AD2012 Ultra-Thin 3D detectors Celeste Fleta Instituto de Microelectrónica de Barcelona Celeste Fleta Instituto de Microelectrónica de Barcelona Centro Nacional de Microelectrónica - CSIC Spain [email protected]Ultra-Thin 3D Silicon Detectors for Active Neutron Detection
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Celeste Fleta Instituto de Microelectrónica de Barcelona
Celeste Fleta Instituto de Microelectrónica de Barcelona Centro Nacional de Microelectrónica - CSIC Spain [email protected]. Ultra-Thin 3D Silicon Detectors for Active Neutron Detection. Motivation. Radiotherapy linacs. Usually dosemeters passive - PowerPoint PPT Presentation
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RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Celeste Fleta
Instituto de Microelectrónica de BarcelonaCentro Nacional de Microelectrónica - CSIC
Ultra-Thin 3D Silicon Detectors for Active Neutron Detection
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Motivation
Radiotherapy linacs
Working at > 8MeV generate neutrons by fotonuclear reaction
Pulsated radiation
Usually dosemeters passive Real time counting and high gamma
rejection factor required
Other applications: nuclear security, avionics, space, …
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Neutron detection with silicon sensors
Silicon radiation sensors
Low bias (few V) Low battery consumption for
transportability Compact: small sizes (mm) and
weight (g) Resistant to shock and inmune to
magnetic fields Fast response (ns)
Adaptation for neutron detection
Converter with high thermal neutron cross section Reaction products with enough energy to reach the detector
Will use 10B-based compounds
)01.1()78.1(
)48.0()84.0()47.1(710
710
MeVLiMeVBn
MeVMeVLiMeVBn
93.7 %6.3 %)01.1()78.1(
)48.0()84.0()47.1(710
710
MeVLiMeVBn
MeVMeVLiMeVBn
93.7 %6.3 %
t
I
particle
Maximum detection efficiency 4.7%
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Traditional “planar PIN” silicon sensors
Thickness: 300 – 1000 µm Depletion voltage: 80-200 V Low charge collection time: ns High γ-ray absorption probability
Standard sensors
Thickness: 10-20 µm Depletion voltage < 10 V Low charge collection time: ns Low γ-ray absorption High capacitance and electronic
noise
Thin sensors
-VCC
P+
N+++---
N+
SCR
gamma rejection/capacitance trade-off
0.001%
0.010%
0.100%
1.000%
10.000%
100.000%
0 2000 4000 6000 8000 10000 12000 14000 16000
Photon energy (keV)
% a
bsor
bed
300 microns10 microns20 microns
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Simulated capacitance
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
0 10 20 30 40 50 60
silicon thickness (microns)
Cap
acita
nce
(nF/
cm2) planar
3D (80µm pitch)
New “Ultra-thin 3D” silicon sensors
3D is advantageous if thickness < 50 µm
Thickness: 10-20 µm Columnar electrodes passing through
substrate Depletion voltage: few V Low charge collection time: ns Low γ-ray absorption Resistant to radiation damage Capacitance lower than the
planar equivalent
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Design and fabrication
Design and fabrication done in-house 0.5 cm2 active area, window <400nm SiO2
Electrode fabrication:1. ICP etching of the holes: ALCATEL 601-E2. Holes partially filled with LPCVD polysilicon3. Holes doped with P or B4. Holes passivated with TEOS SiO2
Electrodes: 5µm diameter, 10µm deep SOI wafer 10µm active thickness
Detail of a sensor designn-contact
n-holes connected together with thin metal lines
p-contact on other side
p-holes
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
In pictures
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Electrical test
Sensors depleted at ~5 volts
50-70 nA/cm2 at 10V 60-80 pF/cm2
Capacitance vs. voltage Current vs. voltage
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
0 10 20 30 40 50 60silicon thickness (microns)
Cap
acita
nce
(nF/
cm2)
planar3D (80µm pitch)3D Measured
0
100
200
300
400
500
600
0 10 20 30 40 50
Vbias (V)
Cur
rent
(nA
/cm
2)
0
100
200
300
400
500
0 5 10 15 20
Vbias (V)
Cap
acita
nce
(pF/
cm2)
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Electronics
The detector is mounted on a separated board to allow testing different detectors with the same system
Compact (50g, 13x2.5cm) Fast (80000 counts/s) Cheap (<100€) towards a portable system
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
300µm sensor 29.0±0.2 c/s90 mCi (2.8x109 γ/s in 4π)
1m distance
Lab source tests
241Am-Be + 137Cs
40 mCi AmBe (88000 n/s)8 mCi 137Cs
10cm polyethilene
800µm sensor 204.0±0.6 c/s
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Hospital tests
sensor
Elekta Synergy (Hospital General de Catalunya) and Siemens Primus (Hospital de Santiago de Compostela)
6MV (γ only) and 15MV (γ + n) 10x10 cm2 field 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 10x10 cm2 field
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Hospital tests
No pile-up counts observed At 6 MV (γ only): 3.8 counts/min
1E6 γ/cm2s Gamma rejection factor: 2x10-9
At 15 MV: γ/n counts = 0.002 (sensor without/with H310BO3)
Fixed rate: Elekta Synergy, 400MU/min
H310BO3
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Hospital tests
Variable rates: Siemens Primus, 15 MV
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
γ/n rate = 0.02System works well in pulsated gamma/neutron environment
H310BO3
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Summary and outlook
Summary Innovative ultra-thin 3D silicon sensors with 10 µm thickness have been
successfully fabricated and adapted to detect neutrons with 10B-enriched compounds.
The detectors show a gamma rejection factor higher than 10-8 for 137Cs for a threshold of 100 keV, and 2x10-9 in a radiotherapy field.
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.
Ongoing work Working to integrate the system in a fully portable dosemeter. Developing 10B- based converter deposition tecniques. Working to obtain absolute efficiencies/gamma rejection factors with
calibrated sources. Developing microstructured detectors for higher neutron detection efficiency.
C. Guardiola et al., “Ultra-thin 3D silicon sensors for neutron detection”, 2012 JINST 7 P03006
RAD2012 Ultra-Thin 3D detectors
Celeste Fleta Instituto de Microelectrónica de Barcelona
Thanks for your attention!Full author list:
C. Fleta, C. Guardiola, D. Quirion, J. Rodríguez, G. Pellegrini, J.P Balbuena, M. LozanoInstituto de Microelectrónica de Barcelona, Barcelona, Spain
F. Gómez, X. González, D. González, J. Pardo Universidad de Santiago de Compostela, Santiago de Compostela, Spain
F. GarcíaHelsinki Institute of Physics, University of Helsinki, Helsinki, Finland