1. Edgeless & Slim Edge Detectors
Andrew Blue, on behalf of the RD50 Collaboration

2. Slim Edge & “Edgeless” sensors
Standard silicon detectors have a relatively large insensitive region around their active area.
This dead region is due to presence of multiple guard rings and the clearance for the dicing street of the sensors
It can extend to more than a few mm’s, depending on the detector application
To remove inactive regions around each sensor reduced edge or “edgeless” sensors are required.
Such sensor designs in conjunction with through-silicon vias (TSV) would also result in a reduction in radiation length, making edgeless sensors a promising option for the particle physics community.
Without the need for shingling/ overlapping of sensors
Such sensors utilize one of a number of methods to reduce the number of guard rings and their pitch so to increase the active area of tiled detectors, and a (non-exhaustive) list of techniques proposed for such a reduction in dead area follows

3. Slim Edge
Slim edges reduce the dead area by reducing the number of guard rings used in tandem with the reduction of the distance from the outer guard ring to the cut edge.
Further reductions can be made in a double sided (n-on-n) process by placing the guard rings on the back surface such that they overlap the edge pixels/strips on the front side
Example of slim edge devices proposed for the IBL, where edge pixels on the sensor surface overlap the guard rings structures on the back.

4. 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

5. 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

6. RD-50 work
Many studies investigating slim edge & edgeless technology being carried out via RD50
Some already covered in this conference
‘3D detectors in ATLAS’: Sebastian Grinstein
‘RD50 Overview’: Marcos Fernandez Garcia
Today I will talk about
Active edge devices with varying thicknesses and levels of irradiations
Irradiations to study the passivation layers used for slim edge devices
Micro focused X-rays for CCE measurements of SCP and Active edge devices

7. Active Edge – FE-I4 Assemblies
Much progress is being made in to the study of Active Edge devices
Latest studies include
Test Beam results with thin pixel sensors at High Eta
Characterization of Active edge pixels after irradiations
Comparison of CCE for pixels sensors of different Active thicknesses
125mm Edge implemented in FE-I3 and FE-I4 sensors
50mm implemented in only FE-I3 devices

8. CCE of Active Edge pixels after irradiations
100 mm thick sensor with 125 mm slim edge bump-bonded to an FE-I3 (1500 e- threshold)
87% CCE at 300V for both inner and edge pixels after irradiations of
1x1015neq/cm2 (KIT)
5x1015neq/cm2 (Ljubljana)
p-type MCZ 100 mm thick sensors with 125 mm slim edge (FEi4 & 1100e- threshold )
Compatible charge collection properties between edge and inner pixels

9. CCE for different thicknesses of Active Edge pixels
The mm thick sensors show higher charge collection up to a fluence of 4-5x1015neq/cm2
At higher fluence the effect of charge trapping teens to equalize the charge collection efficiency for all thicknesses
100mm thick Slim Edge Irradiated devices taking ~500V

10. SCP devices - Observations
How does the processing involved to produce slim edge/edgeless devices affect detector efficiencies of DUT edges before and after irradiation?
Emerging pattern
No issues with Radiation Hardness for N-type devices
However for P-type devices
High currents at low ionisation doses <1x1014ncm-2
No significant excess on the edge for high ionizing dose >1x1014ncm-2
No issues for neutron-irrad. samples
Has led to a series of investigations (Laser, source testbeams, irradiations)
Today will talk about
Irradiations to study the passivation layers used for slim edge devices
Micro focused X-ray for CCE measurements of SCP & active edge devices

11. P-type SCP Devices After Irradiation
To investigate, 12 SCP p-type strip devices (CIS) were irradiated at LANL in 2011
Results were inconclusive
High fluence devices (3/3 at 1x1016neq & 3/3 at 1x1015neq) show expected post-rad leakage current
Low fluence devices (1/3 at 1x1013neq & 1/3 at 1x1014neq) showed early breakdown!
Post-Irrad
8mA
0.8mA
0.1mA
Pre-Irrad
Leakage currents do not scale with fluence
low fluence (< 1x1014): reduced edge performance
high fluence (>1x1014): resistive edge

12. Irradiated P-type SCP devices
Possible issues with the Si-Alumina interface
One theory is that a thin layer of AlxSiOy forming between Si and Al2O3
Forms as part of the ALD process
This oxide layer gains more of its (positive) interface charges with first few Mrad, counteracting the necessary negative oxide from alumina
To check this hypothesis MOS capacitors were fabricated at the CNM microfabrication facility with Al2O3 as the dielectric. The capacitors allow assessment of the effective charge density via C-V curves
We irradiated the devices to figure out how the charge density changes with dose
The capacitors were irradiated at LANL with 800 MeV protons in January The fluence was up to 6.8x1014 p/cm2 (34 Mrad)
(equivalence: 1015 p/cm2 = 0.71x1015 neq/cm2 = 50 Mrad)
Irradiations with gammas took place at BNL in December 2013, up to 30 Mrad

13. Test Devices 4 Wafers: 100 mm-diameter (100) Cz Si P-type
5 Squared shaped MOS
4 Wafers: 100 mm-diameter (100) Cz Si P-type
400nm SiO2 field isolation & patterning
Al2O3 Process 1
Wafer 1: 40nm CNM
Wafer 2: 20nm CNM
Cleaning
ALS (ToC, precursors)
Post-deposition anneal
Atomic Layer Deposition
Al2O3
Al2O3 Process 2
Wafer 3: 20nm NRL
Wafer 4: 40nm NRL
500 nm Al (99.5%)/Cu (0.5%) & patterning
Wafer backside metallization
½ wafer post metallization anneal (PMA)
20 in N2/H2

14. Capacitance-Voltage Wafer Mapping
25 chips
½ wafer
A2 = 2.3·10-3 cm2
Good yield
Good uniformity

15. positive charge trapping gamma-radiation-hardness
C-V Results from Gamma Irradiations
0.1, 0.3, 1, 3, 10 & 30 Mrad
Positive Charge
Rad-hard
positive charge trapping
in process 1 Al2O3
gamma-radiation-hardness
in process 2 Al2O3 with PMA

16. gamma-radiation-hardness positive charge trapping
C-V Results from Proton Irradiations
0.07, 0.35, 0.96,
3.97, 7.35 & 34.2 Mrad
Positive Charge
Rad-hard
gamma-radiation-hardness
in process 2 Al2O3 with PMA
positive charge trapping
in process 1 Al2O3

17. Summary of Al203 Irradiations
MOS capacitors designed to assess the radiation hardness of Al2O3 layer used in Scribing Cleaving Passivation (SCP) process for p-type bulk Si devices have been successfully fabricated. The capacitors allow us to measure the effective dielectric charge density, critical for the SCP performance
Al2O3 was deposited with 2 different processes at 2 facilities
Additionally, we intentionally varied the deposition thickness (20 nm and 40 nm) and post- metallization annealing step
The devices were irradiated at LANL with protons and at BNL with gammas with TID up to 34 Mrad
The initial assessment of post-rad performance indicates an interesting dichotomy between the 2 deposition processes:
In one case the radiation-induced changes in effective charge density are negligible
In another case it scales nearly linearly with dose
We may need to vary the processing with a future fabrication to figure out which of the processing differences influenced the different radiation performance

18. Further CCE studies of SCP devices
Many studies in various technologies (n-type & p-type) have taken place
Would like to use technique for studying
Edge Pixels/Strips
Inter-strip/pixel charge collection profile (<5mm beam spot)
Use Focussed X-rays
Sensor Type
Origin
Edge-Active area Distance (mm)
Signal Readout
Beam
Ref
P-type strips
PPS (CIS)
~200
Binary (PTSM)
90Sr
V. Fadeyev et al
‘Pixel 2012, NIM A 731 ( ) 2013
N-type Strips
GLAST (HPK)
Analog (ALiBaVa)
R. Mori et al
JINST 7 P
P-type 3D pixels
IBL (CNM) 50
FEi3 & FEi4
CERN Testbeam
S Grinstein et al
‘RESMDD12, NIM A 730 (28-32) 2013
G. Pellegrini et al
Pixel 2012, NIM A 731 ( ) 2013
P-type Strips
A. Macchiolo
P-type Strips n-irradiated
Single-channel
Laser-TCT
I Mandić et al.,
NIMA 751 (2014)
150
A. Macchiolo

19. Micro focused X-rays for CCE measurements
Used the Diamond Light Source base in Oxford, UK
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.
The size of the micro-focussed beam was 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 2.5mm

20. 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

21. 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.

22. 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
Analysis to follow (CCE v bias)

23. 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 Timepix2
55mm x 55mm pixels
Measurements taken in pixel counting mode

24. Over Edge Scans - Active Edge/Timepix

25. Side & Corner Scans – Active Edge/Timepix

26. Future Work & Conclusions
A lot of work continues in RD50 investigating slim edge & Edgeless devices
Shown today
Studies of Active Edge Devices
Effect of sensor thickness, geometries, radiation hardness etc.
Investigations into the effect of interface irradiations
AlxSiOy layers effecting p-type SCP devices
Use of micro focus X ray beam for charge collection measurements
Technique developed to study inter-strip/pixel behaviour
Future work (includes)
2nd Production of Active Edge devices at Advacam
50, 100 & 150 mm thicknesses
Pixels & diodes with different edges to investigate post-irradiation breakdown properties
More irradiations and tests planned for SCP devices

27. Backup Slides

28. 5 Selected Wafers 6 proton fluences 6 gamma doses
0.1, 0.3, 1, 3, 10, 30 Mrad
6 proton fluences
20 nm & 40 nm Al2O3 from processes 1 & 2 with PMA
+ 40 nm Al2O3 from process 2 without PMA
6 gamma doses
1.39x1012, 6.94x1012, 1.92x1013,
7.93x1013, 1.47x1014, 6.84x1014 p/cm2
0.070, 0.347, 0.960,
3.965, 7.350, Mrad

29. proton-radiation-hardness
I-V Results from Proton Irradiations
process 1 Al2O3
Fowler-Nordheim conduction regime
(f≈2.8 eV)
proton-radiation-hardness
in process 2 Al2O3 with PMA

30. gamma-radiation-hardness Fowler-Nordheim conduction regime
I-V Results from Gamma Irradiations
gamma-radiation-hardness
in process 2 Al2O3 with PMA
Fowler-Nordheim conduction regime
(f≈2.8 eV)
process 1 Al2O3

31. Capacitance-Voltage Wafer Mapping