Radiation hardness of Monolithic Active Pixel Sensors (MAPS) Outline: Operation principle of MAPS Features of MAPS Radiation hardness tests on MAPS D.Berst,

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:


Particle trajectory

The operation principle of MAPS

~20-40µm

Preamplifier (one per pixel)

Diffusing free electrons


Some simple preamplifiers

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


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


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

200

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



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


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


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


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)


100 200 300 400

1000

2000

3000

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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


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])

Documents

Radiation hardness of Monolithic Active Pixel Sensors (MAPS) Outline: Operation principle of MAPS Features of MAPS Radiation hardness tests on MAPS D.Berst,