Development of Pixel Detectors for the Inner Tracker ... · 4 March 11th 2016 N. Savić –...
Transcript of Development of Pixel Detectors for the Inner Tracker ... · 4 March 11th 2016 N. Savić –...
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Development of Pixel Detectors for the Inner Tracker Upgrade of the ATLAS Experiment Natascha Savić L. Bergbreiter, J. Breuer, A. Macchiolo, R. Nisius, S. Terzo
IMPRS, Munich March 11th 2016
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 2
Overview
• Introduction to the ATLAS Pixel Detector
• Motivation
• Experimental investigations of pixel modules
• charge collection measurements in the
laboratory
• efficiency measurement during test beam
campaigns
• Summary and Outlook
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 3
The ATLAS Pixel Detector
The ATLAS Detector
The Pixel Detector
The Pixel Module
Silicon sensor (thickness ~300 µm)
Read-out chip (thickness ~200 µm)
Sensor and read-out chip connected via bump bonds
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 4
What is a Pixel Detector?
Read-out chip
Bump bond
Sensor
• particles traverse the silicon sensors and release electrons and holes in the depleted bulk which move to the electrodes
è signal is created
• sensor and read-out chip are interconnected through solder bump bonds è signal is processed
negative voltage applied on the sensor backside
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 5
Conditions before 2013
Cross section of the pixel system
20 p-p collisions ever 50 ns
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 6
Conditions in 2013
Insertable B-Layer (IBL): new pixel layer at 3.2 cm from the beamline
25 p-p collisions ever 25 ns
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 7
In view of the high luminosity phase of the LHC in 2024–2026 the ATLAS experiment will undergo a major upgrade of its tracker system
Conditions from 2024 P
ixel
laye
rs 1
to 4
Scale of expected fluences in the different layers
layer 1 layer 2
layer 3
layer 4
Expected radiation for the ATLAS detector
~ 1-1.4x1016 neqcm-2
140-200 pile-up events
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 8
What happens to the pixel detector during irradiation?
• Charge trapping
• defects act as trapping centers
è reduction of collected charge
• Increase of the leakage current
• increase of the power consumption (P ~ I ~ ϕ è P ~ I x U )
è strong cooling requirements • increase of the noise
2x1015 neq/cm-2
10x1015 neq/cm-2
dc
Sensor frontside Sensor backside
defect defect
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 9
Motivation
Goal: radiation hardness of the innermost silicon detector
è optimization of hit efficiency, leakage current and power dissipation
i. reduction of the sensor thickness
è higher electric field and smaller charge collection distance lead to less
charge trapping and hence higher efficiency
è lower operation voltage and thus leakage current lead to less power dissipation
ii. improvement of the pixel design
è increasing efficiencies of pixel cells
è higher granularity
Experimental investigations
i. charge collection measurements in the laboratory
ii. efficiency measurements during test beam campaigns
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 10
Sensors with different active thicknesses at MPP
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 11
Thinning production process flow of sensors
• sensor active thickness: 75 to 200 µm
• afterwards bump bonded to chips
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 12
• Samples : modules with 200 µm thick sensors irradiated to different fluences
• Method : 90Sr radioactive β-source with external trigger via scintillator
• Cooling : in climate chamber down to -40 °C sensor temperature
Laboratory measurements
Charge collection (CC)
incr
easi
ng fl
uenc
e
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 13
• Samples : irradiated modules with sensor thicknesses from 75 to 285 µm
Laboratory measurements
Charge collection (CC)
300
Highest CC for 100 and 150 µm thin sensors
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 14
Efficiencies for different thicknesses
1) DESY in Hamburg with 4 GeV electrons
2) SpS at CERN with 120 GeV pions
using irradiated modules with sensor thickness from 100 to 270 µm
Efficiency measurements with the EUDET telescope at :
Thinner sensors show higher charge collection and hit efficiency after irradiation.
fluence ~ const
Voltage0 100 200 300 400 500 600 700
Effic
ienc
y in
%70
75
80
85
90
95
100Efficiencies for different sensor thicknesses and irradiations
FE-I4 100um, 5e15FE-I4 150um, 4e15FE-I4 200um, 6e15FE-I4 270um, 5e15
incr
easi
ng th
ickn
ess
Hit
effic
ienc
y in
%
97.1 % efficiency at just 300 V
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 15
Optimization of biasing structures and pixel pitches
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 16
Optimization of biasing structures and pixel pitches
Bias dot Bias rail Implant Bump pad Aluminium
Punch-through structure
Guard rings (protect the sensor edges by allowing for a smooth potential drop from the pixels to the cutting edge)
Cut-off sensor surface
Biasing structure is implemented in order to test the sensor before interconnecting to the chip
Biasing ring
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 17
Optimization of biasing structures and pixel pitches
Standard punch-‐through Biasline over punch-‐through dot
Biasline over center
Modified 25x500 µm² pixel
Standard 50x250 µm² pixel
Common punch-‐through
individual punch-through (p-t)
comm
on p-t
MPP designed sensors of 270 µm thickness fabricated and bonded to chips
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 18
Comparison of performance of different p-t designs In-pixel hit efficiency
100 % hit efficiency before irradiation
Irradiated at 5x1015 neq/cm2, U= 500 V
Test beam analysis shows better hit efficiency when the p-t and bias rail is over-imposed to the pixel implant.
all three p-t designs implemented in one module m]µLong Side [
0 20 40 60 80 100 120 140 160 180 200 220 240
m]
µSh
ort S
ide[
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Efficiency Pixel Map DUT 20 Geometry 4
m]µLong Side [0 20 40 60 80 100 120 140 160 180 200 220 240
m]
µSh
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ide[
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Efficiency Pixel Map DUT 20 Geometry 3
Effi
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]
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Effi
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]
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Track x [µm]
Track x [µm]
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Trac
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50x250 µm² pitch 50
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Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 19
Comparison of performance of different p-t designs In-pixel hit efficiency
~ 100 % hit efficiency before irradiation
Irradiated at 5x1015 neq/cm2, U= 500 V
Test beam analysis shows better hit efficiency when the p-t and bias rail are over-imposed to the pixel implant.
all three p-t designs implemented in one module
cut-out of a 50x50 µm² pitch
m]µLong Side [0 20 40 60 80 100 120 140 160 180 200 220 240
m]
µSh
ort S
ide[
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101520253035404550
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Efficiency Pixel Map DUT 20 Geometry 4
m]µLong Side [0 20 40 60 80 100 120 140 160 180 200 220 240
m]
µSh
ort S
ide[
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101520253035404550
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Efficiency Pixel Map DUT 20 Geometry 3
Effi
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100 80
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Effi
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100 80
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Track x [µm]
Track x [µm]
Track x [µm]
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Trac
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50x250 µm² pitch 50
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Trac
k y
[µm
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Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 20
Improved hit efficiency for the biasline over the p-t dot and common p-t after irradiation.
Novel p-t design for 25x500 µm2 pixel In-pixel hit efficiency
96.0 ± 0.3 % 96.0 ± 0.3 %
m]µLong Side [0 50 100 150 200 250 300 350 400 450
m]µShor
t Side[
02468
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Efficiency Pixel Map DUT 21 Geometry 0
25x500 µm² pitch
Voltage0 100 200 300 400 500 600 700 800
Effic
ienc
y in
%
65
70
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80
85
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100Efficiency of different punch-through designs in pixels, 5e15
Common p-t forBiasline over p-t dotStandard p-t designBiasline over center
98.0 %
Δε = 0.3 %
fluence 5x1015 Comparison hit efficiency of different p-t designs
100
50
0
25
15
Effi
cien
cy [%
]
Trac
k y
[µm
]
100 200 300 400 Track x [µm]
5
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 21
Estimation of hit efficiency for a 25x100 µm2 pitch at a fluence of 3x1015 neqcm-2
Inefficiencies appear at the edges of the pixel left: first 40 µm show inefficiency caused by charge sharing right: last 60 µm show inefficiency caused by punch-through • effective pitch of 25x100 µm2
obtained by combining first 40 µm and last 60 µm of pixel cell
• example created to estimate a hit efficiency for the 25x100 µm2 pitch
Hit efficiency at 3x1015 neqcm-2
Estimated hit efficiency for 25x100 µm2 pitch at 500 V : 96.4 % (99.8 % for 25x500 µm2 pitch and 96.5 % for standard 50x250 µm2 pitch and standard p-t at 3x1015 neqcm-2)
25x500 µm2 25x100 µm2
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 22
New design for sensors with small pixel pitch
50x50 µm2 and 25x100 µm2 pixel pitches • foreseen for a new radiation hard chip
with a regular 50x50 µm2 grid • p-t design combination of biasline over p-t
dot and common p-t (best performig ones!)
25x100 µm² pixel pitch • design based on the existing prototype
with 25x500 µm² pitch (results shown before)
50
50
25
20 UBM pad
100
design 2 25x100
design 1 50x50
SOI wafers of new production at MPG-HLL with 100 and 150 µm active thickness successfully tested
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 23
Summary and Outlook
• Thin sensors
• 100 and 150 µm thick sensors show higher charge collection and hit efficiency
• 100 µm thick sensor reaches hit efficiency of up to 97.1 % after irradiation at 5 �1015 neq/cm2 at just 300 V
• Investigations of new pixel cell design
• Improved hit efficiency for the biasline over the p-t and the common p-t with respect to the standard design after irradiation at 5 �1015 neq/cm2
• New MPG-HLL production
• Combines and implements new pixel cell design and best performing biasing structures on thinner sensors
è Promising innovations of sensor design will be connected to the new ATLAS chips with a 50x50 grid and tested by the end of 2017
Max-Planck Institut für Physik March 11th 2016 N. Savić – Development of Pixel Detectors for the Inner Tracker Upgrade of ATLAS 24
Thank you for your attention!