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Radiation hardness of Monolithic Active Pixel Sensors (MAPS)
Outline:• Operation principle of MAPS• Features of MAPS• Radiation hardness tests on MAPS
D.Berst, J.Bol, W. de Boer M. Caccia, G.Claus, C.Colledani, G.Deptuch, M. Deveaux, W.Dulinski, G.Gaycken, D. Grandjean, L.Jungermann,
J.L. Riester, M.Winter
What stands MAPS for?
Monolithic:
Readout-electronics and sensors are integrated on the same substrate.
Active Pixel :
Signal processing microcircuits are integrated in each pixel.
Sensor
MAPS were developed for visible light applications by industry.
MAPS are produced with standard CMOS-processes.
R&D for International Linear Collider VD since 1999 @ IReS/LEPSI
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
The operation principle of MAPS
• A MIP creates ~80e/h pairs per µm in Si
• The Active volume (Epitaxial Epitaxial layerlayer) is not depleted.
• Charge gets collected via thermal diffusion.
4-14µm
1-2µm
Substrate Epitaxial Layer
Diode (N-Well)
P-Well
Diode
Sensor design:
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
Particle trajectory
The operation principle of MAPS
~20-40µm
Preamplifier (one per pixel)
Diffusing free electrons
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
Some simple preamplifiers
Amplifier(Source Follower)
Amplifier(Source Follower)
High resistivity diode
3 Transistor Pixel Self Bias Pixel
Classical MAPS-design
leakage current => Pedestals after CDS
Regular RESET is required
Leakage currents get compensated
No RESET is required
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
The MIMOSA - Technology
Minimum Ionizing Particle MOS Active Pixel Sensor
Features of the MIMOSA (I – VI) – detectors:
• Single point resolution 1.5µm - 2.5µm
• Typical Pixel – pitch ~20µm
• Thinning achieved to 120µm (1 Wafer to 50µm...)
• S/N for MIPs 20 – 40
• Detection efficiency > 99%
• 1MPixel sensor „serial“ readout in ~10ms
• Produced in various commercial CMOS-Processes
• Radiation hardness: several 1011 up to 1012neq/cm²
MIMOSA IV
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
Studies on radiation hardness
MAPS were calibrated with 5,9 keV (55Fe) Photons.
Produce ~1640 free electrons (same order of magnitude as MIPs)
Very local interaction Hit in the depleted area.100% collection efficiency.
Hit in the epitaxial layer. Collection efficiency?
Hit in the substrate close to epitaxial layer. Sensitive with limited efficiency.
Key parameter:Charge collection
Build a „charge collection spectrum“
0 100 200 300 4000
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400
600
800
(c) Michael Deveaux
MIMOSA II before and afterirradiation with 200kRad X-Rays
Entries in Histogram
Charge Collected in 4 Pixels [ADC]
Before After
Irradiation
~ 400kRad
First studies Mimosa 2
Peak from depleted area.No change => Readout electro-nics ok.
Underground from substrate
Peak from epitaxial layer.
Substantial drop in charge collection after irradiation
Conclusion on Mimosa 2 after ~ 400kRad:• Leakage currents increases by a factor ~5.• Noise increases by some percent.• Readout electronics OK.• Charge collection drops by ~50% (kills the chip)
Two preamplifiers, two different results
Amplifier(Source Follower)
Amplifier(Source Follower)
3 transistor pixel
Self bias pixel
High resistivity diode
Mimosa 2 (MIETEC 0.35) Mimosa 4 (AMS 0.35)
Conclusion:
Charge loss observed
• leakage current can be measured
Indication:
No Charge loss
• Leakage current cannot be measured
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
A working hypothesis:
SiO2 non irrad. SiO2 irradiated
Main difference: Presence of an enclosed reset transistor
• Reset transistor + positive charge create locally high fields.
• P-Well barrier gets depleted.
• Parasitic charge collection by the Reset-Transistor.CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
Successor1, a chip to study radiation hardness
Designed within the SUCIMA project (FP5).
Tests: IReS, SUCIMA and GSI.
Process: AMIS 0.35 (Should be similar to MIETEC 0.35)
Design goal: Radiation hard prototype for a medical dosimeter with high spatial resolution.
8 different pixel designs, only 1 discussed here:
• 33 x 32 pixels
• 3.2 x 3.2 µm² diode size.
• Source and drain of reset transistor swapped
• Non uniform pixel pitch (25 and 35 µm steps)
Irradiated: Up to 1MRad X-Rays
Silicon ultra fast cameras for electron and gamma
sources in medical applications
SUCCESSOR = Sucima Cmos ChargE SenSOR
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
Successor1 leakage current before and after irradiation
Observation: • Leakage current increases by a factor 200-300
Leakage currents are very different for identical pixels depending on their position on the chip.
=> Induced heat due to nearby output buffer?
x
y
I
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
Successor1 noise
Noise increase depends on the running conditions:
More than factor 2 for +20°C and 2.5MHz sampling (~1ms integration time)Less than 20% for –15°C and 10MHz sampling (~0.2ms integration time)
Even lower integration time is required for most tracking applications
(Lines to guide the eye) (Lines to guide the eye)
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
100 200 300 400
1000
2000
3000
4000
5000
6000
100 200 300 400
500
1000
1500
2000
2500
Successor1 charge collection
Observations (Priliminary):
No significant influence on gain
Successor1 before and after 1MRad X-Rays
Charge collected in 1 pixel [ADC]
Charge collected in 9 pixels [ADC]
T = -15°C t = ~ 200µs
No significant charge loss
CBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])
Conclusion:
• Charge loss, being the main problem so far, seems stopped.• Noise increase can probably be handled.
• Evidence that a 1MRad resistant MAPS-detector can be build.
Outlook:
Analysis on Successor1-data has to be refined and completed
Beamtests with similar tracking chip were done. Results underway.
Long term: Find a way to reduce leakage currentsCBM collaboration meeting, GSI Darmstadt, 6-8 Oct 2004, Michael Deveaux ([email protected])