1. Anti-Blooming Strategies for LSST or What we can do about all these bloomin’ pixels?

2. LSST Design Parameters

3. Stellar Flux, Charge Accumulation vs. V-band Magnitude

4. Stellar Density vs. V-band Magnitude

5. Flux, Charge, and Blooming in 10 Second LSST Exposures

6. I-band vs. V-band Stellar Densities There are 3 – 5x as many bright stars in I-band

7. So, how big IS the problem of bloomed charge for LSST? ‘Simple’ model predicts a small portion (0.11%) of a ‘typical’ LSST field will be affected by bloomed charge, based on V-band magnitudes I-band stellar brightness suggests a multiplication of this amount by as much as 5x, so that’s maybe 0.5% Corrupted PSFs suggest a multiplication by another 3x to 5x, so that’s maybe 2.5%, that’s starting to be a problem So, what can we do about it? Structural solutions: built-in anti-blooming drains Operational solution: clocked recombination anti-blooming

8. Anti-Blooming Structures: Vertical and Lateral Drains (Graphics stolen shamelessly, err, borrowed, from Scientific Charge-Coupled Devices by James Janesick) Vertical anti-blooming structures are incompatible with backside illumination Lateral anti-blooming structures sacrifice too much fill factor

9. Lincoln Laboratories Blooming Control 100% fill factor >1000x blooming control Drain ‘hidden’ in the channel stop Similar design available from Sarnoff Laboratories

10. Other Possible Anti-Blooming Structures Column end excess charge drain Lateral drain on serial register  Absorbs charge as columns saturate completely  Also serves as a fast clear charge sink  Prevents charge from smearing during readout  Also serves as a fast clear charge sink

11. Clocked Anti-Blooming Diagram “borrowed” from Gary Sims P1 collecting charge, P2 and P3 inverted P1 saturated, excess charge at the Si/SiO2 interface at the surface Excess charge trapped at surface while the charge is moved in the buried channel Trapped charge annihilated by holes flooding surface states when P1 is clocked into inversion

12. Spurious Charge Generated by Clocked Anti-Blooming Plot stolen (let’s just say it) from Sims and McCurnin Spurious charge generation rises with larger clock swing Spurious charge generation rises with shorter clock rise times LSST cannot afford the noise from spurious charge

13. Conclusions, Options, Further Research Without anti-blooming, bloomed charge will affect between 0.5% and 2.5% of a ‘typical’ LSST field, is this a problem? Most ‘built-in’ anti blooming structures are incompatible with LSST MIT/LL, Sarnoff have compatible, effective anti-blooming structures Clocked anti-blooming works, but has a LOT of potential problems  Can MIT/LL produce the required number of CCDs?  Can the design be licensed to another vendor?  How about Sarnoff Laboratories?  Spurious charge, ‘jim-dots’, other effects are not acceptable  Further experiments required before considering this option