DEAR SDD --> SIDDHARTADEAR SDD --> SIDDHARTA

SiSilicon licon DDrift rift DDetector foretector for H Hadronic adronic AAtom tom RResearch and esearch and TTiming iming AApplicationspplications

Carlo FioriniCarlo Fiorini(Politecnico di Milano)(Politecnico di Milano)

 

Development of a soft X-ray detection apparatus,based on Silicon Drift Detectors (SDD),

with high energy resolution and high background reduction

for application in exotic atoms researches

Experimental requirements Experimental requirements

Experimental requirements

Exotic atom

e.m. position

of K line

(keV)

(eV)

(eV)

Required precision 

(eV) (eV)

hydrogen 6.46 160 200 ~ 5 ~ 10

deuterium 7.81 500 800 ~ 25 ~ 100

Working principles of the SDDWorking principles of the SDD

n

n+

p+ -V cc

The classical PIN diode detector

The anode capacitance is proportional to the detector active area

n

n+

p+ -V cc

p+

The Semiconductor Drift Detector

AnodeThe electrons are collected by the small anode,characterised by a low output capacitance.

Advantages: very high energy resolution at fast shaping times, due to the small anode capacitance, independent of the active area of the detector

The Silicon Drift Detector with on-chip JFET

JFET integrated on the detector• capacitive ‘matching’: Cgate = Cdetector

• minimization of the parasitic capacitances• reduction of the microphonic noise• simple solution for the connection detector-electronics in monolithic arrays of several units

The integrated JFET

Detector produced at the MPI Halbleiterlabor, Munich, Germany

Performances of the SDDsPerformances of the SDDs

Quantum efficiency of a 300 m thick SDD 55Fe spectrum measured with a SDD (5 mm2) at –10°C with 0.5 s shaping time

Silicon Drift Detector performances

Silicon Drift Detector Droplet or SD3

T=-30°C a τsh=1µs

5000 5500 6000 6500 7000EN ER G Y [eV ]

0

2000

4000

6000

8000

CO

UN

TS

Fe55

K

K

FW HM =131 eV

Canode= 50 fF

(vs. 100fF conventional SDD)

Resolution in the line shift measurementResolution in the line shift measurement

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1100

200

300

400

500

600

700

800

A (cm-2)

FW

HM

(eV

)

SDD PIN Si(Li) 150 K 5.9 keV line

PIN Tsh=20us

Si(Li) Tsh=20us

SDD Tsh=1us

Spectroscopic resolution: detector comparison - 1

FWHMmeas of monoenergetic emission line 5.9 keV1cm2 detector at 150 K

SDD FWHM=140eV shap =1sSi(Li) FWHM=180eV shap =15s PIN diode FWHM=750eV shap =20sCCD FWHM=140eV frame=1s

Spectroscopic resolution: detector comparison - 2

Measure of the line shift – ideal case *

The case: kaonic hydrogen, 200 cm2 detection systemFor 6000 events (~ 50 pb-1 )Estimated peak position 6.3 keV, line width about 245 eV, peak shift about 160 eVDetection system based on SDDs

* No background contribution considered

222222 )245()140()200( eVeVeVFWHMFWHMFWHM SDDlinemeas

eVeV

N

FWHM

phot

meas 3.16000

10035.2/

%1160

3.1

eV

eV

shiftPeak

Background reductionBackground reduction

hIK

IA

h

tIA

tdr max

Timing with the anode signal

10-2

10-1

100

101

10-8

10-7

10-6

10-5

Area (cm2)

Tdr

ift (

s)

Drift time vs. Active area

A=0.1cm2 Tdrift = 70ns

A=0.5cm2 Tdrift =350ns

A= 1cm2 Tdrift =700ns

With: = 2k/cmH = 450m

Timing resolution with SDD

2

2

HN

A

qTdrift

Dn

s

Triggered acquisition

Kaontrigger

Concidencewindows

Detectedpulses

Consideredpulses

Kaon trigger X-ray pulseBackground pulse

dr max

Background reduction with triggered acquisition

=number of detected kaons per detected X-ray = 103

Br=background rate = 103 events/s

Tw=sinchronization window

Tw = r x drift max = 103 x 1 s = 1ms

B = Br x Tw = 103 s-1 x 10-3 s = 1

S/B = 1/1

    Actual value of the S/B ratio measured with DEAR at DANE

using CCDs

S/B 1/100 in kaonic hydrogen

expected:

S/B 1/500 in kaonic deuterium

Signal/Background with CCD

hIK

IA

Timing with the prompt signal from the backplane

IA

IK

h

t

t

tdr maxEstimated time resolution: about 300 ns

Reliability of the detection set upReliability of the detection set up

1400 1600 1800 2000C ha nne ls

0

1000

2000

3000

Co

un

ts

SDD # 1

1400 1600 1800 2000C ha nne ls

0

1000

2000

3000

Co

un

ts

SDD # 2

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Co

un

ts

SDD # 3

1400 1600 1800 2000C ha nne ls

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Co

un

ts

SDD # 4

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0

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Co

un

ts

SDD # 5

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0

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Co

un

ts

SDD # 6

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0

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Co

un

ts

SDD # 7

600 800 1000 1200 1400C ha nne ls

0

400

800

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Co

un

ts

SDD # 8

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0

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un

ts

SDD # 9

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un

ts

SDD # 10

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SDD # 11

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un

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SDD # 12

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un

tsSDD # 13

1000 1200 1400C ha nne ls

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un

ts

SDD # 14

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un

ts

SDD # 15

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un

ts

SDD # 16

1400 1600 1800 2000C ha nne ls

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un

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SDD # 17

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SDD # 18

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SDD # 19

Monolithic array of Silicon Drift Detectors

Pixel area = 5 mm2

Total array area = 95 mm2

DEAR test setup (SDD) at the BTF

BTF e+/e - beam

e+, e – shower

Pb plateTi foil

Zr foil

SDD X-ray detector (4 chips prototype)

Pb shielding

S2

X-ray lines

S1

scintillators

Operations:

The first stage of the project of the new detector deals with the characterization of the SDD performances.

The characterization concerns the finalization of trigger efficiency and energy resolution, as a function of background environment and time window. This information will fix also the dimension of the single cell. These measurements are planned to be performed with a prototype device. The answers coming from these tests will be used for the construction of the final detector array and associated electronics with optimal characteristics.

Beam conditions at BTF:

Energy: varying between 50 ÷ 750 MeV

Intensity: varying between 1÷ 103 e+/e- s-1 (preference is for positrons)

bunch : 10 ns; bunch frequency: 1 ÷ 49 Hz

Gate window 0.1 – 1 s

BTF run period required:

2-4 weeks in the period June 2003 - October 2003

The detector: 1 cm2 SDD prototype

Front-side: field strips, JFET Back-side: entrance window

• 65 rings, 1 cm2 area• 280m high-resistivity + 12m epi-layer

detector presently under test at Politecnico di Milano

Preliminary measurements

0 20 40 60 80 100Voltage [V ]

-1E-9

0E+0

1E-9

2E-9

3E-9

4E-9

Cur

rent

[A]

Leakage current ~ 3 nA @ room T

-60 -40 -20 0Voltage [V ]

-1 .2E-5

-8.0E-6

-4.0E-6

0.0E+0

Cur

rent

[A]

Voltage divider threshold voltage ~ -50V for 8 rings ( 65 rings biasshould be feasible with ~ - 400V)