1. Active Dosimeters Federico Ravotti Maurice Glaser, Michael Moll
CERN TS-LEA
CEM2 – Montpellier University
Maurice Glaser, Michael Moll
CERN PH-TA1

2. RADWG-RADMON Workshop Day, 01/12/2004
Outline
Introduction;
Total Ionizing Dose (TID) measurement:
Radiation Field Effect Transistors (RadFETs);
Optically Stimulated Luminescent materials (OSLs);
1-MeV neutron equivalent fluence (Feq) measurement:
p-i-n diodes & PAD structures;
Thermal neutrons detection (Fth);
Status Dec & Conclusion.
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

3. RADWG-RADMON Workshop Day, 01/12/2004
Introduction
RADIATION DAMAGES can be caused by:
Ionizing Energy Losses (IEL)  Total Ionizing Dose (TID);
Non-Ionizing Energy Losses (NIEL)  1-MeV neutron eq. fluence (Feq).
Important to monitor separately TID, Feq and maybe Fth;
The best “dosimeter” for electronics is Silicon itself (or similar Zeff);
Accelerator environments are (t)  Active (“on-line”) monitoring;
Monitoring is NOT ONLY for radiation damage survey.
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

4. Active Radiation Monitors
TID (GySi)
Feq (cm-2)
mainly charged particles and photons
mainly fast hadrons
Forward
biased
p-i-n
diodes
RadFETs
Optically Stimulated
Luminescence (OSL)
Reverse biased
PAD structures
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

5. RadFETs General VGS iD Fixed iD  VGS growths  TID
e-/h+ pair generation;
e-/h+ pair recombination;
e- (~psec) / h+ (~sec) transport;
hole trapping;
Interface state delayed buildup.
VGS iD
SiO2
Fixed iD  VGS growths  TID Si
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

6. RADWG-RADMON Workshop Day, 01/12/2004
RadFETs Details
Dosimetric information kept stored;
2 wires, long-distance readout;
Sensitivity vs. Dynamic range is (dox);
Dynamic range up to 100 kGySi;
Several ways to reduce T influence;
“Neutron insensitive” devices.
“Saturation problems” can arise at high Feq if oxide is not well chosen!
CERN-PH-EP-2004/045
Limited lifetime  sensitivity loss (saturation);
Particle-dependent response:
proper calibration!
“Drift-up” when switched on:
proper readout scheme!
Annealing and Interface States generation in oxides:
selection on SiO2 “quality”;
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

7. RadFETs Selection Procedure
Response to some particle fields and at high doses were missing in literature!
Response to single radiation and Room Temp. Annealing
Accelerated procedure based on the
scaling annealing t Û annealing T
SiO2 “quality” evaluation
(Isochronal Annealing)
Response at Low Dose-Rate in Mixed Environment
Devices packaging options
Aim of the 2004 irradiation campaigns
TWO types recommended for CERN purposes !
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

8. Peak Amplitude increases linearly with TID
OSLs General
(collaboration with CEM2 – Montpellier University)
e-/h+ pair generation and trapping;
Infrared stimulation ( nm);
Visible emission ( nm).
SrS:Ce,Sm
Courtesy of L.Dusseau, CEM2
IR stimulation
Peak Amplitude increases linearly with TID
OSL
The readout completely reset the sensitive material!
Photo- sensor
sec
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

9. OSLs Details Sensitivity from 10 mGy to 102 Gy;
Infinite lifetime (readout = reset);
Zeff (~ 30) close to electronics;
Response NOT particle-dependent;
Different ways to built an OSL-based active dosimeter.
Intrinsically neutron insensitive:
We make them sensitive!
Long-distance readout with 5 wires;
Complicate fading behaviour;
The related sensor equipment for active dosimetry must be radhard:
Main problem in the development of this technology at CERN!
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

10. Neutron-sensitive OSLs
FACILITIES NEUTRON SPECTRA
OSL+B
OSL+PE
IRRAD2 Facility
TRIGA Reactor
First measurements match very well the facility spectra
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

11. OSL “on-line” approaches
“sandwich” LED / OSL / photo-sensor;
LED current electronically controlled;
Optimized for long-distance readout;
Hardness in n field under investigation:
(tested for e,p up to Feq=1011 cm-2).
3 cm x
1.5 cm
Integrated Space sensor based on COTS (Version 2)
Courtesy of J. R. Vaillé, CEM2
Gain in sensitivity, reproducibility;
Gain in radiation hardness.
First prototype: 2.3 mV/cGy
OSLs deposed
on “radhard”
photo-sensor & LED
2 fibers inside 20m x  4mm2 pipe with OSL at one end;
Stimulation = Laser 1060 nm; Light detection = PM.
Less radhard constraints (PM/Laser not exposed!)
Fibred
system
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

12. p-i-n & PAD General VF iL iF VR Displacement damage in high r Si-base
Macroscopic effects both linear with Feq
FORWARD BIAS
Fixed iF  voltage increase
REVERSE BIAS
Chosen VR leakage current increase VF iL iF VR
Readout with fast pulse;
Sensitivity depends on:
Injection level;
Base width (W).
Readout under full depletion V;
Sensitivity depends on sensor volume.
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

13. p-i-n & PAD Details FORWARD Operation - vs. - REVERSE Operation
Current pulse;
2 wires, long-distance readout;
Feq range dependent on diode W;
Typically ~ 1.5 mV / 108÷1010 cm-2;
Strong T dependence;
Relative low room T annealing;
Possible to use COTS!
High voltage maybe needed.
2 wires, more complicate read-out;
Very wide Feq range;
Typically ~ 2 nA / 1010 cm-2;
Strong T dependence;
Complex annealing behaviour;
Very reliable devices.
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

14. Commercial p-i-n diodes
Commercial (thin base) BPW34F Feq = 2x1012  4x1014 cm-2
3 – USE CUSTOM-MADE DEVICES
Low Flux irradiation in PS-T7 2004
(Max Feq = 2x1012)
2 – STUDY BPW34F RESPONSE AT DIFFERENT INJECTION LEVELS!
1 – PERFORM PRE-IRRADIATION ON BPW34F
Low Flux irradiation in PS-T7 2004
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

15. RADWG-RADMON Workshop Day, 01/12/2004
Thermal n detection
OSL doped with 10B:
10B + n  7Li + a + g (s2200 = 3840 b);
Dose deposition in OSL by low range reaction fragments.
More: Ravotti, Glaser, et al., RADECS 2004, CERN-PH-EP-2004/022
Damage in npn bipolar transistors:
Boron is usual dopant in p-type Si;
Fragment produce bulk damage in transistor base;
Increase of ib for fixed ic  Dib = kth· Fth+ keq· Feq
More: Mandic, Kramberger, et al., ATLAS-IC-ES-0017 (EDMS ).
100-mm layer Fission converter on Silicon:
235U + n  140X + 95Y + 2n (s2200 = 580 b);
Very high LET fragments  efficient discrimination in mixed field.
More: Rosenfeld, Kaplan, et al., Med. Phys. 26(9), pp. 1989, 1999
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

16. RADWG-RADMON Workshop Day, 01/12/2004
Status Dec. 2004
RadFETs:
9 devices from 4 producers tested: We recommend two types of RadFETs
for low (100m Gy ÷ 10 Gy) and high (1 cGy ÷ 10 kGy) dose ranges;
OSLs: Need some more development for use as radhard active dosimeter;
p-i-n diodes:
COTS devices: ready to be used, some optimization needed;
Custom-made devices: ready to be used;
PAD structure:
Dedicated batch of devices to be produced;
Thermal neutron detectors:
OSL and diodes with fission converter: working principle shown;
npn bipolar transistors ready to be used (ATLAS).
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

17. Conclusion
Several techniques for the ACTIVE monitoring of the TID, Feq and Fth
have been presented;
All presented devices are reliable and were characterized in various
radiation fields;
Most of them are commonly used in Medicine and Space:
customization and calibration for CERN applications needed;
ACTIVE monitors are also PASSIVE dosimeters (don’t forget it !!)
More on: &
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004

18. Acknowledgments
Pr. L. Dusseau, J.R. Vaillé and all the team of the “Electronic and Radiation research Laboratory” at the CEM2, Montpellier University, France;
I. Mandić, G. Kramberger, M. Mikuž from JSI, Ljubljana, Slovenia;
A.G. Holmes-Siedle (REM, UK), G. Sarrabayrouse (CNRS-LAAS, France),
A. Rosenfeld (CMRP, Australia);
C. Joram, E. Tsesmelis and all the personnel of the PH-Bonding Lab (CERN);
All the operators of the CERN-PS accelerator for their assistance during the experiments.
F.Ravotti
RADWG-RADMON Workshop Day, 01/12/2004