3D silicon: The future of radiation-hard silicon sensors ?
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3D silicon: The future of radiation-hard silicon sensors ? Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Outline ● Introduction: Silicon detectors for HEP ● ● ● ● Short interlude: Signal induction in ionization detectors 3D silicon sensors – what is new? Features of 3D sensors ● Radiation hardness ● Active edge ● Other special properties Proposed applications Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Silicon detectors for HEP ● Readout electrode l ona diti sor Tra sen nar pla Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros track Basic idea: Passing particle ionizes the material. Collect electrons and holes => signal! Readout electrode Particle ● Our purpose: Charged particle position measurement Readout electrode Bias electrode Short interlude: Signal induction in ionization detectors (I) ● Signal is induced on the electrodes by approaching charges An approaching charge attracts charges of the opposite polarity on the electrode Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros + Particle track ++ ++ - + ● Short interlude: Signal induction in ionization detectors (II) ● ● ● Mathematically described by the Shockley-Ramo theorem, which introduces a “weighting field” φ0 A moving point-charge q induces a charge Q on an electrode: Q=−q 0 r The current is given by: i=q v⋅E0 r As usual: E0=−∇ 0 Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros 3D silicon sensors – what is new ? ~50µm ● Readout electrode Traditional, planar sensor Bias electrode Made possible by Kyrre Ness Sjøbæk, ~50 µm MEMS technology University of Oslo, EPF Fysikermøtet August 2009, Røros Bias electrode Bias electrode ~2-300µm ● Invented by Parker, Kenney and Segal in 1997 Readout electrode Readout electrode ● “3D” geometry: Electrodes etched vertically into wafer Readout electrode ~2-300µm ● Planar geometry: Electrodes on top and bottom of wafer 3D 3E-sensor, Stanford Sintef MiNaLab “Ganged” pixels; special for this sensor/frontend 1 pixel 3 readout electrodes Bias grid Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Properties of 3D silicon detectors – Radiation hardness ● Radiation introduces crystal defects in silicon ● Charge trapping – – ● ● Conduction band Radiationinduced new level Loss of signal Space charge Increased leakage current 3D geometry: Shorter electrode distance => ● Lower depletion voltage ● Less charge loss Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Valence band Hole Electron Properties of 3D silicon detectors – Active edge (I) Edge of Si wafer often conductive after dicing: ● ● ● Microcracks Dangling bonds Guard electrodes Planar sensor need high depletion voltage (~1000 V) ● ● Readout electrode Edge ● Need for guard electrodes to step down voltage Dead area at edge of sensor Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros E Bias electrode ● Hit efficiency map in corresponding Kyrre Ness Sjøbæk, area University of Oslo, EPF Fysikermøtet August 2009, Røros E Readout electrode Mask detail, 800x100µm centered on an edge pixel Bias electrode => Very little dead area at the edge of the sensor Readout electrode ● No need for guard rings Bias electrode ● With 3D detectors, the edge can be an electrode Edge Properties of 3D silicon detectors – Active edge (II) Other properties of 3D sensors ● Fast charge collection ● Low amount of charge sharing ● Larger signal in the pixel that have been hit ● May be made thicker for greater stopping power ● Higher sensor capacitance ● Low sensitivity in hole region ● More complex to manufacture than planar sensors Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Proposed applications of 3D silicon sensors IBL “inverted” stave layout N. Hartmann ● IBL ● SLHC ● FP420 ● X-ray crystallography Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros ~3.2 cm Summary ● ● ● ● 3D is a promising technology for silicon HEP sensors (tracking and vertexing) Much more radiation tolerant than current silicon technologies Possibility for active edges and/or thick sensors for stopping power Promising candidate for Atlas IBL Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Backup Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros Kyrre Ness Sjøbæk, University of Oslo, EPF Fysikermøtet August 2009, Røros