SDW2005 - Marco Sirianni Marco Sirianni (ESA/STScI) Max Mutchler (STSci) Radiation Damage in HST Detectors

SDW2005 - Marco Sirianni

Marco Sirianni (ESA/STScI)

Max Mutchler (STSci)

Radiation Damage in Radiation Damage in HST DetectorsHST Detectors

Radiation Damage in Radiation Damage in HST DetectorsHST Detectors


Detectors on HST

CCD: (16+2)WFPC 8 3.5 yrWFPC2 4 12 yrSTIS 1 7 yrACS 3 3 yrWFC3 2 0 yr

IR: (3+1))

NICMOS 3 8 yr

WFC3 1 0 yr

UV-MCP: (3+1))STIS 2 7 yrACS 1 3 yrCOS 1 0 yr

1990 : WFC +FOC+FOS+GHRS+HSP

1993 : WFPC2

1997 : STIS + NICMOS

2002 : ACS

????: WFC3 +COS

HST Instruments:


CCDs on HST

ACS/WFC FPA:2x SiTe 4048x2096 Thinned Backside CCDs15m pixel size - MPP (integration only)Site VIS-AR Coating - 4 amps readout T = -77 °C3 m minichannel

WFC-1

A

B

WFC-2

C

D

ACS/HRC FPA:1x SiTe 1024x1024 Thinned Backside CCDs21 m pixel size - MPP - Site NUV AR Coating1 amp readout T = - 81 °C 3 m minichannelSTIS FPA:Same as HRC, different AR coating T = - 83 °CWFPC2 FPA:4x Loral 800x800 Thick Frontside CCDs15 m pixel size - MPP 1 amp readout T = - 88 °C


HST Radiation EnvironmentLEO - alt. ~580 Km, incl. 28.41 - 14.99 rev/day

~ 7/9 orbits/day are SAA free~ 6/8 orbits/day are SAA impacted

LEO are quite shielded orbits… still


Radiation Damage• MPP devices are mainly sensitive to “displacement

damage”

• Vacancies migrate until a stable configuration is reached; mainly:

• P-V centers • V-O centers• V-V centers

• Any new energy level in the bandgap acts as emission/trapping site

Direct impact on:- Dark Current increase- hot pixels ( Field-enhanced dark spikes )- CTE degradation


Single Event effect• On June 2003 one of the four ACS/WFC amplifier showed a jump in read noise ~ 1 e- rms in amplitude.• The change occurred during a SAA transit and stabilized to +0.6 e- after few anneal cycles.

STIS suffered of a similar problem~ six months beforeThe failure of the

side-1 electronics.


Dark Current variation

WFC - 76 C+ 1.8 e-/pix/hr per year

HRC - 81 C+ 2.1 e-/pix/hr per year

As expected the dark rate increases linearly with time


Dark Current comparison

Side-2

May 2001

Dec 1999

21.6

14.4

7.2

e-/

pix/hr

STIS

WFC HRC STIS WFPC2 WF3

Predicted(rad. Test)

1.5 (-81 C) n.a n.a n.a 1.4 (-83 C)

Observed 1.8 2.13.3 (side 1)

2.2 (side 2)

2.0 (0-5 yr)

~ 0 after

Temp. -77 C -81 C -83 C / (< -83 C) -88 C

Dark rate increase: e-/pix/hr/yr


Hot Pixels ACS HRCPre flight dark frame- selected 256x256 pix region


Hot Pixels ACS WFC

Pre Flight 1 Yr 2 Yr 3 Yr


Hot Pixels ACS WFC

0,1,2,3 yrs

Field enhanced dark spikes


Annealing of defects

• In order to remove contamination from the detector windows WFPC2

is heated once a month to +22 C

• It has been noticed a reduction of hot pixels after the CCD warm-up (up to 80%)

• All known traps anneal at much higher temperature (150-320 C)

• STIS and ACS also warm up the CCDs once a month to anneal hot pixels.


Hot pixel annealing

Anneal day

DailyHot Pixelgrowth

PermanentHot pixels

growthAnnealing

rate (A - B) / ( A

- C)

A

BC

Annealing Rate : constant with time depends on the thresholdsame rate for 24,12,6hr soaksame rate at -10 C


Annealing comparison

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.02 0.04 0.06 0.08 0.1 1

signal (e-/pix/sec) (>)

anneal rate

wfc1wfc2HRCSeries4

Instrument Temp

(CCD/ann.)

Threshold

(e-/pix/sec)

Anneal rate Source

STIS -83 / +5 > 0.1 ~ 80 %

~ 75 %

Hayes et al.1998

Kim Quijano et al. 2003

WFPC2 -88 / +22 > 0.02 variable

~ 80 % Koekemoer et al. 2003

WFC3

ground

-83 / +30 >0.01

>0.04

~ 80 %

~ 97 %

Polidan et al. 2004


Life of a hot pixels


Permanent hot pixels

WFCWFC

years

%


Permanent hot pixels..

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

SIDE2

> 0.1

> 1.0

STIS


Permanent hot pixels..

Threshold

e-/pix/secWFC HRC STIS WFPC2

temp - 77 C - 80 C - 83 C - 88 C

Dark curr. 0.003 0.004 0.006 0.008

> 0.02 1.60 1.54 2.99 (0.30--0.11)

>0.04 0.78 0.52

>0.06 0.46 0.29

>0.08 0.30 0.21

>0.10 0.23 0.17 0.36

>1 0.03 0.02 0.08

Permanent hot pixel growth(% of total number of pixels / year)


Annealing lesson learned• We still do not why ~0-20 C annealing is effective

• Only field-enhanced hot pixels are effected, there is no measurable impact on the uniform dark rate.

• The anneal rate depends on the dark rate of the pixel

• 24, 12, or 6 hr at +20 give the same annealing rate

• The same improvement is seen at -10 C (24-48hr)

• Evidence of reverse annealing

• Compete anneal is rare


CTE monitoring

• Different temperature (from -76 C to -88 C)• different clock rate (parallel clock rate from 20 to 60 Hz)• different shielding (different trap population)

• WFPC2/STIS/ACS: empirical correction for point source photometry:– Measurement of charge loss as a function of

signal - position - background and epoch

• ACS: EPER and FPR (only serial for WFC)– Every six months at several signal levels– Every month at the Fe55 level (1620e-)


CTE measurementWe can investigate CTE degradation as a function of time/signal level. Ex: WFC -A EPER

And predict the impact of science data in the nextfew years


CTE trendAt all signal levels CTE degradation is linearwith fluence

WFC

PARALLEL EPER


• Single case:– Signal 1620e-– Low backg. 1e-

– 1000 transfers mag converted into CTE

CTE Degradation rate

• Eper TEST (ACS):– Signal 1620e-


Conclusion • In 15 years more 22 detectors have flown on HST

• Different architectures in the same radiative environment

• Unique possibility:– To try to understand what is really going – To provide information for the development/operation

of future space detectors

• Huge archive but data collection and analysis did not followed any standard.


Conclusions • We have started with CCDs analysis

• Dark rate increase and Hot pixel generation is quite well understood - they are a concern, but not an issue.

• CTE is an issue, little mitigation is possible

• WFPC2 “saturation” to radiation is a “mystery”• We have better understanding of annealing

effectiveness, but we still do not why it occurs

• We will post the data of the analysis on a dedicated web page at STScI.

Documents

SDW2005 - Marco Sirianni Marco Sirianni (ESA/STScI) Max Mutchler (STSci) Radiation Damage in HST Detectors