Radiation-Hard Optical Link for the
ATLAS Pixel Detector
Richard Kass
The Ohio State University
W. Fernando, K.K. Gan, P. D. Jackson, M. Johnson, H. Kagan, R. Kass, A. Rahimi,
C. Rush, S. Smith, R. Ter-Antonian
The Ohio State University
P. Buchholz, M. Holder, A. Roggenbuck, P. Schade, M. Ziolkowski
Universitaet Siegen, Germany
OUTLINE
Introduction
Proton irradiation results
Opto-board production
Summary
R. Kass
IEEE05/Puerto Rico
N37-3 1
The ATLAS Pixel Detector
~380mm
~1850mm
•
•
•
•
•
•
R. Kass
Inner most charged particle tracking
Pixel size 50mm by 400 mm
~100 million pixels
Barrel layers at r = 5.1 - 12.3 cm
Disks at z = 50 - 65 cm
Dosage after 10 years:
– optical link 17 Mrad or 3.7 x 1014 1-MeV neq/cm2
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disks
barrel layers
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ATLAS Pixel Opto-link
VCSEL: Vertical Cavity Surface Emitting Laser diode
VDC:
VCSEL Driver Circuit
PIN:
PiN diode
DORIC: Digital Optical Receiver Integrated Circuit
Opto-board: Holds VDCs, DORICs, PINs, VCSELs
Uses BeO as substrate
R. Kass
IEEE05/Puerto Rico
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VCSEL Driver Circuit Specs

Convert LVDS input signal into single-ended signal appropriate to
drive the VCSEL diode

Output (bright) current: 0 to 20 mA,
controlled by externally controllable current (Iset)

Standing (dim) current: ~ 1 mA for
fast off-to-on switching of VCSEL

Rise & fall times: 1 ns nominal
(40 MHz signals)

Duty cycle: (50 ± 4)%

“On” voltage of VCSEL: up to 2.3 V at 20 mA for 2.5 V supply

Constant current consumption balanced between ON and OFF state

Use IBM 0.25 mm CMOS for radiation hardness

Use TRUELIGHT “high power oxide” common cathode VCSEL arrays
R. Kass
IEEE05/Puerto Rico
N37-3 4
Digital Optical Receiver IC Specs
Decode Bi-Phase Mark encoded (BPM) clock and
command
signals from PIN diode


Input signal size:
40 mA - 1000 mA
Extract 40 MHz clock

Duty cycle: (50 ± 4)%

Total timing error: < 1ns



40MHz
clock
Command
BPM
Bit Error Rate (BER):
< 10-11 at end of life
Use Truelight common
cathode PIN array
Use IBM 0.25 CMOS for
radiation hardness
R. Kass

IEEE05/Puerto Rico
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The Opto-board
Optical signal  electrical signal conversion occurs here
Contains 7 optical links, each link serving one Pixel module
Fabricated in 2 flavors
– Layer B: for inner barrel, two data link per module for high occupancy
Need:
– Layer D: for outer barrel and disks
Fabricated with BeO for heat management
44 B boards
226 D boards
– initial prototypes with FR4 for fast turn around and cost saving
Housing
2cm
Opto-pack
VCSEL
array
Pin array
VDC
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DORIC
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Opto-board Performance & Status
Detailed measurements are done on all critical electrical and optical
parameters to check performance/quality
– LVDS rise/fall times, jitter…,
– Optical power, optical rise/fall times, duty cycle…
– The opto-boards meet or exceed all the pixel detector requirements
Minimum PIN current for No BIT Errors
Optical power
spec.
spec.
Minimum PIN current for no BIT
errors significantly < 40mA spec
Optical power @ 10 mA
significantly > 500mW spec
R. Kass
IEEE05/Puerto Rico
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Radiation Hardness Measurements
• Important to measure/certify radiation hardness of ASICs
and opto-board and its components:
– VCSEL and PIN arrays
– VDC and DORIC chips
– Encapsulant, fibers, glues, etc.
• Use CERN’s T7 beam (24 GeV Proton) for radiation
hardness studies
– “Cold box” setup: electrical testing of DORIC and VDC
 Exposed up to 62 Mrad
– Shuttle setup: testing of optical links on opto-boards
using DORIC and VDC
 Can be moved in and out of beam remotely for VCSEL annealing
 Exposed up to 32 Mrad
R. Kass
IEEE05/Puerto Rico
N37-3 8
Real Time Monitoring in Beam Test
Real time testing of opto-board system using loop-back setup
25 meter optical
fiber cable
Opto-board
clock
bi-phase marked
optical signal
PIN
decoded data
VCSEL
VDC
decoded clock
VCSEL
VDC
DORIC
Signal routed back to
opto-baord via test
board attached to 80pin connector
data
Bit error test board
In control room
In beam
Compare transmitted and decoded data
measure minimum PIN current for no bit errors
Measure optical power
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IEEE05/Puerto Rico
N37-3 9
PIN Current Threshold vs Dosage
24 GeV protons @ CERN
Dosage (Mrad)
4.4
50
10.5
Threshold (m A)
anneal
16.8
anneal
40
spec
anneal
23.8
30.6
anneal
32.3
anneal
30
20
10
0
0
20
40
60
80
100
120
Time (h)
PIN current thresholds for no bit errors remain constant
R. Kass
IEEE05/Puerto Rico
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Optical Power vs. Dosage
Spec
•
•
•
•
Irradiate ~5 Mrad/day (10 hours) with annealing rest of the day
Optical power decreases with dosage as expected due to VCSELs
Limited annealing recovers some lost power
Still acceptable power after 30 Mrad
R. Kass
IEEE05/Puerto Rico
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Opto-board Production Challenges




R. Kass
Rigorous QA procedure:
u 72 hours of burn-in at 50oC
u 18 hours of 10 thermal cycles between -25oC and 50oC
u 8 hours of optical and electrical measurements
Use 2 ovens and 2 environmental chambers
Implemented an “early shift” to extend the work day
But no shifts on weekends.
Aggressive goals:
u produce 10 boards/week
a complete production in early October 2005
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Initial Production Problem


a
Initial plan was not to test chips before mounting
on opto-board due to high yield during pre-production
A bunch of produced boards drew excessive current
u thermal imaging showed power to ground shorts
test all chips before mounting on opto-boards
Chip yield turned out to be ~98%
VDC
R. Kass
DORIC
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Opto-board Production Status
Recovered 18 opto-boards by stacking new chips on top of bad chips
These re-worked boards passed the standard rigorous QA procedure
Will use these boards as spares.
Total
Total Failed
Total (Predicted)
Week
0
4
8
12
16
20
24
28
32
280
240
160 MHz
opto-boards
Board
200
160
80 MHz
opto-boards
120
80
40
0
2/2
5
3/2
5
4/2
2
5/2
0
6/1
7
7/1
5
8/1
2
9/9
10
/7
Date
 Relatively smooth production
 Opto-board yield ~ 93%
Production finished at OSU
R. Kass
IEEE05/Puerto Rico
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Summary
JOpto-boards of ATLAS pixel detector satisfy
design spec. and radiation hardness requirement:
low PIN current thresholds for no bit errors
excellent optical power
radiation hard up to ~ 30 Mrad
JSimple & modular design allows smooth production
opto-board production completed in seven months!
For More Details see:
ATLAS PIXEL OPTO-ELECTRONICS, K. E. Arms et al., Apr 2005.
Submitted to NIM, e-Print Archive: physics/0504142
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IEEE05/Puerto Rico
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Backup Slides
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IEEE05/Puerto Rico
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Setup for Irradiation in Shuttle at CERN
OSU
Shuttle test
electronics prior to
shipping to CERN
25 meter optical fiber
Opto-boards
Rad hard
optical
fibers
CERN T7
Remotely moves
in/out of beam
R. Kass
CERN T7
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Proton Induced Bit Errors in PIN
Convert observed bit errors into bit error rate at opto-link location:
0
0
100
200
300
400
500
600
100
200
300
400
500
600
1.00E-07
1.E-08
1.00E-08
(cm2)
1.E-10
SEU
BER
1.E-09
1.00E-09
1.E-11
1.00E-10
1.E-12
1.00E-11
IPIN (mA)
n
IPIN (mA)
Bit error rate decreases with PIN current as expected
bit error rate ~ 3 x 10-10 at 100 mA (1.4 errors/minute)
FDORIC spec: 10-11
R. Kass
IEEE05/Puerto Rico
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