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

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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

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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

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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

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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

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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

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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

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With Thanks…

Introduction

Timepix

LHCb Upgrade

Testbeam

Telescope