CMOS Active Pixel Research Articles

Dark-current estimation method for CMOS APS sensors in mixed radiation environment

CMOS active pixel sensors (APS) suffer from serious dark-current degradation when they are exposed in radiation environment. Considering the general situation that there are multiple kinds of energetic particles in radiation environment, a dark-current estimation method for pixel sensors due to mixed radiation particles is proposed in this paper. Based on the radiation effects induced by particles of all kinds, the dark-current amplitudes distribution among the pixels can be predicted through probabilistic analysis. Validation is implemented upon the radiation dark-image data of CMOS APS devices, which shows that the predicted dark-current distribution matches very well with the experimental data, and the difference is no more than 15%.

Total-Ionization-Dose Radiation-Induced Noise Modeling and Analysis of a 2k <inline-formula> <tex-math notation="LaTeX">$\times$ </tex-math> </inline-formula> 2k 4T CMOS Active Pixel Sensor for Space Applications

This paper presents modeling techniques of total-ionization-dose (TID) radiation-induced noise characteristics including dark current (DC), fixed pattern noise (FPN), and equivalent noise charge (ENC) of a CMOS active pixel sensor (APS) for space applications. The noise models from theoretical derivation and experimental data analysis are discussed in detail according to the circuit structure of the CMOS APS based on 4-T transistor pixel topology followed by the column-level correlation double sampling and the column-level amplifier. From the simulation of the theoretical models, the amplitude of noise significantly increases with the increase of total dose, and a threshold dose of ~60 krad (Si) exists. When the total dose is below such threshold, DC, FPN, and ENC increase slowly. When the total dose exceeds the threshold value, these noise parameters increase substantially according to the exponential growth. To verify the proposed models, a $\gamma $ -ray radiation experiment using 60Co source is performed on a commercial 2k $\times \,\, 2\text{k}$ CMOS APS chip in 180-nm CMOS technology from Vendor A. The noise performance of two CMOS APS devices at the dose rates of 50 and 10.6 rad(Si)/s has been measured. It shows that experimental results are in accordance with the rules of theoretical deduction. The dose threshold of the abovementioned three noise parameters is around 60 krad (Si). The TID-induced noise models can be applied to both the design of radiation-hardened CMOS APS and the construction of filtering algorithms in the post image processing.

Simultaneous Imaging and Energy Harvesting in CMOS Image Sensor Pixels

We present a prototype CMOS active pixel that is capable of simultaneous imaging and energy harvesting without introducing additional in-plane p-n junctions. The prototype pixel uses a vertical ${p}^{+}/{n}_{\text {well}}/{p}_{\text {sub}}$ junction that is available in standard CMOS processes. Unlike the conventional CMOS electron-based imaging pixels, where the ${n}_{\text {well}}$ region is used as a sensing node for image capture, we adopted a hole-based imaging technique, while exploiting the ${n}_{\text {well}}$ region for energy harvesting at a high fill-factor of >94%. To verify the feasibility, CMOS image sensors are fabricated and characterized. We successfully demonstrated that the energy harvesting can be achieved with a power density of 998 pW/klux/mm2, while capturing images at 74.67 pJ/pixel. The fabricated prototype device has achieved the highest power density among the recent state-of-the-art works and can self-sustain its image capturing operation at 15 fps without external power sources above ~60 klux of illumination.

Photodiode area effect on performance of X-ray CMOS active pixel sensors

Compared to conventional TFT-based X-ray imaging devices, CMOS-based X-ray imaging sensors are considered next generation because they can be manufactured in very small pixel pitches and can acquire high-speed images. In addition, CMOS-based sensors have the advantage of integration of various functional circuits within the sensor. The image quality can also be improved by the high fill-factor in large pixels. If the size of the subject is small, the size of the pixel must be reduced as a consequence. In addition, the fill factor must be reduced to aggregate various functional circuits within the pixel. In this study, 3T-APS (active pixel sensor) with photodiodes of four different sizes were fabricated and evaluated. It is well known that a larger photodiode leads to improved overall performance. Nonetheless, if the size of the photodiode is > 1000 μm2, the degree to which the sensor performance increases as the photodiode size increases, is reduced. As a result, considering the fill factor, pixel-pitch > 32 μm is not necessary to achieve high-efficiency image quality. In addition, poor image quality is to be expected unless special sensor-design techniques are included for sensors with a pixel pitch of 25 μm or less.

CMOS active pixel sensors response to low energy light ions

Recently CMOS active pixel sensors have been used in Hadrontherapy ions fragmentation cross section measurements. Their main goal is to reconstruct tracks generated by the non interacting primary ions or by the produced fragments. In this framework the sensors, unexpectedly, demonstrated the possibility to obtain also some informations that could contribute to the ion type identification. The present analysis shows a clear dependency in charge and number of pixels per cluster (pixels with a collected amount of charge above a given threshold) with both fragment atomic number Z and energy loss in the sensor. This information, in the FIRST (F ragmentation of I ons R elevant for S pace and T herapy) experiment, has been used in the overall particle identification analysis algorithm. The aim of this paper is to present the data analysis and the obtained results. An empirical model was developed, in this paper, that reproduce the cluster size as function of the deposited energy in the sensor.

Subpixel mapping and test beam studies with a HV2FEI4v2 CMOS-Sensor-Hybrid Module for the ATLAS inner detector upgrade

The upgrade to the High Luminosity Large Hadron Collider will increase the instantaneous luminosity by more than a factor of 5, thus creating significant challenges to the tracking systems of all experiments. Recent advancement of active pixel detectors designed in CMOS processes provide attractive alternatives to the well-established hybrid design using passive sensors since they allow for smaller pixel sizes and cost effective production. This article presents studies of a high-voltage CMOS active pixel sensor designed for the ATLAS tracker upgrade. The sensor is glued to the read-out chip of the Insertable B-Layer, forming a capacitively coupled pixel detector. The pixel pitch of the device under test is 33× 125 μm2, while the pixels of the read-out chip have a pitch of 50× 250 μm2. Three pixels of the CMOS device are connected to one read-out pixel, the information of which of these subpixels is hit is encoded in the amplitude of the output signal (subpixel encoding). Test beam measurements are presented that demonstrate the usability of this subpixel encoding scheme.

Radiation damage caused by cold neutrons in boron doped CMOS active pixel sensors

CMOS Monolithic Active Pixel Sensors (MAPS) are considered as an emerging technology in the field of charged particle tracking. They will be used in the vertex detectors of experiments like STAR, CBM and ALICE and are considered for the ILC and the tracker of ATLAS. In those applications, the sensors are exposed to sizeable radiation doses. While the tolerance of MAPS to ionizing radiation and fast hadrons is well known, the damage caused by low energy neutrons was not studied so far. Those slow neutrons may initiate nuclear fission of 10B dopants found in the B-doped silicon active medium of MAPS. This effect was expected to create an unknown amount of radiation damage beyond the predictions of the NIEL (Non Ionizing Energy Loss) model for pure silicon. We estimate the impact of this effect by calculating the additional NIEL created by this fission. Moreover, we show first measured data for CMOS sensors which were irradiated with cold neutrons. The empirical results contradict the prediction of the updated NIEL model both, qualitatively and quantitatively: the sensors irradiated with slow neutrons show an unexpected and strong acceptor removal, which is not observed in sensors irradiated with MeV neutrons.

Task-Based Modeling of a 5k Ultra-High-Resolution Medical Imaging System for Digital Breast Tomosynthesis.

High-resolution, low-noise X-ray detectors based on CMOS active pixel sensor (APS) technology have demonstrated superior imaging performance for digital breast tomosynthesis (DBT). This paper presents a task-based model for a high-resolution medical imaging system to evaluate its ability to detect simulated microcalcifications and masses as lesions for breast cancer. A 3-D cascaded system analysis for a 50- [Formula: see text] pixel pitch CMOS APS X-ray detector was integrated with an object task function, a medical imaging display model, and the human eye contrast sensitivity function to calculate the detectability index and area under the ROC curve (AUC). It was demonstrated that the display pixel pitch and zoom factor should be optimized to improve the AUC for detecting small microcalcifications. In addition, detector electronic noise of smaller than 300 e- and a high display maximum luminance (>1000 cd/cm 2) are desirable to distinguish microcalcifications of [Formula: see text] in size. For low contrast mass detection, a medical imaging display with a minimum of 12-bit gray levels is recommended to realize accurate luminance levels. A wide projection angle range of greater than ±30° in combination with the image gray level magnification could improve the mass detectability especially when the anatomical background noise is high. On the other hand, a narrower projection angle range below ±20° can improve the small, high contrast object detection. Due to the low mass contrast and luminance, the ambient luminance should be controlled below 5 cd/ [Formula: see text]. Task-based modeling provides important firsthand imaging performance of the high-resolution CMOS-based medical imaging system that is still at early stage development for DBT. The modeling results could guide the prototype design and clinical studies in the future.

Geant4-based simulations of charge collection in CMOS Active Pixel Sensors

Geant4 is an object-oriented toolkit for the simulation of the interaction of particles and radiation with matter. It provides a snapshot of the state of a simulated particle in time, as it travels through a specified geometry. One important area of application is the modelling of radiation detector systems. Here, we extend the abilities of such modelling to include charge transport and sharing in pixelated CMOS Active Pixel Sensors (APSs); though similar effects occur in other pixel detectors. The CMOS APSs discussed were developed in the framework of the PRaVDA consortium to assist the design of custom sensors to be used in an energy-range detector for proton Computed Tomography (pCT). The development of ad-hoc classes, providing a charge transport model for a CMOS APS and its integration into the standard Geant4 toolkit, is described. The proposed charge transport model includes, charge generation, diffusion, collection, and sharing across adjacent pixels, as well as the full electronic chain for a CMOS APS. The proposed model is validated against experimental data acquired with protons in an energy range relevant for pCT.

Radiation hardness studies of AMS HV-CMOS 350 nm prototype chip HVStripV1

CMOS active pixel sensors are being investigated for their potential use in the ATLAS inner tracker upgrade at the HL-LHC. The new inner tracker will have to handle a significant increase in luminosity while maintaining a sufficient signal-to-noise ratio and pulse shaping times. This paper focuses on the prototype chip “HVStripV1” (manufactured in the AMS HV-CMOS 350nm process) characterization before and after irradiation up to fluence levels expected for the strip region in the HL-LHC environment. The results indicate an increase of depletion region after irradiation for the same bias voltage by a factor of ≈2.4 and ≈2.8 for two active pixels on the test chip. There was also a notable increase in noise levels from 85 e− to 386 e− and from 75 e− to 277 e− for the corresponding pixels.

γ射线电离辐射对商用CMOS APS性能参数的影响

γ射线电离辐射对商用CMOS APS性能参数的影响

Response to "Comment on 'Large area CMOS active pixel sensor x-ray imager for digital breast tomosynthesis: Analysis, modeling, and characterization' " [Med. Phys. 43, 1578-1579 (2016)

Response to "Comment on 'Large area CMOS active pixel sensor x-ray imager for digital breast tomosynthesis: Analysis, modeling, and characterization' " [Med. Phys. 43, 1578-1579 (2016)

CMOS pixel sensors on high resistive substrate for high-rate, high-radiation environments

A depleted CMOS active pixel sensor (DMAPS) has been developed on a substrate with high resistivity in a high voltage process. High radiation tolerance and high time resolution can be expected because of the charge collection by drift. A prototype of DMAPS was fabricated in a 150nm process by LFoundry. Two variants of the pixel layout were tested, and the measured depletion depths of the variants are 166μm and 80μm. We report the results obtained with the prototype fabricated in this technology.

Multi-MGy Radiation Hard CMOS Image Sensor: Design, Characterization and X/Gamma Rays Total Ionizing Dose Tests

A Radiation Hard CMOS Active Pixel Image Sensor has been designed, manufactured and exposed to X and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{60}{\rm Co}\,\, \gamma $</tex></formula> -ray sources up to several MGy of Total Ionizing Dose (TID). It is demonstrated that a Radiation-Hardened-By-Design (RHBD) CMOS Image Sensor (CIS) can still provide useful images after <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$10~\hbox{MGy}({\rm SiO}_2)$</tex></formula> (i.e. 1 Grad). This paper also presents the first detailed characterizations of CIS opto-electrical performances (i.e. dark current, quantum efficiency, gain, noise, transfer functions, etc.) in the MGy range. These results show that it is possible to design a CIS with good performances even after having absorbed several MGy. Four different RHBD photodiode designs are compared: a standard photodiode design, two well known RHBD layouts and a proposed improvement of the gated photodiode design. The proposed layout exhibits the best performances over the entire studied TID range and further optimizations are discussed. Several original MGy radiation effects are presented and discussed at the device and circuit levels and mitigation techniques are proposed to improve further the radiation hardness of future Rad-Hard CIS developments for extreme TID applications (e.g. for nuclear power plant monitoring/dismantling, experimental reactors (e.g. ITER) or next generation particle physics experiments (e.g. CERN)).

50 μm pixel pitch wafer-scale CMOS active pixel sensor x-ray detector for digital breast tomosynthesis

Wafer-scale CMOS active pixel sensors (APSs) have been developed recently for x-ray imaging applications. The small pixel pitch and low noise are very promising properties for medical imaging applications such as digital breast tomosynthesis (DBT). In this work, we evaluated experimentally and through modeling the imaging properties of a 50 μm pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). A modified cascaded system model was developed for CMOS APS x-ray detectors by taking into account the device nonlinear signal and noise properties. The imaging properties such as modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) were extracted from both measurements and the nonlinear cascaded system analysis. The results show that the DynAMITe x-ray detector achieves a high spatial resolution of 10 mm−1 and a DQE of around 0.5 at spatial frequencies <1 mm−1. In addition, the modeling results were used to calculate the image signal-to-noise ratio (SNRi) of microcalcifications at various mean glandular dose (MGD). For an average breast (5 cm thickness, 50% glandular fraction), 165 μm microcalcifications can be distinguished at a MGD of 27% lower than the clinical value (~1.3 mGy). To detect 100 μm microcalcifications, further optimizations of the CMOS APS x-ray detector, image aquisition geometry and image reconstruction techniques should be considered.

Development of radiation hard CMOS active pixel sensors for HL-LHC

New pixel detectors, based on commercial high voltage and/or high resistivity full CMOS processes, hold promise as next-generation active pixel sensors for inner and intermediate layers of the upgraded ATLAS tracker. The use of commercial CMOS processes allow cost-effective detector construction and simpler hybridisation techniques. The paper gives an overview of the results obtained on AMS-produced CMOS sensors coupled to the ATLAS Pixel FE-I4 readout chips. The SOI (silicon-on-insulator) produced sensors by XFAB hold great promise as radiation hard SOI-CMOS sensors due to their combination of partially depleted SOI transistors reducing back-gate effects. The test results include pre-/post-irradiation comparison, measurements of charge collection regions as well as test beam results.

An Ultra-Low Power Energy Harvesting and Imaging (EHI) Type CMOS APS Imager With Self-Power Capability

A novel ultra-low power energy harvesting and imaging (EHI) type CMOS active pixel sensor (APS) imager with self-power capability is presented. The proposed EHI type CMOS APS pixel harvests one order of magnitude higher power than that of the other pixel technologies reported in the literature. It produces 46 $\mu{\rm W}$ of power under 57 klux illumination. The EHI imager presented has decoupled imaging and harvesting operations such that imaging related circuits are turned off while energy is harvested, and vice versa. The imager can operate on 1 V supply voltage consuming as low as 800 nW while capturing 1 frame per second (fps). Measured minimum full-chip imager FoM is 148 pJ/frame $\ast$ pixel while capturing 21.2 fps. The imager contains a 64 $\times$ 45 array of $18 \mu{\hbox{m}}\times 18 \mu{\hbox{m}}$ EHI pixels. It is manufactured in a standard 2P4M/3.3 V 0.35 $\mu{\rm m}$ CMOS process. Ultra-low power operation is achieved by developing new imaging electronics including current reference generator, readout circuits, and SAR type, 8-bit, analog-to digital converter (ADC). A new polarity inverting charge pump circuit was developed for managing the energy harvested by the new energy harvesting pixels on the focal plane.

Voltage Mode FPN Calibration in the Logarithmic CMOS Imager

The CMOS active pixel sensor (APS) operating in the logarithmic mode is the most common and useful CMOS wide-dynamic-range imager. Notwithstanding, fixed-pattern noise (FPN) between pixels compromises the quality of the image generated by the focal-plane array. Classical techniques as correlated double sampling do not work properly in this mode, and alternative techniques must be applied in order to calibrate FPN. The alternative techniques require either complex pixel circuitry, or external memory and software level calibration. Purposefully to improve image quality at reduced circuitry complexity, a new calibration technique is proposed that can be applied directly to the basic three-FET APS circuit. The efficacy of the proposed technique was experimentally verified with a small pixel array fabricated in a standard 0.35- $\mu \text{m}$ CMOS technology. The experimental results show a steady FPN attenuation within the whole tested illumination range and the improvement of the signal-to-noise and distortion ratio of the array.

Current Sensing-Assisted Active Pixel Sensor for High-Speed CMOS Image Sensors

In this paper, we describe an active pixel CMOS image sensor that employs a current-sensing readout circuit. The readout uses a column-level current-sensing amplifier with negative feedback to increase current driving capability, which gives significantly faster settling time. A prototype $128\,\times \,3$ pixel sensor with a current gain of 10 was fabricated using standard 0.35- $\mu \text{m}$ CMOS technologyand demonstrated a reduction in settling time by a factor of 14 for both negative and positive voltage swings of the output node. The power consumption of the column-level readout amplifier is 110 $\mu \text{W}$ .

A Real-time Auto-detection Method for Random Telegraph Signal (RTS) Noise Detection in CMOS Active pixel sensors

CMOS Active pixel sensors (CMOS APS) are attractive for use in the innermost layers of charged particle trackers, due to their good tradeoffs among the key performances. However, CMOS APS can be greatly influenced by random telegraph signal (RTS) noise, which can cause particle tracking or energy calculation failures. In-depth research of pixels' RTS behavior stimulates the interest of the methods for RTS noise detection, reconstruction and parameters extraction. In this paper, a real-time auto-detection method is proposed, using real-time Gaussian noise standard deviation as the detection threshold. Experimental results show that, compared with current methods using signal standard deviation as the thresholds, the proposed method is more sensitive in multi-level RTS detection and more effective in the case of RTS noise degradation.