mit xis status 16 march 2004

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


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?)


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


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-


Measured XIS BI CCD Quantum Efficiency

BI QE Model Parameters

+ BI Measurements


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)


XIS Effective Area Comparison:1 BI Sensor vs 1 FI Sensor

Includes XRT-I area & transmission of all filters


XIS Spectral Resolution: FI & BI CCDs


XIS Spectral Resolution Comparison: BI vs FISimulated Spectra of SNR E0102 -72.3

Back-illuminated Front-illuminated

OVII

OVIII


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)


XIS Dark Current Comparison: BI vs FI


Radiation Induced Pulse-height Shift in BI CCD

Eve

nt C

ente

r P

ixel

Pul

se-h

eigh

t (ad

u)

Column Number


Radiation-Induced Loss of Spectral ResolutionBI CCD at 5.9 keV

FW

HM

at 5

.9 k

eV (

eV)

Column Number


Radiation-Induced CTI Increasein XIS BI & FI CCDs


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


BI Resolution in PSUM Mode


BI CCD Pulse-height vs Grade (390 eV)


BI CCD Pulse-height vs Grade Selection


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.


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?


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


XIS Sensor Base with Back-illuminated CCD

•CCD calibrated at MIT•Vibration test passed 5 March•Thermal test in progress•Anticipate shipment 24 March


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


FI Resolution & Noise with reduced Serial Clocks


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


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


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


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


CTI at 5.9 keV vs Charge Injection Level Radiation-damaged BI CCD


Radiation-Induced Loss of Spectral Resolutionin BI CCD

FW

HM

at 5

.9 k

eV (

eV)

Column Number


Resolution Improvement with Charge InjectionRadiation-damaged BI CCD at 525 eV


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

mit xis status 16 march 2004

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