No abstract

We present our mechanical design for a very-large-format, 4096x4096 pixel chargecoupled device (CCD) mosaic constructed from a 2x2 array of two-edge-abuttable, 15 pm pixel 2048X2048 CCDs. Each 2048x2048 quadrant is mounted in a custom abuttable package, thus allowing us to assemble the mosaic from the best, separately tested 2048 X 2048 imagers, while keeping the gaps between imaging areas less than 500 pm. We describe the advanced manufacturing techniques used to fabricate our package and mounting structure so that the assembled mosaic is flat ( ± 1 pixel), and the rows and columns of the individual quadrants are aligned. We have also packaged monolithic 4096x4096 CCD arrays cut from the 100 mm silicon wafers that contained four functional 2048x2048 edge-abuttable imagers. The quadrants of the monolithic array are perfectly aligned and flat, and the gaps, as designed on the wafer, are just slightly larger (approximately 550 pm). We describe our design for a modular dewar built to house the 4096x4096 CCD mosaic. The dewar splits into two parts-a camera head housing the mosaic array, and a cryogenic back containing a 3 liter capacity liquidnitrogen (LN 2 ) can, the associated LN 2 fill and vent structures, and the vacuum connections. Thermal connection to the detector is made through a spring-loaded copper contact that allows the two dewar halves to be separated easily. The dewar can be used in any orientation (look-up, look-down, or horizontal) with nearly full LN 2 capacity, by simply inserting a vent extension tube for look-up applications. With a fully wired 4096x4096 mosaic installed and operating at -100 C, the hold time of the dewar exceeds 24 hr.