Performances of the COROT CCDs for high accuracy photometry Pernelle Bernardi and the CCD team From Meudon : Tristan Buey, Vincent Lapeyrere, Régis Schmidt, Bertrand le Ruyet, Jêrome Parisot, Didier Tiphène From CNES : Olivier Gilard, Guy Rolland (for irradiation tests) 2 nd Eddington Worskshop, Mondello (Italy), 9-11 April 2003

2 nd Eddington Workshop, Mondello, 9-11 April Corot CCD E2V Back-thinned, MPP, anti-reflection coating Operating in frame transfer mode Size of image area : 2048 rows, 2048 columns Pixel pitch: 13.5µm 2 outputs, dump drain register Readout frequency: 100kHz Readout timing: 100µs to transfer a row from the image area to the storage area 150µs to transfer a row in the register Three sides buttable  No specific technological developments  Space qualification

2 nd Eddington Workshop, Mondello, 9-11 April Geometrical requirements and packaging Flatness of image section:  3µm Top of view: 14mm  15µm (spec)  10 µm (meas) e(Invar) = 10 mm e(silicon) ~ 625 µm e(thinned silicon) ~ 15 µm 3 shims silicon invar thinned silicon 50µm min (spec) 500µm max 300µm max With this packaging: distance between image areas of 2 CCDs > 1mm

2 nd Eddington Workshop, Mondello, 9-11 April Working point 3 bias voltages are optimised: V OD, V RD, V OG Working range: measurement of the video signal for different values of the bias voltages  5 CCDs have the same working ranges for the 3 bias voltages  1 has a different behaviour: excluded from the flight Sensitivity of the video signal to the bias voltages :  About same order at worst frequency (100kHz, readout frequency).  Higher sensitivities = 4e-/mV  Specification for the electronics: 1mV peak to peak ---> equivalent noise of few e -.

2 nd Eddington Workshop, Mondello, 9-11 April CCD gain (µV/e-) Specification: 3.8 < G CCD < 6.0 µV/e- CCD gain is measured independently of Qe Good homogeneity of 5 CCDs Global gain (e-/ADU) measured at different temperatures from –45°C to 20°C Temperature coefficient of the gain: ~ -900ppm/K CCD Gain at –40°C Temp coefficient of the CCD gain (ppm/K) Left outputRight output

2 nd Eddington Workshop, Mondello, 9-11 April Quantum Efficiency E2V data: Qe max = 0.90 at 650nm average Qe = 0.62 Temperature coefficient of Qe: –Measure of the flux at: - different wavelengths from 400nm to 1000nm - different temperatures from –45°C to –30°C –Calculation of the temperature coefficient of the CCD response –Correction by the temperature coefficient of the CCD gain (  G ~ -900ppm/K)  Temperature coefficient of Qe ~ 2000ppm/K for the center of the bandwith

2 nd Eddington Workshop, Mondello, 9-11 April Dark current CCD is divided into windows of 32*32 pixels For 5 CCDs: at –40°C –Mean dark current value < 0.5e-/px/s –90% of the windows < 0.5e-/px/s Map of dark current Mean dark current = 0.18e-/px/s

2 nd Eddington Workshop, Mondello, 9-11 April Pixel Response Non Uniformity (1/2) = 420nm,  = 10nm = 700nm,  = 10nm = 900nm,  = 10nm Achieved with flat illumination Shows the uniformity of the state of surface and AR coating  Surface Pattern Shows the uniformity of the physical characteristics  High homogeneity Shows the uniformity of the thickness  Fringing Pattern = 900nm  10nm = 900nm  100nm

2 nd Eddington Workshop, Mondello, 9-11 April Pixel Response Non Uniformity (2/2) CCD is divided into windows of 32*32 pixels. Local PRNU = dispersion of the pixel response in a 32*32 pixel window. For 5 CCDs: local PRNU is 5 times lower than specification. Stable with temperature

2 nd Eddington Workshop, Mondello, 9-11 April Cosmetics Definitions: –White spot: > 100e-/px/s at –40°C –Black spot: when pixel response is less than 50% of the local mean response, at -40°C. –Column defect: more than 100 contiguous blemish elements (white and black spots) Specifications: –Less than 750 black and white spots –Less than 6 column defects Measurements: specifications are fullfilled –5 CCDs have no white spots, 1 CCD has 2 white spots –The worst CCD has 2 columns defects (black columns)

2 nd Eddington Workshop, Mondello, 9-11 April Maps of defects 2 maps calculated per CCD: one for each scientific program. –Images of dark current and flat fields in three parts of the bandwith –2 shapes of PSF (seismo and exoplanets) –Performances of the instrument for each program Seismology channel Exoplanet channel Same CCD

2 nd Eddington Workshop, Mondello, 9-11 April Results of the irradiation tests 3 chips tested (4210) Tested characteristics : –Working point. –Gain and Full Well Capacity. –Dark Current (mean value, defects). –Pixel Response Non Uniformity. Irradiation induces local defects (spatial and temporal) in the dark current Global evolution Beginning of life: < 0.5e-/px/s  End of life: 3 to 10e-/px/s Rapid evolution of the dark current with temperature gives strong constraint on the CCD operational temperature  below -40°C.  Appart from the dark current all the other characteristics of the CCD will not be degraded enough to impact on the system performances.

2 nd Eddington Workshop, Mondello, 9-11 April Conclusion Sixth CCD currently under tests Calibration of 10 CCDs FM will be finished before summer Then: sort the 10 CCDs select 4 CCDs for the flight using software tools If necessary, some specific measurements can be done on selected CCDs