1. HG-Cal Simulation using Silvaco TCAD tool at Delhi University Chakresh Jain, Geetika Jain, Ranjeet Dalal, Ashutosh Bhardwaj, Kirti Ranjan CMS simulation Group meeting 14 Feb 2017

2. Outline Detector Layout Structure and Simulation parameters
Non-irradiated Sensor
Cint Comparison : Measurement vs Simulation
Effect of variation of different parameters on Cint
Irradiated detectors
Radiation damage model
Variation in CCE, VFD and Peak Electric Field with Fluence
Summary

3. Detector Layout 21 μm 60 μm • Diameter : 8 inch
• Wafer Thickness : 200 μm
• 235 usable Cells
• Real sensor dimensions approx:
6 sides x 6.4 mm
• 4 Quadrants with different pad to
pad distance
Oxide
Oxide
40 μm
80 μm Al Al
Gap = 21 μm
Gap = 40 μm

4. Structure and Simulation parameters
X Dimension
221 m
Y Dimension
320 m
Active thickness/dd
200 m/120 m
SiO2 thickness
1 m
MO thickness
Bulk Doping Density
3e12 cm-3
n+/p+ Peak Doping Density
1e19 cm-3
p+ Doping depth
1.5 m
n+ Doping depth
120 m
Temperature
253 K
Pixel/Pad –
DC coupling
GAP
Y Dimension
n-type substrate
Deep diffused (dd)
X Dimension
This structure is used with different GAP values: 21 m, 40 m, 60 m, and 80 m
Cint, CCE and VFD simulation have been carried out
Fluence range : 0 to 2e15 1 MeV neqcm-2
AC small signal frequency
103 Hz for Cdiff
106 Hz for Cint

5. Non-irradiated Sensor

6. Measurement vs Simulated Cint
MO = 4 m
CStray
Measured Value ~ [ a*(simulated value) + Stray Capacitance ]
Where, Measured value is the Cint Value for Real sensors and Simulated value is the Cint value for the simulated structure
a = Scaling factor
Assuming, Stray Capacitance = 1e-12 F
We deduced, Scaling factor = 3.7e4
Simulated and measurement results
are having similar trends.
Initial peak for gap 20 and 40 microns
are reproduced in simulation results
also.
Initial dip in Cint for gap 60 and 80
microns are obtained in simulation.
Ratio of measured and simulated Cint
for different gaps are also similar.

7. Effect of variation of difft. parameters on Cint
Following parameters have been varied to investigate their effect on Cint :
(Gap = 21 m)
Bulk doping density (Nb)
Interface charge density (Qf)
Metal Overhang (MO)
Oxide Thickness (tox)
p+ Doping depth

8. Nb and Qf Variation Nb Variation Qf Variation
With increase in the bulk doping the
overall Cint value decreases slightly.
With increase in the interface charge
density the overall Cint value
increases.
- QF value of 3e11 cm-2 is estimated from QF variation (and is used in all other simulations)

9. MO and tox Variation MO Variation tox Variation
The effect of variation in the MO and thickness of oxide layer are
more pronounced for the initial peak.
With decrease in MO the initial peak height decreases and it
vanishes when the metal overhang is removed.
With increase in the thickness of oxide layer the initial peak decays
very fast and goes off for tox=1.5um.

10. p+ Doping depth Variation
With increase in the p+ Doping depth the overall Cint value
seems to increase slightly.

11. Irradiated Sensor

12. Radiation Damage Model
Bulk Damage = 2 Trap Proton Damage Modela (Delhi Model)
Surface Damage = Oxide charge density (Nox/QF)
Trap Type
Energy Level (eV)
Density (cm-3)
e (cm-2)
h (cm-2)
Acceptor
Ec – 0.51
4 x 
2.0 x 10-14
3.8 x 10-15
Donor Ev
3 x 
2.0 x 10-15
2 x 10-15
Irradiation Fluence,  (neq.cm-2)
Oxide Charge Density (cm-2)
5 x 1013
3 x 1011
2 x 1014
5 x 1014
5 x 1011
1 x 1015
1 x 1012
2 x 1015
1.5 x 1012
a R. Dalal et. Al., Vertex-2014 PoS 30

13. CCE : Effect of Fluence Fluence (in 1MeV neq cm-2) used are :
- 0, 5e13, 1e14, 2e14, 5e14, 1e15, 2e15
(Oxide charge is also used)
Infra-red Laser TCT simulation is used to extract CCE
Laser is fired at mid position of pads
For any bias voltage CCE is found to decrease with increase in fluence.
For any fluence CCE is found to increase with increase in applied bias.
Simulation will be compared with the measurements in next stage work

14. VFD, Peak E field : Effect of Fluence
Full depletion voltage and the peak value of the electric field first decrease
with fluence (for low fluences) and then increase with fluence (for higher
fluences) (Double Junction Effect )
Peak Electric field follows the same trend as the full depletion voltage

15. Summary
Delhi University has joined the CMS HG-Cal Phase-II upgrade efforts
2-D simulations for HG-Cal structures has been initiated
Sensitivity study for Cint w.r.t. parameters
(1) Bulk Doping,
(2) MO,
(3) Oxide thickness,
(4) p+ doping depth and
(5) Interface charge density
has been carried out
Effect of gap variation between pad structure is also simulated
Measured Cint trends for different gap values have been reproduced
CCE and VFD simulation for irradiated structure is also carried out
Results will be compared with the measurements
Further simulation are on-going.

16. Thank you.

17. Back up No initial peak is observed without Metal Overhang. Without MO
Gap = 21um
Qf = 5e10 cm-2
tox = 1um
Nb = 2.5e12cm-3
No initial peak is observed without Metal Overhang.