Development and characterization of 3D semiconductor X-rays detectors for medical imaging Marie-Laure Avenel, Eric Gros d Aillon CEA-LETI, DETectors Laboratory marie-laure.avenel@cea.fr
Outlines Problematic 3D detector process 3D CdTe detector First results for 3D GaAs detector Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 2
Study context and problematic Application: Radiography X-rays detectors (20-60 kev energy range) using A semiconductor material A micro-structured detection geometry Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 3
Study context and problematic Application: Radiography X-rays detectors (20-60 kev energy range) using A semiconductor material A micro-structured detection geometry Problematic : State of the art : planar geometry 3D geometry* 1 mm Cathode Anodes Photons Absorption h + e - Charges Collection Photons Absorption 1 mm Anodes 10 µm Cathodes 100 µm h + e - Charges Collection Trade-off between absorption of incident photons efficiency (which increases with material thickness) and collection of free charge carrier efficiency (which decreases when material thickness increases), resulting in a limited choice of detection materials Decoupling photons absorption and charges collection Electrodes placed into the detection volume * S.I. Parker et al., NIM-A, 395, 1997 Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 4
3D detector process Bulk Semiconductor Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 5
3D detector process Bulk Semiconductor Laser drilling* by a Nd-YLF laser (@263 nm, 40 ns, 600 µj, 3 khz) in percussion mode *D. Farcage, CEA-Saclay, LILM Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 6
3D detector process Bulk Semiconductor Laser drilling* by a Nd-YLF laser (@263 nm, 40 ns, 600 µj, 3 khz) in percussion mode Chemical etch to clean surface and holes *D. Farcage, CEA-Saclay, LILM Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 7
3D detector process Bulk Semiconductor Laser drilling* by a Nd-YLF laser (@263 nm, 40 ns, 600 µj, 3 khz) in percussion mode Chemical etch to clean surface and holes Aspect ratio until 50 : 1 1 mm *D. Farcage, CEA-Saclay, LILM 100 µm 20 µm Metal electrodes deposition by electroless or sputtering Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 8
3D detector process Bulk Semiconductor Laser drilling* by a Nd-YLF laser (@263 nm, 40 ns, 600 µj, 3 khz) in percussion mode Chemical etch to clean surface and holes Aspect ratio until 50 : 1 1 mm *D. Farcage, CEA-Saclay, LILM 100 µm 20 µm Surface clean-up Metal electrodes deposition by electroless or sputtering Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 9
3D detector process Bulk Semiconductor Laser drilling* by a Nd-YLF laser (@263 nm, 40 ns, 600 µj, 3 khz) in percussion mode Chemical etch to clean surface and holes Aspect ratio until 50 : 1 1 mm *D. Farcage, CEA-Saclay, LILM Cathode Anode Cathode 100 µm 20 µm Connection to read-out electronics using gold wires Surface clean-up Metal electrodes deposition by electroless or sputtering Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 10
3D CdTe detector Sample CdTe (Cl) Acrorad; thickness = 1,6 mm 3x3 holes matrix (Φentrance = 120 / Φexit = 40 µm ; pitch = 350 µm) Electrodes : gold electroless + gold wires (Φ= 25 µm) 120 µm 350 µm Biasing configurations : Diamond-shaped biasing HT Signal Square-shaped biasing HT Signal Measurement under 241 Am and 57 Co gamma ray irradiation 241 Am et 57 Co 241 Am et 57 Co V V Spectrum Spectrum Measurement under synchrotron X-ray irradiation -Mapping the detection response : measurement of charge efficiency - Comparison with charge efficiency simulation Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 11
3D CdTe detector 241 Am et 57 Co 241 Am et 57 Co V 3000 V Spectrum 2500 Spectrum 2000 Counts 1500 1000 500 0 0 50 100 150 200 250 300 Channel Demonstration of photon-counting ability using a non-optimized design (electrode diameter and pitch have to be optimized) Energy discrimination for both biasing configurations FWHM = 7 kev @ 60 kev and 16 kev @ 122 kev Spectrum tails due to inhomogeneous regions of charge collection and fluorescence in CdTe Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 12
3D CdTe detector Synchrotron beam (ID6 beamline at ESRF) : - Energy : 60 kev (radiography energy) -Size : 20 x 20 µm² -Input rate : 10 5 photons/s Scan parameters : -32 x 32-position top-surface scan of the detector at a pitch of 25 µm -Spectrum collected for 10 s Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 13
3D CdTe detector Synchrotron beam (ID6 beamline at ESRF) : - Energy : 60 kev (radiography energy) -Size : 20 x 20 µm² -Input rate : 10 5 photons/s Scan parameters : -32 x 32-position top-surface scan of the detector at a pitch of 25 µm -Spectrum collected for 10 s Total count map 350 µm HV (Cathodes) Measurement (Anode) Synchrotron beam instabilities Incident photon absorption efficiency is homogeneous over the whole surface of the detector Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 14
3D CdTe detector Measurement of the absorbed charge : normalized peak channel (calibrated measurement set-up) Measurement (-20 V) The normalized peak channel is greater than 0.8 good collection for both carriers The detector response is homogeneous Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 15
3D CdTe detector Measurement of the absorbed charge and comparison with simulated Charge Induction Efficiency Measurement(-20 V) Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 16
3D CdTe detector Measurement of the absorbed charge and comparison with simulated Charge Induction Efficiency Measurement(-20 V) Simulation (-20 V) M. Ruat et al., 3D Semiconductor radiation detectors for medical imaging: simulation and design, IEEE Nucl. Sci. Symposium Conference Record, 2009 Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 17
3D CdTe detector Measurement of the absorbed charge and comparison with simulated Charge Induction Efficiency Measurement(-20 V) Simulation (-20 V) Four-leaf clover shape around central anode in experimental and simulated scan due to electric field distribution in biased 3D structure M. Ruat et al., 3D Semiconductor radiation detectors for medical imaging: simulation and design, IEEE Nucl. Sci. Symposium Conference Record, 2009 Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 18
3D CdTe detector Measurement of the absorbed charge and comparison with simulated Charge Induction Efficiency Measurement(-20 V) Simulation (-20 V) Highest values of charge efficiency around cathodes due to transport properties of electrons upper the holes transport properties in CdTe M. Ruat et al., 3D Semiconductor radiation detectors for medical imaging: simulation and design, IEEE Nucl. Sci. Symposium Conference Record, 2009 Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 19
3D CdTe detector Measurement of the absorbed charge and comparison with simulated Charge Induction Efficiency Measurement(-20 V) Simulation (-20 V) Low electric field and diffusion-dominated regions in the corner of square-shaped configuration: enhanced trapping and reduced charge collection efficiency M. Ruat et al., 3D Semiconductor radiation detectors for medical imaging: simulation and design, IEEE Nucl. Sci. Symposium Conference Record, 2009 Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 20
First results for 3D GaAs detector GaAs 3D prototype : - Semi-insulating GaAs Freiberger; thickness = 600 µm - 3x3 holes matrix : - Entrance diameter = 100 µm / Exit diameter = 50 µm - Pitch: 150 µm - Electrodes : Gold electroless 150 µm Results under gamma rays irradiation ( 241 Am et 57 Co) : Square-shaped biasing configuration @ -60 V Counts 241Am 450 400 350 300 250 200 150 100 50 0 0 10 20 30 40 50 60 70 Channel 241Am 57Co 250 200 150 100 50 0 Counts 57Co Demonstration of photon-counting ability Efficiency for 60 kev = 2% Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 21
Conclusion 3D geometry : Alternative detector for X-rays medical imaging applications for semiconductor whose transport properties are lower (than CdTe for example) Requires technical effort 3D CdTe detector : Proof of concept for 3D geometry Photon-counting ability 60 kev and 122 kev energy discrimination Homogeneous absorption and charge collection under X-rays irradiation 3D Semi-insulating GaAs detector : First prototype has been developed Photons counting under gamma rays irradiation Perspectives : - Electrode : Ti/Pt/Au sputtering - Chemical etch or Reactive Ion Etching to clean holes surface - Holes filling with metal and bonding Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 22
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Contribution of 3D geometry for GaAs CdZnTe (single crystal) GaAs (epitaxy*) (µτ) e (cm²/v) 3.10-3 8.10-5 (µτ) h (cm²/v) 5.10-6 4.10-5 *Epitaxy GaAs: G.C. Sun et al., NIM-A, 546, 2005 60 50 % of total counts 40 30 20 10 Planar 60keV GaAs CZT Planar 0 0 10 20 30 40 50 60 Simulation Energy (kev) Hypothesis: full depletion Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 24
Contribution of 3D geometry for GaAs CdZnTe (single crystal) GaAs (epitaxy*) (µτ) e (cm²/v) 3.10-3 8.10-5 (µτ) h (cm²/v) 5.10-6 4.10-5 3D 60keV *Epitaxy GaAs: G.C. Sun et al., NIM-A, 546, 2005 L D 60 % of total counts 50 40 30 20 10 Planar 60keV GaAs 3D D=70µm L=350µm GaAs CZT Planar 0 0 10 20 30 40 50 60 Simulation Energy (kev) Hypothesis: full depletion Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 25
Contribution of 3D geometry for GaAs CdZnTe (single crystal) GaAs (epitaxy*) (µτ) e (cm²/v) 3.10-3 8.10-5 (µτ) h (cm²/v) 5.10-6 4.10-5 *Epitaxy GaAs: G.C. Sun et al., NIM-A, 546, 2005 3D L D 60keV Thickness CdTe 640µm GaAs 2.3mm Voltage : 2/7, 1V 10/50, 5V 70/350, 50V Planar CdTe 200V Planar GaAs 720V 60 % of total counts 50 40 30 20 10 Planar 60keV GaAs 3D D=70µm L=350µm D=10µm L=50µm GaAs CZT Planar 0 0 10 20 30 40 50 60 Simulation Energy (kev) Hypothesis: full depletion Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 26
Contribution of 3D geometry for GaAs CdZnTe (single crystal) GaAs (epitaxy*) (µτ) e (cm²/v) 3.10-3 8.10-5 (µτ) h (cm²/v) 5.10-6 4.10-5 *Epitaxy GaAs: G.C. Sun et al., NIM-A, 546, 2005 3D L D 60keV Thickness CdTe 640µm GaAs 2.3mm Voltage : 2/7, 1V 10/50, 5V 70/350, 50V Planar CdTe 200V Planar GaAs 720V 60 % of total counts 50 40 30 20 10 Planar 60keV GaAs 3D D=70µm L=350µm D=10µm L=50µm D=2µm L=7µm GaAs CZT Planar 0 0 10 20 30 40 50 60 Simulation Energy (kev) Structuring detector can make spectrometric a material whose transport properties are lower than CdZnTe Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 27
Characterization of laser drilling Available Techniques : - Dry etching - Chemical etching - Mechanical drilling - Laser drilling Laser drilling system : (CEA-Saclay) Mainly developed for Silicon Advantages / disadvantages laser drilling : + : High aspect ratio + : Material independent -: Damaged holes sides -: Holes tapering -: Serial process A Nd-YLF pulsed laser has been used, exhibiting the following parameters: -Wavelength = 263 nm, enabling a small spot size and small hole diameter -Pulse energy = 600 µj -Rate = 3 khz -Pulse width = 40 ns Holes are realised by laser beam percussion and samples are placed in the air. Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 28
Characterization of laser drilling Feasibility of laser drilling 60 000 holes matrix drilled into 1 mm of CdTe with : -Φ= 20 µm -Pitch = 100µm High aspect ratio 50 : 1 Top view Gold has been properly deposited over the whole surface and length of the holes 1 mm 100 µm 20 µm Study of Heat Affected Zone (HAZ) : Crystallographic information (Electron Back-Scattering Diffraction SEM) 3 x 3 holes matrix drilled into 500 µm of GaAs Chemical etch with Br in methanol - No recrystallisation and no amorphous area around laser drilled holes - GaAs stays single crystal <100> No critical HAZ : HAZ suppressed by chemical treatment <100> Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 29
3D CdTe detector 241 Am 110 100 Stabilization of the peak channel in both bias configuration above -10 V full charge collection Peak Channel 90 80 70 60 Square-shaped bias configuration slightly more efficient than diamond-shaped bias configuration 50 40 Diamond shaped Square shaped 0 10 20 30 40 50 Bias Voltage (V) Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 30
3D CdTe detector 241 Am 1,E+07 1,E+07 Stabilization of counts number for both bias configuration In the -20 to -50 V range At -20V, ratio of total counts = 1.7 Counts Number 8,E+06 6,E+06 4,E+06 2,E+06 0,E+00 Diamond shaped Square shaped 0 10 20 30 40 50 Bias Voltage (V) Demonstration of photon counting and 241 Am / 57 Co peak energy discrimination using a non-optimized design (electrode diameter and pitch have to be optimized) Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 31
3D CdTe detector Development and characterization of 3D semiconductor X-rays detectors for medical imaging - Marie-Laure Avenel - 7/07/11 32