1

Irradiation Study of n-on-P Strip Sensors

K. Hara, K. Inoue, A. Mochizuki (Univ. of Tsukuba)Y. Unno, S. Terada, T. Kohriki, Y. Ikegami (KEK)

K. Yamamura, K. Sato (HPK)

Proton irradiation: ~1x1014 to 5x1015 1MeV neq/cm2

1x1 cm2 miniature strip sensors

p-Bulk: FZ <111> and MCz <100> Effect of ｐ -stop concentration and p-spray Various p-stop structures

S. Terada; KEK26 Feb. 2007, ID week @CERN

2

High resistivity ４” wafers available to HPK• p-FZ (5~10 kΩcm, <111>)• p-MCz (0.6~1 kΩcm, <100>)

Strip isolation implant concentration (/cm2):

p-stop only: 5x1012, 2x1013

p-stop (2x1012) + p-splay (2x1012)

1x1 cm2 miniature sensors (of all above combinations) with 6 types of isolation structures (see next):

2 x 3 x 6 = 36 varieties

Proton fluence (6 points):

1, 2, 5, 10, 20, 50x1014 1MeV neq/cm2

3

N-strip isolation structures

IPSTP CPSTP

IPSTPDF CPSTPDF AF

NS

6 types:

4

Proton Irradiation at Cyclotron and Radioisotope Center (CYRIC), Tohoku University Irradiation setup

– Proton beamline 31-2• Energy: 70 MeV• Current: 10 - 500 nA• Beam spot: 4.5 mm FWHM

– Samples• 3 sensors/board (10 boards stack in one run)• scanned over 20x44 mm2 for uniform irradiation• Took about 8 hours for 5x1015neq/cm2 with 350nA

– fluence• dosimetry: Al activation 27Al(p,x)24Na• 1x1014 ~ 5x1015 1 MeV-neq/cm2

Beam line

5

I-V : isolation structures / p-implant concentrations

Pre- irrad: MD more often for MCz Leakage level depends on concentration/structure but less for MCzPost- irrad: Very uniform, little dependence on concentration/structure damage constant 　 ~ ４ x10-17 A/cm (consistent with existing data)

Pstop+Pspray Pstop 5E12 Pstop 2E13

5E152E155E14@ － 20oC

FZ

MCz

Pre-irrad@20oC

6

C-Vlog C vs. log V plots (f=1kHz)

Leakage current may be too much for 5E15?

7

Laser CCE

1064nm lasersingle shot traces@1kVCurrent amp PT~20ns ~5mV/fC

FZ MCz

8

FDV (C-V and CCE) Summary

CV and CCE agree more or less with each other(Difficult to evaluate 5E15)

FZ reaches 600V at about 3E14, while MCz at 1E15MCz higher than 600V at low fluence, below 5E13

9

CCE Summary

CCE: MCz better around 0.5 - 1x10E15Comparable to RD50 data

not fully depletedVB=1kV

p-MCz: H. Hoedlmoser,RD50 workshop 06p-DOFZ: G. Casse et al., NIMA535(2004) 362

1013 1014 1015 1016

0.0

5.0x103

1.0x104

1.5x104

2.0x104

2.5x104

nu

mb

er

of e

lect

ron

s (m

ea

n la

nd

au

)

fluence [cm-2]

p-spray high 100 V p-spray high 300 V p-spray low 100 V p-spray low 300 V G. Casse et al. 2004 @ 900 V

with 24 GeV/c protons

10161013

10

Conclusions and discussions

Fabricated n-on-p microstrip sensors p-FZ and p-MCz wafers, with 6 types of n-strip isolation structures. p-stop implantation concentration: three values and the lowest with p-splay

1x1cm2 miniature sensors irradiated to 70-MeV protons up to 5x1015 1MeV neq/cm2

Still have micro-discharge(MD) particularly to MCz before irradiation, however, MD goes away once irradiated

FDV evaluated from C-V and laser CCE measurements p-MCz: starts at ~1kV, ~400V minimum around 2x1014/cm2, then increases to 600

V at ~1x1015/cm2 p-FZ: starts at ~150V, increases rapidly and reaches to 600V at ~3x1014/cm2

Partial DV operation may be inevitable particularly to MCz at the start, unless we get higher resistivity wafer

Noise studies have been under way

Sensor under fabrication: 6” wafer p-FZ <100>, p-MCz <100>

Next irradiation scheduled at the end of April, (then August, November and March)

11

0

300

600

900

1200

1500

1800

0 10 20 30 40 50 60

fluence x10 14/ cm2

full

depl

etio

n vo

ltage

(V

)

FZMCZ

12

Measurements of sensor characteristics

N+ N+

P-bulk

P-stop

SiO2

Al

LCR meter

A A

1.5MΩ 1.5MΩ

5VVbias

CV measurement

IV measurement

Isolation measurement

I-V 　 ・・・　 micro discharge ?C-V/ CCE (Charge Collection Efficiency ) ・・・　 evaluate full depletion voltageIsolation ・・・　 evaluate electrical isolation between readout strips

AlRead out

CCE measurement

Infrared laser

~1.5 uA if isolated,Larger if not

2200pF

2200pF

13

Fluence evaluation by Al activation

P + Al → 24Na + X

efft EN

tmes

)exp(

Al (6x6cm2)

Al (1x1cm2) on sensor

Nmes : # of γ per second

λ : 24Na→γ decay rate⊿t : time from beam off to measurement Nt : # of Al atomΓ : 24Na→γ Branching ratioσ : cross sectionEeff : SSD efficiency

14

Laser CCE setupQ-switched Nd:YAG(1064nm) laser

headIntensity control (Glan polarizer+ND filters)

Peltier cooling block with cold N2 gas outlets (-20oC)

Reference sample

Amplifier boxCurrent amp (PT=20ns)

Focusing lens

Laser position monitor

15