Progress toward fast, low-noise, low-power CCDs for Lynx and other high-energy astrophysics missions

Several high-throughput, high-resolution X-ray mission concepts now under study, including Lynx, a flagship, and AXIS, a probe, require large-format imaging detectors with performance at least as good as the best current generation devices but with much higher readout rates. We are investigating the potential of new CCD detector technology developed at MIT Lincoln Laboratory for meeting the needs of these missions. This technology features low-voltage charge transfer and fast, low-noise amplifiers. Deployed in a multiple output sensor architecture with low-power (application-specific integrated circuit) signal processing, this technology offers an attractive path to the high frame rates and low power consumption required. This approach is one of three candidates selected for development for Lynx, and it has also been included in the AXIS baseline. Here we report recent progress in developing this technology, with a focus on two characteristics critical to good low-energy response: read noise and charge packet size. We have measured read noise below 4 electrons, RMS (the Lynx requirement) at pixel rates up to 2.5 MHz in both front- and back-illuminated test devices, with transfer clock levels of ±1.5 V. We have also exploited the 8 µm pixel size of test detectors to measure the spatial extent of X-ray induced charge packets as a function of detector bias. We infer a root-mean-square radius 4 µm for charge packets originating at the entrance window of a 50 μm thick back-illuminated detector under high-bias (-20 V) conditions. We note that the high pixel ’aspect ratio’ (thickness : pixel size ≈ 6 : 1) of our test devices is similar to that expected for Lynx and AXIS detectors, and discuss implications of our charge cloud size measurements for noise requirements for these missions