ASELSAN, the largest defense company in Türkiye, develops high performance electro-optical systems for various applications. Research and development activities have been carried out on developing HgCdTe (MCT) detectors for long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR). In this paper, recent results for VGA 15μm pitch MWIR MCT detectors at IDDCA level are presented. P-on-n MCT epilayers are used for FPA fabrication with either mesa or planar pixel structures. Typically, over 99% operability and less than 20mK NETD values are achieved for 15μm pitch 640x512 format MWIR MCT FPAs at IDDCA level (F/4) in a repeatable fashion. Thermal cycle, mechanical shock, vibration and environmental tests (such as storage and operation under hot and cold temperatures) were applied to these MWIR MCT IDDCAs and passed successfully. Besides ongoing efforts on development of FPAs with 15μm pixel pitch, development activities for pixel pitch reduction also initiated recently for MWIR MCT and very promising results are achieved.
Recent advances in short-wave infrared (SWIR) technology including numerous new applications in civil areas, fusion with visible wavelengths, and integration with active imaging systems triggered the SWIR photodetector research at ASELSAN for both passive and active imaging. SWIR focal plane arrays with a 640x512 format and 15μm pitch were developed and coupled with ASEL64015C readout circuits which had been designed at ASELSAN as well. Through extensive research and development dark current density values <10 nA/cm2 (at 20°C) and operabilities >;99% were achieved. This paper reviews the work that has been conducted on SWIR detector development at ASELSAN.
ASELSAN A.S., the largest defense company in Turkey, develops high performance electro-optical systems for land, air and naval applications. Research activities on developing Mercury Cadmium Telluride (MCT) detectors are on-going for MW and LW infrared bands. In this paper, recent results on Cadmium Zinc Telluride substrate growth, long wavelength (LW) Mercury Cadmium Telluride (MCT) detector fabrication and readout integrated circuit design are summarized. LW MCT focal plane arrays with a format of 320×256/30 μm are fabricated. Noise Equivalent Temperature Difference (NETD) of these focal plane arrays (FPA) are 45.7 mK and 59.9 mK (f/1.5, 77K) while the operabilites are 98.14% and 99.28%, respectively.
Many microelectronic devices require bonding dissimilar materials to operate under extreme operating conditions. Furthermore, certain applications, such as cooled infrared (IR) detection, require large temperature cycles between ambient and cryogenic temperatures under ultra-high vacuum (UHV) conditions. The complex expansion and contraction of the various materials within the detector package structure during temperature cycles introduces significant internal stresses that may ultimately result in the failure of the sensor and/or the package. Added to this complexity is the process sensitivity of the fabricated device to elevated temperatures and adhesive application. With orders-ofmagnitude difference between gap sizes, adhesive properties such as viscosity, cure kinetics, and process temperatures become paramount for successful sensor integration. In addition, stringent outgassing requirements associated with ultra-high vacuum application further complicates the selection process for cryogenic adhesives. Under these constraints, a myriad of commercial epoxy adhesives were evaluated. We devised a characterization methodology using a combination of various analytical techniques which elucidated the complex flow properties, and cure kinetics while highlighting critical characteristics necessary for a successful material for this application with a focus on rapid cycles of learning. As the application space matures, we see the need for a next generation of adhesives for demanding and ubiquitous infrared sensing applications.
ASELSAN A.S., the largest defense company in Turkey, initiated research activities on developing Mercury Cadmium Telluride (MCT) detectors in 2014. These research activities include bulk crystal growth and surface preparation of Cadmium Zinc Telluride (CZT) substrates, Molecular Beam Epitaxial (MBE) growth of MCT layers, MCT detector fabrication, Read-Out-Integrated-Circuit (ROIC) design and detector-dewar-cooler (DDCA) assembly development. Focal plane arrays with resolutions/pixel pitches of 320x256/30 μm and 640x512/15 μm are fabricated. Noise Equivalent Temperature Difference (NETD) of 320x256 FPA is 11 mK (f#/1.5, 77K) while the operability is 98.2%. 640x512 FPA provides NETD of 32 mK (f#/1.5, 77K) and the operability is 93.2%.
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