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Edgeless semiconductor sensors for large-area pixel detectors Marten Bosma Annual meeting Nikhef December 12, 2011, Amsterdam
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Outline Introduction to Medipix detectors From single assembly to large-area detectors Edgeless sensors: –Active-edge –Slim-edge December 12, 20111 Marten Bosma, Nikhef annual meeting, Amsterdam
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Hybrid pixel detector December 12, 20112 Marten Bosma, Nikhef annual meeting, Amsterdam Semiconductor sensor: Silicon, gallium arsenide, cadmium telluride Read-out chip: Medipix, Timepix, Medipix3 Bump bonds: Copper/tin, Indium/tin 300 μm – 1mm 20 – 70 μm 200 – 700 μm
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Why Medipix ? Photon counter –High signal-to-noise ratio –Noise rejection High functionality per pixel –Timepix: counting, ToT, ToA –Threshold equalisation –Dark current compensation December 12, 20113 Marten Bosma, Nikhef annual meeting, Amsterdam
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Medipix3 – Tomorrow’s digital radiography ? December 12, 2011 Marten Bosma, Nikhef annual meeting, Amsterdam 4 Medipix3 features ~1600 transistors per pixel: Charge summing circuitry Simultaneous counting and read-out → no dead time Energy dispersive mode: 7 energy bands Medipix3 pixel layout
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Mono-crystalline sensors vs. amorphous selenium December 12, 20115 Marten Bosma, Nikhef annual meeting, Amsterdam a-SeGaAsCdTeSi Z 3431;3348;5214 e - mobility (cm 2 /Vs) 3*10 -3 850011001500 h + mobility (cm 2 /Vs) 1*10 -1 400100450 Eh-pair creation energy (eV) 20 – 504.264.433.6
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2.8 cm Active detector area December 12, 20116 Marten Bosma, Nikhef annual meeting, Amsterdam 35 x 40 cm 2 Medipix quad module with Relaxd read-out x 200 3 inch X-ray imaging: –Digital radiography detectors High-energy physics: –Close-to-beam/forward physics experiments (TOTEM, LHCb Velo)
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Tile-ability December 12, 2011 Marten Bosma, Nikhef annual meeting, Amsterdam 7
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Wire bond → Through-silicon-via December 12, 20118 Marten Bosma, Nikhef annual meeting, Amsterdam Bond padDi-electric LandConductive pathway Through-silicon-via
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Tile-ability: MPX3 pixel-to-edge distance December 12, 20119 Marten Bosma, Nikhef annual meeting, Amsterdam Courtesy of PANalytical
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Tile-ability: Sensor edges December 12, 2011 Marten Bosma, Nikhef annual meeting, Amsterdam 10 Rossi, “Pixel Detectors” Slim edgeActive edge Edge effects: Charge generation Surface currents High-field regions Conventionally solved by guard rings
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Active-edge silicon December 12, 201111 Marten Bosma, Nikhef annual meeting, Amsterdam
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Active-edge silicon: DRIE/ICP + edge doping December 12, 2011 Marten Bosma, Nikhef annual meeting, Amsterdam 12
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Leakage current December 12, 201113 Marten Bosma, Nikhef annual meeting, Amsterdam Blade dicing Etching
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December 12, 201114 Marten Bosma, Nikhef annual meeting, Amsterdam Relaxd read-out interface: 4 detector assemblies in parallel up to 100 frames per second
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Active-edge silicon: Flood-field image December 12, 201115 Marten Bosma, Nikhef annual meeting, Amsterdam
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Active-edge silicon: Laser setup December 12, 201116 Marten Bosma, Nikhef annual meeting, Amsterdam λ 660 nm 980 nm 1060 nm Back face Pixel plane
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Laser data: Edge sensitive volume – 660 nm December 12, 201117 Marten Bosma, Nikhef annual meeting, Amsterdam 1 μm steps -22 μm Indicates VERY small insensitive edge (Spot radius = 20 μm) Effective size of Pixel 1 to 4: 4.62 pixels → {physical width – effective width} = 256.5 μm – 4.62/4 * 220 μm = 2.4 μm insensitive edge 256.5 μm
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Beam test setup - telescope December 12, 201118 Marten Bosma, Nikhef annual meeting, Amsterdam DUT Courtesy of R. Plackett 120 GeV/c muons and pions Longitudinal
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Beam data: Long trails Beam December 12, 2011 Marten Bosma, Nikhef annual meeting, Amsterdam 19 ~ 3 cm RIGHTLEFT
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Beam data: Depth dependence of ToT December 12, 201120 Marten Bosma, Nikhef annual meeting, Amsterdam Beam
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Beam data: Depth dependence of ToT December 12, 201121 Marten Bosma, Nikhef annual meeting, Amsterdam
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Slim-edge CdTe & GaAs December 12, 201122 Marten Bosma, Nikhef annual meeting, Amsterdam
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December 12, 201123 Marten Bosma, Nikhef annual meeting, Amsterdam Detector: 9 slim-edge CdTe pieces Detector readout: Medipix-MXR Sensor specs (Acrorad): Quasi-Ohmic (Pt electrodes) 4.05 x 4.05 x 1 mm 3 36 x 36 pixels of (110 μm) 2 65 μm pixel-to-edge distance
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Laser data: charge collection efficiency December 12, 201124 Marten Bosma, Nikhef annual meeting, Amsterdam Centre pixel: (μτ) e = 1.25 E-4 Edge pixel: (μτ) e = 1.15 E-4 Fit function described by Hecht relation: Q(U) = Q 0 μτ/L 2 (U – U 0 ) [1 – exp(dL/μτ(U – U 0 )]
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December 12, 201125 Marten Bosma, Nikhef annual meeting, Amsterdam The leakage current as a function of time after voltage stepping (-200V → 200V → -200V). The current was monitored for one minute per voltage step of 40V Possibly caused by deep–level defects GaAsCdTe
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High-Z sensor issues December 12, 201126 Marten Bosma, Nikhef annual meeting, Amsterdam General : Material homogeneity and area Grain boundaries – want single crystal Fluorescence Degrades spatial and energy resolution above k-edge CdTe: Only 3” wafers, even smaller dies tellurium inclusions hole trapping/polarisation GaAs: Better single-crystal production (6”) Problem is defects! Shallow defects prevent depletion Carrier lifetimes Te inclusions Edge effect CdTe GaAs
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Polarisation December 12, 2011 Marten Bosma, Nikhef annual meeting, Amsterdam 27 Non-polarising detector Polarising detector Mobility μ (cm 2 /Vs) Lifetime τ (s) μτ-product (cm 2 /V) Electrons1100~3×10 -6 3×10 -3 Holes100~2×10 -6 2×10 -4 Schubweg: λ e/h = μ e/h × τ e/h × E Φ critical ≈ 10 9 ph/mm 2 s Silicon: μτ e/h ≥ 1
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Summary Medipix + mono-crystalline high-Z sensors… … have great potential! However, limited active area… edgeless needed! Active-edge silicon: Factor 10 decrease in pixel-to-edge distance. Sensitive edge very close to physical edge. Slim edge high-Z: (Deep-level) defects and poor hole transport. First results indicate edges may not affect charge collection efficiency and noise performance December 12, 201128 Marten Bosma, Nikhef annual meeting, Amsterdam
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December 12, 201129 Marten Bosma, Nikhef annual meeting, Amsterdam High-energy nuclear interactions with Schottky CdTe. Multipixel-spread splashes, possibly due to polarisation or a cascade of fluorescence effects (?) Bias-voltage and interaction-depth dependence under study. Thank you
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