http://eia.udg.es/%7Eqsalvi/papers/2006-MJ.pdf

Review of CMOS image sensors

This paper presents a new physics-based statistical model for random telegraph noise in Flash memories. From the probabilistic superposition of elementary Markov processes describing the trapping/detrapping events taking place in the cell tunnel oxide, the model can explain the main features of the random telegraph noise threshold-voltage instability. The results on the statistical distribution of the threshold-voltage difference between two subsequent read accesses show good agreement between measurements and model predictions, even considering the time drift of the distribution tails. Moreover, the model gives a detailed spectroscopic analysis of the oxide defects responsible for the random telegraph noise, allowing a spatial and energetic localization of the traps involved in the threshold-voltage instability process.

Statistical Model for Random Telegraph Noise in Flash Memories

Photosensitive devices and associated methods are provided. In one aspect, for example, a photosensitive imager device can include a semiconductor substrate having multiple doped regions forming at least one junction, a textured region coupled to the semiconductor substrate and positioned to interact with electromagnetic radiation, and an electrical transfer element coupled to the semiconductor substrate and operable to transfer an electrical signal from the at least one junction. In one aspect, the textured region is operable to facilitate generation of an electrical signal from the detection of infrared electromagnetic radiation. In another aspect, interacting with electromagnetic radiation further includes increasing the semiconductor substrate's effective absorption wavelength as compared to a semiconductor substrate lacking a textured region.

Photosensitive imaging devices and associated methods

In one aspect, the present invention provides a silicon photodetector having a surface layer that is doped with sulfur inclusions with an average concentration in a range of about 0.5 atom percent to about 1.5 atom percent. The surface layer forms a diode junction with an underlying portion of the substrate. A plurality of electrical contacts allow application of a reverse bias voltage to the junction in order to facilitate generation of an electrical signal, e.g., a photocurrent, in response to irradiation of the surface layer. The photodetector exhibits a responsivity greater than about 1 A/W for incident wavelengths in a range of about 250 nm to about 1050 nm, and a responsivity greater than about 0.1 A/W for longer wavelengths, e.g., up to about 3.5 microns.

Silicon-based visible and near-infrared optoelectric devices

The present invention generally provides semiconductor substrates having submicron-sized surface features generated by irradiating the surface with ultra short laser pulses. In one aspect, a method of processing a semiconductor substrate is disclosed that includes placing at least a portion of a surface of the substrate in contact with a fluid, and exposing that surface portion to one or more femtosecond pulses so as to modify the topography of that portion. The modification can include, e.g., generating a plurality of submicron-sized spikes in an upper layer of the surface.

Femtosecond Laser-Induced Formation Of Submicrometer Spikes On A Semiconductor Substrate

In this work, the 1/f noise of the Source Follower (SF) in pinned-photodiode CMOS pixels is characterized. It is found that the 1/f noise in these pixels is actually due to a very limited number of traps and results in a Random Telegraph Signal (RTS). It is pointed out how the correlated-double sampling (CDS) reacts on this RTS. The temperature dependency of the imager read noise revealed two mechanisms of RTS during CDS.

Random Telegraph Signal in CMOS Image Sensor Pixels

This paper presents a CMOS image sensor with a pinned-photodiode 4T active-pixel design (APS) that uses a buried-channel source follower (BSF) as the in-pixel amplifier. A prototype of the image sensor has been fabricated in a 0.18mum CMOS process. Measurements show that compared to a regular imager with a standard nMOS transistor surface-mode source follower (SSF), the new pixel structure reduces dark random noise by more than 50% and improves output swing by almost 100%.

A CMOS Image Sensor with a Buried-Channel Source Follower

In this work, radiation induced damage mechanisms in deep submicron technology is resolved using finger gated-diodes (FGDs) as a radiation sensitive tool. It is found that these structures are simple yet efficient structures to resolve radiation induced damage in advanced CMOS processes. The degradation of the CMOS image sensors in deep-submicron technology due to γ-ray irradiation is studied by developing a model for the spectral response of the sensor and also by the dark-signal degradation as a function of STI (shallow-trench isolation) parameters. It is found that threshold shifts in the gate-oxide/silicon interface as well as minority carrier life-time variations in the silicon bulk are minimal. The top-layer material properties and the photodiode Si–SiO 2 interface quality are degraded due to γ-ray irradiation. Results further suggest that p-well passivated structures are inevitable for radiation-hard designs. It was found that high electrical fields in submicron technologies pose a threat to high quality imaging in harsh environments.

/pdf/degradation-of-cmos-image-sensors-in-deep-submicron-4nblbh4zht.pdf

Degradation of CMOS image sensors in deep-submicron technology due to γ-irradiation

In this work, radiation induced damage mechanisms in deep submicron technology is resolved using finger gated-diodes (FGDs) as a radiation sensitive tool. It is found that these structures are simple yet efficient structures to resolve radiation induced damage in advanced CMOS processes. The degradation of the CMOS image sensors in deep-submicron technology due to γ-ray irradiation is studied by developing a model for the spectral response of the sensor and also by the dark-signal degradation as a function of STI (shallow-trench isolation) parameters. It is found that threshold shifts in the gate-oxide/silicon interface as well as minority carrier life-time variations in the silicon bulk are minimal. The top-layer material properties and the photodiode Si-SiO 2 interface quality are degraded due to γ-ray irradiation. Results further suggest that p-well passivated structures are inevitable for radiation-hard designs. It was found that high electrical fields in submicron technologies pose a threat to high quality imaging in harsh environments.

In this paper, we present the characterization and analysis of fixed-pattern noise (FPN) in CMOS Image Sensor (CIS) pixels fabricated in CMOS 0.18-?m process. The experimental results demonstrate that the dark signal degradation of pinned 4T CIS is mainly due to the dark current generated from the transmission gate (TG) instead of the photodiode (PD). From our investigations of gate voltage / charge transfer time ? dark current characterization and temperature dependencies, we found that hot-carrier (H-C) induced impact ionization and trap-induced leakage current are the main mechanism of sensor performance degradation.

/pdf/fixed-pattern-noise-induced-by-transmission-gate-in-pinned-ppvdtoxl8p.pdf

Padmakumar Ramachandra Rao

Papers

Random Telegraph Signal in CMOS Image Sensor Pixels

A CMOS Image Sensor with a Buried-Channel Source Follower

Degradation of CMOS image sensors in deep-submicron technology due to γ-irradiation

Degradation of CMOS image sensors in deep-submicron technology due to γ-irradiation

Fixed-Pattern Noise Induced by Transmission Gate in Pinned 4T CMOS Image Sensor Pixels