  Many astronomical optical systems have the disadvantage of generating curved
focal planes requiring flattening optical elements to project the corrected
image on flat detectors. The use of these designs in combination with a
classical flat sensor implies an overall degradation of throughput and system
performances to obtain the proper corrected image. With the recent development
of curved sensor this can be avoided. This new technology has been gathering
more and more attention from a very broad community, as the potential
applications are multiple: from low-cost commercial to high impact scientific
systems, to mass-market and on board cameras, defense and security, and
astronomical community. We describe here the first concave curved CMOS detector
developed within a collaboration between CNRS- LAM and CEA-LETI. This
fully-functional detector 20 Mpix (CMOSIS CMV20000) has been curved down to a
radius of Rc = 150 mm over a size of 24x32 mm^2 . We present here the
methodology adopted for its characterization and describe in detail all the
results obtained. We also discuss the main components of noise, such as the
readout noise, the fixed pattern noise and the dark current. Finally we provide
a comparison with the flat version of the same sensor in order to establish the
impact of the curving process on the main characteristics of the sensor.
