Stephanie Majewski Stanford University Silicon Detectors Stephanie Majewski Stanford University

Semiconductor Refresher Si bandgap energy Eg = 1.12 eV kBT = 0.026 eV @ 300K S. Majewski

Semiconductor Refresher Si bandgap energy Eg = 1.12 eV kBT = 0.026 eV @ 300K Doping: n-type  dopant adds electrons to conduction band (e.g. P, As) S. Majewski

Semiconductor Refresher Si bandgap energy Eg = 1.12 eV kBT = 0.026 eV @ 300K Doping: n-type  dopant adds electrons to conduction band (e.g. P, As) p-type  dopant adds holes to valence band (e.g. B) S. Majewski

Reverse-Biased Diodes sensitive detector region Hamamatsu PIN Diode depletion region p-n junction larger depletion region p-i-n junction (i = intrinsic) S. Majewski

Interaction of Charged Particles A high-energy particle produces uniform e-h density along its path The bias voltage attracts the electrons/holes to either contact S. Majewski

Ionization Energy Less material (1 m): More material (100 m): Most probable energy loss Mean energy loss Less material (1 m): E dominated by counting statistics More material (100 m): Landau distribution with high-energy tail Silicon: Mean ionization energy = 3.6 eV S. Majewski

Energy Loss (dE/dx) dE/dx = # e-h pairs  3.6 eV / (300 m  tan dip)  p d t BAD 1154 Shape is Bethe-Bloch (see M. Spitznagel’s drift chamber talk) dE/dx = # e-h pairs  3.6 eV / (300 m  tan dip) Limited ability to distinguish particles S. Majewski

Advantages of Silicon Low ionization energy: 3.6 eV (e-h creation) Compare to gas ~30 eV Many carriers / event Long mean free path (~100 nm) High charge collection efficiency Large energy loss / distance traveled (3.8 MeV/cm for a minimum ionizing particle) Large signals High carrier mobility ( ) at room temp, even w/ doping Rapid charge collection (~10ns) Detector/electronics integration Easy to fabricate S. Majewski

Silicon Wafer Fabrication p i n S. Majewski

Silicon Detector Geometries Strip Detectors BaBar, Belle, CDF, D0 Hybrid Pixel Detectors (at ATLAS, CMS) Squares instead of strips; integrated electronics Drift Detectors (used in Star at RHIC) Electrons move through the Si bulk to an anode strip at the end CCDs (used for SNAP, SLD) 3-D Silicon Detectors Proposed in ’95 by S. Parker at U. Hawaii Possible LHC detector upgrade S. Majewski

Strip Detector Geometry “Strip Pitch” (~50m) is the distance between strips, whether they are connected to the electronics or not “Readout Pitch” includes floating strips Resolution ~ readout pitch / Readout Pitch Aluminum Strip Pitch n- Bulk Silicon dioxide p+ Implant S. Majewski

The BaBar Silicon Vertex Tracker

Silicon Wafers p+ strip side n+ strip side TOP VIEW Edge guard ring P-stop n+ Implant 55 mm Polysilicon bias resistor p+ Implant Bias ring Al 50 mm Polysilicon bias resistor Edge guard ring p+ strip side n+ strip side TOP VIEW S. Majewski

Si Sensor Schematic Bias Voltage ~ 40 V Leakage Current ~ 10 A AC Coupling SIDE VIEW S. Majewski

Si Sensor Schematic +2 V Bias Voltage ~ 40 V Leakage Current ~ 10 A Pre-Amp Bias Voltage ~ 40 V Leakage Current ~ 10 A AC Coupling +40 V Pre-Amp +40 V S. Majewski +42 V

Readout Strips are AC coupled to preamplifiers Separates signal current from bias current Guard rings to reduce noise and measure bulk bias current Charge sharing between strips Analog readout of strips gives better resolution Convert pulse height (charge) into long pulse in time, then measure time over threshold (TOT) S. Majewski

Readout Electronics AToM chip Radiation hard 128 channels Injected Charge (fC) Time Over Threshold 1 MIP AToM chip Radiation hard 128 channels 1-2 strips/channel Minimum Ionizing Particle: 3.8fC  avg 7.5 counts 1-2 counts = noise S. Majewski

Carbon/Kevlar Fiber Support Ribs SVT Modules Z Side ATOM chip  Side Carbon/Kevlar Fiber Support Ribs Si Wafers S. Majewski

Position Resolution Analog readout allows better resolution than pitch / S. Majewski

Track Finding Efficiency How Many Layers? Number of Hits Found Track Finding Efficiency % BaBar TDR 5 layers 4 layers Define a Helix 4 points confirm a helix in tracking 5 layers needed to compensate for gaps and dead modules Inner 3 layers angle/impact parameter redundancy Outer 2 layers pattern recognition low pT tracking S. Majewski

SVT Data Transmission HDI Power Supplies Back MUX Link Si Wafers DAQ HDI: High Density Interconnect. Mounting fixture and cooling for readout ICs. Kapton Tail: Flexible multi-layer circuit. Power, clock, commands, and data. Matching Card: Connects dissimilar cables. Impedance matching. HDI Link: Reference signals to HDI digital common. DAQ Link: Multiplex control, demultiplex data. Electrical -- optical conversion. HDI Matching Card Kapton Tail Front Cables Si Wafers Back Link DAQ Power Supplies MUX Fiber Optic to DAQ S. Majewski

Radiation Damage Acute damage Bulk damage pinhole – short in AC coupling capacitor p-stop short – short between p-stop and metal contact (DC) Bulk damage radiation displaces Si atoms & creates defects eventual type inversion in bulk (n-type to p-type) can see as change in voltage needed to fully deplete S. Majewski

Radiation Damage Consequences of Defects Recombination/generation centers  increased leakage current Trapping centers  introduce time delay  reduced signal Charge density changes  need increased bias voltage S. Majewski

Radiation Protection See Adam’s talk next week! Silicon is not radiation hard BaBar SVT monitored by PIN diodes and diamond sensors http://www.slac.stanford.edu/BFROOT/www/Detector/SVT/Operations/SVTRAD/ briefIntro.html See Adam’s talk next week! S. Majewski

The BaBar SVT Thin wafers (300 m) to limit multiple scattering 5 Layers 0.94 m2 of Si ~150 000 readout channels S. Majewski

Belle Silicon Vertex Detector SVD 1 3 Layers SVD 2 4 Layers S. Majewski

ATLAS Semiconductor Tracker & Pixel Detectors (SCT) Pixel Detectors S. Majewski

3-D Silicon Detector Brunel Univ. (UK), Stanford, and Hawaii Possible LHC detector upgrade S. Majewski http://www.pparc.ac.uk/frontiers/archive/update.asp?id=16U3&style=update

The Rise of the Silicon Detector S. Majewski

References General Silicon Detectors: Lutz, G. Semiconductor Radiation Detectors: Device Physics. (Springer Verlag, Berlin, 1999). Spieler, H. Lectures on Detector Techniques. 1998. http://www-physics.lbl.gov/~spieler/SLAC_Lectures/index.html Sadrozinski, H. “Applications of Si Detectors”, presented at IEEE 2000. http://scipp.ucsc.edu/~hartmut/IEEE2000_embed.pdf BaBar Silicon Vertex Tracker: SVT Facts and Figures. http://www.slac.stanford.edu/BFROOT/www/Detector/SVT/ Factoids.html TDR http://www.slac.stanford.edu/pubs/slacreports/slac-r-457.html S. Majewski