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Introduction to
Synchrotron Radiation
Detectors
Heinz Graafsma Photon Science Detector Group
DESY-Hamburg; Germany
2
The Detector Challenge:
1900 1960 1980 2000
PETRA-3
Second generation
First generation
X-ray
tubes
ESRF (2000)
ESRF (1994)
1900 1920 1940 1960 1980 2000
ESRF (1994)
2ème generation
1ère génération
Tubes àrayons X
Années
ESRF (futur)
Limite de diffraction
ESRF (2000)3ème
generation
Lasers àélectrons libres
Rayonnementsynchrotron
1020
1018
1016
1014
1012
1010
108
1021
1022
1023
1019
1017
1015
1013
1011
109
107
106
Brillance
(photons/s/mm2/mrad2/0.1%B.F.)
Synchrotron Sources
bri
llia
nce
Free-Electron Lasers
3
The Detector Challenge:
XFEL Beamline Layout
4
5
The Detector Challenge:
• Spectroscopy (determine energy of the X-rays): – meV – 1 keV resolution
– time resolved (100 psec) – static
• Imaging (determine intensity distribution) – Micro-meter – millimeter resolution
– Tomographic
– Time resolved
• Scattering (determine intensity as function momentum transfer = angle) – Small angel – protein crystallography
– Diffuse – Bragg
– Crystals - liquids
6
What are the basic principles ?
1. In order to detect you have to transfer energy from the particle to the detector
2. X-ray light is quantized (photons)
3. A photon is either fully absorbed or not at all (no track like for MIPs)
4. The energy absorbed is transferred into an electrical signal and then into a number (digitized).
7
Signal Generation Needs transfer of Energy
Any form of elementary excitation can be used to detect the radiation signal:
Ionization (gas, liquids, solids)
Excitation of optical states (scintillators)
Excitation of lattice vibrations (phonons)
Breakup of Cooper pairs in superconductors
Typical excitation energies:
Ionization in semiconductors: 1 – 5 eV
Scintillation: appr. 20 eV
Phonons: meV
Breakup of Cooper pairs: meV
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Ge Si GaAs
Eg = 0.7 eV Eg = 1.1 eV Eg = 1.4 eV
Indirect band gap Direct band gap
Band structure (3)
9
What would you like to know about your X-rays?
1. Intensity or flux (photons/sec)
2. Energy (wavelength)
3. Position (or mostly angles)
4. Arrival time (time resolved
experiments)
5. Polarization
10
4 modes of detection
1. Current (=flux) mode operation
2. Integration mode operation
3. Photon counting mode operation
4. Energy dispersive mode operation
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Current mode operation
detector I
X-ray
Integrating mode operation
X-ray
detector C V(t)
12
Photon counting mode
V(t) detector
X-ray
C R
Lower threshold
Upper threshold
13
Energy dispersive mode
detector
X-ray
C V(t) R
Height total charge = energy of the photon
14
Some general detector parameters
• QE = quantum efficiency = fraction of incoming photons
detected (<1.0). You want this to be as high as possible.
• DQE = detective quantum efficiency =
You can never increase signal, nor decrease noise! So
signal to noise will always degrade in the detector. (NB:
signal to noise is the most important parameter when
you measure something!)
• Gain = relation between your signal strength (V, A, ADU)
and the number of photons.
01.in
out
noisesignal
noisesignal
15
Some more parameters for 2D systems
• Point Spread Function (PSF) (Line spread function (LSF) or spatial resolution):
A very small beam (smaller than the pixel size) will produce a spot with a certain size and shape. Very important are the FWHM; and the tails of the PSF.
This is experimentally difficult use sharp edge and LSF
Note: pixel size is not spatial resolution! (but should be close to it in an optimal design).
16
Some more parameters for 2D systems
• Modulation Transfer Function (MTF):
How is a spatially modulated signal (line pattern)
recorded (transferred) by the detector?
This depends on the frequency.
Is directly related to the LSF and the DQE
MinMax
MinMaxcontrastModulation
17
100 %
0 %
18
Some more parameters for 2D systems
• Modulation Transfer Function (MTF) Example
010100
0100.
contrastIdeal:
Effect of noise: 5050150
50150.
contrast
Effect of PSF: 502575
2575.
contrast
• Pulse length: 103 shorter (100 fsec vs 100
psec)
• Emmittance: 102 horizontal, 3 vertical
lower
• Intensity per pulse: 3x102 higher (1012 ph)
• Monochromaticity: 10 better
Peak brilliance: 109 higher
FEL Sources vs. Storage Rings
19
FEL Challenge: Different Science
• Completely new
science
• Fast science 100 fsec
• “Single shot” science
x109
1. Single shot-science: 1012 ph in 100 fsec
(complete) ionization of sample;
followed by coulomb explosion.
• Fortunately scattering is faster: “diffract-and-
destroy”. (<50 fsec) (Nature 406, 752, (2000)).
• Crystal diffraction is “self-gating” (Nature Photonics, 6,
35, (2012)).
Consequences for the detector: (H.Graafsma; Jinst, 4, P12011, (2009))
21
Single shot imaging…
K. J. Gaffney and H. N. Chapman,
Science 8 June 2007
1. Single shot-science: 1012 ph in 100 fsec
(complete) ionization of sample; followed by
coulomb explosion.
• Fortunately scattering is faster: “diffract-and-destroy”.
(<50 fsec) (Nature 406, 752, (2000)).
• Crystal diffraction is “self-gating” (Nature Photonics, 6, 35,
(2012)).
2. Central hole in detector & no beamstop: 1012 ph
@ 12 keV 1K rise in mm3 Cu 3000 K per
bunch train + huge background
Consequences for the detector:
23
Radiation doses: worst case (?)
> 5000 h User-operation per year
> Undulator shared between 2 experiments 2500 hrs/exp./year
> Date taking 50% (rest alignment etc.) 1250 hrs/year
> Each branch can take ½ of the load: 15000 pulses/sec
6.75 1010 pulses/year
> Certain experiments expect 5 x104 photons per pixel (200 mm) per
pulse. Small angle and liquid scattering always same place on detector
3.4 1015 photons/year = 1016 ph/3 years
(@ 12 keV silicon surface dose of 1 Giga Gray!!!)
Angular coverage / detector size:
> 12 keV = 0.1 nm in order to study features (d) to atomic resolution.
> Bragg’s law (2dsin(q) = l) 2q = 60 degrees 120 degrees total
2q
Liquid scattering: momentum transfer 10 A-1 200 degrees back scattering
Angular resolution 2 examples:
Coherent Diffractive Imaging (CDI):
> 0.1 nm spatial features: dmin
> 100 nm samples (e.g. virus): D
Nyquist >2000 sampling points (pixels) 0.5 mrad
D2q = dmin x asin(l/2dmin) / 2D
X-ray Photon Correlation Spectroscopy:
Speckle size: Qs = l/D, D is sample or beam size
Compromise between sample heating (large beam) and speckle size
(small beam)
25 mm beam at l=0.1 nm 4 mrad speckles (80 mm at 20 m)
E-XFEL Challenge: Time structure = difference with “others”
600 ms
99.4 ms
100 ms 100 ms
220 ns
FEL
process
X-ray photons
<100 fs
Electron bunch trains; up to 2700 bunches in 600 msec, repeated 10 times per second.
Producing 100 fsec X-ray pulses (up to 27 000 bunches per second).
27 000 bunches/s
But with
4.5 MHz rep rate
XFEL Detector requirements
4.5 MHz
The XFEL solutions:
Hybrid Pixel Array Detectors
Hybrid Pixel Array Detector (HPAD)
Diode Detection Layer
• Fully depleted, high resistivity
• Direct x-ray conversion
• Silicon, GaAs, CdTe, etc.
Connecting Bumps
• Solder or indium
• 1 per pixel
CMOS Layer
• Signal processing
• Signal storage & output
Gives enormous flexibility!
X-rays
31
Hybrid Pixel Detectors
Particle / X-ray Signal Charge Electr. Amplifier Readout Digital Data
Pixelated
Particle
Sensor
Amplifier &
Readout Chip
CMOS
Indium Solder
Bumpbonds Data Outputs
Power
Clock Inputs
Connection
wire pads
Power
Inputs
Outputs
Particle / X-ray
Qsignal
32
The new generation: Medipix et al.
Au
Sensor Substrate
InGaAs
UBM
Insulator
CMOS ROIC
Au
UBM
Al
bump Au
Sensor Substrate
InGaAs
UBM
Insulator
Au
UBM
Al
Au
Sensor Substrate
Al
UBM
Insulator
UBM
Al
33
Why are HPADs so popular ?
• Custom design of functionality: you design
your readout chip specific for your
application (unlike CCDs).
• Direct detection good spatial resolution
• Massive parallel detection high flux
• But: development takes long and is
expensive.
The Adaptive Gain Integrating Pixel Detector The AGIPD consortium:
PSI/SLS -Villingen: chip design; interconnect and module assembly
Universität Bonn: chip design
Universität Hamburg: radiation damage tests, “charge explosion” studies; and sensor design
DESY: chip design, interface and control electronics, mechanics, cooling; overall coordination
Some Facts
6 years development
~ 20 people
Some Milestones
First 16x16 pixels prototype End 2010
Definition of final design Summer 2011
Production, assembly and test >2013
The Adaptive Gain Integrating Pixel Detector
C1
Leakage comp.
C2
C3
Discr.
Contr
ol lo
gic
Trim DAC
Vthr VADCmax
Analo
gue
encodin
g
Normal Charge
sensitive amplifier
High dynamic range:
Dynamically gain switching system
Extremely fast readout (200ns):
Analogue pipeline storage
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
0 5000 10000 15000Number of 12.4 KeV - Photons
Ou
tpu
t V
olta
ge
[V
]
Cf=100fF Cf=1500fF Cf=4800fF
2,50E+03
3,00E+03
3,50E+03
4,00E+03
4,50E+03
5,00E+03
5,50E+03
6,00E+03
6,50E+03
7,00E+03
0,00E+000 1,00E+003 2,00E+003 3,00E+003 4,00E+003 5,00E+003 6,00E+003 7,00E+003 8,00E+003 9,00E+003 1,00E+004
Charge [Clk]
Am
pli
tud
e [
LS
B]
Analogue Pix 0 Analogue Pix 1 Analogue Pix 2 Analogue Pix 3
Gain Pix 0 Gain Pix 1 Gain Pix 2 Gain Pix 3
2,87E+3 + 3,26E+1x 2,80E+3 + 2,77E+1x 2,75E+3 + 2,52E+1x 2,77E+3 + 2,94E+1x
3,61E+3 + 1,42E+0x 3,54E+3 + 1,20E+0x 3,49E+3 + 1,11E+0x 3,47E+3 + 1,28E+0x
3,96E+3 + 3,03E-1x 3,79E+3 + 2,84E-1x 3,70E+3 + 2,70E-1x 3,76E+3 + 2,87E-1x
AGIPD03 Gains 0 Gy
>Gain Ratios:
>H/M= 23.0 (23.1; 23.0; 22.8; 23.0)
>M/L= 4.37 (4.67; 4.23; 4.10; 4.46)
Not corrected for variation of charge injection circuit
AGIPD – Analogue Memory &
Radiation Hardness
+ -
THR
DAC SW CTRL
Analogue Mem
Analogue Mem
CDS
RO Amp
R O
B u s
>Droop (loss of signal)
•Time
•Radiation dose
600 ms
99.4 ms
100 ms 100 ms
Electron bunch trains; up to 2700 bunches in 600 msec, repeated 10 times per second.
Producing 100 fsec X-ray pulses (up to 27 000 bunches per second).
Store and read: for 100 msec
Write: within 220 nsec
AGIPD - Analogue Memory
100 msec “loss free” Charge Storage in Analogue Pipeline
• Switch design is the challenge
• Thick oxide & MIM caps in IBM process are OK
AGIPD analogue memory:
• DGNCAP (thick oxide n-FET in n-well) caps
• Minimise voltage drop across T1
– Floating n-well
– Special precautions for radiation hardness needed
AGIPD03 Memory Leakage
-120
-100
-80
-60
-40
-20
0
20
1,00E-004 1,00E-003 1,00E-002 1,00E-001 1,00E+000
Storage time [s]
Dro
op
(a
v. r
ed
uc
tio
n o
f d
yn
am
ic r
an
ge
) [%
]
RVT-IN-GND (0Gy) RVT-VDD-GND (0Gy)
RVT-IN-GND (100kGy) RVT-VDD-GND (100kGy)
RVT-IN-GND (1MGy) RVT-VDD-GND (1MGy)
LP-IN-GND (0Gy) LP-VDD-GND (0Gy)
LP-IN-GND (100kGy) LP-VDD-GND (100kGy)
LP-IN-GND (1MGy) LP-VDD-GND (1MGy)
LP-VDD-VDD (0Gy) RVT-VDD-VDD (0Gy)
LP-VDD-VDD (100kGy) RVT-VDD-VDD (100kGy)
LP-VDD-VDD (1MGy) RVT-VDD-VDD (1MGy)
Transistor type – connection of upper n-well – potential of guard ring
AGIPD ASIC
Sensor ASIC per pixel
ASIC
periphery
Chip output driver
Mux
HV
+ -
THR
DAC SW CTRL
Analog Mem
Analog Mem
CDS
RO Amp
Calibration circuitry
Adaptive gain amplifier
352 analog memory cells
… … R
O b
us (
per
colu
mn)
Pixel matrix
Imaging with AGIPD 0.2 prototype
The Adaptive Gain Integrating Pixel Detector
Connector to interface HDI Base plate
sensor chip wire bond bump bond
~ 2mm
~220 mm
1k x 1k (2k x 2k)
64 x 64
pixels
Basic parameters
•1 Megapixel detector (1k 1k)
•200mm 200mm pixels
•Flat detector
•Sensor: Silicon 128 x 512 pixel tiles
•Single shot 2D-imaging
•4.5 MHz frame rate
•2 104 photons dynamic range
•Adaptive gain switching
•Single photon sensitivity at 12keV
•Noise 300e
•Storage depth 350 images
•Analogue readout between bunch-trains
Calibration challenges:
> 106 x 3 gains; with > 10 points per gain curve: O(107)
> 106 x 350 storage cells > 10 points per droop curve: O(109)
> How to store the calibration data and how to correct data?
> How often do we need to recalibrate
> On-chip calibration sources
> Cross calibration with physics (photons, alpha, …)
> How long does this all take?
45
Some reflections on the future
• Active Sensors (DSSC)
DSSC - DEPMOS Sensor with Signal Compression
> MPI-HLL, Munich
> Universität Heidelberg
> Universität Siegen
> Politecnico di Milano
> Università di Bergamo
> DESY, Hamburg
>Hexagonal pixels 200mm pitch
• combines DEPFET
• with small area drift detector (scaleable)
> DEPFET per pixel
> Very low noise (good for soft X-rays)
> non linear gain (good for dynamic range)
> per pixel ADC
> digital storage pipeline
46
Output voltage as function of charge
injected charge
DEPMOS Sensor with Signal Compression
DEPFET: Electrons are collected in a storage well
⇒Influence current from source to drain
source drain
gate
Fully depleted silicon e-
Storage well
injected charge
DSSC
47
48
Some reflections on the future
• Active Sensors (DSSC)
• Built-in intelligence per pixel (AGIPD)
49
Some reflections on the future
• Active Sensors (DSSC)
• Built-in intelligence per pixel (AGIPD)
• Communication pixels (Medipix-3)
50
55m
The winner takes
all
• Charge processed is
summed in every 4
pixel cluster on an
event-by-event basis
• The incoming
quantum is assigned as
a single hit
Medipix3 – charge summing concept
51
Some reflections on the future
• Active Sensors (DSSC)
• Built-in intelligence per pixel (AGIPD)
• Communication pixels (Medipix-3)
• More functionality per area/pixel: 3D-ASIC
technology (Helmholtz Cube)
52
Hybridization
Cut the sensor as close as possible
Use thinned readout chips
Stay within the exact n-fold pixel pitch
53
XFS Module Specification: PSI/SLS
Operate 2x4 (8) Chips per Module. ~78 x 39 mm2
54
PILATUS @ SLS
Courtesy: Ch. Brönnimann, PSI SLS Detector Group
Sensor
Read-out chips
Wire bonds
Base plate
Al support
Module Control Board MCB Cable
55
Current State-of-the-art
The “Helmholtz-Cube” Vertically Integrated Detector Technology
Replace standard sensor with:
3D and edgeless sensors, as well
as High-Z
Replace standard bump-
bonds with new
interconnect techniques
Replace standard ASIC and wire
bonds with thinned ASICs and
TSV as well as ball-grid arrays
Replace standard
ASIC with 3D-ASICs
Develop new high speed IO’s
58
59
3D-ASIC technology
60
The “Helmholtz-Cube” Vertically Integrated Detector Technology
S
Electrical + Cooling + Support
Power-in Optical I/O
Sensor Analogue ASIC Digital ASIC I/O ASIC
62
63
Summary Detectors
• Signal-to-noise ratio most fundamental parameter in measurements.
• A detector is always a compromise (ex. speed vs. noise). Application determines what you compromise.
• Never take a detector as a “perfect black box”, be aware of limitations.
• Understanding your detector is part of understanding your science.
