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Multi-anode linear silicon drift detectors for soft X-ray diffraction and spectroscopy

Multi-anode linear silicon drift detectors for soft X-ray diffraction and spectroscopy. Jan Šonský , R. Koornneef, J. Huizenga, R.W. Hollander, C.W.E. van Eijk Radiation Technology Group, Interfaculty Reactor Institute, TUDelft (e-mail: sonsky@iri.tudelft.nl ) P.M. Sarro, L.K. Nanver

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Multi-anode linear silicon drift detectors for soft X-ray diffraction and spectroscopy

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  1. Multi-anode linear silicon drift detectors for soft X-ray diffraction and spectroscopy Jan Šonský, R. Koornneef, J. Huizenga, R.W. Hollander, C.W.E. van Eijk Radiation Technology Group, Interfaculty Reactor Institute, TUDelft (e-mail: sonsky@iri.tudelft.nl ) P.M. Sarro, L.K. Nanver Delft Institute of Microelectronics and Submicron Technology

  2. Outline • Motivation • Charge sharing: X-ray spectroscopy • Wafer quality • Radiation entrance window • Position resolution • Conclusion

  3. Motivation Detector requirements • large total active area (2.5 x 1.5 cm2) • 1D-position sensitive detector • position resolution of ~ 200 mm • detection of X-rays down to 180 eV • noise of less than 10 rms el. • high count rate operation (105 cps) • near room temperature operation Applications • X-ray diffraction experiments

  4. Motivation - existing technologies Fully depleted pn-CCD • high-ohmic wafer allows detection of X-rays with energies up to 10 keV • energy resolution of 130 eV (~5 rms el.) • position resolution of 150 mm • integrator (~100 cps) Pixel detector • match the required position and energy resolution • small active area per pixel • high number of read-out channels • flip-chip bump bonding

  5. Charge sharing: X-ray spectroscopy Multi-anode linear Silicon Drift Detector • ideal configuration for the diffraction experiments • anode pitch determines the position resolution • low noise features

  6. Charge sharing ... (2) MLSDD prototype • anode pitch of 250 mm • total detector size is 2.5 x 1.3 cm2 • bi-directional with 52 anode pixels on each side • drift field of 390 V/cm X-ray spectrum per anode pixel Results • exceptional bad spectroscopic performance despite of the low noise • shift of peak towards lower energies • low energy tails

  7. Charge sharing ... (3) Traditional MLSDD: X-ray spectrum calculation • charge cloud evolution • lateral spread of the electron cloud due to diffusion • using the spatial map of charge collection • monochromatic X-ray source (6 keV) • energy resolution due to statistic and noise is 400 eV • different anode pitch

  8. Charge sharing ... (4) Traditional MLSDD: experiment vs. calculation • absorption efficiency • given experimental conditions (Ed, T) • energy resolution anode pitch = 250 mm

  9. z x Charge sharing ... (5) Multi-anode Sawtooth SDD • Sawtooth shaped p+ strips induce potential gutters • The depth of the potential gutters depends: • drift field • period px • pitch py • angle a

  10. Charge sharing ... (6) MSSDD: prototype design • large detectors of a total active area of 2.5x1.3 cm2 • 4 sections with a = 0°, 30°, 45°, and 60° • The strip pitch py = 200 mm (180 mm p+ implant, 20 mm oxide) • anode pitch varied from 250 mm or 500 mm • Anodes isolated with p+ implantation 4-in. wafer

  11. Charge sharing ... (7) MSSDD: bonding

  12. Charge sharing ... (8) MSSDD: X-ray spectroscopy • large MSSDD (a = 60°) fabricated on NTD wafers • anode pitch of 250 mm Results • split events elliminated • energy resolution of 190 eV at -60°C • energy resolution of 350 eV at RT

  13. Wafer quality Wafer doping non-uniformity • Deviation of electron trajectories from expected straight lines • Confining potential gutters are disturbed Conclusion: • Neutron Transmutation Doped wafers are must!!!

  14. Radiation entrance window • MSSDD with strips on both sides • Fixed oxide charge between p+ strips • Signal charge trapping, especially for soft X-rays • MSSDD with semi-continuous implant • 8 wide strips on the radiation entrance side • Total area covered with oxide is only a few percent (~3.6%)! • Staircase potential distribution • Drift field or drift length are not limited!

  15. Radiation entrance window ... (2) • Does the confinement work also for the semi-continuous configuration ? • one-side driven confinement

  16. Radiation entrance window ... (3) • How to make a shallow p+ implant (< 100 nm)? • Low energy Boron implantation (<10 keV) • BF2 pre-amorphization • Rapid Thermal processing

  17. Conclusions Detector performance/Status • detector prototype with an area of 2.5 x 1.3 cm2 • design optimized for detection of low energy X-rays • position resolution of 250 mm (~200 mm easily possible) • energy resolution of 190 eV (~18 rms el.) per anode pixel • count-rate: probably around 50-80k cps Could we do better ? • Better position resolution... • Better noise... • Imaging ?

  18. Conclusions MSSDD: achievable position resolution ? • while having the charge confined within one anode pixel • position resolution = anode pitch Results • position resolution of 100 - 150 mm • drift field of ~ 1000 V/cm Results: off-center drift • better than 100 mm @ smaller drift fields charge produced by a 10 keV X-ray photon is confined at any depth of wafer

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