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3/16/04 mwb, sek, MIT/CSR
MIT XIS Status16 March 2004
Overview:• TCE board rebuild status• Back-illuminated CCD performance & status• (Slightly) improved FI resolution w/ new s • Improved BI resolution in PSUM mode• Grades, gain & resolution in BI devices• How should we use charge injection?• Initialization issues
3/16/04 mwb, sek, MIT/CSR
Thermal Control Electronics Board Status
• Four (revised) flight boards passed acceptance level vibration & thermal tests at MIT
• Boards hand-carried to ISAS today• TCE board engineering test script defined, sent to
Japan• Plan to install & test boards in flight AE/TCE in Osaka
next week• Plan workmanship shake at ISAS (April?)
3/16/04 mwb, sek, MIT/CSR
Back-illuminated CCD Progress• At November XIS team meeting we reported results from first
chemisorption-charging XIS BI device.• Progress since then:
– 4 more devices tested (5 total) from 2 wafers (1 CI wafer 1 non-CI wafer)
– Revised clock voltages found (lower noise, no spurious charge)– Two devices calibrated (1 CI, one non-CI); QE model constrained– Charge injection function verified– 40 MeV proton irradiation to check radiation tolerance– Dark current, background rejection efficiency measured– >1000 hours total “CCD clocking” test time; ~50 thermal cycles – Flight sensor base with BI CCD built, passed vibration acceptance
testing; thermal test in progress.
• Generally, performance fulfills promise of first test results
3/16/04 mwb, sek, MIT/CSR
Spectral Resolution & Quantum Efficiency Comparison: Back- & Front-illuminated XIS CCDs
277 eV:QEBI/QEFI = 40.3FWHMBI = 50-55 eVFWHMFI = 50-55 eV
525 eV:QEBI/QEFI = 3.3FWHMBI = 60-65 eVFWHMFI = 45-50 eV
BI split threshold: 7e-
3/16/04 mwb, sek, MIT/CSR
Measured XIS BI CCD Quantum Efficiency
BI QE Model Parameters
+ BI Measurements
3/16/04 mwb, sek, MIT/CSR
Chemisorption Charging ProcessBack Surface Structure
45 m Si
3 nm SiO2
1 nm Ag
5 nm HfO2
[Deadlayer
SensitiveVolume
(not to scale)
(Burke, Lesser et al., 2003)
3/16/04 mwb, sek, MIT/CSR
XIS Effective Area Comparison:1 BI Sensor vs 1 FI Sensor
Includes XRT-I area & transmission of all filters
3/16/04 mwb, sek, MIT/CSR
XIS Spectral Resolution: FI & BI CCDs
3/16/04 mwb, sek, MIT/CSR
XIS Spectral Resolution Comparison: BI vs FISimulated Spectra of SNR E0102 -72.3
Back-illuminated Front-illuminated
OVII
OVIII
3/16/04 mwb, sek, MIT/CSR
BI CCD Spectral Resolution:XIS, Chandra ACIS & XMM-Newton EPIC-PN
Simulated Spectra of SNR E0102 -72.3
XIS BI & FI
Chandra ACIS-S
XMM-Newton EPIC-PN
4.6 c s-1 (4 FI)6.9 c s-1 (2 FI+2 BI)
3.1 c s-1
8.0 c s-1 (EPN)5.0 c s-1 (2EMOS)
10
10
20
0
0 1.5
0 1.5
1.5
ct s
-1 k
eV-1
Energy (keV)
Energy (keV)
ct s
-1 k
eV-1
ct s
-1 k
eV-1
Note: EPIC MOS Resolution comparable to XIS(but is not a BI CCD)
3/16/04 mwb, sek, MIT/CSR
XIS Dark Current Comparison: BI vs FI
3/16/04 mwb, sek, MIT/CSR
Radiation Induced Pulse-height Shift in BI CCD
Eve
nt C
ente
r P
ixel
Pul
se-h
eigh
t (ad
u)
Column Number
3/16/04 mwb, sek, MIT/CSR
Radiation-Induced Loss of Spectral ResolutionBI CCD at 5.9 keV
FW
HM
at 5
.9 k
eV (
eV)
Column Number
3/16/04 mwb, sek, MIT/CSR
Radiation-Induced CTI Increasein XIS BI & FI CCDs
3/16/04 mwb, sek, MIT/CSR
Background Rejection Efficiency Comparison:•BI, FI similar @ E <1 keV•BI better 1-2.5 keV by x 2 (mostly lower Si K fluorescence)
•FI better 2.5-12 keV by x2.5
60Co Gamma/e- Response ComparisonG02346 events
3/16/04 mwb, sek, MIT/CSR
BI Resolution in PSUM Mode
3/16/04 mwb, sek, MIT/CSR
BI CCD Pulse-height vs Grade (390 eV)
3/16/04 mwb, sek, MIT/CSR
BI CCD Pulse-height vs Grade Selection
3/16/04 mwb, sek, MIT/CSR
BI Test Experience Summary
• 5 BI devices tested from 2 wafers
• >1000 hours total cold CCD-clocking time
• > 50 thermal cycles (25 thermal cycles on one device)
• Nominal calibration measurement suite run on 2 devices
• Radiation testing (40 MeV protons) on one device
• 60Co response checked
• BI devices require slightly different clock levels
• Flight-sensor base passed acceptance vibration; thermal test in progress.
• No peculiar gain or QE instabilities noted to date.
3/16/04 mwb, sek, MIT/CSR
Possible Additional BI ‘Stability’ Tests• UV (2600 A) flood test (at CSR):
* Flood CCD with light from EEPROM burner* Look for gain/QE drift at low energies due to interface
charging
• Ly test (at Lincoln Lab):* Have ‘loaned’ one device to UV instrument team at LL* They will check response at Ly * This test will check deadlayer model
• Extended high-temperature (+60C) aging test?* 2-day ‘informal’ test already done
• Others?
3/16/04 mwb, sek, MIT/CSR
Additional BI Calibration Needed • Additional QE data E< 0.5 keV
* ‘Deadlayer is known only to 70 ± 20 nm* Additional data at 180 eV, 390 eV would be useful
• Energy-scale data at E< 2 keV* Energy scale is not linear here
• Spectral resolution with flight AE/TCE (all E)* BI resolution is quite sensitive to AE/TCE noise
• Spatial QE non-uniformity at E> 6 keV* BI CCD seems to be slightly thinner than expected
3/16/04 mwb, sek, MIT/CSR
XIS Sensor Base with Back-illuminated CCD
•CCD calibrated at MIT•Vibration test passed 5 March•Thermal test in progress•Anticipate shipment 24 March
3/16/04 mwb, sek, MIT/CSR
XIS BI Sensor Base Delivery Prospects
• Anticipate 1st BI sensor base (with CCD w1.8c5) ready for shipment 24 March
• Next flight candidate BI CCDs:* w1.8c2 now under test; CTI worse than w1.8c5 but could fly
* w1.8c8 expected at CSR now
* Third wafer still at University of Arizona
• Engineering team has ISS commitments through April
• CCD team (Bev) will calibrate 2nd flight BI device in April
• Expect to deliver 2nd BI sensor base at end of May
3/16/04 mwb, sek, MIT/CSR
FI Resolution & Noise with reduced Serial Clocks
3/16/04 mwb, sek, MIT/CSR
How should we use charge injection?
• Two possible uses:– CTI measurement (with checkered flag to allow ground correction)– CTI reduction (with grid to fill traps)
• Tsuru-san finds poor correlation between injected amplitude & X-ray amplitude:– Very interesting & useful analysis; we had not done this!– Injected charge must be summed as events for stable injection (why?)– Inherent CTI in w1.3c6 is rather small (< 5 x 10-6)– I think there is hope for this method but I haven’t done my homework
• So-called ‘grid’ method is very promising:– Improves resolution for radiation-damaged FI & BI chips– Loss of QE seems as expected (or better!)– How will DE handle injected grid? What about extra hot pixel rate?
• Main questions: How & when do we decide about use of CI?
Massachusetts Institute of TechnologyCenter For Space Research
27
Massachusetts Institute of TechnologyCenter For Space Research
28
An Example: Injecting a Grid Pattern
•Charge injection is programmable.
•Purpose of “Grid” program is to reduce radiation damage effects:
*Charge is injected in each column of every 54th row.*Injected charge (temporarily) fills radiation-induced traps.*Filled traps cannot contribute to charge transfer inefficiency.*Result is better spectral resolution.
Rows filled by charge injection
Chargemoves down duringreadout
ID/IG Input RegisterCharge moves right during injection
Massachusetts Institute of TechnologyCenter For Space Research
29
Effect of Proton Irradiation on XIS Response
Prelaunch: FWHM: 132 eV.
Post-irradiation (2 yr on-orbit equivalent):Gain shift 1.3%; FWHM: 210 eV
Without Charge Injection
Massachusetts Institute of TechnologyCenter For Space Research
30
Effect of Proton Irradiation on XIS Response
Prelaunch: FWHM: 132 eV.
Post-irradiation with charge injection:Gain shift 0.5%; FWHM: 144 eV
With Charge Injection
3/16/04 mwb, sek, MIT/CSR
CTI at 5.9 keV vs Charge Injection Level Radiation-damaged BI CCD
3/16/04 mwb, sek, MIT/CSR
Radiation-Induced Loss of Spectral Resolutionin BI CCD
FW
HM
at 5
.9 k
eV (
eV)
Column Number
3/16/04 mwb, sek, MIT/CSR
Resolution Improvement with Charge InjectionRadiation-damaged BI CCD at 525 eV
3/16/04 mwb, sek, MIT/CSR
CI Grid Period(rows)/
Open Fraction277 eV 525 eV 1.5 keV 5.9 keV*
54/0.981 0.955 0.947 0.954 0.978
114/0.991 0.982 0.981 0.986 1.008
Relative QE with Grid Charge InjectionRadiation Damaged BI device
• For quad B of BI w1.8c6 after 40 MeV proton irradation• Based on ‘counts under peak’; statistical precision ~0.005• Injected charge rows treated as 0 in event finding * NB: 5.9 keV data do NOT have hot pixels removed
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