Backside Illuminated Drift Backside Illuminated Drift Silicon Photomultiplier Silicon Photomultiplier BID- -SiPM SiPM BID Jelena Ninkovic Ninkovic Jelena on behalf of the BID SiPM group* group* on behalf of the BID- -SiPM *MPI for Physics: J. Ninkovi ć , C. Merck, R. Mirzoyan, R. Richter, H.G. Moser, A. Otte, M. Teshima, G. Valceanu *PNSensor: R. Eckhart, G. Lutz, R. Hartmann, P. Holl, C. Koitsch and H. Soltau.
Outline Outline � Motivation Motivation � � Concept of the BID Concept of the BID- -SiPM SiPM � � First measurements of the test structures First measurements of the test structures � � Future plans Future plans � Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 2 Jelena Light 07, 2
Gamma Ray Astronomy Gamma Ray Astronomy Gamma Ray induces electromagnetic cascade relativistic particle shower in atmosphere Cherenkov light High QE photo sensors!!! fast light flash (nanoseconds) 100 photons per m² (1 TeV Gamma Ray) MAGIC: world largest air Cherenkov telescope http://wwwmagic.mppmu.mpg.de/ 30° 30° ≈ ≈ ≈ ≈ Fluorescence in the atmosphere 400 km 400 km ≈ ≈ EECR EECR JEM - EUSO Atmosphere Atmosphere Fluorescence Fluorescence Č erenkov Č erenkov 230 km 230 km Earth Earth M .C .M . M .C .M . ‘02 ‘02 Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 3 Jelena Light 07, 3
SiPM SiPM Conventional SiPM - an array of avalanche photo diodes operated in Geiger mode avalanche regions photon Si Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 4 Jelena Light 07, 4
BID- -SiPM SiPM BID Conventional SiPM - an array of avalanche photo diodes operated in Geiger mode avalanche regions photon Si BID SiPM – combined principle of avalanche photodiode and drift diode photon path of the photo electron depleted bulk avalanche regions Si 50µm … 450µm output Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 5 Jelena Light 07, 5
BID- -SiPM SiPM BID Zoom to a single cell photon drift path of the photo electron shallow p + n type depleted bulk 50 ... 450 µm µm drift rings p + deep n deep p + n + Modulated avalanche region avalanche region quenching resistor output line 100 µm G. Lutz et al., IEEE Trans.Nuc. Sci., 52, (2005) 1156-1159. G. Lutz et al., Proc.Int. Con. New Dev. Photodet., Beaune 2005, to be published in NIM A. Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 6 Jelena Light 07, 6
Pro & Con Pro & Con Advantages: Advantages: Unstructured thin entrance window Unstructured thin entrance window • • 100% fill factor 100% fill factor • • High conversion efficiency (especially at short wavelength) High conversion efficiency (especially at short wavelength) • • Lateral drift field focuses electrons into high field region Lateral drift field focuses electrons into high field region • • High Geiger efficiency (always electrons trigger breakdown) High Geiger efficiency (always electrons trigger breakdown) • • Small diode capacitance (short recovery, reduced x- -talk) talk) Small diode capacitance (short recovery, reduced x • • Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 7 Jelena Light 07, 7
BID- -SiPM radiation entrance window SiPM radiation entrance window BID Non-structured backside allows engineering of the radiation entrance window Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 8 Jelena Light 07, 8
Geiger Efficiency of electrons and holes Geiger Efficiency of electrons and holes Avalanche Efficiency (1 μ m high field region) Electrons have a higher probability to trigger an 1 Efficiency avalanche breakdown 0.9 then holes 0.8 0.7 Electrons Efficiency depends on 0.6 Holes depth of photon 0.5 conversion and hence 0.4 on the wavelength 0.3 0.2 Solutions: 0.1 - Increase overvoltage 0 250000 350000 450000 550000 650000 750000 Or: Field (V/cm) - Ensure that only electrons trigger an avalanche n+ p+ holes el. p+ n+ el. p - epi n - epi holes p-substrate n-substrate Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 9 Jelena Light 07, 9
Sensitivity at different wavelengths Sensitivity at different wavelengths 10000 1000 light absorption in Silicon Absorption length ( μ m) 100 10 Electrons trigger avalanche 1 0.1 Holes trigger Example: avalanche p-substrate holes electrons 0.01 Thin entrance window needed 0.001 250 450 650 850 1050 Wavelength (nm) p-substrate: photons < 450 nm: only holes contribute photons > 700 nm: lost in insensitive bulk n-substrate: ok for short wavelengths, hole efficiency dominates for λ > 500 nm Back illumination: whole thick (> 50 μ m) bulk absorbs photons design for electron collection Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 10 Jelena Light 07, 10
Pro & Con Pro & Con Advantages: Advantages: Unstructured thin entrance window Unstructured thin entrance window • • 100% fill factor 100% fill factor • • High conversion efficiency (especially at short wavelength) High conversion efficiency (especially at short wavelength) • • Lateral drift field focuses electrons into high field region Lateral drift field focuses electrons into high field region • • High Geiger efficiency (always electrons trigger breakdown) High Geiger efficiency (always electrons trigger breakdown) • • Small diode capacitance (short recovery, reduced x- -talk) talk) Small diode capacitance (short recovery, reduced x • • Disadvantages: Disadvantages: Large volume for thermal generated currents ( � � increased dark rate) increased dark rate) Large volume for thermal generated currents ( • • Maintain low leakage currents aintain low leakage currents M • • Cooling Cooling • • μ m instead of 450 μ m) Thinning ( < 50 μ m instead of 450 μ Thinning ( < 50 m) • • Large volume for internal photon conversion ( � � increases x increases x- -talk) talk) Large volume for internal photon conversion ( • • Lower gain (small diode capacitance helps) Lower gain (small diode capacitance helps) • • μ m instead of 450 μ m) Thinning ( < 50 μ m instead of 450 μ Thinning ( < 50 m) • • Possible show stopper! Possible show stopper! Electron drift increases time jitter Electron drift increases time jitter • • Small pixels, Small pixels, • • Increased mobility at low temperature <2 ns possible Increased mobility at low temperature <2 ns possible • • Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 11 Jelena Light 07, 11
Design of Devices Design of Devices Hexagonal Cells 100-200 μ m diameter 3 drift rings Central HF region with 8 μ m diameter Capacitance ~ 12 fF Gain: O(10 5 ) ~ 1 μ m depth 95% Geiger efficiency @ 8V overvoltage (electrons) Drift field extends into bulk Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 12 Jelena Light 07, 12
Test structure production in 2005/06 Test structure production in 2005/06 -> fix parameters of avalanche cell (radius, depth, resistor values…) -> no backside illumination yet Single pixel structures Small arrays Large arrays (20 x 25 pixel 180 μ m pitch) HF diameter: 5-25 μ m Successfully tested 6000 5000 5860 4000 5185 Coincidence 4510 3000 3835 Y Axis [ μ m] 3160 2000 2485 1810 1000 1135 460,0 0 18,850 18,855 18,860 18,865 18,870 18,875 X Axis [mm] 1,940 18,880 1,935 1,930 1,925 18,885 1,920 18,890 1,915 1,910 18,895 1,905 Y Axis [m m ] 1,900 18,900 1,895 18,905 1,890 1,885 Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 13 Jelena Light 07, 13
Test structures Test structures Breakdown voltage were expected from simulations Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 14 Jelena Light 07, 14
Test structures Test structures � Homogeneity Homogeneity � Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 15 Jelena Light 07, 15
Test structures Test structures � Stress conditioning Stress conditioning � Jelena Ninkovic Ninkovic Light 07, Ringberg Ringberg Castle Castle, Tegernsee, 23 , Tegernsee, 23- -27 September 2007 27 September 2007 16 Jelena Light 07, 16
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