LHCb Vertex Detector and Beetle Chip Outline: Introduction VErtex LOcator Pile-up trigger Radiation hardness of electronics Architecture of Beetle chip Test beam results Conclusions & outlook Radhardness in general:is sidestep 18 December 2002 1

The LHCb Vertex Locator (VELO) The VELO provides an accurate reconstruction of primary & secondary (displaced) vertices Typical b-event Location of rest of LHCb Hole for beam in silicon r-phi readout geometry Pile-up 18 December 2002 2

Vertex Locator 21 VELO + 2 Pile-Up stations R/ Silicon strip detectors ~ 180k strips Typical hit resolution 8 mm CO2 cooling: 2 kW @-10 C Radiation dose 100 kGy (4 years) Vacuum feedthrough: 20k pins Large vacuum box 18 December 2002 3

RF shielding Explain: hybrid green, silicon blue Improper guidance of beam induced currents leads to enormous EM fields in the vacuum vessel Secondary vacuum 26 A peak current through box 300 mm Al foil  11 mm hole for the beam !! Detectors are retracted during beam injection 18 December 2002 4

Pile-up trigger (veto) RA Rb = ZPV - ZA ZPV - ZB = k Detection of multiple primary vertices R-strip detectors only L0-trigger: prompt binary signals needed Processing time < 2.2 s Max ratio single to two primary vertices Lines: one lines for each vertex interval Create new histogram every 25 ns 16 combinations     Logic OR of 4 detector signals in Beetle 1024 binary signals @ 80 Mbit/sec Special (complex) hybrid Connectivity challenge !  18 December 2002 5

Front-end chip requirements Pulse from charge sensitive amplifier 40 MHz sampling rate Peaking time < 20 ns Remainder of peak after 25 ns < 30 % (spill over) S/N > 14 (300 mm Si) L0-trigger rate: 1.1 MHz => Readout time 900 ns Trigger latency up to 4 ms Buffering of 16 events Power consumption < 6 mW / channel Radiation hardness >100 kGy time Overspill -> persistent hits -> ghost tracks 18 December 2002 6

Radiation hardness of CMOS Problem: Single Event Upsets (SEU) i.e. bit-flips Cure : Triple redundancy + majority voting for all registers Problem: Hole trapping in SiO2 (Total Ionizing Dose) Cure: Use deep submicron process + special layout techniques MOS transistor characteristics are determined by width (W) and length (L) V+ Gate oxide Only highlight 2 main problems Explain basic mosfet Source /drain area Flow current Controling terminal : gate Characteristics determined by W and L + + + + 18 December 2002 7

Radiation hardness(2) Hole trapping => threshold shift Deep Sub Micron process => thinner gate oxide Tox < 10 nm : tunneling decreases the amount of trapped holes in the gate-oxide Solution to parasitic transistors: enclosed layout (only for nMOS) Guard rings around nMOS Field oxide ++ Disadvantages of enclosed layout: Larger area / capacitance No “long” transistors possible 18 December 2002 8

Beetle functional diagram Beetle chip is designed in 0.25 mm technology Readout (4x) Pipeline (186 deep) 4 * readout for high trigger rate Front-end (128 x) comparator 18 December 2002 9

Beetle front-end Pulse shape depends on: Shaper feedback resistance (Vfs) Shaper current (Isha) Noise is related to the current in the pre-amplifier (Ipre) Pre-amplifier: Ipre thermal noise power Shaper: slower pulse: noise spillover 10 ns 20 ns 25 + 40 ns 18 December 2002 10

Layout of beetle Beetle: Designed by ASIC lab Heidelberg and NIKHEF 0.25 mm CMOS technology Pipeline depth 186 cells Size (5.5 x 6.1) mm2 Front-end (128 x) Pipeline cells 18 December 2002 11

Radiation hardness test Single chips were tested with X-ray facility at CERN time [ns] Vout [V] Beetle showed full functionality up to 300 kGy (12 LHCb years): All digital functions worked up to 450 kGy Analog performance degradations are small 18 December 2002 12

Hybrid & Silicon Micron PR02-R detector Thickness: 300 mm 2048 strips pitch: 40 – 92 mm length: 6.4 – 66.6 mm angular coverage 182° 2 layer pitch adapter 16 Beetle chips High yield 4 layer hybrid (NIKHEF design) 75 mm kapton / layer 17 mm copper / layer 8 mm 42 mm 18 December 2002 13

Test beam setup 120 GeV pions / muons Trigger scintillators X-Y Si tracking station Hybrid under test “Continuous” beam => no fixed relation between particle and Beetle clock signal (40 MHz) Readout 8 time samples of Beetle Measure time between trigger and next Beetle clock time Collected > 10 Million events in 4 days 18 December 2002 14

Pulse shape analysis Data after baseline correction & common mode noise subtraction s = 1 Noise distribution Most probable value 18 December 2002 15

Pulse shape analysis (2) Rise time (10 to 90 %) Peak height (Signal) Spill over 25ns 18 December 2002 16

S/N results Short strips: Sstrip/Nstrip = 19 Spill over = 32 % Long strips: Sstrip/Nstrip = 13 Spill over = 37 % The new design of the silicon sensor will have only 45  strips => expected S/N of long strips > 15 18 December 2002 17

Conclusions Radiation hardness of Beetle demonstrated up to 300 kGy Performance degradation due to hybrid is minimal Pulse shape characteristics: Spill over < 30 % S/N > 15 Beetle is compliant with all LHCb requirements Beetle was chosen by VELO group Inner tracker will also use Beetles 18 December 2002 18

Outlook Next version of Beetle (1.2) + next version of hybrid is planned to be tested in the test beam of summer 2003 Small design improvements => new Beetle (1.3) submission in spring 2003 The more complex Pile-Up hybrid is currently under construction (4 times more signals!), to be tested 18 December 2002 19

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Radiation effects Total Dose effects Single Event effects Ionising Bulk damage Hole trapping (SiO2) Non-Ionising Bulk damage Upsets Yes Triple redundancy +majority voting Damage Latch-up No problem For LHCb Silicon Detectors Readout chips 18 December 2002 22

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