Radiation hardness simulation of silicon thin detectors

Transcription

1 Radiation hardness simulation of silicon thin detectors F.Moscatelli 1,2, M. Petasecca 1, G.U. Pignatel 1 1 DIEI - Università, via G.Duranti,93 - Italy 2 IMM-CNR sez.di Bologna, via Gobetti Italy

2 Outline Radiation damage modelling (F. Moscatelli) Thin structures (M. Petasecca)

3 Simulation Tool Simulation tool: ISE-TCAD discrete time and spatial solutions to equations Damage modelling: - Deep levels: N t, E t, σ n and σ p - SRH statistics. - Donor removal mechanism - Other effects: high density defect concentration (clusters) produces an increase of the leakage current.

4 Four levels*: Radiation Damage Model - V -/0 2 located at E=E C C i O i located at E=E V V 2 O located at E= E C E(70) located at E=E C Direct charge exchange between V -/0 2 and E(70) to reproduce cluster effects. Donor removal mechanism. Reproduce variation of the V dep and I leakage as a function of the fluence Over Φ= n/cm 2 computational problems *F. Moscatelli, et al.nuclear Instruments and Methods in Physics Research B 186 (2002)

5 ISE-TCAD Damage Model Three levels*: - V -/0 2 located at E=E C C i O i located at E=E V V 2 O located at E= E C To o reproduce cluster effects,, we use increased V -/0 2 occupancy Donor removal mechanism. D. Passeri, P. Ciampolini, G. Bilei and F. Moscatelli, IEEE Trans. Nucl. Sci., vol. 48, pp. 1688, 200

6 Three-level model Level characteristics: V -/0 2 V 2 O C i O i E E c -0.42eV E c -0.50eV E v +0.36eV σ p cm 2 15 cm cm cm 2 σ n cm cm cm 2 η 26 cm cm -1 1 cm -1

7 Effective Doping Concentration and Leakage Current I/Volume = αφ,, with α =(2.9 10) A/cm.

8 Simulations results as a function of T 5 1E measurements simulations Temperature [K] Φ= protons/cm 2 σ p V 2 [cm 2 ] 1E-14 1E Temperature [K] E Temperature [K] measurements simulations Φ= protons/cm 2 σ p V 2 O [cm 2 ] 1E Temperature [K]

9 Thin detectors Thin detectors have been proposed to investigate the possibility to get a low depletion voltage and to limit the leakage current of heavily irradiated silicon devices

10 Simulation setup ulated structures: D 58µ m = 300µ m thin device thick device Guard Ring Diode Guard Ri Simulated device structure and parameters Doping profiles: n-doped substrate ( cm -3 ) 6kΩcm. Charge concentration at the siliconoxide interface of : cm -3 pre-irradiation cm -3 post-irradiation D 9µm 15µm 40µm 6µm Back

11 Simulation setup Variable mesh definition: the mesh is better refined in correspondence of the critical points of the device to improve simulator performance. Diode Guard Ring The typical electric field distribution at the full depletion voltage of the diodes: red areas correspond to the maximum

12 Simulation results Simulated Depletion Voltage as function of the fluence V dep [V] µ m x x10 14 Fluence [(1MeV) n/cm 2 ] V dep [V] µ m x x10 14 Fluence [(1MeV) n/cm 2 ] -V dep in thin structures is one order of magnitude lower than in thick one -V dep of thin diode at a fluence of n/cm 2 is about 120 V while in thick diode is more than 3000 V!

13 CCE Simulation results Q = I ( t) dt MIP: 80 e-h pairs/ µm Cylinder diameter= 2µm

14 CCE Simulation results

15 CCE Simulation results

16 CCE Simulation results

17 CCE Simulation results

18 CCE Simulation results

19 CCE Simulation results

20 CCE Simulation results

21 Simulated CCE as function of the fluence Φ=2e14 n/cm 2 Thick = 1.6 fc CCE = 45% Exp. [1, 2] CCE = 42% Thin = 0.58 fc CCE = 98% Φ=1e15 n/cm 2 = 1 fc CCE = 27% Exp.CCE = 20-30% = 0.57 fc CCE = 95% For Φ=1e15 n/cm 2 Q thin =57% Q thick 120V NO Breakdown risk and full depleted [1] L.Beattie et al./ NIM 412A (98) [2] M.Bruzzi et al./ NIM 61B(98)

22 Conclusions rradiated thin and thick diodes have been analyzed considering ree levels simulation model until Φ=1e15 n/cm 2 hin features: V dep in thin structures is one order of magnitude lower CCE at very high fluence (10 15 n/cm 2 ) is 95% for th structures. Q thin =57% Q thick ext step is to simulate thin structures at higher fluences (1e1 /cm 2 ) and measure irradiated ones.