range.