The Pennsylvania State University High-Energy Astrophysics Detector and Instrumentation (HEADI) Lab, in collaboration with Teledyne Imaging Sensors (TIS), has continued its efforts to improve soft x-ray Hybrid CMOS detectors (HCDs) on several fronts. We report on the read noise and energy resolution for the H1RG and the H2RG using a cryogenic SIDECARTM, which gained TRL 9 and flight heritage through the Water Recovery x-ray Rocket Mission in 2018. We also describe the 40-μm event-driven Speedster-EXD HCD, which has been scaled up from a 64×64 array to an 550×550 array. The readout circuitry within the ROIC for the Speedster-EXD contains a high-gain capacitive transimpedance amplifier (CTIA) to negate pixel cross-talk, in-pixel correlated double sampling (CDS) for correction of reset noise variations, and an in-pixel comparator enabling event-driven readout. Here we report on read noise and energy resolution measurements for the Speedster-EXD and discuss the upcoming BlackCAT CubeSAT, on which the Speedster-EXD550 will fly, raising the TRL of these HCDs. Further, to meet the requirements of future high-throughput and high spatial resolution Lynx-like x-ray observatories, HCDs with fast readout and small pixel sizes have been developed. Here we report on the energy resolution and the lowest measured read noise of any x-ray HCD to-date for the 12.5-μm 128×128 prototype Small-pixel HCD, as well as present the current results for the newest x-ray HCD, the Small-pixel1024. The Small-pixel1024 is a 12.5μm 1024×1024 HCD utilizing a high-gain CTIA and in-pixel CDS. Finally, we report on the development efforts between Penn State and Teledyne on a new event-driven HCD, which will retain the low read noise of the Small-pixel HCD while having event-driven capabilities like the Speedster-EXD.
The BlackCAT CubeSat is an X-ray coded-aperture-telescope observatory that is expected to launch in 2025. It is designed for observations of bright X-ray sources in the 0.5–20 keV band. The instrument will have a wide field of view (0.85 steradian) and be capable of catching gamma ray bursts (GRBs) from the distant universe, galactic transients, and flares from blazars, while monitoring the X-ray sky. In addition to the primary high-redshift GRB science, BlackCAT can monitor known source variability and search for rare and exciting events including gravitational-wave X-ray counterparts, magnetar flares, supernova shock breakouts, and tidal disruption events. The mission will thus function as a multiwavelength and multi-messenger complement to present and future facilities including LIGO, VIRGO, KAGRA, IceCube, KM3NET, LSST, LOFAR, SKA, and CTA. Rapid notifications of burst positions will be transmitted to the ground via satellite network and then relayed to the GCN. The name BlackCAT is derived from its scientific emphasis on black-holerelated transient events being observed with a coded aperture telescope (CAT). BlackCAT will serve as the scientific payload aboard a commercial 6U CubeSat spacecraft provided by NanoAvionics US. Novel event-driven X-ray hybrid CMOS detectors will form the focal plane array. In addition to carrying out science programs related to distant GRBs, transients, and X-ray sky monitoring, BlackCAT will also serve as a pathfinder for future economical missions combining multiple BlackCAT modules on either a single small satellite or on multiple CubeSats. BlackCAT will also serve as a platform for new X-ray hybrid CMOS detector development. An overview of BlackCAT in its current development state and its current status will be presented.
BlackCAT is a NASA-funded 6U CubeSat mission planned to be launch-ready in 2025. BlackCAT will use its wide field-of-view and arcminute-scale localization to identify gamma-ray bursts (GRBs), gravitational-wave counterparts, and other high-energy transient events. The mission will send rapid alerts after detection of a transient event, enabling prompt follow-up from other ground- and space-based observatories. The science instrument is a coded aperture telescope, using a focal plane with four Speedster-EXD550 event-driven X-ray hybrid CMOS detectors (HCDs) and a gold-plated nickel coded mask to localize source positions. We describe methods for the calibration of the detectors and the assembled coded-aperture instrument. We also briefly discuss plans for in-flight commissioning and calibration.
Future x-ray observatories will require imaging detectors with fast readout speeds that simultaneously achieve or exceed the other high-performance parameters of x-ray charge-coupled devices used in many missions over the past three decades. Fast readout will reduce the impact of pile-up in missions with large collecting areas while improving the performance in other respects, such as timing resolution. Event-driven readout, in which only pixels with charge from x-ray events are read out, can be used to achieve these faster operating speeds. Speedster-EXD550 detectors are hybrid complementary metal-oxide semiconductor detectors capable of event-driven readout that were developed by Teledyne Imaging Sensors and Penn State University. We present the initial results from measurements of the first of these detectors, demonstrating their capabilities and performance in both full-frame and event-driven readout modes. These include dark current, read noise, gain variation, and energy resolution measurements from the first two engineering-grade devices.
The novel Speedster-EXD550 is a 550×550-pixel x-ray Hybrid CMOS Detector (HCD) with event-driven readout capabilities and 40-micron pixel pitch. In event-driven readout mode, only the pixels that contain sufficient liberated charge from the absorption of an x-ray will be read out. Event-driven readout allows for even faster readout speed than other HCDs, reaching readout speeds up to 10,000 frames/sec. The high frame rate of the Speedster-EXD550 is desirable for future missions as the effects of dark current and x-ray pile-up will be reduced. The readout circuitry within the ROIC for the Speedster-EXD550 contains a high-gain capacitive transimpedance amplifier, in-pixel correlated double sampling, and an in-pixel comparator enabling event-driven readout. The Speedster-EXD550 also utilizes column-parallel on-chip digitization. The ability of the Speedster-EXD550 will be demonstrated on BlackCAT, a funded NASA CubeSat mission. Testing and characterization of the Speedster-EXD550 has been done by the Penn State High Energy Astrophysics Detector and Instrumentation lab in both full-frame and event-driven readout modes. A radioactive 55Fe source was used for the measurements presented. Here, we discuss the methods and recent results for the characterization of the Speedster-EXD550 dark current, read noise, gain, and gain variation.
BlackCAT is a NASA CubeSat mission planned to be launch-ready in early 2025. Using a wide-field telescope, this 6U CubeSat will monitor the soft x-ray sky, searching for high-redshift Gamma-Ray Bursts (GRBs), gravitational-wave counterparts, and other transient events. After detecting burst events, BlackCAT will be capable of transmitting rapid alerts to enable prompt follow-up observations. The instrument is composed of a coded-aperture telescope using an array of event-driven x-ray Hybrid CMOS Detectors (HCDs) in its focal plane. In this paper, we provide a brief update on the design and status of the mission.
The BlackCAT CubeSat will monitor the soft x-ray sky, searching for high-redshift gamma-ray bursts (GRBs), gravitational-wave counterparts, and other high-energy transient events. BlackCAT will utilize a coded-aperture mask to localize sources to sub-arcminute precision. We investigate the primary forms of background that will affect this mission and present different methods to suppress these sources in order to increase the sensitivity of this mission. In the absence of mitigation, the optical and ultraviolet backgrounds could increase noise in the hybrid CMOS detectors (HCDs) used in this mission and potentially trigger spurious events. We plan to use a polyimide filter to suppress extreme ultraviolet emission produced by the geocorona. The HCDs and polyimide filter will be coated with a thin aluminum layer to block optical light. We estimate the magnitude of the observed cosmic and galactic X-ray backgrounds. Additionally, we investigate the impact of trapped particles on the sensitivity and duty cycle of the mission. We discuss the effect of these various sources of background on the sensitivity of BlackCAT to GRBs and other transient events.
The BlackCAT observatory makes use of a 6U CubeSat platform with an x-ray coded aperture telescope payload. BlackCAT, utilizing its wide field-of-view (0.9 steradians), will monitor deep space for a variety of x-ray transients and flares, with a primary focus on high redshift gamma-ray bursts. The payload consists of a detector module (DM), a dedicated electronics package, mechanical mounts, and thermal straps for passive cooling. The DM includes the DM housing, coded aperture mask, optical blocking filter (OBF), and a focal plane array (FPA) consisting of four x-ray hybrid CMOS detectors (HCDs). Each of these four detectors is a 550×550-pixel Speedster-EXD silicon sensor with a molybdenum package to provide a low-strain thermal and mechanical mounting structure. The primary purpose of the electronics package is reading out and processing data from the HCDs. For optimal scientific performance, the FPA must be maintained at a temperature of -40°C or below. The detectors have an aluminum OBF directly deposited because the silicon detectors are sensitive to optical light. For additional optical blocking against the brightest optical background and UV light, a separate OBF will be mounted in front of the detector surface. The coded aperture mask is a wire mesh made of nickel with a thin layer of gold coating all sides. The mask allows approximately 40% of incident x-rays to strike the detector in a unique pattern that is dependent upon source position and the open cell geometry. This allows for the angular position of the source to be determined to sub-arcminute precision. To prevent deformation due to thermal strain, the mask is required to maintain a set temperature between 10°C and 20°C. The DM housing acts as the primary support structure for the payload and is thick enough to provide shielding from off-axis x-rays and optical/UV light. The OBF is directly connected to the DM housing, while the mask and FPA are both thermally isolated via standoffs to meet respective temperature requirements. Additionally, the DM housing is the interface between the payload components and the chassis. We present an overview of the mechanical and thermal payload requirements, as well as design constraints imposed by the 6U CubeSat form factor. We describe the designs used to meet these requirements and present analyses to demonstrate the efficacy of these designs. The mechanical requirements and information from thermal analyses will drive the overall design of the BlackCAT CubeSat to achieve the science goals throughout the mission lifetime.
Next-generation x-ray observatories, such as the Lynx X-ray Observatory Mission Concept or other similar concepts in the coming decade, will require detectors with high quantum efficiency (QE) across the soft x-ray band to observe the faint objects that drive their mission science objectives. Hybrid CMOS detectors (HCDs), a form of active-pixel sensor, are promising candidates for use on these missions because of their fast read-out, low power consumption, and intrinsic radiation hardness. We present QE measurements of a Teledyne H2RG HCD, performed using a gas-flow proportional counter as a reference detector. We find that this detector achieves high QE across the soft x-ray band, with an effective QE of 94.6 ± 1.1 % at the Mn Kα / Kβ energies (5.90/6.49 keV), 98.3 ± 1.9 % at the Al Kα energy (1.49 keV), 85.6 ± 2.8 % at the O Kα energy (0.52 keV), and 61.3 ± 1.1 % at the C Kα energy (0.28 keV). These values are in good agreement with our model, based on the absorption of detector layers. We find similar results in a more restrictive analysis considering only high-quality events, with only somewhat reduced QE at lower energies.
Next-generation X-ray observatories, such as the Lynx X-ray Observatory Mission Concept, will require detectors with high quantum efficiency (QE) across the soft X-ray band to observe the faint objects that drive their mission science cases. Hybrid CMOS Detectors (HCDs), a form of active-pixel sensor, are promising candidates for use on these missions because of their faster read-out, lower power consumption, and greater radiation hardness than detectors used in the current generation of X-ray telescopes. In this work, we present QE measurements of a Teledyne H2RG HCD. These measurements were performed using a gas-flow proportional counter as a reference detector to measure the absolute flux incident on the HCD. We find an effective QE of 95:0 ± 1:1% at the Mn ∝/Kβ lines (at 5.9 and 6.5 keV), 98:5 ± 1:8% at the Al Ka line (1.5 keV), and 85:0 ± 2:8% at the O K∝ line (0.52 keV).
We report on the results of an experiment to determine the effects of radiation damage caused by high-energy protons on an x-ray hybrid CMOS detector. This detector was utilized in a previous proton radiation experiment, which delivered a total dose to a selected region of ∼3 krad (Si). With updated hardware and experimental procedures, we further irradiated the detector with 7-MeV protons, delivering an additional 1.5 krad (Si) (2.78 × 109 protons / cm2 10 MeV equivalent) with increased uniformity to an overlapping region. The effects of this radiation on several important detector characteristics were analyzed after delivering doses of 0.5 and 1.0 krad. After 16 h of annealing at room temperature, detector performance was found to be unchanged in both cases.
The Water Recovery X-Ray Rocket (WRXR) was a suborbital rocket payload that was launched and recovered in April 2018. The WRXR flew two technologies being developed for future large x-ray missions: x-ray reflection gratings and a hybrid CMOS detector (HCD). The large-format replicated gratings on the WRXR were measured in ground calibrations to have absolute single-order diffraction efficiency of ∼60 % , ∼50 % , and ∼35 % at CVI, OVII, and OVIII emission energies, respectively. The HCD was operated with ∼6 e − read noise and ∼88 eV energy resolution at 0.5 keV. The WRXR was also part of a two-payload campaign that successfully demonstrated NASA sounding rocket water recovery technology for science payloads. The primary instrument, a soft x-ray grating spectrometer, targeted diffuse emission from the Vela supernova remnant over a field-of-view >10 deg2. The flight data show that the detector was operational during flight and detected x-ray events from an on-board calibration source, but there was no definitive detection of x-ray events from Vela. Flight results are presented along with a discussion of factors that could have contributed to the null detection.
The High Definition X-ray Imager (HDXI) is one of three planned instruments for the next generation Lynx mission concept and would provide fine spatial resolution X-ray imaging and moderate spectral resolution over a wide field-of-view. The instrument is baselined to rapidly read out large silicon focal plane arrays consisting of small pixels. We present the most recent results from small-pixel X-ray hybrid CMOS detectors that are designed to meet these needs. These devices implement crosstalk-eliminating capacitive transimpedance amplifiers as well the ability to perform in-pixel correlated double sampling, and have achieved noise and spectral resolution approaching the notional requirements of Lynx-HDXI. Read noise as low as 5.4 e- (RMS) has been measured, along with energy resolution (FWHM) as good as 158 eV at 5.9 keV, 78 eV at 0.52 keV, and 71 eV at 0.28 keV.
Understanding the effects of high energy proton radiation is essential in planning for the next generation of X-ray space telescopes. We report on the results of an experiment in which an X-ray hybrid CMOS detector was incrementally irradiated with 8 MeV protons up to a total absorbed dose of approximately 3 krad(Si) (4.5 x 109 protons/cm2). The effect of the damage caused by the high energy protons is then analyzed in the context of several detector characteristics, including read noise, dark current, and energy resolution.
The Water Recovery X-ray Rocket (WRXR) mission was a sounding rocket flight that targeted the northern part of the Vela supernova remnant with a camera designed to image the diffracted X-rays using a grating spectrometer optimized for OVII, OVIII, and CVI emissions. The readout camera for WRXR utilized a silicon hybrid CMOS detector (HCD) with an active area of 36.9 36.9 mm. A modified H2RG X-ray HCD, with 1024 1024 active silicon pixels bonded to the H2RG read-out integrated circuit, was selected for this mission based on its characteristics, technology maturation, and ease of implementation into the existing payload. This required a new camera package for the HCD to be designed, built, calibrated, and operated. This detector and camera system were successfully operated in-flight and its characteristics were demonstrated using the on-board calibration X-ray source. In this paper, a detailed description of this process, from design concept to flight performance, will be given. A full integrated instrument calibration will also be discussed, as well as the temperature dependency measurements of gain variation, read noise, and energy resolution for the HCD.
X-ray hybrid CMOS detectors (HCDs) are a promising candidate for future x-ray missions requiring high throughput and fine angular resolution along with large field-of-view, such as the high-definition x-ray imager (HDXI) instrument on the Lynx x-ray surveyor mission concept. These devices offer fast readout capability, low power consumption, and radiation hardness while maintaining high detection efficiency from 0.2 to 10 keV. In addition, x-ray hybrid CMOS sensors may be fabricated with small pixel sizes to accommodate high-resolution optics and have shown great improvements in recent years in noise and spectral resolution performance. In particular, 12.5-μm pitch prototype devices that include in-pixel correlated double sampling capability and crosstalk eliminating capacitive transimpedance amplifiers, have been fabricated and tested. These detectors have achieved read noise as low as 5.4 e − , and we measure the best energy resolution to be 148 eV (2.5%) at 5.9 keV and 78 eV (14.9%) at 0.53 keV. We will describe the characterization of these prototype small-pixel x-ray HCDs, and we will discuss their applicability to the HDXI instrument on Lynx.
Soft x-rays (0.1 to 10 keV) will liberate between tens and thousands of electrons from the absorber array of a depleted silicon detector. These electrons tend to diffuse outward into what is referred to as the charge cloud, which is then picked up by several pixels and forms a specific pattern based on the exact incident location of the x-ray. By performing the first ever application of a “mesh experiment” on a hybrid CMOS detector (HCD), we have experimentally determined the charge cloud shape and used it to perform subpixel localization of incident x-rays on a photon-by-photon basis for a custom 36-μm pixel pitch H2RG HCD. We find that significant spatial resolution improvement is possible for all events, with 68% confidence regions equal to 7.1 × 7.1, 0.4 × 7.1, and 0.4 × 0.4 μm for 1-pixel, 2-pixel, and 3- to 4-pixel events, respectively. This represents a much finer resolution than that provided by containment within a single pixel.
Publisher’s Note: This paper, originally published on 20 July 2018, was replaced with a corrected/revised version on 12 October 2018. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
Next generation X-ray mission concepts (e.g. Lynx) call for a wide field X-ray imager with high detection
efficiency from 0.2 keV to 10 keV and fast readout capability (> 10 Hz frame rate). In order to properly sample
the planned fine angular resolution of the optical assembly (0:5’’ HPD), small pixel sizes of less than or equal to
16 microns are required. Hybrid CMOS detectors are a type of active pixel sensor that is well suited to the high
throughput and wide bandpass requirements of such instruments, and the pixel size goals are well within reach.
In collaboration with Teledyne Imaging Sensors, the Penn State X-ray detector lab has developed new small
pixel Hybrid CMOS sensors to meet these needs. These prototype 128 x 128 pixel devices have 12.5 micron pixel
pitch, 100 micron fully depleted depth, and include crosstalk-eliminating CTIA amplifiers and in-pixel correlated
double sampling capability. We report on characteristics of one of these new detectors, including read noise,
energy resolution, and pixel-to-pixel gain variation. The read noise was measured to be as low as 5:54 e- ± 0:05
e-, while the gain variation was found to be 1:12% ± 0:06%. The energy resolution, including calibration for
gain variation, was measured to be as good as 148 eV (2.5%) at 5.9 keV.
We report on the initial results of an experiment to determine the effects of proton radiation damage on an X-ray hybrid CMOS detector (HCD). The device was irradiated at the Edwards Accelerator Lab at Ohio University with 8 MeV protons, up to a total absorbed dose of 3 krad(Si) (4.5 x 109 protons/cm2). The effects of this radiation on read noise, dark current, gain, and energy resolution are then analyzed. This exposure is the first of several which will be used for characterizing detector performance at absorbed dose levels that are relevant for imaging devices operating in a deep-space environment.
X-ray Hybrid CMOS Detectors (HCDs) have advantages over X-ray CCDs due to their higher readout rate abilities, flexible readout, inherent radiation hardness, and low power, which make them more suitable for the next generation large-area X-ray telescope missions. The Penn State high energy astronomy laboratory has been working on the development and characterization of HCDs in collaboration with Teledyne Imaging Sensors (TIS). A custom-made H2RG detector with 36 μm pixel pitch and 18 μm ROIC shows an improved performance over standard H1RG detectors, primarily due to a reduced level of inter-pixel capacitance crosstalk (IPC). However, the energy resolution and the noise of the detector and readout system are still limited when utilizing a SIDECAR at non-cryogenic temperatures. We characterized an H2RG detector with a Cryo-SIDECAR readout and controller, and we find an improved energy resolution of ∼2.7 % at 5.9 keV and read noise of ∼6.5 e- . Detections of the ∼0.525 keV Oxygen Kα and ∼0.277 keV Carbon Kα lines with this detector display an improved sensitivity level at lower energies. This detector was successfully flown on NASA’s first water recovery sounding rocket flight on April 4th, 2018. We have also been developing several new HCDs with potential applications for future X-ray astronomy missions. We are characterizing the performance of small-pixel HCDs (12.5 μm pitch), which are important for the development of a next-generation high-resolution imager with HCDs. The latest results on these small pixel detectors has shown them to have the best read noise and energy resolution to-date for any X-ray HCD, with a measured 5.5 e- read noise for a detector with in-pixel correlated double sampling. Event recognition in HCDs is another exciting prospect. We characterized a 64 × 64 pixel prototype Speedster-EXD detector that uses comparators in each pixel to read out only those pixels having detectable signal, thereby providing an order of magnitude improvement in the effective readout rate. Currently, we are working on the development of a large area Speedster-EXD with a 550 × 550 pixel array. HCDs can also be utilized as a large FOV instrument to study the prompt and afterglow emissions of GRBs and detect black hole transients. In this context, we are characterizing a Lobster-HCD system for future CubeSat experiments. This paper briefly presents these new developments and experimental results.
X-ray lobster optics provide a unique way to focus X-rays onto a small focal plane imager with wide field of view imaging. Such an instrument with angular resolution of a few arcminutes can be used to study GRB afterglows, as well as the variability and spectroscopic characteristics for other astrophysical objects. At Penn state University, we characterize these lobster optics with an H1RG CMOS sensor (100 μm thick Silicon with 18 μm pixel size), procured from Teledyne Imaging Sensors at its focal plane. The light-weight compact lobster optic with a 25 cm focal length provides two dimensional imaging with ~25 cm^2 effective area at 2 keV. We chose the hybrid CMOS detector (HCD) since X-ray HCDs offer several advantages (e.g. radiation hard, low power, faster and flexible readout rate) over CCDs for future X-ray missions. We utilize 47 m long X-ray beam line at Penn state University to do our experiments where we characterize the overall effective area of the instrument at 1.5 - 8 keV for both on-axis and off-axis angles. In this presentation, we will describe the characterization test stand and methods, as well as the detailed results. We perform ray-tracing simulations to theoretically validate the results which would also be briefly discussed here. While this is simply a proof-of-concept experiment, such an instrument with significant collecting area can be explored for future rocket or CubeSat experiments.
The Water Recovery X-ray Rocket (WRXR) is a sounding rocket payload that will launch from the Kwajalein Atoll in April 2018 and seeks to be the first astrophysics sounding rocket payload to be water recovered by NASA. WRXR's primary instrument is a grating spectrometer that consists of a mechanical collimator, X-ray reflection gratings, grazing-incidence mirrors, and a hybrid CMOS detector. The instrument will obtain a spectrum of the diffuse soft X-ray emission from the northern part of the Vela supernova remnant and is optimized for 3rd and 4th order OVII emission. Utilizing a field of view of 3.25° × 3.25° and resolving power of λ/δλ ≈40-50 in the lines of interest, the WRXR spectrometer aims to achieve the most highly-resolved spectrum of Vela's diffuse soft X-ray emission. This paper presents introductions to the payload and the science target.
The Penn State X-ray detector lab, in collaboration with Teledyne Imaging Sensors (TIS), have progressed their efforts to improve soft X-ray Hybrid CMOS detector (HCD) technology on multiple fronts. Having newly acquired a Teledyne cryogenic SIDECARTM ASIC for use with HxRG devices, measurements were performed with an H2RG HCD and the cooled SIDECARTM. We report new energy resolution and read noise measurements, which show a significant improvement over room temperature SIDECARTM operation. Further, in order to meet the demands of future high-throughput and high spatial resolution X-ray observatories, detectors with fast readout and small pixel sizes are being developed. We report on characteristics of new X-ray HCDs with 12.5 micron pitch that include in-pixel CDS circuitry and crosstalk-eliminating CTIA amplifiers. In addition, PSU and TIS are developing a new large-scale array Speedster-EXD device. The original 64 × 64 pixel Speedster-EXD prototype used comparators in each pixel to enable event driven readout with order of magnitude higher effective readout rates, which will now be implemented in a 550 × 550 pixel device. Finally, the detector lab is involved in a sounding rocket mission that is slated to fly in 2018 with an off-plane reflection grating array and an H2RG X-ray HCD. We report on the planned detector configuration for this mission, which will increase the NASA technology readiness level of X-ray HCDs to TRL 9.
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