Download MEMS telescope

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)
1 mm
SiPM
42 µm
20 µm
1 mm
500 ~ 1000 pixels
Pixels of the SiPM
Each pixel :
A SiPM output :
Independent binary device
Sum of all pixels
working in Geiger Mode
 Photon counting
with gain of ~ 10^6
Single Photon Counting Sensors
Visible Light
Photon Counter
Operates at a few Kelvin
Hybrid Photodiode
Operates with high
bias voltage
Hamamatsu SiPM
SiPM Micropixel Structure
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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
thermally produced charge carriers.
Electrical decoupling of the pixels by
resistive 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
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Quantum Efficiency of Micropixel
– wavelength and optical absorption
function 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
limitation of the sensitive area
Breakdown Mode is statistical process
– probability that a photoelectron triggers
an avalanche process in Si
The Depletion Area is ~5 mm: Low Resistive Si, Low Biase Voltage
SiPM signal
• Signal of Silicon Photomultiplier
with preamplifier (Gain 20)
Dark rate signal
LED Signal
LED Signal
From V. Saveliev
Signal of Silicon Photomultiplier can be readout without Frontend Electronics
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
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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
the 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
Spectrums of 22Na (511 keV) with
LSO
Silicon Photomultiplier is most promising Photodetector for the Modern
Scintillator Material and Medical Imaging Systems
Silicon Photomultiplier Applications : Space
• SiPM in space
Silicon Photomultiplier is most promising Photodetector for the space
applicatioin
MEMS Telescope
Cosmic Ray Flux
4
Extensive Air Shower (EAS)
Pierre Auger
1930s
• 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
Principle of EUSO :
Use whole atmosphere as a detector
1020 eV
TPC-like
natural
chamber
Image of Air-shower on Focal Surface
x-t view
y-t view
photoelectrons
Y
simulation
X
1020eV
50 events of
proton
showers are superimposed
on the EUSO focal surface
with 192 k pixels.
time(msec)
Proton E=1020eV, =60º
GTU = 2.5 msec
4
The Focal Surface : PMT -> SiPM
(164PDMs = 0.2M pixels)
2.26 m max
5900 PMTs on the focal surface!
A pixel side = 0.77 km on ground
26.2 mm
MAPMT
(6x6 pixels)
Idea of MEMS Tracking Mirror Telescope
Air Shower
이동체
광검출기
Photodetector
VLSI 칩
Micromirrors
Control Circuit
마이크로미
러
•Archimedes Mirror : Mirror segments by soldiers
•Proposed Mirror : Mirrormirror segments by VLSI
Aberration free focusing, Wide FOV,
Fast Tracking capability
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 mm2 in size or less
• Each cell controlled independently
• Types
• DMD : Digital, electrostatic actuator, TI
• Others (Piezoelectric, thermal, membrane, …)
Concept of MEMSTEL (MEMS Space Telescope)
• MEMS compound mirror reflector
• Perfect focusing & Tracking
capability
• Small number of
detector/electronics channels
UHECR
(1020 eV)
fluorescence
~ 1m x 1m
Mirror Array
Trigger Detector
(poor resolution,
wide FOV, PMTs)
Zoom-in Detector
(high resolution,
narrow FOV, MAPMTs)
Cerenkov
Earth
MEMS Tracking
Mirror Telescope
Fabricated 2-axis Silicon Analog Micromirror (Ewha)
Size of mirror array:
3 mm x 3 mm
Torsion spring
Tilted comb actuator
(mirror plate removed)
Mirror plate
8 x 8 mirror mask layout
Mirror plate
Mirror plate and actuator
bonding
Addressing line
(back side view)
MTEL (Pathfinder)
Russian Microsatellite Tatyana-2
(2008.7 발사)
탑재체 : MTEL (MEMS
Telescope for Extreme
Lightning),
3x3 mm2 aperture
주탑재체
전리층 (ionosphere)
극한 대기현상의 메가번개
Extremely Large
Transient Sparks
성층권 (stratosphere)
지상으로 치는 일반 번개
Ewha University, Seoul National University, Moscow State University
Concept of Zoom & Tracking of KAMTEL
MEMS mirror
Trigger Array
Detector
Electronics
Zoom
Hole
Trigger Mirror :
1-axis on/off
Zoom Mirror :
2-axis analog tilting
Detector image
한국우주인임무를 위한 극소형 MEMS 우주망원경
Spectrophotometer
Zoom mirror
Detector
IR camera
Trigger mirror
Detector (MAPMT)
IR camera
Trigger mirror
Zoom mirror
aperture
Electronics box
(Analog, Digital, MEMS driver)
Design, Simulation of SiPM
for MEMS Telescope
Design for SiPM
Conduct: Al
SiO2
- Cross section
Contact: Al
Resistor: Poly-Si(1MΩ)
N+
P+
Epitaxy layer: boron doping
Trench:
fill Polyimide
• 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
leakage current.
Design of a Micropixel and the connection
Design for SiPM - Mask(7 layers)
<N+ implant>
<P+ implant>
<Resistor>
<Contact>
<metal>
<Trench>
<Polyimide>
2×2
4×4
8×8
Design for SiPM- mask
16×16
Design area
4" wafer
32×32
Design for SiPM - Geometrical Efficiency
29
3
23
• Cell area :
32ⅹ35=1120um
3
• Sensitive area : 632um
26
32
3
8
4
8
Unit : um
– 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%
21
Simulation Study
Depletion Depth
Electric Field
Vertical Profile for SIPM
Simulation of Operation
IV Characteristics
Photon Detection Efficiency
Our first attempt of SiPM fabrication
Wafer condition
Photo Mask
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
Fabrication 55 Steps
SiPM wafer in the final process