The Speedster-EXD is a new 64×64 pixel2, 40-μm pixel pitch, 100-μm depletion depth hybrid CMOS x-ray detector with the capability of reading out only those pixels containing event charge, thus enabling fast effective frame rates. A global charge threshold can be specified, and pixels containing charge above this threshold are flagged and read out. The Speedster detector has also been designed with other advanced in-pixel features to improve performance, including a low-noise, high-gain capacitive transimpedance amplifier that eliminates interpixel capacitance crosstalk (IPC), and in-pixel correlated double sampling subtraction to reduce reset noise. We measure the best energy resolution on the Speedster-EXD detector to be 206 eV (3.5%) at 5.89 keV and 172 eV (10.0%) at 1.49 keV. The average IPC to the four adjacent pixels is measured to be 0.25%±0.2% (i.e., consistent with zero). The pixel-to-pixel gain variation is measured to be 0.80%±0.03%, and a Monte Carlo simulation is applied to better characterize the contributions to the energy resolution.
We present the characterization of a new event-driven X-ray hybrid CMOS detector developed by Penn State University in collaboration with Teledyne Imaging Sensors. Along with its low susceptibility to radiation damage, low power consumption, and fast readout time to avoid pile-up, the Speedster-EXD has been designed with the capability to limit its readout to only those pixels containing charge, thus enabling even faster effective frame rates. The threshold for the comparator in each pixel can be set by the user so that only pixels with signal above the set threshold are read out. The Speedster-EXD hybrid CMOS detector also has two new in-pixel features that reduce noise from known noise sources: (1) a low-noise, high-gain CTIA amplifier to eliminate crosstalk from interpixel capacitance (IPC) and (2) in-pixel CDS subtraction to reduce kTC noise. We present the read noise, dark current, IPC, energy resolution, and gain variation measurements of one Speedster-EXD detector.
NASA's Chandra X-ray Observatory continues to provide an unparalleled means for exploring the high-energy universe. With its half-arcsecond angular resolution, Chandra studies have deepened our understanding of galaxy clusters, active galactic nuclei, galaxies, supernova remnants, neutron stars, black holes, and solar system objects. As we look beyond Chandra, it is clear that comparable or even better angular resolution with greatly increased photon throughput is essential to address ever more demanding science questions—such as the formation and growth of black hole seeds at very high redshifts; the emergence of the first galaxy groups; and details of feedback over a large range of scales from galaxies to galaxy clusters. Recently, we initiated a concept study for such a mission, dubbed X-ray Surveyor. The X-ray Surveyor strawman payload is comprised of a high-resolution mirror assembly and an instrument set, which may include an X-ray microcalorimeter, a high-definition imager, and a dispersive grating spectrometer and its readout. The mirror assembly will consist of highly nested, thin, grazing-incidence mirrors, for which a number of technical approaches are currently under development—including adjustable X-ray optics, differential deposition, and new polishing techniques applied to a variety of substrates. This study benefits from previous studies of large missions carried out over the past two decades and, in most areas, points to mission requirements no more stringent than those of Chandra.
The proposed SMART-X telescope consists of a pixelated array of a piezoelectric lead zirconate titanate (PZT) thin film
deposited on flexible glass substrates. These cells or pixels are used to actively control the overall shape of the mirror
surface. It is anticipated that the telescope will consist of 8,000 mirror panels with 400-800 cells on each panel. This
creates an enormous number (6.4 million) of traces and contacts needed to address the PZT. In order to simplify the
design, a row/column addressing scheme using ZnO thin film transistors (TFTs) is proposed. In addition, connection of
the gate and drain lines on the mirror segment to an external supply via a flexible cable was investigated through use of
an anisotropic conductive film (ACF). This paper outlines the design of the ZnO TFTs, use of ACF for bonding, and
describes a specially designed electronics box with associated software to address the desired cells.
We present preliminary characterization of the Speedster-EXD, a new event driven hybrid CMOS detector (HCD) developed in collaboration with Penn State University and Teledyne Imaging Systems. HCDs have advantages over CCDs including lower susceptibility to radiation damage, lower power consumption, and faster read-out time to avoid pile-up. They are deeply depleted and able to detect x-rays down to approximately 0.1 keV. The Speedster-EXD has additional in-pixel features compared to previously published HCDs including: (1) an in-pixel comparator that enables read out of only the pixels with signal from an x-ray event, (2) four different gain modes to optimize either full well capacity or energy resolution, (3) in-pixel CDS subtraction to reduce read noise, and (4) a low-noise, high-gain CTIA amplifier to eliminate interpixel capacitance crosstalk. When using the comparator feature, the user can set a comparator threshold and only pixels above the threshold will be read out. This feature can be run in two modes including single pixel readout in which only pixels above the threshold are read out and 3x3 readout where a 3×3 region centered on the central pixel of the X-ray event is read out. The comparator feature of the Speedster-EXD increases the detector array effective frame rate by orders of magnitude. The new features of the Speedster-EXD hybrid CMOS x-ray detector are particularly relevant to future high throughput x-ray missions requiring large-format silicon imagers.
Si Hybrid CMOS detectors (HCDs) are sensitive to X-rays between approximately 0.2 – 20 keV. HCDs can provide superior performance to traditional CCDs in multiple areas: faster read out time, windowed read out mode, less susceptible to radiation & micrometeoroid damage, and lower power consumption. X-ray detectors designed for use in astronomical observatories must have an optical blocking filter to prevent the detectors from being saturated by optical light. We have previously reported on the successful deposition of an Al optical blocking layer directly onto the surface of HCDs. These blocking filters were deposited with multiple thicknesses from 180 – 1000 Å and successfully block optical light at all thicknesses, with minimal impact expected on quantum efficiency at the energies of interest for these detectors. The thin Al layer is not expected to impact quantum efficiency at the energies of interest for these detectors. We report energy dependent soft X-ray quantum efficiency measurements for multiple HCDs with different optical blocking filter thicknesses.
We report on the characterization of four HAWAII Hybrid Si CMOS detectors (HCD) developed for use as X-ray
detectors as part of a joint program between Penn State University and Teledyne Imaging Sensors (TIS).
Interpixel capacitive crosstalk (IPC) has been measured for standard H1RG detectors as well as a specially
developed H2RG that uses a unique bonding structure. The H2RG shows significant reduction in IPC, as reported
by Griffith et al. 2012. Energy resolution at 1.5 & 5.9 keV was measured as well as read noise for each detector.
Dark current as a function of temperature is reported from 150 – 210 K and dark current figures of merit are
estimated for each detector. We also discuss upcoming projects including testing of a new HCD called the
Speedster-EXD. This prototype detector will have a low noise, high gain CTIA to reduce IPC and read noise as
well as in-pixel CDS and event flagging. In the coming year PSU and TIS will begin work on a project to
incorporate CTIA and CDS circuitry into the ROIC of a HAWAII HCD like detector to satisfy the small pixel and
high rate needs of future X-ray observatories.
Future space-based X-ray telescope missions are likely to have significantly increased demands on detector read out
rates due to increased collection area, and there will be a desire to minimize radiation damage in the interests of
maintaining spectral resolution. While CCDs have met the requirements of past missions, active pixel sensors are likely
to be a standard choice for some future missions due to their inherent radiation hardness and fast, flexible read-out
architecture. One form of active pixel sensor is the hybrid CMOS sensor. In a joint program of Penn State University
and Teledyne Imaging Sensors, hybrid CMOS sensors have been developed for use as X-ray detectors. Results of this
development effort and tests of fabricated detectors will be presented, along with potential applications for future
We present the results of x-ray measurements on a hybrid CMOS detector that uses a H2RG ROIC and a unique
bonding structure. The silicon absorber array has a 36μm pixel size, and the readout array has a pitch of 18μm;
but only one readout circuit line is bonded to each 36x36μm absorber pixel. This unique bonding structure gives
the readout an effective pitch of 36μm. We find the increased pitch between readout bonds significantly reduces
the interpixel capacitance of the CMOS detector reported by Bongiorno et al. 20101 and Kenter et al. 2005.2
The Gravity and Extreme Magnetism Small Explorer (GEMS) is an astrophysical observatory dedicated to X-ray
polarimetry (2-10 keV) and is being developed for launch in 2014. To maximize the polarization sensitivity of the
observatory, GEMS uses polarimeters based on the photoelectric effect with a gas micropattern time projection chamber
(TPC). We describe the TPC polarimeter concept and the details of the GEMS implementation, including factors that
affect the ultimate polarization sensitivity, including quantum efficiency, modulation factor, systematic errors, and
A gamma-ray burst polarimeter (GRBP) is being developed at NASA Goddard Space Flight Center for measuring the Xray
polarization of energetic transients in the 2 - 10 keV energy range. The primary goal is to measure the polarization
of the prompt X-ray emission from gamma-ray bursts (GRBs) in order to distinguish between the possible emission
mechanisms. The instrument could also be capable of measuring polarization from other X-ray transients, such as soft
gamma repeaters (SGRs) or black hole transients. An instrument with a wide field of view is required to detect transient
events and a large collecting area is required to have sufficient sensitivity. The GRBP is a time projection chamber
(TPC) that uses negative ions as a charge carrier enabling a large volume, high spatial resolution detector. We describe a
GRBP prototype that is suitable for a sounding rocket measurement of the Crab Nebula or for measurements of bright
transient sources from a small satellite.