In recent years, high-operation temperature (HOT) detector applications in the mid-wave infrared spectral range (MWIR) have widely attracted attention [1, 2]. In the LWIR and VLWIR spectral ranges, an increase in operating temperature while keeping the detector performance obtained at lower temperatures proved to be significantly more difficult. The demands on detector material quality and detector processing are much higher. With LWIR HOT detector applications more and more evolving, AIM as a leader in LWIR MCT detectors has addressed the challenge. We like to note that AIM has a long standing track record on dark-current reduction, especially by extrinsic Au doping in the LWIR and VLWIR spectral range [3, 4, 5, 6]. During the last couple of years we matured our p-on-n LWIR technology, a key technology for high-performance small pixel pitch planar LWIR HOT MCT devices . In this paper we present the status of our n-on-p and p-on-n low dark current planar MCT photodiode technology. The development was funded by ESA TRP contracts and resulted in follow-on contracts to even further optimize LWIR and VLWIR MCT and corresponding ROICs, especially for low-temperature, large area, astronomy applications. AIM’s manufacturing of HOT MCT devices is based on the liquid phase epitaxial (LPE) growth on latticematched in-house grown CdZnTe (CZT) substrates from a Te-rich melt, using the vertical dipping method [7, 8]. This method allows growing large MCT wafers with currently fair homogeneity in layer thickness (±1μm) as well as in composition (±0.3μm cut-off wavelength) across an area of 1.5 inch diameter in the LWIR-VLWIR cut-off wavelength range. We have investigated and compared technological constraints and performance of n-on-p and p-on-n growth for different doping levels and other process parameters. In the following we present the results for both technologies on 512 x 320 pixel format arrays with 20μm pixel pitch.
To push HOT-performance, AIMs existing n-on-p technology has been improved by introducing Gold as an acceptor and reducing its concentration to the lower 10<sup>15</sup>/cm<sup>3</sup> range as well as by optimizing the passivation process. This results in a substantial reduction in dark current density, a prerequisite for HOT operation. Recent dark current data are compared to ones previously obtained as well as to Tennant`s Rule07 , a generally accepted bench mark in this context.<p> </p>Furthermore, we present electro-optical parameters obtained in the temperature range from 120 K to 170 K on resulting FPAs with 640x512 pixels, a pitch of 15 μm and a typical (80 K) cutoff wavelength of 5.1 μm.
In this paper we describe a cryogenic testbed designed to offer complete characterisation-via a minimal number of experimental configurations— of mercury cadmium telluride (MCT) detector arrays for low-photon background applications, including exoplanet science and solar system exploration. Specifically, the testbed offers a platform to measure the dark current of detector arrays at various temperatures, whilst also characterising their optical response in numerous spectral bands. The average modulation transfer function (MTF) can be found in both dimensions of the array along with the overall quantum efficiency. Working from a liquid-helium bath allows for measurement of arrays from 4.2 K and active-temperature control of the surface to which the array is mounted allows for characterisation of arrays at temperatures up to 80 K, with the temperature of the array holder known to an accuracy of at least 1 mK, with the same level of long-term stability.
Cryogenically cooled HgCdTe (MCT) quantum detectors are unequalled for applications requiring high imaging as well as high radiometric performance in the infrared spectral range. Compared with other technologies, they provide several advantages, such as the highest quantum efficiency, lower power dissipation compared to photoconductive devices, and fast response times, hence outperforming micro-bolometer arrays. AIM will present its latest results on n-on-p as well as p-on-n low dark current planar MCT photodiode focal plane detector arrays at cut-off wavelengths >11 μm at 80 K. Dark current densities below the Rule’07 have been demonstrated for n-on-p devices. Slightly higher dark current densities and excellent cosmetics with very low cluster and point defect densities have been demonstrated for p-on-n devices.
In the framework of this paper, AIM presents the actual status of some of its currently ongoing focal plane detector
module developments for space applications covering the spectral range from the short-wavelength infrared (SWIR) to the long-wavelength infrared (LWIR) and very-long-wavelength infrared (VLWIR), where both imaging and spectroscopy applications will be addressed. In particular, the integrated detector cooler assemblies for a mid-wavelength infrared (MWIR) push-broom imaging satellite mission, for the German hyperspectral satellite mission EnMAP will be elaborated. Additionally dedicated detector modules for LWIR/VLWIR sounding, providing the possibility to have two different PVs driven by one ROIC will be addressed.
In the framework of this paper, AIM presents the actual status of some of its currently ongoing focal plane detector
module developments for space applications covering the spectral range from the short-wavelength infrared (SWIR) to
the long-wavelength infrared (LWIR) and very-long-wavelength infrared (VLWIR), where both imaging and
spectroscopy applications will be addressed. In particular, the integrated detector cooler assemblies for a mid-wavelength
infrared (MWIR) push-broom imaging satellite mission, for the German hyperspectral satellite mission EnMAP will be
elaborated. Additionally dedicated detector modules for LWIR/VLWIR sounding, providing the possibility to have two
different PVs driven by one ROIC will be addressed.
An increasing need for high-precision atmospheric data especially in the long wavelength infrared (LWIR) and very long
wavelength infrared (VLWIR) spectral ranges has arisen in the past years not only for the analysis of climate change and
its effect on the earth's ecosystem, but also for weather forecast and atmospheric monitoring purposes.
Spatially and spectrally resolved atmospheric emission data are advantageously gathered through limb or nadir sounding
using an imaging Fourier transform (FT) interferometer with a two-dimensional (2D) high-speed focal plane detector
In this paper, AIM reports on its latest results on MCT VLWIR FPAs for Fourier transform infrared sounding
applications in the 8-15μm spectral range. The performance of a (112x112) pixel photodiode array with a 40μm pixel
pitch incorporating extrinsic p-doping for low dark current, a technique for linearity improvement at high photon fluxes,
pixel guards, pixel select/de-select, and a (2x2) super-pixel architecture is discussed. The customized read-out integrated
circuit (ROIC) supporting integrate while-read (IWR) operation has a buffered direct injection (BDI) input stage and a
full well capacity (FWC) of 143 Megaelectrons per super-pixel. It consists of two independently operating halves with
two analog video outputs each. The full frame rate is typically 4k frames/sec, making it suitable for use with rapid scan
FT infrared spectrometers.
At a 55K operating temperature and an ~14.4μm cut-off wavelength, a photo response of 12.1mV/K and a noise
equivalent temperature difference of 24.8mK at half well filling are demonstrated for a 286K reference scene. The nonlinearity
error is <0.5%.
The mission success of the geostationary operational satellite system Meteosat Third Generation (MTG) will
significantly depend on the instrument performance in the very long wavelength infrared (VLWIR) spectral range. As far
as dark current behavior, homogeneity, and operability are concerned, the VLWIR constitutes a major challenge for
sensor material improvement and device development. This paper reports on the latest results on HgCdTe (MCT)
VLWIR photovoltaic sensor development and characterization for possible use with MTG.
In order to achieve low enough dark currents, extrinsically p-doped MCT material with various cut-off wavelengths in
the long wavelength infrared (LWIR)/VLWIR has been developed and manufactured. Compared to standard intrinsic
MCT, a reduction in dark current by more than an order of magnitude is achieved, meeting the challenging MTG
In a (256x256) VLWIR MCT focal plane array (FPA) with an ~14.7μm cut-off wavelength at a 55K operating
temperature, a dark current density of about 1pA/μm<sup>2</sup> is demonstrated. For a 291K reference scene and at half-well
integration capacity, we obtain a noise equivalent temperature difference of (24.0±3.0)mK and a photo response of
Next generation infrared sensor space applications are based on technological evolutions on many frontiers. Sensor
material improvements and device developments are two of them. This presentation reports on the latest results on
HgCdTe (MCT) very long wavelength infrared (VLWIR) photovoltaic (PV) sensors and on the development of short
wavelength infrared (SWIR) avalanche photodiodes (APDs).
The dark current of photodiodes increases exponentially with increasing cut-off wavelength. To keep the dark current at
an acceptable level, operational temperatures of MCT PV sensors with photo-sensitivity above 12 μm wavelength are
typically around 50 K. Therefore, until recently, VLWIR MCT detectors have been built with photoconductive (PC)
linear arrays or small 2D arrays enabling the higher operational temperatures of PC sensors (80 K - 120 K). The increasing
interest in VLWIR imaging spectrometers requires larger 2D arrays excluding PC technology. One approach for
feasible PV arrays is a significant reduction of the dark current by using extrinsically doped (in contrast to vacancy
doped) p-MCT material. This allows for enhanced performance at convenient temperatures of 50 - 55 K. Alternatively,
standard performance at higher operational temperatures at 60 K - 70 K is possible. AIM presents the latest results on its
extrinsically p-doped VLWIR MCT photodiodes with a 15 μm cut-off wavelength.
At the other side of the IR spectrum, AIM has a strong focus on focal plane arrays for low-photon flux SWIR applications.
For some applications, the sensitivity of SWIR arrays with capacitive transimpedance amplifier input stages is not
sufficient and APDs are required. AIM presents the latest results on its SWIR APD devices.
In all recent missions our forces are faced with various types of asymmetric threads like snipers, IEDs, RPGs or
MANPADS. 2<sup>nd</sup> and 3<sup>rd</sup> Gen IR technology is a backbone of modern force protection by providing situational
awareness and accurate target engagement at day/night. 3<sup>rd</sup> Gen sensors are developed for thread warning capabilities
by use of spectral or spatial information. The progress on a
dual-color IR module is discussed in a separate paper .
A 1024x256 SWIR array with flexure bearing compressor and pulse tube cold finger provides > 50,000h lifetime for
space or airborne hyperspectral imaging in pushbroom geometry with 256 spectral channels for improved change
detection and remote sensing of IEDs or chemical agents. Similar concepts are pursued in the LWIR with either
spectroscopic imaging or a system of LWIR FPA combined with a cooled tunable Laser to do spectroscopy with
stimulated absorption of specific wavelengths.
AIM introduced the RangIR sight to match the requirements of sniper teams, AGLs and weapon stations, extending the
outstanding optronic performance of the fielded HuntIR with position data of a target by a laser range finder (LRF), a 3
axis digital magnetic compass (DMC) and a ballistic computer for accurate engagement of remote targets. A version
with flexure bearing cooler with >30,000h life time is being developed for continuous operation in e.g. gunfire detection
systems. This paper gives an overview of AIM's technologies for enhanced force protection.
In recent years, the interest in infrared imaging systems has broadened from the classical MWIR (3-5 &mgr;m) and LWIR
(8-12 &mgr;m) spectral bands to the SWIR (1-3 &mgr;m) and VLWIR (12-15 &mgr;m). The atmospheric transmission windows
(MWIR, LWIR) are the preferred spectral region for panchromatic night vision systems to display temperature contrasts.
Whereas the characteristic absorption and emission signatures in the SWIR and VLWIR make these bands well suited
for remote sensing of material composition (hyperspectral imaging). In the standard bands, AIM has constantly
improved homogeneity and reduced the number of defects of its FPAs. We obtain for instance 0.38% defective pixels
for 384 x 288 LW arrays. Our FPAs withstand >9'000 thermal cycles without degradation. The improved reliability is
based on substrate removal and applying a thermally matched underfiller. For hyperspectral imaging applications, a
1024 x 256 SWIR array with 245 Hz frame rate for low photon fluxes with CTIA input stage was developed. For
VLWIR applications we built a 256 x 256 array with 880 Hz frame rate that has a cut-off wavelength of >13 &mgr;m at 40 K.
AIM's IR detectors cover the whole spectral range from 0.9 to 13 &mgr;m.
Remote sensing from space is an emerging market for applications in security, climate research, weather forecast, and global environmental monitoring, to mention a few. In particular, next generation systems demand for large, two-dimensional arrays in the short (SWIR, 0.9-2.5 μm) and the very long wavelength infrared (VLWIR) spectral range up to 15 μm. AIM's developments for space applications benefit from AIM's experiences in high-performance thermal imaging and seeker-head applications. AIM has delivered a 13 μm cut-off demonstrator for a high resolution Fourier-transform imaging spectrometer in limb geometry. For this 256 x 256 VLWIR sensor we measured a responsivity of 100 LSB/K and a noise equivalent temperature difference of 22 mK with 14 bit ADCs at 880 Hz full frame-rate. The substrate and epitaxial layer grown at AIM exhibit very good uniformity and low dark currents. Currently, AIM develops a 1024 x 256 SWIR detector (0.9-2.5 μm) with a capacitance transimpedance amplifier (CTIA) for hyperspectral imaging. The radiation hardness of AIM's FPA technology (MCT sensor and Silicon read-out integrated circuit) has been successfully tested by a total ionization dose (TID) experiment using ESTEC's <sup>60</sup>Co γ-source. Our reference module withstands 30 krad TID. For enhanced reliability of the IDCA, AIM has developed a compact 1 W pulse-tube cooler with flexure bearing compressor, which induces also a very low vibration output. In summary, AIM will be able to supply space qualified detector modules covering the spectral range from 0.9 to 13 μm in the near future.