1. Development of Multi-Pixel Photon Counters (1)
S.Gomi, T.Nakaya,
M.Yokoyama, M.Taguchi, (Kyoto University)
T.Nakadaira, K.Yoshimura, (KEK)
for KEK-DTP photon sensor group
Oct Hawaii

2. 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)

3. Introduction

4. Multi-Pixel Photon Counter ( MPPC )
Multi-Pixel Photon Counter ( = MPPC ) is a new type of photo detector developed by Hamamathu Photonics (HPK).
MPPC consists of 100~1600 small avalanche photo diodes( APD ) in 1mm×1mm sensitive region.
1pixel
6mm
MPPC
Sensitive region of MPPC
400pixel type

5. Operation principle of MPPC
Each APD pixel operate in Geiger mode. Gain is proportional to the an applied voltage above the breakdown voltage( Vbd ).
In Geiger mode, the output charge Q from a single pixel is independent of the number of injected photons within the pixel.
Vbd
Extrapolated to GAIN=0 V

6. the MPPC is an excellent photon counting device
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
6mm
5mm
the MPPC is an excellent photon counting device
We measured the basic performance of two kinds of MPPC, 100 pixel type, and 400 pixel type.

7. Measure the fundamental performance
check the MPPC raw signal
gain
noise rate
cross-talk rate
Photon Detection Efficiency ( PDE )
Linearity

8. The raw signal of MPPC
MPPC has good photon counting capability. We can observe 1p.e signal peak, 2p.e signal peak, …
* ADC distribution *
1p.e signal
2p.e
1p.e
2p.e …
3p.e
pedestal
4p.e …

9. The gain can be estimated at intervals between 1p.e and the pedestal.
Gain of MPPC is defined as this equation.
Gain is measured by analyzing ADC distributions of MPPC signals.
ADC distribution
* STATUS DATA *
400 pixel MPPC
BIAS : 70.0V / VBD =68.8V
( with PM AMP, ×102 )
1p.e signal
set up
Measuring the little light from the blue LED by MPPC.
Gain is measured by ADC distribution.
blue LED
MPPC
2p.e
3p.e
pedestal
4p.e …
The gain can be estimated at intervals between 1p.e and the pedestal.

10. Gain MPPC is a high gain device.
Gain 100pixel
Gain 400pixel
Bias voltage [V]
Bias voltage [V]
MPPC is a high gain device.
Blue : 15degree
Green : 20degree
Red : 25degree
From gain-voltage relation, the break down voltage can be measured.
The break down voltage depends on the temperature.

11. Gain Gain is a function of DV. Gain 100pixel Gain 400pixel DV DV
Gain is a function of DV.
Blue : 15degree
Green : 20degree
Red : 25degree

12. Noise signal of 100pixel MPPC at 25 degree.
Noise rate
MPPC is a noisy photo detector, so the noise rate is one of the important parameter to use actually. 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 .
“ 1p.e noise ”
0.5 p.e = threshold
“ 2p.e noise ”
1 p.e
Noise signal of 100pixel MPPC at 25 degree.
( integrated )
1.5 p.e = threshold

13. Noise rate 1p.e noise rate is about 100~400 kHz.
Blue : 15degree
Green : 20degree
Red : 25degree
Noise rate
Noise rate [ MHz ] 100pixel
Noise rate [ kHz ] 400pixel
400kHz
500kHz
1p.e
2p.e
1p.e noise
2p.e noise
100kHz
100kHz
69.1
69.5 70
Bias voltage [V]
Bias voltage [V]
1p.e noise rate is about 100~400 kHz.
2p.e noise rate is about 0~200 kHz.

14. Noise rate
Noise rate [ MHz ] 100pixel
Noise rate [ kHz ] 400pixel
400kHz
500kHz
1p.e
2p.e
1p.e
2p.e
100kHz
100kHz
0.4 1
1.6 DV DV
1p.e noise rate is a function of both temperature and bias voltage.
Blue : 15degree
Green : 20degree
Red : 25degree
2p.e noise rate seem to be a function of Delta V. This is due to “Cross-talk”.

15. 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.
Neighborhood pixel
Avalanche g
“ Cross-talk “ g

16. Cross-talk rate measurement
The probability of cross-talk is estimated by the number of 1p.e .
The number of pedestal are free to cross-talk
measurement
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.
The cross talk rate is determined.

17. Blue : 15degree
Green : 20degree
Red : 25degree
Cross-talk rate
Cross-talk rate 100pixel
Cross-talk rate 400pixel
50%
50%
10%
10%
Bias voltage [V]
Bias voltage [V]
Cross-talk rate at operation voltage defined by Hamamatsu Photonics(HPK) is about 20% at 20degree. ( We measured within the wider range about bias voltage. )

18. Cross-talk rate Cross-talk rate is a function of Delta V.
Cross-talk rate 100pixel
Cross-talk rate 400pixel
50%
50%
10%
10% 1 2
Delta V DV DV
Cross-talk rate is a function of Delta V.
Blue : 15degree
Green : 20degree
Red : 25degree

19. Photon Detection Efficiency
Photon Detection Efficiency ( = PDE ) is defined as this equation. PDE consists of three elements.
Geometrical Efficiency. A ratio of active area to total area (30%~70%)
Quantum Efficiency of active area (60~80%)
Probability of Geiger discharge (60~80%)
Depending on MPPC type
Depending on wavelength of injected light
Depending on bias V
MPPC have the highest QE in Green light.

20. relative PDE measurement
・only the light going through 1mmφslit is detected.
set up
Moving stage
1mmφslit
・The ratio of MPPC p.e to that of PMT p.e is taken as relative PDE of MPPC.
PMT
Blue LED
MPPC
( total area 1mm2)
PMT made by HPK, type H8643

21. relative PDE PDE is about 2~3 times higher than that of PMT.
Relative PDE 100pixel
Relative PDE 400pixel 3 2 2 1 1
Bias voltage [V]
Bias voltage [V]
Blue : 15degree
Green : 20degree
Red : 25degree
PDE is about 2~3 times higher than that of PMT.

22. relative PDE Relative PDE is a function of Delta V.
Relative PDE 100pixel
Relative PDE 400pixel 3 2 2 1 1 DV DV
Relative PDE is a function of Delta V.
Blue : 15degree
Green : 20degree
Red : 25degree

23. MPPC have the fixed number of pixel
Linearity
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.
The linearity become those equation.

24. Linearity
Linearity 100pixel
Linearity 400pixel
linear
linear
Fired pixel [ % ]
Fired pixel [ % ]
25%
25%
Blue : DATA plot
Green : expectation
Blue : DATA plot
Green : expectation
Injected photoelectron per pixel
Injected photoelectron per pixel
The green line shows the expectation value calculated from number of pixels.
MPPC can operate as linear device.
~25p.e about 100pixel type
~100p.e about 400pixel type.

25. LASER test (using KEK-DTP LASER system)

26. Laser test at KEK, Japan Motivation
Picture of microscope
100μm
microscope
Motivation
・study the response of each pixel of MPPC
Uniformity within 1pixel
Uniformity in each pixel
Laser source
λ=825nm
width 50ps
Laser spot size
　≒10μm
MPPC
Uniformity…
gain
Moving stage
1μm pitch (x , y)
cross-talk rate
efficiency
Feed back this information to HPK

27. Uniformity within 1pixel
efficiency
Sensitive region
Uniformity within 1pixel
Efficiency, Gain
(in sensitive region)
Cross-talk rate
(in sensitive region)
RMS/mean=2%
100pixel
Response within 1 pixels is uniform
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
GAIN
0.25
RMS/mean=2%

28. Uniformity of each pixel
Response of each pixel is uniform
100pixel
efficiency
GAIN
RMS/mean=3%
RMS/mean=3%

29. Summary MPPC has good performance ! 100pixel 400pixel Gain
Noise rate(1p.e) [ kHz ]
Cross-talk rate
PDE
Uniformity
within 1 pixel
of each pixel
uniform
MPPC has good performance !

30. Supplements

31. MPPC ceramic package for T2K
This ceramic package make their alignment by the out side frame.

32. 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. ( measured by M.Taguchi, kyoto university )

33. Set up for measuring linearity
Paper
set up
( to shade off LED light )
MPPC
The number of photons emitted to MPPC are monitored by PMT.
PMT

34. Uniformity within 1pixel
efficiency
Uniformity within 1pixel
400pixel
RMS/mean=1.7%
Cross talk rate
GAIN
0.25
RMS/mean=1.6%

35. Uniformity of each pixel
efficiency
Uniformity of each pixel
RMS/mean=3.4%
400pixel
Cross talk rate
GAIN
0.18
RMS/mean=2.9%