9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Numerical Modelling of Si Sensors for HEP Experiments and XFEL A.Srivastava, D. Eckstein, E. Fretwurst, R. Klanner, G. Steinbrück Institute for Experimental Physics, University of Hamburg, Germany Work within RD-50, CEC (within CMS) and AGIPD Collaboration 9 th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors, Florence, Italy

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Outline Motivation to develop radiation harder detectors Introduction – Macroscopic radiation damage in Si detectors Sensor simulation :Sensor model/experiment :Physical models and Synopsis-TCAD simulation procedure :Simulation work done  Inclusion of radiation effects (surface, bulk) Conclusion and next steps 2

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava  LHC, L=10 34 cm -2 s -1 (14 TeV pp collider, 25 ns bunch spacing Φ neq. (r=4cm) ~ 3 · cm -2  Super-LHC, L=10 35 cm -2 s -1 Φ neq. (r=4cm) ~ 1.6 · cm -2 Detector for European Free-Electron-Laser XFEL at DESY, Hamburg (start in 2013) :Photon fluxes up to: (12 keV  /cm 2 ≙ 10 9 Gy [10 9 J/kg] (200 ns distance between the pulses) 5 years 2500 fb -1  5 5 Main Motivations for R & D on Radiation Tolerant Detectors 10 years 500 fb -1 (Simulation by M. Huntinen for CMS) 3

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava  Bulk (crystal) damage due to Non Ionizing Energy Loss (NIEL) (displacement damage, point defects and cluster defects) I. Change of effective doping concentration N eff (full depletion voltage V FD ) II. Increase of leakage current (increase of shot noise, thermal runaway) III. Increase of charge carrier trapping (reduced charge collection efficiency (CCE))  Surface damage due to Ionizing Energy Loss (IEL) I. Charge build-up in SiO 2 ( shift of flatband voltage V fb, breakdown at critical corners, change of interpixel capacitance/resistance) II. Traps at Si-SiO 2 interface III. Surface generation current (increase shot noise) Macroscopic Radiation Damage Effects in Silicon Detectors Introduction 4

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava SRH (Shockley-Read-Hall) recombination statistics  Recombination through deep level traps Impact ionization (  determine breakdown voltage ) Trap model Doping dependent mobility and high field saturation model Trap to trap interaction model for charge exchange Fixed oxide charges+ traps at Si/SiO2 interface Physical model used:  Compare results to analytical calculations for cross-check Sensor Simulation including Radiation Effects 1). Simulation of non-irradiated sensors 2). Inclusion of radiation effects based on experimental results Program used: TCAD from Synopsis 5

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Sensor Simulation: for Particle Physics Simulated PAD Si Sensor model Method: Obtain parameters from experimental data and put into simulation to check data are reproduced Simple p + on n PAD diode (0.25 cm 2 ) to verify simulations S.N o. Physical parameters Values 1.Doping Concentration (N D ) 4.94x10 12 cm -3 2.Oxide thickness (t ox ) 0.5 μm 3.Junction depth (X j ) 1 μm 4.Guard ring spacing GS) 10 μm 5.Guard ring width (GW) 100 μm 6.Device depth (W n ) 280 μm 7.Thickness of (W n+ ) 1 μm 8.Fixed oxide charge (N ox ) 1x10 12 cm -2 6

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava  *Modified cross-sections for n-type MCz Si β n =3.66x cm 2 /ns and β p =4.92x cm 2 /ns  **σ p for E 5,H152K to agree with data  ***Cluster effect taken into account by increasing the introduction rate of the cluster related defect center E 5 by an one order of magnitude Four Trap Level Model for n-type MCz Si Sensors 7

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Comparison with Experiments  Good agreement between simulation, experimental data and model (ii) for V FD and Leakage current  Theoretical calculations underestimate simulated and experimental current values No charge exchange taken in E 5 (-/0)  H152K (0/-) 8

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Effect of Generation Life Time on E-field for 1x10 14 n eq. /cm 2  Double junction for fluence of 1x10 14 n eq. /cm 2 due to occupation of traps  Generation life time (deep traps) affects the E-field Electric field (V/cm) versus device depth (μm) In base region-field –> 100 – 1000 V/cm depends on  g  g =4.5x10 -7 sec  g =4.5x10 -9 sec E-Field expected from double junction 9

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Sensor Simulation: In the Framework of CEC (CMS) Layout for Near-Far Strixel Baby Si strixel Sensor  First step in simulation: Compare 2-D AC-coupled strixel sensor with 3-D AC- coupled strixel sensor 10

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava 2-D and 3-D Strixel Sensor Simulation  Different Strixel design proposed under CEC like Si strixel (1 metal), double metal layer, near far strixel, pitch adapter integrated into Si strixel sensor 11

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Sensor Simulation: Potential and E-field 12

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Comparison of I/V Characterstics for 2-D and 3-D 2-Strixel Si Sensor 13

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Comparison of C/V Characterstics for 2-D and 3-D Strixel Si Sensor 2-D C/V 3-D C/V  C AC in good agreement with theoretical calculation for both 2-D/3-D  Detector capacitances FD with surface charges  Up to 0.7x10 11 cm -2 N ox, capacitance b/w the p + -strips (C int ) higher than Al-strips. But, for N ox =1x10 12 cm -2, vice versa C IiIj (C int ), N ox =0 C IiM2, C IjM1, N ox =0 C IiIj (C int ), N ox= 0.7e11 C IiM2, C IjM1, N ox =0.7e11 C IiM2, C IjM1, N ox =1e12 C AC  Diff. of C/V curve due to different geometry of the 2-D and 3-D p + electrodes Applied bias=100 V, frequency=1 MHz C AC C IiM2, C IjM1, N ox =0.7e11 C IiIj, N ox= 0.7e11 C IiIj (C int ), N ox= 1e12 C IiM2, C IjM1, N ox =1e12 C IiIj (C int ), N ox= 1e12 14

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Sensor Simulation: for X-FEL X-ray Sensor (AGIPD) CTR- current terminating ring, CR- Current ring, GR- Guard ring 15

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Surface Damage due to 10 keV X-Rays Results from gated diode measurements for 5 MGy N ox =2 x10 12 cm -2, c -E=0.35eV,σ=0.05 eV,N it =4x10 12 cm -2 c -E=0.6 eV,σ=0.05 eV,N it =4x10 13 cm -2 16

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Simulation of Guard ring Structure for 5 MGy  V BD V, E max observed on curvature of junction  Compensation of electric field in presence of interface trap and thus low field and high V BD (V BD =299V for N ox =2x10 12 cm -2 ) 17

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Conclusion and Next Steps Detailed sensors simulation for radiation damage effects -Bulk damage induced by hadrons Good description of leakage current + depletion voltage including “double junction” Simulation of CEC strixel sensors started (comparison of 2-D with 3-D simulation) -Surface damage induced by X-Rays Detailed simulation of measurements with gated diodes (not shown)  extraction of relevant parameters Simulation of radiation damage for guard ring started Next Steps Mixed irradiation model for n-type MCz Si – In process of upgrade  for CCE study of an irradiated sensors (for Avalanche Multiplication effect Comparison of n+ in n and p+ in n pixel for I/V and C/V: AGIPD 18

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava 19

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Advanced SFH models for Avalanche Multiplication The recipe: 1.Relax the assumption on the trap introduction rate (changes with fluence and particles) 2.Let the parameters (N A, N D – vary with fluences,  A/D e,  A/D h – fitting and 3.Keep the traps energy levels (E A, E D ) to the exp. values 4.Normalized to Exp. Room 293K Constraints to the model: 1.Charge collection profiles (at different V bias and Φ eq ) 2.Trapping rates 3.Generated leakage current β calculated/experimental from G.K. thesis F eq known β calculated/experimental from G.K. thesis F eq known 20

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Detector simulation Charge deposit Charge transport Trapping Trapping times from literature Electronic response + data formatting ROC+FED response ROOT Analysis n-MCz four level deep traps models (DESSIS) 3-D Electric field mesh Synopsis ISE TCAD PIXELAV 21

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava Numerical modelling of radiation damage of Si sensor based on emission-capture dynamics of deep trap The leakage current at full depletion (V FD ) and effective doping concentration can be calculated by following expressions;   (i)  (ii)   i.e. I(300K) =1.76 x I(293K) 22

9 th International conference “RD09, Italy” on 30 September-02 October 2009 A. Srivastava 23  For 2-D simulaton, half of strixel width (W/2)=12.5µm, Length of strixel (L)= 1 µm (default length) and for 3-D simulation, L=75 µm Theoretical Calculation  Ignoring surface effects, the leakage FD (generation current of the depletion region: I GEN ) can be calculated for 2 strixel Si sensor S.No. W/2 ( Half of strixel width) L (Length of strixel) CMS values for Coupling capacitance (C AC ) and interstrip capcitance (c int ) Analytical calculation (A)Simulation result(S) µm 1µm (2-D) 75µm (3-D) 18pF/cm 1.3 pF/cm 2.16 x F/µm=21.6 pF/cm 1.62 x F/75 µm=21.6pF/cm 2.4 x F/µm=24 pF/cm 1.82 x F/75 µm =24.2 pF/cm Coupling capacitance, and