RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 1

Radiation hardness of the Avalanche Photodiodes for ECAL CMS detector

at CERN

A. Singovski The University of Minnesota

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 2

APD’s in the CMS detector

PbWO4 crystal

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 3

Radiation level after 10 years

Radiation doses are in red, 104 Gy. Neutron fluence in green 1013 neutrons/cm 2 with E > 100 keV.

Levels outside of the detector are down by a factor of 100 or more.

Crystal calorimeter

100

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 4

APD’s for CMS

Manufacturer:•Hamamatsu Photonics, Japan.

Quantity:•Two APD’s per crystal– 124,000 APD’s with spares.

Accessibility during operation:•None.

Radiation levels:•Maximum expected dose 200 kGy and 2 1013 neutrons/cm2.

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 5

Basic APD Structure:

APD is grown epitaxially on an n++ wafer.

Junction

Si2N4 AR coating

Groove to minimize

surface leakage current.

5 5 mm2

active area

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 6

APD radiation damage

Radiation damage of APD can influence ECAL performance by essentially two effects:

-rise of the bulk current increase APD noise contribution to the energy resolution

-early breakdown breakdown happens before APD can reach operation point at Gain=50

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 7

APD contribution to the ECAL resolution

Resolution:

where, a : due to intrinsic shower fluctuations & photo statistics

b : related to stability and reproducibility c : noise contributions CMS design goal : a ~3%, b~0.5%, c~200 MeV APD contributions: a - photo statistics (area, QE) & excess noise factor b - gain variation with bias voltage and temperature c - capacitance as series noise and dark current as parallel noise

E

cb

GeVE

a

E

E⊕⊕=

)(σ

σ σ σtotal parallel series= +2 2

( ) τσ qFMII dbdsparallel ⋅+= 2

⎟⎟⎠

⎞⎜⎜⎝

⎛+⋅

⋅= R

gCkT

series

7.02

4 2

τσ

M = APD gain F = excess noise factor τ=shapingtimeconstantq=electronchargeIds=darksurfacecurrentIdb=darkbulkcurrentR=seriesresistanceC=capacitanceofAPDandamplifierk=BoltzmannconstantT=absolutetemperatureg=transconductanceofamplifierfirststage

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 8

Irradiation Tests.

Irradiation with protons:•70 MeV protons beam at PSI – Switzerland.

•11013 hadrons/cm2 in ~ 2 hours.

Irradiation with gammas.•All irradiation with 60C0 source.

Irradiation with neutrons.•Californium source (252Cf) for irradiation at the University of Minnesota.

•2 1013 neutrons/cm2 in ~ 2 days.

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 9

Device failure

0

5

10

15

20

25

30

35

0 1000 2000 3000 4000 5000 6000 7000 8000Time (s)

Dark Current (

μ)A

Irradiation in a 70 MeV proton beam.

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 10

Neutron irradiation facility

Draws for irradiation

Use old tandem laboratory facility in Minneapolis to store and operate two 7 mg sources for irradiation samples.

•High and low flux areas 1013 and 1011

n/cm2 in 2 – 4 days.

•Must provide biases to components during irradiation.

•Return sources after 4 years of operation.

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 11

Neutron irradiation results

705 APD's Irradiated - Includes Source Decay

y = 1.3954E-11x

R2 = 8.6333E-01

0

50

100

150

200

250

300

0.0E+00 5.0E+12 1.0E+13 1.5E+13 2.0E+13

Integrated Neutron Flux (neutrons cm-2)

Id/M (nA) at Gain 50

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 12

Durk current

Total Current (dark current + ionisation current)

02468

101214161820

0.00E+00 5.00E+12 1.00E+13 1.50E+13 2.00E+13

total Neutron Flux / cm2

Current [

μ]A

Current vs Flux

0

5

10

15

20

25

0 2E+12 4E+12 6E+12 8E+12 1E+13 1.2E+13 1.4E+13

Total neutron flux

Current at M=50, mkA

3003006176

2802004514

70 MeV protons

1 MeV neutrons from 252Cf

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 13

Neutron irradiation summary

1.All APD tested so far survived -> no significant shift in breakdown voltage.

2.The mean bulk current after 2x1013 neutrons/cm2 is Id280nA (non-amplified value).

3.It corresponds to 14μA at Gain=50 and ~ 80MeV noise contribution (no-recovery case, CMS TDR).

Acceptable for CMS ECAL detector

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 14

Gamma irradiation

APDs

32 wires containing 60Co surround the probe and give a very uniform irradiation field.

Present activity is 2.5 kGy/h

60Co irradiation facility at PSI

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 15

Gamma irradiation results

Lot 34 Breakdown Voltage Comparison

-30

-25

-20

-15

-10

-5

0

5

8900 9000 9100 9200 9300 9400 9500 9600

APD #

VB(irradiated)-V

B(Hamamatsu) [V]

Rejected

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 16

Gamma irradiation results 2

APD with a significant shift of Vb after 60Co

irradiation

(vs. good one)

Id/Gain

Noise

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 17

Screening

Method:

- irradiate 100% of APD`s (0.5 Mrad) with Co-60 gamma source (at PSI);

- measure VB and Id(V) of all irradiated APD`s 1 day after irradiation (at PSI);

- measure noise at M=1, 50, 150, 300 before annealing (at CERN APD Lab)

- anneal all APD`s in the oven (for 4 weeks at T=80C, at CERN APD Lab);

- measure VB, Id(V) after annealing/ageing (at CERN APD Lab);

-reject potentially non-reliable APD`s: ones showing

-Shift of Vb more than 5V

-high Id

-high noise

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 18

APD rejection

High dark current High noise

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 19

Screening efficiency

Double irradiation (225 APDs from lot##33,34)

-5

-4

-3

-2

-1

0

1

2

3

0 50 100 150 200 250

APD #

Change of VB [V]dVB(after first Co-irr.)

dVB(after annealing)

dVB(after second Co-irr.)

225 APD`s which passed 1st irradiation and annealing were irradiated the 2nd time. No change of VB>2V was

found for all APD`s !!!

RESMDD02 July 10-12 2002, Florence, A.Singovski, University of Minnesota 20

Gamma irradiation summary

1.APDs are sensitive to the gamma irradiation.

2.Several percents “die” after irradiation -> get a breakdown close to the operation point.

3.Screening, applied to 100% of APDs make them 99.9% rad. Hard.