Zohir Dibi

Analytical analysis of nanoscale multiple gate MOSFETs including effects of hot-carrier induced interface charges

As the channel length rapidly shrinks down to the nanoscale regime, the multiple gate MOSFETs structures have been considered as potential candidates for a CMOS device scaling due to its good short-channel-effects (SCEs) immunity. Therefore, in this work we investigate the scaling capability of Double Gate (DG) and Gate All Around (GAA) MOSFETs using an analytical analysis of the two dimensional Poisson equation in which the hot-carrier induced interface charge effects have been considered. Basing on this analysis, we have found that the degradation becomes more important when the channel length gets shorter, and the minimum surface potential position is affected by the hot-carrier induced localized interface charge density. Using this analysis, we have studied the scaling limits of DG and GAA MOSFETs and compared their performances including the hot-carrier effects. Our obtained results showed that the analytical analysis is in close agreement with the 2-D numerical simulation over a wide range of devices parameters. The proposed analytical approach may provide a theoretical basis and physical insights for multiple gate MOSFETs design including the hot-carrier degradation effects.

A Novel Neural Network-Based Technique for Smart Gas Sensors Operating in a Dynamic Environment

Thanks to their high sensitivity and low-cost, metal oxide gas sensors (MOX) are widely used in gas detection, although they present well-known problems (lack of selectivity and environmental effects…). We present in this paper a novel neural network- based technique to remedy these problems. The idea is to create intelligent models; the first one, called corrector, can automatically linearize a sensors response characteristics and eliminate its dependency on the environmental parameters. The correctors responses are processed with the second intelligent model which has the role of discriminating exactly the detected gas (nature and concentration). The gas sensors used are industrial resistive kind (TGS8xx, by Figaro Engineering). The MATLAB environment is used during the design phase and optimization. The sensor models, the corrector, and the selective model were implemented and tested in the PSPICE simulator. The sensor model accurately expresses the nonlinear character of the response and the dependence on temperature and relative humidity in addition to their gas nature dependency. The corrector linearizes and compensates the sensors responses. The method discriminates qualitatively and quantitatively between seven gases. The advantage of the method is that it uses a small representative database so we can easily implement the model in an electrical simulator. This method can be extended to other sensors.

Characterisation and modelling of the mismatch of TCRs and their effects on the drift of the offset voltage of piezoresistive pressure sensors

Abstract Based on the assumption that each piezoresistor of a silicon pressure sensor has its own temperature coefficients (TCRs of the first and second order), a theoretical model has been developed in order to study the thermal behaviour of the offset voltage. We first derive the expression for the drift of the output voltage of each potentiometric circuit obtained from the whole bridge, and then that for the thermal variations of the offset voltage itself. It is shown that the existence of a small difference between the temperature coefficients of the four piezoresistors can provoke thermal variations of the output voltages whose shapes can obey to a linear or a parabolic law. On the other hand, we have used an experimental procedure, on our test pressure sensors, allowing us to extract the piezoresistors TCRs, to measure the thermal drifts of the output voltage of each half-bridge, and those of the whole bridge. The application of the theoretical model shows that there exists a good accordance with the experimental results. The parabolic shapes of the outputs of the two half-bridges, and also that of the offset voltage, are explained by the mismatch of the TCRs of the four piezoresistors.

Depth Resolution Enhancement Technique for CMOS Time-of-Flight 3-D Image Sensors

Introducing Time-of-Flight 3-D image sensors to actual engineering applications, such as pattern recognition, is constrained not only by their limited depth and lateral resolution, but also by how similar the precision of depth measurement throughout the whole pixel-matrix is. In real operating environment, an observed 3-D-scene hardly exhibits a homogeneous reflectance factor. Moreover, the light-beam (laser source) presents a nonuniform optical power distribution in space. Thus, the amount of the incident light on the sensor surface varies drastically from one pixel to another, and so does the signal-to-noise ratio. To address this problem, this paper investigates the impact of both scene and light-source non-ideal characteristics on the sensor performance. An adaptive on-pixel analog signal processing technique is also presented and applied to the design of a 32 × 32 complementary metal oxide semiconductor (CMOS) range camera, featuring an interesting cost-efficient solution.

On the Capability of Artificial Neural Networks to Compensate Nonlinearities in Wavelength Sensing

An intelligent sensor for light wavelength readout, suitable for visible range optical applications, has been developed. Using buried triple photo-junction as basic pixel sensing element in combination with artificial neural network (ANN), the wavelength readout with a full-scale error of less than 1.5% over the range of 400 to 780 nm can be achieved. Through this work, the applicability of the ANN approach in optical sensing is investigated and compared with conventional methods, and a good compromise between accuracy and the possibility for on-chip implementation was thus found. Indeed, this technique can serve different purposes and may replace conventional methods.

A Masking Model of HVS for Image Watermaking in the DCT Domain

A substantial amount of work has been devoted to understanding the human visual system (HVS) and applying this knowledge to image processing applications. In this paper, we present a novel watermarking approach for applications in copy protection and digital archives based on perceptual masking. In the proposed scheme, local properties of the image and the features of the human visual system in discrete cosine transform (DCT) domain are taken into consideration in order to optimize the watermark strength. Based on NVF (noise visibility function) of the cover image, the mask is of the same size, and we incorporate the luminance masking effect of the HVS in the masking image, since the human eye is less sensitive to change in regions with high brightness as well as in very dark regions compared to mid-grey regions, where the distortion is most noticeable. Experimental results demonstrate that the new embedding rule enhances the quality of the watermarked images both subjectively and objectively. A comparison is made between the results of our proposed algorithm with that use only the textured area to demonstrate the superior performance of our new algorithm, while not degrading the watermark detection performance.

A Two‐Dimensional Numerical Analysis of Subthreshold Performances for Double‐Gate GaN‐MESFETs

In this paper, a new deep submicron double‐gate (DG) GaN‐MESFET structure and its 2‐D numerical model have been proposed, investigated and expected to suppress the short‐ channel‐effects (SCEs) and improve the subthreshold behavior for deep submicron GaN‐MESFET‐based applications. The models have been used to predict and compare the performances of downscaled DG and conventional GaN‐MESFETs, where the comparison of device architectures shows that the proposed DG GaN‐Based MESFET exhibits a superior performance with respect to the conventional MESFET both in terms of threshold voltage and DIBL (Drain Induced Barrier Lowering) effect in deep submicron domain. The obtained results make (DG) GaN‐MESFET a promising candidate for future MESFET‐based circuits.

Combined effect of the membrane flatness defect and real dimension gauges on the sensitivity of a silicon piezoresistive pressure sensor

Presents a new approach to the sensitivity loss of a silicon piezoresistive pressure sensor. The loss origin is due to the parallelism defect of the two sides of the membrane cumulated to the real dimensions of the gauges, considered usually as being as points. The work we present deals with the modelling of a structure, realised by micro-electronic techniques and chemical etching, containing four piezoresistors of the P type connected in Wheatstone bridge. We modelled, firstly, the parallelism defects of a square membrane, secondly the effects of real dimension gauges according to their positions on the membrane. Then we examined their combined effects on the sensitivity of the sensor. The lack of flatness collected experimentally for a 30 /spl mu/m membrane thickness is less than 1%, however, it gives rises to an over-estimation of sensitivity of about 1.5%. If only the real dimensions of the gauges are considered an over-estimation of the sensitivity of approximately 10% is made for a 100 /spl mu/m gauge length.

Effect of the silicon membrane flatness defect on the piezoresistive pressure sensor response

In this paper, we present a new approach of the sensitivity loss of a silicon piezoresistive pressure sensor. This loss of sensitivity is due to the lack of parallelism of the two membrane sides. An experimental topographical result of bottom membrane realised in LAAS, is simulated to quantify the effects on the gauges electrical responses and on the sensor sensitivity. A bridge of four piezoresistors forms our sensor. A flatness defect less than 1% obtained experimentally on 30 /spl mu/m membrane has lead to an electrical response loss around 3% of each gauges while the full bridge give 1.5% loss of sensitivity as a result of the simulation. These values increase significantly as the membrane thickness decreases. The irregularity of the surface could be an important source of information about the voltage offset.

Halftone image watermarking based on visual cryptography

The advancement of digital image emphasizes the need for copyright protection. Digital watermarking is one of the most popular techniques and a very active research area for copyright protection of documents and media. In this paper, we propose a watermark technique for halftone image based on visual cryptography technique. The proposed method is simple and efficient. We introduce error diffusion techniques for halftoning; three most known filters of error were used: Floyd and Steinberg, Jarvis and Judice and Ninke and Stucki methods. The system security is guaranteed by using a visual cryptography approach to generate two random shares of a watermark; public watermark and secret watermark.