1. 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 ns ns
0 ns ns ns
0 ns ns ns
0 ns ns ns 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: nm nm 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: 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)