www.rmdinc.com erik johnson 1 christopher stapels 1, sharmistha mukhopadhyay 1, paul linsay 1, rory...

www.rmdinc.com

Erik Johnson1

Christopher Stapels1, Sharmistha Mukhopadhyay1, Paul Linsay1, Rory Miskimen2, Skip Augustine3,

and James Christian1

1Radiation Monitoring Devices, Inc., Watertown, MA2University of Massachusetts, Amherst, MA3Augustine Engineering, Encinitas, CA

Support from DOE

Instrument Research & Development Group

Instrument Research& Development

Solid-State Photomultiplier for the PRIMEX PbWO4 Calorimeter

www.rmdinc.com 2 DNP: Oct. 26, 2008

Solid-State Photomultipliers Used for detecting light

pulses from scintillation events.

Array of photodiodes readout in parallel.

Each diode has a binary response to single photons.

The response to each diode is associated with a large gain, providing good signal to noise.

The number of triggered diodes is proportional to the incident light intensity.

Radiation Monitoring Devices, Inc. has built these devices using CMOS technology, which allows integrated circuits on the same silicon die.

0

500

1000

1500

0 100 200 300 400 500

Channel

Cou

nts

1 p.e.

2 p.e.

3 p.e.

4 p.e.

5 p.e.

6 p.e.

7 p.e.

8 p.e.

9 p.e.

10 p.e.

11 p.e.

12 p.e.

13 p.e.

14 p.e.

15 p.e.

16 p.e.


Geiger Photodiodes

SSPMs are built as an array of Geiger Photo-Diodes (GPD).

GPD is a reversed biased photodiode operated beyond the diode breakdown voltage.

Single pixel DE = Quantum Efficiency•Geiger Probability Geiger Probability is the potential of an electron-hole

pair to generate a self-sustained avalanche. Quenching:

Passive: ballast resistor, Rq

Active: Use transistor to drop the voltage to quench the diode.

p-layer

n-layer

Vb

-

+

Optical Photon

Rq


SSPM Design

2 x 2 SSPM array 1.5x1.5mm2 ea. Fill Factor: 61% Gain @ 1 V: 2x106

QEmax: 48% at 520 nm

Number of Pixels: 2024

3 mm

3 mm


Spectral Response

Electronic noise: Small effect (large signal gain) Scintillator: Major contribution Detector: Various factors contribute

Photon detection (statistical fluctuations) Thermally generated dark noise (dark counts) Excess noise (cross-talk, after pulsing) SSPM Statistics

2

Detector

2

orScintillat

2

Electronic

2

EEEEEEEE

Energy Resolution:

0 500 1000 15000.0

0.5

1.0

1.5

2.0

2.5 CsI(Tl)

3 x 3 x 3 mm3

22Na12.4 % FWHM @ 511 keV

T = 0 oC

Nor

mal

ized

Cou

nts

Energy (keV)


Detection Efficiency

guard ring

p-substrate

n+ p+

n-well

p-substrate )()(, XgX VPQEVDE

300 400 500 600 700 8000

10

20

30

40

50

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1

Qu

an

tum

Effi

cie

ncy

(%

)

Wavelength (nm)

2

Re

lativ

e P

WO

4 Em

issi

on

0 2 4 6 8 10 12 140

20

40

60

80

100

120

Ge

ige

r P

rob

ab

ility

(%

)

Excess Bias (V)

632 nm 420 nm

Junction is fully depleted, QE ~ independent of excess bias. Electron and hole ionization rates are different. Geiger probability is dependent on whether electron or hole

creates the avalanche.

1. Nuclear Instruments and Methods in Physics Research A 376 (1996) 319-3342. IEEE Transactions on Nuclear Science, 55, 3 (2008) 1289-1294


Standard Noise SourcesCross Talk

Adjacent pixels trigger due to hot-carrier emission.

After PulsingGeiger pulses due to trapped

carriers.

0 2 4 6 8 100

100

200

300

Da

rk C

ou

nt R

ate

(H

z/m

2 )

Excess Bias (V)

T = 22 oC

0 2 4 6 8 10

1.00

1.02

1.04

1.06

1.08

1.10

Afte

r P

ulse

Mu

ltip

lier

Excess Bias (V)

T = 22 oC

Dark CountsThermally excited carriers

inducing an avalanche.

Magnitude of the noise sources Fluctuations due to these sources effect the noise. Fluctuation is proportional to the magnitude Dark counts are handled with Poisson statistics. Cross talk and after pulsing are handled as excess noise terms.

All sources increase with excess bias.

0 1 2 3 4 5 6 7 8 9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

Cro

ss T

alk

Mul

tiplie

r

Excess Bias (V)

T = 22 oC


250 260 270 280 290 300 310 3200

20

40

60

80

100

120

140

160

Da

rk C

ou

nt R

ate

(H

z/m

2 )

Temperature (K)

Vx = 5 V

Maxwell-Boltzmann

DCR = n*e-E/kT

Temperature DependenceCross Talk

Adjacent pixels trigger due to hot-carrier emission.

After PulsingGeiger pulses due to trapped

carriers

250 260 270 280 290 300 310 3200.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

Afte

r P

uls

e M

ulti

plie

r

Temperature (K)

Vx = 5V

Dark CountsThermally excited carriers

inducing an avalanche.

Decreases Dark counts: thermal excitation is suppressed. Cross talk: hot carrier emission is reduced. (Preliminary)

Increase in after pulsing Longer trap life times Mitigated by two effects

• Fast scintillators (integration times): sample fewer after pulses.• Noise is affected by fluctuations in output charge: the charge from after pulses is

smallest near the initial pulse in time.

250 260 270 280 290 300 310 320

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

Cro

ss T

alk

Mul

tiplie

r

Temperature (K)

Vx = 5V


Non-Linear Behavior

0 500 1000 15000

5000

10000

15000

20000

Cou

nts

Energy (keV)

FWHM = 22% • 22Na • LYSO: 1.5 x 1.5 x 3 mm3

• Few Pixels• Illustration of Saturation

Effect

Non-linear response of SSPM.

Non-linear transformation between number of triggered pixels and event energy.

Account for non-linear response for accurate energy resolution

An “effective integration time” may effectively increase the total number of pixels in the SSPM

0 200 400 6000

200

400

600

800

1000

1200

1400 Na-22

1275 keV

511 keV (12.1% FWHM)

Cou

nts

Pixels Triggered

0 5k 10k 15k 20k 25k 30k0

59

117

176

234

293

351

410

468

<

Trig

gere

d P

ixel

s>

Light Intensity (photons)

Max. Pixels = 441


SSPM Statistics

0 10000 20000 300000

5

10

15 Measured w/o noise w/ noise

Wid

th in

Pix

els

Trig

gere

d (1)

Light Intensity

2

2 1

t

dark

t

ttl

t

SSPMt

n

n

n

n

n

n

Fnt

Excess NoiseCross-talkAfter Pulsing

BinomialSSPM Statistics

Poisson Dark Counts

Pulsed Laser: 635-nm: ~5 ns wide

2

22

Detector

1

t

dark

tSSPM

t

nE

n

n

nF

nEt

Poisson – Good approximationin Linear Response Region

Energy resolution affected by SSPM statistics when event triggers > 30% of total pixels

The distribution function for the SSPM has a lower and upper bound: Use binomial statistics.


Core Design Energy Resolution

2 V Excess Bias Not Optimized T = 0 °C

0 500 1000 15000.0

0.5

1.0

1.5

2.0

2.5 CsI(Tl)

3 x 3 x 3 mm3

22NaFWHM @ 511 keV

SSPM 12.4 % PMT 11.7 %

Nor

mal

ized

Cou

nts

Energy (keV)

300 400 500 600 700 8000

10

20

30

40

50

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

CsI

Qu

an

tum

Effi

cie

ncy

(%

)

Wavelength (nm)

PWO4

Re

lativ

e E

mis

sio

n

PWO4: 38.2%

CsI: 38.4%


All-Digital SSPM All-Digital SSPM Pixel-level comparator

(signal processing) & active quenching qSSPM Vx(T): (Linear) Fill factor trade-off (reflected

light recovery) Provide feedback to make

excess bias constant qSSPM is constant

16% Fill Factor 400 pixels per quadrant Testing in progress Feedback Pixel

xJtrigSSPM VCNq


Plans for PRIMEXPhase-I Task List

Determine the detector and readout requirements for the photodetector and ADC.

Establish a robust readout protocol for monolithic integration of detector channels.

Examine temperature dependences for SSPMs and PMTs.

Develop external ADC modules with temperature compensation.

Evaluate performance of ADC unit when coupled to PMT and SSPM.

Provide a cost analysis of design options. Develop design concepts for SSPM integrated with

an ADC. Write Phase I report and Phase II proposal.

Key Task Evaluate at RMD using 60Co

source. Packaging: light tight and cooled Ship to Jefferson Lab for test

beam evaluation. Recently Started Phase-II proposal due mid-March

PbWO4

SSPM

PMT Cooled and Dry Vessel


Cost AnalysisResearch Prototype Intermediate Production

20 x 20 m2 pixel

50k pixel device

8.2 x 8.2 mm2 Device Size

2 133 1333

Part or Process per Unit Costs

SSPM $5,000 $75 $8

Design and Layout $10,000 $0 $0

CMOS Mask Set Included $675 NRE $0

Packaging Included $75 $8

PCB $100 $50* $5 - $50

Data Interface $650 (ADI: HSC-ADC-EVALCZ) $6* (USB Interface) $6

ADC $220 (ADI: AD9230-250EBZ) $60* (ADI: AD9230BCPZ-250) $0† - $60

Power Supply Regulator $50 $12* $0†

Voltage Supply (AC Adapter) $10 $10 $10

Assembly $800 $50 $10

Total per Device $17,130 $1013 $47 - $152

• Costs are in US Dollars and are best estimates* Bulk purchase reduction † Inclusion in the CMOS layout Photodetector and power supply


Summary

Solid-State Photomultipliers Compact High Gain CMOS: Integrated Signal Processing Low Cost Provide PMT-like Energy Resolution

Future Plans Evaluation at RMD with test sources Evaluation at JLab Provide a more complete cost analysis (compare PMT to

SSPM with integrated signal processing).


Application with SSPMs

0 500 1000 15000.0

0.5

1.0

1.5

2.0

2.5 CsI(Tl)

3 x 3 x 3 mm3

22Na12.4 % FWHM @511 keV

No

rma

lize

d C

ou

nts

Energy (keV)


Temperature Dependence Accommodate large temperature range for useful device

TVVTCTVVPQENq BAJBAGttlSSPM )(

Breakdown voltage, VB

Proportional to temperature (~50mV per °C) Excess bias inversely proportional.

PG is proportional to the excess bias. (~9% per V)

Junction Capacitance, CJ (Preliminary) Inversely proportional to temperature (0.5fF per °C)

Constant applied bias, temperature decreases: Number of pixels increases Output charge per pixel increases

32 TTCTVq JXSSPM Junction CapacitanceGeiger Probability Excess Bias, Vx


Device Conditions

2k

…

- Vb +

substrate

Preamp

Pulser

220 pF

ShapingAmp

MCA

Quadrant PixelC (fF)

PixelR

(k)

Recharge Time (ns)

Q1 130 160 21

Q2 270 250 67

Q3 330 290 96

Q4 170 200 34t

V

RC

t

V CVxVx

10 nF

Not Needed

Used for Signal Integration


Electron/Hole Ionization

IEEE Transactions on Nuclear Science, 19, 9 (1972) 1056-1060

www.rmdinc.com erik johnson 1 christopher stapels 1, sharmistha mukhopadhyay 1, paul linsay 1, rory...

Documents

dark noise dark

excess noise crosstalk

noise sources fluctuations

calorimeter slide

magnitude dark counts

excess noise terms

pulsing geiger pulses

trapped carriers dark