R. Kass IEEE05/Puerto Rico N37-3 1

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

OUTLINEIntroduction

Proton irradiation results

Opto-board production

Summary

R. Kass IEEE05/Puerto Rico N37-3 2

The ATLAS Pixel Detector

• Inner most charged particle tracking• Pixel size 50m by 400 m• ~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

disks

barrel layers

~380mm

~1850mm

R. Kass IEEE05/Puerto Rico N37-3 3

ATLAS Pixel Opto-link

VCSEL: Vertical Cavity Surface Emitting Laser diodeVDC: VCSEL Driver Circuit

PIN: PiN diodeDORIC: Digital Optical Receiver Integrated Circuit

Opto-board: Holds VDCs, DORICs, PINs, VCSELs Uses BeO as substrate

R. Kass IEEE05/Puerto Rico N37-3 4

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 m CMOS for radiation hardness

Use TRUELIGHT “high power oxide” common cathode VCSEL arrays

VCSEL Driver Circuit Specs

R. Kass IEEE05/Puerto Rico N37-3 5

Decode Bi-Phase Mark encoded (BPM) clock and command signals from PIN diode

Input signal size:

40 A - 1000 A

Extract 40 MHz clock

Duty cycle: (50 ± 4)%

Total timing error: < 1ns

Bit Error Rate (BER): < 10-11 at end of life Use Truelight common cathode PIN array

Use IBM 0.25 CMOS for radiation hardness

Digital Optical Receiver IC Specs

40MHzclock

Command

BPM

R. Kass IEEE05/Puerto Rico N37-3 6

The Opto-boardOptical 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 – Layer D: for outer barrel and disks

Fabricated with BeO for heat management– initial prototypes with FR4 for fast turn around and cost saving

Need:44 B boards226 D boards

Opto-pack

Housing

Pin array

DORIC

VCSEL array

VDC

2cm

R. Kass IEEE05/Puerto Rico N37-3 7

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

spec.

Optical power @ 10 mA

significantly > 500W spec

Optical power

spec.

Minimum PIN current for No BIT Errors

Minimum PIN current for no BIT

errors significantly < 40A spec

R. Kass IEEE05/Puerto Rico N37-3 8

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 9

Real Time Monitoring in Beam TestReal time testing of opto-board system using loop-back setup

dataDORIC

clockPIN

VDCVCSEL

Opto-board

VDCVCSEL

bi-phase marked optical signal

decoded data

decoded clock

Signal routed back to opto-baord via test

board attached to 80-pin connector

Bit error test board

Compare transmitted and decoded data measure minimum PIN current for no bit errors

Measure optical power

In control room

25 meter optical fiber cable

In beam

R. Kass IEEE05/Puerto Rico N37-3 10

PIN Current Threshold vs Dosage

PIN current thresholds for no bit errors remain constant

spec

24 GeV protons @ CERN

R. Kass IEEE05/Puerto Rico N37-3 11

Optical Power vs. Dosage

• 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

Spec

R. Kass IEEE05/Puerto Rico N37-3 12

Opto-board Production Challenges

Rigorous QA procedure:72 hours of burn-in at 50oC18 hours of 10 thermal cycles between -25oC and 50oC8 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:produce 10 boards/weekcomplete production in early October 2005

R. Kass IEEE05/Puerto Rico N37-3 13

Initial plan was not to test chips before mountingon opto-board due to high yield during pre-production

A bunch of produced boards drew excessive currentthermal imaging showed power to ground shorts

test all chips before mounting on opto-boards Chip yield turned out to be ~98%

Initial Production Problem

VDC DORIC

R. Kass IEEE05/Puerto Rico N37-3 14

0

40

80

120

160

200

240

280

2/253/25

4/225/20

6/177/15

8/12 9/910/7

Date

Bo

ard

0 4 8 12 16 20 24 28 32

Week

TotalTotal FailedTotal (Predicted)

Opto-board Production Status

Relatively smooth productionOpto-board yield ~ 93%

Production finished at OSU

80 MHzopto-boards

160 MHzopto-boards

Recovered 18 opto-boards by stacking new chips on top of bad chipsThese re-worked boards passed the standard rigorous QA procedureWill use these boards as spares.

R. Kass IEEE05/Puerto Rico N37-3 15

Summary

Opto-boards of ATLAS pixel detector satisfy design spec. and radiation hardness requirement:

low PIN current thresholds for no bit errorsexcellent optical power

radiation hard up to ~ 30 Mrad

Simple & modular design allows smooth productionopto-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

R. Kass IEEE05/Puerto Rico N37-3 16

Backup Slides

R. Kass N37-3 17

Setup for Irradiation in Shuttle at CERN

Opto-boards

Rad hard optical fibers

25 meter optical fiber

Shuttle test electronics prior to shipping to CERN

Remotely moves in/out of beam

OSUOSU

CERN T7 CERN T7

R. Kass IEEE05/Puerto Rico N37-3 18

Proton Induced Bit Errors in PIN

Bit error rate decreases with PIN current as expected

bit error rate ~ 3 x 10-10 at 100 A (1.4 errors/minute)

DORIC spec: 10-11

Convert observed bit errors into bit error rate at opto-link location:

1.00E-11

1.00E-10

1.00E-09

1.00E-08

1.00E-07

0 100 200 300 400 500 600

IPIN (A)S

EU (c

m2 )

SE

U

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

0 100 200 300 400 500 600

IPIN (A)

BE

R