Development of Multi-Pixel Photon Counters (1)

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Development ofMulti-Pixel Photon Counters (1)

S.Gomi, T.Nakaya,M.Yokoyama, M.Taguchi, (Kyoto University)

T.Nakadaira, K.Yoshimura, (KEK)

Oct.31.2006 Hawaii

for KEK-DTP photon sensor group

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Contents• Introduction

• Measure the fundamental performance– Check the MPPC raw signal– GAIN– noise rate– Cross-talk rate– Photon Detection Efficiency ( PDE )– Linearity

• LASER test ( KEK-DTP LASER system)

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Introduction

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Multi-Pixel Photon Counter ( MPPC )• Multi-Pixel Photon Counter ( = MPPC ) is a new type o

f photo detector developed by Hamamatsu Photonics (HPK).

• MPPC consists of 100~1600 small avalanche photo diodes( APD ) in 1mm×1mm sensitive region.

MPPC

1pixel

mm 5050

Sensitive region of MPPC400pixel type

6mm

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Operation principle of MPPC

• Each APD pixel operate in Geiger mode. Gain is proportional to the applied voltage above the breakdown voltage( Vbd ).

VVVbdbd

• In Geiger mode, the output charge Q from a single pixel is independent of the number of injected photons within the pixel.

)V-(V e

C

e

Q GAIN bd

Extrapolated to GAIN=0

66mm

5mm

MPPC character• Combining the output from all the pixels, the

total charge from one MPPC is quantized to multiples of Q .

• MPPC advantages– Compact– Insensitive to magnetic field– High gain( ~106 ), low bias voltage( ~70V )– Low-cost

• We measured the basic performance of two kinds of MPPC, 100 pixel type, and 400 pixel type.

the MPPC is an excellent photon counting device

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Measure the fundamental performance

• check the MPPC raw signal• gain• noise rate• cross-talk rate• Photon Detection Efficiency ( PDE )• Linearity

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The raw signal of MPPC• MPPC has good photon counting capability. We can

observe 1p.e signal peak, 2p.e signal peak, …

* ADC distribution *

pedestal

1p.e signal

2p.e

3p.e

4p.e …

1p.e

2p.e

…

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set up

•Measuring the little light from the blue LED by MPPC.

•Gain is measured by ADC distribution.

blue LED

MPPC

Gain

e

)Q(pedestal - Q(1p.e.) GAIN

The gain can be estimated at intervals The gain can be estimated at intervals between 1p.e and the pedestal. between 1p.e and the pedestal.

ADC distribution

* STATUS DATA *400 pixel MPPC

BIAS : 70.0V / VBD =68.8V

• Gain of MPPC is defined as this equation.• Gain is measured by analyzing ADC distributions of

MPPC signals.

pedestal

1p.e signal

2p.e

3p.e

4p.e …

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Gain

• From gain-voltage relation, the break down voltage can be measured.

BlueBlue : : 15degree15degreeGreenGreen : : 20degree20degreeRedRed : : 25degree25degree

MPPC is a high gain device.MPPC is a high gain device.

The break down voltage depends on the temperature.

Gain 400pixel

610

5105

Bias voltage [V]69.6 70 70.6

Gain 100pixel

6103

610

Bias voltage [V]69 69.5 69.8

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Gain

• Gain is a function of V.

bdBIAS V V V


610

6105

Gain 400pixelGain 100pixel

6103

610

0.2 1 1.6 0.8 1 2 2.4

V V

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Noise rate• MPPC is a noisy photo detector. The origin of

these noises is the thermo electron. So, the signals of noise are 1p.e signal typically.

• The noise rate is measured by counting the rate of signal with their height over the threshold, imposed on 0.5p.e and 1.5p.e .

Noise signal of 100pixel MPPC at 25 degree.

( integrated )

1 p.e

0.5 p.e = threshold

1.5 p.e = threshold

“ 1p.e noise ”

“ 2p.e noise ”

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Noise rate

• 1p.e noise rate is about 100~400 kHz.

• 2p.e noise rate is about 0~200 kHz.

100kHz

400kHz


Noise rate [ kHz ] 400pixelNoise rate [ MHz ] 100pixel

100kHz

500kHz

Bias voltage [V]

69.1 69.5 70


1p.e noise

2p.e noise

1p.e

2p.e

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Noise rate

• 1p.e noise rate is a function of both temperature and V.

100kHz

400kHz

Noise rate [ kHz ] 400pixelNoise rate [ MHz ] 100pixel

100kHz

500kHz

0.4 1 1.6 0.5 1 1.5 2 2.3

1p.e

2p.e

2p.e noise rate seem to be a function of V. This is due to “Cross-talk”.

V V

bdBIAS V V V

1p.e

2p.e

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Cross-talk rate.• The origin of the cross-talk is presumed to be

optical photons emitted during avalanche which enter neighboring pixels and trigger another Geiger discharge.

APD that should not detect any photons from outside also operate signals.

“ Cross-talk “

Neighborhood pixel

Avalanche

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• The probability of cross-talk is estimated by the number of 1p.e .

Cross-talk rate measurement

ondistributi-Poisson

-measuredondistributi-Poisson

)1(P

P(1)- )1(P rate talk cross

The cross talk rate is determined.

The number of pedestal are free to cross-talk

• the number of each p.e is assumed to be follow the Poisson distribution

The number of 1p.e : P(1)( estimated by pedestal )

||without cross-talk

The number of 1p.e : P(1)( measured )

||with cross-talk

This difference corresponds to the decrease by cross-talk.

measurement

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Cross-talk rate

• Cross-talk rate at operation voltage defined by HPK is about 20% at 20degree. ( We measured within the wider range about bias voltage. )

10%

50%

Cross-talk rate 400pixelCross-talk rate 100pixel

10%

50%




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Cross-talk rate

• Cross-talk rate is a function of V.

10%

50%

1 2Delta V

Cross-talk rate 400pixelCross-talk rate 100pixel

10%

50%

0.2 1 1.6 0.8 1 2 2.4


V V

bdBIAS V V V

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Photon Detection Efficiency• Photon Detection Efficiency ( = PDE ) is

defined as this equation. PDE consists of three elements.

GeigerlGeometrica QE PDE

Geometrical Efficiency. A ratio of active area to total area (50%~70%)

Quantum Efficiency of active area (60~80%)

Probability of Geiger discharge (60~90%)

Depending on MPPC type

Depending on wavelength of injected light

Depending on bias V

MPPC have the highest QE in Green light.

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relative PDE measurement

・ only the light going through 1mmφslit is detected.

・ The ratio of p.e of MPPC to that of PMT is taken as relative PDE of MPPC.

MPPC

1mmφslit

Blue LED

( total area 1mm2)

PMT

p.e.(PMT)

p.e.(MPPC)PDE relative

PMT made by HPK, type H8643

set up Moving stage

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relative PDE

• PDE is about 2~3 times higher than that of PMT.

1

2

Relative PDE 400pixelRelative PDE 100pixel

1

2

3




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relative PDE

• PDE is a function of Delta V.

1

2

Relative PDE 400pixelRelative PDE 100pixel

1

2

3

0.2 1 1.6 0.8 1 2 2.4


V V

bdBIAS V V V

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Linearity

• The linearity become those equation.

) PMTby monitor ron(photoelect injected

) MPPC (number pixel firedLinearity

MPPC have the fixed number of pixel( 100pixel, 400pixel,… )

MPPC is non-linear device when the number of injected photons is not small compared to pixel number.

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00fired N

exp1NNx

Linearity

• The green line shows the expectation value calculated from number of pixels.

ronphotoelect injected :

pixels ofnumber the:N0

x

BlueBlue : DATA plot: DATA plotGreenGreen : expectation: expectation

Linearity 400pixel

Injected photoelectron per pixel F

ired

pix

el [

% ]

MPPC can operate as linear device.MPPC can operate as linear device.~25p.e about 100pixel type~100p.e about 400pixel type.

linear

Linearity 100pixel

Fir

ed p

ixel

[ %

]

Injected photoelectron per pixel

linear

25%25%

BlueBlue : DATA plot: DATA plotGreenGreen : expectation: expectation

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LASER test(using KEK-DTP LASER system)

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Laser test at KEK, Japan

Motivation

・ study the response of each pixel of MPPC

• Uniformity within 1pixel

• Uniformity in each pixel

Feed back this information to HPK

microscop

e

Laser source

λ=825nmwidth 50ps

Moving stage1μm pitch (x , y)

Laser spot size 　≒ 10μm

Picture of microscope

MPPC

100μm

Uniformity…• gain• cross-talk rate• efficiency

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RMS/mean=2%

RMS/mean=2%

0.25

Uniformity within 1pixel

100pixel

efficiency

GAINCross talk rateResponse within

1 pixels is uniform

Efficiency, Gain Efficiency, Gain (in sensitive region)(in sensitive region)

High at edge of sensitive region

When the avalanche occur at edge of pixel, it is easy to

emit to the next pixel (this is cross-talk).

Cross-talk rate Cross-talk rate (in sensitive region)(in sensitive region)

Sensitive region

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RMS/mean=3%

RMS/mean=3%

Uniformity of each pixel

100pixel

efficiency GAIN

Response of each pixel is uniform

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Summary

• MPPC has good performance !

100pixel 400pixel

Gain

Noise rate(1p.e) [ kHz ]

Cross-talk rate

PDE

Uniformitywithin 1 pixel

of each pixelUniform(2~3%)

66 103~101 65 102~104 400~100 400~100

%50~0 %50~0

PMT 3~ PMT 2~

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Supplements

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MPPC ceramic package for T2K

• This ceramic package make their alignment by the out side frame.

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The principle of operation of 1APD pixel• APD (Avalanche Photo Diode) is a photo-diode t

hat amplify the signal by operating the electron avalanche, that occur on the regions of pn-connection with high electric field. This high electric field is formed by applying bias voltage oppositely.

p+ absorption region p n

E

γ

e-hole

When the bias voltage exceed the threshold voltage ( that is named “Break Down Voltage” ), very little light can make APD to occur the electrical discharge. This amplify is become about 106, and the height of signal doesn’t relate to the number of injected photon.

We can know only “the We can know only “the photon has come” or “not”.photon has come” or “not”.

GND

V+Amplifying by electron avalanche

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Temperature dependent of VBD

VBD [V]

100pixel 400pixel

25degree 68.80 68.83

20degree 68.52 68.51

15degree 68.25 68.20

• The results become linear.

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Set up for measuring linearity

set up

MPPCThe number of photons emitted to MPPC are monitored by PMT.

PM

T

Paper ( to shade off LED light )

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RMS/mean=1.7%

RMS/mean=1.6%

Uniformity within 1pixel

0.25

400pixel

efficiency

GAINCross talk rate

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RMS/mean=2.9%

RMS/mean=3.4%

Uniformity of each pixel

0.18

400pixel

efficiency

GAINCross talk rate

Documents

Development of Multi-Pixel Photon Counters (1)