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.
The quality of surface finishing of CdZnTe wafers plays an essential role for the development of high-performance HgCdTe detectors. The surface processing of CdZnTe wafers is regarded as one of the most challenging tasks due to the soft-brittle material characteristics of CdZnTe crystals. The HgCdTe-based detector technology requires CdZnTe wafers with atomatically smooth surfaces because of the HgCdTe epitaxial growth. The wafer processing cycle consists of multiple steps starting with as-cut wafers from in-house grown CdZnTe boules followed by a series of consecutive polishing processes. CdZnTe wafers are then cleaned prior to wafer characterization and final inspection. The objective of this work is to demonstrate the current status of CdZnTe wafer processing technology at Aselsan through the as-cut wafers to the polished wafers promoted as finished products. The current wafer processing technology produces in-house grown epi-ready CdZnTe substrates with low surface roughness (<0.5 nm) and low flatness (<1 μm) in a repeatable fashion.
As the largest defense company in Turkey, ASELSAN A.S. pioneers the development of high performance electro-optical systems. Starting from 2014, significant progress has been made for the mid-wave infrared (MWIR) HgCdTe detector technology including development of Cadmium Zinc Telluride (CZT) substrate, Mercury Cadmium Telluride (MCT) growth and focal plane array (FPA) fabrication as well as Readout Integrated Circuit (ROIC) design. In this paper, recent process optimization studies on MWIR MCT detector technology are presented. p-on-n MWIR MCT layers with Cadmium (Cd) composition of ~0.3 are used for the FPA fabrication. 640x512/15 µm FPAs, which demonstrate the state-of-the-art performances, have been fabricated. Typically, over 99.0% operability and less than 25 mK Noise Equivalent Temperature Difference (NETD) values are attained with a cut-off wavelength of 5 µm at 77K. Among these remarkable results, major improvements have been recorded in pixel uniformity, reliability and reproducibility by revisiting process steps. As a result, process yield has been considerably increased.
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.
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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