Large format 17µm high-end VOx µ-bolometer infrared detector U. Mizrahi, N. Argaman, S. Elkind, A. Giladi, Y. Hirsh, M. Labilov, I. Pivnik, N. Shiloah, M. Singer, A. Tuito*, M. Ben-Ezra*, I. Shtrichman SemiConductor Devices P.O. Box 2250, Haifa 31021, Israel ( *) Israeli MOD ABSTRACT Long range sights and targeting systems require a combination of high spatial resolution, low temporal NETD, and wide field of view. For practical electro-optical systems it is hard to support these constraints simultaneously. Moreover, achieving these needs with the relatively low-cost Uncooled µ-bolometer technology is a major challenge in the design and implementation of both the bolometer pixel and the Readout Integrated Circuit (ROIC). In this work we present measured results from a new, large format (1024 768) detector array, with 17µm pitch. This detector meets the demands of a typical armored vehicle sight with its high resolution and large format, together with low NETD of better than 35mK (at F/1, 30Hz). We estimate a Recognition Range for a NATO target of better than 4 km at all relevant atmospheric conditions, which is better than standard 2nd generation scanning array cooled detector. A new design of the detector package enables improved stability of the Non-Uniformity Correction (NUC) to environmental temperature drifts. Keywords: VOx µ-bolometer, 17µm pitch, XGA, LWIR, Long range sight 1. INTRODUCTION In this paper we report on the development of XGA (1024 768) detector (1) using SCD s VO x µ-bolometer 17µm pitch technology (2). The main target of the XGA detector is to address the segment of high-end applications which demand simultaneously high spatial resolution (small pitch), low temporal NETD (enabling work with high f-number and smaller optics) and a wide enough field of view (large format). The first part of this paper is devoted to the XGA detector, which is a high-sensitivity 35mK (at F/1, 30Hz) detector with 17 µm pitch. We will describe the basic architecture of the ROIC, the various package solutions and supporting electronics, and the radiometric characterization results. In the second part we present TRM3 system performance simulations comparing the predicted performance of an XGA based system with 2 nd generation scanning LWIR arrays, such as MCT-TDI-288x4. It will be shown that similar and even better recognition ranges may be achieved using the uncooled detector, under various system constraints. 2. XGA DETECTOR FOR LONG RANGE SIGHTS 2.1 ROIC Architecture The basic architecture of the ROIC is presented in Figure 1. It closely follows the successful framework of the previous VGA 17 µm design maintaining the "full bridge" analog concept (3). We use the proven capabilities of the 0.18µm CMOS process to support an internal compensation mechanism and a more sophisticated interface management unit. This in turn considerably facilitates the user interface. Following is a list of the key features that were implemented in the ROIC: Full support of all existing special features (4)
Single 50% duty cycle clock (up to 60MHz). Two modes for system configuration interface: 1. UART (8N1, auto baud track). 2. Synchronous bidirectional 6bit parallel Programmable on-chip gain selection for wide FPA and ambient temperature span. 1.8V digital I/O interface. Four video outputs for higher frame rates. Max frame rate is 60Hz, for full frame. Direct (or "glue-less") interface to the external ADC (eliminates the need for extra buffers). Frame timing: either internal ("free running") or external synchronization. 1024x768 Figure 1, Basic Architecture of the XGA ROIC 2.2 Package The package was designed to ensure vacuum level integrity for at least 14 years (in ambient temperature). The base of the package is used as mounting surface and features high accuracy design in order to ensure proper parallelism. Special I/O pins are connected to an internally mounted Getter that can be re-activated by the user to ensure vacuum integrity for very long periods. The package was tested to withstand temperature cycles, random and sine vibration and shocks in alignment with the stringent military demands of TWS and Tank applications. The XGA detector supports both windows housing configuration as presented in Figure 2. The common package that will fit most of the systems with f/# >1 has a window close to the FPA. This package configuration is suitable for systems with relative low f/#. Another configuration of packaging involves a radiation shield and large distance between window and FPA, configuration which is suitable for systems with high f/#, and requires a reimaging optics, similar to cooled detector systems. The motivation for the radiation shield is to maintain a low Residual Non Uniformity (RNU) during environmental temperature drifts, thus increasing the time span between Non-Uniformity Corrections (NUC). The window housing is designed such that radiation from out of the system s field of view will be absorbed in a highly emissive, temperature
stabilized surface, and when the FPA looks at the window housing (excluding the window), it sees the highly emissive, temperature stabilized, surface. Therefore the detector is immune to radiation from out of the system field of view.
DPE DETECTOR PS DETECTOR MESSAGES& SYNC IR Detector ANALOG VIDEO Detector Bias P.S SYSTEM MAIN PS BIRD & DPE Control RS232&CONTROL VIDEO SAMPLING& PREPROCESS SERIALIZED VIDEO DPE ELECTRONICS PS SYSTEM COMMANDS CONTROL Camera Link Frame Graber BIT TEMP Readout TEC CURRENT Close/Open TEC LOOP& Contol TEC DRIVE PS TEC PS Shutter Driver Gen_diag1 Figure 4, DPE block diagram, and XGA module 2.4 Preliminary Electro-Optical Results Some preliminary characterization results are exhibited in Figure 5. On the right hand side we demonstrate the temporal NETD distribution measured with F/1 optics and frame rate of 30Hz. The peak of the distribution is around 20mK as shown previously with the BIRD640 17HS (1) detector. The left hand side presents uniform image of the NETD without bold spatial disturbances. Distribution of the measured thermal time constant of the High Sensitive (HS) pixel in XGA detector is presented in Figure 6, and the average value is ~12mSec. Even for the first production lots we have already achieved excellent uniformity with pixel operability better than 99.5%. These figures translate into high image quality as shown in Figure 7. Figure 5, Measured temporal NETD (mk) at F/1, 30Hz: 2D map (left) and its histogram (right)
Pixel Counts τ (msec) Figure 6, Thermal Time Constant of High Sensitive (HS) Pixel in XGA Detector The XGA detector was integrated into a demonstration camera with 210mm focal length and F/1.4 optics and some representative images are shown in Figure 7. The combination of an exceptionally small IFOV of 80µRad and system temporal NETD of roughly 45mK enables the recognition of a human at fairly large distances. Figure 7, Captured images with a 210mm focal length, f/1.4 system: The houses in the picture are 2km away. The image on the right hand side is using digital zoom for the same scene.
2.5 Product status Following the successful production of prototypes, we are accelerating our activity towards full production. Our goal is to qualify the product and move to production during 2013. 3. SYSTEM PERFORMANCE SIMULATIONS The XGA detector has the potential to replace or upgrade existing cooled LWIR scanning systems (1). In order to validate this assumption, we have performed TRM3 (6) system simulations comparing the expected performance of the uncooled XGA 17µm with state of the art 288x4 MCT TDI scanning arrays operating at 77K. The requirements and system constraints are as follows: NATO target: 2.3m X 2.3m T (Target-Background) = 2 C Atmosphere Extinction coefficient = 0.16 0.4 (variable) Optical aperture = 120mm (system constraint) Table 1 summarizes the system parameters for the uncooled XGA and typical SADAII 288x 4 Time Delayed Integration (TDI) cameras. Both systems are assumed to operate at 30Hz frame rate. For the sake of comparison we assume identical optical transmission (approximately 80%) and display properties. Detector Parameter 2 nd Gen MCT TDI 288 X 4 Uncooled XGA F-number 1.86 1.67 Detector Pixel 28 x 25 µm 17 x 17 µm Focal length 225 mm 200 mm IFOV 110 µrad 85 µrad FOV 2.7 0 x 2 0 5 0 x 3.75 0 Spectral Range 7.8 10.2 µm 8 14 µm Table 1, System parameters used in the TRM3 calculation The TRM3 calculation results for the systems described in Table 1 are shown in Figure 8. We present the target recognition range as a function of atmospheric extinction for the µ-bolometer XGA and MCT TDI 288x4 array respectively. The global RNU is assumed to be 70% of the NETD. This is a remarkable challenge for µ-bolometer systems and requires special image processing algorithms. These simulations show that under a wide range of atmospheric conditions the XGA performs better than the TDI 288x4. The margin diminishes for poorer atmospheric conditions. The XGA detector also supports a considerably larger FOV which is extremely important for high end applications. Another important segment is Remote Weapon Stations (RWS) where we consider human recognition. In this case the target size is 0.5m x 1.6m with T = 5 0 C. Figure 9 presents the calculated recognition range for a 120mm aperture. The range is slightly above 1Km and as expected is hardly affected by atmospheric conditions. In conclusion, high-end µ-bolometer systems hold a great potential for replacing or upgrading 2 nd generation cooled scanning systems. The introduction of µ-bolometer technology can reduce dramatically the "cost of ownership" of such systems and as a result increase their proliferation.
5 4.8 Recognition Range [Km ] 4.6 4.4 4.2 4 3.8 3.6 3.4 XGA TDI 288x4 3.2 3 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Atmospheric Extinction [1/Km] Figure 8, Calculated recognition ranges for a NATO target vs. atmospheric extinction for uncooled XGA and cooled MCT- TDI 288x4 based systems. (RNU = 0.7*NETD) 1.3 Recognition Range [Km] 1.25 1.2 1.15 1.1 1.05 XGA 1 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Atmospheric Extinction [1/Km] Figure 9, Calculated human target recognition ranges for similar system and atmospheric conditions. 4. SUMMARY AND CONCLUSIONS In this paper presented SCD's state of the art micro-bolometer VO x uncooled XGA detector array. We showed the main features and performance of the new detector optimized for long-range, large FOV sights. In the last part we presented system simulations comparing the expected performance of an XGA µ-bolometer detector with 2nd generation scanning MCT LWIR 288x4 TDI arrays. The calculations show that similar recognition ranges
maybe achieved under various system constraints. Hence, high-end µ-bolometer systems have the potential for upgrading 2nd generation scanning systems, with all the cost and reliability related benefits. ACKNOWLEDGEMENTS The development of the detector was supported by the Israeli Ministry of Defense (IMoD). We are in debt to the numerous engineers and technicians participating in the project, for their dedicated contribution to the development and production of the detectors. REFERENCES 1. U. Mizrahi et al. "Advanced µ-bolometer detectors for high-end applications", Proc. SPIE 8353 (2012). 2. U. Mizrahi et al. "New Developments in SCD's 17µm VOx µ-bolometer Product Line", Proc. SPIE 7660 (2010). 3. A. Fraenkel et al. "SCD's Uncooled Detectors and Video Engines for a Wide Range of Applications", Proc. SPIE 8012, 8012-04 (2011). 4. A. Fraenkel et al. "Advanced Features of SCD's Uncooled Detectors", Opto-Electronics Review 14(1), 47-54 (2005). 5. A. Fraenkel et al. BIRD640: SCD's High Sensitivity VGA VOx µ-bolometer Detector, Proc. SPIE 6737, 6737-0U (2007). 6. W. Wittenstein "Thermal range model TRM3" Proc. SPIE Vol. 3436, pp. 413-424, Infrared Technology and Applications XXIV.