Capteur photographique | EPFL Graph Search

Un capteur photographique est un composant électronique photosensible servant à convertir un rayonnement électromagnétique (UV, visible ou IR) en un signal électrique analogique. Ce signal est ensuite amplifié, puis numérisé par un convertisseur analogique-numérique et enfin traité pour obtenir une . Le capteur est donc le composant de base des appareils photo et des caméras numériques, l'équivalent du film (ou pellicule) en photographie argentique. Le capteur photographique met à profit l'effet photoélectrique, qui permet aux photons incidents d'arracher des électrons à chaque élément actif (photosite) d'une matrice de capteurs élémentaires constitués de photodiodes ou photomos. Il est nettement plus efficace que la pellicule : jusqu'à 99 % (en théorie) et près de 50 % (en pratique) des photons reçus permettent de collecter un électron, contre environ 5 % de photons qui révèlent le grain photosensible de la pellicule, d'où son essor initial en astrophotographie. Deux grandes fami

Ultra Low Noise CMOS Image Sensors

Assim Boukhayma

CMOS Image Sensors (CIS) overtook the charge coupled devices (CCDs) in low noise performance. Photoelectron counting capability is the next step for CIS for ultimate low light performance and new imaging paradigms. This work presents a review of CMOS image sensors based on pinned photo diodes (PPDs). The latter includes the historical background, the PPD physics and the readout chain circuits used for low-noise performance. The physical mechanisms behind the random fluctuations affecting the signal at different levels of conventional CIS readout chains are reviewed and clarified. This thesis dedicates a particular focus to the readout circuit noise given that it precludes photoelectron counting in conventional CIS. A detailed analytical calculation of the temporal read noise (TRN) in conventional CIS readout chain is presented. The latter suggests different noise reduction techniques at process and circuit design level. Among the noise reduction techniques suggested by the analytical noise calculation, the increase of the oxide capacitance by using a thin oxide in-pixel amplifying transistor, for low 1/f noise, is suggested for the first time. A test chip designed in a 180 nm CIS process and embedding optimized readout chains exploiting the new pixels together with state-of-the-art 4T pixels optimized at process level for low 1/f noise. A mean input-referred noise of 0.4 e-rms has been measured. Compared with the state-of-the-art pixels, also present onto the test chip, the mean RMS noise is divided by more than 2. Based on these encouraging result, a full VGA (640H×480V) imager has been integrated in a standard CIS process. The presented imager relies on a 4T pixel of 6.5 µm pitch with a properly sized and biased thin oxide PMOS source follower. A full characterization of the proposed image sensor, at room temperature, is presented. The sensor chip features an input-referred noise histogram from 0.25 e-rms to a few e-rms peaking at 0.48 e-rms. This sub-0.5 electron noise performance is obtained with a full well capacity of 6400 e- and a frame rate that can go up to 80 fps. The VGA imager also features a fixed pattern noise as low as 0.77%, a lag of 0.1% and a dark current of 5.6 e-/s. Correlated multiple sampling (CMS) is a noise reduction technique commonly used in low noise CIS. This work presents an original design for CMS based on a passive switched-capacitor network, with a minimum number of capacitors. The proposed circuit requires no additional active circuitry, has no impact on the output dynamic range and does not need multiple analog-to-digital conversions. It was verified with transient noise simulations and shows a noise reduction in perfect agreement with ideal CMS. For a future perspective, the impact of the technology downscale on CIS sensitivity from an electronic read noise aspect is investigated. Active imaging in the Terahertz (THz) band is an emerging technology. Source modulation combined with a selective filtering can be used to reduce the noise in CMOS THz imagers. This work presents the first integration of a 1 kpixel CMOS THz imager integrating, in each pixel, a metal antenna with a MOS rectifier, low noise amplification and highly selective filtering, based on a switch-capacitor N-path filter combined with a broad band Gm-C filter. The latter has been tested successfully. An input-referred noise of 0.2 µV RMS corresponding to a total noise equivalent THz power of 0.6 nW at 270 GHz and 0.8 nW at 600 GHz.

EPFL2016

Multispectral image sensor and method for fabrication of an image sensor

Assim Boukhayma

The present invention relates to a multispectral image sensor having a pixel array for detecting images with light components in different wavelength ranges, comprising a plurality of imaging layers each embedded in a semiconductor substrate, wherein in each of the imaging layers an array of photodetecting regions is provided, wherein the photodetecting regions are configured with different absorption characteristics, wherein the imaging layers are stacked so that the photodetecting regions of the arrays are aligned, wherein the absorption characteristics allow a preferred absorption of light components of at least one predetermined wavelength range.

2020

Ultra Low Noise CMOS Image Sensors

Assim Boukhayma

EPFL2016