The Type II superlattice (T2SL) technology is an industrial solution for manufacturing of infrared (IR) imaging sensors that cover the entire IR range, including the vital eSWIR band. These stable III/V materials are uniformly grown on large GaSb wafers (up to 6") and have demonstrated excellent manufacturing yield with maintained high performance and space environment robustness. These unique properties make T2SL the most suitable technology to design and manufacture large area eSWIR FPAs which can meet the stringent requirements of future European civilian and military space programs. In this paper, the performance of IRnova’s VGA format (640 x 512 pixels, 15 μm pitch) eSWIR T2SL detectors designed for industrial applications will be presented along with the development route towards large footprint (2048 x 512 pixels, 15 μm pitch) HD eSWIR FPAs with CTIA ROICs targeting space applications within the EU-funded STEP project (Silicon and T2SL EuroPean collaboration for a non-dependent supply chain for large eSWIR FPAs). From initial results, a cut-off wavelength of 2.5 μm, quantum efficiency > 80% and a dark current density lower than 0.1μA/cm2 @ 200 K have been demonstrated.
Thanks to their high technology readiness level, quantum well infrared photodetectors (QWIP) provide an efficient and swift solution for meeting the increased demand for advanced LWIR imaging systems. IRnova’s present portfolio includes QWIP detectors for LWIR dual-colour, gas detection, and polarimetric imaging on 30 and 15 μm pitch, while the development of large-format HD arrays on 10 μm pitch is ongoing.
In this work, the latest advancements for LWIR QWIP detectors (peak absorption at 8.5 μm) are presented: firstly, focusing on the progress on HD-format detectors on 10 μm pitch and secondly, presenting the enhanced polarization contrast in IRnova’s VGA-format polarimetric detector Fenrir (640×512 on 15 μm pitch). In the new Fenrir, the polarization contrast has increased from ~25% to ~40%, resulting in improved tracing of the polarimetric signatures as visualized by field tests. Furthermore, by employing array-wide pixel-level spectroscopy, excellent spatial uniformity across detector arrays has been confirmed.
In this paper, the first extended SWIR (eSWIR, 1-2.5 μm) focal plane array (FPA) results, based on IRnova’s 2.5 μm cutoff T2SL design are presented. High sensitivity is demonstrated with a signal to noise ratio (SNR) of 215 @ 50% well fill and a dynamic range of 1750 for a full well size of 118 ke- of the CTIA ROIC. Good uniformity across the detectors is evidenced by narrow SNR histograms, uniform response maps and low signal non-uniformity (~1 %). This work is part of the development route towards large footprint (2048 × 512 pixels, 15 μm pitch) HD space prototype eSWIR FPAs, currently performed within the EU-project STEP (Silicon and T2SL EuroPean collaboration for a non-dependent supply chain for large eSWIR FPAs). In addition, a first preview of the HD FPA performance enabled by IRnova’s midwave infrared (MWIR) T2SL small pitch technology is presented, showing an NETD of 32 mK at 120 K with F/3, 60 Hz and 10 ms integration time.
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.
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