RAD 2012 Ultra-Thin 3 D detectors Ultra-Thin 3

RAD 2012 Ultra-Thin 3 D detectors Ultra-Thin 3 D Silicon Detectors for Active Neutron Detection Celeste Fleta Instituto de Microelectrónica de Barcelona Centro Nacional de Microelectrónica - CSIC Spain Celeste. Fleta@csic. es Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Radiotherapy linacs Motivation Ø Usually dosemeters passive Ø Real time counting and high gamma rejection factor required Ø Working at > 8 Me. V generate neutrons by fotonuclear reaction Ø Pulsated radiation Other applications: nuclear security, avionics, space, … Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Neutron detection with silicon sensors Ultra-Thin 3 D detectors Silicon radiation sensors Adaptation for neutron detection Ø Converter with high thermal neutron cross section Ø Reaction products with enough energy to reach the detector particle I t Ø Low bias (few V) Ø Low battery consumption for transportability Ø Compact: small sizes (mm) and weight (g) Ø Resistant to shock and inmune to magnetic fields Ø Fast response (ns) Celeste Fleta Ø Will use 10 B-based compounds Maximum detection efficiency 4. 7% Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Traditional “planar PIN” silicon sensors Standard sensors Ø Thickness: 300 – 1000 µm K Depletion voltage: 80 -200 V J Low charge collection time: ns L High γ-ray absorption probability Thin sensors Ø Thickness: 10 -20 µm J Depletion voltage < 10 V J Low charge collection time: ns J Low γ-ray absorption L High capacitance and electronic noise gamma rejection/capacitance trade-off Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors New “Ultra-thin 3 D” silicon sensors Ø Thickness: 10 -20 µm Ø Columnar electrodes passing through substrate J J J Depletion voltage: few V Low charge collection time: ns Low γ-ray absorption Resistant to radiation damage Capacitance lower than the planar equivalent Celeste Fleta 3 D is advantageous if thickness < 50 µm Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Design and fabrication Ø Design and fabrication done in-house Ø 0. 5 cm 2 active area, window <400 nm Si. O 2 Ø Electrode fabrication: Detail of a sensor design n-contact 1. ICP etching of the holes: ALCATEL 601 -E 2. Holes partially filled with LPCVD polysilicon 3. Holes doped with P or B 4. Holes passivated with TEOS Si. O 2 Electrodes: 5µm diameter, 10µm deep SOI wafer 10µm active thickness n-holes connected together with thin metal lines p-holes p-contact on other side Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors In pictures Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Electrical test Capacitance vs. voltage Current vs. voltage Ø Sensors depleted at ~5 volts Ø 50 -70 n. A/cm 2 at 10 V Ø 60 -80 p. F/cm 2 Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Electronics Ø Compact (50 g, 13 x 2. 5 cm) Ø Fast (80000 counts/s) Ø Cheap (<100€) towards a portable system The detector is mounted on a separated board to allow testing different detectors with the same system Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors 137 Cs 90 m. Ci (2. 8 x 109 γ/s in 4π) 1 m distance 241 Am-Be + Lab source tests 10µm sensor Ø Threshold = 100 ke. V Ø 1 count/10 min Ø 1 gamma counted every 108 300µm sensor Ø 29. 0± 0. 2 c/s 800µm sensor Ø 204. 0± 0. 6 c/s 137 Cs 40 m. Ci Am. Be (88000 n/s) 8 m. Ci 137 Cs 10 cm polyethilene Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Hospital tests Ø Elekta Synergy (Hospital General de Catalunya) and Siemens Primus (Hospital de Santiago de Compostela) Ø 6 MV (γ only) and 15 MV (γ + n) Ø 10 x 10 cm 2 field sensor Ø 50 to 500 MU/min* *MU: a Monitor Unit is a measure of the machine output of a linac which is calibrated to deliver an absorbed dose under particular conditions, e. g. 100 MU gives 1 Gray in water at 100 cm SSD for a 10 x 10 cm 2 field Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Hospital tests Fixed rate: Elekta Synergy, 400 MU/min H 310 BO 3 Ø No pile-up counts observed Ø At 6 MV (γ only): 3. 8 counts/min Ø 1 E 6 γ/cm 2 s Gamma rejection factor: 2 x 10 -9 Ø At 15 MV: γ/n counts = 0. 002 (sensor without/with H 310 BO 3) Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Hospital tests Variable rates: Siemens Primus, 15 MV H 310 BO 3 Ø Linear response: no pile-up up to 500 MU/min • 50 MU/min: 4010± 100 counts in 10 minutes • 500 MU/min: 4062± 48 counts in 1 minute Ø γ/n rate = 0. 02 System works well in pulsated gamma/neutron environment Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Summary and outlook Summary p Innovative ultra-thin 3 D silicon sensors with 10 µm thickness have been successfully fabricated and adapted to detect neutrons with 10 B-enriched compounds. p The detectors show a gamma rejection factor higher than 10 -8 for a threshold of 100 ke. V, and 2 x 10 -9 in a radiotherapy field. p Preliminary tests of the detectors in clinical linacs show their usefulness in these complex gamma-neutron pulsated radiation fields: low gamma count rate, linear up to at least 500 MU/min. 137 Cs for Ongoing work p Working to integrate the system in a fully portable dosemeter. p Developing p Working to obtain absolute efficiencies/gamma rejection factors with calibrated sources. p Developing microstructured detectors for higher neutron detection efficiency. 10 B- based converter deposition tecniques. C. Guardiola et al. , “Ultra-thin 3 D silicon sensors for neutron detection”, 2012 JINST 7 P 03006 Celeste Fleta Instituto de Microelectrónica de Barcelona

RAD 2012 Ultra-Thin 3 D detectors Thanks for your attention! Full author list: C. Fleta, C. Guardiola, D. Quirion, J. Rodríguez, G. Pellegrini, J. P Balbuena, M. Lozano Instituto de Microelectrónica de Barcelona, Spain F. Gómez, X. González, D. González, J. Pardo Universidad de Santiago de Compostela, Spain F. García Helsinki Institute of Physics, University of Helsinki, Finland Celeste Fleta Instituto de Microelectrónica de Barcelona