1. Radiation Sensor Characterization for the LHC Experiments
Federico Ravotti, Maurice Glaser, Michael Moll
CERN PH/DT2 and TS/LEA

2. Outline Sensor Catalogue;
Quality Assurance (QA) procedure for sensors;
RadFETs packaging;
Sensors readout board for LHC Experiments;
Sensors R&D:
Readout procedure optimization for BPW34 p-i-n diodes;
New p-i-n diodes from Czech Republic (LBSD);
On-line dosimeter based on fibred OSL.
Conclusion.
F.Ravotti
5th LHC Radiation Day

3. Sensor Catalogue (www.cern.ch/lhc-expt-radmon/) 2 x RadFETs (TID);
Specifies sensors suitable for dosimetry in
the LHC experiments environment:
Mixed-LET radiation field;
~ 5 orders of magnitude in intensity.
Many devices tested but only a few selected (e.g. only 2 out of 9 RadFETs)
2 x RadFETs (TID);
[REM, UK and LASS, France]
2 x p-i-n diodes (1-MeV Feq);
[CMRP, AU and OSRAM BPW34]
1 x Silicon detectors (1-MeV Feq).
[CERN RD-50 Mask]
Detailed discussion on the sensors selection criteria  see talk at 4th LHC Radiation Day!
F.Ravotti
5th LHC Radiation Day

4. Sensors QA Procedure
Suitable radiation response and intrinsic stability are not enough to guarantee reliable measurements over a long time (e.g. 10 y. LHC).
Example of different radiation response curves for Thin Oxide RadFETs from REM (see Catalogue).
Example of Annealing Behaviour at different doses for Thick Oxide RadFETs from LAAS
(see Catalogue).
Compliance with electrical specifications to
keep working correctly under irradiation;
Homogeneous initial values to insure
reproducible measurements;
Sensors must be identified one by one using their pre-irradiation characteristics!
F.Ravotti
5th LHC Radiation Day

5. Delivery to the LHC Experiments
Sensors QA Procedure
Electrical Tests on the purchased sensor batches to complies with specifications
Acceptance Tests
For the Experiments with proper readout boards
Mounting bare-die sensors in a proper packaging
Issue for TID Measurement
(RadFETs Packaging)
Functional Verification Test
Integration in a specific PCB circuit “sensor carrier”
For the Experiments that need a readout board
Functional Verification Test
Delivery to the LHC Experiments
F.Ravotti
5th LHC Radiation Day

6. Electrical Tests RadFETs: Ids – Vgs in linear and saturation regime;
Ids – Vds in function of Vgs;
Read-time stability of Vth;
p-i-n diodes:
I-V in forward bias;
Stability of VF  (t);
Silicon Detectors:
I-V & C-V in reverse bias;
Stability of bulk IL  (t).
Example of I/V characteristics of not-irradiated BPW34 diodes.
Example of I/V and C/V characteristics of not-irradiated Detectors.
F.Ravotti
5th LHC Radiation Day

7. RadFETs Characteristics
Idss VT
Sensors Acceptance/Rejection based on:
Vth,0
Idss
Ids-Vds immune to kink effects
Stability of Vth (t).
 Tech. Spec. document existent
F.Ravotti
5th LHC Radiation Day

8. RadFETs Packaging ~10 mm2 36-pin Al2O3 carrier
Commercial Packaging (i.e. TO-5, DIL) cannot satisfy all Experiment Requirements
(dimensions/materials)
Development / study in-house at CERN
High Integration level:
up to 10 devices covering from mGy to kGy dose range;
Customizable internal layout;
Standard external connectivity;
1.8 mm
~10 mm2 36-pin Al2O3 carrier
Calculated Radiation Transport Characteristics (0.4 mm Al2O3):
X = 3-4 % X0;
e cut-off  550 KeV;
p cut-off  10 MeV;
photons transmission  20 KeV;
n attenuation  2-3 %;
Packaging under validation (including lids effect) with GEANT4 model in collaboration with Genova INFN (Riccardo Capra)
Full-Package Geometry designed in GEANT4
F.Ravotti
5th LHC Radiation Day

9. Integration Issues ATLAS ID (RMSB Hybrid) CMS (BCM 1) Rest of ATLAS
4 x RADFETs
DMILL structure
(nth damage)
CMS (BCM 1)
BPW34 diodes
PCB with T control
PAD diode
PT1000
p-i-n diode
[I. Mandic, JSI]
ELMB (ADC) + DAQ
[A. Macpherson, CERN]
Rest of ATLAS
General-purpose plug-on I/O module for the monitoring and control of sub-detector front-end equipment
F.Ravotti
5th LHC Radiation Day

10. Sensors Readout Board PCB designed to host:
1 x RadFETs Packaging (5 channels)
5 x p-i-n sensors;
1 x Temperature sensor;
Fully customizable;
Small size (15 mm x 25 mm x 5 mm);
Signals available on a standard connector plug (12 pins) or
direct wire connection.
Board readable with commercial electronics:
Keithley Source-Meter 2400 and Agilent Switch Matrix;
Price ~ 130 CHF/channel (if > 60 channels)
PCB can be used as passive dosimeter.
F.Ravotti
5th LHC Radiation Day

11. Outline Sensor Catalogue;
Quality Assurance (QA) procedure for sensors;
RadFETs packaging;
Sensors readout board for LHC Experiments;
Sensors R&D:
Readout procedure optimization for BPW34 p-i-n diodes;
New p-i-n diodes from Czech Republic (LBSD);
On-line dosimeter based on fibred OSL.
Conclusion.
F.Ravotti
5th LHC Radiation Day

12. BPW34 Readout Optimization
1) Devices not manufactured to be dosimeters
(e.g. not sensitive to low F);
2) Pre-irradiation helps to shift operation point
(see our last years talk);
To be studied in more detail:
Influence of readout parameters (current density and pulse length) on diode’s response;
Long-term annealing of VF as function of IF and Temperature.
iF = 1 mA  200 ms
Current density:
Feq > 21013 cm-2  “thyristor - like” behaviour;
Keep IF < 50 mA is a good precaution!
Tested readout currents 1 mA, 10 mA, 25 mA
Feq
(1x1011 to 1x1015 cm-2)
F.Ravotti
5th LHC Radiation Day

13. BPW34 Readout Optimization
Current density
(radiation response at 25 mA vs. 1 mA):
Feq < 21012 cm-2 negligible sensitivity increase;
Feq > 21012 cm-2; S (25 mA) > 36 % S (1 mA);
Signs of heating effects Feq ~ 11014 cm-2;
iF = 25 mA  100 ms
Pulse Length:
 Keep the readout-time  200 ms is advisable;
 “optimized” pulse-length of 50 ms.
after ~ 11013 cm-2
IF = 1 mA; VF = 6.7 V
Conclusion:
Current density and pulse length have to be adopted to the user requirements (fluence range, current density limitations in electronics, etc….)
F.Ravotti
5th LHC Radiation Day

14. BPW34 Readout Optimization
Annealing of VF (IF):
Relative change of the voltage less significant at high injection levels!
(detailed study ongoing in the Temperature range 20 – 100 ºC)
F.Ravotti
5th LHC Radiation Day

15. Czech p-i-n diodes (LBSD)
Long Base Silicon Diodes from CMI, Prague
Cheaper compared to the High Sensitivity diodes currently presented in the Catalogue;
Two types are produced: one MORE SENSITIVE than the currently used devices;
Recommended IF pulse for readout: 25 mA x 40 ms.
Type “Si-1”:
KERMA: Gy (Feq ~ 1.2x1012 cm-2)
nF sensitivity: ~ 3 mV/109 cm-2
Type “Si-2”:
KERMA: Gy (Feq ~ 2x1011 cm-2)
nF sensitivity: ~ 3 mV/108 cm-2
Annealing studies ongoing to include these products into Sensor Catalogue!
F.Ravotti
5th LHC Radiation Day

16. Fibred OSLs System Quartz Radhard Fibers Laser System Driver
Laser Light 60 mW
Visible light
~ 5 mg
OSL
Crystal
Oscilloscope
1 mA/nW OSL l)
5 V/div
1 MW DC
50 ms/div
Tested at the TRIGA Reactor of the JSI, Ljubljana (Slovenia)
F.Ravotti
5th LHC Radiation Day

17. Dose integrated in 6 sec time.
Fibred OSLs System
Preliminary Results (last week!!!) show the feasibility of such a system in harsh and intense environment;
Test condition ~200 mGy/s with feq ~1.9x109 cm-2s-1 (values referred to 250 W reactor power at Z = 0).
Dose integrated in 6 sec time.
Sensitivity of the tested prototype ~ 0.1 mGy, but minimal sensitivity probably higher;
probe edge dimension < 1 mm2
F.Ravotti
5th LHC Radiation Day

18. Conclusion
Over 1200 sensors have been procured and ~ 1/3 have been tested following the QA procedure here described. About 100 samples have been delivered to LHC Experiments;
A dedicate packaging and a readout board for the sensors have been produced;
R&D on sensors is carried out in parallel:
Improvement in the BPW34 readout protocol;
More sensitive p-i-n diodes are under studies  added soon to the Sensor Catalogue;
Very promising results obtained in OSL on-line dosimetry!
F.Ravotti
5th LHC Radiation Day