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.
QWIPs are renowned for unmatched image uniformity and stability. Still, in popular belief they are often associated with only stationary platforms due to low operating temperature and quantum efficiency. Challenging this myth, we demonstrate the performance of VLWIR QWIP in such demanding applications as handheld camera for gas detection and microsatellite for remote sensing. In the former, NETD of <25 mK is routinely achieved on 15 μm pitch sensor (target 30 C, 30 Hz frame rate, F/1.2, 10.5 μm peak absorption) consuming <9 W. In the latter, the 30 μm pitch array has two IR channels (10 and 10.8 μm) employing monolithically integrated bandpass filters. IDDCA delivers NETD <50 mK for 2 ms integration time (17 °C target, F/1.2) consuming 10 W. It comprises technology demonstrator for evaluating the use of microsatellites for precise temperature monitoring in Earth Observation applications. Stability of its non-uniformity correction, which is paramount for space-born applications, is also demonstrated.
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.
The III-V material system has proven to be a solid base for building infrared detector focal plane arrays (FPAs), enabling well-established designs such as bulk InSb-photodiodes, GaAs-based quantum well infrared photodetectors (QWIP) and GaSb-based type-II superlattices (T2SL). The remarkable advancement in the sensitivity and stability of such FPAs seen in the past decades calls for revision of the merits and the acceptance criteria used for the performance evaluation of infrared imaging arrays. Specifically, the early skepticism toward QWIP has largely been focused on their low quantum efficiency, and consequently low specific detectivity of the FPA pixels, as compared to the counterparts with bulk design. It was later demonstrated that unrivalled spatial uniformity of QWIP arrays (typically with a residual non-uniformity <0.05 %) not only compensated for this drawback, but rendered them superior in terms of the sensitivity, with typical noise equivalent temperature difference (NETD) <30 mK (when staring at 30 °C source through F/2.24 aperture, FPA on 15 μm pitch operated at 70 K and 60 Hz frame rate, peak absorption at 8.6 μm). This introduced QWIPs to the demanding applications, such as tactical or gas sensing, in spite of the design’s inherently low detectivity. In this paper, we propose the tightened criteria for marking the defective pixels and demonstrate how IRnova’s III-V based long-wave QWIP and mid-wave T2SL FPAs with 15 μm pitch live up to them. High spatial uniformity is reflected in symmetric and almost tail-free NETD histograms for both detector types. Only 0.13 % of the pixels exhibit NETD above ×1.5 of the median value for QWIP and 0.14 % - for T2SL detectors. At the same time, there are virtually no pixels falling outside less stringent limit of ×3 the median value. For QWIPs, this observation is consistent with flat noise spectra, which are completely free from the low-frequency “1/f”-component, as measured on the test cells. Finally, our attesting procedure allows tracing even solitary pixels exhibiting deviating types of noisy behavior, including random telegraph signal (RTS)-like, whenever they are present in the array. Low number of RTS-like pixels is a key advantage of III-V based FPAs that enables them to be used for high-operating-temperature (HOT) applications. Another characteristic feature of III-V based detectors is the outstanding stability of their performance. For IRnova’s mid-wave T2SL FPA on 30 μm pitch, using a 3-year-old non-uniformity correction map even without refreshing the offset is penalized by a mere 100 % increase in the residual fixed pattern noise relative to its temporal NETD. In the paper, we complement this with a study on the stability of the non-uniformity correction of IRnova’s QWIP and T2SL detectors on 15 μm pitch.
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.