1. 2nd Institute Of Physics, Georg-August-Universität Göttingen
The Planar Pixel Sensor project
Introduction
IBL sensor candidates
Selected R&D areas
Dr. Jens Weingarten
2nd Institute Of Physics, Georg-August-Universität Göttingen
20/03/2017
5th "Trento" Workshop, University of Manchester

2. Planar Pixel Sensor Proposal
R & D within the planar pixel proposal:
slim edge sensors to reduce inactive area
radiation damage in planar sensors
bulk materials (n-in-n, n-in-p, DOFZ, MCz)
simulation of sensor design and detector layout
low threshold operation of FE readout
low cost, large scale pixel production (interconnect technology)
Participating institutes:
CERN
AS, Prague
LAL Orsay
LPNHE Paris
Bonn University
HU Berlin
DESY
TU Dortmund
Goettingen University
MPP and HLL Munich
Udine University and INFN
KEK
IFAE-CNM Barcelona
Liverpool University
UC Berkeley and LBNL
UNM Albuquerque
UC Santa Cruz
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

3. Planar Pixel Sensors Advantages Challenges
mature technology
standard processing (implantation and metallization)
many qualified vendors of sensor-grade silicon
high yield
relatively low cost
lots of research done
experience with sensor design and optimization
radiation hardness models
Challenges
trapping lowers signal charge after irradiation  increase bias voltage  need small-signal readout electronics
increasing leakage current with fluence  need serious cooling  annealing reduces leakage current
sensor edge usually conductive  need guardrings  significant inactive area
Sensor specifications for IBL
maximum bias voltage: 1000 V
sensor thickness: 225 ± 25 mm
coolant temperature: -30 C
sensor temperature: -15 C
sensor max. power dissipation: 200 mW/cm2 at -15 C
edge width: 450 mm
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

4. Charge Collection Efficiency
Charge multiplication
observe charge multiplication in highly irradiated strips and diodes (RD50)
CCEs frequently exceeds 100% (especially thin sensors)
 over a wide region, CCE is nearly linear function of bias voltage
At projected IBL end-of-lifetime fluence (5x1015 neq/cm2) and 1 kV bias:
9ke- for 300mm sensor thickness
12ke- for 140mm sensor thickness
 above 2x threshold
 thin sensors:
superior charge collection at high fluence
less material
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

5. Leakage Current Power dissipation
can be reduced significantly through annealing
‘all annealing is beneficial annealing’
 leakage current expected to be under control at -15 C
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

6. Slim Edges Requirement: inactive width ≤ 450 mm
reduce number of guard rings
reduce guard ring width
shift guard rings closer to (underneath) pixel implants
reduced space allows for 10 – 14 guard rings  Vbr > 200 V
after irradiation, even fewer guard rings necessary (~5)
 200 – 100 mm seem feasible
 trials underway to go to 100 – 50 mm using picosecond laser dicing
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

7. IBL Production Candidates
Three candidate designs were sent to IBL management:
conservative design (ATLAS-like), n-in-n: CiS
slim edge design (~100 mm inactive edge), n-in-n: CiS
thin sensors (~150 mm thickness), n-in-p: HLL Munich
Additional productions:
thin (~150 mm) n-in-p sensors: HPK
thin (~200 mm) n-in-p sensors: Micron
finish sensor production in August
bump bonding until end of September
testbeams and irradiation until Xmas
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

8. Official Design A Conservative design
goal is to resemble current ATLAS design as far as possible
13 (out of 16) guard rings, to stay within 450 mm
 proven to be sufficient
ATLAS Pixel sensor, outer guard rings cut off, before (top) and after (bottom) irradiation
450 um
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

9. Official Design B Slim edge design
minimize inactive edge by shifting guard rings underneath active pixel region  200 – 100 mm inactive edge achievable
simulation shows uniform depletion of edge pixels
first IV curves show standard behavior
100 um
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

10. Production I PPS/RD50 production @ CiS dedicated IBL production @ CiS
production finished, UBM being applied
~10 FE-I4 SC sensors each of conservative and slim edge design available
~6 4x1 FE-I4 MCM sensors available
dedicated IBL CiS
2x1 MCMs adopted as IBL baseline after previous submission
new submission soon:
1 conservative, 1 slim edge MCM/wafer
2 conservative, 2 slim edge SC/wafer
FE-I3 SCs, diodes and test structures
expect production to be finished in september
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

11. Official Design C Thin design Production II
utilize advantages of thin sensors at limited bias voltage
edge width 450 mm
design validated with CiS n-in-p production of FE-I3 sensors
thinning done using handle wafer  stable frame around thinned area
additional passivation layer for improved HV protection of FE
Production II
6” FZ n-in-p wafers, active thickness ~150 mm
5 wafers a 6 FE-I4 MCMs, 6 FE-I4 SCs, 2 FE-I3 SCs
available for bump bonding early september
450 um
SC FE-I4
SC FE-I4
SC FE-I4
SC FE-I4
2x2 FE-I4
2x1 FE-I4
SC FE-I4
SC FE-I4
2x1 FE-I4
2x1 FE-I4
2x1 FE-I4
2x1 FE-I4
2x1 FE-I4
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

12. Additional Productions
KEK with HPK:
edge space in the longitudinal pixel direction of mm
3 types (of 2x1 FE-I4 sensors) x 2 sensors/type/wafer
3 types of FE-I4 SCs x 2 sensors/type/wafer
6 types of FE-I3 SCs per wafer
320 μm and thinned (150 μm) wafers
Delivery due in June (320 mm) and July (150 mm)
Micron:
40 FE-I4 n-in-p SCs and
70 FE-I3 n-in-p SCs available for UBM
300 mm thick
2x1 MCM production with reduced edges planned later.
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

13. Selected non-IBL activities 20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

14. Slim Edge II: Trench Idea
Reduce leakage current by shielding cut-edge from high-field region
produce trench using Deep Reactive Ion Etching
thermally oxidize trench (anneal possible damage)
fill trench with poly-silicon (mechanical stability)
continue sensor processing
cut very close to trench
DRIE cut
vary width
vary width
Trench
p-stop
Guard ring
courtesy of IFAE/CNM Barcelona
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

15. Slim Edge II: Trench Initial pixel production: Plan
6 different layouts produced
13 sensors were tested (≥1 of each type)
 all types show high leakage current, but Vbd > 100 V  suspect low p-stop dose
 no correlation of leakage current with distance cut – guard ring  trench effectively isolates active area from diced edge
Plan
Repeat production changing p-stop dose and punch-through bias structure.
Start FE-I4 design.
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

16. Device Simulation Charge multiplication Assumptions: Can reproduce
trap-assisted band-to-band tunneling
impact ionization
Can reproduce
‘soft breakdown’ (‘escalation’) of leakage current
CCE exceeding 100% at high bias voltages
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

17. Low-Cost Production Handling Flip chip process
no test steps before bare module assembly  less FE/module  good yield for rework
less chips per module  bigger Fes (FE-I4 ≈ 4x FE-I3)
Flip chip process
reduce pick-and-place machine time
use less precise flip-chip machine (DataCon)
much faster, ~5 sec per die instead of 2 min
minimum specs: 80 µm pitch, 40 µm bump diameter
needs staggered bump pads to achieve 50 µm effective pitch
bigger alignment marks, placed diagonally across FE area  test impact on sensor performance
 evaluating usability of this machine
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

18. resistance measurement
Low-Cost Production
Bump bonding
larger pitch would reduce cost significantly
 try to increase pitch by staggering bump pads
wafers with FE-I4 sized structures, both chip- and sensor-dummies are produced to explore possibilities with IZM
resistance measurement
Traces
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen

19. Thank you for your attention
Further Activities
Quite a few PPS institutes are here and will present their own work.
Preview:
Munich
thin sensor production
SLID interconnects on thin sensors
through-silicon vias
 more details in Annas talk
KEK
n-in-p strip and pixel sensors
 more details in Nobus talk
Liverpool
charge collection in highly irradiated silicon
 more details in Gianluigis and Tonys talks
LAL
device simulation
 more details in Mathieus talk
and many more
Thank you for your attention
20/03/2017
Jens Weingarten, II. Institute of Physics, University of Goettingen