Progress in R&D on silicon edgeless strip detectors with Current Terminating Structure

1

Progress in R&D on silicon edgeless strip detectors with

Current Terminating Structure

E. Verbitskaya1, A. Cavallini2, V. Eremin1, S. Golubkov3

G. Pellegrini4, G. Ruggiero5, T. Tuuva6

1Ioffe Physico-Technical Institute RAS, St. Petersburg, Russia2University of Bologna, Bologna, Italy

3Research Institute of Material Science and Technology4Centro Nacional de Microelectrónica, CNM-IMB, Barcelona, Spain

5CERN, Switzerland6Lappeenranta University of Technology, Finland

13 RD50 WoskshopCERN, Geneva, Nov 10-12, 2008

http://user.web.cern.ch/user/Welcome.asp

http://www.lut.fi/en

2

Outline

Overview of the approaches for rad-hard edgeless detectors Edgeless detector with CTS: design Models for potential and electric field distribution in p-on-n

edgeless detector and experimental results Simulation of irradiated detectors Experimental results on CCE (test beam) Development of n-on-p edgeless detectors Conclusions

E. Verbitskaya et al., 13 RD50 Workshop, CERN, Nov 10-12, 2008

3

Close-to-beam applications (CERN, TOTEM, Roman pot) - maximal dead area width less than 50 µm

Other applications: imaging tileable arrays for diagnostics(medicine, biology etc.)

Requirements


Solution: edgeless detectors (diced or cut)

Problem: elimination of the influence of high current from damaged cut on the properties of detector sensitive bulk

Requirement: diminished dead area adjacent to detector sensitive area

4

Prehistory

Z. Li et al., IEEE Trans. Nucl. Sci. NS-49 (2002) 1040-1046

I-V improvement: • Dicing from the back side• Aging at RT


Pad detectors diced across p-n junction

5

Overview of the approachesfor edgeless detectors

Regular planar strip detectorwith Voltage Terminating Structure (VTS)

Sensitive area (p+)

Voltage terminating structure (VTS)(floating rings)

V=VbV=0

> 2d (>600 µ)

d

Vb

(n+)

Sensitive area (p+)

Current terminating structure (CTS)(grounded rings)

I=IbulkI=Iedge

<50 µ

d

Vb

(n+)

Sensitive area (p+)


V=VbV=0

> 2d (>600 µ)

d

Vb

(n+)

Sensitive area (p+)


V=VbV=0

> 2d (>600 µ)

d

Vb

(n+)

Sensitive area (p+)


I=IbulkI=Iedge

<50 µ

d

Vb

(n+)

Sensitive area (p+)


I=IbulkI=Iedge

<50 µ

d

Vb

(n+)

Strip -


6

TOTEM:Edgeless p+-n-n+ strip detector with CTS

Approach: Edgeless strip detectorwith Current Terminating Structure

(CTS)

1. G. Ruggiero et al. IEEE Trans. Nucl. Sci. 52 (2005) 1899.2. E. Noschis et al. Nucl. Instr. and Meth. A 563 (2006) 41.

Sensitive area (p+)


V=VbV=0

> 2d (>600 µ)

d

Vb

(n+)

Sensitive area (p+)


I=IbulkI=Iedge

<50 µ

d

Vb

(n+)

Sensitive area (p+)


V=VbV=0

> 2d (>600 µ)

d

Vb

(n+)

Sensitive area (p+)


V=VbV=0

> 2d (>600 µ)

d

Vb

(n+)

Sensitive area (p+)


I=IbulkI=Iedge

<50 µ

d

Vb

(n+)

Sensitive area (p+)


I=IbulkI=Iedge

<50 µ

d

Vb

(n+)

Regular p+-n-n+ stripdetector with VoltageTerminating Structure (VTS)

Cut throughp+ outer ring


7

Alternative approach:full 3D active edge detectors

C. Da Via et al., NIM A587 (2008) 243-249 Main features of design: • p+ and n+ through entire bulk• p+ active edge

collection distance ≤ 50 m fast response higher electric field due to cylindrical geometryradiation hardness

butComplicated technology


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Further development of edgeless detectors with CTS:

INTAS-CERN project TOSTER:TOtem STrip Edgeless Radiation hard detectors

# 05-103-7533 Started: July 2006

CONSORTIUMCERN - SwitzerlandIoffe Physico-Technical Institute RAS - RussiaResearch Institute of Material Science and Technology - RussiaCentro Nacional de Microelectronica - CSIC – Barcelona, SpainUniversity of Bologna - ItalyLappeenranta University of Technology – Finland

Head of the project: Gennaro Ruggiero (CERN)


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Voltage Terminating Rings(floating)

The current of CTR: ohmic current along the damaged cutThe current of CUR: diffusion current from the cut to the bulkThe current of sensitive area: bulk generated current

Sensitive area

Non-sensitive corner

Current Terminating Structure (grounded)

Current Terminating Ring (CTR)

Clean-Up Ring (CUR)

Conceptual designof edgeless detector with

CTS


10

Performanceof edgeless detector with

CTS

Dead area 47 m


11

Electrical characteristicsof p-on-n edgeless detectors

I(U), w3-15 (4)

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1 10 100 1000U (V)

I (A

)

CTR

CUR

bulk

0 100 200 300 400 500 600 700 800 900 1000 11000

20

40

60

80

num

ber

current (nA)

statistics on 204 detectors

I-V characteristics

Statistics of reverse current

n-Si,·cm Vfd: ~20 V; S = 8 cm2

512 strips with a pitch of 66 µm

Processed by Ioffe&RIMST

Bulk current:Imean = 120 nAJmean ~ 12 nA/cm2

Istrip = 20 pA

V = 100 V


12

0

50

100

150

200

0 50 100 150 200 250 300

bias voltag e (V)

po

ten

tial (

V)

ring 1

ring 2ring 3

a)

Potential distribution on VTS rings in p-on-n detector before and after

scribingBefore cut After cut

0

50

100

150

200

250

300

0 50 100 150 200 250 300

bias voltag e (V)

po

ten

tial (

V)

ring 1

ring 2

ring 3

b)

Before the cut: potential distribution occurs via punch-though effect, and potentials between the rings are distributed linearly. After cut: potential distribution is controlled by the increased

current across the damage surface (~mA). VTS operates and distributes potential outside the detector active area and eventually prevents the electric field focusing at the border of the detector

active area.

Test detectors


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Potential in the bulk Vxb ~ x2

X

Exb ~ x

In x direction:

Vxs, Exs

Vxb, Exb

In z direction:

Ez – normal to the cut

at the cut (s) and inside the bulk (b)

x

Ez

0 z

Surfacecurrent Is

p+

n+

Exs Exb


Ez ≈ (Vsurf –Vbulk)/Wz

Wz – distance at which Vxs dissipates to Vxb

Models of potential and electric field distribution at the sensitive

cutComponents of potential and electric field

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Damaged edge with high concentration of defect levels

1. Model of resistive edge layer

E. Verbitskaya, RESMDD’08, Florence, Oct 15-17, 2008

z

x

Nd

z

Nd

z

1: Resistive layer:controls potential distribution Vxs(x)

2: Generation layer: electrons and holes are generated


Free carriers in the generation layer do not disturb Is and Vxs

15

Potential at the cut Vxs

X

Potential in the bulk Vxb

X

X

Ez

Exb – constExb - linear

Model of resistive edge layer


X

Vxb

Vxs

p+

n+

Su

rfac

e o

hm

ic c

urr

ent

E(z)

Generated carriers: holes move to CTS;electrons may partially flow inside the bulk

16

2. Model of amorphous edge layer

IhIe

I = Ie + Ih

x

Ez

0 z p+

n+

Exs Exb


X

Vxb

Vxs

Vx

X

Ez

Inversion of Ez sign! – forces holes to move towards the bulk

jh = gh(d - x)

je = (ge – ηe )x

ηe ↑

g – generation rate

17

Tools for study of potential and electric field

distribution

Simulation of potential, electric field and hole trajectories (Ioffe Institute)

Conductive MicroProbe Technique (Bologna University)

Scanning Transient Current Technique (Ioffe Institute)

E(x) simulation using ISE-TCAD with implemented Poisson and continuity equations (CNM Barcelona)

Additionally:

Optical Beam Induced Current (Bologna Univ.) Scanning Electron Microscope (LUT)


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Neff = 31011 cm-3; Vfd = 15 V

Simulations: potential and electric field distribution, resistive edge

Ez ≈ (Vsurf –Vbulk)/Wz

Wz = 300 m


-160

-140

-120

-100

-80

-60

-40

-20

0

20

0 0.005 0.01 0.015 0.02 0.025 0.03

x (cm)

Vb

, Vs

(Vo

lt)

Vb, 20 VVs, 20 VVb, 50 VVs, 50 VVb, 100 VVs, 100 VVb, 150 VVs, 150 V

0

50

100

150

200

250

300

0 0.005 0.01 0.015 0.02 0.025 0.03

x (cm)E

z (V

/cm

) 20 V

50 V

100 V

150 V

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Experimental results on MicroProbe Technique: surface potential SP(x), and E(x)

at the cut edge

Main features:

Potential is nonlinear E(x) is not constant Slope of E(x) grows with voltage

-10 to -150 V

disagreement with

resistive edge model


20

Potential and Ez distributions based on CMPT data

-150

-130

-110

-90

-70

-50

-30

-10

0 0.005 0.01 0.015 0.02 0.025 0.03

Coordinate, cm

Po

ten

tial

, V

-1.0E+03

-8.0E+02

-6.0E+02

-4.0E+02

-2.0E+02

0.0E+00

2.0E+02

0 0.005 0.01 0.015 0.02 0.025 0.03

Coordinate, cmEl

ectr

ic fi

eld

Ez, V

/cm

20V

50V

100V

150V

Ez sign inversion

red: Vs (CMPT)blue: Vb

Experimental results on surface potential are in agreement to the amorphous edge model


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0.0E+00

1.0E-02

2.0E-02

3.0E-02

4.0E-02

5.0E-02

6.0E-02

7.0E-02

8.0E-02

9.0E-02

1.0E-01

0 10 20 30 40 50

Time, ns

Cu

rren

t, m

kA

Exs derived from STCT

d

VV

d

x

d

VxE fdfd

1

2)(At V > Vfd

V = 100 V, Vfd = 20 V, d = 300 m

0

1000

2000

3000

4000

5000

0 0.005 0.01 0.015 0.02 0.025 0.03

Coordinate (cm)

Ele

ctr

ic f

ield

(V

/cm

)

STCT data

Ebulk

Trend of CMPTdata

p+

n+


Results on Ex(x) derived from CMPT and STCT show the same tendency of Es reduction

22

Ez simulation in irradiated p-on-n edgeless detectors

-120

-100

-80

-60

-40

-20

0

0 0.005 0.01 0.015 0.02 0.025 0.03

x (cm)

po

ten

tia

l (V

olt

)

Vbulk

Vsurface

Vbulk afterirradiation

-1000

-800

-600

-400

-200

0

0 0.005 0.01 0.015 0.02 0.025 0.03

x (cm)

Ez

(V/c

m)

non-irradiated

Fn = 5E13 cm-2

E. Verbitskaya, RESMDD’08, Florence, Oct 15-17, 2008

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Ez simulation in irradiated p-on-n detectors


Ez is ~kV/cm and increases with fluence predicts the increase of the hole current flow into the bulk and corresponding increase of the bulk current.

V = 400 V

-400

-350

-300

-250

-200

-150

-100

-50

0

0 0.01 0.02 0.03

Coordinate (cm)

Po

ten

tial

(V

)

red: Vsblue: Vb

F ↑

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

0 0.01 0.02 0.03Coordinate (cm)

Ele

ctri

c fi

eld

Ex

(V/c

m)

E(z); 2e14E(z); 1e14E(z); 2e13

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E(x) simulation using ISE-TCAD

J.P. Balbuena et al., CNM, Barcelona, presented at NSS-2008 and are in progress

Electric field at the front contact is maximal at CTR (10 to 50 m from the edge) and becomes

lower under the strips

p-on-n detector, saw cut edgeCTR


25

Ez simulation in irradiated p-on-n detectors

(preliminary)Non-irradiated Fn = 4·1014 cm-2


26

The left-most vertical line indicates the reconstructed position of the physical edge, the

other two vertical lines indicate the 10%-90% efficiency rise interval.

Recent experimental results on CCE

in p-on-n edgeless detectors with CTS

G. Ruggiero et al. Planar Edgeless Silicon Detectors for the TOTEM Experiment. Pres. 8th Intern.Conf. on Position Sensitive Detectors (PSD8), Glasgow, Sept 1-5, 2008, Nucl. Instr. and Meth. A (in press).

Efficiency of CTS detector at the sensitive edge


Diminished non-sensitive width of 47 μm is achieved!

27

CCE in irradiated p-on-n edgeless detectors with

CTS

1.0

0.8

0.6

0.4

0.2

Eff

icie

ncy

500400300200100

Bias Voltage, V

1*1013

pcm-2

5*1013

pcm-2

1.4*1014

pcm-2

The efficiency has been calculated by comparing the hits in the irradiated detector with the hits in a non-irradiated detector placed in front, along the beam axis.

24 GeV/c protonsT = -18C


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Development of n-on-p edgeless detectors with

CTS

Sensitive area

Voltage terminating rings(floating)Current terminating ring

Clean-up ring

P+

N+Sensitive area

Voltage terminating rings(floating)Current terminating ring

Clean-up ring

P+

N+

P+

N+

12345678910

a b c d e f g h

d1

d5

c4

c2 f2

h6

e3

f7

g4

d8

e9

b7

f10

b)

12345678910

a b c d e f g h

d1

d5

c4

c2 f2

h6

e3

f7

g4

d8

e9

b7

f10

12345678910

a b c d e f g h

d1

d5

c4

c2 f2

h6

e3

f7

g4

d8

e9

b7

f10

b)

Layout: 10 different designs

MCZ p-type Si

Processed by Ioffe&RIMST


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0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40 45 50 55

Current, nA

Qu

an

tity

a)

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35 40 45 50 55

Current, nA

Qu

an

tity

a)

I-V characteristics of n-on-p edgeless detectors

I-V characteristics Statistics of reverse current

0.E+00

5.E-09

1.E-08

2.E-08

2.E-08

3.E-08

3.E-08

4.E-08

4.E-08

5.E-08

5.E-08

0 50 100 150 200 250

Bias, V

Cu

rre

nt,

A

Series1

Series2

Series3

Series4

Series5

Series6

Series7

Series8

Series9

Series10

Series11

Series12

Series13

Series14

b)

0.E+00

5.E-09

1.E-08

2.E-08

2.E-08

3.E-08

3.E-08

4.E-08

4.E-08

5.E-08

5.E-08

0 50 100 150 200 250

Bias, V

Cu

rre

nt,

A

Series1

Series2

Series3

Series4

Series5

Series6

Series7

Series8

Series9

Series10

Series11

Series12

Series13

Series14

b)

14 randomly selected detectors with different design

V = 200 V; S = 8x8 mm2

MPT and TCT measurements are in progress!

10-30 nA 84 samplesJmean = 30 nA/cm2


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Conclusions

Performance of edgeless detectors with CTS allows realization of edgeless detectors which characteristics are controlled by the bulk properties

The model of amorphous edge is adequate to the experimental results on n-on-p edgeless detectors

In detectors with CTS diminished non-sensitive width of 47 μm is achieved

N-on-P edgeless strip detector seems to be radiation hard that needs experimental testing


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Acknowledgements

This work was done in the frame of INTAS-CERN project # 03-52-5744

and supported in part by:• RF President Grant # 2951.2008.2, • contract of Russian Agency on Science and Innovation # 2.516.11.6098

Thank you for your attention!


Progress in R&D on silicon edgeless strip detectors with Current Terminating Structure

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