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 µm 20 µm 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 Light Photon Counter Operates at a few Kelvin Hybrid Photodiode Operates 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)10 5 V/cm Drift region: few micron epitaxy layer on low resistive p substrate. Gain ~10 ~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 ~10 6 ), 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 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  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, )

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 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 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 그림 1). 지구에서 관측된 고에너지 입자의 에너지에 따른 분포 (Nagano & Watson 2000). 그림 1 의 y- 축에 E 3 을 곱한 결과이다.

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) ~10 10 particles at Ground from 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-like natural chamber eV

Image of Air-shower on Focal Surface 50 events of eV proton showers are superimposed on the EUSO focal surface with 192 k pixels. x-t viewy-t view 4 simulation X Y time(  sec) photoelectrons Proton E=10 20 eV,  =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 마이크로미 러 광검출기 이동체 Air Shower Micromirrors Control 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  m 2 in size or less Each cell controlled independently Types DMD : Digital, electrostatic actuator, TI Others (Piezoelectric, thermal, membrane, …)

Earth UHECR (10 20 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 ( 발사 ) Extremely Large Transient Sparks 주탑재체

Concept of Zoom & Tracking of KAMTEL Detector image Detector MEMS mirror Array Electronics Hole Trigger Zoom Trigger Mirror : 1-axis on/off Zoom Mirror : 2-axis analog tilting

Trigger mirror Zoom mirror IR camera Detector Spectrophotometer Zoom mirror Trigger mirror Electronics box (Analog, Digital, MEMS driver) Detector (MAPMT) IR camera aperture 한국우주인임무를 위한 극소형 MEMS 우주망원경

Design, Simulation of SiPM for MEMS Telescope

Conduct: Al Resistor: Poly-Si(1MΩ) P+ N+ SiO 2 Epitaxy layer: boron doping Trench: 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 leakage current. Design for SiPM - Cross section

Design of a Micropixel and the connection

<Trench> <Resistor> <Contact> <metal> <Polyimide> Design for SiPM - Mask(7 layers)

32×32 16×16 8×8 2×2 4×4 Design area 4" wafer Design for SiPM- mask

Design for SiPM - Geometrical Efficiency Cell area : 32 ⅹ 35=1120um Sensitive area : 632um –Metal : 8*8+32*3 = 160 –Resistor : 3*21+5.5*3+26*3-2*6.5 = –Trench : 32*3+29*3 = 183 –Total non-sensitive area : Geometrical efficiency(%) = 632.5/1120 *100 = 56.5% Unit : um

Vertical Profile for SIPM Depletion Depth Simulation Study Electric Field

Simulation of Operation Photon Detection Efficiency IV Characteristics

Our 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