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
Overview
Introduction
Timepix
LHCb
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Introducing the Medipix 2 and Timepix Chips
Timepix and Time over Threshold Mode
Recent LHCb VELO upgrade Testbeam results
Testbeam
Telescope
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Timepix Particle Telescope
Hybrid Pixel Detectors
Ionizing
Particle
Introduction
Timepix
sensor
h+
e-
LHCb
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Solder bump
bonds
Testbeam
Telescope
Positive or
negative
sensor bias
Analogue
amplification
Digital
processing
Readout Chip
Medipix or
Timepix in 250um
IBM CMOS
Chip read-out
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Medipix2
Single photon counting readout
provides low noise, high
contrast images with very high
dynamic range
Introduction
Timepix
LHCb
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Testbeam
Telescope
55um pixel matrix (256 by
256) reading Si, 3D,
CdTe, GaAs sensors
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Configurable ‘shutter’
allows many different
applications
Timepix
Introduction
Timepix
LHCb
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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.
Testbeam
Telescope
Time of Arrival Mode
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Counts from passing
threshold to closing shutter
Allows accurate timing of hits
in individual pixels
Threshold
Timepix Time over Threshold
Timepix ToT mode is similar in principle to ATLAS pixel..
Introduction
Preamp has fast rise (90ns) but slow (500ns -2500ns)
constant current return to zero
Timepix
LHCb
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Threshold
Telescope
Clock
Linearity of one pixel measured at
three different threshold values
E.g. 20ke- ~1us = 40 x 25ns
Residual errors come from non linearity with small
charge signals and a slow return to baseline
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Timepix GEM foil event
Introduction
Timepix
LHCb
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A GEM foil event with a ‘chess
board’ ToT & ToA pattern set on
the pixel matrix
ToT
ToA
Testbeam
Telescope
DESY testbeam in November 2006 (A.Bamberger et al)
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ToT silicon event
Introduction
Timepix
LHCb
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Testbeam
Telescope
Images courtesy of Erik Heijne
Although conceived for gas detectors
Timepix retains the Medipix2 sensor features
eg
Pixel leakage current correction
Positive and negative biasing
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Upgrading LHCb
Introduction
Timepix
LHCb
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Testbeam
Telescope
The Problem:
LHCb is currently optimised for
single interactions, to search for
new physics a large increase in
statistics is required, significantly
complicating the trigger.
HCAL ECAL
RICH2
Tracker
Magnet
TT RICH1
The idea:
Aim to operate at L=2.1033
Perform entire trigger on
CPU farm. No hardware
Trigger!
In Addition:
The consequence:
A strong case for an upgrade
even without SLHC as LHCb does
not use all current LHC luminosity
Read out all sub-systems
at 40 MHz
Replace all FE-electronics;
all silicon modules,
RICH-HPDs,
FE boards of Calorimeter,
Outer Tracker FE
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Muon
10x increase in Leptonic channels
20x increase in Hadronic channels
For more information on LHCb
upgrade see the talk tomorrow by JC
VELO
LHCb VELO Upgrade
Introduction
Timepix
LHCb
Upgrade
Closest LHC detector to the
beam and highest resolution
requirements
Currently 21 perpendicular two
sided strip planes
Upgrade to strip or pixel system
Testbeam
Telescope
silicon edge
just 7 mm
from beam!
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Potential Module Design
Silicon (1-3 pieces) 55x55 mm
10 Timepix chips
pixels, 800 mm pixels in areas
(periphery indicated in white)
under chip periphery
Diamond thermal plane with
cutouts immediately above TSV regions
Introduction
Timepix
LHCb
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Testbeam
Telescope
Cooling channel
Power strips and
signal routing area
With a Pixel VELO we can have a low scattering module with
high resolution and no strip detector ambiguities
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Recent Testbeam Activity
Timepix
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Required to demonstrate suitability for tracking
Measure efficiency and resolution
Provide information for VELOPIX design
LHCb
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3 testbeams at CERN SPS with 120GeV Pions
Introduction
Testbeam
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June: as Medipix Group to test Telescope concept
July: Running parasitically from CMS SiBit telescope
August: Running parasitically from EUDET/LCFI testbeam
Telescope
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Significant improvements to
telescope design at each
testbeam
Timepix Telescope
4 Timepix, 2 Medipix planes in
telescope
Introduction
Timepix
LHCb
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Symmetric positioning of planes
around Timepix DUT
Telescope planes mounted at nine
degrees in x and y
Testbeam
Telescope
DUT position and angle
controlled remotely by stepper
motors
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Measurements of resolution
with angle, threshold, sensor
bias, 3D sensor and timewalk
Angled Planes to Boost Resolution
Hits that only affect one pixel have limited resolution
(30um pixel region)
Introduction
Timepix
Angling the sensor means all tracks charge share and
use the ToT information
55um
LHCb
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Testbeam
300um
10o
Telescope
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Timepix (ToT) tracked position vs cluster reconstructed position
Results – Resolution Vs Track Angle
Introduction
Timepix
LHCb
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Testbeam
Rotation about Y axis
Telescope
2.5um Estimated
track contribution
to residual
PRELIMINARY: UNCALIBRATED DATA!!
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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)
Results - Residual Width vs Sensor Bias
The residual width shows a clear
dependence on orientation as the
Introduction sensor bias is changed.
Timepix
LHCb
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This is as expected, and illustrates
the 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
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Width of y residual
perpendicular
Width of x residual
18 degrees
High Angle:
As the charge diffusion shrinks you
still have a large number of charge
sharing hits, holding residual width
constant
Results – Residual Mean vs Sensor Bias
Varying the sensor bias shows a clear shift in the residual means for highly angled tracks
Introduction
Timepix
LHCb
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6 degrees
18 degrees
perpendicular
perpendicular
angled
Testbeam
angled
Telescope
Perpendicular:
As the charge collection shrinks you
do not affect the position of the
reconstructed hit
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High Angle:
As the charge collection shrinks you
can see the position of the
reconstructed hit being pulled
Results – 3D Sensors
Efficiency
Glasgow double sided
CNM sensor
Introduction
Timepix
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Perpendicular particles
passing through a doped
hole will deposit less
charge in the silicon
The sub-pixel resolution of the telescope allows
us to see the efficiency losses due to the anode
and cathode holes in the silicon.
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Special acknowledgement to
Marco Gersabeck who
produced this plot and the 3D
group at Glasgow who
provided the sensor
Design Lessons for VELOPIX
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Analogue IS better than Binary, even with 55um pixels, even with
clusters and charge sharing
Timepix
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Clustering WILL significantly increase hit multiplicity
LHCb
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•
Interactions within the sensor will occur often and need to be handled
to avoid overflowing the chips for that event
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From this data we will determine how many bits ToT we need and
optimise on chip the data transport
Introduction
Testbeam
Telescope
Timepix (ToT)
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5um
Medipix (binary) 11um
More Measurements Coming Soon
Lots of data from July and august still to analyse
Introduction
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Timepix
LHCb
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Testbeam
Telescope
Resolution as a function of
threshold
2d rotation
Number of bits used
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Efficiency and Noise study
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Pulse shape reconstructed directly from ToT data
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Timewalk measurements
• 3d sensor
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Vertex reconstruction using telescope
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Etc…
Also gain calibration still
has to be done with to get
optimum performance
from TImepix chips
In Conclusion
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The Medipix2 and Timepix chips are versatile creatures, and are
spinning back into HEP
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A Timepix like chip is a candidate for LHCb VELO upgrade
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At testbeams over the summer Timepix has been demonstrated
to run reliably with unexpectedly good resolution
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A very large data set has been recorded so expect nonpreliminary results soon…
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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
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Current Telescope
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Successful going on to do a testbeam with
SPS collimators
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All versions based on the USB interface
developed by CTU Prague
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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
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Data is saved to text files so extremely easy to
work with
Sensor Bias
Introduction
Timepix
LHCb
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Testbeam
Telescope
timing
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USB
Limitations
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Timing between modules has large uncertainty (500ns) due to
the USB readout systems
LHCb
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•
Long readout dead time (1 second), due to USB 1.1 readout
Testbeam
•
Either ToT or ToA, as limited number of Timpix chips
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Inclined sensor planes good for ToT, bad for ToA as charge
sharing clusters can cause timewalk
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At current resolution (~2.5um) scattering from PCB is becoming
a dominant error
Introduction
Timepix
Telescope
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Future Timepix Telescope
Introduction
Timepix
LHCb
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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…..
Future Timepix Telescope
Introduction
Timepix
LHCb
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Testbeam
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
Telescope
DUT
RUIN
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RUIN
TIMING
With Thanks…
Introduction
Timepix
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