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
H. Pernegger, CERN, IPRD 2004, May 2004
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)
H. Pernegger, CERN, IPRD 2004, May 2004
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)
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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]
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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)
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
Preparation of pixel test assembly
Test assembly Underbump metalization
SiLab/ Bonn
H. Pernegger, CERN, IPRD 2004, May 2004
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)
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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)
H. Pernegger, CERN, IPRD 2004, May 2004
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)
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
Signal timing properties
Average pulse shape Single shot
Rise time : 340ps Duration: 1.4ns
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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
H. Pernegger, CERN, IPRD 2004, May 2004
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%
H. Pernegger, CERN, IPRD 2004, May 2004
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