low energy x-ray spectroscopic applications of very large area silicon drift detector
DESCRIPTION
Low energy X-Ray Spectroscopic Applications of Very Large Area Silicon Drift Detector. ABSTRACT - PowerPoint PPT PresentationTRANSCRIPT
Andrea Vacchi Infn Trieste
Low energy X-Ray SpectroscopicLow energy X-Ray SpectroscopicApplications of Very Large AreaApplications of Very Large Area
Silicon Drift DetectorSilicon Drift Detector
ABSTRACTABSTRACT
The spectroscopic performances of a very large sensitive area SDD (about 53 cm2) at the
energies of 241Am and 55Fe sources shows that the goal of a high energy resolution
combined with large sensitive areas can be achieved. This result has moved a large
interest and the present project proposes a further development of this detectors in the
direction of high performances x ray spectroscopy.
Andrea Vacchi Infn Trieste
INFN Trieste laboratories Silicon Drift Detectors from device modeling to mass production - practical experience
INFN Trieste laboratories Silicon Drift Detectors from device modeling to mass production - practical experience
From specs to detector
–HV divider & stability
–Injectors & drift speed variations
–NTD fluctuations
–Safe design & yield
– Radiation damage
–Mass production
From specs to detector
–HV divider & stability
–Injectors & drift speed variations
–NTD fluctuations
–Safe design & yield
– Radiation damage
–Mass production
SDD first proposed by E. Gatti P. Rehak 1984
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Silicon drift detectors (SDD)
• due to their collection electrode geometry, SDD have excellent noise performance and are well suited for low-energy X-ray spectroscopy applications.
n-side
p-side
divider
anodes
oxide (SiO2)
metal
depletionpotential-U
driftpotential
anode drift distance
By means of a series of cathodes (biased with a scaling potential) a highly-linear drift field is established from the center of the detector towards two arrays of anodes placed at opposite sides of the SDD.
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This design of this SDD originates from the primary need to perform unambiguous measurement of
the impact point of charged particles along both the X and Y axis in presence of high multiplicity,
together with a large sensitive area.
The ionizing radiation create electron-hole pairs: the electron
cloud is focused at the center of the silicon bulk and drifts to
the anodes, while the holes are collected by the cathodes.
When the electrons reach the end of the drift zone, they are
abruptly pushed towards the anodes by an electrode (placed
beneath them) in order to minimize the collecting time.
The X coordinate is measured along the anodes where the
charge is collected, the Y coordinate corresponds to the
travel time of the electrons.anode
electrons
The silicon drift detector (SDD)The silicon drift detector (SDD)
Simulation of the potential distribution in the SDD
Ionising radiation
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256 readout anodes256 readout anodes
256 readout anodes256 readout anodes
driftdrift
Wafer type:Wafer type: 5” Neutron Transmutation Doped
<111> 3 k.cm, 300 m thickArea:Area:
sensitive: 7.02 7.53 cm2, divided into two drift regions
total: 7.25 8.76 cm2, (ratio = 0.83)
Each drift region:Each drift region: 35 mm long 291 cathodes driven by built-in voltage
divider 256 anodes – 294 m pitch 3 rows of 33 MOS charge injectors (for
the drift velocity calibration)Guard regions:Guard regions:
independent built-in voltage dividers
Typical operating parameters:Typical operating parameters: Drift bias voltage: -2.4 kV, 8V/cathode E=670V/cm Maximum drift time : 4.3 s, vd =8 m/ns
Power dissipation on board:Power dissipation on board: 0.95 W0.95 W equivalent Rtot of all drift + guard dividers 4781 kΩ total current in all dividers ~0.40 mA
The SDD was selected to equip the 3rd and 4th layers of the Inner Tracking System (ITS) of the ALICE experiment at LHC. The finger print of this silicon drift detector is:
256 readout anodes256 readout anodes 256 readout anodes256 readout anodes
driftdrift
256 readout anodes256 readout anodes
256 readout anodes256 readout anodes
driftdrift
256 readout anodes256 readout anodes
256 readout anodes256 readout anodes
driftdrift
256 readout anodes256 readout anodes
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guard cathodes (32 guard cathodes (32 m pitch)m pitch)
292 drift cathodes (120 292 drift cathodes (120 m pitch)m pitch)
implanted HV voltage dividersimplanted HV voltage dividers
256 collection anodes (294 256 collection anodes (294 m pitch)m pitch)
collection zone close-up
injector lines close-up
injector line bonding pad injector line bonding pad
MOS injector (every 8MOS injector (every 8thth anode) anode)
Detector design featuresintegrated dividers generate the biases for all of the drift cathodes and the guard region which used to scale down gradually the negative high-voltage to ground at the edge of the SDD.sets of MOS injectors placed at different distances from the anodes are used for the drift velocity calibration.
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Drift distance (mm)
Res
olu
tion
(m
) anode axis (Z)
drift-time axis (R-)
About 600 detectors have been produced using a dedicated double sided process.
Due to the redundant design and production technology the yield was grater than 60% .
260 detectors (84 in layer 3 and 176 in layer 4) have been mounted on the barrel of the ALICE-ITS
now in the commissioning phase acquiring cosmic muons data.
Beam-test dataBeam-test data
reconstruct the impact position of the ionizing particles with a resolution
better than 30µm in both X and Y axis.
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suitable for low-energy X-ray spectroscopy applications:
+ anode capacitance is about 50 fF,
+ the leakage current at the anode measured at room temperature is very low
This allows a very-low noise contribution from the front-end electronics. Considering its sensitive area, more than an order of magnitude larger than that of the standard SDDs, this detector could open the way to application areas of the X-ray spectroscopy that require wide surface coverage.
Each anode sees a 10 mm2 surface - the reported current values correspond to 4 anodes read-out together
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The measurement setupThe measurement setup Climatic chamber
The detector and the front-end electronics are placed in a climatic chamber able to control the temperature.
This also acts as shield detector and electronics from irradiated noise.
Bias board
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The last 6 drift cathodes near the anodes are decoupled directly on the detector board to minimize noise coupling.
An aluminum block is used to collimate the radioactive source. This minimizes the partial charge collection.
The collimator, 4cm high, has a thin slit (about 0.5mm) that allows to illuminate almost the whole drift length of a set of anodes. It sits 5mm above the detector.
Bias board
RADIOACTIVESOURCE
COLLIMATOR
BIAS CONNECTOR
TO PREAMPLIFIERS
JFETs
Detector board
A low capacitance JFET (CGS = 0.4pF) is connected to a
group of 4 anodes (CDet,tot = 0.2pF) and read out by a
multi-channel preamplifier board.
The JFET integrates a feedback capacitor CF = 50fF,
and a transistor to discharge the capacitor realizing the
reset of the preamplifier.
The total capacitance measured at the input of the
preamplifier (the gate of the JFET) is about 1pF
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560 eV FWHM @ 13.95keV 4%
Co
un
ts
ADC channels
241Am spectrum measured at +16°C with a trapezoidal shaping having a rise/fall time tR = 0.4µs and a flat top of 0.2µs. The high voltage bias of the detector is -1600V. The leakage current of the four anodes is ~ 5pA
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Co
un
ts
ADC channels
386 eV FWHM 7%
Mn kα
Mn kβ
55Fe spectrum measured at 0°C with a trapezoidal shaping having a rise/fall time tR = 1.2µs and a flat top of 0.2µs. The high voltage bias of the detector is -1300V. The leakage current of the four anodes is ~ 1pA. The red line represents the fit function used to determine the energy resolution.
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Next step on board first stageDetail fet F2 for
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ConcludingConcluding
Largest drift detectorActive area: 52 cm2Anode pitch: 294µm512 anodes on two rowsPosition resolution: <50µmMOS injectors for calibration
Participants:- Isaf Roma
Marco Feroci - Ictp Trieste
Dipak Debnath
Debashis Bhowmick Ritabrata Sarkar Claudio Tuniz
Andres Cicuttin Mliz Crespo
- Infn TriesteGianluigi ZampaAndrea VacchiAlexandre RashevskyValter BonviciniErik Vallazza
- Iasf Bologna Labanti
- Infn BolognaGiuseppe
Baldazzi- PoliMilano
Longoni-
Targets: High-resolution low noise large area silicon detectors based on the Silicon Drift Detector principle.
o Low energy X-ray spectroscopyo Radioactivity contamination detectorso Atomic physics studieso X - ray astronomyo Medical applications