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27 pages, 8781 KiB

Open AccessArticle

Design of Monolithic Bi-Layer High-Z PAL-Si Hard X-ray CMOS Image Sensors for Quantum Efficiency Enhancement

by Eldred Lee, Kevin D. Larkin, Xin Yue, Zhehui Wang, Eric R. Fossum and Jifeng Liu

Instruments 2023, 7(3), 24; https://doi.org/10.3390/instruments7030024 - 28 Aug 2023

Viewed by 2271

This article experimentally investigates the inception of an innovative hard X-ray photon energy attenuation layer (PAL) to advance high-energy X-ray detection (20–50 keV). A bi-layer design with a thin film high-Z PAL on the top and Si image sensor on the bottom has [...] Read more.

This article experimentally investigates the inception of an innovative hard X-ray photon energy attenuation layer (PAL) to advance high-energy X-ray detection (20–50 keV). A bi-layer design with a thin film high-Z PAL on the top and Si image sensor on the bottom has previously demon-strated quantum yield enhancement via computational methods by the principle of photon energy down conversion (PEDC), where high-energy X-ray photon energies are attenuated via inelastic scattering down to ≤10 keV, which is suitable for efficient photoelectric absorption by Si. Quantum yield enhancement has been experimentally confirmed via a preliminary demonstration using PAL-integrated Si-based CMOS image sensors (Si CIS). Furthermore, substituting the high-Z PAL with a lower-Z material—Sn—and alternatively coupling it with a conventional scintillator ma-terial—Lutetium-yttrium oxyorthosilicate (LYSO)—have been compared to demonstrate the most prominent efficacy of monolithic integration of high-Z PAL on Si CIS to detect hard X-rays, paving the way for next-generation high-energy X-ray detection methods. Full article

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16 pages, 4192 KiB

Open AccessArticle

Design and Characterization of a Burst Mode 20 Mfps Low Noise CMOS Image Sensor

by Xin Yue and Eric R. Fossum

Sensors 2023, 23(14), 6356; https://doi.org/10.3390/s23146356 - 13 Jul 2023

Cited by 3 | Viewed by 3523

Abstract

This paper presents a novel ultra-high speed, high conversion-gain, low noise CMOS image sensor (CIS) based on charge-sweep transfer gates implemented in a standard 180 nm CIS process. Through the optimization of the photodiode geometry and the utilization of charge-sweep transfer gates, the [...] Read more.

This paper presents a novel ultra-high speed, high conversion-gain, low noise CMOS image sensor (CIS) based on charge-sweep transfer gates implemented in a standard 180 nm CIS process. Through the optimization of the photodiode geometry and the utilization of charge-sweep transfer gates, the proposed pixels achieve a charge transfer time of less than 10 ns without requiring any process modifications. Moreover, the gate structure significantly reduces the floating diffusion capacitance, resulting in an increased conversion gain of 183 µV/e−. This advancement enables the image sensor to achieve the lowest reported noise of 5.1 e− rms. To demonstrate the effectiveness of both optimizations, a proof-of-concept CMOS image sensor is designed, taped-out and characterized. Full article

(This article belongs to the Special Issue Recent Advances in CMOS Image Sensor)

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12 pages, 5438 KiB

Open AccessArticle

Threshold Uniformity Improvement in 1b Quanta Image Sensor Readout Circuit

by Zhaoyang Yin, Jiaju Ma, Saleh Masoodian and Eric R. Fossum

Sensors 2022, 22(7), 2578; https://doi.org/10.3390/s22072578 - 28 Mar 2022

Cited by 6 | Viewed by 2567

Abstract

A new readout architecture for single-bit quanta image sensor (QIS) consisting of a capacitive transimpedance amplifier (CTIA) before a 1-bit quantizer to improve the threshold uniformity of the readout cluster is proposed in this paper. The 1-bit quantizer in the previous single-bit QIS [...] Read more.

A new readout architecture for single-bit quanta image sensor (QIS) consisting of a capacitive transimpedance amplifier (CTIA) before a 1-bit quantizer to improve the threshold uniformity of the readout cluster is proposed in this paper. The 1-bit quantizer in the previous single-bit QIS had significant threshold non-uniformity likely caused by the fluctuation of the common-mode voltage of the jot output. To guarantee the stability of the common-mode voltage of input signals fed to the 1-bit quantizer, the CTIA is added before the 1-bit quantizer. A pipeline operation mode is also proposed so the CTIA and 1-bit ADC can work at the same time, thereby reducing the CTIA power consumption. A 2048 × 1024 high-speed test chip was implemented with 45 nm/65 nm stacked backside illuminated (BSI) CMOS image sensor (CIS) process and tested. According to the measured D-log-H results, a good threshold uniformity in the range of 0.3 to 0.8 e− for all readout clusters is demonstrated at 500 frame per second (fps) equivalent timing with 68 mW power consumption. Full article

(This article belongs to the Section Sensing and Imaging)

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12 pages, 3083 KiB

Open AccessArticle

Simulating 50 keV X-ray Photon Detection in Silicon with a Down-Conversion Layer

by Kaitlin M. Anagnost, Eldred Lee, Zhehui Wang, Jifeng Liu and Eric R. Fossum

Sensors 2021, 21(22), 7566; https://doi.org/10.3390/s21227566 - 14 Nov 2021

Cited by 4 | Viewed by 3942

Abstract

Simulation results are presented that explore an innovative, new design for X-ray detection in the 20–50 keV range that is an alternative to traditional direct and indirect detection methods. Typical indirect detection using a scintillator must trade-off between absorption efficiency and spatial resolution. [...] Read more.

Simulation results are presented that explore an innovative, new design for X-ray detection in the 20–50 keV range that is an alternative to traditional direct and indirect detection methods. Typical indirect detection using a scintillator must trade-off between absorption efficiency and spatial resolution. With a high-Z layer that down-converts incident photons on top of a silicon detector, this design has increased absorption efficiency without sacrificing spatial resolution. Simulation results elucidate the relationship between the thickness of each layer and the number of photoelectrons generated. Further, the physics behind the production of electron-hole pairs in the silicon layer is studied via a second model to shed more light on the detector’s functionality. Together, the two models provide a greater understanding of this detector and reveal the potential of this novel form of X-ray detection. Full article

(This article belongs to the Special Issue Solid State Image Sensors for Emerging Space, Nuclear and Scientific Applications)

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17 pages, 5278 KiB

Open AccessArticle

Monte Carlo Modeling and Design of Photon Energy Attenuation Layers for >10× Quantum Yield Enhancement in Si-Based Hard X-ray Detectors

by Eldred Lee, Kaitlin M. Anagnost, Zhehui Wang, Michael R. James, Eric R. Fossum and Jifeng Liu

Instruments 2021, 5(2), 17; https://doi.org/10.3390/instruments5020017 - 30 Apr 2021

Cited by 4 | Viewed by 4286

Abstract

High-energy (>20 keV) X-ray photon detection at high quantum yield, high spatial resolution, and short response time has long been an important area of study in physics. Scintillation is a prevalent method but limited in various ways. Directly detecting high-energy X-ray photons has [...] Read more.

High-energy (>20 keV) X-ray photon detection at high quantum yield, high spatial resolution, and short response time has long been an important area of study in physics. Scintillation is a prevalent method but limited in various ways. Directly detecting high-energy X-ray photons has been a challenge to this day, mainly due to low photon-to-photoelectron conversion efficiencies. Commercially available state-of-the-art Si direct detection products such as the Si charge-coupled device (CCD) are inefficient for >10 keV photons. Here, we present Monte Carlo simulation results and analyses to introduce a highly effective yet simple high-energy X-ray detection concept with significantly enhanced photon-to-electron conversion efficiencies composed of two layers: a top high-Z photon energy attenuation layer (PAL) and a bottom Si detector. We use the principle of photon energy down conversion, where high-energy X-ray photon energies are attenuated down to ≤10 keV via inelastic scattering suitable for efficient photoelectric absorption by Si. Our Monte Carlo simulation results demonstrate that a 10–30× increase in quantum yield can be achieved using PbTe PAL on Si, potentially advancing high-resolution, high-efficiency X-ray detection using PAL-enhanced Si CMOS image sensors. Full article

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16 pages, 6644 KiB

Open AccessFeature PaperArticle

1/f Noise Modelling and Characterization for CMOS Quanta Image Sensors

by Wei Deng and Eric R. Fossum

Sensors 2019, 19(24), 5459; https://doi.org/10.3390/s19245459 - 11 Dec 2019

Cited by 15 | Viewed by 7690

Abstract

This work fits the measured in-pixel source-follower noise in a CMOS Quanta Image Sensor (QIS) prototype chip using physics-based 1/f noise models, rather than the widely-used fitting model for analog designers. This paper discusses the different origins of 1/f noise in [...] Read more.

This work fits the measured in-pixel source-follower noise in a CMOS Quanta Image Sensor (QIS) prototype chip using physics-based 1/f noise models, rather than the widely-used fitting model for analog designers. This paper discusses the different origins of 1/f noise in QIS devices and includes correlated double sampling (CDS). The modelling results based on the Hooge mobility fluctuation, which uses one adjustable parameter, match the experimental measurements, including the variation in noise from room temperature to –70 °C. This work provides useful information for the implementation of QIS in scientific applications and suggests that even lower read noise is attainable by further cooling and may be applicable to other CMOS analog circuits and CMOS image sensors. Full article

(This article belongs to the Special Issue Special issue on the 2019 International Image Sensor Workshop (IISW2019))

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25 pages, 7848 KiB

Open AccessReview

The Quanta Image Sensor: Every Photon Counts

by Eric R. Fossum, Jiaju Ma, Saleh Masoodian, Leo Anzagira and Rachel Zizza

Sensors 2016, 16(8), 1260; https://doi.org/10.3390/s16081260 - 10 Aug 2016

Cited by 95 | Viewed by 25805

Abstract

The Quanta Image Sensor (QIS) was conceived when contemplating shrinking pixel sizes and storage capacities, and the steady increase in digital processing power. In the single-bit QIS, the output of each field is a binary bit plane, where each bit represents the presence [...] Read more.

The Quanta Image Sensor (QIS) was conceived when contemplating shrinking pixel sizes and storage capacities, and the steady increase in digital processing power. In the single-bit QIS, the output of each field is a binary bit plane, where each bit represents the presence or absence of at least one photoelectron in a photodetector. A series of bit planes is generated through high-speed readout, and a kernel or “cubicle” of bits (x, y, t) is used to create a single output image pixel. The size of the cubicle can be adjusted post-acquisition to optimize image quality. The specialized sub-diffraction-limit photodetectors in the QIS are referred to as “jots” and a QIS may have a gigajot or more, read out at 1000 fps, for a data rate exceeding 1 Tb/s. Basically, we are trying to count photons as they arrive at the sensor. This paper reviews the QIS concept and its imaging characteristics. Recent progress towards realizing the QIS for commercial and scientific purposes is discussed. This includes implementation of a pump-gate jot device in a 65 nm CIS BSI process yielding read noise as low as 0.22 e− r.m.s. and conversion gain as high as 420 µV/e−, power efficient readout electronics, currently as low as 0.4 pJ/b in the same process, creating high dynamic range images from jot data, and understanding the imaging characteristics of single-bit and multi-bit QIS devices. The QIS represents a possible major paradigm shift in image capture. Full article

(This article belongs to the Special Issue Photon-Counting Image Sensors)

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8 pages, 1260 KiB

Open AccessArticle

Quantum Random Number Generation Using a Quanta Image Sensor

by Emna Amri, Yacine Felk, Damien Stucki, Jiaju Ma and Eric R. Fossum

Sensors 2016, 16(7), 1002; https://doi.org/10.3390/s16071002 - 29 Jun 2016

Cited by 7 | Viewed by 10976

Abstract

A new quantum random number generation method is proposed. The method is based on the randomness of the photon emission process and the single photon counting capability of the Quanta Image Sensor (QIS). It has the potential to generate high-quality random numbers with [...] Read more.

A new quantum random number generation method is proposed. The method is based on the randomness of the photon emission process and the single photon counting capability of the Quanta Image Sensor (QIS). It has the potential to generate high-quality random numbers with remarkable data output rate. In this paper, the principle of photon statistics and theory of entropy are discussed. Sample data were collected with QIS jot device, and its randomness quality was analyzed. The randomness assessment method and results are discussed. Full article

(This article belongs to the Special Issue Photon-Counting Image Sensors)

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