Large Pixel Arrays Research Articles

A 14-Bit Digital to Analog Converter for a Topmetal-CEE Pixel Readout Chip

The Lanzhou Heavy Ion Research Facility (LIRF) is the largest heavy ion research facility in China, providing a substantial volume of experimental data for fundamental research in nuclear physics. The Topmetal-CEE is a pixel readout chip specifically designed for tracking detectors. Within the Topmetal-CEE framework, the front-end amplifier and comparator necessitate precisely adjustable bias voltages. Hence, in this paper, a 14-bit resolution DAC with an R-2R resistor network structure is designed, along with an amplifier featuring high driving capabilities as the DAC driver, thus preventing potential impedance issues when driving large pixel arrays. Test results demonstrate that the DAC module, operating under a 3.3 V supply voltage, can consistently output voltages ranging from 0 to 1.8 V. Furthermore, the differential non-linearity error is less than 1.07 LSB, and the integral non-linearity error is less than 1.57 LSB.

A 3.06 μm Single-Photon Avalanche Diode Pixel with Embedded Metal Contact and Power Grid on Deep Trench Pixel Isolation for High-Resolution Photon Counting.

In this study, a 3.06 μm pitch single-photon avalanche diode (SPAD) pixel with an embedded metal contact and power grid on two-step deep trench isolation in the pixel is presented. The embedded metal contact can suppress edge breakdown and reduce the dark count rate to 15.8 cps with the optimized potential design. The embedded metal for the contact is also used as an optical shield and a low crosstalk probability of 0.4% is achieved, while the photon detection efficiency is as high as 57%. In addition, the integration of a power grid and the polysilicon resistor on SPAD pixels can help to reduce the voltage drop in anode power supply and reduce the power consumption with SPAD multiplication, respectively, in a large SPAD pixel array for a high-resolution photon-counting image sensor.

Front-End Electronics of CXPD for Measuring Transient X-Ray Sources

The Low Energy Polarization Detector (LPD), a payload of the POLAR-2 mission, is a soft X-ray polarization detector with a wide field of view and a large array aimed at measuring X-ray transients. These transients exhibit rapid intensity changes of several orders of magnitude, making it crucial for polarization detectors to have front-end electronics with low dead time, fast readout capabilities, high time resolution, and good energy resolution. In this paper, we present the design of the front-end electronics, which consist of a rolling shutter CMOS pixel charge sensor - Topmetal- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">II</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> , and a gas microchannel plate (GMCP) bottom amplifier circuit. Topmetal- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">II</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ’s rolling shutter readout provides fast scanning of large pixel arrays without dead time and acquires two-dimensional images of photoelectron tracks. Meanwhile, the GMCP’s bottom amplifier circuit measures the energy and time of the X-ray. The front-end electronics are employed by the CubeSat CXPD (Cosmic X-ray Polarimeter Detector), a proto-flight model of the LPD, achieving a timing resolution of 19 ns, and an energy resolution of 16.5% for linearly polarized X-rays at 8 keV.

Pixel Parameters Optimization in PWM Image Sensor for Quantization Error Suppression

This article established the error model based on pixel parameters to predict the light intensity quantization error in pulse width modulation (PWM) image sensor, attributed to non-linear response, comparator delay and synchronous reading mechanism. The PWM image sensor encodes light intensity into time interval of consecutive pulses, makes the quantization process of light intensity exceptionally impact the accuracy of the imaging quality. Especially in large pixel array, the synchronous readout scheme introduces quantization error. A PWM image sensor with 400(H) × 250(V) pixel array was tested to evaluate the model, and the measurements show that the pixel parameters affect the fluctuation of quantization error. With 300lux illuminance and 25μs reading period, the smallest error fluctuation range (11%-15%) can be obtained. The proposed model can suppress the fluctuation of the quantization error in PWM image sensor and help to achieve improved performance of image quality.

GPU Supported Simulation of Transition-Edge Sensor Arrays

We present numerical simulations of full transition-edge sensor (TES) arrays utilizing graphical processing units (GPUs). With the support of GPUs, it is possible to perform simulations of large pixel arrays to assist detector development. Comparisons with TES small-signal and noise theory confirm the representativity of the simulated data. In order to demonstrate the capabilities of this approach, we present its implementation in xifusim, a simulator for the X-ray Integral Field Unit, a cryogenic X-ray spectrometer on board the future Athena X-ray observatory.

Multiabsorber transition-edge sensors for x-ray astronomy

We are developing arrays of position-sensitive microcalorimeters for future x-ray astronomy applications. These position-sensitive devices commonly referred to as hydras consist of multiple x-ray absorbers, each with a different thermal coupling to a single-transition-edge sensor microcalorimeter. Their development is motivated by a desire to achieve very large pixel arrays with some modest compromise in performance. We report on the design, optimization, and first results from devices with small pitch pixels (<75 μm) being developed for a high-angular and energy resolution imaging spectrometer for Lynx. The Lynx x-ray space telescope is a flagship mission concept under study for the National Academy of Science 2020 decadal survey. Broadband full-width-half-maximum (FWHM) resolution measurements on a 9-pixel hydra have demonstrated ΔEFWHM = 2.23 ± 0.14 eV at Al-Kα, ΔEFWHM = 2.44 ± 0.29 eV at Mn-Kα, and ΔEFWHM = 3.39 ± 0.23 eV at Cu-Kα. Position discrimination is demonstrated to energies below <1 keV and the device performance is well-described by a finite-element model. Results from a prototype 20-pixel hydra with absorbers on a 50-μm pitch have shown ΔEFWHM = 3.38 ± 0.20 eV at Cr-Kα1. We are now optimizing designs specifically for Lynx and extending the number of absorbers up to 25/hydra. Numerical simulation suggests optimized designs could achieve ∼3 eV while being compatible with the bandwidth requirements of the state-of-the art multiplexed readout schemes, thus making a 100,000 pixel microcalorimeter instrument a realistic goal.

An Analog-Front ROIC with On-Chip Non-Uniformity Compensation for Diode-Based Infrared Image Sensors.

This paper proposes a CMOS front-end readout-integrated circuit (ROIC) with on-chip non-uniformity compensation technique for a diode-based uncooled infrared image sensor. Two techniques are adopted to achieve on-chip non-uniformity compensation: a reference dummy metal line is introduced to alleviate the dominant non-uniformity with IR-drop presented in large pixel array, and a current splitting architecture-based variable current source for diode bias is proposed to compensate other residual non-uniformity. A differential integrator is chosen as the main amplifier of readout circuit for its superior noise performance. For low power design, a pulse-powered row buffer is designed in this work. The proposed ROIC for 384 × 288 diode-based detector array is fabricated with a 0.35-m CMOS process. It occupies an area of 4.4 mm × 15 mm, and the power consumption is 180 mW. The measured result shows that with the proposed on-chip non-uniformity compensation, the output voltage variation is greatly reduced from 2.5 V to 60 mV.

NE-CAT: Crystallography Beamlines for Challenging Structural Biology Research

The NorthEastern Collaborative Access Team (NE-CAT) focuses on the design and operation of synchrotron X-ray beamlines for the solution of technically challenging structural biology problems and provides an important resource for the national and international research community. Currently, NE-CAT operates two undulator beamlines: a 6 - 22 keV tunable energy beamline (24-ID-C) and a 12.662 keV single energy beamline (24-ID-E). Both beamlines are equipped with state-of-the-art instrumentation. MD2 microdiffractometers installed at both beamlines provide very clean beams down to 5 microns in diameter and are capable of visualizing micron-sized crystals. Large area pixel array detectors (Pilatus6M and Eiger16M) provide fast noiseless data collection and make possible it to resolve large unit cells. Both beamlines are equipped with custom-built ALS-style robotic sample automounters with dewars capable of holding 14 pucks. Our locally developed software suite RAPD provides data collection strategies, quasi-real time data integration, scaling and simple automated MR/SAD pipeline through a 384-core compute cluster. Towards improving the diffraction from low resolution crystals, NE-CAT has installed humidity controlled device, HC1 in the 24ID-E hutch. Users of the beamlines are supported 24/7 by experienced resident crystallographers. Funding for NE-CAT is provided through a P41 grant from the NIGMS and from the NE-CAT member institutions.

Quantitative performance evaluation of a back-illuminated sCMOS camera with 95% QE for super-resolution localization microscopy.

Scientific Complementary Metal Oxide Semiconductor (sCMOS) cameras were introduced into the market in 2009 and are now becoming a major type of commercial cameras for low-light imaging. sCMOS cameras provide simultaneously low read noise, high readout speed, and large pixel array; however, the relatively low quantum efficiency (QE) of sCMOS cameras has been a major limitation for its application in single molecule imaging, especially super-resolution localization microscopy which requires high detection sensitivity. Here we report the imaging performance of a newly released back-illuminated sCMOS camera (called Dhyana 95 from Tucsen) which is claimed to be the world's first 95% QE sCMOS camera. The imaging performance evaluation is based on a new methodology which is designed to provide paired images from two tested cameras under almost identical experimental conditions. We verified that this new 95% QE sCMOS camera is able to provide superior imaging performance over a representative front-illuminated sCMOS camera (Hamamatsu Flash 4.0 V2) and a popular back-illuminated EMCCD camera (Andor iXon 897 Ultra) in a wide signal range. We hope this study will inspire more studies on using sCMOS cameras in super-resolution localization microscopy, or even single molecule imaging. © 2017 International Society for Advancement of Cytometry.

Compact SPAD-Based Pixel Architectures for Time-Resolved Image Sensors.

This paper reviews the state of the art of single-photon avalanche diode (SPAD) image sensors for time-resolved imaging. The focus of the paper is on pixel architectures featuring small pixel size (<25 μm) and high fill factor (>20%) as a key enabling technology for the successful implementation of high spatial resolution SPAD-based image sensors. A summary of the main CMOS SPAD implementations, their characteristics and integration challenges, is provided from the perspective of targeting large pixel arrays, where one of the key drivers is the spatial uniformity. The main analog techniques aimed at time-gated photon counting and photon timestamping suitable for compact and low-power pixels are critically discussed. The main features of these solutions are the adoption of analog counting techniques and time-to-analog conversion, in NMOS-only pixels. Reliable quantum-limited single-photon counting, self-referenced analog-to-digital conversion, time gating down to 0.75 ns and timestamping with 368 ps jitter are achieved.

FRAP, FLIM, and FRET: Detection and analysis of cellular dynamics on a molecular scale using fluorescence microscopy.

The combination of fluorescent-probe technology plus modern optical microscopes allows investigators to monitor dynamic events in living cells with exquisite temporal and spatial resolution. Fluorescence recovery after photobleaching (FRAP), for example, has long been used to monitor molecular dynamics both within cells and on cellular surfaces. Although bound by the diffraction limit imposed on all optical microscopes, the combination of digital cameras and the application of fluorescence intensity information on large-pixel arrays have allowed such dynamic information to be monitored and quantified. Fluorescence lifetime imaging microscopy (FLIM), on the other hand, utilizes the information from an ensemble of fluorophores to probe changes in the local environment. Using either fluorescence-intensity or lifetime approaches, fluorescence resonance energy transfer (FRET) microscopy provides information about molecular interactions, with Ångstrom resolution. In this review, we summarize the theoretical framework underlying these methods and illustrate their utility in addressing important problems in reproductive and developmental systems.

Laser beam induced current microscopy and photocurrent mapping for junction characterization of infrared photodetectors

For non-destructive optical characterization, laser beam induced current (LBIC) microscopy has been developed into as a quantitative tool to examine individual photodiodes within a large pixel array. Two-dimensional LBIC microscopy, also generally called photocurrent mapping (PC mapping), can provide spatially resolved information about local electrical properties and p-n junction formation in photovoltaic infrared (including visible light) photodetectors from which it is possible to extract material and device parameters such as junction area, junction depth, diffusion length, leakage current position and minority carrier diffusion length etc. This paper presents a comprehensive review of research background, operating principle, fundamental issues, and applications of LBIC or PC mapping.

Capacity of screen–camera communications under perspective distortions

Cameras are ubiquitous and increasingly being used not just for capturing images but also for communicating information. For example, the pervasive QR codes can be viewed as communicating a short code to camera-equipped sensors. Such communications could be particularly attractive in pervasive camera based applications, where such camera communications can reuse the existing camera hardware and also leverage from the large pixel array structure for high data-rate communication. While several prototypes have been constructed, the fundamental capacity limits of the screen–camera communication channel in all but the simplest scenarios remains unknown. The visual medium differs from RF in that the information capacity of this channel largely depends on the perspective distortions while multipath becomes negligible. In this paper, we create a model of this communication system to allow predicting the capacity based on receiver perspective (distance and angle to the transmitter). We calibrate and validate this model through lab experiments wherein information is transmitted from a screen and received with a tablet camera. Our capacity estimates indicate that tens of Mbps is possible using a smartphone camera even when the short code on the screen images onto only 15% of the camera frame. Our estimates also indicate that there is room for at least 2.5× improvement in throughput of existing screen–camera communication prototypes.

Single-Photon Avalanche Diode Imagers Applied to Near-Infrared Imaging

Single-photon avalanche diodes (SPADs) can be integrated into large pixel arrays. The aim of this paper is to present a view on how these imagers change the paradigm of wide-field near-infrared imaging (NIRI). Thanks to the large number of pixels that they offer and to their advanced time-resolved measurement capabilities, new approaches in the image reconstruction can be applied. A SPAD imager was integrated in a NIRI setup to demonstrate how it can improve spatial resolution in reconstructed images. The SPAD imager has a time resolution of 97 ps and a picosecond laser source with an average output power of 3 mW was employed. The large amount of data produced by this new setup could not directly be analyzed with state-of-the art image reconstruction algorithms. Therefore a new theoretical framework was developed. Simulations show that millimetric resolution is achievable with this setup. Experimental results have demonstrated that a resolution of at least 5 mm is possible with the current setup. A discussion about how different characteristics of the SPAD imagers affect the NIRI measurements is presented and possible future improvements are introduced.

Wide bandwidth room-temperature THz imaging array based on antenna-coupled MOSFET bolometer

We report on the design, fabrication and measurements of a new THz sensor concept based on an antenna-coupled MOSFET bolometer for room-temperature passive THz imaging for security and medical-diagnostic applications. The device is fabricated in a 180-nm CMOS SOI technology followed by a post-CMOS MEMS process which guaranties a very high thermal insulation of the sensor. In this sensor, the wide bandwidth THz antenna absorbing the electromagnetic field is directly coupled to the bolometer for maximum energy collection, whereas its design aims at minimizing its thermal mass as is necessary for fast frame rates. DC measurements before and after the MEMS process as well as sensor output signal time constant and THz antenna pattern measurements are presented. The final sensor is part of a large pixel array of 117 elements. Simulated array characteristic is presented proving that the mutual interaction between the pixels is small enough for imaging applications.

A 70μm × 70μm CMOS digital active pixel sensor for digital mammography and X-ray imaging

This work presents an architecture for CMOS active pixel sensors (APS) based on a novel lossless charge integration method, proposed for X-ray imagers in general but specifically optimized for full-field digital mammography. The objective is to provide all the required functionality inside the pixel, so to use full digital control and read-out signals only, therefore avoiding crosstalk between analog lines over large pixel arrays. It includes a novel lossless A/D conversion scheme besides a self-calibrating dark current cancellation circuit, a self-biasing circuitry, biphasic current sensing for the collection of electrons (e-) or holes (h+) and built-in test. Furthermore, FPN compensation is available by individually addressing the pixel's internal DAC controlling the gain. Implemented in a 0.18μm 1P6M CMOS technology with MiM capacitors, everything fits into a 70μm by 70μm due to the extensive reuse of available blocks and aggressive layout techniques. Also, thanks to the MOSFET subthreshold operation, the average power consumption is as low as 8μW/pixel.

Particle Display System — Virtually Perceivable Pixels with Randomly Distributed Physical Pixels —

In this study, the authors propose and implement a particle display system (PDS) that consists of hundreds of randomly distributed pixels. The wireless capability of this system enables each node to move freely without distant limitation of the use of wire cables. The authors also propose effective visual presentation techniques for a display system with randomly distributed pixels. One of the optimization techniques involves the extension of a well-known phenomenon where humans can perceive two-dimensional static or moving images from a set of high-frequency flashing one-dimensional pixel arrays, such as LED arrays, as a characteristic of a human's vision system. While this technique can only extend the virtual resolution of a display in a direction perpendicular to the aligned pixels, our technique enables the display of multi-directional scrolling of two-dimensional images with randomly distributed pixels. In addition, the advantages of presenting information on a display with nonuniform pixel distribution and virtual pixels with fast flash of pixels are discussed. The proposed techniques help in reducing the cost of installing a large-scale display and the time taken for the initial preparation of the setup, which involves carrying large pixel arrays and determining the precise size and shape of the display.

Development of High Count Rate TES Microcalorimeters

To realize new TES imaging for high energy X-ray or gamma-ray spectrometer with a large pixel array and high count rate, we will try to develop a new radiation absorber self-adjusting the operating temperature and adopting an original reading out method of large pixel array using parallel biasing scheme. Our first prototype TES pixel using Au/Ti/Au tri-layer which consists of the small heat sensors and the radiation absorption area, and these are biased in serial. In this device, the current pulse with the decay time constant of less than 20 microseconds of incident X-rays from 55Fe source were observed.

X-ray Microcalorimeter Based on Superconducting Transition Edge Sensors

We have tried to realize an X-ray imaging spectrometer based on the superconducting transition edge sensor (TES) with high energy resolution, a large pixel array, a relatively high absorption efficiency and a high count rate. Our single pixel of Ir/Au TES achieved an excellent energy resolution of 9.4 eV for 5.9 keV X-rays. We have also proposed a pixellated array of Ir-TES where we slightly modify the bias point of each pixel and identify the pixel from the response function of each pixel. Our 10-pixel device, where all pixels are parallel biased, obtained 13 eV (FWHM) at 3 keV energy resolution and 80 microm position resolution. So far, we could successfully operate a 20-pixels device. Further, we are now trying to improve the count rate and the absorption efficiency of TESes, by developing our original new TES geometry which having a radiation absorber that self-adjusts the operating temperature.

Recent progress in the development of a monolithic active pixel detector for a B factory

Monolithic Active Pixel Sensors (MAPS) may become the building blocks of vertex detectors at future high luminosity e + e - colliders. Requiring an active layer only a few tens of microns thick, MAPS can be thinned to ∼ 50 μ m , which reduces the multiple scattering of primary particles. Deep sub-micron CMOS processes allow for small pixel size, needed for adequate single point resolution and low occupancy at a Super B factory. Major concerns with MAPS are readout speed and signal stability for large pixel arrays. Laser bench test results of a full size prototype (CAP3) with 118,784 readout pixels and a 5-deep correlated double sampling pipeline are presented. Lessons learned are applied to a design iteration and investigation of two new digital readout sensor designs, all included in the CAP4 prototype chip.