The Nancy Grace Roman Space Telescope project is NASA's next flagship astrophysics mission to study dark energy, dark matter, and exoplanets along with the innumerable topics that will be enabled by the infrared survey telescope's instruments. The Wide Field Instrument contains a focal plane of 18 newly developed Teledyne H4RG-10 HgCdTe detectors. Roman's focal plane completed its first system level thermal vacuum test at NASA Goddard in 2022, when an increase in dark current compared to component level testing was observed for several detectors. Roman chartered an anomaly review board (ARB) and in collaboration with Teledyne undertook a testing program to help identify possible root cause and select from Roman's spare inventory suitable replacement detectors for devices that had significantly degraded. A possible root cause was determined by the ARB along with recommendations for how to prevent further degradation. We summarize the initial observation of the detector anomaly, present the detector testing strategy to find suitable spares and provide evidence of root cause, share the general findings of the ARB, and show new data showing the improved dark current performance.
KEYWORDS: Sensors, Crosstalk, Signal to noise ratio, Signal detection, Field effect transistors, Interference (communication), Resistors, Equipment, Observatories, Cryogenics
The Hawaii-4RG near-infrared detectors offer several output configurations in which the detectors can be interfaced with the European Southern Observatory cryogenic preamplifiers. The buffered mode of output operation has the advantages of higher speed and lower electrical crosstalk between the outputs, reduced unit cell current, etc. One of the effects of the buffered mode operation is increased glow at the bottom of the array due to the operation of the output buffers compared to the unbuffered mode. The excess glow can be a limiting source to achieve low noise in long integrations using the up-the-ramp sampling readout mode. The glow can be significantly reduced by optimally biasing the output buffer stages. This work presents the output buffer glow issue, its quantification in terms of glow per read, glow per unit integration time, its dependency on pixel speed, and its mitigation by optimization of buffered mode operation.
In this paper, we present the test results of a flight-grade 13μm pixel pitch 6000-element 1.7μm InGaAs linear array in a hermetic package, designed and developed for space remote sensing and imaging applications. The array consists of a single 13μm pixel pitch 6000-element InGaAs linear array and a custom single digital 2.0 Mecapacitance trans-impedance amplifier (CTIA) readout integrated circuit (ROIC) with four gains. We have achieved greater than 80% peak quantum efficiency and higher than 1100 signal-to-noise ratio (SNR) at 90% well fill. The focal plane array is in a vacuum hermatically sealed package with an anti-reflective (AR)-coated Sapphire window and 29 pins, including four for low voltage differential signaling (LVDS) outputs.
The CHROMA (Configurable Hyperspectral Readout for Multiple Applications) is an advanced Focal Plane Array (FPA) designed for visible-infrared imaging spectroscopy. Using Teledyne’s latest substrateremoved HgCdTe detector, the CHROMA FPA has very low dark current, low readout noise and high, stable quantum efficiency from the deep blue (390nm) to the cutoff wavelength. CHROMA has a pixel pitch of 30 microns and is available in array formats ranging from 320×480 to 1600×480 pixels. Users generally disperse spectra over the 480 pixel-length columns and image spatially over the n×160 pixellength rows, where n=2, 4, 8, 10. The CHROMA Readout Integrated Circuit (ROIC) has Correlated Double Sampling (CDS) in pixel and generates its own internal bias signals and clocks. This paper presents the measured performance of the CHROMA FPA with 2.5 micron cutoff wavelength including the characterization of noise versus pixel gain, power dissipation and quantum efficiency.
Teledyne Imaging Sensors develops and produces high performance silicon-based CMOS image sensors, with associated
electronics and packaging for astronomy and civil space. Teledyne's silicon detector sensors use two technologies:
monolithic CMOS, and silicon PIN hybrid CMOS. Teledyne's monolithic CMOS sensors are large (up to 59 million
pixels), low noise (2.8 e- readout noise demonstrated, 1-2 e- noise in development), low dark current (<10 pA/cm2 at
295K) and can provide in-pixel snapshot shuttering with >103 extinction and microsecond time resolution. The QE
limitation of frontside-illuminated CMOS is being addressed with specialized microlenses and backside illumination. A
monolithic CMOS imager is under development for laser guide star wavefront sensing. Teledyne's hybrid silicon PIN
CMOS sensors, called HyViSITM, provide high QE for the
x-ray through near IR spectral range and large arrays
(2K×2K, 4K×4K) are being produced with >99.9% operability. HyViSI dark current is 5-10 nA/cm2 (298K), and further reduction is expected from ongoing development. HyViSI presently achieves <10 e- readout noise, and new high speed
HyViSI arrays being produced in 2008 should achieve <4 e- readout noise at 900 Hz frame rate. A Teledyne 640×480
pixel HyViSI array is operating in the Mars Reconnaissance Orbiter, a 1K×1K HyViSI array will be launched in 2008 in
the Orbiting Carbon Observatory, and HyViSI arrays are under test at several astronomical observatories. The
advantages of CMOS in comparison to CCD include programmable readout modes, faster readout, lower power,
radiation hardness, and the ability to put specialized processing within each pixel. We present one example of in-pixel
processing: event driven readout that is optimal for lightning detection and x-ray imaging.
Inter-Pixel capacitance (IPC) is an effect that can occur in bump-bonded hybrid CMOS pixel arrays that employ a source
follower pixel amplifier. IPC can result in the signal in one pixel being sensed by adjacent pixels that are capacitively
coupled. IPC effect is more pronounced in full-depletion silicon hybrid CMOS focal plane arrays than infrared arrays
because of the stronger coupling path through the silicon detector layer. IPC can degrade the image resolution and it can
cause an overestimation of conversion gain (electrons per mV) determined from conventional photon-transfer method
because the IPC "blur" reduces the variance of photon noise. However, the IPC effect can be minimized with
improvements in pixel design, and the conversion gain can be properly calculated, and image resolution can be restored
with deconvolution techniques. In this paper, we report the results of a recent effort to reduce IPC in Teledyne's visible
silicon hybrid CMOS focal plane arrays through pixel design improvements.
A numerical program was developed to simulate the performance of fiber optic transmission systems and its accuracy was verified by comparisons between the calculated results and experiment data. Using this program, soliton transmission and dispersion compensation schemes at 40 Gbit/s were compared. It was shown that by using dispersion compensation, linear transmissions over 3000 km with non-return to zero (NRZ) and over 4000 km with return to zero (RZ) data forms are possible. Without special soliton transmission control techniques, single channel soliton transmission has no advantage over dispersion compensation transmission.
Experimental results from directly modulated semiconductor lasers at 30 Gbit/s are presented. Critical problems for 30 Gbit/s electronic TDM systems are discussed as well as advances in component technology for 30 Gbit/s transmission systems.
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