Study of the MPPC Performance

- contents -• Introduction• Fundamental properties• microscopic laser scan

– check variation within a sensor

• Summary and plans

Sep-29 2006 France-Japan Joint MeetingSatoru Uozum T. Maeda, H. Yamazaki, Y. Sudo

for the GLD Calorimeter group

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~ 1 mm

20~100 m

Depletion region ~ 2 m

~ 8 m

Substrate

1600 pixels

400 pixels

substrate p+

p-

Guard ring n-

Al conductorp+ n+

Si Resistor Bias voltage (~70V)

The Multi-Pixel Photon Counter (MPPC)

… novel type photon sensor being developed by Hamamatsu

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Required performance for the GLD Calorimeter

• Gain: ~ Best to have 106 , at least 105

• Dynamic range: can measure ~1000 p.e.– satisfactory to measure EM shower maximum– need > 2500 pixels

• Photon Detection Efficiency ~ 30 %– to distinguish MIP signal

• Noise rate : < 1 MHz (threshold = 0.5 p.e., threshold =1.5 p.e is also acceptable) • good uniformity, small cross-talk• Timing Resolution ~ 1 nsec

– Necessary for bunch ID, slow neutron separation• Sensor area: 1.5 x 1.5 mm

– to put more number of pixels• Should be stable against bias voltage / temperature / time

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• To achieve our goal, we are studying basic properties of the MPPC collaborating with Hamamatsu.

• Now we are measuring performance of the latest 1600 pixel MPPC sample.

• Based on its results, we provide feedback to Hamamatsu to have improved samples.

Our R&D Status

Evaluate performance of the MPPC prototypes

Provide feedback to HPK

Improved samples from HPK

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Basic Properties of the 1600 pixel MPPC• Check fundamental performance against bias voltage

– Gain, Noise Rate, Cross-talk probability– Photon Detection Efficiency, Response curve

(measurements still ongoing)• Temperature dependence is also measured

– MPPC performance is known to be sensitive to temperature

Thermostatic Chamber

Green LED MPPC

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Gain measurement

)( oBias VVe

CGain

・30℃・25℃・20℃・15℃・10℃・ 0℃・ -20℃

d

eA

dSGain

S : ADC sensitivity = 0.25 pC/ADCcount

A : Amp gain = 63e : electron charge = 1.6 x10-19 C

C : Pixel capacityV0: Breakdown voltage

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C, V0 against Temperature

V0 = aT +b

a = (5.67 ± 0.03) x10-2

b = 66.2 ± 0.1

• C looks not sensitive to temperature in under < 20oC

• V0 is linear to temperature

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Noise Rate … rate of fake avalanche signal induced by thermal electrons

Over voltage [V] = Vbias – V0(T)

・30℃・25℃・20℃・15℃・10℃・ 0℃・ -20℃

Lower temperature Lower noise rate

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Cross-talk

• Cross-talk probability looks stable with temperature in over voltage < 2.5V.

.).5.0(

.).5.1(

epRate

epRatePcrosstalk

・30℃・25℃・20℃・15℃・10℃・ 0℃・ -20℃

Over voltage [V] = Vbias – V0(T)

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Cross-talk to adjacent pixelsis caused by photons created inan avalanche.

Cross-talk probability ismeasured from dark noise rates :

Measurement with Microscopic Laser

１６００ pixel MPPC

• YAG Laser, = 532 nm (green)

• Pulse width ~ 2 nsec, rate ~ 8 kHz

• Spot size ~ 1 m

• Light yield = 0~1 p.e. (reduced by filters)

• Can perform precise pinpoint scan with the well-focused laser

~25m

Laser spot（ before inserting filters ） 10

Using the laser, we perform

• scan within a pixel

• pixel-by-pixel scan

to see the variation of

• Gain

• Photon Detection Efficiency

• Cross-talk

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)(

.).5.0(

allN

epNEfficiency

ev

ev

Efficiency v.s. Bias Voltage• Inject laser to center of a pixel.

The efficiency depends on bias voltage,but is stabilized in Vbias > 70 V.

Pedestal

１ pix. fired

2 pix. fired (cross-talk)

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Efficiency Variation within a Pixel

• Fraction of sensitive region ～ 20%• Variation within a sensitive region

~9.2%

1 pixel

• The shape of sensitive region is not changed with bias voltage

Bias voltage・ -71.0V・ -70.0V・ -69.5V・ -69.0V

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Gain Variation within a PixelGain (x105)

•Center part have higher gain•Gain variation in a sensitive region ~ 2.7%

y-point (1 m pitch)

x-point (1 m pitch)

Edge of a sensor

Vbias = 70.0 V

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Cross-talk within a Pixel

.)2(.)1(

.)2(

pixNpixN

pixNP

evev

evXtalk

• Shape of the cross-talk probability depends on bias voltage• Edge part show larger cross-talk

Bias voltage

・ -71.0V・ -70.0V・ -69.5V

・ -6９ .0V

Sensitive region in a pixel

Pedestal

１ pix. fired

2 pix. fired (cross-talk)

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Pixel-by-pixel Scan• Scan pixels in quadrant of a sensor

(The quadrant is divided into 4 sub-regions for some technical reasons)

• Inject laser at the center of each pixel

20 x 20 pixels

Sensor

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Pixel-by-pixel Scan - Efficiency

0.44

0.55

edge of a sensor

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Total variation ~4.0 ％

Pixel-by-pixel Scan - Gain

3.2(x105)

3.8 (x105)

edge of a sensor

• Edge pixels have

higher gain• Strange oblique

structure is seen, reason unknown

Total variation ~3.2 ％

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Summary• We are evaluating the MPPC performance from the vi

ewpoint of the GLD calorimeter readout use• The MPPC properties are sensitive to over voltage

(=Vbias-V0(T)), thus affected by temperature changeNeed of accurate voltage / temperature control• As a result of the microscopic laser scan, the MPPC p

roperties are observed to be uniform within a sensor.

• Measure P.D.E. and Response curve (Input light yield v.s. output pulse height), I-V curve

• Figure out device-by-device variation– 20 samples will be delivered in next week

Plans

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