Material developments for the HL-LHC upgrade of the CMS tracker

Joachim [email protected]

Material developments for the HL-LHC upgrade of the CMS tracker

19 January 2012

Joachim ErfleUniversity of Hamburg

Material developments for the HL-LHC upgrade of the CMS tracker 19/01/12

page 1



Overview

• The tracker and its challenges at HL-LHC• Some layout possibilities for a new tracker and sensor modules• The basic working principle of silicon sensors• A campaign to find the next tracker‘s sensor material• First results of this campaign

19/01/12page 2



The current tracker

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• Over 200m2 active silicon• About 26000 sensors• 9.6 million strip channels +

66 million pixel channels



Challenges for the tracker at HL-LHC

19/01/12page 4

Required features for HL-LHC:• Higher radiation tolerance• More (smaller) channels for a

lower occupancy at high pile-up• Trigger information for level 1

New tracker needed



Two possible new sensor module layouts

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courtesy of S. Mersi, CERN

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N



Possible new tracker layout

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courtesy of S. Mersi, CERN



Strip sensors

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Basic layout of a strip sensor

Basically two different types:• N doped bulk:

• Holes readout slower

• Easier to produce• Tends to undergo type inversion

• P doped bulk:• Electron readout

faster, less trapping• Harder to produce

Depletion of a n-bulk sensor

Depletion of a p-bulk sensor



Radiation damage in silicon

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Two types of radiation damage: • Surface damage• Bulk damage main problem for hadronic irradiation

• Subdivided in three damage types:

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HH

C

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Changes effective doping concentration full depletion voltage

Reduces charge collection

Increases leakage current



Goals of the HKP-campaign

The main challenges for the tracker at the HL-LHC will be:• Higher radiation dose (up to a fluence of Φeq = 1016 cm-2)

• Higher occupancy

The current tracker would not withstand the radiation and also develop occupancy problems→ Find best best suitable silicon material and layout for a future tracking detector

To achieve that we investigate a large variety of materials:• Different oxygen, carbon,… content

• Different bulk doping (n and p)

Test sensor geometries and layoutsIrradiations with neutrons or/and protons to simulate HL-LHC radiation dose

19/01/12page 9


structure to study

pad diodes material

baby strip sensor reference design / material

baby strip sensor with integrated pitch adapter

design

pixel sensor reference Design / material

multigeometry pixel layout parameters

multigeometry strips layout parameters

baby strixel design

test-structures process parameters

Wafer overview: HPK-campaign


page 10


Silicon material


material thinning method active thickness physical thickness

FZ deep diffusion 120,200,300 μm 320 μm

FZ --- 200 μm 200 μm

FZ handling wafer 120 μm 320 μm

MCz --- 200 μm 200 μm

Epi handling wafer 50,100 μm 320 μm

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Of each material there are 3 different types:- n-type (N)Two different strip isolation technologies for p-bulk:- p-type with p-stop (P)- p-type with p-spray (Y)


Wafer-Processing (deep diffusion)

page 12

• Standard method for thinning: wafer bonding of Si to Si-substrate (low ohmic)

• Well known process

• Relatively expensive

• New method: deep diffusion

• Active volume of a 320μm wafer reduced by diffusing high doping from the back.

• At high irradiation thick sensors not fully depletable

• Mean free path of charge carriers severely reduced due to trapping for highly irradiated sensors

→ In thin sensors less charge is trapped and

voltage needed for full depletion is lower.


pn-junctionactive thickness

active volume inactive volume

physical thickness



Sequence of Measurements and irradiations

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1. Pre qualification2. First irradiation3. Single irradiation qualification4. Second irradiation5. Measurements and time development

of defect (annealing) studies

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courtesy of S. Müller, KIT

HL-LHC: Lint=3000 fb-1



Irradations

Neutrons: 1 MeV (TRIGA Reactor Ljubljana)Protons: 23 MeV (Karlsruhe cyclotron)

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radius protons Φeq [cm-2] neutrons Φeq [cm-2] total Φeq [cm-2] active thickness40 cm 3 10∙ 14 4 10∙ 14 7 10∙ 14 ≥ 200 μm

20 cm 1 10∙ 15 5 10∙ 14 1.5 10∙ 15 ≥ 200 μm

15 cm 1.5 10∙ 15 6 10∙ 14 2.1 10∙ 15 ≥ 200 μm

10 cm 3 10∙ 15 7 10∙ 14 3.7 10∙ 15 ≤ 200 μm

5 cm 1.3 10∙ 16 1 10∙ 15 1.4 10∙ 16 < 200 μm

courtesy of S. Müller, KIT

HL-LHC: Lint=3000 fb-1


Volume current versus fluence


Currents match expected value from literature (M. Moll‘s thesis) within the uncertainties. -> dose measurements are ok.

page 15

currents are measured after annealing of 10 min@ 60°C at 0°C and scaled to 20°C

Δ 𝐼𝑉 =𝛼Φ𝑒𝑞

J. Erfle, UHH

neutrons

neutrons

protons

protons



Type-inversion and the effective doping

19/01/12page 17

Effective thickness reduced,but fully functional

Partly depleted sensor, type inverted

Readout channels are somewhat „isolated“ from collected charge

Partly depleted sensor, not type inverted

Defects close to the bandgap perform like dopants, so they change the effective doping by providing a free electron or hole

Influence on:• Full depletion voltage• Type of bulk doping

Possible problems:• full depletion voltage can rise above the

value that can be applied• If that happens in the type inverted case,

the charge measurement is disturbed


Neff for different materials / irradiations


page 18

protons

neutrons

All measured n-type materials (FZ and MCz) are type-inverted after neutron or proton irradiation.

n-type

capacitances are measured at 0°C, 1kHz after annealing of 10min@60°C

J. Erfle, UHH

J. Erfle, UHH


Neff for different materials / irradiations


page 19

n-type p-type

protons

neutrons

capa

cita

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are

mea

sure

d at

0°

C, 1

kHz

afte

r ann

ealin

g of

10

min

@60

°C

J. E

rfle,

UH

HJ.

Erfl

e, U

HH

J. Erfle, UHH

J. Erfle, UHH

All n-type materials undergo type inversionNo p-type material undergoes type inversionAll p-type materials show a steep increase in Neff and therefore depletion voltage



Time resolved charge collection measurement with TCT shows type inversion

19/01/12page 20

FZ320P FZ320N

not type inverted type inverted

unirradiated

p@3E14

courtesy of T. Pöhlsen, UHH courtesy of T. Pöhlsen, UHH

- holes - electrons

U=300VU=600V

courtesy of J. Lange

Laser: 672 nm, red3µm penetration depth

type inversion of FZ and MCz n-type materials is confirmed by TCT.

Signals are measured at 0°C, after annealing of 10min@60°C

E

depth

RearFront

red



CCE of diodes, after p@3E14

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p-type:holecollection

n-type:electroncollection

infrared laserred laser, front injection

p-typen-type

measurements are performed at 0°C and 600V, with 20ns integration time

unirradiated

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, UH

H

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, UH

H

courtesy of J. Lange

infrared laser: CCE is about 90%

Electrons only: CCE ~ 85%, holes collection only: CCE ~ 67%Electron readout performs better

infrared



Signal of FZ320P baby sensor, after p@3E14

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Signal induced by a 90Sr source, readout by ALiBaVa

Vdepl

courtesy of K. Hoffman, KIT

CCE of FZ320 p-type is about 87% at p@3E14, compared to non-irradiated

measurements are performed at -20°C


Some experimental structures


Seite 23

• Idea to reduce occupancy and increase resolution

• To be able to read out from the sides, inner strips are routed out in the first metal layer

Strip-sensor with integrated Pitchadapter in the first metal layer

Strixel-sensor

• Pitchadapter needed for readout-chip connection

• Is it possible to integrate it on the sensor without loosing active area?

courtesy of A. Kornmayer, KIT


First results for integrated pitch adapter

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Electron from a Sr90-sourceat different positions

Flat S/N in standard region of about 17

Reduced S/N in PA-region, noise stays constant

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First results for strixel sensors

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Seed strip (far)

1. far neighbour

1. near neighbour

Seed strip (near)

1. near neighbour1. far neighbour

Electron from a Sr90-source at near area Electron from a Sr90-source at far area

Seed strip (far)1. far neighbour

1. near neighbour

Signal in the far area only measured on strips in the far area.Signals in near area appear also on far strips

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HL-LHC: CMS needs completely new tracking detectors:• Higher granularity• More radiation toleranceHPK-campaign to identify Si-material, polarity, sensor-layout

First results:• Diode currents increase as a function of fluence as expected• Neff shows:

• - type inversion for all n-type materials• - no type inversion for p-type, with steep increase• Not expected:

• CCE with baby sensors and diodes reduced to ~90% after 3E14 proton irradiation

Conclusions


page 26



Outlook

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• More irradiations to come: Higher fluences!• Trying to understand material properties in detail• Full annealing studies to be done Define the material and layout to be used in the Phase II upgrade of the tracker

Thank You !



Backup

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CCE of FZ320 after proton irradiation

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measurements are performed at 0°C

courtesy of T. Pöhlsen



TCT pulses – p-type

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FZ200P FZ320P MCZ200P

not type inverted

courtesy of T. Pöhlsencourtesy of T. Pöhlsencourtesy of T. Pöhlsen

300V 600V 250V

measurements are performed at 0°C, using a red laser



TCT pulses – n-type

19/01/12page 31

FZ200N FZ320N MCZ200N

type invertedmeasurements are performed at 0°C, using a red laser

courtesy of T. Pöhlsencourtesy of T. Pöhlsencourtesy of T. Pöhlsen

200V300V300V



oxygen content

19/01/12page 32

material bulk resistivity oxide concentration

FZ320P 3-8 3,50E+016

FZ200P 3-8 3,00E+017

FZ120P 3-8 5,00E+017

FZ320N 1.2-2.4 1,80E+016

FZ200P 1.2-2.4 3,00E+017

FZ120P 1.2-2.4 5,00E+017

MCZ200P >2 3,75E+017

MCZ200N >0.5 3,00E+017

Material developments for the HL-LHC upgrade of the CMS tracker

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