medipix and timepix chip developments recent measurements with timepix as a particle tracker richard...
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MEDIPIX AND TIMEPIX CHIP DEVELOPMENTS
Recent Measurements with Timepix as a Particle Tracker
Richard Plackett – CERN Medipix Group
VERTEX 2009, Mooi Veluwe, 16th September ‘09
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Overview
Introducing the Medipix 2 and Timepix Chips
Timepix and Time over Threshold Mode
Recent LHCb VELO upgrade Testbeam results
Timepix Particle Telescope
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
-3-
Hybrid Pixel Detectors
sensor
Analogue amplification
Ionizing Particle
e-
h+
Digital processing
Chip read-out
Solder bump bonds
Readout ChipMedipix or
Timepix in 250um IBM CMOS
Positive or negative
sensor bias
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Medipix2
Single photon counting readout provides low noise, high
contrast images with very high dynamic range
55um pixel matrix (256 by 256) reading Si, 3D,
CdTe, GaAs sensors
Configurable ‘shutter’ allows many different
applications
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Timepix
• Timepix is a derivative of Medipix2• Addition of a global clock (up 100MHz) which is propagated to
every pixel• Originally conceived for GEM foil detectors• The clock can be used for Time of Arrival (ToA) and Time over
Threshold (ToT) modes.
ThresholdTime of Arrival Mode
• Counts from passing threshold to closing shutter
• Allows accurate timing of hits in individual pixels
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
-6-
Timepix Time over Threshold
Timepix ToT mode is similar in principle to ATLAS pixel..
Preamp has fast rise (90ns) but slow (500ns -2500ns) constant current return to zero
E.g. 20ke- ~1us = 40 x 25ns
Residual errors come from non linearity with small charge signals and a slow return to baseline
Clock
Threshold
Linearity of one pixel measured at three different threshold values
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Timepix GEM foil event
DESY testbeam in November 2006 (A.Bamberger et al)
ToT ToA
A GEM foil event with a ‘chess board’ ToT & ToA pattern set on the pixel matrix
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
-8-
ToT silicon event
Although conceived for gas detectors Timepix retains the Medipix2 sensor featuresegPixel leakage current correction Positive and negative biasing
Images courtesy of Erik Heijne
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Upgrading LHCb
The idea:Aim to operate at L=2.1033
Perform entire trigger on CPU farm. No hardware Trigger!
The consequence:Read out all sub-systemsat 40 MHzReplace all FE-electronics; all silicon modules, RICH-HPDs, FE boards of Calorimeter, Outer Tracker FE
MuonHCAL ECAL RICH2
Tracker MagnetTT RICH1
VELOThe Problem:LHCb is currently optimised for single interactions, to search for new physics a large increase in statistics is required, significantly complicating the trigger.
In Addition:A strong case for an upgrade even without SLHC as LHCb does not use all current LHC luminosity
10x increase in Leptonic channels20x increase in Hadronic channels
For more information on LHCb upgrade see the talk tomorrow by JC
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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LHCb VELO Upgrade
silicon edge just 7 mm
from beam!
Closest LHC detector to the beam and highest resolution requirements
Currently 21 perpendicular two sided strip planes
Upgrade to strip or pixel system
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Potential Module DesignSilicon (1-3 pieces) 55x55
mm pixels, 800 mm pixels in areas under chip periphery
10 Timepix chips(periphery indicated in white)
Diamond thermal plane withcutouts immediately above TSV regions
Power strips andsignal routing area
Cooling channel
With a Pixel VELO we can have a low scattering module with high resolution and no strip detector ambiguities
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Recent Testbeam Activity
• Required to demonstrate suitability for tracking• Measure efficiency and resolution• Provide information for VELOPIX design
• 3 testbeams at CERN SPS with 120GeV Pions– June: as Medipix Group to test Telescope concept– July: Running parasitically from CMS SiBit telescope – August: Running parasitically from EUDET/LCFI testbeam
• Significant improvements to telescope design at each testbeam
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
-13-
Timepix Telescope
4 Timepix, 2 Medipix planes in telescope
Symmetric positioning of planes around Timepix DUT
Telescope planes mounted at nine degrees in x and y
DUT position and angle controlled remotely by stepper motors
Measurements of resolution with angle, threshold, sensor bias, 3D sensor and timewalk
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Angled Planes to Boost Resolution
Hits that only affect one pixel have limited resolution (30um pixel region)
Angling the sensor means all tracks charge share and use the ToT information
55um
300um 10o
Timepix (ToT) tracked position vs cluster reconstructed position
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Results – Resolution Vs Track Angle
2.5um Estimated track contribution
to residual
Rotation about Y axis
PRELIMINARY: UNCALIBRATED DATA!!
The tracking uncertainty of the telescope is very competitive, with uncalibrated, uncut data, 2.5um is comparable to EUDET running with
30um pixels (timepix is 55um)
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Results - Residual Width vs Sensor Bias
Width of y residualperpendicular
Width of x residual18 degrees
The residual width shows a clear dependence on orientation as the sensor bias is changed.
This is as expected, and illustratesthe sensitivity of the measurement
The sensor bias was scanned up and down again to ensure any change seen was not a drift
Perpendicular:As the charge diffusion shrinks you have more single pixel hits, increasing the width of the residual width
High Angle:As the charge diffusion shrinks you still have a large number of charge sharing hits, holding residual width constant
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Results – Residual Mean vs Sensor Bias
Varying the sensor bias shows a clear shift in the residual means for highly angled tracks
Perpendicular:As the charge collection shrinks you do not affect the position of the reconstructed hit
High Angle:As the charge collection shrinks you can see the position of the reconstructed hit being pulled
angled
perpendicular
angled
perpendicular
6 degrees 18 degreesIntroduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Results – 3D Sensors
Efficiency
The sub-pixel resolution of the telescope allows us to see the efficiency losses due to the anode and cathode holes in the silicon.
Perpendicular particles passing through a doped hole will deposit less charge in the silicon
Special acknowledgement to Marco Gersabeck who produced this plot and the 3D group at Glasgow who provided the sensor
Glasgow double sided CNM sensorIntroduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Design Lessons for VELOPIX
• Analogue IS better than Binary, even with 55um pixels, even with clusters and charge sharing
• Clustering WILL significantly increase hit multiplicity
• Interactions within the sensor will occur often and need to be handled to avoid overflowing the chips for that event
• From this data we will determine how many bits ToT we need and optimise on chip the data transport
Timepix (ToT) 5um Medipix (binary) 11um
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
-20-
More Measurements Coming Soon
Lots of data from July and august still to analyse
• Resolution as a function of– threshold– 2d rotation– Number of bits used
• Efficiency and Noise study
• Pulse shape reconstructed directly from ToT data
• Timewalk measurements
• 3d sensor
• Vertex reconstruction using telescope
• Etc…
Also gain calibration still has to be done with to get optimum performance from TImepix chips
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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In Conclusion
• The Medipix2 and Timepix chips are versatile creatures, and are spinning back into HEP
• A Timepix like chip is a candidate for LHCb VELO upgrade
• At testbeams over the summer Timepix has been demonstrated to run reliably with unexpectedly good resolution
• A very large data set has been recorded so expect non-preliminary results soon…
• A series of telescopes were developed for these tests. A possible future system could be made available to the community if there is interest … another couple of slides on that …
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Current Telescope
• Successful going on to do a testbeam with SPS collimators
• All versions based on the USB interface developed by CTU Prague
• Main strength is simplicity, each module powered, biased and read out by USB. DAQ consists of 6 usb lines to a PC and a NIM crate for a pulse-per-second synchronization signal
• Data is saved to text files so extremely easy to work with
USB
timing
Sensor Bias
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Limitations
• Timing between modules has large uncertainty (500ns) due to the USB readout systems
• Long readout dead time (1 second), due to USB 1.1 readout
• Either ToT or ToA, as limited number of Timpix chips
• Inclined sensor planes good for ToT, bad for ToA as charge sharing clusters can cause timewalk
• At current resolution (~2.5um) scattering from PCB is becoming a dominant error
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
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Future Timepix Telescope
Solution…• Add an external timing readout to sync systems (and
scintillators?)• Replace USB with RUIN, Relaxed or similar (coming soon)
allows 100x faster readout over (USB2 or Ethernet)• 4 Timepix chips per arm, with one dedicated to ToA• New PCB with cut out behind chip• Possible further upgrade with Timepix2…..
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
-25-
Future Timepix Telescope
Results in• High resolution (<3um) as current telescope• Track timing down to 10ns• Link to PMT/external device for trigger and integration of DUTs• Minimum rate 100Hz, max 20kHz• Portable device with text file data output as current telescope
• If anyone is interested please let me know
RUIN RUIN
TIMING
DUT
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope
-26-
With Thanks…
Introduction
Timepix
LHCb Upgrade
Testbeam
Telescope