Sensor Chip Assemblies Research Articles

Teledyne's high‐performance 4 K × 4 K infrared detectors

AbstractWe present the test results of science grade 4 K × 4 K HgCdTe H4RG‐15 and H4RG‐10 SWIR 2.5 μm sensor chip assemblies (SCAs). Teledyne's 4 K × 4 K, 15 and 10 μm pixel pitch infrared arrays are developed for space and era of Extremely Large Telescopes. They are currently being used in new instrumentation on existing telescopes and missions. We report data on H4RG‐15 and H4RG‐10 arrays that have achieved science grade performance. For H4RG‐15 and H4RG‐10: very low dark current (<0.005 e−/pixel/s at 80 K and <0.01 e−/pixel/s at 95 K), high quantum efficiency >70–90%, single CDS readout noise <20 e−, operability >99%, total crosstalk <1.5%, well capacity >70 ke−, and power dissipation less than 4 mW are routinely achieved. These SCAs are substrate‐removed HgCdTe, which simultaneously detect visible and infrared light, enabling spectrographs to use a single SCA for visible‐IR sensitivity. Larger focal plane arrays can be constructed by assembling mosaics of individual arrays.

A joint Roman Space Telescope and Rubin Observatory synthetic wide-field imaging survey

ABSTRACT We present and validate 20 deg2 of overlapping synthetic imaging surveys representing the full depth of the Nancy Grace Roman Space Telescope High-Latitude Imaging Survey (HLIS) and 5 yr of observations of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). The two synthetic surveys are summarized, with reference to the existing 300 deg2 of LSST simulated imaging produced as part of Dark Energy Science Collaboration (DESC) Data Challenge 2 (DC2). Both synthetic surveys observe the same simulated DESC DC2 universe. For the synthetic Roman survey, we simulate for the first time fully chromatic images along with the detailed physics of the Sensor Chip Assemblies derived from lab measurements using the flight detectors. The simulated imaging and resulting pixel-level measurements of photometric properties of objects span a wavelength range of ∼0.3–2.0 μm. We also describe updates to the Roman simulation pipeline, changes in how astrophysical objects are simulated relative to the original DC2 simulations, and the resulting simulated Roman data products. We use these simulations to explore the relative fraction of unrecognized blends in LSST images, finding that 20–30 per cent of objects identified in LSST images with i-band magnitudes brighter than 25 can be identified as multiple objects in Roman images. These simulations provide a unique testing ground for the development and validation of joint pixel-level analysis techniques of ground- and space-based imaging data sets in the second half of the 2020s – in particular the case of joint Roman–LSST analyses.

Landsat 8 Thermal Infrared Sensor Scene Select Mechanism Open Loop Operations

The Landsat 8 (L8) spacecraft and its two instruments, the operational land imager (OLI) and thermal infrared sensor (TIRS), have been consistently characterized and calibrated since its launch in February 2013. These performance metrics and calibration updates are determined through the U.S. Geological Survey (USGS) Landsat image assessment system (IAS), which has been performing this function since its launch. The TIRS on-orbit geometric calibration procedures include TIRS-to-OLI alignment, TIRS sensor chip assembly (SCA) alignment, and TIRS band alignment. In December 2014, the TIRS instrument experienced an anomalous condition related to the instrument’s ability to accurately measure the location of the scene select mechanism (SSM). The SSM is a rotating mirror that allows the instrument’s field of view to be pointed at the Earth, for normal imaging, or at either deep space or an onboard black body, for radiometric calibration purposes. This anomalous condition in the SSM’s position sensor made it necessary to implement a new mode of operation for this mirror, termed mode-0. Mode-0 involves operating the mirror in an open-loop control state during normal mission operations when acquiring Earth data. Closed-loop mode-4 is needed for directing the mirror towards the radiometric calibration targets and is used approximately once every two weeks to collect radiometric calibration data. Mode-0 is used for most operational imaging because it does not require SSM encoder data, thereby allowing the SSM encoder electronics to remain unpowered most of the time, reducing its use throughout the lifetime of the TIRS instrument, thus helping to preserve its nominal behavior during it use. This paper discusses the geometric calibration of the SSM mirror during its current normal mode-0 set of image operations, as its open-loop control allows the mirror to drift over time in its uncontrolled state and its effects on products. The results shown in this paper demonstrate that the ability to have ongoing updates to the modeling of the TIRS SSM mirror model, in both an automated fashion and with a set of more manual operations, allows accuracy that approaches mode-4 results within days from the start of a mode-0 event.

Brighter-fatter Effect in Near-infrared Detectors—III. Fourier-domain Treatment of Flat Field Correlations and Application to WFIRST

Weak gravitational lensing has emerged as a leading probe of the growth of cosmic structure. However, the shear signal is very small and accurate measurement depends critically on our ability to understand how non-ideal instrumental effects affect astronomical images. The Wide-Field Infrared Survey Telescope (WFIRST) will fly a focal plane containing 18 Teledyne H4RG-10 near-infrared detector arrays, which present different instrument calibration challenges from previous weak lensing observations. Previous work [Paper I: Hirata & Choi, PASP, 132, 014501 (2020); and Paper II: Choi & Hirata, PASP, 132, 014502 (2020)] has shown that correlation functions of flat field images, including cross-correlations between different time slices that are enabled by the non-destructive read capability of the infrared detectors, are effective tools for disentangling linear and nonlinear inter-pixel capacitance (IPC) and the brighter-fatter effect (BFE). Here we present a Fourier-domain treatment of the flat field correlations, which allows us to expand the previous formalism to all orders in IPC, BFE, and classical nonlinearity. We show that biases in simulated flat field analyses in Paper I are greatly reduced through the use of this formalism. We then apply this updated formalism to flat field data from three WFIRST flight candidate detectors, and explore the robustness to variations in the analysis. We find that the BFE is present in all three detectors, and that its contribution to the flat field correlations dominates over the nonlinear IPC, in accordance with the results from Paper II on a development detector. The magnitude of the BFE is such that the effective area of a pixel is increased by (3.54 ± 0.03) × 10−7 for every electron deposited in a neighboring pixel (sensor chip assembly [SCA] 20829, statistical error, not IPC-deconvolved). We compare IPC maps from flat field autocorrelation measurements to those obtained from the single pixel reset method and find a median difference of 0.113% for SCA 20829. After further diagnosis of this difference, we ascribe it largely to an additional source of cross-talk, the vertical trailing pixel effect, and recommend further work to develop a model for this effect. These results represent a significant step toward calibration of the non-ideal effects in WFIRST detectors.

State-of-the-Art HgCdTe at Raytheon Vision Systems

Dark current density data recorded over the past 14 years at Raytheon Vision Systems on short-wavelength infrared (SWIR) and medium-wavelength infrared (MWIR) devices were examined. This included HgCdTe detector arrays grown by liquid-phase epitaxy on CdZnTe and molecular beam epitaxy on both silicon and CdZnTe substrates. This study analyzed zero-bias resistance–area product and current–voltage measurements from test structure assemblies included on every detector wafer. The data span cutoff wavelengths from 1.7 μm to 7.5 μm and operating temperatures from 40 K to 300 K. A basis is derived for a simple manufacturing trend model for a wide range of cutoffs and temperatures. This model uses a function similar to Tennant’s Rule’07 but includes a generation–recombination (GR) term. Dark current densities below the test set limit are extrapolated assuming GR-limited performance. Model assumptions are tested using sensor chip assembly (SCA) median dark current density values at the same inverse cutoff–temperature products. This model allows probabilistic determination of array manufacturability and prediction of yield, and provides a statistical basis for Raytheon’s state-of-the-art performance.

New and Better Detectors for the JWST Near-Infrared Spectrograph

ESA and NASA recently selected two 5 μm cutoff Teledyne H2RG sensor chip assemblies (SCA) for flight on the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). These HgCdTe SCAs incorporate Teledyne’s “improved barrier layer” design that eliminates the degradation that affected earlier JWST H2RGs. The better indium barrier, together with other design changes that Teledyne phased in from other programs over the years, has improved the performance and reliability of JWST’s SCAs. In this article, we describe the measured performance characteristics that most directly affect scientific observations including read noise, total noise, dark current, quantum efficiency (QE), and image persistence. As part of measuring QE, we inferred the quantum yield over the full NIRSpec pass band of λ = 0.6–5 μm and found that it exceeds unity for photon energies Eγ > (2.65 ± .2)Eg, where Eg is the HgCdTe bandgap energy. This corresponds to λ ≲ 2 μm for NIRSpec’s 5 μm cutoff HgCdTe.

Pixelated Detector With Photon Address Event Driven Time Stamping and Correlation

To allow measurement of the equilibrium density fluctuations on a nanometer-length scale using small angle X-ray scattering, an asynchronous event-driven-address time-stamped (EDATS) pixelated array detector, operational over correlation time spans ranging from less than 10-6 to greater than 104 seconds, was designed, fabricated, and tested. Its performance was validated for use in X-ray photon correlation spectroscopy (XPCS) experiments. The EDATS pixelated detector arrays each include a custom readout integrated circuit (ROIC), the Voxtel model VX-807, hybridized to a silicon photodiode array optimized for 500 eV to 2000 eV X-ray photons. The 492 × 492-element array is composed of each 40-micrometer × 40-micrometer pixel unit cell. The unit cell circuits of the VX-807 ROIC include a low-noise capacitive transimpedence amplifier (CTIA) followed by a C-RC shaping amplifier. These analog front-end (AFE) circuits are used to convert the absorbed X-ray photon signal to a voltage pulse, which may trigger a user-programmable threshold comparator. The detected X-ray photon events are broadcast to token-based address arbitration circuits, at the periphery of the X-ray sensitive pixel array, which recover the address of the photon event and communicate the address to a time-to-digital converter (TDC), where the address is time stamped, with a maximum temporal jitter of 85 nanoseconds. Separate digital arbitration blocks are used in each of the four quadrants of the ROIC, allowing an overall count rate of 100 MHz to be achieved. The VX-807 ROICs were hybridized to pin photodiode arrays fabricated on six-inch silicon-on-insulator (SOI) wafers, with a fully depleted 20-micrometer-thick X-ray-sensitive silicon layer. The hybridized EDATS sensor chip assemblies (SCAs) were then tested and their performance was verified.

A Highly Sensitive Multi-element HgCdTe e-APD Detector for IPDA Lidar Applications

An HgCdTe electron avalanche photodiode (e-APD) detector has been developed for lidar receivers, one application of which is integrated path differential absorption lidar measurements of such atmospheric trace gases as CO2 and CH4. The HgCdTe APD has a wide, visible to mid-wave-infrared, spectral response, high dynamic range, substantially improved sensitivity, and an expected improvement in operational lifetime. A demonstration sensor-chip assembly consisting of a 4.3 μm cutoff HgCdTe 4 × 4 APD detector array with 80 μm pitch pixels and a custom complementary metal–oxide–semiconductor readout integrated circuit was developed. For one typical array the APD gain was 654 at 12 V with corresponding gain normalized dark currents ranging from 1.2 fA to 3.2 fA. The 4 × 4 detector system was characterized at 77 K with a 1.55 μm wavelength, 1 μs wide, laser pulse. The measured unit gain detector photon conversion efficiency was 91.1%. At 11 V bias the mean measured APD gain at 77 K was 307.8 with σ/mean uniformity of 1.23%. The average, noise-bandwidth normalized, system noise-equivalent power (NEP) was 1.04 fW/Hz1/2 with a σ/mean of 3.8%. The measured, electronics-limited, bandwidth of 6.8 MHz was more than adequate for 1 μs pulse detection. The system had an NEP (3 MHz) of 0.4 fW/Hz1/2 at 12 V APD bias and a linear dynamic range close to 1000. A gain-independent quantum-limited SNR of 80% of full theoretical was indicative of a gain-independent excess noise factor very close to 1.0 and the expected APD mode quantum efficiency.

Cross calibration of the Landsat-7 ETM+ and EO-1 ALI sensor

As part of the Earth Observer 1 (EO-1) Mission, the Advanced Land Imager (ALI) demonstrates a potential technological direction for Landsat Data Continuity Missions. To evaluate ALI's capabilities in this role, a cross-calibration methodology has been developed using image pairs from the Landsat-7 (L7) Enhanced Thematic Mapper Plus (ETM+) and EO-1 (ALI) to verify the radiometric calibration of ALI with respect to the well-calibrated L7 ETM+ sensor. Results have been obtained using two different approaches. The first approach involves calibration of nearly simultaneous surface observations based on image statistics from areas observed simultaneously by the two sensors. The second approach uses vicarious calibration techniques to compare the predicted top-of-atmosphere radiance derived from ground reference data collected during the overpass to the measured radiance obtained from the sensor. The results indicate that the relative sensor chip assemblies gains agree with the ETM+ visible and near-infrared bands to within 2% and the shortwave infrared bands to within 4%.

A geometric performance assessment of the EO-1 advanced land imager

The Earth Observing 1 (EO-1) Advanced Land Imager (ALI) demonstrates technology applicable to a successor system to the Landsat Thematic Mapper series. A study of the geometric performance characteristics of the ALI was conducted under the auspices of the EO-1 Science Validation Team. This study evaluated ALI performance with respect to absolute pointing knowledge, focal plane sensor chip assembly alignment, and band-to-band registration for purposes of comparing this new technology to the heritage Landsat systems. On-orbit geometric calibration procedures were developed that allowed the generation of ALI geometrically corrected products that compare favorably with their Landsat 7 counterparts with respect to absolute geodetic accuracy, internal image geometry, and band registration.

Precision and accuracy of eo-1 advanced land imager (ali) data for semiarid vegetation studies

Landsat Thematic Mapper (TM) data and spectral mixture analysis have been used to estimate vegetation green cover in the Great Basin, western United States, to /spl plusmn/4.0% green cover (%GC). In this paper, we compare estimates of percent green cover derived from EO-1 Advanced Land Imager (ALI) data to estimates derived from field-based analyses and to results derived from Landsat Enhanced Thematic Mapper plus (ETM+) data. These analyses define the precision and accuracy of ALI and ETM+ for making quantitative measurements of earth for semiarid ecological studies. The benefits of using ALI were not observed in the calculated uncertainty values (/spl plusmn/5.61%GC and /spl plusmn/6.15%GC for ETM+ and ALI, respectively). However, ALI did not return as many negative green cover estimates and exhibited lower spatial variance in regions of low green cover. These results were attributed to the better signal to noise and data precision inherent to the ALI sensor, and not to the increased number of multispectral bands. ALI was found to be internally inconsistent in that the third sensor chip assembly image swath contained multispectral band coregistration errors. This caused a less than 25%GC error in the ALI estimate of percent green cover along large vegetation gradients.

A miniature pan-tilt actuator: the spherical pointing motor

A pan-tilt mechanism is a computer-controlled actuator designed to point an object such as a camera sensor. For applications in active vision, a pan-tilt mechanism should be accurate, fast, small, inexpensive and have low power requirements. The authors have designed and constructed a new type of actuator meeting these requirements, which incorporates both pan and tilt into a single, two-degree-of-freedom device. The spherical pointing motor (SPM) consists of three orthogonal motor windings in a permanent magnetic field, configured to move a small camera mounted on a gimbal. It is an absolute positioning device and is run open-loop. The SPM is capable of panning and tilting a load of 15 grams, for example a CCD image sensor, at rotational velocities of several hundred degrees per second with a repeatability of .15/spl deg/. The authors have also built a miniature camera consisting of a single CCD sensor chip and miniature lens assembly that fits on the rotor of this motor. In this paper, the authors discuss the theory of the SPM, which includes its basic electromagnetic principles, and derive the relationship between applied currents and resultant motor position. The authors present an automatic calibration procedure and discuss open- and closed-loop control strategies. Finally, the authors present the physical characteristics and results of their prototype.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>