High sensitivity near-ultraviolet (NUV) avalanche photodiodes operating at wavelengths longer than 300 nm are useful for various applications, including surface exploration of Ocean Worlds and other planetary bodies via Raman spectroscopy. 4H-SiC has long been established as a proven UV detector technology; however, the responsivity of 4H–SiC avalanche photodiodes (APDs) diminishes dramatically at wavelengths longer than ≈ 280 nm due to its weak absorption at wavelengths approaching the indirect bandgap. The authors will present on the design and optimization of 4H-SiC separate absorption, charge and multiplication (SACM) APDs for broadband absorption from 266 to 340 nm.
The far-infrared (IR) region is rich with information needed to characterize interstellar dust and to investigate the cold outer planets of the solar system and their icy moons. The proposed sub-orbital observatory the balloon experiment for galactic infrared science (BEGINS) will utilize cryogenic instruments to map spectral energy distributions (SEDs) of interstellar dust in the Cygnus molecular cloud complex. A future high priority flagship mission Uranus Orbiter and Probe carrying a net flux radiometer (NFR) will study the in situ heat flux of the icy giants atmosphere to 10 bar pressure. These instruments require far-IR filters to define the instrument spectral bandwidths. Our ultimate goal is to define the instrument bands of BEGINS and the NFR with linear-variable filters (LVFs) and discrete-variable filters (DVFs). The LVFs and DVFs will be made of metal mesh band-pass filters (MMBF) comprised of a 100 nm thick gold film with cross-shaped slots of varying sizes along a silicon (Si) substrate with cyclic olefin copolymer (COC) anti-reflection (AR) coatings. We present our progress towards LVFs and DVFs with simulated and measured transmission of a room temperature, non-AR coated, single-band 44 µm MMBF filter. We have successfully fabricated, measured, and modeled a non-AR coated, room temperature 44 µm MMBF. The transmission at room temperature and non-AR coated was measured to be 27% with a resolving power of 11. When COC-AR coated on both sides the transmission is expected to increase to 69% with a resolving power of ten.
More sophisticated non-dispersive infrared (NDIR) sensors for gas analysis have been developed in recent years, with many references in the literature. This technique is one of the most cost-effective methods to quantify the concentration of a target gas by measuring its absorption of infrared radiation. Dual channel thermopiles comprised of target and reference filter channels are reliably used to monitor the target gas for NDIR sensors. In recent years, commercial off-the-shelf quad-channel thermopiles with integrated passband infrared absorption filters have become available and enable up to three gas mixture detection and quantification, but there is no truly parallel readout circuit available for signal post processing. These sensors with their high sensitivity, fast response time and no cooling requirement makes them ideal candidates for applications that require monitoring multiple gases in real time. Usually, an NDIR sensor uses a cost-effective micro-controller for signal post processing, this limits the monitoring of multiple gases to a serial readout architecture. In this paper, we present a proof-of-concept non-dispersive infrared-red (NDIR) gas analyzer that has been realized with a quad-channel thermopile and a parallel readout circuitry consisting of a multi-channel digitizer (MCD) application specific integrated circuit (ASIC) and a field programmable gate array (FPGA). The parallel readout architecture will help considerably in the calibration schema. The NDIR gas analyzer will be used in a future space-based instrument application to ensure the safe transfer of sublimated volatiles from a comet sample containment system to a gas containment system within the operational pressure-temperature condition.
Planetary science exploration is transitioning from a focus on remote sensing techniques to in situ instruments for landed missions, and Raman spectrometers are quickly gaining ground as essential to these payloads. To accurately identify targets of interest to planetary science, the Raman spectrometer spectral resolution is required to be better than 0.19 nm. While dispersive spectrometers are a direct way to separate optical radiation into its constituent irradiance spectrum, they have major disadvantage of very inefficient light throughput for high resolution applications because they require very small entrances slits, ~50 μm. This is a major drawback for a stand-off system where target sample illumination size is large and return signals are very weak. Fluorescence is typically brighter than the Raman signal, and in conventional Raman spectroscopy, a slow detector integrates both signals and obscures the Raman signature. To mitigate this, we are developing an ultra-compact, high resolution, high throughput, time-resolved VIS-NIR Raman spatial heterodyne spectrometer (SHS). The SHS replaces the modulation mirror in a high resolution and throughput of a traditional Fourier Transform Spectrometer (FTS) with a stationary grating. The SHS has the same advantage of the FTS, which has two orders of magnitude larger acceptance angle than dispersive spectrometers without sacrificing resolution. In this work we focus on applications to stand-off Raman SHS spectroscopy for the detection of biomarkers and characterization of habitability on planetary surfaces.
Advances in optical testing are as important as advances in fabrication because one can make only what one can measure. A high-precision metrology capability is utilized to close the gap between interferometric testing and lower precision metrology, laser radar, or contact-probe-based coordinate measuring machines (CMM) to accurately measure surfaces with large form error. This nearly universal optical testing method employs a precision CMM equipped with a non-contact, confocal probe. This technique was developed to characterize and align a broad spectrum of optical surfaces including ones with high slopes that are nearly impossible to measure using traditional interferometric testing without custom-made optics. Optical components covering a wide range of prescriptions, such as large convex conics, high-sloped aspherics, grazing-incidence x-ray optics, and highly deformed flats, were successfully measured. The resulting data were processed using custom-developed routines to determine the optic’s alignment, the departure from design surface, and the as-built prescription parameters. This information was used to verify and guide the development and fabrication of novel optics.
With the rapid advancement of imaging technology, space-based remote sensing instruments are becoming more sophisticated and are producing substantially more amounts of data for downloading. Data alteration is very likely to occur during the transmission over the long distances from probes to carrier spacecraft and subsequently back to Earth,. Cyclic Redundancy Check (CRC) is the most well-known data package error check technique which has been used in many applications. Unfortunately, due to its serial computation process, it could be a bottleneck for critical applications that require rapid processing. To overcome such issue, we present here a parallel CRC computational method based on an FPGA with simulation and testing to validate the methodology.
NASA Goddard Space Flight Center (GSFC) has successfully developed and tested a custom-designed low-noise multi-channel digitizer (MCD) application specific integrated circuit (ASIC) for operation in harsh radiation environments. The MCD-ASIC is optimized for low-frequency and low-voltage signal measurements from sensors and transducers. It has 20 input channels where each channel is comprised of auto-zeroed chopper variable-gain amplifier, post amplifier, and a second order ΣΔ modulator. ΣΔ analog-to-digital converter (ADC) relies on oversampling and noise shaping to achieve high-resolution conversion. However, the MCD-ASIC requires digital filtering and decimation to convert the output single bit streams from the ADC to useful data words. A parallel digital platform such as a field-programmable-gate-array (FPGA) is highly suitable to fully leverage the capabilities of the MCD-ASIC. The FPGA controls the MCD-ASIC via serial peripheral interface (SPI) protocol and acquires data from it. A Python-script communicates with the FPGA board through a USB interface on a cross operating platform. Using this architecture, the system is capable of monitoring up to 20 voltage readout channels simultaneously in a real-time manner. Each channel’s parameters can be programmed independently allowing maximum user versatility. In this paper, we present analysis of the analog front-end, the implementation of the digital processing unit on the FPGA, and provide noise performance results from the MCD-ASIC readout.
A proof-of-concept, compact, portable Fourier Ptychographic Microscope (FPM) to perform wide field-of-view, high spatial resolution imaging (<1 μm) for biosignature motility in liquid samples, is presented. The FPM has the potential method to be developed as a space-based payload for future landers destined to the Ocean Worlds. A portable FPM using an existing Fourier ptychography (FP) algorithm adapted for reconstruction is demonstrated. A NVIDIA Jetson Nano board and camera combined with FP, is used to computationally reconstruct sub-micron resolution images. Additionally, deep learning was employed to perform inferencing prediction which enables the on-edge FPM device.
Pamela Clark, Tilak Hewagama, Shahid Aslam, James Bauer, Michael Daly, Lori Feaga, Dave Folta, Nicolas Gorius, Kyle Hughes, Terry Hurford, Donald Jennings, Timothy Livengood, Michael Mumma, Conor Nixon, Jessica Sunshine, Geronimo Villanueva, Kevin Brown, Ben Malphrus, Aaron Zucherman
Here we describe the Primitive Object Volatile Explorer (PrOVE), a smallsat mission concept to study the surface structure and volatile inventory of comets in their perihelion passage phase when volatile activity is near peak. CubeSat infrastructure imposes limits on propulsion systems, which are compounded by sensitivity to the spacecraft disposal state from the launch platform and potential launch delays. We propose circumventing launch platform complications by using waypoints in space to park a deep space SmallSat or CubeSat while awaiting the opportunity to enter a trajectory to flyby a suitable target. In our Planetary Science Deep Space SmallSat Studies (PSDS3) project, we investigated scientific goals, waypoint options, potential concept of operations (ConOps) for periodic and new comets, spacecraft bus infrastructure requirements, launch platforms, and mission operations and phases. Our payload would include two low-risk instruments: a visible image (VisCAM) for 5-10 m resolution surface maps; and a highly versatile multispectral Comet CAMera (ComCAM) will measure 1) H2O, CO2, CO, and organics non-thermal fluorescence signatures in the 2-5 μm MWIR, and 2) 7-10 and 8-14 μm thermal (LWIR) emission. This payload would return unique data not obtainable from ground-based telescopes and complement data from Earth-orbiting observatories. Thus, the PrOVE mission would (1) acquire visible surface maps, (2) investigate chemical heterogeneity of a comet nucleus by quantifying volatile species abundance and changes with solar insolation, (3) map the spatial distribution of volatiles and determine any variations, and (4) determine the frequency and distribution of outbursts.
Gas Abundance Sensor Package (GASP) is a stand-alone scientific instrument that has the capability to measure the concentration of target gases based on a non-dispersive infrared sensor system along with atmospheric reference parameters. The main objective of this work is to develop a GASP system which takes advantage of available technologies and off-the-shelf components to provide a cost-effective solution for localized sampling of gas concentrations. GASP will enable scientists to study the atmosphere and will identify the conditions of the target’s planetary local environment. Moreover, due to a recent trend of miniaturization of electronic components and thermopiles detectors, a small size and robust instrument with a reduction in power consumption is developed in this work. This allows GASP to be easily integrated into a variety of small space vehicles such as CubeSats or small satellite system, especially the Micro-Reentry Capsule (MIRCA) prototype vehicle. This prototype is one of the most advanced concepts of small satellites that has the capability to survive the rapid dive into the atmosphere of a planet. In this paper, a fully-operational instrument system will be developed and tested in the laboratory environment as well as flight preparation for a field test of the instrument suite will be described.
Noise was studied in an MgB2 thin film grown on a SiN substrate, with a superconducting transition
temperature, Tc, near 39K. At the mid-point of the transition and at 10Hz a noise spectral density
Sv = 0.34nVHz1/2 was measured. The temperature noise, Kn , of the MgB2 film at different frequencies is
compared to that of cuprate high temperature superconducting (HTS) thin films (with Tc ~ 90 K) used
currently in transition-edge devices. Kn values predict that 2-D arrays of high performance infrared devices
can be developed using MgB2.
KEYWORDS: Thin films, Superconductors, Bolometers, Silicon, Infrared detectors, Resistance, Temperature metrology, Signal to noise ratio, Sensors, Silicon films
An MgB2 thin film was grown on a SiN-Si substrate, with a superconducting transition temperature, Tc, near 39K. At the mid-point of the transition (T= 38.24K) and at 10Hz a noise spectral density SV = 0.34nV/ √Hz was measured. The temperature noise, Kn, of the MgB2 film at different frequencies is compared to that of cuprate high temperature superconducting (HTS) thin films (with Tc ~ 90 K) used currently in transition-edge bolometers. Κn values predict that high performance far-IR thermal detectors (i.e bolometers) can be developed using MgB2 as a thermistor.
Rapid progress in the AlGaN (Eg=3.4-6.2eV), 4H-SiC (Eg=3.2eV) and ZnMgO (Eg=2.8-7.9eV) material systems over the last five years has led to the demonstration of a number of opto-electronic devices. These wide energy band gap devices offer several key advantages for space applications, over conventional Si (Eg=1.1eV) based devices, such as visible-blind detection, high thermal stability, better radiation hardness, high breakdown electric field, high chemical inertness and greater mechanical strength. Furthermore, the shorter cut-off wavelength of these material systems eliminates the need for bulky and expensive optical filtering components mitigating risk and allowing for simpler optical design of instrumentation. In this paper, we report on the development at NASA/Goddard of ultra-sensitive, high quantum efficiency AlGaN and 4H-SiC Schottky barrier UV-EUV photodiodes, 4H-SiC UV single photon avalanche diodes, large format 256x256 AlGaN UV p-i-n photodiode arrays and recent progress in elemental substitution for p-type and enhanced n-type doping of ZnO.
The development of high quantum efficiency photemissive detectors is recognized as a significant advancement for astronomical missions requiring photon-counting detection. For solar-blind NUV detection, current missions (GALEX, STIS) using Cs2Te detectors are limited to ~10% DQE. Emphasis in recent years has been to develop high QE (>50%) GaN and AlGaN photocathodes (among a few others) that can then be integrated into imaging detectors suitable for future UV missions. We report on progress we have made in developing GaN photocathodes and discuss our observations related to parameters that effect efficiency and stability, including intrinsic material properties, surface preparation, and vacuum environment. We have achieved a QE in one case of 65% at 185 nm and are evaluating the stability of these high QEs. We also discuss plans for incorporating photocathodes into imaging and non-imaging sealed devices in order to demonstrate long term stability.
The performance of a high Tc (~90 K) transition-edge superconducting (TES) bolometer on a monolithic sapphire membrane is presented and discussed. It is compared to the performance of a previous TES bolometer on non-monolithic sapphire substrate. The development and optimization of monolithic sapphire membranes is critical for the fabrication of 1 and 2-D arrays of TES bolometers. Moderately cooled and optimized TES bolometers are expected to be the replacements of choice for thermopiles and other room temperature thermal sensors on far IR instruments on future planetary missions.
KEYWORDS: Camera shutters, Electrodes, Silicon, Semiconducting wafers, Magnetism, Oxides, Deep reactive ion etching, Etching, Reactive ion etching, Space telescopes
Two-dimensional microshutter arrays are being developed at NASA Goddard Space Flight Center (GSFC) for the Next Generation Space Telescope (NGST) for use in the near-infrared region. Functioning as focal plane object selection devices, the microshutter arrays are 2-D programmable masks with high efficiency and high contrast. The NGST environment requires cryogenic operation at 45 K. Arrays are close-packed silicon nitride membranes with a unit cell size of 100x100 micrometer. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with minimized mechanical stress concentration. The mechanical shutter arrays are fabricated with MEMS technologies. The processing includes a RIE front-etch to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, and a deep RIE (DRIE) back-etch down to the nitride shutter membrane to form frames and to relieve the shutters from the silicon substrate. A layer of magnetic material is deposited onto each shutter. Onto the side-wall of the support structure a metal layer is deposited that acts as a vertical hold electrode. Shutters are rotated into the support structure by means of an external magnet that is swept across the shutter array for opening. Addressing is performed through a scheme using row and column address lines on each chip and external addressing electronics.
We are developing novel photodetector arrays based on superconducting transition-edge sensor (TES) and pop-up detector (PUD) technologies. The TES has the potential for a new generation of high sensitivity photodetectors from the IR to the x-ray. This is directly due to the sharpness of the resistance change with temperature at the superconducting transition. The TESs are deposited on the PUD arrays and serve as the sensing elements. The PUDs are close-packed, folded membrane arrays that provide the TES substrate and the thermal isolation required by the bolometers and microcalorimeters. This paper presents the processing-related characterization result of preliminary TES and PUD designs. The gaol of this work is to fabricate a new generation of x-ray calorimeters and IR bolometers for space flight projects.
Reactive ion etching (RIE) is commonly used, as a process tool, for the etching of polysilicon, silicon dioxide, silicon nitride and other thin film deposits. One of the key requirements of the etching process is the accurate end-point detection of the process. There exist a number of process monitoring techniques for end-point detection, these however are costly to install and maintain. In response to this requirement, a new method for end-point detection of polysilicon topography etching in single wafer plasma reactive ion etcher is presented here, which incurs no added costs. The method is based upon experimental results correlating polysilicon etching end-point with the increase in the cathodic self-bias voltage developed across the substrate. It is shown that the end-point of polysilicon topography etching can be found by monitoring the first derivative of the self- bias voltage with time. Using this method it has been demonstrated that accurate end-point detection of polysilicon etching can be obtained with a residue free field, near- vertical polysilicon profile and critical dimension loss of less than 0.05 micrometer.
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