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Claudio Piemonte Trento, Feb nd Trento workshop Device simulation of Single-Type-Column 3D silicon detectors Claudio Piemonte ITC-irst Trento (Italy)

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Claudio Piemonte Trento, Feb nd Trento workshop Outline Introduction Single-Type Column 3D detector concept Simulation of the static characteristics Simulation of the signal response Conclusion

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Claudio Piemonte Trento, Feb nd Trento workshop Introduction Development of 3D sensors is being carried out at ITC-irst in collaboration with INFN. Work done so far is described in 3+1 talks: Simulations of 3D-STC detectors - Claudio Piemonte (ITC-irst) Technology used in the first two fab. runs - Sabina Ronchin (ITC-irst) Electrical characterization of first prototypes - Nicola Zorzi (ITC-irst) + Electrical characterization at Glasgow - D. Pennicard (Glasgow University)

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Claudio Piemonte Trento, Feb nd Trento workshop Standard 3D detectors - concept Proposed by Parker et al. NIMA395 (1997) n-columns p-columns wafer surface ionizing particle Short distance between electrodes: low full depletion voltage short collection distance more radiation tolerant than planar detectors!! n-type substrate

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Claudio Piemonte Trento, Feb nd Trento workshop Single-Type-Column 3D detectors - concept Sketch of the detector: grid-like bulk contact ionizing particle cross-section between two electrodes n+n+ n+n+ electrons are swept away by the transversal field holes drift in the central region and diffuse towards p+ contact n-columns p-type substrate Functioning: [ Presented in June 2004 at the Hiroshima conference ]

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Claudio Piemonte Trento, Feb nd Trento workshop 3DSTC detectors - concept (2) Main feature: hole etching and doping are performed only once Further simplification: holes not etched all through the wafer p-type substrate n + electrodes Uniform p+ layer Bulk contact is provided by a backside uniform p+ implant single side process. No need of support wafer.

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Claudio Piemonte Trento, Feb nd Trento workshop Structure used for static simulations 3D simulations are necessary DEVICE3D tool by Silvaco Important to exploit the structure symmetries to minimize the region to be simulated n+n+ cell 50 m p-type substrate Wafer thickness:300 m Holes: 5 m-radius 250 m-deep

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Claudio Piemonte Trento, Feb nd Trento workshop Simulated potential distribution (1) Potential distribution (vertical cross-section) Potential distribution (horizontal cross-section) null field lines 50 m 300 m 0V -10V -5V -15V in scale not in scale

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Claudio Piemonte Trento, Feb nd Trento workshop Potential and Electric field along a cut-line from the electrode to the center of the cell To increase the electric field strength one can act on the substrate doping concentration Na=1e12 1/cm 3 Na=5e12 1/cm 3 Na=1e13 1/cm 3 Na=1e12 1/cm 3 Na=5e12 1/cm 3 Na=1e13 1/cm 3 Simulated potential distribution (2)

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Claudio Piemonte Trento, Feb nd Trento workshop Capacitance in 3D-STC diode = matrix of 10x10 holes Back C backTot C intTot Structure for simulation of C back half pitch C back =4 x simulated value Structure for simulation of C int C int =2 x simulated value oxide not included in the structure guard ring 3D diode C back =C backTot /100 C int =C intTot /40

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Claudio Piemonte Trento, Feb nd Trento workshop Capacitance simulation on a 300 m thick wafer with 150 m deep columns, 80 m picth, Na=5e12cm -3 Capacitance simulations (1) Phase 1 Phase 2 high C back ~ zero C int max C int slowly dec. C back Phase 1 Phase 2 undepleted Si

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Claudio Piemonte Trento, Feb nd Trento workshop Capacitance simulations (2) Comparison between measurements (on 3D diodes) and simulations 100 m col. pitch 80 m col. pitch 100 m col. pitch 80 m col. pitch 1/C 2 characteristic 300 m thick wafer 190 m deep columns 2e12cm -3 subst. conc. From 1/C 2 curves: full depl. between columns clearly visible (higher for 100 m pitch) diode-like behavior in phase 2 col-to-back capacitance meas. simul.

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Claudio Piemonte Trento, Feb nd Trento workshop Capacitance simulations (3) 1) V bias =0V 2) V bias =2V 3) V bias =5V 4) V bias =20V The 1/C 2 curve of the col-to-back capacitance can be used to extract both the intercolumn as well as the col-to-back full depletion Do not consider the hot spot in the pictures, it is the charge released by a particle.

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Claudio Piemonte Trento, Feb nd Trento workshop Signal in 3D-STC detectors (1) e h First phase Transversal movement generation 10 m from column generation in the middle between two columns induced by e induced by h induced by e induced by h Ramo theorem: electric field weighting field 50 m 250 m 50 m

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Claudio Piemonte Trento, Feb nd Trento workshop Signal in 3D-STC detectors (2) Second phase Hole vertical movement 180um from top 140um from top hole velocity orthogonal to weighting field no signal induced weighting field no longer orthogonal signal induced a hole moving towards the back induces a current pulse shifted in time according to the generation depth

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Claudio Piemonte Trento, Feb nd Trento workshop Simulation of a localized charge deposition Only the transversal movement is visible The current plot in log-log scale shows very clearly the fast transversal component and the slow hole vertical one x y transv. movem.vert. movem. induced by e induced by h total current z (10,10) 80 m 50 m 250 m 50 m electrons holes

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Claudio Piemonte Trento, Feb nd Trento workshop Simulation of a uniform charge deposition (1) Uniform Vertical deposition (10,10) Bias voltage = 50V (> full depl.) All the electrons collected by electrode 1 electron collection peak vertical hole movement transversal hole movement induced by e induced by h total current log-log plot linear scale plot

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Claudio Piemonte Trento, Feb nd Trento workshop Simulation of a uniform charge deposition (2) Uniform Vertical deposition (25,25) Bias voltage = 50V (> full depl.) Electrons equally shared between four columns same signals on the four columns log-log current plot linear-scale current plot

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Claudio Piemonte Trento, Feb nd Trento workshop In the worst case of a track centered the central region, 50% of the charge is collected at t ~ 300ns Outside this region, 50% of the charge is collected within 1ns. Full charge collection time (25,25) (20,20) (10,10) Same V bias, different impact point tail independent from impact position charge collected is ¼ for interaction in the middle point

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Claudio Piemonte Trento, Feb nd Trento workshop Conclusion 3D-STC detector: Advantage: simple fabrication process. Disadvantage: Very long full charge collection times. => extremely interesting device to tune the technology for the production of standard 3D detectors can be used in those applications not requiring charge information in short time

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Claudio Piemonte Trento, Feb nd Trento workshop Additional slides

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Claudio Piemonte Trento, Feb nd Trento workshop CCE versus bias voltage V bias =2V

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