Mark Downing , Dietrich Baade, Sebastian Deiries, (ESO/Instrumentation Division),

1. Bulk Silicon CCDs, Point Spread Functions, and Photon Transfer Curves: CCD Testing Activities at ESO Mark Downing, Dietrich Baade, Sebastian Deiries, (ESO/Instrumentation Division), Paul Jorden (e2v technologies). Agenda: • Bulk Silicon CCDs • PSF • Photon Transfer Curves DfA 2009: Bulk CCD, PSF, & PTC.

2. The CCD Silicon Family • System designers can now choose the silicon thickness that best suits their application. • 16 um standard silicon - 100 ohm-cm. DfA 2009: Bulk CCD, PSF, & PTC.

3. The CCD Silicon Family • System designers can now choose the silicon thickness that best suits their application. • 16 um standard silicon - 100 ohm-cm. • 40 um deep depletion - 1500 ohm-cm. DfA 2009: Bulk CCD, PSF, & PTC.

4. The CCD Silicon Family • System designers can now choose the silicon thickness that best suits their application. • 16 um standard silicon - 100 ohm-cm. • 40 um deep depletion - 1500 ohm-cm. • 70 um bulk silicon - > 3000 ohm-cm. DfA 2009: Bulk CCD, PSF, & PTC.

5. The CCD Silicon Family • System designers can now choose the silicon thickness that best suits their application. • 16 um standard silicon - 100 ohm-cm. • 40 um deep depletion - 1500 ohm-cm. • 70 um bulk silicon - > 3000 ohm-cm. • 150 um high-rho - > 3000 ohm-cm. DfA 2009: Bulk CCD, PSF, & PTC.

6. The CCD Silicon Family • System designers can now chose the silicon thickness that best suit their application. • 16 um standard silicon - 100 ohm-cm. • 40 um deep depletion - 1500 ohm-cm. • 70 um bulk silicon - > 3000 ohm-cm. • 150 um high-rho - > 3000 ohm-cm. • 300 um high-rho - > 3000 ohm-cm. DfA 2009: Bulk CCD, PSF, & PTC.

7. Bulk Silicon CCD DfA 2009: Bulk CCD, PSF, & PTC.

8. Why the Interest in Bulk Silicon? • Pin and mechanically compatible with existing detector family. • Upgrades are plug and play • No rewiring of cryostats, • No modification to controllers (to provide high voltages), • Standard clock and bias voltages used • No re-writing of timing patterns. • Improve observing efficiency in the “red” without major costs in manpower, controller, instrument down time or schedule risk. • Objective - to prove performance is as good as current CCDs. • One engineering and one science grade loaned by e2v for test and evaluation. DfA 2009: Bulk CCD, PSF, & PTC.

9. Nothing unusual in performance and as good as other family members DfA 2009: Bulk CCD, PSF, & PTC.

10. ESO-e2v QE agree • Good agreement between e2v and ESO results. • Determining QE depends on knowing gain precisely and care must be taken as: • calculated gain varies with signal level when using the photon transfer curve (SPIE 2006 Downing et. al.). • Recommend using binning (2x2 or 4x4) to determine gain. DfA 2009: Bulk CCD, PSF, & PTC.

11. ESO-e2v QE agree • Good agreement between e2v and ESO results. • Determining QE depends on knowing gain precisely and care must be taken as: • calculated gain varies with signal level when using the photon transfer curve (SPIE 2006 Downing et. al.). • Recommend using binning (2x2 or 4x4) to determine gain. DfA 2009: Bulk CCD, PSF, & PTC.

12. ESO-e2v QE agree • Good agreement between e2v and ESO results. • Determining QE depends on knowing gain precisely and care must be taken as: • calculated gain varies with signal level when using the photon transfer curve (SPIE 2006 Downing et. al.). • Recommend using binning (2x2 or 4x4) to determine gain. DfA 2009: Bulk CCD, PSF, & PTC.

13. PRNU Measured with 7nm Bandwidth • PRNU shows very low fringing in the “red”. • 70 um bulk silicon DfA 2009: Bulk CCD, PSF, & PTC.

14. PRNU Measured with 7nm Bandwidth • PRNU shows very low fringing in the “red”. • 70 um bulk silicon • 40 um deep depletion • 16 um standard silicon DfA 2009: Bulk CCD, PSF, & PTC.

15. PRNU Measured with 7nm Bandwidth • PRNU shows very low fringing in the “red”. 900nm Images • 70 um bulk silicon • 40um deep depletion • 16 um standard silicon 70um Bulk 16um Std Si 40um DD 5 – 95% Histogram Scaling DfA 2009: Bulk CCD, PSF, & PTC.

16. PRNU Measured with 7nm Bandwidth • PRNU shows very low fringing in the “red”. • At shorter wavelengths (< 400 nm) PRNU is a little worse due to thinning and laser annealing. 350nm Images • 70 um bulk silicon • 40um deep depletion • 16 um standard silicon 40um DD 16um Std Si 70um Bulk 5 – 95% Histogram Scaling DfA 2009: Bulk CCD, PSF, & PTC.

17. Very acceptable cosmetics at -120 DegC Traps DfA 2009: Bulk CCD, PSF, & PTC.

18. At higher temperatures, hot pixels become a problem. Hot pixels are highly temperature dependent. At < -120 DegC, hot pixels are not a problem and the device is of excellent scientific grade. -120 DegC is ESO’s standard operating temperature for all CCD44-82s at the observatories. Hot pixels are due to impurities in the silicon. DfA 2009: Bulk CCD, PSF, & PTC.

19. -80DegC -100DegC -120DegC At higher temperatures, hot pixels become a problem. Hot pixels are highly temperature dependent. At < -120 DegC, hot pixels are not a problem and the device is of excellent scientific grade. -120 DegC is ESO’s standard operating temperature for all CCD44-82s at the observatories. Hot pixels are due to impurities in the silicon. DfA 2009: Bulk CCD, PSF, & PTC.

20. Hot pixels are fixable. • Note no hot pixels at the edges. • e2v are working on it to have the whole device as good as the edges. -80DegC 1 hour dark CCD Top CCD Bottom Overscan Pixels Overscan Pixels Edges have no hot pixels Overscan Pixels Edges have no hot pixels DfA 2009: Bulk CCD, PSF, & PTC.

21. Effect of cosmic rays become worse with thicker devices • The thicker the device, the more chance that a cosmic ray will affect more than one pixel. • Standard Silicon - mostly single pixel events • Deep Depletion – mix of single and multiple pixel events • Bulk – mostly multiple pixel events • Expect number of events to scale with thickness. • Deep Depletion Cosmic hit event rate: ~ 1.8 events/min/cm² • Bulk Cosmic hit event rate: ~ 3.0 events/min/cm² • ~ ratio of 70/40 70um Bulk 16um Std Si 40um DD DfA 2009: Bulk CCD, PSF, & PTC.

22. PSF DfA 2009: Bulk CCD, PSF, & PTC.

23. UV 400nm Collection phase VIS 600nm Potential Well RED 900nm CCD Frontside Electric Field Extent PSF depends on CCD design and wavelength PSF depends on: • Thickness of the undepleted region (XUNDEP) at the back of the CCD. • The strength of the electric field to draw the electrons into the potential well depends on: • (Vc – Vsub) • XTHICK • Wavelength and depth of penetration of the photon • Blue photons are in general absorbed nearer the silicon surface and have farther to travel. • While red photons penetrate on the average deeper into the silicon. Vsub XTHICK Vc CCD Backside Cross Section of CCD XUNDEP DfA 2009: Bulk CCD, PSF, & PTC.

24. UV 400nm Collection phase VIS 600nm Potential Well RED 900nm CCD Frontside Electric Field Extent Virtual Knife Edge Sub Window 1um Spot Pixel PSF can be improved by increasing the number of collection phases and the voltage across the CCD PSF can be improved by : • Increasing the extent (i.e. reduce undepleted region at back of CCD) and strength of the electric field by: • Increasing the collection phase voltage (Vc). • Decreasing the substrate voltage (Vsub). • Increasing the number of collecting phases (2 for 3 phase device or 3 for 4 phase device). Vsub XTHICK Vc CCD Backside Cross Section of CCD Spot scanning used to measure PSF DfA 2009: Bulk CCD, PSF, & PTC.

25. 16um e2v Std Si PSF Results 40um e2v Deep Depletion Vc Vc Vc Vc 40um MIT/LL Hi Rho 70um Bulk CCD DfA 2009: Bulk CCD, PSF, & PTC.

26. Photon Transfer Curves DfA 2009: Bulk CCD, PSF, & PTC.

27. Photon Transfer Family of Curves 40um e2v Deep Depletion 16um e2v Std Si • Increasing the collection phase voltage to improve the PSF impacts the well depth. 70um Bulk CCD Gain ~ 11e/ADU DfA 2009: Bulk CCD, PSF, & PTC.

28. 16um Standard Silicon is well behaved; text book 40um E2v Deep Depletion 16um e2v Std Si Optimum full well = ~ 2V Surface Full Well BFW=SFW 70um Bulk CCD Vc Bloomed Full Well Gain ~ 11e/ADU DfA 2009: Bulk CCD, PSF, & PTC.

29. 40 um Deep Depletion starts to show interesting behaviour 40um e2v Deep Depletion 16um E2v Std Si Note interesting behaviour at 2-5V. Surface Full Well BFW=SFW 70um Bulk CCD Vc Bloomed Full Well Gain ~ 11e/ADU DfA 2009: Bulk CCD, PSF, & PTC.

30. Interesting behaviour up to where surface full well dominate • Behaviour enables a larger full well and different optimum full well voltage to standard silicon; 6V versus 2V. • No explanation yet for the behaviour. Minimal blooming No blooming No blooming Blooming Blooming Between 2-4V, starts to bloom at low signal level but then recovers at higher levels. At 6V, no blooming is observed. DfA 2009: Bulk CCD, PSF, & PTC.

31. 70 um Bulk is even more pronounced 40um E2v Deep Depletion 16um E2v Std Si 70um Bulk CCD Gain ~ 11e/ADU DfA 2009: Bulk CCD, PSF, & PTC.

32. Full Well versus Collection Phase Voltage • Choose trade between PSF improvement and well depth Optimum full well = ~ 6V Vc Vc 70um Bulk CCD DfA 2009: Bulk CCD, PSF, & PTC.

33. Conclusion • Performance at -120DegC of noise, gain, linearity, cosmetic, dark current, and CTE is as good as previous e2v CCD44-82s. • Below -120DegC, hot pixels are not a problem. • Bulk delivers better QE in the “red” and much less fringing. • With PSF of ~ 1 pixel, the bulk CCD is very suitable for not too demanding optical designs. • PSF can be improved by increasing collection phase voltage or running at a lower active substrate voltage. • When increasing collection phase voltage, one has to be careful about change in well depth. • As the resistivity of the silicon is increased, the photon transfer curve becomes more interesting and does not agree with the text books. DfA 2009: Bulk CCD, PSF, & PTC.

34. END Many thanks DfA 2009: Bulk CCD, PSF, & PTC.