Backside-Illuminated, high QE, 3e- RoN, fast 700fps, 1760x1680 pixels CMOS Imager for AO with highly parallel readout Mark Downing* a , Johann Kolb a , Gert Finger a , Olaf Iwert a , Norbert Hubin a , Javier Reyes a , Philippe Feautrier b , Jean-Luc Gach c , Philippe Balard c , Christian Guillaume d , Eric Stadler b , Martin Fryer, Paul Jorden, Andrew Walker, Andrew Pike, Paul Jerram, Jerome Pratlong, Bart Dierickx, Benoit Dupont, Arnaud Defernez. a ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany; b e2v technologies,106 Waterhouse Lane, Chelmsford, Essex, CM1 2QU, England; c Caeleste, Generaal Capiaumontstraat 1, 2600 Antwerp, Belgium, BE 0885.890.904; d Institut de Planétologie et d’Astrophysique, BP 53 38041 Grenoble France; e LAM, Laboratoire d’Astrophysique de Marseille, 2 place Le Verrier, 13248 Marseille France; f OHP, Observatoire de Haute Provence, 04870 St.Michel l'Observatoire, France. ABSTRACT The success of the next generation of instruments for 8 to 40-m class telescopes will depend upon improving the image quality (correcting the distortion caused by atmospheric turbulence) by exploiting sophisticated Adaptive Optics (AO) systems. One of the critical components of the AO systems for the E-ELT has been identified as the Laser/Natural Guide Star (LGS/NGS) WaveFront Sensing (WFS) detector. The combination of large format, 1760x1680 pixels to finely sample (84x84 sub-apertures) the wavefront and the spot elongation of laser guide stars, fast frame rate of 700 (up to 1000) frames per second, low read noise (< 3e-), and high QE (> 90%) makes the development of such a device extremely challenging. Design studies by industry concluded that a thinned and backside-illuminated CMOS Imager as the most promising technology. This paper describes the multi-phased development plan that will ensure devices are available on-time for E-ELT first-light AO systems; the different CMOS pixel architectures studied; measured results of technology demonstrators that have validated the CMOS Imager approach; the design explaining the approach of massive parallelism (70,000 ADCs) needed to achieve low noise at high pixel rates of ~3 Gpixel/s ; the 88 channel LVDS data interface; the restriction that stitching (required due to the 5x6cm size) posed on the design and the solutions found to overcome these limitations. Two generations of the CMOS Imager will be built: a pioneering quarter sized device of 880x840 pixels capable of meeting first light needs of the E-ELT called NGSD (Natural Guide Star Detector); followed by the full size device, the LGSD (Laser Guide Star Detector). Funding sources: OPTICON FP6 and FP7 from European Commission and ESO. Keywords: Adaptive Optics Detector, AO Wavefront Detector, Wavefront Sensor, L3Vision CCD, CCD220, CMOS Imager, CMOS Image Sensor, LGSD, E-ELT. 1. INTRODUCTION ESO has a long history of developing custom devices to meet the demanding requirements of Adaptive Optics (AO) wavefront sensing (WFS). Detectors with the required combination of fast frame rate, high quantum efficiency, low read noise, and large number and size of pixels are not available off the shelf and thus specialized custom developments are necessary. This paper begins by reporting on the status of the current generation of optical AO WFS detector, the e2v [1] L3Vision CCD220 (the fastest/lowest noise AO detector to date), the excellent performance results of sub-electron read noise and extremely low dark current which are now being routinely achieved, and the deployment of a large number of camera systems on 2nd Generation VLT instruments. Attention then focuses on the main topic of the paper, the E-ELT challenge and how advances in CMOS Imagers make them an attractive technology to solve the need for a large advanced Laser/natural Guide-Star WFS Detector, the LGSD, that has been identified as critical for the success of ESO’s E-ELT. The paper continues by describing: a) the multi-