1. A Comparative Sensor Testbeam Using Micro-Focused X-rays
A. Blue, R. Bates, C. Buttar, D. Maneuski & K. Wraight

2. Measurement Techniques
Currently there are many techniques for studying charge collection and electrical field variation within detectors
Lasers (TCT)
Radioactive Source
Particle Testbeams
However we were looking for a technique that would allow for the examination of
Inter-strip/pixel charge collection profile (<5mm beam spot)
Variation of electrical field towards the device edge (controllable & movable beam)
Accurate charge collection with varying detector biases (fixed energy deposition in the material)
Requires NO reconstruction (no track fitting)
Use Focussed X-rays
2/18

3. Diamond Synchrotron
Diamond Light Source opened in 2007 near Oxford, UK
Currently has 26 beamlines
Another 4 under construction
3GeV Beam
Energy Range between 0.6meV & 80KeV
3/18

4. X-rays are not MIPs! Important to stress X-rays are not MIP like!
A MIP (every time) will travel through your DUT creating charge of ~70e/micron (for Silicon)
An X-ray (sometimes) will interact with your DUT depositing the entire charge of the X-ray in the DUT
The higher the X-ray energy
The more energy is deposited
The less likely the interaction is (attenuation co –efficient is to blame)
The X-ray can deposst at any point in the thickness of the DUT
Charge cloud size can vary (but can be simulated)
4/18

5. Micro focused X-rays Beam station B16
Comprises of a water-cooled fixed-exit double crystal monochromator that is capable of providing monochromatic beams over a 2-20 Kev photon energy range.
An unfocused monochromatic beam is provided to the experimental hutch.
A compound refractive lens (CRL) was used to produce a 15 Kev micro-focused X-ray beam.
4/18

6. We move the DUT which is mounted on an X,Y,Z stage
Beam Alignment
We move the DUT which is mounted on an X,Y,Z stage
Micron precision
All controlled by python scripts
Can then be integrated to DAQ by
OK/go signals
Simple delay (time for events + movement
time)
Simplest way
Beam on
Use Lasers are “rough guide”
Find hit pixel/strip
Work out position of beam
Move in 5 or 10mm Steps
5/18

7. Beam Size
The size of the micro-focused beam is determined by measuring transmissions scans with a 200 mm gold wire.
The derivative of these scans gave a beam shape which had a FWHM of 3.27 x 1.7mm
6/18

8. At Synchrotrons, you always have X-rays (photons) with fixed energy
Beam ‘Strength’
At Synchrotrons, you always have X-rays (photons) with fixed energy
Each 15keV interaction deposits ~4.2k electrons (due to the 3.6eV electron hole pair creation energy of Silicon).
However you can vary the intensity
Calculated from the beam current
2-3 photons/25ns
Each 15keV photon has 51.07% chance of interaction with 320mm silicon.
You can add Al layer to attenuate the photons
However it can increase the beam spot
7/18

9. Reconstruction and Analysis
There isn’t any necessary
There is no telescope
Analysis
Very simple
In the data we have a ‘scan’
Each scan has a no. of events per position
Extremely simple to construct plots of hits per position
All plots shown today were made on the 5hr train from Oxford to Glasgow…

10. Cooling and Vacuum systems Dry Air, N2
Misc
Safety courses
Cooling and Vacuum systems
Dry Air, N2
Start at 9am on first day. End at 9am on the last day
24 hours access
1 time in 7 visits has the beam been
down
You have your own Control Room
8/18

11. Work at Diamond Require written proposals for beamtime
Free if you publish
£24K /day if you don’t..
Written 6 proposals over 5 years
We learn something new every time
Last beam we managed to use a beam trigger!
We’ve tested
SCP edgeless strips – Unirradiated & irradiated (ALiBaVa)
Active Edge pixels (Timepix)
Thin pixel sensors (Timepix)
3D sensors (Timepix)
LGAD sensors (ALiBaVa)
CdTe (Timepix)
ATLAS upgrade barrel strip module (ATLYS FPGA board)
ATLAS upgrade endcap module (ATLYS FPGA board)
HV-CMOS pixel (USBpix)
HV-CMOS strip (ATLYS FPGA board)
HR-CMOS strip (ATLYS FPGA board)
9/18

12. Scribe Cleave & Passivate
Diamond Stylus
Laser
XeF2 Etch
DRIE Etch
Saw cut
Tweezers (manual)
Loomis Industries
LSD-100
Dynatex, GTS-150
Native Oxide + Radiation or
N-type
Native SiO2 + UV light or High T
PEVCD SiO2
PEVCD Si3N4
ALD “nanostack” of SiO2 & Al203
P-type
ALD of AL2O3
All treatment is post processing & low temperatures
Etch scribing can be done during fabrication
10/18

13. Active Edge
Active Edge devices turn the physical cut edge of the sensor into a junction
Allows the depletion of the silicon all the way to the physical edge.
The sensors sidewalls are cut using dry etch techniques to eliminate the microscopic damage associated with the sawing.
The sidewalls of the cut edges are then doped to compensate for the high level of defects at the sidewall, and passivated with a thermal oxide layer
Active edge pixel senor under test, showing less than 50mm from the edge pixel to the sensor edge
11/18

14. SCP devices SCP strip sensors N-type & P-type 80mm Strip pitch
Irradiated
Bulk
Thickness (mm)
Strip Pitch (mm)
Edge strip to edge (mm) 1 - N
200 80 28 2
4.8x1014 ncm-2 P
100
170
SCP strip sensors
N-type & P-type
80mm Strip pitch
Wire bonded to ALiBaVa readout system
Irradiated samples cooled to -15oC With peltier + chiller
12/18

15. Micro-focussed X-Ray beam: CCE of SCP
Scan of the edge of the strip detector with full guard ring structures
a) shows the mean signal size with an ADC cut of 10, (b) has an ADC cut of 40.
(b)
(a)
Scan of the cleaved edge of the strip detector.
(a) Shows the mean signal size with an ADC cut of 10, (b) has an ADC cut of 40.
13/18

16. Irradiated SCP devices
Edge Strip: 305mm to SCP edge
Preliminary results from latest testbeam. After 4.8x1014 ncm-2, charge is collected on edge strips
12KeV beam, 2.5mm FWHM
10mm Step size,. T= -8oC
14/18

17. Calculated Full depletion voltage (V)
Active Edge devices
Device
Implant
Bulk
Thickness (mm)
Pixel to Edge (mm)
Calculated Full depletion voltage (V) NN N
200 50 28 NP P
100 10 NP
VTT/Advacam Active Edge sensors
Sensors flip-chip bonded to Timepix
55mm x 55mm pixels
Measurements taken in pixel counting mode
15/18

18. Over Edge Scans - Active Edge/Timepix
16/18

19. Side & Corner Scans – Active Edge/Timepix
17/18

20. Future Work & Conclusions
Micro-focussed X-rays have been successfully used to study
Pixel detectors utilising Active edge technology with varying material
SCP micro strip detectors pre and post irradiation
They don’t replace conventional testbeams
However it is a very good complimentary technique
The main message is
They strongly overlap with our techniques
More often than not the beam is “across the road” from many of our testbeam halls
18/18