This PDF file contains the front matter associated with SPIE Proceedings Volume 11723, including the Title Page, Copyright information and Table of Contents

In this presentation, we will report our recent efforts in achieving high performance in Antimonides type-II superlattice (T2SL) based infrared photodetectors using the barrier infrared detector (BIRD) architecture. The high operating temperature (HOT) BIRD focal plane arrays (FPAs) offer the same high performance, uniformity, operability, manufacturability, and affordability advantages as InSb. However, mid-wavelength infrared (MWIR) HOT-BIRD FPAs can operate at significantly higher temperatures (>150K) than InSb FPAs (typically 80K). Moreover, while InSb has a fixed cutoff wavelength (~5.4 μm), the HOT-BIRD offers a continuous adjustable cutoff wavelength, ranging from ~4 μm to >15 μm, and is therefore also suitable for long wavelength infrared (LWIR) as well. The LWIR detectors based on the BIRD architecture has also demonstrated significant operating temperature advantages over those based on traditional p-n junction designs. Two 6U SmalSat missions CIRAS (Cubesat Infrared Atmospheric Sounder) and HyTI (Hyperspectral Thermal Imager) are based on JPL’s T2SL BIRD focal plane arrays (FPAs). Based on III-V compound semiconductors, the BIRD FPAs offer a breakthrough solution for the realization of low cost (high yield), high-performance FPAs with excellent uniformity and pixel-to-pixel operability. We have also exploring the possibilities of implementing either metasurface resonator cavity or metasurface based flatlens to improve the signal-to-noise ratio of the detectors.

For MWIR IR detectors, we designed a meta-surface to enhance QE across 2 to 6 microns. The relative enhancement depends on the intrinsic absorption coefficient, α, of the material. If α is large at 2x10⁴/cm, a 0.1 micron-thick metadetector can have a peak QE of 90%, which is 2.6 times higher than the conventional detector. The improvement is larger at a smaller α. When it is 2000/cm, the improvement is about 10 times with a peak QE of 49%. For energy harvesting devices, we designed several nanostructures etched on top of silicon solar cells to enhance their absorption. Employing an array of nano-columns increases absorption from 55% to 93% at 0.7 microns and from 5.0% to 20% at 1.0 microns. An array of nano-cones further increases the average absorption to 95% between 0.4 to 0.8 microns. The overall integrated absorption is increased by 71% for nano-columns and 91% for nano-cones. For GaAs solar cells, a metasurface can improve photocurrent by 26% from a planar solar cell with a 100 nm-thick absorber.

The mid-wave infrared (MWIR) waveband (3-5 µm) contains numerous invaluable spectral /thermal signatures. Tunable MWIR filters are thus highly desirable in a variety of imaging and spectroscopic applications. We introduce phase-change tunable filters (PCTFs) which enable actively tunable spectral filtering across the MWIR waveband from a single solid-state element. This is achieved through the integration of the chalcogenide phase-change material GeSbTe (GST) into a plasmonic nanohole metasurface. We demonstrate polarization-insensitive PCTFs with >70% transmittance, 60nm bandwidth, and high-speed switching (MHz-GHz) across the MWIR waveband using a nanosecond laser pulse. We further show PCTF-based multispectral thermal imaging and dynamic gas sensing.

High−speed photodetectors operating at short−wavelength infrared (SWIR) telecommunication waveband have been well studied with the development of optical fiber−based communication system. Recent innovations of photonic systems have raised new requirements on the bandwidth of photodetectors with cutoff wavelengths from extended short−wavelength infrared (eSWIR) to mid−wavelength infrared (MWIR). However, the frequency response and gain performance of photodetectors in these longer wavelength bands is less studied, and the performances of the current high-speed photodetectors in these bands are still not comparable with those in the telecommunication band. There are two major material systems are able to cover whole infrared spectrum from short− to long−wavelength infrared; HgCdTe well-developed ternary alloys and antimonide−based type−II superlattices (T2SLs). T2SLs are a developing new material system with intrinsic advantages such as great flexibility in bandgap engineering, low growth and manufacturing cost, high−uniformity, auger recombination suppression, and high carrier effective mass that are becoming an attractive candidate for infrared detection and imaging. Thanks to T2SLs’ extreme design flexibility one can demonstrate many different device architectures that could not been realized in other material systems to achieve higher gain and speed such as hetero−junction phototransistor (HPT) and avalanche photodiodes (APD) with bandstructure−engineered multiplication regions. We are going to present an overview of eSWIR and MWIR gain−based devices (such as HPTs and APDs) in T2SLs material system and possible routes to achieve higher gain and faster speed in these devices.

Improving heat insulation in microelectromechanical system based thermal-type infrared sensor is crucial to increase its performance. The concept of phonon engineering allows us to change material thermal conductivity by several orders of magnitudes, which can be a potential technique for thermal management of such microelectronic devices. Here, we introduced a phononic crystal structure in a prototype thermopile sensor to investigate the effectiveness of phonon engineering. We demonstrate that ultrafine phononic crystal structure, which was consisted of through-holes periodically arranged at 38 nm, resulted in ten-fold reduction in Si thermal conductivity. This led to improvement of the sensitivity of IR detection by a factor of ten. In addition, our phononic crystal could suppress thermal conductivity while maintaining the electrical conductivity, which enable us to increase the noise equivalent temperature difference by 5.6 times. The present study demonstrates great potential of phonon engineering for infrared sensor technology to reach for smaller pixel size and lower device cost.

We discuss our recent work in development of 1280 x 1024/12μm pitch bulk InAsSb MWIR/MWIR twocolor focal planes with cutoff wavelengths of 4.2μm and 5.1μm in the two bands as well as SWIR/MWIR focal planes with cutoff wavelengths of 3.0μm and 4.9μm. Barrier detectors based on the InAsSb materials system have recently been developed to realize substantial improvements in the performance of MWIR detectors operating in a single MWIR wavelength band, enabling FPA performance at operating temperatures as high as 150K. We have extended this detector architecture to encompass two-color detectors operating in a sequential mode utilizing back-to-back barrier devices. These detectors utilize the ternary alloy InAsSb materials system grown by molecular-beam epitaxy on GaAs substrates as a pathway to cost-effective production of large-area focal-plane arrays. Based on extensive FPA characterization, NEDT values of 18.3mK (Band-1) and 14.2mK (Band-2) were measured under f/2.3 illumination at an array operating temperature of T = 120K, with high NEDT operabilities (2x median) of 99.93% and 99.7% in Band-1 and Band-2, respectively. No significant performance degradation was observed in epoxystabilized hybrids after 500 thermal cycles between 300K and 110K. Finally, we discuss the progress that has been made in SWIR/MWIR array development and present measurements of 1280 x 1024 FPA performance for SWIR/MWIR focal planes with cutoff wavelengths of 3.0μm and 4.9μm at T = 120K. NEDT values (f/2.3 illumination) of 18.5mK (SWIR) and 15.0mK (MWIR) and high operabilities of 99.96% (SWIR) and 99.3% (MWIR) for cutoff wavelengths of 3.0μm and 4.9μm were measured.

An 8-inch wafer scale process was developed that provides low cost availability of back-side illuminated (BSI) imaging sensors. The process has been optimized to convert standard CMOS and CCD 6-inch or 8-inch wafers from front side illuminated (FSI) sensors to BSI sensors. The process successfully demonstrates wafer planarization, bow correction, bonding to carrier wafers, wafer thinning, re-planarization, anti-reflection coating, through silicon vias (TSVs) and back side metallization. Good wafer thinning control was obtained for a wide range of epi thicknesses varying from 4 microns to 15 microns. The thinner epi is optimized for UV and visible sensing while the thicker epi material is optimized for near-infrared (NIR) sensing. The processed wafers demonstrate backside passivation and anti-reflection (AR) coatings that optimize the QE performance in a variety of bands such as 200nm-300nm, 300nm-400nm and 400nm-900nm.

Long wave infrared imaging systems require small, low cost and low power systems operating at room-temperature. Seebeck nanoantennas are room temperature detectors which generate voltage due to incident electromagnetic radiation, they also provide polarization sensitivity, directivity, small footprint, tunability and the possibility of integration into electronic and photonic circuits. In this work different materials and fabrication processes used in Seebeck bowtie nanoantennas are numerically simulated in order to optimize its response in the long wave infrared region of the electromagnetic spectrum (8–14 μm.) Gold bowtie nanoantennas with thermoelectric connections made of Bi₃Te₂ and Sb₃Te₂ showed the highest responsivity values of 9 V/W for gold bowtie nanoantennas on a SiO₂ substrate and 240 V/W for gold bowtie free-standing structures. Computer simulations also showed that the thermoelectric response of these detectors add linearly when connecting them in series.

The longwave infrared (LWIR) spectral region from 8 to 12 μm is widely used for day/night sensing and imaging applications as it corresponds to an atmospheric window as well as the peak region of the terrestrial blackbody emission. Some of these applications require use of compact spectrally tunable notch or bandstop filters, which reflect a narrowband of incident light while transmitting the rest. At the Army Research Laboratory (ARL), we are developing such spectral filters based on two different thin-film technologies—(i) metasurfaces that utilize the guided-mode resonance (GMR) effect in dielectric materials and (ii) electronically tunable plasmonic graphene metasurfaces with an array of nanoantennas. Both these approaches use nano-engineered subwavelength structures metasurfaces to develop very compact low-cost, rugged, lightweight spectrally tunable LWIR notch filters. Such filters are designed to reflect the incident broadband light at one (or more) narrow spectral band while fully transmitting the rest. The optical filter based on the GMR effect consists of a subwavelength dielectric grating and a planar waveguide using high-index dielectric transparent materials, i.e., germanium (Ge) and on top of a zinc selenide (ZnSe) substrate and spectral tuning is achieved by mechanically tilting the filter. In the second approach, we fabricate the graphene plasmonic nanoantennas on a dielectric coated substrate. This approach uses four independent plasmonic metasurfaces to cover the full LWIR range, each individually tunable over one μm and a gating voltage is applied to each metasurface to obtain a spectral notch. Diameter of the nanoantenna determines the resonant wavelength. Each of these two approaches use high-precision nanofabrication technologies. We will present modeling and simulation results for both approaches as well as some fabrication and characterization results.

Dangerous materials present in factories and military combat locations, can cause negative effects to the human body and can be life threatening. Due to this, a portable, easily maintained, and robust sensor is required to detect CWA’s, TIC’s, and TIM’s. We present a method to grow MOFs on quartz crystal microbalances (QCM’s) for sensitive, selective detection of CWA’s. Our next step is to test the sensitivity and selectivity of the MOF to dimethyl methylphosphonate (DMMP) when under varying environmental conditions.

Magnetic nanoparticles (mNPs)are used where localized heat is required, such as in induction cook tops, laser welding, nano-material welding, and hyperthermia therapy for cancer patients. It is known that mNPs can provide heat based on three mechanisms: hysteresis, Neel’s Relaxation, and Brownian (friction) motion. The studies have shown for biomedical applications that the mNPs generate heat based on frictional losses and do not exhibit hysteresis.¹ It is not as thoroughly understood how the mNPs behave in rigid environments, particularly when dispersed throughout a material. The main goal of this paper is to understand the dominant mechanism of heating when mNPs are in a rigid structure and use this understanding to optimize mNPs for localized heat applications. We experiment with the mNPs, induction heat, and heat sensitive paint to demonstrate the mNPs ability to create heat when embedded in rigid matrices. A commercially available induction heater operating at 30 - 104 kHz is used to create a high strength alternating magnetic field to test whether the energy at these frequencies leads to heating when mNPs are present. Studies are done for powdered carbon and iron (Fe₂O₃) particles and for particles when embedded in polyurethane, rubber, and thermochromic paint. The results suggest that the mNPs exhibit hysteresis in rigid systems. We demonstrate this heating using thermochromic paint on mNP-infused solids.

Far-field infrared (IR) spectroscopy techniques, such as ellipsometry and FTIR, can yield extremely accurate measurements of the optical constants (n,k) which characterize the electronic and lattice-structural degrees of freedom in novel materials and devices. However, large systematic uncertainty has plagued extensions of these techniques to small length scales. A low uncertainty embodiment would enable high quality studies of, for example, the newest correlated condensed matter systems - where typically only a small sample is available early on. Here we present mature far-field IR microscope. Most notably, an asymmetric interferometer is used to directly measure the infrared reflectance amplitude and absolute phase shift. The complex optical constants can then be extracted without the large uncertainty that arises with an amplitude measurement alone.

Broadband antireflection (AR) optical coatings covering the ultraviolet (UV) to infrared (IR) spectral bands have many potential applications for various NASA systems. The performance of these systems is substantially limited by signal loss due to reflection off substrates and optical components. Tunable nanoengineered optical layers offer omnidirectional suppression of light reflection/scattering with increased optical transmission to enhance detector and system performance. Nanostructured AR coatings enable realization of optimal AR coatings with high laser damage thresholds and reliability in extreme low temperature environments and under launch conditions for various NASA applications. We are developing and advancing high-performance AR coatings on various substrates for spectral bands ranging from the UV to IR. The nanostructured AR coatings enhance the transmission of light through optical components and devices by significantly minimizing reflection losses, providing substantial improvements over conventional thin film AR coating technologies. The optical properties of the AR coatings have been measured and fine-tuned to achieve high levels of performance. In this paper, we review our latest work on high performance nanostructure-based AR coatings, including recent efforts in the development of the nanostructured AR coatings for UV band applications.

Motion Amplification is a video-processing technique that detects subtle motion and enhances that motion to a level visible with the naked eye. Motion Amplification Technology can resolve motions as small as 250 nanometers at 1 meter and can be performed live and in real-time on even a modest laptop. The process involves the use of a high definition and high dynamic range video cameras where every pixel becomes an independent point sensor creating millions of continuous data points in an instant. This essentially turns a high definition camera into a full field vibration acquisition device with over 2.3 million independent sampling locations. The technology allows the user to measure calibrated absolute displacement across the full field of view providing a time waveform and spectrum for each measured location. A comprehensive set of examples and applications will be discussed along with a live demonstration.

Event-based cameras use in-pixel analog processing to respond to changes in illumination (events). Pixels report events asynchronously, enabling very fast response and reduced data volumes compared to conventional frame- based arrays. The asynchronous event reporting circuit timestamps events to 1 microsecond resolution, but latency in the circuit and the serial nature of the output lead to variable latency when many pixels are stimulated simultaneously. To characterize this variability, three iniVation cameras and one Prophesee camera were exposed to single step-function ashes with varying amplitude and diameter. The Median Absolute Deviation of pixel response times ranged between 0 and 6086μs, increasing with the fraction of array exposed. The number of events generated per pixel generally decreased with pixel stimulation percent, with all cameras producing fewer than 59 events per pixel. In three cameras, an increased stimulus amplitude caused an increase in event generation, while the fourth camera generated fewer events with increasing stimulus amplitude, down to 0.32 events per stimulus. The instantaneous event throughput exceeded manufacturer specifications for 3 of 4 cameras, though the average throughput was lower than specified over longer time scales. While individual pixels may be able to accurately detect microsecond-scale change, data bottlenecks may cause missed events or erroneous timestamps.

High performance detector technology is being developed for sensing over the mid-wave infrared (MWIR) band for NASA Earth Science, defense, and commercial applications. The graphene-based HgCdTe detector technology involves the integration of graphene with HgCdTe photodetectors that combines the best of both materials, and allows for higher MWIR (2-5 μm) detection performance compared with photodetectors using only HgCdTe material. The interfacial barriers between the HgCdTe-based absorber and the graphene act as a tunable rectifier that reduces the recombination of photogenerated carriers in the detector. The graphene layer also acts as high mobility channel that whisks away carriers before they recombine, further enhancing detection performance. This makes them much more practical and useful for MWIR sensing applications such as remote sensing and earth observation, e.g., in smaller satellite platforms (CubeSat) for measurement of thermal dynamics with better spatial resolution. The objective of this work is to demonstrate graphene-based HgCdTe room temperature MWIR detectors and arrays through modeling, material development, and device optimization. The primary driver for this technology development is the enablement of a scalable, low cost, low power, and small footprint infrared technology component that offers high performance, while opening doors for new earth observation measurement capabilities.

The long-wave infrared (LWIR) spectroscopy has emerged as a promising technique for applications ranging from medical diagnosis to satellite imaging and terrestrial imaging. However, traditional optical elements are not realized well for the LWIR region. In this work, notch filters for LWIR spectral range (8 ~ 12 μm) based on the guided mode resonance (GMR) effect were designed, fabricated, and characterized with Germanium (Ge) thin film on Zinc Selenide (ZnSe) substrates. In contrast to the typical photolithography process, which faces challenge of resolution limit, we used e-beam lithography process to pattern the grating. By using a reactive ion etching process with a mixture of etching and passivation gases, we fabricated grating with well-defined vertical sidewalls. Finite-difference time-domain (FDTD) method was used to calculate the optical responses and model the geometry of the notch filters, and the optical transmittance of fabricated filters agrees well with the calculations. Moreover, we demonstrate the improved notch filtering response with reduced Fabry-Perot noise by introducing anti-reflection layer on the bottom of the ZnSe substrate. Therefore, findings of this work will be useful for various filter fabrications that prefer high spatial resolution in the LWIR spectral region.

Calculations are presented of vibrational absorption spectra for isolated PFAS molecules using density function theory (DFT). These contaminants are among widely spread carcinogens in the environment of industrial countries. DFT calculated absorption spectra of isolated molecules represent quantitative estimates that can be correlated with additional information obtained from laboratory measurements. The DFT software GAUSSIAN was used for calculating the infrared (IR) spectra presented here. DFT calculated spectra can be used to construct templates, which are for spectral-feature comparison, and thus detection of spectral-signature features associated with target materials.

Ultrasonic transducer is a sensor that realizes the mutual conversion of ultrasonic and electrical signals, and it is widely used in quality inspection, biomedical imaging and other fields. Commonly used ultrasonic transducers have a small detection range and low sensitivity due to the diffraction of sound waves. Focused transducers are used to improve detection sensitivity. Unfortunately, focused transducers have narrow depth of field. Here, we developed a Bessel ultrasonic transducer for large depth of field by using conical acoustic lens. An acoustic lens is attached to a unfocused ultrasonic. And the acoustic lens is a cuboid prism with a concave cone on the bottom, made of fused silica. Similar to an axicon that can generate a Bessel beam, the Bessel ultrasonic transducer can produce nondiffracting Bessel ultrasonic beams. Therefore, extended depth of field with uniformly high resolution and high detection sensitivity can be obtained. We used COMSOL to simulate the transmission of ultrasonic field of the designed conical acoustic lens, and compare it with the spherical focused ultrasonic transducer. The results show that the depth of field of the Bessel ultrasonic transducer is about 8 times that of the conventional spherical focused ultrasonic transducer. And the depth of field of the Bessel ultrasonic transducer can be further adjusted by adjusting the cone angle of the conical acoustic lens. The Bessel ultrasonic transducer will help improve the capabilities of the ultrasound probe and expand its application range. For example, an ultrasonic probe with a large depth of field will expand the imaging depth of photoacoustic microscopy and enhance its ability in non-destructive testing.