karl gill cern, geneva

[email protected]

High statistics testing of radiation High statistics testing of radiation hardness and reliability of lasers and hardness and reliability of lasers and

photodiodes for CMS optical linksphotodiodes for CMS optical links

Karl Gill

CERN, Geneva

[email protected] LECC 2004

OverviewOverview

• Optical links in CMS• Environment• Advance validation test (AVT)• Results, lasers then photodiodes:

– Radiation damage– Annealing– Ageing

• Summary and Conclusions


CMS optical link projects at CERNCMS optical link projects at CERN

3 optical link systems developed at CERN, with Univ. Minnesota, HEPHY Vienna, INFN Perugia

• Tracker analogue readout

• Control links for Tracker, ECAL, Preshower, Pixels, RPC

• ECAL readout

60000 fibre channels

Aim to share as many components as possible

Focus here on tests on lasers and photodiodes pre-production


Lasers under testLasers under test

1310nm InGaAsP/InP multi-quantum-well edge-emitting lasers

Based on commercial off-the-shelf (COTS) Mitsubishi laser die, ML7CP8 Packaged by STMicroelectronics

Custom mini-pill package for CERN

Typical starting L-I characteristics:

Initial Threshold: 6mA at 20C Output efficiency (out of fibre): 40W/mA

600

500

400

300

200

100

0

pow

er, P

(uW

)

20161284current, I (mA)

L-I data 20 lasers


Photodiodes under testPhotodiodes under test

InGaAs/InP p-i-n photodiodes

Based on commercial off-the-shelf (COTS)

Fermionics FD80S8F

Package includes CERN qualified fibre pigtail and connector

Initial characteristics:

Leakage current <100pA at –5V Responsivity 0.85A/W Capacitance ~1pF at –2V

2photodiodes and 2 lasers on a digital optohybrid (DOH)


Operating environmentOperating environment• Temperature: Tracker -10C, ECAL 20C• Magnetic field 4T• Radiation environment

– 21014/cm2 (E ~ 200MeV)– 100kGy

• Inaccessible over 10 year lifetime

Charged hadron fluence (/cm2) over first 10yrs

r (cm

)

z (cm)

• LHC p p at 14TeV– 150 tracks per pp collision– ~10 collisions every 25ns


Quality Assurance programmeQuality Assurance programme

AVT is essential for COTS parts

Prototype sample validation

Pre-production Qualification

Pre-productionAdvance validation test (AVT)

Lot acceptance

FunctionalityRadiation hardness

FunctionalityRadiation hardnessReliability

Radiation hardnessReliability

Functionality

1996-2000

2000-2002

2003-2004

2003-2005


Advance validation testAdvance validation test

10 devices80C

20 devices(same as test A & B)80C

20 devices100kGy and 51014n/cm2

20-30C

Sampling

Radiationdamage

Tests A & B

Annealing

AcceleratedageingTest C

AcceleratedageingTest D

Success?

Success?

Failureanalysis

Interact withmanufacturer

Procure newwafer

Repeat test

Finalclearance

Advanceclearance

unirr

adia

ted

sam

ples

Yes

No

Yes

No

30 samples

AVT is a unique opportunity to gather and study a large amount of data on radiation damage and reliability


Failure criteriaFailure criteria

Current

Ligh

t pow

er

Laseroutput

Opticalsignal

Inputmodulation

signal

Max

imum

curr

ent

Current

Ligh

t pow

erLaseroutput

Opticalsignal

Inputmodulation

signalM

axim

umcu

rren

t

(a)

(b)

Ligh

t pow

er

Laseroutput

Opticalsignal

Inputmodulation

signal

(c)

• Normal working device

• Device failure due to threshold increase

• Device failure due to efficiency loss

e.g. lasers


Ageing and ReliabilityAgeing and Reliability

• Accelerated ageing examining wearout degradation– Burn in should eliminate early failures and random failures difficult to test

• Thermally activated

early failureperiod

random failure period wear-out failure period

wear-outfailure rate

total failure rate

random failure rate

TIME, t

FAIL

UR

E R

ATE

212

1 11exp)()(

TTkE

TMTTFTMTTF

b

a


Gamma irradiation at SCK-CENGamma irradiation at SCK-CENUp to 60 parts in each AVT

100kGy in 48 hours

30C

In-situ measurements of device characterictics

e.g. laser measurements


Neutron irradiation at UCLNeutron irradiation at UCL

deut

eron

sneutro

ns

Up to 60 parts (3 x 20) in each AVT

51014n/cm2 in 7 hoursEneutron ~ 20MeV

25C

In-situ measurements

[email protected]

Laser resultsLaser results


Radiation Damage in lasers – Radiation Damage in lasers – 6060Co gammaCo gamma

• No significant change after 100kGy

7

6

5

4

Thre

shol

d (m

A)

605040302010Laser sample number

before after 100kGy

H I L

50

45

40

35

30

Effi

cien

cy (

W/m

A)

605040302010

Laser sample number

before after 100kGy

H I L

Threshold currents

Efficiency

Data for 60 lasers from 3 wafers in AVT 3


Radiation Damage in lasers – 20MeV neutronsRadiation Damage in lasers – 20MeV neutrons

• A lot of damage from neutrons

– Increase in laser threshold current

– Decrease of laser efficiency

Typical L-I characteristics before and after 5x1014n/cm2

1000

800

600

400

200

0

Out

put l

ight

pow

er, L

(W

)

50403020100Current, I (mA)

before irrad after 5x1014n/cm2


Neutron damage effects in lasersNeutron damage effects in lasers

• Damage proportional to fluence

– Degradation of carrier lifetime

• After 4.5x1014n/cm2

– Threshold increase ~20mA– Efficiency loss ~20%

25

20

15

10

5

0

thre

shol

d in

crea

se (m

A)

1.0 2.0 3.0 4.0

~20MeV neutron fluence (1014n/cm2)

1.00

0.95

0.90

0.85

0.80

0.75

0.70

relative efficiency, E/E

(0)

efficiency

threshold

Data for 20 lasers from 1 wafer

00 1

knr


Laser wafer comparison: thresholdsLaser wafer comparison: thresholds

• 5 AVTs = 4 to 61014n/cm2

time 6 – 7.5 hrs• To compare wafers, normalized results

51014n/cm2 using only first 6 hr of data

30

20

10

0thre

shol

d in

crea

se (m

A)

6420

time, t (hrs)

5

05

0

Num

ber o

f las

ers

5

0

threshold increase after 5x1014neutrons/cm2 (mA)

5

05

05

05

05

05

05

05

05

05

020

10

0343230282624222018

A

B

C

D

E

F

G

H

I

L

M

N

O

All wafers

• Similar damage in lasers from a given wafer• Some variation across wafers• Average damage 24mA

– 400% of initial threshold value


Laser wafer comparison: efficiencyLaser wafer comparison: efficiency

• Larger spread across a wafer• Similar results from wafer to wafer• Average damage 23%

1.0

0.9

0.8

0.7

0.6Effi

cien

cy c

hang

e, u

W/m

A

6420

time, hours

420420

Num

ber o

f las

ers

420

relative efficiency loss (/E0) after 5x1014n/cm2

420420420420420420420420420420

2010

00.400.350.300.250.200.150.10

A

B

C

D

E

F

G

H

I

L

M

N

O

All wafers


Annealing in lasersAnnealing in lasers• Significant amount of annealing

– Proportional to log(tanneal)• distribution of activation energies

for annealing

• Similar rate for efficiency

– damage mechanism same as Ithr

• Expect at least 70% annealing after 10 years

102 105103 104

1.0

0.8

0.6

0.4

fract

ion

of d

amag

e re

mai

ning

1.0

0.8

0.6

0.40.1 1 10 100

annealing time (hrs)

wafer E

threshold damage

efficiency damage

0.4

0.2


Thermally accelerated ageing of unirradiated Thermally accelerated ageing of unirradiated laserslasers

• Most wafers (11 out of 13) very little wearout degradation observed• Wafer M is one of 2 wafers with lower reliability• 1000 hours at 80ºC corresponds to 4x106 hours at –10ºC (CMS Tracker)

– assuming Ea=0.7eV

10

9

8

7

6

thre

shol

d cu

rren

t at 2

0ºC

(mA

)

6.0

5.5

5.0

4.5

4.0

6.0

5.5

5.0

4.5

4.01400120010008006004002000

ageing time at 80ºC (hrs)

M

N

O

50

45

40

35

30

effic

ienc

y at

20º

C (

W/m

A)

50

45

40

35

30

50

45

40

35

30120010008006004002000

ageing time at 80ºC(hrs)

M

N

O


Distribution of device lifetimes in unirradiated Distribution of device lifetimes in unirradiated laserslasers• Wearout data extrapolated to failure criteria

• Log-normal distribution of failures– Typical of semiconductor devices

• Long lifetimes compared to project timescale– Especially at CMS operating temperatures– Estimate failure rates after 10 years

• 20FITs in CMS Tracker• 1000FITs in CMS ECAL

• Few devices will wear out. – Probably will be dominated by random failures.

• Failure distributions similar for most wafers– Except A and M, will try to avoid using these

10

20

30

40

50

60

70

80

90

Cum

ulat

ive

failu

res

105 106 107 108

Time to failure at 80ºC (hours)

threshold failure (I=55mA)

10

20

30

40

50

60

70

80

90

Cum

ulat

ive

failu

res

103 104 105 106 107

Time to failure at 80ºC (hours)

efficiency failure(

A M

AM


Thermally accelerated ageing of irradiated lasersThermally accelerated ageing of irradiated lasers

• Measurements made at 20ºC at periodic intervals

– (no lasing at 80ºC)

• No wearout observable

• Only annealing– Perhaps this masks the wearout

30

20

10

0

thre

shol

d cu

rren

t mea

sure

d at

20º

C (m

A)

30

20

10

0

30

20

10

010008006004002000

ageing time at 80ºC (hours)

H

I

L

[email protected]

Photodiode resultsPhotodiode results


Radiation Damage in photodiodes – leakage Radiation Damage in photodiodes – leakage currentscurrents

• Increase in leakage current after neutron irradiation– Similar level across all 60 devices– Expect maximum 10A after 10 years at LHC (2x1014/cm2 equivalent to 5x1014n/cm2 at CRC)

• Damage not a problem • dc optical levels generate greater currents in photodiode

– Small amount of annealing just after irradiation

• [No damage from 100kGy gammas]

0.01

0.1

1

10

100

leak

age

curr

ent,

I dar

k (1

0-6A

)

0.1 1 10

neutron fluence, (1014/cm2)

5V

1.00

0.95

0.90

0.85

0.80

0.75

0.70

un-a

nnea

led

dam

age

fract

ion

4003002001000

annealing time, tanneal (hrs)


Radiation Damage in photodiodes – Radiation Damage in photodiodes – photocurrentsphotocurrents

• Complicated evolution of photocurrent [responsivity] with fluence– Not understood but fairly consistent from device to device– No more than 32% loss over fluence range tested– Again, only small amount of annealing just after irradiation

• Not same rate as for leakage current so probably different defects responsible for the two effects

• [Again, no damage from 100kGy gammas]

1.0

0.9

0.8

0.7

0.6

rela

tive

phot

ocur

rent

, Iph

oto/

I pho

to(0

)

121086420

neutron fluence, (1014/cm2)

1.0

0.9

0.8

0.7

0.6

1.0

0.9

0.8

0.7

0.6

wafer 1

wafer 2

wafer 3

1.00

0.95

0.90

0.85

0.80

0.75

0.70

un-a

nnea

led

dam

age

fract

ion

4003002001000

annealing time, tanneal (hrs)


Thermally accelerated ageing of photodiodesThermally accelerated ageing of photodiodes

• No wearout degradation observed in any of the 60 devices• Only annealing of leakage current (but not photocurrent)• 800 hours at 80ºC corresponds to ~107 hours at –10ºC (CMS Tracker)

– assuming Ea=1eV

500

400

300

200

100

0

Leak

age

curr

ent,

I leak

(10-6

A)

8006004002000

time, t (hours)

5V

Unirradiated samples

200

180

160

140

120

100

80

60

Pho

tocu

rren

t, I p

hoto

(10-6

A)

8006004002000

time, t (hours)

5V


Summary and ConclusionsSummary and Conclusions• AVT procedure established as part of ongoing QA Programme

– Aim to reject unsuitable parts before mass production• 390 Lasers tested out of 60000 from 13 wafers in 5 AVTs• 90 Photodiodes tested out of >4000 from 3 wafers in 1 AVT

• Radiation damage very well characterised, great statistics:– No damage from 100kGy gammas but significant damage from 5x1014n/cm2

– Equivalent to worst case in CMS (first 10 years)• Lasers

– Average 24mA increase of threshold current, 23% efficiency loss, significant annealing– Final damage in CMS will be limited to ~6mA threshold increase, 6% efficiency loss

• Photodiodes– Increase of leakage current up to 10A, and up to 30% signal loss expected in CMS

• Very little wearout degradation under thermally accelerated ageing– Lasers

• Device lifetimes >106 hours under CMS conditions.• Two wafers are 10x less reliable than others, will try to avoid using them

– Photodiodes• No wearout. Device lifetimes extraordinarily large.

• Program of tests started in 1996 almost finished!

karl gill cern, geneva

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