Euclid CCDs Douglas Jordan Precision Astronomy with Fully

Euclid CCDs Douglas Jordan Precision Astronomy with Fully Depleted CCDs Brookhaven National Laboratory, December 4 -5, 2014.

Euclid CCDs – Introduction • This presentation will present a summary of the Euclid mission and the requirements of the CCD 273 -84. • Followed by MTF and QE measurements from recently delivered EM (Electrical Model) samples. Slide 2

The Euclid Mission • Euclid is an ESA medium class astronomy and astrophysics space mission. Launch is planned in 2020. • 36 CCD 273 -84 image sensors will make the focal plane of the high quality panoramic visible imager (VIS). • The main task of this instrument is to enable weak lensing measurements. Slide 3

The CCD 273 -84 • The baseline sensor for the mission was e 2 v’s CCD 203 -82 initially developed for NASA’s Solar Dynamics Observatory (SDO) • The CCD 203 -82 is a 4 k x 4 k pixel sensor with each pixel 12 x 12μm. • To optimise the device for Euclid, e 2 v have designed and manufactured the CCD 273 -84 considering the following critical specifications. • High QE at long wavelengths • Tight requirements on PSF. • Close butted package. Slide 4

The CCD 273 -84 vs CCD 203 -82 • This device has a higher-responsivity lower-noise amplifier. • • ~7µV/e- vs ~4µV/e- Enhanced response through the adoption of thicker deep depleted silicon. • 40µm nominal thickness, 1500Ωcm. • Four output ports, each reading out a 2 k x 2 k quadrant of the device. • Further design considerations to mitigate for radiation. Slide 5

Radiation Damage Mitigation • There additional factors to consider when we remember that this device is going into space and as such will be subjected to a radiative environment. • Traps are the main cause of CTE degradation. • Radiation induced traps act on a particular volume so it follows that by reducing the interaction volume, one could reduce the frequency of traps Build the device with a thinner register channel. • Introduce a charge injection structure to fill traps with a “fat zero” prior to readout. Slide 6

Radiation Damage Mitigation • Another undesired impact of the incident ionising radiation is the build-up of charge in the dielectric introducing a flat-band voltage shift. • Electrons readily swept out of the oxide but holes get trapped at one of the interfaces Flat-band voltage shift. • This can seriously affect the operation of the device rendering it unusable within the recommended voltages. • This effect is more pronounced for thicker oxides, so as mitigation, thin -gate technology was adopted. Slide 7

The CCD 273 -84 (front-face sample) Deep Depleted Silicon. 1500Ωcm, 40µm nom. thickness Si. C Package 4Ø Image area (Thin-gate technology) FWC ~ 200 Ke 4096 x 4096 Active, 12µm Pixels 4 x 2 -stage outputs ~2. 5 e-r. m. s Injection Structure Bi-Directional, 3Ø Register FWC ~ 350 Ke 70 KHz Readout Frequency Flexi Connectors to minimize dead space Slide 8

Quantum efficiency Slide 9

Quantum efficiency - red Slide 10

MTF – measurement technique • • • “Pseudo” MTF measured using the vernier technique. A 10µm slit is de-magnified by 20 times and projected on to the device. A gradient of 1 in 8 is used in both serial and parallel directions. Slide 11

MTF – measurement technique • A line response function (LRF) is generated, which is then Fourier transformed to obtain the MTF vs sampling frequency. • This is normalised to 100% at zero frequency. MTF calculated in this way is the total measured MTF • ������ = ������ ×������. �� �� • • Which are the diffusion, geometric and optical MTF components of the system. The results stated in this presentation are presented at Nyquist frequency (1/(2*pixel pitch)) with the optical component of MTF removed. ������. NY= ������ T/������ �� Slide 12

MTF Results from EM deliverables Wavelength (nm) Horizontal MTF (Vertical Slit) Vertical MTF (Horizontal Slit) 550 nm 750 nm 900 nm Specification (%) Average Min Max 30 43. 2 35 47. 2 40 50. 5 30 42. 0 35 46. 1 40 48. 5 Min Max 39. 3 44. 5 49. 2 38. 6 43. 7 47. 4 46. 0 49. 0 51. 5 44. 4 48. 0 49. 7 Slide 13

Is the device fully depleted? • Early MTF data is shown with a model of MTF for two different thicknesses of un-depleted silicon. I. Swindells ; R. Wheeler ; S. Darby ; S. Bowring ; D. Burt, et al. "MTF and PSF measurements of the CCD 273 -84 detector for the Euclid visible channel ", Proc. SPIE 9143, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 91432 V Slide 14

Is the device fully depleted? X-ray PSF • By measuring the σ of Gaussian fit of Fe 55 x-rays the point at which a back-thinned device becomes fully depleted can be easily seen. • Data from 150µm thick CCD 261 hi-rho device is shown for two different back substrate voltages. • When two peaks are visible there is evidence that the surface is un-depleted. Slide 15

X-ray PSF – full depletion? • The Euclid device clearly shows only one peak. • Indicating that the device is fully depleted. • Note the values of sigma are pretty high, much higher than what would match the MTF results. • Clearly more work is needed to get the analysis in line but as a measure of if full depletion is reached it works quite well. Slide 16

Tree ring characterisation? X-ray PSF • A quick question for the community. • Would this kind of analysis be helpful in characterising the resistivity inhomogeneity which produces the tree ring effect? Slide 17

• Any questions? • For more information: I. Swindells ; R. Wheeler ; S. Darby ; S. Bowring ; D. Burt, et al. "MTF and PSF measurements of the CCD 273 -84 detector for the Euclid visible channel ", Proc. SPIE 9143, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 91432 V J. Endicott ; S. Darby ; S. Bowring ; D. Burt ; T. Eaton, et al. " Charge-coupled devices for the ESA Euclid M-class Mission ", Proc. SPIE 8453, High Energy, Optical, and Infrared Detectors for Astronomy V, 845304 http: //www. euclid-ec. org/ Slide 18