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 R _ { \mathrm { c } } = 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 .