h. pernegger, cern, iprd 2004, may 2004 cvd diamonds: recent developments and applications h....

H. Pernegger, CERN, IPRD 2004, May 2004

CVD diamonds: Recent Developments and Applications

H. Pernegger, CERN for the CERN RD42 collaboration

Overview Detector principle Recent advancements in CVD diamonds and their understanding

Signal collection Radiation hardness New CVD diamonds

Applications in HEP and other fields Pixel detector for HEP Beam monitoring & diagnistics Medical application


Motivation to use CVD diamonds

Use at LHC/SLHC (or similar environments) Precision tracking at inner layer required Must survive the radiation levels typically present at small radia

Material properties Radiation hard (no frequent replacements) Fast signal collection time Compact + low Z solid state detector Room temperature operation

Basic types of material Poly-crystalline CVD diamond (pCVD) Single-crystal CVD diamond (scCVD)


Basic material constants in comparison

Low dielectric constant- low capacitance

High bandgap - low leakage current Fast signal collection

Mip signal only 50% of Silicon for same radiation length

Collection efficiency <100% (pCVD)


Basic Principle of Operation

“Solid state Ionization chamber” Contacts both sides No doping or junction

required “planar”

Structured electrodes with sizes from m to cm

Signal Typically use integrated

amplifiers for readout Collection distance d = E Measured charge Q = d/t Q0


Characterization of CVD diamonds

Measure charge collection distance (through integrating amplifiers)

pCVD diamond “pumps” : signal increase by a factor 1.5-1.8 Filling of charge traps

Contacts: Cr/Au, Ti/W, Ti/Pt/Au Use dots -> strip -> pixel on same diamond (contacts can be

removed) Typically use 1V/m as operation point


CVD diamonds

Growth side pCVD diamonds wafer grown up to 5 inch

RD42 in research project with Element Six Ltd to increase charge collection distance in pCVD diamond material


Collection distance on recent pCVD diamonds

Now reach signals of 9800 e- mean charge

Most probable signal 8000e-

CCD = 275m Research program

worked Diamond available in

large sizes


Irradiation studies: Protons up to 2.2 x 1015 /cm2

Signal (or SNR) and spatial resolution before and after irradiation

Signal decrease starts at 2 x 1015 /cm2

Resolution 11m (before) to 7.4m (after) Measured on 50m pitch strip detector


New type of CVD diamond: CVD Single Crystals

Motivation: Avoid defects and charge trapping present in pCVD diamonds remove grain boundaries (homogeneous detector) Reduce (or eliminate) charge trapping

Signal distribution in a single crystal CVD diamond

[Isberg et al., Science 297 (2002) 1670]


Single Crystal CVD diamonds

HV and pumping characteristics

Current work with single crystals in cooperation with Element Six Improve sample “engineering” (reduce variation)

Full signal at 0.2 V/mNo pumping


Single Crystal : Trancient Current Measurements (TCT)

Measure charge carrier properties important for signal formation electrons and holes separately

Use -source (Am 241) to inject charge

Injection Depth about 14m compared

to 470m sample thickness Use positive or negative drift

voltage to measure material parameters for electrons or holes separately

Amplify ionization current

V

Electrons onlyOrHoles only


Ionization current in a sample of scCVD diamond

Extracted parameters Transit time Velocity Pulse shape

Transit time of charge cloud Signal edges mark start and

arrival time of drifting charge cloud

Error-function fit to rising and falling edge

Total signal charge

t_c


Preliminary measurement of velocity on a single crystal

Average drift velocity for electrons and holes

Extract 0 and saturation velocity

0 for this sample: Electrons: 1714 cm2/Vs Holes: 2064 cm2/Vs

Saturation velocity: Electrons: 0.96 107 cm/s Holes: 1.41 107 cm/s


Preliminary carrier lifetime measurements

Extract carrier lifetimes from measurement of total charge

Lifetime: >35 ns for electrons and holes -> larger than transit time Charge trapping doesn’t seems to limit signal lifetime -> full charge collection (for typical operation

voltages and thickness)


Applications of CVD diamonds

In general CVD diamond is used as detector material in several fields HEP and nuclear phyics Heavy ion beam diagnostics Synchroton radiation monitoring Neutron and detection ….

(Short) Selection of Applications in this presentation

Pixel detector developments using CVD diamond detector Beam Conditions Monitoring (e.g. at LHC) Beam diagnostics for radiotheraphy with proton beams


Application I:Pixel Detectors with ATLAS & CMS FE chips

Use present implementation of radhard FE chips together with pCVD (later possible scCVD) diamonds

Bumpbonding yields ≈ 100% now


Preparation of pixel test assembly

Test assembly Underbump metalization

SiLab/ Bonn


Example: FE chip with pCVD diamond

Source & Testbeam results with pCVD diamond mounted to Atlas Pixel chip

M. Keil / SiLab/ Bonn

Spatial resolution (pad size = 50x400m)


Application II: Beam Conditions Monitoring

“DC current” Uses beam induced DC current

to measure dose rate close to IP Benefits from very low intrinsic

leakage current of diamond Can measure at very high

particle rates Simple DC (or slow

amplification) readout Examples: See talk by M.Bruinsma for

BaBar Similar in Belle Similar method planned for CMS

Single particle counting Counts single particles Benefits from fast diamond

signal Allows more sophisticated logic

coincidences, timing measurements

Used at high particle rates up to Requires fast electronics (GHz

range) with very low noise

Examples CMS and Atlas Beam conditions

monitor

Common Goal: measure interaction rates & background levels in high radiation environment

Input to background alarm & beam abort


Beamloss scenario: study for CMS (1)

E.g. accidental unsynchronized beam abort Instantaneous , difficult to protect against

Unsynchronised beam abort: ~1012 protons lost in IP 5 (CMS) in 260ns

(M. Huhtinen, LHC Machine Protection WG, Oct. 2003)


Beamloss scenario: study for CMS (2)

E.g. Loss of protons on collimators close to experiments (“TAS”) Worse in dose rate (>up to 1000 x unsynchronized abort if

consecutive bunches are lost) Slower (several turns) therefore possible to protect against

if early signs are detected

(dose [Gy])

(M. Huhtinen, LHC Machine Protection WG, Oct. 2003)


CMS tests with Cern PS fast beam extraction

Single pulses from diamond• Bias on Diamond = +1 V/um• Readout of signal:

• 16m of cable• no electronics• 20dB attenuation on signal cable (factor 10)

Almost identical diamond response to PS beam monitor response (pulse length 40ns)

Diamond signal current is 1-2 A !

2 DiamondsPS beam monitor

A. MacPherson et al. / CMS-BCM


Atlas Beam Conditions Monitoring

Time-Of-Flight measurement to distinguish collisions from back ground during normal running

Located behind pixel disks in pixel support tube

Time difference

12ns

Need to measure single MIPs radiation hard!

… and very fast: rise time <1ns, width <3ns


Atlas BCM: single-MIP detector with <1ns rise time

90Sr source or 5GeV/c pions

(Pb collimator)

Diamond on support

Scintillator

Different versions of FE electronics (Fotec/Austria) 500Mhz (40 dB) (2 stages) 1 Ghz (60 dB) (3 stages)

2 pCVD diamond detector back-to-backw =360 µm, CCD ~ 130 µmHV Bias 2V/m

Source tests and test beam


Preliminary test results

MIP signal (testbeam & Sr90 source) after 16m of cable perpendicular to beam, double diamond assembly Rise time 900ps, FWHM = 2.1ns

SNR = 7.3:1

preliminary


Application III: Diamonds in Proton Therapy:

Conventional X-Ray Therapy Ion-Therapy

C-Ions 1 cm

Protons 1 cm

Austrian medical accelerator facility Cancer treatment and non-clinical

research with protons and C-ions


Facility Layout

Synchrotron

2 Experimental rooms

4 Treatment rooms

Injector

Preliminary layout

Proton & Carbon Beam Energy: 60-240 MeV protons and

120-400 MeV/u C-ions Intensity: 1x1010 protons (1,6 nA)

and 4x108 C-ions (0,4 nA) Beam size: 4x4 mm2 to 10x10

mm2

Diamonds used for Beam Diagnostics:

High-speed Counting of single particles in extraction line

Resolve beam time structure


Testbeam results for Proton Beam Diagnostics

2 diamond with different pad size + scintilator as “telescopes” tested at Indiana University Cyclotron Facility 2.5 x 2.5 mm2 (in trigger) CCD = 190 m, D= 500 m 7.5 x 7.5 mm2 (for analog measurements) CCD = 190 m,

D= 500 m

trigger measured


Signal timing properties

Average pulse shape Single shot

Rise time : 340ps Duration: 1.4ns


Signal/Noise and energy dependence

Measured most probable S/N ranges from 15:1 to 7:1

200 MeV104 MeV55 MeV

SNR

Signal energy dependence


Summary

CVD diamonds as radiation hard detectors High quality polycrystalline CVD diamonds (ccd up to 270m) are readily

available now in large sizes Radiation tests showed radiation hardness up to 2 x 1015 p/cm2

Single crystal CVD diamonds promise to overcome limitations of polycrystalline CVD diamonds Full signal collection already at lower voltages Long charge lifetime Very little charge trapping and uniform detector (no grain boudaries)

There are many applications around which benefit from diamond’s intrinsic properties Strip or Pixel detectors for future high luminosity accelerators Beam diagnostics and monitoring


High-bandwidth amplifier for fast signal measurements

Use current amplifier to measure induced current Bandwidth 2 GHz Amplification 11.5 Rise time 350ps

Inputimpedance 45 Ohm Readout with LeCroy 564A

scope (1GHz 4Gsps) Correct in analysis for detector

capacitance (integrating effect)

Cross calibrated with Sintef 1mm silicon diode e = 1520 cm2/Vs I = 3.77 eV +/- 15%


Irradiation studies: Pions up to 2.9 x 1015 /cm2

Signal (or SNR) and spatial resolution before and after irradiation

50% Signal decrease at approx 3 x 1015 /cm2 * (TO BE CONFIRMED) Narrower signal distribution after irradiation 25% Resolution improvement

Preliminary results

h. pernegger, cern, iprd 2004, may 2004 cvd diamonds: recent developments and applications h....

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