In this paper we review the physics and performance of back-illuminated CCDs. Models of back-illuminated CCDs are used to derive requirements for stable, strong surface passivation in space-relevant environments. Models and data are used to compare state-of-the-art surface passivation methods with 2D-doped surfaces. MBE growth of 2D-doped silicon on back-illuminated CCDs and CMOS image sensors enables near 100% charge collection efficiency with exceptional stability in space and other harsh environments. Lifetime tests performed on 2D-doped CMOS image sensors using pulsed DUV lasers have demonstrated the unique stability of 2D-doped detectors against high levels of radiation-induced surface damage. The insensitivity of 2D-doped detectors to Si-SiO2 traps has facilitated the development of a variety of coatings and filters with science-enabling capabilities for NASA instruments and missions in the far and near ultraviolet spectral range. We discuss the status and goals of a strategic partnership between JPL and Teledyne e2v for the certification of 2Ddoping processes, and report initial results from our collaboration.
Scientists are constantly pushing the boundaries, discovering new frontiers of exploration of the Universe; as space missions pursue these challenges it places a greater demand on detector technology advancement. I will present the status of our delta-doped Electron Multiplying CCD (EMCCD) for a UV multi-object spectrograph, the Faint Intergalactic Redshifted Emission Balloon (FB-2). FB-2 demonstrates this new technology, in a low risk suborbital environment, to prove the performance of EMCCDs for future space missions and Technology Readiness Level (TRL) advancement. It uses a new generation controller for counting photons from Nuvucameras. Part of this endeavor will be testing EMCCDs in a radiation environment; initial results will presented in this paper. EMCCDs have proven to be a versatile technology due to its photon counting (PC) capabilities to achieve extremely low readout noise (<< 1 electron). I will present results from the most recent flight and recent noise optimization.
The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat whose mission will be to observe M stars in two ultraviolet (UV) bands—SPARCS far UV (S-FUV: 153-171 nm) and SPARCS near UV (S-NUV: 260-300 nm). SPARCS would be the first mission to provide time-dependent spectral slope, intensity and evolution of M dwarf stellar radiation; measurements that are critical to deciphering observations of planetary atmosphere from missions such as JWST. The baseline UV camera for SPARCS (SPARCam) includes the electronics boards and two UV detectors, one optimized for each of the SPARCS bands. The camera’s low-noise electronics are based on JPL’s compact, modular design and provide dynamic observation capabilities. For its detectors, SPARCam uses 2D-doped (i.e. delta-doped) CCDs for both channels. Here we present SPARCam development and characterization results prior to payload integration. Copyright 2019. All rights reserved.
We present the status of on-going detector development efforts for our joint NASA/Centre National d’Études Spatiales balloon-borne UV multiobject spectrograph, the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2; FB-2). FB-2 demonstrates a UV detector technology, the delta-doped electron-multiplying CCD (EMCCD), in a low-risk suborbital environment, to prove the performance of EMCCDs for future space missions and technology readiness level advancement. EMCCDs can be used in photon-counting mode to achieve extremely low readout noise (<1 electron). Our testing has focused on reducing clock-induced-charge (CIC) through wave shaping and well-depth optimization with a Nüvü V2 CCCP controller, measuring CIC at 0.001 e − / pixel / frame. This optimization also includes methods for reducing dark current, via cooling, and substrate voltage levels. We discuss the challenges of removing cosmic rays, which are also amplified by these detectors, as well as a data reduction pipeline designed for our noise measurement objectives. FB-2 flew in 2018, providing the first time an EMCCD, was used for UV observations in the stratosphere. FB-2 is currently being built up to fly again in 2020, and improvements are being made to the EMCCD to continue optimizing its performance for better noise control.
Here we discuss high-performance UV detectors to be used with the planned Star-Planet Activity Research CubeSat (SPARCS). SPARCS is a 6U cubesat designed to monitor M stars (0.1 – 0.6 solar masses) in two photometric bands in the near UV and far UV (S-NUV, 260-300 nm; S-FUV, 150-170 nm). SPARCS targets range in mass and age, including young stars (10-20 Myr), which are likely forming terrestrial planets, to old stars with known transiting planets, allowing us to map the evolution of UV emission and flare rates. The spectral slope, variability and evolution of a host star’s highenergy radiation would provide realistic input stellar fluxes to planet atmospheric models, which would aide in understanding the evolution and habitability of a planet and in interpreting its transmission and emission spectrum. The baseline S-NUV detector is a 2D-doped (delta-doped or superlattice-doped) charge coupled device (CCD) optimized with a custom antireflection (AR) coating to achieve quantum efficiency (QE)>70% throughout the S-NUV band. The SNUV detector would be coupled with a stand-alone red-blocking filter that provides at least three orders of magnitude (i.e., ≥OD3) out-of-band suppression, critical for the observations of such cool, red stars. Their combined throughput would be >25% (peak) in the S-NUV. The baseline S-FUV detector is a 2D-doped CCD optimized for the S-FUV band; it includes an integrated filter designed to maximize in-band throughput with good red-leak suppression. As designed, the solar-blind silicon detector achieves peak QE>35% in the S-FUV band and ≥OD2 out-of-band suppression. SPARCS has baselined a dichroic design that allows for simultaneous S-NUV and S-FUV observation. SPARCS would advance 2D-doped detectors and detector-integrated out-of-band-rejection filter technologies for their potential application in future mission concepts such as LUVOIR and HabEx.
Exciting concepts are under development for flagship, probe class, explorer class, and suborbital class NASA missions in the ultraviolet/optical spectral range. These missions will depend on high-performance silicon detector arrays being delivered affordably and in high numbers. To that end, we have advanced delta-doping technology to high-throughput and high-yield wafer-scale processing, encompassing a multitude of state-of-the-art silicon-based detector formats and designs. We have embarked on a number of field observations, instrument integrations, and independent evaluations of delta-doped arrays. We present recent data and innovations from JPL’s Advanced Detectors and Systems Program, including two-dimensional doping technology, JPL’s end-to-end postfabrication processing of high-performance UV/optical/NIR arrays and advanced coatings for detectors. While this paper is primarily intended to provide an overview of past work, developments are identified and discussed throughout. Additionally, we present examples of past, in-progress, and planned observations and deployments of delta-doped arrays.
Imaging and Imaging Spectroscopy in the ultraviolet (UV), visible, and near infrared (NIR) part have a wide range of applications in astrophysics, planetary studies, heliophysics, commercial and medical diagnostics. A major part of system performance is contributed by the detector metrics. JPL-developed sensors developed using 2D-doping and custom coatings provide high performance across the UV, visible, and NIR region of the spectrum. Applying these 2-D surface and interface engineering technologies to detector structures with gain (e.g., Avalanche Photodiodes or APDs or electron multiplying charged-coupled devices or EMCCDs) enables photon-counting capabilities in solid state format rather than image tube detectors. Initially developed for space exploration applications for detecting faint signals in harsh environments while using low voltage and low power, these high efficiency detectors can be repurposed for medical applications that have much of the same requirements. For example, endogenous and induced fluorescence signatures in tissues as emergent diagnostic tools for abnormal tissue behaviors can potentially be detected using these detectors with high efficiency.
Using JPL high efficiency imaging arrays, transient fluorescence signatures could be detected with small amount of stimulation. This brings the added advantage of precise fluorescence signature quantification, without damage to the host organism or tissue. In this work, we present fluorescence detection of phantom samples that serve as proof of concept demonstration while calibrating the instrument.
We report on multilayer high efficiency antireflection coating (ARC) design and development for use at UV wavelengths on CCDs and other Si-based detectors. We have previously demonstrated a set of single-layer coatings, which achieve >50% quantum efficiency (QE) in four bands from 130 to 300 nm. We now present multilayer coating designs that significantly outperform our previous work between 195 and 215 nm. Using up to 11 layers, we present several model designs to reach QE above 80%. We also demonstrate the successful performance of 5 and 11 layer ARCs on silicon and fused silica substrates. Finally, we present a five-layer coating deposited onto a thinned, delta-doped CCD and demonstrate external QE greater than 60% between 202 and 208 nm, with a peak of 67.6% at 206 nm.
We present an overview of the detector for the upcoming Faint Intergalactic Red-shifted Emission Balloon (FIREBall-2) experiment, with a particular focus on the development of device-integrated optical coatings and detector quantum efficiency (QE). FIREBall-2 is designed to measure emission from the strong resonance lines of HI, OVI, and CIV, all red-shifted to 195-225 nm window; its detector is a delta-doped electron multiplying charge coupled device (EM-CCD). Delta-doped arrays, invented at JPL, achieve 100% internal QE from the UV through the visible. External losses due to reflection (~70% in some UV regions) can be mitigated with antireflection coatings (ARCs). Using atomic layer deposition (ALD), thin-film optical filters are incorporated with existing detector technologies. ALD offers nanometer-scale control over film thickness and interface quality, allowing for precision growth of multilayer films. Several AR coatings, including single and multi-layer designs, were tested for FIREBall-2. QE measurements match modeled transmittance behavior remarkably well, showing improved performance in the target wavelength range. Also under development are ALD coatings to enhance QE for a variety of spectral regions throughout the UV (90-320 nm) and visible (320-1000 nm) range both for space-based imaging and spectroscopy as well as for ground-based telescopes.
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