Development of enhanced double-sided 3D radiation sensors...

Development of enhanced double-sided 3D

radiation sensors for pixel detector

upgrades at HL-LHC

Marco Povoli1

1Dipartimento di Ingegneria e Scienza dell’Informazione

University of Trento, Italy

Trento, Italy - February 20, 2012

[Work supported by INFN CSN V, projects "TREDI" (2005-2008) and "TRIDEAS" (2009-2011)]

Outline

High Energy Physics experiments at LHC

The Large Hadron Collider

The ATLAS experiment

The current ATLAS silicon tracker

The ATLAS Insertable B-Layer (IBL)

Radiation damage in silicon

Summary

Countermeasures

3D detectors

Originally proposed architecture

The ATLAS 3D sensor collaboration

Enhanced 3D technology at FBK

Design choices and motivations

Detailed electrical characterization

Functional characterization

Possible technological improvements

Additional applications

2 / 46 Marco Povoli

The Large Hadron Collider (LHC)

The Large Hadron Collider (LHC)

• Largest particle collider ever built

• Near Geneva, underneath the

swiss/french border

• Total ring length of about 27 Km

• First started in 2008

• The official physics program

started in 2009

Basic machine parameters

• Proton or Lead Ion collisions

• Nominal proton energy of 7 TeV

(per beam)

• Bunch spacing of 25 ns

• Design luminosity 1034 cm−2s−1

Physics program

• Discovery of new particles/theories

• Particles collide inside the four experiments

• ATLAS and CMS: general purpose

• ALICE: study lead ions collision

• LHCb: specialized in b-physics

3 / 46 Marco Povoli

General purpose experiments

A Toroidal LHC ApparatuS (ATLAS)

Basic parameters

• 45 meters long

• 25 meters in diameter

• weights about 7000 tons

Structure (inside-out)

1. Inner detector

2. Calorimeters

3. 2 Tesla solenoid magnets

4. Muon spectrometers

The inner detector

• Several layers of silicon detectors and one layer of straw tube detectors

• Needed to reconstruct the particle interaction point

• Required to be very fast

• Operates in extremely harsh conditions

4 / 46 Marco Povoli

The current ATLAS silicon tracker

Barrel cross-section

• Total radius of roughly 1 m

• Pixel detector: 3 layers of n-in-n pixel sensors

• Strip detector: 4 layers of p-in-n strip sensors

• Transition Radiation Tracker: straw tubes interleaved

with scintillating fibers

The pixel detector

• Three barrel layers at radiuses 50.5, 88.5, 122.5 mm

• 6 end-caps (three on each side)

• Pixel size 50×400 µm2

• Covers an area of ∼1.7 m2

• Approximately 67 million channels

• Designed to withstand a fluence of

1×1015 1 MeV neqcm−2

5 / 46 Marco Povoli


Planned installation during the first long shutdown (2013-2014)

CURRENT PIXEL DETECTOR

RENDERING OF THE IBL

Addition of a fourth pixel layer close to

the beam pipe

Motivations

• Maintain the event pile-up under

control as LHC luminosity increases

• Add redundancy to recover partial

failure of modules in the other pixel

layers

• Increase tracking and reconstruction

accuracy

Main design parameters

• Need to reduce the beam pipe radius

by 4mm

• Placed at 33.25 mm from the center of

the beam pipe

• Will need to withstand a fluence of

5×1015 neq cm−2

[M. Capeans, (The ATLAS Collaboration), ATLAS-TDR-019]

6 / 46 Marco Povoli


Sensor requirements

Parameter Value unit

Total number of staves 14 -

Pixel size (Φ, z) 50, 250 µm

Dead edge extension 200 µm

Sensor thickness <250 µm

NIEL dose tolerance 5×1015 neq /cm2

Hit efficiency in active area >97% -

Operating bias voltage <1000 V

Operating temperature -15 ◦C

• Reduced pixel size in the z direction

(250 µm) to increase the spatial

resolution

• No tilt possible in the z direction →

need for reduced dead area at the

edges

[A. Clark, et al., (The ATLAS IBL collaboration),

(2012) JINST 7 P11010]

NEED FOR ADVANCED RADIATION HARD DETECTORS

7 / 46 Marco Povoli

Radiation damage in silicon (summary)

Bulk damage

• Due to Non Ionizing Energy Loss (NIEL)

• Displacement of atoms in the Silicon lattice

• Built-up of crystal defects

Consequences

• Change in effective doping concentration

(higher depletion, under-depletion)

• Increase of leakage current

(shot noise, thermal runaway)

• Increase of charge trapping

(charge losses)

Surface damage

• Due to Ionizing Energy Loss (IEL)

• Radiation generates carriers in SiO2

• Electrons can escape while holes get trapped at the

Si/SiO2 interface

Consequences

• Accumulation of charge at the SiO2 /Si interface

(inter-pixel capacitance and isolation and

breakdown behavior)

• Increased charge trapping at the Si/SiO2

• Increased surface recombination velocity

LOWERING OF THE S/N RATIO![Michael Moll - MC-PAD Network Training, Ljubljana, 27.9.2010]

8 / 46 Marco Povoli

Countermeasures

Material engineering

Deliberate incorporation of impurities or defects into the

silicon bulk to improve radiation tolerance of the

detectors

• Oxygen rich Silicon (FZ, DOFZ, Cz, MCZ)

• Pre-irradiated Silicon

New Materials

• Silicon carbide (SiC)

• Amorphous Silicon

• Diamond

Surface isolation

• Important to assure inter-electrode isolation

• Typically achieved using p-spray, p-stop or a

combination of the two

Device engineering

• p-type silicon detectors (n-in-p)

• Thin detectors

• 3D detectors

[Michael Moll - MC-PAD Network Training, Ljubljana, 27.9.2010]

9 / 46 Marco Povoli

Full 3D detectors

Original idea - PROS and CONS

Features of 3D detectors

• First proposed by S. Parker and

collaborators in the mid ’90s

[NIMA 395 (1997), 328]

• Decouple the active volume from the

inter-electrode distance

• Low full depletion voltage (<10 V)

• Short collection distances (∼50 µm)

• Low trapping probability after

irradiation

• Small dead area along the edges

Disadvantages of 3D detectors

• Columns are partially dead regions

• Non uniform response (low field

regions are present)

• Higher capacitance (higher noise)

• Fabrication process complex and more

expensive

10 / 46 Marco Povoli

The ATLAS 3D sensor collaboration

Institutes and processing facilities

• 18 Institutes

• 4 processing facilities:

◮ SNF (Stanford, USA)◮ SINTEF (Oslo, Norway)◮ CNM (Barcelona, Spain)◮ FBK (Trento, Italy)

Available 3D technologies

• Full 3D with active-edges

(SNF and SINTEF)

• 3D-DDTC with slim-edges (FBK, CNM)

• Full 3D-DDTC with slim-edges (FBK)

Main targets

1. Speed-up the test and industrialization of 3D silicon sensors

2. Production and testing of 3D sensors for the IBL

[C. Da Vià, et al., NIMA694 (2012), 321]


3D technology for the IBL developed at FBK

Main geometrical features

• Double-type column approach

• Fully double-sided

• Columns etched from both wafer sides

• Fully passing through columns

• Empty electrodes (no polysilicon filling)

• Surface isolation by means on p-spray

implantations on both wafer sides

SEM cross-section

• Very good etching uniformity

• Columns are all passing through

• Slight shrinking of the column tip (not

affecting device behavior)

[G. Giacomini, et al., to appear in IEEE TNS (2013)]


3D technology for the IBL developed at FBK

The common wafer layout and pixel layout

Common wafer layout

• 4 inches wafers

• 8 ATLAS FE-I4 pixel detectors

• 9 FE-I3 pixel detectors

• 3 CMS pixel detectors

• 4 strip detectors (80µm pitch)

• Several planar and 3D test structures

−→ z direction

Single pixel layout

• Pixel size: 50×250 µm2

• 2E configuration: 2 n+ columns per pixel

• Inter-electrode distance (d): ∼67 µm

• With field-plate

[C. Da Vià, et al., NIMA694 (2012), 321]


Motivation for FE-I4 pixel layout

Results from previous technologies

!

Previous 3D-DDTC technology at FBK

• Non-passing through columns

• Pixel size 50×400 µm2 (FE-I3)

• Three pixel layouts (2E, 3E, 4E)

Best performances from 3E devices (71 µm)

• Noise ∼205 e−

• Good CCE up to 1×1015 neq /cm2

• Tracking efficiency >98% at 1×1015 neq /cm2

Φeq =1×1015 neq /cm2

[A. Micelli, NIMA650 (2011), 150]

Φeq =1×1015 neq /cm2

0

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 140

Ch

arg

e [

ke

- ]

Reverse voltage [V]

2E - simulated2E - measured3E - simulated3E - measured4E - simulated4E - measured

[A. La Rosa, NIMA681 (2012), 25]


Edge termination (SLIM-EDGE)

Motivation and design

Slim-edges in the z direction

• Requirement: 6200 µm in the beam (z) direction

• Motivation: not possible to tilt modules in the z

direction due to space constrains

• Fence of ohmic columns to prevent the depletion

region to reach the scribe line

• Designed with the aid of numerical simulations

Computer aided design

• Simulation of a structure including the last junction

column and the ohmic fence

• Simulation domain highlighted with the dashed

rectangle

• Scribe line model with a low lifetime region (<1 ns)

• Monitor the current of the last junction column

• No avalanche models


Edge termination (SLIM-EDGE)

Motivation and design

[M. Povoli, et al.,

JINST 7 (2012) C01015]

5

10

15

20

25

30

35

40

45

0 100 200 300 400 500

Cu

rren

t [p

A/c

olu

mn

]

Reverse voltage [V]

Nd=1.0x1011

cm-3

Nd=2.5x1011

cm-3

Nd=5.0x1011

cm-3

Nd=1.0x1012

cm-3

[G.-F. Dalla Betta, et al., NSS10 Conf. Record, pp. 382-387]

Simulation results

• Different bulk doping concentrations tested

• No signs of current increase up to 500 V (well above

expected operation voltage)

• The depletion region extends outside the active area by

about 75 µm at 300 V

• Safe device operation with a 200 µm slim-edge

• Note: conservative design!


On wafer selection

Motivation and procedure

BUMP-BONDING

1.

2.

3.

4.

[G. Giacomini, et al., to appear in IEEE TNS (2013)]

On-wafer sensor selection

• The bump-bonding is complex and very expensive

• Assemble only good sensor tiles

• Wafer with more than 3 good sensors are sent for bump-bonding

Temporary metal layer

• Deposited on top of the frontside passivation

• Strip-like metalization

• 80 strips connecting 336 pixels each

• Automatic current measurements

• The sum of all strip currents gives the total sensor current


On wafer selection

Example test results

GOOD WAFER (ATLAS12)

100

101

102

103

104

105

106

107

0 10 20 30 40 50 60 70 80

Cu

rren

ts [

nA

]

Reverse voltage [V]

W2

S1S2S3S4S5S6S7S8

100

101

102

103

104

0 10 20 30 40 50 60 70 80

Cu

rren

ts [

nA

]

Reverse voltage [V]

ATLAS09 - W14-S3

On waferFlip-chipped

[C. Da Vià, et al., NIMA694 (2012), 321]

Parameter Symbol Value

Operation temperature Top 20-24◦C

Depletion voltage Vdepl <15 V

Operation voltage Vop >Vdepl +10 V

Leakage current at Vop I(Vop) <2 µA

Breakdown voltage Vbd >25 V

Current "slope" I(Vop )/I(Vop -5V) <2

Wafer/sensor selection

• Good sensors always have currents much lower than the

set limit

• Breakdown voltages are typically higher than 30 V for

good detectors

• Confirmation of the selection method comparing current

pre/after bump-bonding

• Yield of IBL production at FBK: 56.82%

NOTE: further investigation needed on some aspects

• The breakdown is lower than for standard planar detectors

(can be critical after irradiation)

• In some cases the behavior is not very uniform

• Necessary to perform a thorough electrical

characterization


Detailed electrical characterization

3D diodes

FE-I4 with field-plate FE-I4 80 µm pitchCMS - 1E

3D diode

• Two terminal device having an area of roughly 10 mm2

• Electrodes of the same type are shorted together

• All the geometries of larger detectors are reproduced

• Eases the characterization

Performed tests

• I-V and C-V measurements as a function of the temperature

• Numerical simulations to confirm the findings and gain a deeper understanding of

the device behavior

[M. Povoli, et al., NIMA699, (2013), 22]

FE-I4 (backside)


IV measurements with variable temperature

IV Curves

0

1e-08

2e-08

3e-08

4e-08

5e-08

6e-08

7e-08

8e-08

0 10 20 30 40 50 60 70 80

Cu

rren

ts [

A]

Reverse voltage [V]

I-V 80BIG

35°C30°C25°C20°C15°C10°C

5°C0°C

-5°C-10°C-15°C-20°C

0

1e-08

2e-08

3e-08

4e-08

5e-08

6e-08

7e-08

8e-08

0 10 20 30 40 50 60 70 80

Cu

rren

ts [

A]

Reverse voltage [V]

I-V FEI4

35°C30°C25°C20°C15°C10°C

5°C0°C

-5°C-10°C-15°C-20°C

0

1e-08

2e-08

3e-08

4e-08

5e-08

6e-08

7e-08

8e-08

0 10 20 30 40 50 60 70 80

Cu

rren

ts [

A]

Reverse voltage [V]

I-V CMS

35°C30°C25°C20°C15°C10°C

5°C0°C

-5°C-10°C-15°C-20°C

0

1e-08

2e-08

3e-08

4e-08

5e-08

6e-08

7e-08

8e-08

0 10 20 30 40 50 60 70 80

Cu

rren

ts [

A]

Reverse voltage [V]

I-V FEI4-FP

35°C30°C25°C20°C15°C10°C

5°C0°C

-5°C-10°C-15°C-20°C

Setup

• Devices coming from wafer

W20 of the ATLAS09 batch

• Devices were diced and wire

bonded on small PCBs

• Wire bonding contribution is

negligible

• Temperature variation

between −20◦C and 35◦C

inside a climatic chamber

• Measurements performed

with HP4145

Preliminary results

• Each type of device has its own characteristic behavior

• Breakdown voltages between 40 and 50V

• Different current slope for different devices

• More details in the next slide...


Data analysis

Intrinsic electric behavior

Breakdown voltages (all devices)

35

40

45

50

55

60

-20 -10 0 10 20 30 40

Bre

akd

ow

n v

olt

ag

e [

V]

Temperature [°C]

UVBD= 48.50 mV/°C

UVBD= 76.82 mV/°C

UVBD= 50.72 mV/°C

UVBD= 55.42 mV/°C

80BIGFEI4-FP

CMSFEI4

Breakdown voltages

• Breakdown between 40 and 50V

• Linear increase with temperature

• The increase is between ∼ 50 and

∼ 80mV/◦C

• In agreement with the expectation

[Crowell, C. R. and S. M. Sze, Appl. Phys. Lett. 9, 6 (1966)

242-244.]

1e-11

1e-10

1e-09

1e-08

1e-07

3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4

Cu

rren

ts [

A]

1000/T [°K-1

]

Arrhenius plot - FEI4-FP

Meas. at 10VCalc. at 10V

Meas. at 30VCalc. at 30V

Purpose

Distinction between thermal and avalanche

generation

Equation

I(T) = I(TR)(

TTR

)2

exp[

E2kB

(

1TR

− 1T

)]

Results

• TR=293.15 ◦K

• Very good agreement at low biases

• The agreement is lost as breakdown

approaches21 / 46 Marco Povoli

Investigation through numerical simulations

Simulated structure

• A quarter of elementary cell (thanks to symmetry)

• Bulk doping: 7×1011 cm−3 (p-type, measured)

• One columnar electrode per type

• Measured p-spray profiles

• Measured n+ and p+ surface implantations

• Device layout fully reproduced

Incremental addition of the layout details

• Used to estimate the contribution of each component of

the device capacitance

• Allows discriminate between inter-electrode and surface

capacitance

Simulation of the full structure

• Estimation of the expected breakdown voltage and

current levels

• Analysis of the distribution of electrical quantities (e.g.

Electric field and Electrostatic potential)


C-V measurements vs. C-V simulations

FE-I4 diode with field-plate

0

50

100

150

200

250

300

350

400

450

500

0 10 20 30 40 50

Cap

acit

an

ce [

pF

]

Reverse voltage [V]

Columnsp-spray

P+ implantation

N+ implantation

FullMeasured

Results

• Electrodes contribution: ∼ 51.4pF (constant)

• p-spray causes an increase of ∼ 30pF (basically constant)

• P+ implantation and metal on the back side do not cause much increase

• N+ implantation and metal on the front side cause an increase of ∼ 63pF at a bias voltage of 20V

• At higher biases the contribution of front side saturates to a value similar to the one obtained only with electrodes

and p-spray (∼ 103pF)

• Measured capacitance does not fully saturate at 40V (instrument limitations)


Distribution of electrical quantities

FE-I4 diode - Electric field

FE-I4 with FP FE-I4

1

1.5

2

2.5

3

0 5 10 15 20 25 30 35

Ele

ctr

ic f

ield

[10

5 V

/cm

]

Distance [µm]

N+

column

Backside

peaks

Frontside

peaks

Field-plate

Vbias=40V

• Large field peaks on both the upper

and lower surfaces

• Peaks are placed at the n+ to

p-spray junction

• Particularly critical due to the high

dose p-spray implantation

• Both structures have similar

field-peaks on the backside

• The field-plate redistributes and

lowers the field on the frontside


Front-side surface irradiation

X-Rays - 2 Mrad (60 minutes irradiation)

P-spray compensation to increase the breakdown voltage

How large is the increase?

91

92

93

94

95

96

97

-300 -200 -100 0

Cap

acit

an

ce [

pF

]

Gate voltage [V]

Qox=1.8x1011

cm-2

Qox=1.2x1012

cm-2

Qox=3.9x1012

cm-2

12

PRE

POST (un-biased)POST (Vgate=20V)

• Irradiation performed at "Laboratori Nazionali di

Legnaro" (LNL, Padova, Italy, thanks to Serena

Mattiazzo)

• Use of MOS capacitors to monitor the increase

in oxide charge

• Two irradiations: without and with bias (20 V)

• Considerably larger charge when irradiation is

performed under bias

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60 70 80 90

Cu

rren

t [n

A]

Reverse voltage [V]

1. UQox

2. Surfacerecomb.

3. VBD

FE-I4 #1 - PRE

FE-I4 #1 - POST (unbiased)

FE-I4 #2 - PRE

FE-I4 #2 - POST (biased)

• Two different FE-I4 diodes with field-plate

• Current increase do to surface generation

• Limited breakdown increase

• Pre-irradiation trend maintained after

• Confirm that the breakdown occurs on the

backside


Functional characterization of FE-I4 pixel detectors

Readout chip and measurement setups

[A. Clark, et al., (The ATLAS IBL collaboration),

(2012) JINST 7 P11010]

ATLAS FE-I4 readout chip

• Designed to withstand a TID of 250 Mrad

• Leakage compensation

• Double stage charge amplifier with constant current

discharge

• Discriminator after charge amplifier

• Operates in Time Over Threshold (ToT) mode

• The ToT is representative of the collected charge

The USBPix system[http://icwiki.physik.uni-

bonn.de/twiki/bin/view/Systems/UsbPix]

The EUDET Telescope[D. Haas, EUDET-Report-2007-07]



Radioactive source scans (90Sr, Lab)

5

6

7

8

9

10

11

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

To

T (

MP

V)

Bias voltage (V)

90Sr - Pre-irradiation lab tests

FBK13 - un-irradiated

FBK13 - Simulation

CNM101 - un-irradiated

PRE-irradiation

• Comparison between FBK and CNM detectors

• Calibration: 10 ToT at 20 ke−

• Most Probable Value of the "all-cluster" charge

distribution

• FBK → charge saturation before 10 V

• CNM → charge saturation at roughly 25 V

• Numerical simulations (dashed line) confirm the

measurement results

0

1

2

3

4

5

6

7

8

9

10

0 25 50 75 100 125 150 175 200 225 250 275 300

To

T (

MP

V)

Bias voltage (V)

90Sr - Post-irradiation lab tests

pre-irrad

FBK13 - un-irradiated

CNM101 - un-irradiated

FBK87 - p-irrad - 5x1015

neq/cm2

FBK - p-irrad - 2x1015

- SIMULATED

FBK - p-irrad - 5x1015

- SIMULATED

CNM100 - p-irrad - 2x1015

neq/cm2

CNM36 - p-irrad - 6x1015

neq/cm2

POST-irradiation

• Lowering of charge collection due to trapping

• FBK detector irradiated at 5×1015 neq /cm2 (red)

shows a hint of charge saturation at roughly 150 V

• Confirmed by numerical simulations (red dashed

line)

• Measurement not available for 2×1015 neq /cm2 but

simulations can be trusted (violet dashed line)

• Satisfactory performances

[G.-F. Dalla Betta, et al., VERTEX2012, submitted to POS]



Test-beam results (tracking efficiency)

[P. Grenier, et al., "IBL TestBeam Results", presented at the

IBL Sensor Review, CERN, 4-5 July 2011]

Beam tests during 2011-2012

• CERN - SPS: 120 GeV pions

• DESY: 4 GeV positrons

• EUDET Telescope

• Both un-irradiated and irradiated samples

• IBL operating conditions

• Planar sensor always used as reference

(b) PRE-irrad. efficiency map

• Good tracking efficiency (98.8%)

• Electrodes appear as less efficient regions

• Possible to obtain higher efficiency by tilting the

device with respect to the beam

(c,d) POST-irrad. efficiency map

• FBK90 (2×1015 neq /cm2) shows great efficiency

(99.2%) at 60 V of bias when tilted by 15◦

• FBK87 (5×1015 neq /cm2) exhibits not sufficient

efficiency (95.6%) at the chosen bias (140 V)

• NOTE: when the proper bias is used (e.g. 160 V)

the efficiency is back within IBL requirements

(98.2%)


Proton irradiated 3D diodes

80µm pitch

0

10

20

30

40

50

60

70

80

90

100

0 25 50 75 100 125 150 175 200 225 250

Cu

rren

ts [µ

A]

Reverse voltage [V]

{eq=2.1x1015

neq/cm2

-20°C-15°C-10°C-5°C0°C5°C

10°C15°C20°C

FE-I4

0

10

20

30

40

50

60

70

80

90

100

0 25 50 75 100 125 150 175 200 225 250

Cu

rren

ts [µ

A]

Reverse voltage [V]

{eq=2.1x1015

neq/cm2

-20°C-15°C-10°C-5°C0°C5°C

10°C15°C20°C

-50

-25

0

25

50

75

100

125

150

175

-30 -20 -10 0 10 20 30

Bre

akd

ow

n v

olt

ag

e [

V]

Temperature [°C]

80µm - {eq=2.1x1015

neq/cm2

FE-I4 - {eq=2.1x1015

neq/cm2

80µm - {eq=5.2x1014

neq/cm2

CMS - {eq=5.2x1014

neq/cm2

CMS - {eq=2.4x1014

neq/cm2

• Irradiation performed at Los Alamos with 800 MeV protons

(thanks to Martin Hoeferkamp)

• Only half of the requested fluence was delivered

• Increase in breakdown between few volts and ∼100 V

Important!

• Devices were selected prior to irradiation

• The FE-I4 diode irradiated at 2×1015 neq /cm2 shows a

breakdown voltage of roughly 125 V

• A proper sensor selection will assure optimal

operating voltages after irradiation!


SLIM-EDGE characterization

Electrical tests

Performed test

• Several cuts performed by means of a

diamond saw

• Each cut is closer to the active area

• I-V measurement after each cut

[M. Povoli, et al., JINST 7 (2012) C01015]

10-9

10-8

10-7

10-6

10-5

10-4

10-3

0 10 20 30 40 50 60 70 80 90 100

Cu

rren

ts [

A]

Reverse voltage [V]

scribe linecut #1cut #2cut #3cut #4cut #5cut #6

Results

• Intrinsic device behavior is equal to

roughly 60 V

• No increase in reverse current up to

the fourth cut

• Possible to reduce the total edge

extension to roughly 100 µm

• NOTE: critical only before irradiation


SLIM-EDGE characterization

Functional tests (FE-I4 diode)

Laser scan Vb=15 V

Layout

Numerical simulation

[M. Povoli, et al., JINST 7 (2012) C01015]

Edge efficiency

(Test beam data, 2 × 1015 neq/cm2)

[G.-F. Dalla Betta, et al., VERTEX2012, submitted to POS]

Laser scan (Lab)

• Laser: λ=1060 nm

• Readout: CSA + 20 ns shaper

• Very good agreement with simulations

Edge efficiency after irradiation (test beam)

• Full efficiency inside the active-area

• Roughly 25 µm of the slim-edge are active


Possible technological improvements

Investigation through numerical simulations

• The high field region on the backside can be critical!

• It is of paramount importance to use large operating

voltages!

• Lifting the n+ column tip will eliminate the critical

region on the backside

• At the same time the fabrication will be easier and

faster

[M. Povoli, et al., IEEE NSS12 Conf. Record, pp. 1334-1338]

• Important to also improve the field distribution on

the frontside

• The field-plate is important

• Some of the designed structures include a floating

n+ ring which is intended to interrupt the

electrostatic potential of the p-spray

• The design is performed by means of numerical

simulations


Simulation results

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eld

[V

/µm

]

Ep

ot [V

]

distance [µm]

Vbias= -65V

N+

N+ ring

field-plate

Efield - NO RINGEpot - NO RING

Efield - RINGEpot - RING

Effect of the floating ring

• The potential of the inner p-spray is lower

• The field at the main junction is lower and the

field-plate works properly

• Large peak on the outer ring junction → causes

breakdown

• The ring placement is critical due to space

constrains

Simulated I-Vs

• All devices show larger breakdown than in the

previous technology

• The floating ring limits the performances but could

act as additional shielding from surface currents

• Raising the n+ column should deliver breakdown

voltages larger than 100 V

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Cu

rre

nts

[n

A]

Reverse voltage [V]

DTC-4breakdown

RINGNORING

80µm

80µmFE-I4FP

FE-I4, N-ringCMS1ECMS2ECMS3ECMS4E

CMS1E, N-ringCMS2E, N-ringCMS3E, N-ringCMS4E, N-ring


New SLIM-EDGE implementation

Pixel detectors slim-edge

• Reduced by 50 µm following the indications obtain from

previous tests

• Conservative design to avoid problems

New slim-edge implementation for some 3D diodes

• Double row of short trenches (mimicking the active-edge)

• Dead area of roughly 50µm

• Maintains the mechanical integrity and does not require support

wafer

• Simulation results at 50 V of bias show how this solutions does

not allow the depletion region to reach the scribe line



Fabricated devices

Preliminary electrical characterization

Available devices

• 4 FE-I4 pixel detectors (2 versions)

• 26 CMS pixel detectors (8 versions)

• 2 MEDIPIX-II detectors

• 3D diodes in several different flavors

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Cu

rren

ts [

nA

]

Reverse voltage [V]

FE-I4 diodesMEASURED

W2

W8

Preliminary results

• Batch completed in mid October 2012

• A few IV measurements on 3D diodes

here reported

• Leakage current higher than expected

but acceptable

• Sizable increase of breakdown voltage

[M. Povoli, et al., IEEE NSS12 Conf. Record, pp. 1334-1338]


The ATLAS Forward Physics (AFP)

Motivation and requirements

• Measure protons scattered from the collision

• Located at roughly 200 m both upstreams and

downstreams

• Requires reduced edge extension

• FE-I4 modules are investigated

[The ATLAS Collaboration, CERN-LHCC-2011-012]

Performed tests

• The edge of interest is the one not "IBL-like"

• Same cut and measure tests were performed

• Proper operation up to the 6th cut (75 µm edge)

Aspect to investigate...

• Very un-uniform irradiation

• Tests are being performed on CNM devices

[S. Grinstein, RESMDD12, submitted to NIMA]

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Cu

rre

nts

[n

A]

Reverse voltage [V]

strip-75

cut-1cut-2cut-3cut-4cut-5cut-6cut-7cut-8


Planar detectors with active-edges

Standard vs. Active Edge detectors

Standard detectors

• In standard detectors a dead border

region must be present

• In a good design cracks and damages

on the edges should be at least at a

few hundreds of micrometers away

from the depleted region

• Total dead region a + d > 500µm

How to limit dead region?

• Cut lines not sawed but etched with

Deep Reactive Ion Etching (DRIE) and

doped

[C. Kenney, et al., IEEE TNS 48-6 (2001) 2405]

Problems

• Process is more complicated

• Need for support wafer

• Finding the correct "d" to limit early

break-down phenomena[M. Povoli, NIMA658 (2011), 103]



Device and wafer layout

Single-sided p-in-n devices

(support wafer)

General device layout (test diode)

1. Distance between n+ and

p+ doping (GAP)

2. Field-plate

3. Bias pad (connected to the

doped trench)

4. Floating p+ ring

Trench etching

• Designed to be 4 µm

• Not well defined at first

• Optimized etching in the

second part of the batch

(roughly 10 µm width)

• Partial polysilicon filling

needed to restore the

surface planarity

Wafer layout

• Strip detectors with

inter-strip pitches of 50, 80

and 100 µm (AC or DC

coupled)

• Pixel detectors compatible

with the readout chips of

the ALICE experiment

• Several test diodes in many

different flavors

• Standard planar test

structures



Electrical and functional characterization

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0 100 200 300 400 500 600

Revers

e c

urr

en

t [n

A]

Reverse voltage [V]

GAP=10 µmGAP=15 µmGAP=20 µmGAP=25 µmGAP=30 µmGAP=35 µmGAP=40 µmGAP=50 µmGAP=70 µmGAP=80 µmGAP=90 µm

GAP=100 µmGAP=120 µmGAP=150 µm

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500

0 20 40 60 80 100 120 140 160

Bre

akd

ow

n v

olt

ag

e [

V]

Gap dimension [µm]

no FPFP=5 µm


Electrical characterization (I-V)

• Good reverse current values and uniformity

• Clear trend with GAP size

• Once again the field-plate proves its

effectiveness

Functional tests

• Bi-dimensional X-Ray scan performed at

Diamond Light Source, Didcot, UK.

• 15 keV X-rays, spot size ∼3 µm FWHM

• Very good signal efficiency up to less than

20 µm away from the edge

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Sig

na

l [a

.u.]

x [mm]

D2, GAP=15µm D3, GAP=20µm

D2 - Vb=100V

D2 - Vb=20V

D2 - Vb=5V

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4 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.1

Sig

na

l [a

.u.]

x [mm]

D2, GAP=15µm D3, GAP=20µm

D3 - Vb=100V

D3 - Vb=20V

D3 - Vb=5V

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[M. Povoli, et al., NIMA (2012)

http://dx.doi.org/10.1016/j.nima.2012.09.035]


Thin 3D detectors with built-in charge multiplication

Evidence and exploitation of this effect

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Co

llecte

d c

harg

e [

fC]

Reverse voltage [V]

{=5e14 cm-2

- Simulated {=1e15 cm

-2 - Simulated

{=2e15 cm-2

- Simulated {=5e14 cm

-2 - Measured

{=1e15 cm-2

- Measured {=2e15 cm

-2 - Measured

Charge multiplication (CM)

• Evidence of CM was found in irradiated planar and

3D detectors

• CM was observed in older generations of both FBK

and CNM 3D detectors

[A. Zoboli, et al., NSS08 Conf. Record, 2721]

[M. Köhler, et al., NIMA659 (2011), 272]

• Triggered by high electric field at the tip of the

junction columns

• Confirmed by numerical simulations

[G. Giacomini, et al., VERTEX2011, POS]

• Can charge multiplication be exploited?!?

Motivation

• Increasing interest in reducing the total material

budget

• Reduction of the sensor thickness

• Lower thickness → less detection volume

• Reduction in available charge for particle detection

Idea and investigation through numerical simulations

• A shrinking of all geometries by a factor of ∼3 will

allow to also reduce inter-electrode spacing and

column diameter

• Bulk thickness: ∼70 µm

• Column diameter: ∼4 µm

• Higher field at lower voltages

[M. Povoli, et al., submitted to NIMA (2013)]



Simulation results

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Gain

Reverse voltage [V]

1N-1P1N-2P1N-3P

1N-SqP1N-RoP

1N-HexP

Gain before irradiation

• All investigated structures show CM

• The onset of CM changes with

geometry

• Lower operating voltages for structures

having trench ohmic electrodes

• A good gain uniformity was found

within the entire investigated cell

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Gain

Reverse voltage [V]

1N-SqP

PRE-irradiation

{eq=1x1015

neqcm-2

{eq=5x1015

neqcm-2

{eq=1x1016

neqcm-2

{eq=2x1016

neqcm-2

Gain after HEAVY irradiation

• Results reported only for the

rectangular cell

• Bulk radiation damage modeled with a

3 level trap model

• Reduction of the collected charge due

to trapping (expected)

• No change in CM onset voltage

• Completely recover charge trapping



Surface isolation and electrode efficiency

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Efi

eld

[V

/µm

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X [µm]

Field-plate

n+

p+

Vbias=110V

TOP (Y=0.01 µm)MIDDLE (Y=27.5 µm)

TIP (Y=55 µm)

Final sensor geometry

• Rectangular cell shape

• P-spray and ∼4 µm field-plate

• Raise the n+ column to avoid critical regions on the

backside

• Modification of the tip shape in order to avoid early

breakdown phenomena

• Extracted 1D electric field profiles show that the

surface and tip field are under control

• Possible to operate in CM mode

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Gain

Reverse voltage [V]

Tp=10ns

silicon

n+ electrode

p+ electrode

Electrode response

• Crucial to have polysilicon filling and sufficiently

large lifetimes in it

• Lifetimes calibrated to match the electrode

efficiency found for Stanford detectors

Full 3D MIP simulation (proposed shaping time of 10 ns)

• Three hit points investigated (bulk and both

electrode types)

• CM properties similar to the simplified structure

• p+ electrode is fully efficient and show good CM

• n+ electrode is less efficient and shows lower CM

• Multiplication of the charge generated under the tip


HYbrid DEtectors for neutrons (HYDE)

Neutron detection

• Bare silicon is not able to detect neutrons

• Need for a converting material

• The most used converter is LiF

• Most of the commercial devices are able to only

detect thermal neutron

Neutron detectors produced with 3D technology

• Purposely designed cavities

• Cavities are filled with the converter

• Increased interaction probability between

reaction products and silicon

The HYDE project (INFN)

• Innovative polysiloxane converter

• Detects both thermal and fast neutrons

• Reaction products: recoil protons and light in the

blue to red range

Realized detectors

• The cavities are connected through columnar pillars

• Both with an without polysilicon filling

• Good leakage currents and breakdown voltages

• The converter is deposited at Laboratori Nazionali di

Legnaro

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Cu

rren

t [n

A]

Reverse bias [V]

d=400, Up+=50

d=400, Up+=100

d=400, Up+=150

d=400, Up+=200


HYbrid DEtectors for neutrons (HYDE)

SEM pictures

• Fabricated cavity with connecting pillars (LEFT)

• The same after filling with converter (RIGHT)

α-particle measurements

• Measurements from both sides of the sensors

• Main peak correspond to 241Am alphas (except for

the energy loss in air)

• Lower peak from the trench side: geometrical

motivations

Neutron beam measurements

• Calibration with radioactive sources (α,γ)

• Bare sensor as comparison and two sensors with

converter

• Indication of increased statistics in the range from

0.5 to 1.25 MeV (VERY PRELIMINARY)

0.0001

0.001

0.01

0.1

1

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No

rmali

zed

co

un

ts

Energy [MeV]

Vbias = 40 V

METAL CONTACT SIDETRENCH SIDE

100

101

102

103

0 0.25 0.5 0.75 1 1.25 1.5

Co

un

ts

Energy [MeV]

Gamma source calibration, NO-conv.n28-350-150, WITH-conv. (Vbias=50V)

n8-300-50, WITH-conv. (Vbias=35V)n21-400-100, NO-conv. (Vbias=50V)


CONCLUSIONS

• An enhanced 3D-DDTC sensor concept with fully passing

through columns was designed at University of Trento and

fabricated at FBK

• All the performed studies allowed to gain a better

understanding of the behavior of 3D detectors both from the

electrical and the functional point of views

• 3D Pixel detectors compatible with the FE-I4 readout chip

proved to operate efficiently in IBL operating conditions

• These devices were chosen, together with CNM 3D detectors

and planar 3D detectors, to populate the ATLAS Insertable

B-Layer which will be installed during the first long shutdown

of the LHC (2013-2014)

• The large amount of activities performed in the framework of

the ATLAS 3D sensor collaboration triggered new ideas that

are currently being investigated and will be soon tested


Thank you!


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Development of enhanced double-sided 3D radiation sensors...

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