SiPM R&D and MEMS Telescope

Shinwoo Nam

Ewha W. University

• SiPM

• MEMS Telescope

• Our R&D of SiPM for MEMS Telescope

SiPM

Silicon Photomultiplier (G-APD, MPPC)

Pixels of the SiPM

42 µm20 µm

1 mm

1 mm

500 ~ 1000 pixels

A SiPM output :

Sum of all pixels

Photon counting

Each pixel :

Independent binary device

working in Geiger Mode

with gain of ~ 10^6

SiPM

Single Photon Counting Sensors

Hamamatsu SiPM

Visible LightPhoton CounterOperates at a few Kelvin

Hybrid PhotodiodeOperates with high bias voltage

SiPM Micropixel Structure

• Breakdown Mode Operation of Micro Cells (PN-junction biased in the reverse direction over the breakdown)

• Avalanche region: 0.7~0.8um between p+ and n+ layer with high electric field (3~5)105 V/cm

• Drift region: few micron epitaxy layer on low resistive p substrate.

• Gain ~106 @ ~50 V working bias• Dark rate(~2 MHz) is originated from ther

mally produced charge carriers.• Electrical decoupling of the pixels by resi

stive strips.• Common Al strips for readout.

Uniformity of the electric field

Silicon Photomultiplier

• Detection efficiency ~25%-60%• Single photon performance (Intrinsic Gain ~106),• Proportional mode for the photon flux

(Dynamic range depends on the number of micropixels 500 ~ 3000),• Fast Time response (rising time ~30 ps), • Operation conditions:

– Low Operational Voltage ~50-60 V,– Room Temperature,– Non Sensitive to Magnetic Field,– Minimum Required Electronics,

• Miniature size and possibility to combine in matrix.• Low cost ( in mass production conditions)

Detection Efficiency

• Quantum Efficiency of Micropixel– wavelength and optical absorption func

tion dependent– UV region of Light is limited by present

technology topology (dead layer on the top),

– IR region of Light is limited by thickness of sensitive layer

• Geometry Efficiency – the technology topology gives the limit

ation of the sensitive area • Breakdown Mode is statistical process

– probability that a photoelectron triggers an avalanche process in Si

The Depletion Area is ~5 m: Low Resistive Si, Low Biase Voltage

SiPM signal

• Signal of Silicon Photomultiplier with preamplifier (Gain 20)

Signal of Silicon Photomultiplier can be readout without Frontend Electronics

LED Signal

Dark rate signal

LED Signal

From V. Saveliev

Silicon Photomultiplier in Magnetic Field

• Silicon Photomultiplier in Strong Magnetic Field

Test of SiPM in Strong Magnetic Field up to 4 Tesla (Amplitude of SiPM signal in magnetic field with different orientations) (V. Saveliev, CALICE Meeting, DESY, 30.01.2004)

Silicon Photomultiplier Noise

• Dark Count Rate – Probability that bulk thermal electrons trigger an avalanche process

(Voltage Dependent) - characterized by frequency– Bias Voltage, Temperature

• The noise signal amplitude – is amplitude of single photoelectron– For the measurement of Photons Flux on the level more than ~ 4-5

photoelectrons this dark current factor can be ignored.

Hamamatsu

Silicon Photomultiplier Crosstalk

• Optic Crosstalk– During avalanche breakdown t

he micropixel emits photons. These photons should not reach nearby cells because this would initiate breakdowns there. – Optical Crosstalk.

Spectrum of Photons emitted during

the Avalanche process in Si

Hamamatsu ->

Silicon Photomultiplier Applications : HEP

• DESY International LInear Collider Group, in particularly Scintillator Tile Hadron Calorimeter Activity

Silicon photomultiplier readout of Scintillator Tile with WLS

Silicon Photomultiplier Applications : Medical Instrument

• Positron Emission Tomography

Silicon Photomultiplier is most promising Photodetector for the Modern Scintillator Material and Medical Imaging Systems

Spectrums of 22Na (511 keV) with LSO

Silicon Photomultiplier Applications : Space

• SiPM in space

Silicon Photomultiplier is most promising Photodetector for the space applicatioin

MEMS Telescope

Cosmic Ray Flux

4

그림지구에서 관측된고에너지입자의에너지에따른분포그림의축에 을곱한결과이다

Extensive Air Shower (EAS)

• Initiated by Hadronic int. of Primary with Air Molecules 1. collimated hadronic core (charged pions source of muons)2. EM subshowers along the axis from pi^0 decays (90% of shower) • ~1010 particles at Ground from 1019 eV primary CR

• Shower Detection - Fluorescence UV photons - Particles (muon,e+,e-,photon) - Cerenkov Radiation

Pierre Auger 1930s

Principle of EUSO :Use whole atmosphere as a detector

TPC-likenaturalchamber1020 eV

Image of Air-shower on Focal Surface

50 events of 1020eV proton showers are superimposed on the EUSO focal surface with 192 k pixels.

x-t view y-t view

4

simulation

X

Y

time(sec)

phot

oele

ctro

ns

Proton E=1020eV, =60º GTU = 2.5 sec

The Focal Surface : PMT -> SiPM

(164PDMs = 0.2M pixels)

2.26 m max

MAPMT(6x6 pixels)

26.2

mm

5900 PMTs on the focal surface!A pixel side = 0.77 km on ground

Idea of MEMS Tracking Mirror Telescope

•Archimedes Mirror : Mirror segments by soldiers•Proposed Mirror : Mirrormirror segments by VLSI

Aberration free focusing, Wide FOV,Fast Tracking capability

VLSI 칩 마이크로미러

광검출기

이동체Air Shower

MicromirrorsControl Circuit

Photodetector

What is MEMS Mirror ?• MEMS (MicroElectroMechanical Systems)

• Recent technological advance in silicon industry

• Originally developed for optical communication & display industry

• Cost effectiveness due to standard silicon fab available

• 100x100 m2 in size or less • Each cell controlled independently

• Types• DMD : Digital, electrostatic actuator, TI• Others (Piezoelectric, thermal, membrane,

…)

Earth

UHECR(1020 eV) fluorescence

Cerenkov

Trigger Detector (poor resolution, wide FOV, PMTs)

Zoom-in Detector (high resolution, narrow FOV, MAPMTs)

MEMS Tracking Mirror Telescope

Concept of MEMSTEL (MEMS Space Telescope)

•MEMS compound mirror reflector•Perfect focusing & Tracking

capability•Small number of

detector/electronics channels

~ 1m x 1m Mirror Array

Size of mirror array: 3 mm x 3 mm

Tilted comb actuator(mirror plate removed)

Torsion spring

Mirror plate

Addressing line (back side view)

Mirror plate and actuator bonding

Mirror plate

8 x 8 mirror mask layout

Fabricated 2-axis Silicon Analog Micromirror (Ewha)

지상으로 치는 일반 번개

Ewha University, Seoul National University, Moscow State University

전리층 (ionosphere)

성층권 (stratosphere)

극한 대기현상의 메가번개

탑재체 : MTEL (MEMS Telescope for Extreme Lightning), 3x3 mm2 aperture

MTEL (Pathfinder)Russian Microsatellite Tatyana-2 (2008.7 발사 )

Extremely Large Transient Sparks

주탑재체

Concept of Zoom & Tracking of KAMTELConcept of Zoom & Tracking of KAMTEL

Detector image

Detector

MEMS mirrorArray

Electronics

Hole

Trigger Zoom

Trigger Mirror : 1-axis on/offZoom Mirror : 2-axis analog tilting

Trigger mirror

Zoom mirror

IR camera

Detector

Spectrophotometer Zoom mirrorTrigger mirror

Electronics box(Analog, Digital, MEMS driver)

Detector (MAPMT)

IR camera

aperture

한국우주인임무를 위한 극소형 MEMS 우주망원경

Design, Simulation of SiPMfor MEMS Telescope

Conduct: Al Resistor: Poly-Si(1MΩ)

P+

N+

SiO2

Epitaxy layer: boron dopingTrench:fill Polyimide

Contact: Al

• Each micropixel is isolated by trench • Resister is formed by Poly silicon.• P+ region of pn junction is a small size than n+ region to reduce le

akage current.

Design for SiPM - Cross section

Design of a Micropixel and the connection

<Trench><Trench><N+ implant><N+ implant>

<Resistor><Resistor> <Contact><Contact> <metal><metal>

<P+ implant><P+ implant>

<Polyimide><Polyimide>

Design for SiPM - Mask(7 layers)

32×32

16×16

8×

82×

2

4×

4

Design area

4" wafer4" wafer

Design for SiPM- maskDesign for SiPM- mask

Design for SiPM - Geometrical EfficiencyDesign for SiPM - Geometrical Efficiency

• Cell area : 32ⅹ35=1120um

• Sensitive area : 632um

–Metal : 8*8+32*3 = 160–Resistor : 3*21+5.5*3+26*3-2*6.5 =

144.5–Trench : 32*3+29*3 = 183–Total non-sensitive area : 487.5

•Geometrical efficiency(%)

= 632.5/1120 *100

= 56.5%

29

32

23

26

3

3

21

3

8

8

4

Unit : um

Vertical Profile for SIPM

Depletion Depth

Simulation StudySimulation Study

Electric Field

Simulation of OperationSimulation of Operation

Photon Detection EfficiencyIV Characteristics

Our first attempt of SiPM fabricationOur first attempt of SiPM fabrication

SiPM wafer in the final process

Photo Mask

Fabrication 55 Steps

Wafer condition

1. Si Substrate * Type/Dopant: P(bor) * Thickness: ~550um * Resistivity: 5ohm.cm 2. Epitaxy * Type/Dopant: P(bor) * Thickness: 5um ± 5% * Resistivity: 1~ 5ohm.cm