KEYWORDS: Modulation transfer functions, Medium wave, Dark current, Staring arrays, Quantum efficiency, Temperature metrology, Signal detection, Detector arrays, Infrared detectors, Image quality, Type II superlattice infrared photodetectors
In this paper, the main parameters contributing to the high-imaging quality of IRnova’s Type-II superlattice (T2SL) detectors are studied: the sensitivity, uniformity, modulation transfer function (MTF) and random telegraph signal (RTS). High-sensitivity and good uniformity across the detectors are displayed by their low-noise equivalent temperature difference (NETD) with average values of 22 mK (@ F/5.5, 125 K) and very narrow histograms. MTF values very close to the ideal ones have been demonstrated for Oden MW detectors, reaching 0.6 at the Nyquist frequency, along with a single-digit number of flickering pixels. Furthermore, thanks to the optimization of design and fabrication processes of Oden MW detectors, diffusion-limited dark current densities have been reached that are independent of the perimeter/area ratio for the pitch sizes down to 10 μm. Leveraging this achievement is the upcoming Njord MW HD detector (1280×1024 pixels, 10 μm pitch), for which the bias- and temperature-dependence have been assessed using IRnova’s in-house simulations tools. NETD values lower than 25 mK are shown for temperatures up to 140 K. The simulations were based on measured bias- and temperature- dependencies of the detectors on 10 μm pitch, combined with parameters of the dedicated 1280×1024 ROIC on 10 μm pitch design.
In 2019, IRnova announced the serial production of Oden MW, a reduced SWaP (Size, Weight and Power) integrated detector dewar cooler assembly. Oden MW relies on HOT T2SL array (640 × 512, 15 μm pitch) with full MWIR spectral band coverage (3-5 µm) without compromises on electro-optical performances. Ever since, IRnova maintained significant research efforts to further reduce the SWaP footprint, focusing on increased focal plane operating temperature above 110 K, targeting lower demand for cryocooling power thus further reducing overall power consumption. This has now resulted in small pitch T2SL detector arrays with diffusion limited dark current density, which is approaching the Rule07 with a level of around 6.5 × 10-6 A/cm2 at 150 K and a box quantum efficiency (3-5 μm) as high as 67 %. Excellent performance is demonstrated for 640 × 512, 15 μm pitch FPAs with average temporal NETD and spatial NETD values of 21 mK and 6 mK, respectively, when measured with F/5.5 aperture and 60 Hz frame rate at 140 K. These NETD values are insensitive to the temperature in the 80 K – 140 K range. High uniformity and excellent operability (~ 99.84 %) were also obtained at 140 K. In addition, arrays with 10 μm pitch were fabricated which showed similar dark current values, clearly demonstrating material maturity for the short coming small pitch HD HOT T2SL detectors at IRnova.
In 2019, IRnova launched a full-scale production of a reduced size, weight and power integrated detector dewar cooler assemblies (Oden MW; VGA format with 15 μm pixel pitch) covering the full mid-wavelength infrared spectral domain (3.7 μm – 5.1 μm). Oden MW exhibits excellent performance with operating temperatures up to 110 K at F/5.5 with typical values of temporal and spatial noise equivalent temperature of 22 mK and 7 mK, respectively, and an operability higher than 99.85%. More recently, IRnova developed a new detector design with a cut-off wavelength of 5.3 μm which can potentially allow an operating temperature of the detector up to 150K with excellent performance demonstrated on single pixels with a quantum efficiency as high as 46% at 4 µm without antireflection coating, a turn on bias lower than -100 mV and a dark current density as low as 8 × 10-6 A/cm2, which is a factor of < 5 higher than Rule07. The dark current was also found independent of the device size ranging from 10 μm to 223 μm indicating that surface leakage currents are not limiting the dark current. The achievable operating temperature of an FPA made of this new detector design has been estimated to be <150 K with F/5.5 optics. These outstanding results demonstrate that this new generation of detector design is an excellent candidate for future high operating temperature and high-definition focal plane array.
Midwave infrared (MWIR) type-II superlattices (T2SL) have revolutionized the market with possibility of low Size, Weight and Power (SWaP) detectors. IRnova currently has a full-scale production of SWaP T2SL detectors (Oden MW, 640×512 on 15μm pitch), which have demonstrated excellent performance for operating temperatures up to 110 K at F/5.5. Development of high-resolution detectors with small pixel pitch (HD, 1280×1024 pixels) for MWIR as well as long wave and very long wave infrared (LWIR/VLWIR) detection is currently ongoing. In this paper, it has been demonstrated that the low dark current density and high sensitivity needed for high operating temperatures are maintained also for these small pixel pitch detectors, which makes IRnova’s T2SL technology fully compatible with next generation HD detectors.
In this paper, the performance of small, lightweight, and low power (SWaP) midwave infrared (MWIR) type-II superlattice detectors have been studied. The detectors cover the MWIR range from 3.7 μm to 5.1 μm with quantum efficiency higher than 60% in the entire range. Statistics from the focal plane array (FPA) production show excellent reproducibility with average temporal NETD of 20 mK, spatial NETD of 5 mK and operability values typically higher than 99.85%. Good uniformity across the arrays is demonstrated with narrow NETD histograms and highly uniform gain-correction maps. Temperature studies of the FPA performance show that the low NETD values, good uniformity and high operability are maintained up to 110 K. After integration of these FPAs in SWaP integrated detector dewar cooler assemblies (IDDCAs) with F/5.5, the high FPA performance is maintained with good imaging properties.
In this paper, results from the development of InAs/GaSb superlattice focal plane arrays (FPAs) at IRnova will be presented. A versatile and robust detector design is used that allows for adjustment of the detection cut-off wavelength from 2.5 μm up to 14.5 μm with only minor changes in the detector design. Performance of the fabricated detectors has been reviewed in terms of external quantum efficiency (EQE), dark current and noise for three designs with cut-off wavelengths of 4, 5.5 and 11 μm at 80 K (referred to as DEEP BLUE, RED HOT and VLWIR, respectively). Measurements on the 15 μm sized photodiodes demonstrated 70% EQE for the MWIR designs, and almost 40% - for VLWIR. At the same time, the dark current stayed close to the Rule07 benchmark for all studied samples. Noise mechanisms have been discussed and their relation to the passivation was examined. Mature in-house processing and passivation technique of resulted in very high spatial uniformity of VGA focal plane arrays (FPAs), i.e. low relative deviations of EQE (< 6%) and of dark current density (< 12%) and narrow noise distributions for both RED HOT and DEEP BLUE FPAs. We show also that <99.5% of these arrays operate close to the fundamental noise limit.
In this paper, the performance of high operating temperature (HOT) type-II superlattice FPAs (640 × 512 pixels @ 15 μm pitch), are demonstrated. The type-II superlattice design used for these FPAs has a cut-off wavelength of 5.3 μm and the quantum efficiency is extracted to 80% at FPA level. The HOT FPAs are integrated in IDDCAs with small size, weight and power (SWaP) with F#4 configuration. Excellent imaging performance is demonstrated at 110 K with temporal NETD of 21 mK, spatial NETD of 7 mK, 10 ms integration time and typical operability > 99.8 %. From modelling and studies of the temperature dependence of the FPA performance, further increase of the operating temperature up 130 K is predicted for the 5.3μm design.
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