1K x 1K and Larger Staring Focal Plane Arrays

Abstract

Until recently, very large focal plane arrays (> 1K x 1K pixels) could only be fabricated using low density ≥ 2 µm CMOS processes employing full wafer projection lithography. Higher density processes use steppers to expose the patterns on the wafer which have limited the die size to the area able to be exposed in a single step. This placed an upper limit on the readout die size of about 18-22 mm along a side. While stitching techniques have been used to pattern larger die, most silicon foundries are unwilling to accept such projects. Raytheon has recently pioneered a foundry friendly technique that allows an arbitrarily large readout to be fabricated using advanced submicron (0.6 to 0.8 µm) and deep submicron (0.25 to 0.35 µm) CMOS processes.In July 1998, Raytheon fabricated a 2,052 x 2,052 readout with 25 µm x 25 µm pixels for a low background astronomy application. This readout was 54.7 mm x 54.7 mm in size -more than 4x the area of the 22 mm x 22 mm mask size. In 1999, Raytheon has produced two different tactical imaging InSb FPAs in > 1K x 1K formats using pixel sizes ranging from 20-25 µm. These tactical FPAs have been processed in a triple metal, 0.5 µm CMOS process and range in size from 23 mm x 23 mm to nearly 40 mm x 40 mm.Excellent FPA uniformity and sensitivity have been measured on a 1,344 x 1,344 InSb FPA. An f/2.0 NE∆T of 25 mK with an operability of > 99.9% has been achieved. The array uniformity is also outstanding with an uncorrected responsivity sigma/mean of only 3.2% and an offset non-uniformity of only 1.4% of full swing. This FPA has a charge capacity of over 31 million carriers and can be operated at frame rates up to 30Hz.