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

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

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

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

Non-irradiated Sensor

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.

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

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)

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.

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

Irradiated Sensor

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 + 0.48 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

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

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

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.

Thank you.

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.