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Dive into the research topics where Jérôme Vaillant is active.

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Featured researches published by Jérôme Vaillant.


Detectors and associated signal processing. Conference | 2004

Source follower noise limitations in CMOS active pixel sensors

Keith Findlater; Jérôme Vaillant; Donald Baxter; Christine Augier; Didier Hérault; Robert Henderson; Jed Hurwitz; Lindsay A. Grant; Jean-Marc Volle

CMOS imagers are commonly employing pinned photodiode pixels and true correlated double sampling to eliminate kTC noise and achieve low noise performance. Low noise performance also depends on optimisation of the readout circuitry. This paper investigates the effect of the pixel source follower transistor on the overall noise performance through several characterization methods. The characterization methods are described, and experimental results are detailed. It is shown that the source follower noise can be the limiting factor of the image sensor and requires optimisation.


Optics Express | 2007

Uniform illumination and rigorous electromagnetic simulations applied to CMOS image sensors.

Jérôme Vaillant; Axel Crocherie; Flavien Hirigoyen; Adam Cadien; James Pond

This paper describes a new methodology we have developed for the optical simulation of CMOS image sensors. Finite Difference Time Domain (FDTD) software is used to simulate light propagation and diffraction effects throughout the stack of dielectrics layers. With the use of an incoherent summation of plane wave sources and Bloch Periodic Boundary Conditions, this new methodology allows not only the rigorous simulation of a diffuse-like source which reproduces real conditions, but also an important gain of simulation efficiency for 2D or 3D electromagnetic simulations. This paper presents a theoretical demonstration of the methodology as well as simulation results with FDTD software from Lumerical Solutions.


Photonics Europe | 2004

Optical simulation for CMOS imager microlens optimization

Jérôme Vaillant; Flavien Hirigoyen

This paper describes a new methodology we have developed for microlens optimization for CMOS image sensors in order to achieve good optical performances. On one hand, the real pixel is simulated in an optical simulation software and on the other hand simulation results are post-processed with a numerical software. In a first part, we describe our methodology. We start from the pixel layout description from standard micro-electronic CAD software and we generate a three-dimensional model on an optical ray tracing software. This optical model aims to be as realistic as possible taking into account the geometrical shape of all the components of the pixel and the optical properties of the materials. A specific ray source has also been developed to simulate the pixel illumination in real conditions (behind an objective lens). After the optical simulation itself, the results are transferred to another software for more convenient post-processing where we use as photosensitive area a weighted surface determined from the fit of angular response simulation results to the measurements. Using this surface we count the ray density inside the substrate to evaluate the simulated output signal of the sensor. Then we give some results obtained with that simulation process. At first, the optimization of the microlens parameters for different pixel pitches (from 5.6um to 4um). We also have studied the polarization effects inside the pixel. Finally, we compare the measured and the simulated vignetting of the sensor, demonstrating the relevance of our optical simulation process and allowing us to study solutions for a pixel pitch of 3μm and less.


electronic imaging | 2008

FDTD-based optical simulations methodology for CMOS image sensor pixels architecture and process optimization

Flavien Hirigoyen; Axel Crocherie; Jérôme Vaillant; Yvon Cazaux

This paper presents a new FDTD-based optical simulation model dedicated to describe the optical performances of CMOS image sensors taking into account diffraction effects. Following market trend and industrialization constraints, CMOS image sensors must be easily embedded into even smaller packages, which are now equipped with auto-focus and short-term coming zoom system. Due to miniaturization, the ray-tracing models used to evaluate pixels optical performances are not accurate anymore to describe the light propagation inside the sensor, because of diffraction effects. Thus we adopt a more fundamental description to take into account these diffraction effects: we chose to use Maxwell-Boltzmann based modeling to compute the propagation of light, and to use a software with an FDTD-based (Finite Difference Time Domain) engine to solve this propagation. We present in this article the complete methodology of this modeling: on one hand incoherent plane waves are propagated to approximate a product-use diffuse-like source, on the other hand we use periodic conditions to limit the size of the simulated model and both memory and computation time. After having presented the correlation of the model with measurements we will illustrate its use in the case of the optimization of a 1.75&mgr;m pixel.


Proceedings of SPIE, the International Society for Optical Engineering | 2008

Three-dimensional broadband FDTD optical simulations of CMOS image sensor

Axel Crocherie; Jérôme Vaillant; Flavien Hirigoyen

In this paper, we present the results of rigorous electromagnetic broadband simulations applied to CMOS image sensors as well as experimental measurements. We firstly compare the results of 1D, 2D, and 3D broadband simulations in the visible range (380nm-720nm) of a 1.75μm CMOS image sensor, emphasizing the limitations of 1D and 2D simulations and the need of 3D modeling, particularly to rigorously simulate parameters like Quantum Efficiency. Then we illustrate broadband simulations by two proposed solutions that improve the spectral response of the sensor: an antireflective coating, and the reduction of the optical stack. We finally show that results from experimental measurements are in agreement with the simulated results.


electronic imaging | 2008

Versatile method for optical performances characterization of off-axis CMOS pixels with microlens radial shift

Jérôme Vaillant; Thomas Decroux; Emilie Huss; Frédéric Barbier; Didier Hérault; Flavien Hirigoyen; Nicolas Virollet

In this paper, we present a versatile characterization method we developed at STMicroelectronics for off-axis pixels (i.e. over the image plane) on CMOS image sensor. The solution does not require optics, making it suitable for early design phases as for optimizations and investigations. It is based on a specific design of color filters and microlens masks, which consists in several blocks. Inside each block, the filters and the microlens are shifted by a given amount, relatively to the pixel. Each block is related to a given chief ray and then defines a point in the chief ray angle space. Then, the performances of these angular points can be measured by rotating the sensor, using conventional uniform illumination setup with controlled f-number. Then it is possible to map these data on the image plane, knowing the chief ray angle versus focal plane coordinate function. Finally, we present some characterizations and optimizations based on the fact that the shift is arbitrary defined during circuit layout step, so it is possible to test the sensor with higher chief ray angles than those present in the product, or to optimize the shift of the microlens versus the chief ray angle for a given pixel architecture.


Proceedings of SPIE | 2010

Evaluation of color error and noise on simulated images

Clémence Mornet; Jérôme Vaillant; Thomas Decroux; Didier Hérault; Isabelle Schanen

The evaluation of CMOS sensors performance in terms of color accuracy and noise is a big challenge for camera phone manufacturers. On this paper, we present a tool developed with Matlab at STMicroelectronics which allows quality parameters to be evaluated on simulated images. These images are computed based on measured or predicted Quantum Efficiency (QE) curves and noise model. By setting the parameters of integration time and illumination, the tool optimizes the color correction matrix (CCM) and calculates the color error, color saturation and signal-to-noise ratio (SNR). After this color correction optimization step, a Graphics User Interface (GUI) has been designed to display a simulated image at a chosen illumination level, with all the characteristics of a real image taken by the sensor with the previous color correction. Simulated images can be a synthetic Macbeth ColorChecker, for which reflectance of each patch is known, or a multi-spectral image, described by the reflectance spectrum of each pixel or an image taken at high-light level. A validation of the results has been performed with ST under development sensors. Finally we present two applications one based on the trade-offs between color saturation and noise by optimizing the CCM and the other based on demosaicking SNR trade-offs.


Proceedings of SPIE | 2010

Finite-difference time domain based electro-optical methodologies to improve CMOS image sensor pixels performances

Flavien Hirigoyen; Axel Crocherie; Pierre Boulenc; Jérôme Vaillant; C. Tavernier; Didier Hérault

The current CMOS image sensors market trend leads to achieve good image resolution at small package size and price, thus CMOS image sensors roadmap is driven by pixel size reduction while maintaining good electro-optical performances. As both diffraction and electrical effects become of greater importance, it is mandatory to have a simulation tool able to early help process and design development of next generation pixels. We have previously introduced and developed FDTD-based optical simulations methodologies to describe diffraction phenomena. We recently achieved to couple them to an electrical simulation tool to take into account carrier diffusion and precise front-end process simulation. We propose in this paper to show the advances of this methodology. After having detailed the complete methodology, we present how we reconstruct the spectral quantum efficiency of a pixel. This methodology requires heavy-to-compute realistic 3D modeling for each wavelength: the material optical properties are described over the full spectral bandwidth by a multi-coefficient model, while the electrical properties are set by the given process and design. We optically simulate the propagation of a dozen of wavelengths at normal incidence and collect the distribution of the optical generation then we insert it in the electrical simulation tool and collect the final output quantum efficiency. Besides, we compare the off-axis performance evaluations of a pixel by simulating its relative illumination in a given wavelength. In this methodology several plane waves are propagated with different angles of incidence along a specific direction.


Proceedings of SPIE | 2011

An image quality evaluation tool simulating image sensors including quantum efficiency off-axis effect

Clémence Mornet; Jérôme Vaillant; Thomas Decroux; Nicolas Virollet; Didier Hérault; Isabelle Schanen

The image quality evaluation of CMOS sensors is a big challenge for camera module manufacturers. In this paper, we present an update of the Image Quality Evaluation Tool, a graphical user interface simulating image sensors to assess the performance of a pixel. The simulated images are computed from operating conditions and sensors characteristics like Quantum Efficiency including off-axis effect. Simulation of QE off-axis impact has been based on characterization data. The method does not require optics, making it suitable for early design phases as for optimizations and investigations. Both measurement and implementation in the tool will be explained. The QE degradation with angle effect will be highlighted on simulated images. A uniform gray scene or coloured image simulation from QE off-axis measurement will help engineers to calculate post-processing digital correction like colour shading correction or colour correction matrix versus pixel position.


Proceedings of SPIE | 2011

Characterization of pixel crosstalk and impact of Bayer patterning by quantum efficiency measurement

Jérôme Vaillant; Clémence Mornet; Thomas Decroux; Didier Hérault; Isabelle Schanen

Development of small pixels for high resolution image sensors implies a lot of challenges. A high level of performance should be guaranteed whereas the overall size must be reduced and so the degree of freedom in design and process. One key parameter of this constant improvement is the knowledge and the control of the crosstalk between pixels. In this paper, we present an advance in crosstalk characterization method based on the design of specific color patterns and the measurement of quantum efficiency. In a first part, we describe the color patterns designed to isolate one pixel or to simulate un-patterned colored pixels. These patterns have been implemented on test-chip and characterized. The second part deals with the characterization setup for quantum efficiency. Indeed, the use of spectral measurements allows us to discriminate pixels based on the color filter placed on top of them and to probe the crosstalk as a function of the depth in silicon, thanks to the photon absorption length variation with the wavelength. In the last part, results are presented showing the impact of color filters patterning, i.e. pixels in a Bayer pattern versus un-patterned pixels. The crosstalk directions and amplitudes are also analyzed in relation to pixel layout.

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