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

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

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

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

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

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

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

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

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…

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

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

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

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

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

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

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

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

Over Edge Scans - Active Edge/Timepix 16/18

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

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