CMOS Active Pixel Sensor Research Articles

Noise assessment of CMOS active pixel sensors for the CYGNO Experiment

Active Pixel sensors play a crucial role in enabling successful low-light scientific experiments due to their inherent advantages and capabilities. Such devices not only offer high spatial resolution but also feature individual pixels with integrated amplifiers, allowing for direct signal amplification at the pixel level. This results in reduced readout noise and improved signal-to-noise ratio (SNR), which are particularly vital when dealing with limited photon counts in low-light environments. This holds particularly true for scientific CMOS (sCMOS) sensors, acknowledged as an advanced evolution of Active Pixel sensors. However, despite their advantages, such sensors can still exhibit limitations such as higher cost and presence of noise artifacts that should be closely investigated. In particular, CYGNO project fits in a global effort aimed at direct detection of Dark Matter particles. CYGNO collaboration intends to build a detector based on a Time Projection Chamber making use of Gas Electron Multipliers for the amplification of ionization electrons. The GEM multiplication process produces photons that can be readout by a high-resolution sCMOS sensor. Such detection system is being designed to have enough sensitivity to detect low-energy particles and to measure released energy with enough granularity so to reconstruct direction and energy profile along their trajectories. The image sensor has an important role in the detector performance, having a direct impact on the SNR of the experiment. This work proposes a study on the performance of three different sCMOS sensors with respect to their sensitivity to low-energy particles and their intrinsic noise, which are of the utmost importance for various scientific experiments.

The Principle and Design of CMOS Active Pixel Sensor

In today's increasingly prosperous global semiconductor development, CMOS image sensors have always been in the spotlight. The many advantages of CMOS such as lower production costs, smaller sensor sizes and lower production costs have allowed them to be used in a wide variety of devices. In this paper, the working principle of the 3-T active pixel sensor and its current applications are introduced, and the architecture and working mode of APS itself are also highlighted. The simulation software coolspice is then used to simulate the output values and timing of the circuit. In this paper, nine inputs of the same value and six pulse voltages are used to control the output sequence. The paper also describes the key technical problems of the APS itself and the solutions to these problems.

An All-Day Attitude Sensor Integrating Stars and Sun Measurement Based on Extended Pixel Response of CMOS APS Imager

For celestial measurement, it is difficult to enable a single optical system to image and measure both stars and the sun due to vastly different light intensity of targets and limited response capability of the image sensor pixel. Here, we develop an all-day optical attitude sensor integrating stars and the sun measurement based on extended pixel response model of the CMOS APS (Active-pixel sensor) imager. For extremely large light intensity, we extend the conventional pixel response model to the oversaturated stage where the pixel values reverse and drop below the saturation value. Based on this, the integration of the star sensor and the sun sensor is realized. The pixels image the starry sky with linear response, and make use of the oversaturation response to image the sun and obtain a black spot on the bright background. This principle enables the capability of all-day high-precision attitude measurement using a single miniaturized sensor. An integrated optical attitude sensor is designed and manufactured. Ground-based observation results show that the orientation accuracy from sun measurement is better than 9" (3σ), and the attitude accuracy from star measurement is better than 5" (3σ) for pointing and 11" (3σ) for rolling. The sensor can be applied to high-precision all-day navigation systems for miniaturized spacecrafts and aircrafts.

High-Voltage CMOS Active Pixel Sensor Chip With Counting Electronics for Beam Monitoring

This article presents the monolithic active high-voltage CMOS (HV-CMOS) pixel sensor HitPix with counting electronics and frame-based readout. It has been developed for high rate ion-beam monitoring, as used, e.g., in medical facilities for radiation therapy. The sensor elements are lowly doped n-well in p-substrate diodes. Pixel electronics is implemented within the sensor cathode (n-well). The substrate can be biased to −120 V. In this way, a large depletion zone is induced and radiation tolerance is improved. We could show the overall functionality of the sensor by laboratory measurements of the signal response characteristics and threshold distribution. Furthermore, testing the sensor in the medical ion beam of Heidelberg Ion-Beam Therapy Center (HIT) has proven the suitability of this beam monitor approach.

Characterisation of analogue front end and time walk in CMOS active pixel sensor

In this work we investigated a method to determine time walk in an active silicon pixel sensor prototype using Edge-TCT with infrared laser charge injection. Samples were investigated before and after neutron irradiation to 5· 10^14n_ eq/cm^2. Threshold, noise and calibration of the analogue front end were determined with external charge injection. A spatially sensitive measurement of collected charge and time walk was carried out with Edge-TCT, showing a uniform charge collection and output delay in pixel centre. On pixel edges charge sharing was observed due to finite beam width resulting in smaller signals and larger output delay. Time walk below 25 ns was observed for charge above 2000 e^- at a threshold above the noise level. Time walk measurement with external charge injection yielded identical results.

High-Voltage CMOS Active Pixel Sensor

The high-voltage CMOS (HVCMOS) sensors are a novel type of CMOS active pixel sensors for ionizing particles that can be implemented in CMOS processes with deep n-well option. The pixel contains one sensor electrode formed with a deep n-well implanted in a p-type substrate. CMOS pixel electronics, embedded in shallow wells, are placed inside the deep n-well. By biasing the substrate with a high negative voltage and by the use of a lowly doped substrate, a depleted region depth of at least 30 μm can be achieved. The electrons generated by a particle are collected by drift, which induces fast detectable signals. This publication presents a 4.2-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> large HVCMOS pixel sensor implemented in a commercial 180-nm process on a lowly doped substrate and its characterization.

A 24-Channel Digitizer With a JESD204B-Compliant Serial Interface for High-Speed Detectors

A 24-channel application-specific integrated circuit (ASIC) for the readout of high-speed CMOS active pixel sensors for charged particle detection is presented. The chip comprises 24 preamplifiers, 24 distinct 12-bit, 25 MSPS Pipelined analog-to-digital converters (ADCs) with self-calibration, an internal phase-locked loop (PLL), and a 3 Gbps serial interface that conforms to the JESD204B standard. To simplify interfacing with a variety of sensors, the ASIC also includes an automatic offset calibration loop. The high level of integration of the ASIC reduces overall system cost and area, and exploiting the signal characteristics of the image sensor allows the ADC to be optimized for reduced power dissipation. The use of an integrated serializer and an industry standard protocol simplifies integration of the ASIC into a complete camera system. The ASIC, called the High-Speed Image Preprocessor Targeted for Electron Readout, or HIPSTER, with a die area of 64.26 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , is packaged in a 480-ball grid array (BGA) and is fabricated in 180-nm CMOS technology. HIPSTER achieves typical differential nonlinearity (DNL) <; 0.55 LSB, input-referred thermal noise of 114.5 μV-rms, and a bit error rate (BER) of better than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14</sup> . The power dissipation is 98 mW/channel.

Single-Slope Look-Ahead Ramp ADC for CMOS Image Sensors

Integrating type analog-to-digital converters (ADC) used in column-parallel CMOS image sensors trade conversion speed with size, power, and complexity to achieve optimal performance. A new integrating ADC architecture called single-slope look-ahead ramp (SSLAR) ADC is introduced in this paper. It utilizes a statistical approach and code-prediction methods to improve the conversion speed of standard single-slope ramp (SSR) ADC. It is shown that SSLAR ADC reduces power consumption while achieving an increased frame rate. This is achieved by the SSLAR algorithm that was optimized for column-parallel CMOS active pixel sensor (APS) imager architecture. A 10-bit SSLAR ADC was designed in a 0.5μm CMOS (2P3M) process and integrated with a column-parallel CMOS image sensor that has 200 × 150 array with 15μm pixels. Measurements showed that a 6× frame rate increase can be achieved while reducing power consumption 13% with minimal impact on image quality.

A Monolithic Amorphous-Selenium/CMOS Visible-Light Imager With Sub-9-μm Pixel Pitch and Extended Full-Well Capacity

We present a monolithic hybrid visible-light imager composed of an amorphous selenium (a-Se) photoconductor thin film integrated on a CMOS active pixel sensor (APS) array readout integrated circuit. We achieve more than 14-dB signal-to-noise ratio under monochromatic light at an illuminance of 0.04 lux in one quadrant of the imager containing $7.8\times 7.8-\mu \,\,\text{m}^{2}$ pixels using a 1.6-s exposure (integration) time without operating the a-Se sensor in avalanche mode. Long integration times are made possible by exploiting the low dark-current of a 20- $\mu \text{m}$ -thick a-Se sensor layer and by implementing dark-current reduction techniques in the APS, such as series stacking reset and protection devices. In addition, use of a relatively thick 20- $\mu \text{m}$ a-Se layer obviates the need for an additional planarization step of the sensing layer as was done with a previously-reported avalanche-mode a-Se/CMOS imager that incorporated a 0.5- $\mu \text{m}$ -thick sensing layer. We also demonstrate an improved APS design, with $7.8\times 8.7-\mu \,\,\text{m}^{2}$ dimensions, containing a programmable in-pixel integration capacitor to provide enhanced full-well capacity (FWC) for a-Se/CMOS imagers. Measured results show that our APS achieves a FWC of approximately 230 ke−, which is comparable to several previously-reported photodiode-based CMOS imagers with extended FWC. Our imager can also resolve an effective object size of approximately $12.5~\mu \text{m}$ , demonstrated through measurement of the modulation transfer function.

Design of ePixM, a fully-depleted monolithic CMOS active pixel sensor for soft X-ray experiments at LCLS-II

The LCLS-II Free Electron Laser (FEL) will produce X-ray pulses with a repetition rate of up to 1 MHz and energies between 250 eV and 5 keV. Experiments conducted at LCLS-II will require 2D imaging detectors with a unique set of features, such as high-spatial resolution, low-noise performance, high-dynamic range and high-frame rates up to 1 MHz. We present the design of ePixM, a fully-depleted monolithic CMOS detector tailored for soft X-rays applications at high-repetition rates FEL. It consists of an array of 384×192 active pixel sensors, with a pixel size of 50×50 μm2 and a total sensitive area of 2×1 cm2. ePixM has been designed in a 150 nm CMOS technology on high-resistivity substrate to achieve full depletion of the substrate. Each pixel includes a Charge Sensitive Amplifier (CSA) with gain auto-ranging capability and a noise-shaper performing Correlated Double Sampling (CDS). A novel technique named correlated pre-charging removes the excess noise introduced by the gain-switching mechanism. The performance of the design has been evaluated through post-layout simulations. The Equivalent Noise Charge (ENC) of 11.3 electrons enables single-photon detection at X-ray energies down to 250 eV, and the dynamic range exceeds 103 photons at 500 eV thanks to the auto-ranging circuitry.

2019 Leonard Medal to Hisayoshi Yurimoto

2019 Leonard Medal to Hisayoshi Yurimoto

Proton Irradiation-Induced Random Telegraph Signal Noise in a $2\text{k}\times2\text{k}$ 4T CMOS Active Pixel Sensor: Testing, Detection, and Modeling

This paper presents our recent study progress on proton-irradiated-induced random telegraph signal (RTS) in a high-resolution CMOS active pixel sensor (APS). First, RTS waveforms of a commercial $2\text{k} \times2\text{k}$ 4T CMOS APS chip in 180-nm CMOS technology are tested under the 10-MeV proton irradiation. Second, a novel adaptive automatic detection method (AADM) based on real-time thresholds is proposed for the sequential processing of a large batch of RTS pixels. Real-time thresholds and two-stage reconstruction algorithms are employed to improve the validity and correctness of RTS reconstruction. The proposed detection method which can realize the batch autoprocessing by using an adaptive filter will improve the detection efficiency. Third, a new approach to model the RTS maximum transition amplitude distribution is presented. It has been proven that the double exponential distribution can fit the RTS maximum transition amplitude distribution better. Two models are proposed to predict the contributions due to the ionizing effects and displacement damage effects. Finally, the error analysis is given. The errors between the simulated data of the proposed models and experimental results are all less than 5.5 %.

Single event transient effects on 3T and 4T CMOS active pixel sensors for different technologies

ABSTRACTThe widely used CMOS Active Pixel Sensors (APS) in space imaging mission are vulnerable to radiations known as Single Event Transient (SET). This paper focus on 3T and 4T CMOS APS with technology from 130 nm scaling down to 32 nm, simulated using various Linear Energy Transfer (LET) magnitudes ranging from 3.3 to 67.7 MeV.cm2/mg. Larger transient currents were observed at higher LET for both APS architectures. The peak drain current of 3T increases with slightly steeper slope by roughly 8% than 4T due to the difficulty of electron transfer in 4T. In 3T, 130 nm, 90 nm, 65 nm and 45 nm override the 32 nm technology by 13.93%, 9.09%, 4.43% and 2.06%, respectively. The total charge collection of the 3T is constantly higher than the 4T APS by the ratio of at least 1.25 indicates 4T has a higher radiation hardness. A bright spot degradation is expected to occur in the image if the transient signal is more than 20% of the original signal which mainly attributed to the lower operating voltage and smaller nodal capacitance. From this study, 4T CMOS APS shown more radiation hardness than the 3T CMOS APS and 32 nm technology exhibits lowest radiation-tolerant.

The Monopix chips: depleted monolithic active pixel sensors with a column-drain read-out architecture for the ATLAS Inner Tracker upgrade

Two different depleted monolithic CMOS active pixel sensor (DMAPS) prototypes with a fully synchronous column-drain read-out architecture were designed and tested: LF-Monopix and TJ-Monopix. These chips are part of a R&D effort towards a suitable implementation of a CMOS DMAPS for the HL-LHC ATLAS Inner Tracker. LF-Monopix was developed using a 150nm CMOS process on a highly resistive substrate (>2 kΩ cm), while TJ-Monopix was fabricated using a modified 180 nm CMOS process with a 1 kΩ cm epi-layer for depletion. The chips differ in their front-end design, biasing scheme, pixel pitch, dimensions of the collecting electrode relative to the pixel size (large and small electrode design, respectively) and the placement of read-out electronics within such electrode. Both chips were operational after thinning down to 100 μm and additional back-side processing in LF-Monopix for total bulk depletion. The results in this work include measurements of their leakage current, noise, threshold dispersion, response to minimum ionizing particles and efficiency in test beam campaigns. In addition, the outcome from measurements after irradiation with neutrons up to a dose of 1×1015 neq / cm2 and its implications for future designs are discussed.

A large area CMOS Active Pixel Sensor for imaging in proton therapy

There is an increased interest in developing imaging systems in proton therapy, with the aim of reducing range uncertainty in treatment planning, assisting in patient positioning and verifying anatomical changes at the time of the treatment. Recently, the PRaVDA collaboration has developed two different solid-state detector technologies for imaging in proton therapy: Silicon Strip Detectors and CMOS Active Pixel Sensors (APSs). This paper reports on the design and optimisation process of the PRaVDA CMOS APSs. Optimisation of parameters, such as epitaxial thickness and resistivity, and performance for individual proton detection and proton radiography are reported.

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 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\times$ &lt;/tex-math&gt; &lt;/inline-formula&gt; 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.

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.

A 99.95% linearity readout circuit with 72 dB dynamic range for active pixel sensors

SummaryOne of the main sources of nonlinearity and sensitivity degradation in conventional active pixel sensor (APS) architectures is the source follower buffer amplifier that isolates the photodiode node from the column bus. To extend the linear region of the output voltage, correct the sensitivity degradation, and improve the imager dynamic range, an output regulated voltage follower is proposed. All these enhancements are achieved without decreasing the pixel fill factor nor increasing the number of transistors and the addressing circuits complexity of a conventional 4T CMOS APS. The performance of the circuit is assessed using a 0.35‐μm CMOS technology. The obtained results show a 14‐dB dynamic range improvement for highly linear applications over the conventional APS readout circuit.

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.