3D micro-structuring of diamond for radiation detector applications

Diamond Sensors Laboratory

3D micro-structuring of diamond for radiation detector applications

B.Caylar, M.Pomorski, P.BergonzoDiamond Sensors Laboratory CEA-LIST, Gif-Sur-Yvette, France

José AlvarezLaboratoire de génie électrique de Paris (LGEP), Gif-sur-Yvette, France

Alexander OhUniversity of Manchester, School of Physics and Astronomy, Manchester, United Kingdom

Thorsten WenglerCERN, Geneva, Switzerland


Advantages1: Higher electric field for a given applied bias voltage Shorter drift path thus drift time Lower probability of trapping

2

Context – Why using 3D electrodes?

[1] J.Morse, C.J. Kenney, E.M. Westbrook et al. / Nuclear Instruments and Methods in Physics Research Section A, 524 (2004) 236.

2DElectrodes

3DElectrodes

Ionizing particle


3


Planar 3D

0 2 4 6 80.0

3.0x10-6

6.0x10-6

9.0x10-6

1.2x10-5

1.5x10-5

Perfect cristal

= 250ns

= 2ns

Cur

rent

(A)

Time (ns)0 2 4 6 8

0.0

3.0x10-6

6.0x10-6

9.0x10-6

1.2x10-5

1.5x10-5

Perfect Cristal

= 250ns

= 2ns

Cur

rent

(A)

Time (ns)

Analytically calculated currents generated by a MIP


4

NIEL induces bulk defects

When flux increases :

Defects number increases Carrier lifetime reduction CCE decreases

[2] Michal Pomorski – PhD debate, Frankfurt University 07/08/2008

0 5 10 15 20 250

1

Nor

mal

ized

cou

nts

Collected charge [ke]

before irradiation after 1.2 x 1014 20MeV n.cm-2

after 1.97 x 1014 20MeV n.cm-2

Signal decrease



5

3D geometry is faster : 8ns vs 208ps. 3D geometry makes the detector more radiation hard

0 2 4 6 80.0

0.5

1.0

1.5

2.0

2.5

3.0

99.99%

Col

lect

ed c

harg

e (fC

)

Time (ns)

Perfect cristal

= 250ns

= 2ns

95%

0 2 4 6 80.0

0.5

1.0

1.5

2.0

2.5

3.0

Perfect cristal

= 250ns

= 2ns

Col

lect

ed c

harg

e (fC

)

Time (ns)

47%

99.6%


Planar 3D


• Burried electrodes Laser setup & Fabrication Structural characterization Electrical characterization

• pc-CVD Detector (e6 detector grade) Electrical characterization Characterization under alpha particles

• sc-CVD Detector (e6 electronic grade) Optical characterization Electrical characterization Transient current measurements

• Conclusion 6

Outline


BURRIED ELECTRODESLASER SETUP & FRABRICATION

7


8

Burried electrodes – Laser setup

Tunable parameters Scan velocity 1-1000 µm/s Laser power 0-160µJ/pulse Repetition rate 1-30 Hz

Sample holder

Nitrogen laser λ = 337nm

τ = 3ns

XYZMotorized stage

Webcam

20x Lens


9

Burried electrodes – Fabrication

997000 997500 998000 998500 9990000.00020

0.00021

0.00022

0.00023

0.00024

0.00025

0.00026

Am

plitu

de (V

)

Time (ms)XYZ

Motorized stage

Photoluminescence during laser processing

Translation

Graphitization


10

BURRIED ELECTRODESSTRUCTURAL CHARACTERIZATION


11

Clean surface (Where graphitization starts)

Cracked Surface (Where graphitization ends)

Tilted sample

150 µm

Optical grade sc-CVD sample

Structural characterization – Optical microscopy

10µm diameter

20-100 µm diameter

700µm depth


12

Structural characterization – 2D Raman mapping

2D Raman depth mapping obtained by integrating diamond peak

No micro-channel Micro-channel with cracks

1000 CCD cts

0 CCD cts

1000 CCD cts

0 CCD cts10µm 10µm

Depth


13

Structural characterization – SEM imaging

Channel’s clean side after laser processing

Channel’s clean side after H2 plasma

H2

Plasma


14

BURRIED ELECTRODESELECTRICAL CHARACTERIZATION


15

Electrical characterization – I(V) measurements

Graphite’s channel resitivity

[3] T.Ohana, T.Nakamura, A.Goto et al. / Diamond and Related Materials, 12 (2003) 2011

ρ(average) = 5.7x10-1 Ω.cm

R(500µm) ~ 2kΩ

-2 0 2 4 6 8 10-1

0

1

2

3

4

5

6

Voltage (V)

Cur

rent

(mA

)

Match with nanocrystalline graphite given in literature3

A


16

PC-CVD DETECTORELECTRICAL CHARACTERIZATION

E6 detector grade10 x 10 x 0.7 mm3

Sample courtesy Alexander Oh


0 200 400 6001E-14

1E-13

1E-12

1E-11

Cur

rent

(A)

Voltage (V)

17

Electrical characterization – Device leakage current

0 200 400 6001E-14

1E-13

1E-12

1E-11

Planar 3D

Cur

rent

(A)

Voltage (V)

A

Comparison between planar and 3D geometry

Planar 3D


18

PC-CVD DETECTORCHARACTERIZATION UNDER ALPHA

PARTICLES


19

α

Al front contact

Al backcontact

Am-241 Source5.486MeV

R

Vbias = ±500V

Characterization under alpha particles – Experimental setup

FCSA

Fast Charge Sensitive Amplifier M.Ciobanu, GSI, Germany

Signal

Scope

Collimator


0 200 400 600 800 10000

20

40

60

80

100 Single hit Trend

Hit number

CCE

(%)

0 200 400 600 800 10000

102030405060708090

100

Single hit Trend

CCE

(%)

Hit number 20

Characterization under alpha particles - Results

Polarization study – Holes drift (pc-CVD sample)

Planar 3D


0 500 1000 1500 20000

102030405060708090

100

Single hit Trend

CCE

(%)

Hit number0 500 1000 1500 2000

0102030405060708090

100

Single hit Trend

CCE

(%)

Hit number 21


Polarization study – Electrons drift (pc-CVD sample)

Planar 3D


0 20 40 60 80 1001

10

100

Cou

nts

CCE (%)

Planar 3D

0 20 40 60 80 1001

10

100

Cou

nts

CCE (%)

Planar 3D

22


Holes drift (pc-CVD sample)α

α

Amplitude has been normalized with the signal of a sc-CVD « e6 electronic grade » diamond


23


Electrons drift (pc-CVD sample)

0 20 40 60 80 1001

10

100

Cou

nts

CEE (%)

Planar 3D

0 20 40 60 80 1001

10

100

Cou

nts

CCE (%)

Planar 3D

αα

Amplitude has been normalized with the signal of a sc-CVD « e6 electronic grade » diamond

michal

why not larger graphs


24

Characterization under alpha particles - Analysis

α

α

Low CCE

High CCE

Electric field simulation 3D Geometry but pseudo–3D detector

700µm

200µm

HV +500V V/µm

5

4.5

4

3.5

3

2.5

2

1.5

1

0.5

0


25

SC-CVD DETECTOR

E6 electronic grade - <100> oriented3 x 3 x 0.3 mm3

Sample courtesy Eleni Berdermann


26

SC-CVD DETECTOROPTICAL CHARACTERIZATION


27

Bulk strain mapping after graphitization

Micro structured sc-CVD diamond observed with crossed polarizers

Test areas

Detector area

Detector’s optical characterization – Optical microscopy


28

Detector’s optical characterization – Optical microscopy

Detector after metallization


29

SC-CVD DETECTORELECTRICAL CHARACTERIZATION


30

Electrical characterization – Device leakage current

sc-CVD sample after plasma O2 etching

HV on cracked surface HV on clean surface

-200 -100 0 100 2001E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4 Increasing Voltage Decreasing Voltage

Cur

rent

(A)

Voltage (V)-200 -100 0 100 200

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4 Increasing Voltage Decreasing Voltage

Cur

rent

(A)

Voltage (V)


31

SC-CVD DETECTORTRANSIENT CURRENT

MEASUREMENTS


32

2D Zone

HV +100V

ELECTRICAL CHARACTERIZATION – SETUP AND METHODS

2D Zone

Signal

ScopeAmpli

Transient current measurements

300µm

Ultra-Fast 40 dB, 2 GHz Broadband Amplifier


Signal 3D~500mV

Electrons drift

Mixed e/h drift

Signal 2D~100mV

Signal 2D~80mV

Holes drift

33

TRANSIENT CURRENT MEASUREMENTS - RESULTS

Without collimator

Alphas’ injection on cracked side Alphas’ injection on clean side

1 ns


34


With collimator

1 nsMixed e/h drift

Alphas’ injection on cracked side


V/µm

35

TRANSIENT CURRENT MEASUREMENTS - ANALYSIS

Electric field simulation

3

2.5

2

1.5

1

0.5

0

300µm

+100 Vα

α

Planar+3D signal

Planar signal only


36


Experimental results

-2 0 2 4 6 8 100.0

0.1

0.2

0.3

0.4

0.5

0.6 Planar 3D

Sig

nal a

mpl

itude

(V)

Time (ns) Selection of relevant events

Amplitude ratio = 6


-2 0 2 4 6 8 100,0

5,0x10-5

1,0x10-4

1,5x10-4

2,0x10-4

2,5x10-4

Ana

lytic

ally

cal

ulat

ed s

igna

ls (A

)Time (ns)

Planar 3D

Amplitude ratio = 23.8

2GHz low pass filter

37


Analytically calculated signals

-2 0 2 4 6 8 100,0

5,0x10-5

1,0x10-4

1,5x10-4

2,0x10-4

2,5x10-4

Ana

lytic

ally

cal

ulat

ed s

igna

ls (A

)

Time (ns)

Planar 3D

Theoritical response

Amplitude ratio = 22


Amplitude’s ratio = 6.2

38


Analytically calculated signals

350 MHz low pass filter

Ampli + device bandwith ~350MHz

Rdevice ~ 520Ω

12 channels connected

Rchannel ~ 6 kΩ

-2 0 2 4 6 8 100,0

5,0x10-5

1,0x10-4

1,5x10-4

2,0x10-4

2,5x10-4

Ana

lytic

ally

cal

ulat

ed s

igna

ls (A

)

Time (ns)

Planar 3D


39

Conclusion

• Conductive graphitic structures has been achieved on both pc- and sc-CVD sample

• These structures are suitable for detectors applications

• Two dectetors using 3D-geometry electrodes has been produced

• A real improvement between planar and 3D geometry has ben observed Higher signal Faster response « Polarization effect » decrease on pc-CVD detector

But real 3D detector hasn’t been achieved yet…


40

Thanks for your attention !

3D micro-structuring of diamond for radiation detector applications

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