Sub-electron CIS noise analysis in 65 nm process

For a 4T pixel-based CMOS image sensors (CIS) readout chain, with column-level amplification and CDS, we show that the input-referred total noise in a standard 65 nm process can be reduced to 0.37 e-rms. Based on transient noise simulation using Eldo, the deep sub-electron noise performance have been reached using only circuit techniques and optimal device choices. The simulation results have been favorably compared with analytical noise calculations. The shot noise associated to the gate tunneling current has been simulated and the possibility of photoelectron counting in this 65 nm process has been demonstrated

Three-dimensional view of ultrafast dynamics in photoexcited bacteriorhodopsin

Bacteriorhodopsin (bR) is a light-driven proton pump. The primary photochemical event upon light absorption is isomerization of the retinal chromophore. Here we used time-resolved crystallography at an X-ray free-electron laser to follow the structural changes in multiphoton-excited bR from 250 femtoseconds to 10 picoseconds. Quantum chemistry and ultrafast spectroscopy were used to identify a sequential two-photon absorption process, leading to excitation of a tryptophan residue flanking the retinal chromophore, as a first manifestation of multiphoton effects. We resolve distinct stages in the structural dynamics of the all-trans retinal in photoexcited bR to a highly twisted 13-cis conformation. Other active site sub-picosecond rearrangements include correlated vibrational motions of the electronically excited retinal chromophore, the surrounding amino acids and water molecules as well as their hydrogen bonding network. These results show that this extended photo-active network forms an electronically and vibrationally coupled system in bR, and most likely in all retinal proteins

Radiation effects on CMOS image sensors with sub-2µm pinned photodiodes

A group of four commercial sensors with pixel pitches below 2μm has been irradiated with 60Co source at several total ionizing dose levels related to space applications. A phenomenological approach is proposed through behavior analysis of multiple sensors embedding different technological choices (pitch, isolation or buried oxide). A complete characterization including dark current, activation energy and temporal noise analysis allows to discuss about a degradation scheme

Probing Ultrafast Dynamics with Time-resolved Multi-dimensional Coincidence Imaging: Butadiene

Time-resolved coincidence imaging of photoelectrons and photoions represents the most complete experimental measurement of ultrafast excited state dynamics, a multi-dimensional measurement for a multi-dimensional problem. Here we present the experimental data from recent coincidence imaging experiments, undertaken with the aim of gaining insight into the complex ultrafast excited-state dynamics of 1,3-butadiene initiated by absorption of 200 nm light. We discuss photoion and photoelectron mappings of increasing dimensionality, and focus particularly on the time-resolved photoelectron angular distributions (TRPADs), expected to be a sensitive probe of the electronic evolution of the excited state and to provide significant information beyond the time-resolved photoelectron spectrum (TRPES). Complex temporal behaviour is observed in the TRPADs, revealing their sensitivity to the dynamics while also emphasising the difficulty of interpretation of these complex observables. From the experimental data some details of the wavepacket dynamics are discerned relatively directly, and we make some tentative comparisons with existing ab initio calculations in order to gain deeper insight into the experimental measurements; finally, we sketch out some considerations for taking this comparison further in order to bridge the gap between experiment and theory.Comment: 18 pages, 10 figures. Pre-print of JMO submissio

Radiation Effects on CMOS Image Sensors With Sub-2 µm Pinned Photodiodes

CMOS image sensor hardness under irradiation is a key parameter for application fields such as space or medical. In this paper, four commercial sensors featuring different technological characteristics (pitch, isolation or buried oxide) have been irradiated with 60Co source. Based on dark current and temporal noise analysis, we develop and propose a phenomenological model to explain pixel performance degradation

Modelling and characterization of small photosensors in advanced CMOS technologies

The rapid scaling of CMOS technologies and the development of optimized CIS (CMOS Image Sensor) processes for CMOS vision products has not been met by a similar effort in a comprehensive study of the main physical phenomena dominating the behavior of pixels at these technological nodes. This work provides a study of the behaviour of small photodetectors in advanced CMOS technologies in order to evaluate the impact of the geometry on the pixel photoresponse. Several models were developed paying special attention to the peripheral collection. The results suggest that the largest active area no longer necessarily guarantees the optimum response and show the significance of the lateral contribution for small photodiodes. That is, they establish the need to find a trade-off between the active area and the collecting area surrounding the junction to maximize the response. Based on the solution of the two-dimensional steady-state equation in the surroundings of the junction, an analytical model for uniformly illuminated p-n+ junction photodiodes was proposed. It is compact, general and scalable. In order to be used in Computer Aided Design (CAD) tools, the model was implemented in a Hardware Description Language (HDL) and used for circuit simulations to illustrate the potential of the model for the optimization of the pixel performance