Characterization and modelling of signal dynamics in 3D-DDTC detectors Andrea Zoboli c, Maurizio Boscardina , Luciano Bosisio b, Gian-Franco Dalla Betta c , Paolo Gabos c , Claudio Piemonte a , Sabina Ronchin a , Nicola Zorzi a a FBK MT-Lab, Trento - Italy , b University of Trieste and INFN sez. Trieste - Italy, c University of Trento e INFN sez. Trento - Italy Abstract - In the past few years we have proposed modified 3D architectures aimed at simplifying the fabrication technology with respect to the original Full-3D structure. In particular, we have designed and fabricated at FBK MT-Lab 3D Double-sided Double-Type Column (3D-DDTC) detectors featuring 10-mm wide columnar electrodes of both doping types. Columns are etched from alternated wafer sides and stopped a short distance (ideally not exceeding few tens of um) from the opposite surface. Owing to high column overlap and to electron read-out, the proposed devices are made on 220-mm thick p-type substrate. We present the functional characterization of 3D-DDTC diode detectors in response to fast laser pulses of different wavelength with the aim of investigating the signal dynamics. Experimental results on signal shape and relative charge collection efficiency are compared to TCAD simulations and analytical modeling based on Ramo’s theorem. Full-3D detectors - concept Double-sided Double-Type Column 3D detectors - concept Proposed by Parker et al. NIMA395 (1997) n-columns Main feature of proposed 3D-DDTC: column etching and doping performed on both sides columns not etched all through the wafer bulk contact by a backside uniform p+ implant d2 p-columns n-columns Simplification of the fabrication process Vertical columnar electrodes: short collection distances short collection times low full depletion voltage wafer surface p-type substrate Low field region - f(d2) p-columns High field region much radiation harder than planar detectors!! d1 Low field region - f(d1) n-type substrate Vertical Section Quarter of a cell Signal formation – Ramo Theorem Fabricated Structure (30,30,3) 80 mm Tail due to the low field n-type columns: 190 mm in the Optimized Structure 120 mm in the Fabricated Structure (30,30,100) 220 mm Lower column overlap More extended low field regions Higher depletion voltage (30,30,130) Structure Potential Hole density Charge generated in 3 different points Estimation of the current signal shape on the read-out n-type column Three dimensional domain Bias: 16 Volt Laterally depleted Vertical depletion in progress Signal Evaluation – TCAD Simulations MIP penetrating from (30,30,0) MIP penetrating the device from (30,30,0) Evaluation of the current signal Two dimensional domain Full depletion not reached at the bottom Slow tail due to diffusion Generation (30,30,15) Generation (30,30,100) Generation (30,30,130) 0 ns 0.5 ns 1 ns 0 ns 0.5 ns 1 ns 0 ns 0.5 ns 1 ns 0 ns 0.5 ns 1 ns 1.5 ns Electron/hole pair generated in 3 different points Evaluation of the current signal Two dimensional domain Good agreement with Ramo’s theorem Charge collected in about 1 ns Induced signal peaks at less than 1 ns fast collection between columns where the electric field is high Sensor Setup Measurement system LASER pulse width < 1ns Light focussed down to 20µm onto diode surface Amplification stage: 40dB Results Induced signal Integrated signal guard ring junction column LASER wavelengths: 850nm 980nm 1060nm Charge generation at different depths Absorption lengths in silicon: 17 µm @ 850 nm 80 µm @ 980 nm 840 µm @ 1060 nm p-stop ohmic column Signal induced by lasers are slower than simulations, probably due to amplifier band limitation. for MIP like charge deposition (λ=1060nm) the collection time is only 8ns. Response to 980nm LASER is the fastest one since charge is deposited mainly where columns overlap (higher electric field) 3D diode features: Lateral depletion: 3V Full depletion: 20 V Matrix of 20 x 20 columns 3D diode area: 0.256 mm2 Good performances are expected for fast response and rad-hard applications (i.e. ATLAS B-layer) XI Pisa Meeting on Advanced Detectors, May 24-30, 2009 La Biodola, Isola d'Elba (Italy)